Paper 1: BCS, CP

Question 1

Describe denture base material

Answer 1

PMMA powder + MMA liquid

• PMMA = MMA pre-polymerised into powder via suspension polymerisation
• acts as filler as doesn’t polymerise more

Powder + Liquid HC using Dough Technique

Question 2

Advantages of using HC Dough Technique

Answer 2

Using MMA alone: vol. shrinkage 21% (7% linear shrinkage)
- 2/3 replace w/ PMMA vol. shrinkage 7% (~2% linear)

Exotherm red.

Question 3

Discuss composition of denture base PMMA

Answer 3

Powder

• PMMA spherical beads 10-200mmetre
• benzoyl peroxide (0.2-0.5%); initiator
• pigments (1-2%)
• Ti/Zn oxides; opacifiers

Liquid
- MMA
— volatile, flammable
— store dark glass bottle; avoid spontaneous polymerisation = extend shelf life
- ethylene glycol dimethacrylate (10%); cross-linking monomer
— form covalent bonds b/w PMMA chains
— improve craze resistance
— too much = brittle
- hydroquinone (0.0006%); inhibitor
— react w/ FRs that form in bottle
— form stabilised FRs; can’t initiate polymerisation

Question 4

Activation requirements for HC polymerisation

Answer 4

Initiator (benzoyl peroxide) + heat (~80)

Question 5

Discuss stages of HC polymerisation of PMMA

Answer 5

PMMA + MMA mixed -> Dough formed which is heated (80)
FR polymerisation occurs forms cured plastic polymer

Initiation: FR attack MMA double bond
Propagation: (chain growth); MMA monomers add to chain
Termination: 2 growing chains meet; FRs combine form stable covalent bond

Question 6

Discuss the formation of crazes in denture bases

Answer 6

Internal strains due to thermal contraction
- minimise: use acrylic teeth, allow flask to cool slowly
Relieving produce tiny defects (crazes)
- form cracks which grow = #

Form in response to;

• heat; polishing
• differential thermal contraction around porcelain teeth
• attack by solvents; pt drinking alcohol

Question 7

Discuss the formation of porosities in denture bases and why this is problematic

Answer 7

Exothermic: if over BPt (MMA 100.3)
Gaseous: incorrect curing; monomer vaporises leading voids
Contraction: flasks not kept under Constant Spring pressure during curing cycle
Granular: incorrect mixing/packing; structural deficiency due to loss of monomer

Problem

• H2O fills voids
• unreacted monomer (toxic) leach out
• further voids -> more H2O absorbed
• leads to crazes + failure

Question 8

Advantages of HC PMMA denture base

Answer 8

Glass transition temp: 105/125 (high)
- well above temp. encountered in use
— polishing, cleaning

Specific gravity: low; doesn’t fall out

Aesthetic
Manufacture + repair easy
Good longevity: 5-10yr

Question 9

Disadvantages of HC PMMA denture base

Answer 9

Toxicity: residual monomer (0.5%)
- contact dermatitis, mucosal irritation

Elastic modulus: 2.6GPa (low)
Impact strength: low (cracks grow), brittle
Fatigue strength: low; major cause failure
Abrasion resistance: low
Thermal conductivity/diffusivity: low; is insulator
- potentially scald as don’t feel temp.

Dimensional stability: polymerisation shrinkage

Question 10

Discuss rubber reinforcement of HC acrylics

Answer 10

Butadiene styrene

• introduce rubber phase
• high impact acrylics
• cracks stop growing when rubber domains reached
• high degree of resistance to #
• lower flexural modulus; long term fatigue failure due to excessive flexure

Question 11

Discuss potential fibre reinforcements of HC acrylics

Answer 11

Carbon: difficult handling, poor aesthetic
Polyaramid plain fabric (Kevlar)
- ineffective: poor bonding b/w resin and fibres
Ultra-high MWt polyethylene (UHMPE)
- neutral colour
- biocompatible
- low density
- surface treated for bonding to resin
- fabrication T consuming
Glass: most promise
- hydrophilic glass + hydrophobic PMMA problematic
- incorporated in resin as short fibres; in cloth or loose form

Question 12

Explain why HC PMMA dentures need to be kept in H2O

Answer 12

In storage/mouth absorbs ~2% H2O
If drys out will absorb >2% H2O
If this continues crazes form
- due to relieving IS + residual monomer leaching
- crazes -> cracks -> fail; red. longevity

Question 13

Uses for RT PMMA

Answer 13

Denture repair 
Relining denture bases 
Additions to denture
Special trays 
Temp. crown and bridge

Question 14

How is RT cured acrylic mixed?

Answer 14

RT PMMA (pre-polymerised MMA) powder + RT MMA monomer liquid mixed in Dough Technique

Question 15

Composition of RT cured PMMA

Answer 15

Powder

• PMMA; finer particle size cf HC
• BP; initiator
• colour pigments
• Ti/Zn oxides; opacifiers

Liquid

• MMA monomer
• hydroquinone; inhibitor
• N,N-dimethyl-p-toluidine (DMPT); activator

Question 16

Describe the RT polymerisation process of RT PMMA

Answer 16

Liquid + powder mixed
PMMA beads dissolve in MMA liquid
Activation: DMPT breakdowns BP liberating FRs
FRs attack MMA double bonds
- follows initiation, propagation + termination stages

~10min cure

Question 17

How does the finer particle size of RT PMMA powder affect the curing process?

Answer 17

More rapid diffusion of MMA into PMMA beads

- rapidly gelates to hard mass

Question 18

Advantages of RT PMMA cf HC PMMA

Answer 18

Cheaper
Less technician T; don’t have to send to lab
Chair side use

Question 19

Disadvantages of RT PMMA cf HC PMMA

Answer 19

Physically weaker
- low MWt PMMA affect mechanical properties
- > residual monomer (3-5%) (not all able to polymerise)
— leaches -> porosities

Aesthetics: poor stability; DHPT causes yellowing
Tg: lower (70-80)

Porosity

• more rapid gelation
• hand mixing incorporate air

Inc. H2O uptake

• low MWt
• loss of residual monomer
• porosity

Question 20

Discuss PEMA; what it is, monomers it can be mixed with, Tg

Answer 20

Higher methacrylate (cf PMMA) powder mixed w/ (usually) higher MWt monomers using Dough Technique

Monomers

• can’t use MMA = incoherently mixed product
• none = tissue conditioner
• higher MWt monomers (ethyl, butyl, hexyl)

Tg: 65 (

Question 21

Uses of RT PEMA acrylics

Answer 21

Tissue conditioner (no monomer)
Hard reliner
Soft lining material
Extension of special trays and dentures 
Temp. crown + bridge

Question 22

Discuss PEMA tissue conditioners

Answer 22

PEMA mixed w/ no monomer

• no polymerisation occurs
• forms viscoelastic gel via polymer chain entanglement
• short life (3d); no polymerisation, alcohol volatile, plasticiser leaching

Uses

• denture lining; allow tissues to recover
• maxillofacial prosthesis; obturators
• functional impression materials

Question 23

What is the function of PEMA powder in PEMA/EMA?

Answer 23

Same as PMMA
Acts as virtual filler
- dec. shrinkage
- lower exotherm

Question 24

What is the purpose of soft lining materials?

Answer 24

Make denture more comfortable for pt in area has traumatised soft tissues

Question 25

Function of plasticisers

Answer 25

Adjust viscosity of material - make natural rigid material soft and rubbery Lower Tg and elastic modulus

Question 26

Dis/adv of soft lining PEMA

Answer 26

``` Adv - soft, rubbery acrylic - adheres well to acrylic denture base — contains acrylic group - Tg lowered by plasticiser ``` ``` Disadvantages - hardens w/ T as plasticiser leaches — use as little as possible - short life due to hardening - biocompatibility; phthalate (banned in EU - use citrate) ```

Question 27

Function of temp. crown

Answer 27

Mimic natural tooth Protect prep. tooth while permanent crown being made Made @ chair side

Question 28

Composition of crown and bridge/extension PEMA

Answer 28

Powder - PEMA - BP - colour pigments - opacifiers Liquid - butyl methacrylate monomer - hydroquinone - DMPT

Question 29

Adv of PEMA/BMA

Answer 29

``` Lower exotherm cf PMMA/MMA Less pulpal and soft tissue irritancy Non-volatile monomer Good handling Not brittle, ductile ```

Question 30

Discuss light cure dimethacrylate materials

Answer 30

Uses - composite filling - temp. crown + bridge Properties - high modulus - low exotherm - adequate polymerisation shrinkage Composition; 1 paste - BisGMA/urethane dimethacrylate - camphorquinone - diluents - fillers - pigments - DMPT

Question 31

Discuss HEMA

Answer 31

Low viscosity liquid Dry state: forms hard resin Wet state: soft rubbery - hydrogel - absorbs 10-100% H2O Uses - RMGIC, dentine bonding agent - unsuccessful as soft lining — absorbed too much liquid causing to swell

Question 32

Discuss cyanoacrylates

Answer 32

Polymerise v quickly @ body temp ``` Used as surgical glue Dental uses - PD surgery - adhesive for dentine (bonds to collagen) - endodontic cement ``` Full strength within 24h - higher moisture + thinner bond-line = faster cure

Question 33

6 factors which keep dentures in place

Answer 33

1. Saliva 2. Muscles 3. U and L teeth when biting 4. Gravity (L denture) 5. Denture clasps (direct) 6. Denture rests (indirect)

Question 34

Discuss how saliva can aid denture retention and the factors affecting this

Answer 34

Weak glue: b/w denture and tissues - clinically unlikely to resist displacement Suction: peripheral seal around denture Factors - dry mouth (poor) - thin saliva layer (good) - well-fitting denture (good); flange fills width of sulcus Posterior ‘post. dam’ seal: artificial ridge created in denture to seal saliva - border b/w hard and soft palate

Question 35

Discuss how muscles and teeth can support dentures

Answer 35

Muscles - learn to control denture using musculature; dependent on health - post. tongue naturally rest on post. denture Teeth biting together - uneven/stable: dentures will slide - correct occlusion (bite together in RCP); dentures stable

Question 36

Define denture support, retention, stability

Answer 36

Support: ability to resist displacement towards tissue (O loading) Retention: ability to resist displacement away from denture bearing area perp. to tissue surface at rest Stability: ability to resist displacement in relation to underlying bone during function in any direction

Question 37

Discuss what affects denture support and how to check support

Answer 37

Depends - amount of coverage of underlying tissues/denture bearing area (more = better) - condition (firmness) of underlying tissues/denature bearing area (firmer = better) Check - press O surface bilaterally; see if moves - see how much area covered; denture extension ideal? - signs of trauma?

Question 38

Explain why an U complete denture has better support and is less likely to cause trauma

Answer 38

Larger fit surface and covers more underlying tissue and bone (more support) Thus O forces distributed over larger surface area (less trauma)

Question 39

Discuss factors affecting denture retention and how to check retention

Answer 39

Depends - adhesion b/w denture, saliva, mucosa - area covered - adaptation to tissue - border seal (suction) - muscular control (tongue, cheek) - gravity (L) Check - hold onto denture teeth, try to pull away from tissues - press incisal edge U ant.; does back lift?

Question 40

Discuss factors affecting denture stability and how to check stability

Answer 40

Depends - degree of support and retention - degree of alveolar bone reposition - area covered - freedom to make excursive movement - consistency of supporting tissue - position of teeth and design of polished surfaces - correct vertical and horizontal O relationship - level of O plane Check - history - press O surface unilateral - observe denture during function

Question 41

Ideal properties of successful denture

Answer 41

``` Comfortable Strong enough Tolerable Adequate stability Atraumatic Aesthetic ```

Question 42

Main components of RPD

Answer 42

Saddles Rests Clasps Major + minor connectors

Question 43

Discuss RPD saddles

Answer 43

Part that covers edentulous ridge Usually (not always) incl. replacement teeth Note: not all edentulous ridges restored by saddles

Question 44

Function and types of RPD rests

Answer 44

Main support provider Function - transmit O forces to teeth along longitudinal axes - maintain O relationship of denture base to abutment teeth - prevent trauma to gingiva - provide some lat. stability - prevent food packing b/w abutment teeth and base Types - occlusal: pre/molars - cingulum: canines - incisal: outdated - ring: wraps all way round tooth

Question 45

What is a rest seat? Function

Answer 45

Any prepared surface on abutment teeth to take rest Function - provide O space b/w U+L teeth to allow adequate metal thickness - provide more suitably inclined bearing surfaces cf natural teeth - provide shape of surface desirable for amount of bracing

Question 46

How to decide where to position RPD rests?

Answer 46

Adjacent to saddle Adequate PD attachment of abutment teeth Equally distributed; opposite Adequate O space

Question 47

Function, types, components and location of clasps

Answer 47

Provide retention Function - utilise resistance of metal to deformation - engage extra-coronal undercuts - usually natural undercuts Types - occlusally approaching - gingivally approaching - ring Components - rest - retentive arm; engages undercut - reciprocal arm; thicker, firm, doesn’t engage, resists displacement - minor connector Location - adjacent to saddle - spread around arch - only need 2 diametrically opposed

Question 48

Discuss Kennedy classification of dentures

Answer 48

Suggests/governs partial denture design 1: bilateral edentulous areas post. to remaining teeth; free end saddles 2: unilateral edentulous area post. to remaining teeth 3: unilateral edentulous area w/ teeth ant. + post.; bounded saddle 4: single, bilateral edentulous area ant. to remaining teeth; crosses midline

Question 49

Discuss Applegate’s rules applied to Kennedy Classification

Answer 49

Missing 7+8 discounted if not being replaced Most post. edentulous area determines classification Modification spaces: additional edentulous areas (Class 2 mod 2) Class 4: no modifications

Question 50

Importance of denture support and how it can be gained

Answer 50

Importance - red. movement on loading - red. trauma - improve distribution loading ``` Gaining: any part of denture that sits on bearing surface - hard tissue: teeth, hard palate — tolerate axial loading — feedback prevents overloading — as low as 20microm displacement - soft tissue: alveolar ridge, hard palate — loading can cause pain/trauma — limited feedback — displacement >500microm ```

Question 51

Ways in which denture retention can be gained w/ natural teeth

Answer 51

Frictional contact Clasps Sectional denture Precision attachments

Question 52

Discuss frictional contact, sectional dentures and precision attachments

Answer 52

Frictional Contact - most mucosa-borne acrylic dentures req. friction b/w base + natural teeth for retention - guide planes enhance effect — also improve clasps; restrict path of removal to 1 path Sectional Dentures - 2 parts w/ different paths of insertion - when seated lock together by hinge or parallel split posts - exploit undercuts on M and or D of abutment teeth Precision Attachments - depend on friction b/w machined M and F parts - req. cast restorations on abutment teeth - usually intra-coronal; may be extra-coronal

Question 53

Define major connector (RPD)

Answer 53

Unit of denture that connects components on 1 side of arch to the opposite side Part of denture to which all other components are attached

Question 54

Principles of major connector design

Answer 54

Rigidity Must not impinge moving tissue Avoid pressure on gingiva Adequate relief when indicated; bony prominences, tori Supported by rests Borders sited and contoured for tolerance

Question 55

Types of mandibular major connector

Answer 55

Lingual Bar Dental Bar Lingual Plate Buccal Bar

Question 56

Discuss lingual bar and space req.

Answer 56

Conventional and sub-lingual types Kennedy connector Not sit on gingival margins Space - at least 3mm clear of gingival margins - clear of moving tissues of FOM - adequate dimensions for rigidity - at least 7mm b/w gingival margin and FOM

Question 57

Discuss dental Bar/connector

Answer 57

``` Sits across teeth Req. crown height of 8mm - 2mm clear of incisal edge; don’t see - 2mm clear of gingival margin - 4mm depth for rigidity (+ 2mm thickness) ```

Question 58

Discuss lingual plate

Answer 58

``` Only used when necessary Covers all gingival margins + teeth - unfavourable - accumulation of plaque - difficult to clean Thin, wide Contoured for intimate contact w/ lingual surface ```

Question 59

Maxillary major connectors

Answer 59

Palatal Bar - ant., mid., post. - usually ant. + post. - narrow, thick (rigid) but bulky - min. palate + gingival margin coverage Palatal Strap - thin, wide metal - lots of palatal coverage, min. gingival coverage Palatal Plate - max. coverage; soft tissue hyperplasia, poor hygiene - most comfortable, best support, rigid Palatal Horseshoe - covers gingival margin - avoids palatal coverage; gag reflex

Question 60

Discuss minor connectors

Answer 60

Connect major connectors to other components Req. - adequate O space - emerge at 90 degree to gingival margin - avoid sharp internal line angles

Question 61

Discuss hygienic denture design and why it is important

Answer 61

Minimal amount of gingival margin coverage; free wherever possible Why - don’t cause plaque formation - promote inc. in amount of plaque where gingival margin covered - alter quality of plaque

Question 62

Discuss how to minimise gingival damage in RPD design

Answer 62

Provide at least 3mm relief or none at all If <3mm; gingival hypertrophy into small spaces making difficult to clean Thus >3mm req. or none

Question 63

Requirements of endodontic instruments

Answer 63

Flexible Maintain cutting edge Not corrode

Question 64

Discuss SS endodontic material

Answer 64

Alloy of ace and <0.8% C; some Ni and Cr Files prepared by twisting wire or machined (Hedstrom) Flexibility depends on geometry, diameter, taper, twists - rhombohedral (K-flex) most flexible

Question 65

What is the only movement twisted SS endo instruments can be used in? Why?

Answer 65

Reciprocating up to 90 degrees As - clockwise: untwists file -> ductile failure - anti-clockwise: tightens twist -> brittle failure — usually fail anti-clockwise

Question 66

Discuss the structure of endodontic Ni-Ti

Answer 66

Can exist in 2 crystal structures w/ different properties Martensite - low temp. form; body centred cubic - low modulus (flexible), high strain @ break Austenite - high temp. form; monoclinic - high modulus (rigid), low strain @ break

Question 67

Discuss shape memory of Ni-Ti

Answer 67

Unique property Deform NiTi with v low force @ lower temp When heated through transformation temp recover original shape - ortho use: apply pressure to teeth as recovers shape Remove deformations by heating to 125 degrees - endo: curve file for canal, removed by sterilising

Question 68

Discuss superelasticity of NiTi

Answer 68

Can be strained much higher cf conventional alloys before permanent deformation occurs Elastic deformation up to 8% cf SS 1%

Question 69

Discuss causes of NiTi # and how it can be improved

Answer 69

``` Both ductile and brittle aspects Due to; - low yield stress - work hardening - structural imperfections produced during manufacture - fatigue ``` Improved by - electropolishing machined surfaces - ion implantation or surface coating to harden

Question 70

Compare NiTi and SS properties

Answer 70

``` Strain: 8% vs 1% NiTi - higher strength, lower modulus - machines; continuous rotation - expensive - better fatigue life, flexibility ``` SS - used for hand instruments - cheaper, can be pre-curved Both suffer fatigue

Question 71

Discuss 3 main irrigants used in endo

Answer 71

NaOCl (0.5-5.25%) 1% - dissolves proteolytic debris - antibacterial - affects instruments - possible toxicity Chlorhexidine 2% - usually chlorhexidine deglutonate - alternative to NaOCl - antibacterial - adheres to dentine - not proteolytic Ethylene Diamine Tetra-acetic Acid (EDTA) 10-18% - lubricant - dissolves smear layer; calcified canals - use in conjunction w/ NaOCl

Question 72

Discuss endodontic medicaments

Answer 72

Non-setting Ca(OH)2 (pulpdent) - most common - alkaline pH12 - antibacterial: OH- release -> damage bacteria preventing growth Ledermix - mix; cortisone derivative and broad spectrum AB — 1% triamcinolone (anti-inflammatory) — 3% demeclocycline (AB) - good for pulpal or PD inflammation - endo-Perio lesion: spread from pulp -> PD tissue ``` Phenolic compounds Quaternary ammonium compounds - not effective - used near toxic level 1% Iodine - 2% Potassium-Iodide - low toxicity, antibacterial - staining; rinse w/ NaOCl ```

Question 73

Discuss phases of gutta percha

Answer 73

60% crystalline, hard, rigid ``` Alpha - high temp., cooled slowly - softer - thermoplastic techniques — heated and injected into canal ``` Beta - high temp., cooled rapidly - rigid - GP points

Question 74

Composition of GP points

Answer 74

GP 19-22% ZnO 59-75% filler Heavy metal salts 1-17% radio-pacifier Wax/resin 1-4% plasticiser

Question 75

Properties of GP

Answer 75

``` Biocompatible Insoluble Thermoplastic - softens 60-65 - melts 100 (can’t heat sterilise) Light degradable (brittle) Swells in solvents (acetone, chloroform) ```

Question 76

Alternatives to GP

Answer 76

Resilon - thermoplastic polyurethane - bioactive glass + radiopaque filler - similar handle cf GP - similar filling techniques - softened by heat, soluble in solvents - req. EDTA Tx and self-etch Prime for good bond Silver - rigid, corrodes - discolour Acrylic or Ti: solve corrosion problem

Question 77

Discuss composition of ZOE for canal sealing

Answer 77

``` Powder - ZnO (MgO) - fillers; SiO2, Al2O3 - dicalcium phosphate - Zn salt Liquid - eugenol - other oils; olive, cotton seed - acetic acid (accelerate) - H2O (essential) Additive - iodides: bactericidal - Ag, Ba, bismuth salta: radiopacity - resins: improve adhesion to canal ```

Question 78

Properties of ZOE

Answer 78

``` Moisture accelerate set Eugenol: allergy, inflammatory reaction, inhibit polymerisation Soluble H2O Obtundant Thermal insulator Good seal ```

Question 79

Composition of setting Ca(OH)2

Answer 79

Paste 1: Base - salicylate Ester: butylene glycol disalicylate - TiO2, CaSO4, BaSO4 (fillers) Paste 2: Catalyst - Ca(OH)2 - ZnO - toluene sulphonamide, Zn stearate (plasticiser)

Question 80

Properties of Ca(OH)2

Answer 80

``` Alkaline: bactericidal Long working T Biocompatible High solubility; water weakens Moisture accelerate set ```

Question 81

Discuss resin based canal sealers

Answer 81

``` Epoxy amine - good handle - good seal Polyketone/Polyvinyl resin, reinforced ZOE - cytotoxic when set Urethane dimethacrylate/BisGMA ``` Properties - insoluble - polymerisation shrinkage - long working T - good flow - radiopaque

Question 82

Discuss GI as canal sealer

Answer 82

Glass powder + PAA Bonds to tooth Short working T Sets hard, difficult to remove

Question 83

Discuss polydimethysiloxane canal sealer

Answer 83

Addition cured silicone (impression material) ``` Good working T Smooth, homogenous mix Good flow Insoluble No bonding Not antibacterial ```

Question 84

Discuss mineral trioxide aggregate

Answer 84

Complex reaction - hydration of tricalcium silicate -> hydrated calcium silicate gel + Ca(OH)2 ``` Sets hard, mixed w/ H2O Strong Alkaline: initial 10.2, set pH12.5 Long set: 3-4h Expensive, difficult to handle ```

Question 85

Classification of dental alloys

Answer 85

High noble - >40% Au - >60% noble metal; Pt, Pd Noble: >25% noble Base metal (Co-Cr, Ni-Cr, Ti) - <25% noble

Question 86

Requirements of RPD alloy

Answer 86

``` Biocompatible Easy to cast - high density: easily force out air of mould, fill w/ alloy - low MPt = low shrinkage Low casting shrinkage Easy to join/solder Easy to finish/polish Easy to adjust High modulus (rigid) High yield stress Good fatigue strength Good wear resistance Good corrosion/tarnish resistance ```

Question 87

Composition of Co-Cr alloys

Answer 87

Co (50-65%); strength, hardness - interchange Ni (0-30%); inc. ductility, dec. hardness Cr (25-30%); hardness (solution hardening), resist corrosion (passive oxide layer) Mo (4-6%); red. grain size, hardness (solution hardening) C (0.2-0.5%); hardness + strength - forms carbides which precipitate on slow cooling - excess carbides = brittle Small amounts: Fe, W, Mn, SI

Question 88

Dis/adv Co-Cr alloy

Answer 88

Adv - cheap - hard, abrasion resistant - high modulus (use in thin section) - high yield stress - low density, lightweight - Ni-free biocompatible - good thermal response Disadv - poor handling — high casting temp, high cast shrinkage (~2%) - low ductility - rapid work hardening (can’t be adjusted) - Ni sensitivity - difficult to finish/polish (due to hardness) — req. electrolytic polishing of fit surfaces

Question 89

Composition of Ni-Cr alloys

Answer 89

Ni (60-80%); hardness, strength Cr (10-27%); hardness (solution hardening) corrosion resistance (passive oxide layer) Mo (2-14%) Be (0-2%); carcinogenic + Al, C, Co, Cu, Mn, Ti - fluidity, castability - limit carbide precipitation, too much = brittle

Question 90

Composition of T4 gold alloys

Answer 90

``` Au 60-70%; lowest amount as ductile Ag 4-20% Cu 11-16% Pt 0-4% Pd 0-5% Zn 1-2% ```

Question 91

General rules for properties of gold alloys from T1-4

Answer 91

As go from T1-4 - hardness (Vickers), elastic modulus (rigidity), tensile strength inc. - ductility, elongation @ break dec.

Question 92

Compare properties of T4 gold cast and hard

Answer 92

Vickers hardness: 130-160; 200-240VH Tensile: 410-520; 690-830MPa Modulus: 95; 103GPa Elongation: 5-25; 1-6%

Question 93

Dis/adv of T4 gold alloys

Answer 93

``` Advantages - biocompatible - easy to — cast; low MPt, shrinkage 1% — finish/polish — solder - corrosion resistant - can be heat hardened (order hardening) ``` Disadvantages - high density; uncomfortable for pt - low yield stress; weaker - low modulus; thick sections - expensive

Question 94

Discuss forms of Ti/alloys

Answer 94

Commercially pure Ti - 4 grades of 99% Ti + varying amounts N, C, H, Fe, O - Inc. O, Fe: inc. strength, Dec. ductility ``` Alloys - alpha: low temp., hexagonal - beta: high temp., cubic centred body - Ti6Al4V alpha + beta — V toxin replaced by Nb: Ti6Al7Nb ```

Question 95

Compare properties of Ti6Al4V and cpTi (G1 vs G4)

Answer 95

``` Hardness: 320; 126-263VHN Tensile: 930; 240-550MPa Yield: 860; 170-480MPa Modulus: 113; 102-104GPa Elongation: 10-15; 24-15% ```

Question 96

Discuss materials used for denture clasps

Answer 96

Wrought - pre-mode, bought clasps, soldered on to framework - SS, Au - better flexibility (esp. Au) and strength - Au: easy to adjust + solder, possible corrosion @ join w/ base metal Cast - cast w/ framework - Co-Cr, T4 Au Base metal clasps have limited adjustment (work hardening) Aesthetic clasps - thermoplastic acetal resin (polyoxymethylene) - used w/ acrylic or Co-Cr RPDs

Question 97

What are cold cure soft acrylics? What is their use?

Answer 97

Temporary soft lining materials Soft, viscoelastic material Use: Tx irritated mucosa supporting denture - allow recovery of inflamed tissue from ill-fitting denture - absorb some energy prod. by masticatory forces - shock absorber b/w O surface denture + underlying tissue - promote healing

Question 98

Discuss properties of temporary SLM/RT soft acrylic

Answer 98

Generally inf. HC soft acrylic (long-term SLM) 3-5% residual monomer: irritant + fungal infection Higher H2O uptake; monomer leach, space filled w/ H2O cf HC Poorer mechanical properties cf HC Temporary: 1-2 wk

Question 99

Discuss composition of RT soft acrylics (temporary SLM)

Answer 99

``` Powder - PEMA — or copolymer of butyl and ethyl methacrylate — or PMMA - residual BP - opacifiers - pigments ``` ``` Liquid - EMA — or BMA — or MMA - ethylene glycol dimethacrylate; cross-linking agent - dibutyl phthalate (or citrate) — phthalate = carcinogen — no chemical bond = leaching - DMPT; 3ry amine activator - hydroquinone ```

Question 100

Compare functions or short term SLM and TC

Answer 100

Similar function, differ; Composition: polymerisable monomer; ethanol, no polymerisable monomer Setting: FR addition polymerisation; gelation + chain entanglement Lifespan: 1-2 wk; 3d

Question 101

What are tissue conditioners? What are their uses?

Answer 101

Soft, viscoelastic materials Uses - Tx irritated mucosa supporting denture (temp. SLM) - temp. (3d) denture liner; Tx denture stomatitis - functional impression material; wear provisional denture 24h - piezograph — impression moulded by tongue, lips, cheeks over 5-10min - maxillofacial prostheses

Question 102

Compare composition of Viscogel and Coe-comfort (TCs)

Answer 102

``` Viscogel Powder - PEMA — or copolymer B/EMA Liquid - plasticiser — butyl phthalyl, butyl glycollate, dibutyl phthalate — acetyl tributyl citrate - ethanol 6-15% - no monomer = no polymerisation ``` Coe-Comfort Powder - Zn undecylenate — Zn: red. irritation + swelling of fungal infection — Fatty acid: prevent growth fungus Liquid - Benzyl Benzoate: plasticiser, preservative - ethyl alcohol: solvent; accelerate gelation

Question 103

Discuss setting of TCs

Answer 103

Set via gelation (chain entanglement), physical process On mixing, polymer beads (chains) swell in alcohol - allows penetration of plasticiser b/w polymer chains - polymer chains move more easily Gel formed by polymer chain entanglement

Question 104

Discuss factors than can affect handling of TC

Answer 104

Inc. powder:liquid - inc. viscosity of gel - affect final compliance (softness) - inc. rate To inc. rate - inc. temp - dec. MWt + particle size of polymer powder - inc. ethanol

Question 105

Advantages and disadvantages of TC

Answer 105

Adv - simple - use chair-side - bond PMMA - compliant (soft) - viscoelastic Disadv - harden in mouth: ethanol + plasticiser leach — ethanol lost within 24h (may be irritant) - possible toxicity of plasticiser - porous: ingress of microorganisms - difficult to remove from denture

Question 106

Discuss general properties of temporary SLM and TCs in relation to interaction w/ fluids and denture cleansers

Answer 106

Fluids - high H2O uptake; stain, microbial colonisation - plasticisers can leach — inc. in presence of long-chain fatty acids, alcohol - inc. surface roughness esp. soft acrylics - more affected cf silicones (long term SLM) Cleanser - all affect SLM and TCs - hypochlorite bleaches - alkaline peroxide roughens surface, bleaches - brush w/ soap

Question 107

What are long-term SLMs? What are their functions?

Answer 107

Group polymeric materials Last in OC >wks/mnths/yrs Intended inc. comfort + support prosthetic Tx Can’t red. forces transmitted by denture bearing area Function - evenly distribute masticatory forces + absorb some energy — relieve mucosa from high mechanical stress - deforms elastically, energy release as returns to original form

Question 108

4 types of long term SLMs

Answer 108

HC addition silicone RT vulcanised cured condensation silicone RT vulcanised cured addition silicone HC soft acrylic

Question 109

Uses of long-term SLM

Answer 109

``` Long-term (wks-yrs), resilient linings Pt can’t tolerate hard denture base Utilise undercuts for retention Retention of complete dentures to implants Obturators and other prostheses ```

Question 110

Disadvantages of long term SLM

Answer 110

Expensive: HC sent to lab Difficult to modify and polish Dec. denture thickness, inc. rigidity/hardness - 1mm thick hardness as support of underlying tissue comes through More prone to #

Question 111

Ideal properties of SLMs

Answer 111

``` Nontoxic, nonirritant Bond PMMA Not support growth of Candida Permanently resilient + compliant Low H2O uptake (similar to PMMA 2%) Not affected by denture cleansers Easy to clean, not easily stained Sufficient mechanical strength + abrasion resistance Wetted by saliva ```

Question 112

Compare the viscoelasticity of silicone-based and soft acrylic SLM

Answer 112

Silicone based recovery rate is faster | Soft acrylics can permanently deform

Question 113

Discuss the composition and setting of HC addition silicone SLMs

Answer 113

Composition: one paste - vinyl terminated poly(dimethyl siloxane) - gamma-methacryloxypropyltrimethoxy silane (MPTS); cross-linker - BP: initiator - PMMA: filler - colouring agents Setting - HC 100degrees for ~2hr; can be microwaved - addition, FR polymerisation - BP oxidises CH3 on neighbour siloxane chains to form cross-links - silane acts as cross-linker - methacrylate group reacts w/ denture base to form bond

Question 114

Composition of RT vulcanised condensation silicone

Answer 114

``` Similar to impression material Base - silicone polymer w/ terminal OH groups - inert filler Catalyst - tetraethoxy orthosilicate; cross-linker - dibutyl tin dilaurate; catalyst - inert filler ```

Question 115

Composition of RT vulcanised addition silicone

Answer 115

``` Base - vinyl terminated poly(dimethylsiloxane) - H+ terminated poly(dimethylsiloxane) - inert filler Catalyst - vinyl terminated poly(dimethylsiloxane) - Pt-based catalyst: chloroplatinic acid - inert filler ```

Question 116

Other components in silicone SLMs

Answer 116

Bonding agent/Primer (all silicones) - polymer in solvent - can contain silane - can contain MMA; bond PMMA denture Glaze/Polish (RT vulcanised) - smooth and seal trimmed areas - not used in contact w/ tissue - unfilled AS, some w/ solvent

Question 117

Compare general properties of SLM silicones

Answer 117

RT vulcanised AS: better mechanical and adhesion to PMMA cf CS HC AS: best adhesion and lower H2O cf RT vulcanised

Question 118

Advantages and disadvantages of SLM silicones

Answer 118

Adv - resilient - compliant - not adversely affected by OC Disadv - poor adhesion to PMMA - poor tear strength - hydrophobic: not wetted by saliva - support growth of Candida - 1-paste HC req. refrigeration (short shelf-life)

Question 119

Composition of HC soft acrylic SLMs

Answer 119

``` Long-term SLM Powder - PEMA — E/BMA copolymer - residual peroxide ``` Liquid - higher methacrylate monomer: E/BMA — contribute to softness - cross-linker: ethylene glycol dimethacrylate - plasticiser: butyl phthalyl, acetyl tributyl citrate — red. Tg below mouth temp

Question 120

Discuss setting of HC soft acrylic SLM

Answer 120

As w/ HC PMMA: FR addition polymerisation on heating Dough technique Initiation: FR attack double bond Propagation: monomers add to chain, chain growth Termination: 2 growing chains meet, FRs combine forming stable covalent bond

Question 121

Advantages and disadvantages of HC soft acrylic SLM

Answer 121

Adv - initial compliance is good: retains softness - wetted by saliva (hydrophilic) - bond PMMA - good tear resistance - polished if chilled Disadv - hardens (plasticiser leach); toxicity - high H2O absorption; plasticiser leach - less resilient cf silicones; don’t remain soft - permanent deformation can occur

Question 122

Discuss waxes and dental waxes

Answer 122

Organic crystalline compounds; natural or synthetic Thermoplastic moulding material - solid @ RT - heated to liquid phase thus is mouldable Pyrolysed; melt and/or decompose -> H2O vapour + CO2 Individual wax - sharp, well-defined MPt - little use Dental - blend 2/+ waxes - material w/ softening temp range over which is mouldable material

Question 123

Composition of dental waxes

Answer 123

``` Wax: synthetic and 2/+ natural Small amount additives - gums: gum Arabic, tragacanth - fats: esters of FAs w/ glycerol - fatty acids - oils - natural (dammar, rosin) and synthetic (shellac) resins - pigments ```

Question 124

Aim of additives in dental waxes

Answer 124

To give set of given properties of specific range of temps Contain range of MWt that affect melting and flow properties Chemical components of natural and synthetic waxes impart characteristic physical properties

Question 125

7 types of natural wax

Answer 125

Paraffin: petroleum - straight chain HC - melt: 40-70 Microcrystalline: heavier petroleum fractions - branched HC - melt: 60-90 Ceresin: petroleum or lignite refining - melt: 61-78 - use: inc. melting range paraffin Carnauba: Carnauba Palm - melt: 84-91 - use: inc. melting range + harden paraffin Candelilla: small shrub - melt: 68-75 - use: harden paraffin Beeswax - melt: 63-70 - use: modify paraffin Spermaceti: sperm whale - use: coating on floss

Question 126

Discuss synthetic waxes w/ examples

Answer 126

Production - combination of chemicals in lab OR - chemical action on natural wax Usage inc.; higher degree of refinement ``` Polyethylene: 100-105 Polyoxyethylene glycol: 37-63 Halogenated HC Hydrogenated HC Wax esters: reacting FAs + alcohol ```

Question 127

Define melting range and flow (waxes)

Answer 127

Melting range - range of temps at which each component begins to soften and then flows Flow: movement of wax molecules which slip over each other (at high temp wax has low viscosity and flows) - mobile as approaches melting range - control of flow/melting range important in manipulating wax - clinic: melting range of bite registration wax only slightly > mouth temp — too high would be uncomfortable for pt - lab: much higher melting range

Question 128

Discuss excess residue and dimensional change (waxes)

Answer 128

Excess residue: wax film remaining on object after removal - may result in inaccuracies in item being produced - important in lost wax technique Dimensional change - waxes have greater thermal expansion and contraction cf any other DM - important in pattern wax: duplicate restoration carved in wax - if heated > melting range/unevenly = expansion > acceptable standards = inaccuracies - on standing dimensional change due to release of residual stress — invest and cast within 30 min after carving wax

Question 129

How are stresses formed in wax?

Answer 129

Heating Carving Bending Manipulating

Question 130

Discuss types and uses of inlay wax

Answer 130

Is pattern wax T1: medium, direct technique T2: soft, indirect technique - restoration made in wax -> metal/ceramic Use: patterns for inlays, onlays, crowns

Question 131

Ideal properties of inlay wax

Answer 131

Direct: soft, plastic > mouth temp Indirect: solidifies < mouth temp Carved w/o flaking or distortion Colour contrast from tooth/die V low residue on vaporisation (<0.1% @ 500 degrees) Low thermal expansion (but high cf DMs) No distortion @ moulding temp (no stress build up) Softens w/ dry heat

Question 132

Composition of inlay wax

Answer 132

Paraffin (60%): weak, flakes thus need additives Carnauba (25%): inc. melting range/glossy finish Ceresin (10%): modify toughness and carving Beeswax (4%): red. flow @ mouth temp, red. brittleness @ RT Dammar resin (1%): improve smoothness, crack and flake resistance, glossy finish

Question 133

Discuss casting wax

Answer 133

Type of pattern wax Use: patterns for partial denture framework Composition: unknown, similar to inlay wax Highly ductile: bend double @ 23 degrees w/o cracking Class 1: easily adaptable 40-45 Class 2: adapts well to surface, not brittle on cooling Class 3: burnt out w/o leaving residue

Question 134

Discuss modelling wax

Answer 134

Use: set up artificial teeth for C denture Composition - paraffin or ceresin (70-80%) - beeswax (12%) - resins: natural or synthetic (3%) - carnauba (2.5%) - microcrystalline or synthetic waxes (2.5%) Properties - easily mouldable w/o cracking, flaking, tearing - easy to carve - melt and solidify repeatedly w/o changing properties - no residue after removal w/ boiling water and detergent

Question 135

Discuss boxing-in wax

Answer 135

Type of processing wax - box wax as sheets - heading as ribbon Use - build up vertical walls around impression before pouring - beading: adapt around impression borders Properties - pliable @ RT - retain shame @ 35 degrees - slightly tacky

Question 136

Discuss sticky wax

Answer 136

Type of processing wax - adhesive wax Use: temp joining of articles - align # parts of acrylic denture - align fixed partial denture parts before soldering Composition - rosin - beeswax - dammar Properties - RT: hard, brittle - melted: sticky, adheres closely to applied surface - #s on movement rather than distorting

Question 137

Discuss impression wax

Answer 137

``` Use: O registry (edentulous impression) Composition - HC waxes: paraffin, ceresin, beeswax - Al or Cu: improve integrity and shape Properties - distorts when removed from undercut areas: only edentulous areas - soft/flows @ mouth temp; rigid @ RT ```

Question 138

Discuss 4 other dental waxes

Answer 138

Wax rim/Bite rim: pattern wax - use: restore O relationship, arrangement of teeth - softening temp > mouth temp - tough, resists # Utility/Rope wax: adapt border of impression Shellac denture base - stable @ mouth temp - high softening point Base plate wax: pattern wax - use: preparing wax patterns for prosthesis - red or pink sheets

Question 139

Compare mucocompressive and mucostatic impression materials

Answer 139

Mucocompressive/displacive - viscous, record mucosa under load - appliance has wider distribution of load during function (stable) — compensates for differing compressibility of bearing area — red. risk # due to flexion - retention compromised as soft tissues return to original position @ rest - examples: impression compound, high viscosity alginate/elastomer (polyether) Mucostatic - fluid, displace less - record un-displaced tissue - better retention as closer adaptation to tissue @ rest - instability during function as tissues distort - examples: impression plaster, ZOE, low viscosity alginate, light body addition silicone

Question 140

Discuss non-elastic impression materials

Answer 140

Rigid materials; little/no elasticity Any significant deformation = permanent deformation Use: no undercuts, edentulous pt

Question 141

Composition, properties and handling of impression plaster

Answer 141

Composition - CaSO4 B-hemihydrate - K2SO4; accelerator, anti-expansion - borax; retarder (counteract K2SO4) - colouring agents; contrast model plaster Properties - mix w/ H2O hemihydrate -> dihydrate - expands on set; sets hard - thinner mix cf model plaster - flows into fine details e.g. ridges - mucostatic - no trays req. - edentulous cases only Handling - mix; load tray, position, hold till sets - may # on removal; retrieve and glue together - beading wax adapted to periphery; indicate where impression ends

Question 142

Discuss impression compound; composition, properties, handling

Answer 142

Composition - resins - waxes - talc; filler - stearic acid; lubricant Properties - thermoplastic - poor thermal conductivity/flow - not reproduce undercuts - mucocompressive - high viscosity; record full depth of sulcus if req. Handling - soften by heating in H2O @ ~60 degree - load stock tray, position

Question 143

Discuss ZOE impression paste; composition, properties, handling

Answer 143

``` Composition - paste 1 — ZnO — Zn acetate - paste 2 — eugenol — inert filler; kaolin, talc ``` Properties - brittle when sets; #s - accurate in thin sections - initial low viscosity and pseudoplasticity - mucostatic Handling - Zn eugenolate formed on mixing - use v close fitting tray or existing denture Use diminishing due to elastomers - edentulous or relining

Question 144

Uses of hydrocolloid impression materials

Answer 144

``` C/P dentures Ortho: base plate Mouth protectors Study models, working casts Duplicating models ```

Question 145

Dis/advantages of alginates

Answer 145

``` Adv - setting behaviour — Na3PO4 (retarder) = viscous paste while seating — rapid once begins = min. impression T - cheap, reliable ``` Disadv - H2O loss — continual shrinkage post-set (cast immediately) = poor dimensional stability — cover w/ damp gauze in plastic bag (few hrs) - H2O/disinfectant immersion — imbibition; initially swells — shrinks; H2O soluble salts eluted — prolonged immersion impractical and unsolved - poor tear strength; large undercuts can’t be reproduced - highly viscoelastic — snap removal technique — permanent deformation up to 1.5%; diminished if undercuts not deep

Question 146

Dis/advantages of agar

Answer 146

Adv - easy to use - cheap - good surface detail Disadv - syneresis (cast immediately) = poor dimensional stability - imbibition; distortion - poor tear strength; better cf alginate - compatibility w/ model materials - highly viscoelastic; permanent deformation up to 1%

Question 147

Uses of elastomers

Answer 147

Accurate replica teeth + supporting tissues - C/P denture, crown, bridge, inlay Border moulding of special trays (polyether) Duplicating of refectory casts Bite reg

Question 148

Dis/advantages of poly(dimethyl siloxane) impression material

Answer 148

Condensation silicone Adv - strength, dimensional stability cf alginate - more elastic cf polyether/sulphide - tear strength, elongation @ break adequate; undercuts reproduced Disadv - dimensional stability; 0.3-0.5% shrinkage 24h - hydrophobic; detergents incorporated (may expand) - mouth dry as possible - mainly lab use - erratic setting: liquid catalyst - limited shelf-life: liquid catalyst

Question 149

Dis/advantages of poly(vinyl dimethylsiloxane)

Answer 149

Addition silicone impression material Adv - best dimensional stability; <0.05% 24h - elastic recovery v good cf polysulphide/ether Disadv - free H2O (plaster) react w/ unreacted Si-H -> H2 = porous model — wait 20-30mins before casting - tear strength, elongation @ break adequate; less cf CS - hydrophobic - natural rubber retard set; S poison Pt catalyst - poor shelf-life, long set

Question 150

Dis/advantages of polyether

Answer 150

Adv - dimensional stability in air - quick set cf polysulphide - reliable - clean handle Disadv - high modulus + low elongation @ break = tears easily (original impregum) - dimensional stability in H2O/vapour; disinfection problematic - permanent deformation

Question 151

Dis/advantages of polysulphide

Answer 151

Adv - strongest impression material: elongation @ break ~500% Disadv - dimensional stability: 0.1-0.2% shrinkage - slow set - dirty handling, unpleasant odour - elastic recovery poor cf silicones, polyether

Question 152

What are investment materials?

Answer 152

Ceramic material used to form moulds for dental castings | Used to compensate for shrinkage of alloy due to change from liquid to solid and thermal contraction

Question 153

General requirements of investment materials

Answer 153

``` Withstand high temp and pressure Easy to manipulate, fast set Smooth surface to give smooth finish to casting and preserve fine detail Chemically stale @ temps used Porous enough to allow air/gas to escape Easily break away from casting Not react w/ alloy Sufficient strength to withstand casting Expand to compensate for shrinkage Inexpensive ```

Question 154

3 general components of investment materials

Answer 154

Refractory: withstand temp, shrinkage compensation - crystalline SiO2: quartz, cristobalite, tridymite Bind: hold refractory particles together Other additions: modify physical properties

Question 155

Mechanisms of expansion of investment materials

Answer 155

Setting expansion of binding - greater in presence of refractory - interferes w/ interlocking of crystals as they form - finer particle size = greater expansion Thermal expansion Inversion expansion of refractory - all crystalline forms undergo sudden expansion as change a -> b form - silica used singly or together to give desired expansion Hygroscopic expansion: in contact w/ H2O during set

Question 156

3 types of investment materials

Answer 156

Gypsum bonded Phosphate bonded Silica bonded

Question 157

Composition of gypsum bonded investment

Answer 157

Refractory: a-hemihydrate CaSO4 (stone) 25-55% Binder: cristobalite and/or quartz 55-75% Additives: 2-3% - C; reducing agent - boric acid, NaCl; regulate set, expansion

Question 158

Properties of gypsum bonded investment

Answer 158

``` 35% hemihydrate, 65% cristobalite: thermal expansion 1.2% @ 700 Setting expansion: max 0.6% in air Hygroscopic expansion: 1.2-2.2% - immersed in H2O or wet liner in casting ring - continues setting reaction - promote crystal growth Cheap Sufficiently strong Porous for Au alloys Req. metal ring for support ```

Question 159

Use of gypsum bonded investment

Answer 159

Gold alloys MPt up to 700

Question 160

Composition of phosphate bonded investment

Answer 160

Refractory: formed by acid/base reaction; 20% Binder: cristobalite and/or quartz; 80% C: red. agent - not for Ag-Pd alloys >1500 as causes brittleness

Question 161

Properties of phosphate bonded investment

Answer 161

``` Mixed w/ H2O - thermal: 1% - setting: 0.5% Mixed w/ colloidal silica suspension - thermal: 1.3-1.6% - setting: 0.5% Hygroscopic: possible when mixed w/ colloidal silica ``` Stronger cf gypsum; don’t req. metal rings Finer particle size = smooth surface cf gypsum Set affected by temp

Question 162

Use of phosphate bonded investment

Answer 162

Higher MPt alloys up to 1000 - gold, base metal, metal-ceramic, all ceramic Preferred choice as can be used for all alloys up to 1200

Question 163

Composition of silica bonded investment

Answer 163

Powder: MgO (neutraliser) Liquid: HCl, ethyl silicate Refractory: cristobalite and/or quartz Binder: formed on mixing liquids - ethyl silicate + H2O -> silicic acid + EtOH - mix powder: silicic acid + MgO -> silica (gel) - dry @ 100 degrees - heat: silica gel -> cristobalite

Question 164

Properties of silica bonded investment

Answer 164

``` Shrinks when dried (remove H2O, EtOH) No setting expansion High thermal expansion: 1.6% Ethyl silicate: hazardous, short shelf life - sodium silicate better EtOH: hazard, flammable Not porous; req. vents Complicated, expensive ```

Question 165

Use of silica bonded investment

Answer 165

High MPt base metal alloys up to 1200 | Mainly partial dentures

Question 166

Requirements of die materials

Answer 166

``` Highly accurate Compatible w/ impression material Dimensionally stable Good # strength Good wear resistance ```

Question 167

Discuss die stones

Answer 167

Improved stone (densite): a-hemihydrate - T4: high strength, max expansion 0.1% - T5: high strength + expansion (0.1-0.3%) - gypsum bonded investment - smooth surface, denser, harder Surface Hardened - filled w/ polymer - die hardener; colloidal silica - cyanoacrylate

Question 168

6 alternative die materials

Answer 168

``` Filled acrylic: autopolymerised, high shrinkage Epoxy - some shrinkage: 0.03-0.3% - can be filled - hard, strong - can be Cu plated - can’t use w/ alginate Polyurethane: good wear + # resistance Amalgam: only w/ inelastic impression material Flexible: silicone, polyether ```

Question 169

Discuss alternative technique for die formation

Answer 169

``` Cu/Ag Plating - directly plate impression w/ pure Ag/Cu - adv — dimensionally stable — good abrasion resistance — good surface detail — strong - disadv — Ag: uses AgCN — can’t use alginate ``` Metal sprayed impressions: bismuth-tin alloy

Question 170

Define immediate, transitional, diagnostic and definitive denture

Answer 170

Immediate: constructed and fitted in same appt teeth XLA Transitional: pt about to loose all/many teeth, add teeth to denture as lost Diagnostic: test inc. OVD or aesthetics Definitive: final set of complete dentures

Question 171

EO findings important in Tx planning denture

Answer 171

``` Jaws: opening, closing Palpate TMJ, MoM Smile line: happy? Change? Lip support: req. more? Overclosed or propped open? Pathology: angular cheilitis Appearance: tooth missing, U lip support ```

Question 172

IO findings important in Tx planning denture

Answer 172

``` All pathology noted + Tx prior to constructing dentures OH and caries assessment Perio health: abutment teeth Existing restorations sound Arches: edentulous areas described Over-eruption Tilting? Drifting? Space: enough width within arch and height b/w arches for teeth ```

Question 173

5 stages in Tx planning for denture

Answer 173

``` Relief of Symptoms - pain resolved immediately - trauma common; ulcer, granuloma Prevention: OHI, diet, F- application Stabilisation - PD/caries paramount - good plaque control - Diagnostic — articulate + survey study casts — provisional denture design - initial denture design Definitive Tx Phase - plastic/cast restorations - RCT - denture construction Maintenance: review ```

Question 174

Discuss the shortened dental arch

Answer 174

Adequate oral function can be maintained w/ 10 occluding pairs of teeth - U&L1-5 ``` Factors affecting prognosis - premolar c ant. teeth healthy - tooth contacts favourable; avoid malocclusion (Class 2/3, ant. open bite) - tooth wear likely? Young, bruxism? — load inc. as no Ms - caution if TMJ problems or bruxist ```

Question 175

6 main reasons for replacing missing teeth

Answer 175

``` Appearance Chewing Speech Swallowing Occlusal maintenance Psychological comfort ```

Question 176

Importance of occlusal maintenance following tooth loss

Answer 176

Teeth will over-erupt/tilt if opposing tooth lost - 92% of cases - ~30% >2mm Factors - occlusal relationship - periodontal support - soft tissues Problems may occur when restorations req. after over-eruption

Question 177

Discuss when dentures need to be provided

Answer 177

Only when req. functionally or psychologically - SDA may be acceptable - fixed options preferred? - benefits > risks - stabilised mouth - pt request Indications - large spans - replacement of supporting tissue - obturation of defects - immediate replacement

Question 178

Why and when are jaw registrations used?

Answer 178

``` Why - allow articulation of master casts — analysis of occlusion — construction of denture components — set teeth according to chosen occlusion ``` When: only when req. - not enough occlusal contacts for casts to be correctly located

Question 179

Compare ICP and RCP/centric relation in choosing for denture

Answer 179

Intercuspal Position - sufficient teeth present - stable occlusion - conformation occlusal approach; use wherever possible RCP/CR - jaw relationships not tooth - insufficient teeth to stabilise occlusion - reorganised occlusal approach; req. extensive fixed restorations - use: inc. OVD, edentulous pt

Question 180

Importance of denture teeth position

Answer 180

Appearance Stability Speech Planning of implant placement

Question 181

What are the general principles when deciding how to position artificial teeth?

Answer 181

Denture surfaces modelled to replace part of pt’s tissue or part of existing denture Usually, want artificial teeth to occupy same space as natural teeth In partially dentate, position usually straightforward to determine

Question 182

Define neutral zone and denture space

Answer 182

Neutral zone: inward pressure from cheeks balanced by outward pressure from tongue Denture space: area limited by tongue, lips, cheeks, residual alveolar ridge

Question 183

3 main clinical scenarios that may present w/ denture pt

Answer 183

Planned transition to edentulism Pt has existing dentures Pt is edentulous but has no existing dentures

Question 184

Tx options when plan is planned transition to edentulism

Answer 184

``` Add to existing partial dentures: best Tx option Transitional denture - construct simple acrylic partial first — convert to C/C later - restores jaw relationship - allows period of habituation Immediate insertion C/C; same day as XLA ```

Question 185

If pt has an existing denture what is important to check with regards to tooth position?

Answer 185

Are teeth in correct position? - lip support - appropriate incisal edge - jaw relationship changed - enough space for tongue - dentures displaced by soft tissues

Question 186

If edentulous pt has never had dentures how do you determine the previous O relationship?

Answer 186

Check gross skeletal abnormalities; easily identified Old photos Anatomical landmarks; incisive papilla, palatal gingival remnant Patterns of muscular activity Function methods of recording denture space: piezography

Question 187

Landmarks used in determining denture tooth position

Answer 187

Incisive papilla: labial surface 1s ~10mm | Palatal gingival remnant: 10mm to buccal surface

Question 188

In new C/C denture how is O height, O anteroposterior orientation, lip support, arch width and arch contour determined on O rim?

Answer 188

``` O height - lip line - 17-21mm below ant. nasal spine - parallel to interpupillary line O orientation: parallel to ala-tragal line Lip support - naso-labial angle - position of incisive papilla; labial 1s 10mm ant. Arch width: palatal gingival remnant Arch contour: residual ridge contour ```

Question 189

How to assess correct OVD in new C/C cases?

Answer 189

``` Aim: FWS 2-4mm Measure: Willis Gauge or Callipers - FWS = RVD - OVD Assess - observe swallowing - watch speaking — S sounds — count 60-70 w/ rims in situ ```

Question 190

In new C/C case, discuss adjustment of L O rim after U O rim adjustment

Answer 190

``` Adjust orientation of L to U Adjust height of L - retromolar pad - FWS (2-4mm) Adjust contour L - U rim contour - lip activity ```

Question 191

Problems and solution to pt who has worn same dentures for long time

Answer 191

Pt unlikely to be able to adapt to marked changes in - extension - form of polished surfaces - occlusal height Solution - copy old denture w/ modifications - compensate for changes taken place since old dentures made

Question 192

Discuss use of piezography in making dentures

Answer 192

Form of functional impression Pt has maxillary denture or adjusted O rim in Viscogel applied to lower base and base seated Pt sips and swallows water to mould Viscogel

Question 193

Reasons for and against acrylic partial dentures

Answer 193

For - cheaper; corners may be cut - fewer stages to construct; test pt tolerance - easier to add teeth to; poor prognosis teeth ``` Against - difficult gaining tooth support — uncomfortable, cause trauma - difficult avoiding gingival margins — plate connectors; strength — U arch possible; trauma - more bulk; is it tolerable? ```

Question 194

Indications for partial acrylic denture

Answer 194

``` Large saddles - influence of tooth support red. Immediate replacement denture Provisional prostheses - test pt tolerance - inc. OVD ```

Question 195

What is the desired denture relief @ gingival margins? Why?

Answer 195

3mm or none at all | Gingival hypertrophy into small areas of relief making v difficult to clean and plaque control difficult

Question 196

Dis/advantages of immediate partial dentures

Answer 196

Adv - maintain aesthetics - replicate tooth space - prevent tongue spread Disadv - may exacerbate post-XLA complications; pain - loss of fit - may need reline/remake; resorption - more post-insertion appt; within 24h

Question 197

Define impression

Answer 197

-ve likeness of teeth and oral structures allowing manufacture of accurate model of structures

Question 198

Classification of impression materials

Answer 198

Properties of when set - Rigid: compound, plaster, ZOE - Elastomeric: PVS, polyether - Hydrocolloid: alginate, reversible hydrocolloid Setting Reaction - Polymerisation: PVS, polyether - Thermoplastic: compound, reversible hydrocolloid - Gellation: reversible hydrocolloid, alginate - Chellation: alginate, ZOE

Question 199

Properties of alginate

Answer 199

``` Stable over short period Hydrophilic - tolerate OC - imbibition, syneresis Accuracy depends on handling Tears easily Elastic Cheap ```

Question 200

Properties of impression compound

Answer 200

``` Inaccurate Rigid Resinous taste Hydrophobic; tolerate disinfection Mucodisplasive Cheap ```

Question 201

Properties of PVS

Answer 201

Poly(vinyl dimethyl siloxane) = addition silicone ``` Expensive Best dimensional stability Hydrophobic; disinfection good, but mouth dry as possible V accurate Elastic Good tear resistance Delayed pouring possible (stable) ```

Question 202

Properties of polyether

Answer 202

``` Hydrophilic Stability; good in air, expands in H2O Good shelf-life (2yr) Good elastic recovery Low setting contraction Tears easily Excellent surface detail ```

Question 203

ZOE impression material properties

Answer 203

Cheap Stable Accurate in thin sections but breaks easily Rigid V strong taste; eugenol (cloves) Hydrophobic; H2O streaks surface, disinfects well

Question 204

Different impression taking techniques

Answer 204

Single stage, single phase Single stage, dual phase 2 stage

Question 205

Discuss single stage, single phase impression technique

Answer 205

Alginate in stock tray - quick, easy, cheap - poor accuracy - difficult to do well Good for 1ry impression for P/C dentures

Question 206

Discuss single stage, dual phase impression technique

Answer 206

Alginate + putty/compound - PVS putty fill edentulous space - putty extend/adapt tray - ensure alginate supported

Question 207

Discuss 2 stage impression technique

Answer 207

Uses 1ry and 2ry impression ``` 1ry impression make special tray - has predictable thickness of impression material 2ry impression is wash impression - min. inaccuracies - supports material @ borders — use material to extend/adapt periphery ```

Question 208

4 criteria for assessing impressions

Answer 208

Extension Rolled Border Anatomical Landmarks Surface Detail

Question 209

Discuss extension and rolled border when judging impression

Answer 209

Extension - over B sulcus - depth and width of sulcus - to vibrating line Rolled Border - indicate correct height and width of border - knife edge: under extended - tray showing: over extended

Question 210

Anatomical landmarks to check for on impression

Answer 210

U - incisive papilla, gingival palatal remnant - residual alveolar ridge, tuberosities - frenae, sulci - hamular notches, fovae palatini L - retromolar pads - residual alveolar ridge - frenae, sulci

Question 211

What should be avoided on impression surface?

Answer 211

Air blows Unsupported areas Tears, drags Saliva

Question 212

General management of occlusal errors for dentures

Answer 212

Decide O relationship @ start of Tx - remember horizontal and vertical component Choose O relationship reproducible in pt - must be kept same at all stages throughout Tx If know natural ICP and have tooth support design around natural ICP If many post. teeth lost use RCP Post. teeth need to intercuspate to function well

Question 213

Discuss ways to check for occlusal errors during denture try in

Answer 213

``` Check tooth position on articulator - intercuspation of post - appearance and position Hold C/C together see if wobbles High spots; shimstock - P denture; check w/ denture in and out ```

Question 214

Outline process of flasking denture

Answer 214

After wax try-in ``` Place wax try-in on master cast Fill 1/2 flask w/ plaster - place cast w/ try-in in plaster - let plaster set Fill other 1/2 flask w/ plaster - paint separating medium on plaster Push 2 flasks together - metal MUST touch Boil off wax; teeth MUST NOT move - ensure all wax removed Mix acrylic + place in flask - push together; ensure metal touching - cure — HC: H2O-bath, low heat, long time Open flask, remove denture -> trim + polish ```

Question 215

5 key areas that errors during FPF can affect

Answer 215

``` Fit Aesthetics Strength Biocompatibility Deterioration/longevity ```

Question 216

How can FPF affect fit of denture?

Answer 216

If wax try-in correct shape and fits, denture should fit If not = flasking errors ``` Use cast for fit surfaces - impression quality important - cast goes in flask Teeth held firmly throughout flasking Wax contours on try-in replicated in acrylic ```

Question 217

How can FPF affect denture aesthetics?

Answer 217

All errors in flasking Acrylic should be translucent not opaque Polished surfaces v smooth (finishing); except where stippled Gingiva + teeth colour natural Teeth not moved from desired position Characterisation; veins etc

Question 218

How can FPF affect strength of denture?

Answer 218

Errors of flasking Acrylic base thick enough; check during try-in Acrylic correct commotion + thoroughly set Join b/w base + teeth strong - ensure all wax boiled off No porosity; mixing, heating

Question 219

How can FPF affect biocompatibility of denture?

Answer 219

Most down to polishing ``` Acrylic cured properly (flasking) Ensure no sharp edges Surfaces smooth where possible Disinfect before fitting Advise don’t wear @ night ```

Question 220

How can FPF affect longevity of denture?

Answer 220

Acrylic maintain appearance; doesn’t absorb stains, colour stability, polished surface - HC better cf cold cure Easy to clean - smooth - no stagnation areas (deep groove where food packs, difficult to clean)

Question 221

When is tooth wear Tx w/ removable pros indicated?

Answer 221

When teeth missing - not all teeth need replacing Wear is so extensive that restoring is not feasible

Question 222

3 areas requiring assessment for tooth wear Tx w/ removable pros

Answer 222

Tooth restorability - enamel (bonding) - reduce lat. forces on restorations - resistance form OVD - wear accompanied by alveolar compensation = FWS normal - pt over closing, no compensation = FWS inc. Initial contact in RCP, pt slide to ICP - difficult to guide pt into RCP - wear facets on teeth help locate — D last standing L + M U tooth contact

Question 223

Importance of FWS assessment for removable pros

Answer 223

If inc. FWS - prosthesis will restore OVD - well tolerated - Tx more simple ``` If FWS normal - prosthesis inc. OVD — use fixed appliance where possible - less tolerable - provisional appliance may be req. — splint ```

Question 224

Indications and req. of provisional removable prosthesis for wear cases

Answer 224

``` Indications - inc. OVD — maintenance of occlusal stops during restorative phase - assess appearance - assess tolerance - protect from further wear/trauma ``` ``` Req. - pt able to eat; review 1-2/12 - night wearing — to protect restorations — min. gingival coverage - OVD inc. tooth supported — use on/overlays — design similar to Michigan splint ```

Question 225

Discuss the definitive prosthesis for Tx tooth wear and possible alternatives

Answer 225

Provisional design completed before tooth preparation - allows to plan restorations of abutment teeth - plan design features; guide planes, rests, attachments Alternatives - onlay denture - overlay denture - overdenture - combination

Question 226

Compare onlay, overlay and overdenture

Answer 226

Onlay: covers O and palatal occluding surfaces - O contacts maintained Overlay: covers O surface to level of gingival margin Overdenture: covers O surface + flange extends beyond gingival margin - root retention helps maintain alveolar bone + proprioception - metal copings may be req. to prevent # — endo Tx - attachments incorporated onto copings; inc. retention — req. 8mm vertical space — good maintenance

Question 227

Common causes of failure of overlay and overdentures

Answer 227

due to failure of components - bruxism - lack of interdental space Longevity must be factored into design

Question 228

What order is denture checked during fit appt?

Answer 228

1. Fitting surface 2. Flanges 3. Occlusion 4. Retention + stability 5. Aesthetics 6. Ensure pt can remove/reinsert 7. Give pt written instructions Review 1wk

Question 229

Before seating denture in mouth during fit appt what should be checked?

Answer 229

``` Any sharp edges using straight probe - saddle borders - fit surfaces Check for acrylic pearls on fit surface No acrylic flash over Co-Cr; where metal in direct contact w/ teeth ```

Question 230

How to check denture is seated correctly?

Answer 230

Rests contacting teeth, P connector contacting mucosa Clasps in correct position - tip in undercut - relief under gingivally approaching - traumatise tissue? Relief under lingual bars; 0.5mm Metal framework against teeth - occlude spray rubs off @ high spots - GHM b/w teeth + framework marks high spots - preventable; good impression, careful planning of tooth preps

Question 231

Discuss how to check occlusion of denture

Answer 231

``` Visual first - natural teeth occlude as should w/ denture in Opposing tooth contacts: GHM, shimstock Pt feedback - meet evenly? - fell natural teeth in contact? ``` Compare occlusion w/ dentures out and in - make sure get same

Question 232

What is the medical devices directive? How does it apply to dentures?

Answer 232

``` Legislation outlining what all medical devices must comply to Instructions for dentures Eating: smaller pieces, softer foods Speaking: req. T to get used to Pain: take out, wear on day of review Night time: remove + soak Cleaning: warm H2O + soap over basin ``` Bring old + new denture to review in ~1wk

Question 233

Why are denture cleansers used? What are their requirements?

Answer 233

Why - remove deposits; food, calculus, bacteria, stains - prevent unpleasant tastes/odours - prevent infection: stomatitis, angular cheilitis Req. - remove plaque, calculus, stains - non-toxic, safe to handle - doesn’t damage denture - antibacterial, antifungal - simple to use

Question 234

5 types of denture cleansers

Answer 234

``` Soap + H2O Denture Pastes Alkaline Peroxides Dilute Acids Alkaline Hypochlorites ```

Question 235

Compare denture cleansers

Answer 235

Pastes - mechanical cleaner - soft, nylon brush - gentle action to red. wear Alkaline Peroxides - immersion cleaning - O2 bubbles dislodge debris - safe, pleasant to use - harmful to temp. soft lining Dilute Acids - softens calculus then brushed off - 5% HCl: damages clothes, corrodes metal - sulfamic acid: less damaging - use infrequently; v effective Alkaline Hypochlorites - v effective: remove plaque + staining - disinfectant: good for stomatitis - corrodes metal, may cause bleaching - suitable for silicone/temp. soft lining

Question 236

How can denture stomatitis been prevented?

Answer 236

Remove dentures at night Good denture hygiene Hypochlorite soaks Topical antifungal: miconazole gel

Question 237

Possible cause of pain under denture, how to detect

Answer 237

Palpate tissues Possibly - nerve - buried root - bony prominence

Question 238

Possible problems that may present at denture review

Answer 238

Localised swollen tissue under denture; uneven contact (high spot) - occlusal problem Loose denture - @ rest (retention); fit surface + border - during function (stability); check all - pt factor: saliva, muscle control L denture lifts up - polished surface problem - lingual undercut Pain on lat. excursion - polished surface problem - PIP rub off in lat. excursion Cheek biting - polished surface problem - provide B overjet Heel contacts; polished surface problem; remove Gagging - U denture loose; fit/polished surface - excessive OVD: occlusal surface - lack of tongue space; polished surface

Question 239

Common causes of denture failure

Answer 239

``` Flexural fatigue; usually old denture Dropped: impact # Midline # - open flanged - midline diastema - deep frenal notch - alveolar resorption under denture - tooth wear -> unfavourable O forces Previous repair Permanent soft lining: thins acrylic Denture base thinning: abrasive cleaning U midline P torus; relief in master cast Bruxism, clenching ```

Question 240

Possible methods of repairing acrylic #s

Answer 240

If clean # (pieces locate out of mouth) - fix w/ sticky wax - pour plaster cast - repair w/ cold-cure acrylic Complex # - alginate ‘pick up’ impression of all/some pieces to relocate - v difficult, remake likely

Question 241

Methods of preventing denture failure

Answer 241

``` Adequate acrylic thickness Strengtheners - selenesse fibres, SS mesh embedded - mechanical retention High impact acrylics (flex) Incorporate Co-Cr denture base ```

Question 242

Tx for debonded/broken denture tooth

Answer 242

Will debond if this film wax left on tooth during boiling out Kept tooth: lab repair w/ cold-cure Missing tooth: impression of opposing arch, send to lab for repair

Question 243

Difference between denture reline and rebase

Answer 243

Reline: resurface tissue side to make denture fit more accurately Rebase: refitting denture by replacing most/all denture base

Question 244

Indication for denture reline/rebase

Answer 244

``` Doesn’t fit; loose, painful Resorption: XLA, surgery Alternative to new denture + flange + permanent soft lining ```

Question 245

Problems w/ denture reline/rebase

Answer 245

Inc. OVD; use thin wash O errors; use closed mouth technique Damage Irreversible changes

Question 246

Define ant. and post. guidance

Answer 246

Ant. - influence of teeth on guidance - can be post. teeth: Class 2 Div 1, Class 3 Post. - influence of TMJ + MoM on guidance - usually only edentulous/severely depleted dentition

Question 247

Discuss mutually protected occlusion and group function

Answer 247

Mutually protected Occlusion/Canine guidance - ICP = RCP - multiple even contacts in ICP on all teeth — tight contact post. — light contacts ant. - complete disclusion of all teeth on lat. excursion using 3s only - complete disclusion of post. on protrusion using even contacts on all ant. - why 3s — longest root: crown:root favourable — P surface morphology suits smooth guidance — in front of masseter = weaker forces Group function - where 3 guidance is impossible use next teeth back to share guidance

Question 248

Discuss strategies used when deciding what Tx approach to use for Tx wear

Answer 248

Conformative - don’t alter current O scheme - teeth restored as individual units - ICP + RCP may/not be coincident Reorganised - purposely alter O scheme - make ICP = RCP - may inc. OVD

Question 249

Discuss methods of creating space for restorations

Answer 249

Crown Lengthening - bone removal + repositioning of flaps apically to inc. tooth length - allows enough retention even when O red. complete - root must be long enough ``` Dahl Principle: restorations @ inc. OVD - vertical ortho - open O by purposely making high restoration on Tx teeth — others move into space - forces must be vertical — jiggling forces = pain + loose teeth - teeth OE into contact + Tx teeth intrude - 4-6/12 for teeth to re-occlude ```

Question 250

Define crown

Answer 250

Rigid restoration which covers part/whole of external aspects of tooth Usually req. some form of tooth prep Constructed in Ag, ceramic, composite or combination

Question 251

Indications for crowns

Answer 251

Protect remaining tooth structure - weakened by caries, large restorations, wear, endo Tx - Ferrule: req. 1.5-2mm beyond margin to protect tooth Aesthetic demands Abutments for fixed/RPD Alter O plane

Question 252

5 types of crown

Answer 252

``` Full Ag Partial Ag Ceramo-metal All ceramic Composite ```

Question 253

Compare indications for FGC and PGC

Answer 253

FGC - max. retention req. - min. aesthetic demands - caries/restorations on all axial walls - perseveration of tooth structure PGC - mod. aesthetic demands - parts of axial walls intact - cuspal protection req. - preservation of tooth structure

Question 254

Compare indications for CMC and all ceramic crowns

Answer 254

CMC - max. retention req. - caries/restorations on all axial walls - high aesthetics All ceramic - caries/restorations on all axial walls - max. aesthetic demands - mod. strength req.

Question 255

5 principles of tooth preparation for crown

Answer 255

1. Preservation of tooth structure 2. Retention + Resistance 3. Structural durability 4. Marginal Integrity 5. Preservation of periodontium

Question 256

Discuss preservation of tooth structure and structural durability for crowns

Answer 256

Preservation of tooth structure - restoration must preserve remaining tooth structure + replace lost tooth - intact tooth structure preserved whenever retention + pt acceptance allow Structural Durability - restorations must contain a bulk of materials that is adequate to withstand O forces + meet aesthetic demands - materials must be confined to space created by tooth prep

Question 257

Discuss retention and resistance of crowns

Answer 257

Retention: resist removal in direct inserted Resistance: resist displacement apically - interrelated, often inseparable Prep taper inc., retention dec. Tooth length inc., retention inc. (at least 1mm prep)

Question 258

How can retention + resistance be improved for crowns?

Answer 258

Auxiliary features: grooves, boxes | Limiting path of withdrawal

Question 259

Discuss marginal integrity and preservation of periodontium for crowns

Answer 259

Restoration will only survive in OC if margins are closely adapted to finishing of preparation Supraginival + well defined margins - aid impression taking - health - accuracy in die construction Biological width - margins >2mm from alveolar crest — combined width of epithelial + connective tissue attahcemtn - encroaching in width = gingiva inflammation, loss of alveolar height, Perio pockets

Question 260

Define 4 parameters of colour

Answer 260

Hue - quality by which possible to distinguish one colour family from another - corresponds to wavelength of light Value - achromatic measure of lightness or darkness of colour - pure black to pure white Chroma: degree of saturation of colour Translucency - high = transparent - low = opacity

Question 261

6 factors affecting colour of tooth

Answer 261

Lighting: look different under different light source - colour corrected (5500K) Value Contrast - relative lightness of object affected by lightness of background - lighter on darker background Hue Contrast - viewed on different background colour, appear to take on complementary colour of background Matamerism - appear same colour under 1 light source, different under different source - due to non-matching spectral analysis curves Opalescence: light scattering caused by fine particles Fluorescence: emission of visible light when exposed to UV

Question 262

Physical factors affecting tooth colour

Answer 262

Natural tooth colour - depends on composition, thickness, structure of tissue - not uniform: true colour mosaic in yellowish-white range - mainly determined by dentine colour Surface Texture - macro: developmental loves + ridges: mamelons - micro: surface detail

Question 263

Special Characteristics of teeth affecting their colour

Answer 263

Complex in/external features - # lines, fissures, cracks - white spots, staining Degree of fluorescence when illuminated by UV Degree of opalescence due to HA crystals Translucency: depends on extent + hue

Question 264

Disadv of using shade guides for determining restoration colour

Answer 264

Subjective Restricted + inadequate range of shades Made from thick, high fusing porcelain: no variation in thickness No surface texture or characteristics Material different from ceramic restoration: different optical properties

Question 265

Adv of technology based shade matching

Answer 265

Objective measurement No influence of surroundings/lighting conditions Improved communication b/w lab + dentist Reproducible Integration w/ hardware + image enhancing software

Question 266

2 types of luting cement

Answer 266

Adhesive | Non-adhesive

Question 267

Compare 2 types of luting cements

Answer 267

``` Non-adhesive - reliant on retentive prep — crowns — retentive onlay — custom cast posts — some prefabricated posts - ZnPO, Zn polycarboxylate, GI ``` ``` Adhesive - reliant on micro-mechanical bond — crowns — RBB — on/inlay — prefabricated posts, non-metal posts - RMGIC, resin ```

Question 268

What to check when crown in die?

Answer 268

``` Fit surface: defects, casting nodules, bubbles Damage - marginal deficiencies - proximal contacts of adjacent teeth Margins - over/under extended - ledges - casting should only touch margins ```

Question 269

Why is no LA preferred when fitting crowns?

Answer 269

Proprioception not impaired | Valuable for assessing occlusion + tight proximal contacts

Question 270

Common errors causing failure to seat crown

Answer 270

Correctable - tight proximal contacts - casting blebs on fit surface - no die spacer (req. sand blasting) - defective margins Remake - impression distortion — will fit casts but not in mouth

Question 271

Types of defective margins + reasons for occurrence

Answer 271

Over-Extended - poor impression - incorrectly trimmed die - surplus untrained wax/ceramic Under-Extended (ledge) - poor impression - incorrectly trimmed die - over-polished casting - difficulty identifying finish line Over Contoured (thick): over waxed Open Margin - poor impression - incorrectly trimmed die - over-polished casting - casting not completely seated - incomplete casting

Question 272

4 parameters to be checked when crown seated

Answer 272

Proximal contacts Marginal fit Occlusion Aesthetics

Question 273

Discuss assessment of proximal contacts and marginal fit of seated crown

Answer 273

``` Proximal contacts - tight as others in mouth - hold crown firmly, test w/ floss - too tight = adjust tighter 1st - adjust — mark w/ articulating paper — rubber wheel, straight hand piece, polish - open contact: Au solder/ceramic in lab ``` Marginal fit - 100microm opening borderline acceptability - over-extended: adjust crown from axial - deficient/ledge: remake

Question 274

Discuss assessment of crown occlusion

Answer 274

Always 1st and last thing to do Know what trying to achieve: have idea of pattern Assess resistance of shimstock on adjacent occluding teeth w/o crown seated - should be same w/ crown in situ Adjusting - mark high spots w/ GHM (black) - adjust w/ large flame diamond - post. hold shimstock firm, ant. light - check lat. excursion; remove non-working side interference - recheck absence of deflective contacts from RCP to ICP

Question 275

Discuss assessing aesthetics of seated crown

Answer 275

CMC: adjust using diamond bur + additional of ceramic Shade improved by adding stains Gross changes anticipated - try-in during biscuit stage - glaze after adjustments Ensure pt happy before cementing

Question 276

Discuss finishing + polishing of crown before cementing

Answer 276

Use sequence of abrasives to achieve smooth surface Au - finishing burs -> rubber abrasive points + white stone - solfex for proximal contacts CMC/Ceramic - soflex, comp finishing diamonds - rubber abrasive points, rubber cup w/ diamond paste

Question 277

Indications, dis/advs for ZnPO as luting

Answer 277

Indications - single FM/CM/Li disilicate/Zirconia C w/ retentive feature - fixed-partial metal-ceramic denture - posts: material of choice as expands - multiple cementation Adv - low film thickness - longest track record - high compressive strength - resistance to H2O dissolution Disadv - acid dissolution - low tensile strength - no molecular adhesion to tooth or crown - technique sensitive; P:L, mixing

Question 278

Indications, dis/advantages of GIC for luting

Answer 278

Indications - single FM/CMC - fixed-partial metal-ceramic denture - high caries risk Adv - F- release - high compressive - low film thickness - post-set: resistant to H2O - considerable bond to tooth Disadv - acid dissolution - sensitive to moisture during set - no molecular adhesion to crown - low tensile

Question 279

Indications, dis/advantages of RMGIC for luting

Answer 279

Indications - single FM/CMC - fixed-partial denture - poor geometry of prep Adv - F- release - high tensile + compressive - low film thickness - molecular adhesion to tooth - resistant to H2O dissolution Disadv - short track record - H2O absorption: expansion + cracking on ceramic

Question 280

Indications, dis/advantages of resin luting cement

Answer 280

Indications - porcelain veneer, RBB metal - onlay: ceramic, zirconia, comp - Crown/FPD: ceramic, zirconia - FM/CMC/zirconia/FPD w/ poor prep geometry Adv - high compressive + v high tensile - H2O + acid resistant - molecular adhesion: tooth + crown Disadv - highly technique sensitive - variable film thickness - difficulty removing proximal + subgingival excess - polymerisation shrinkage = marginal leakage - post-op sensitivity depending on technique + materials

Question 281

Why must PD health be obtained pre-crown prep?

Answer 281

``` Un-Tx gingivitis - swollen - inflamed - loose gingival tissues Creat difficulties w/ - assessing - preping finish line - moisture control - reproducing finish lines Leads to - suboptimal fit -> — further PD deterioration — caries ```

Question 282

Discuss need for soft tissue management during impression stage + rationale

Answer 282

Need - assess margins: supra? in crevice? sub? - if some/all margins @/subgingival req. management Rationale - prevent bleeding - act as physical barrier - retract soft tissue - allow accurate impression of margins

Question 283

Aim of soft tissue retraction + ideal properties of good retraction

Answer 283

Aim: allow reproduction of entire prep Ideal - achieve haemostasis - effective gingival displacement - no irreversible damage - no systemic effects

Question 284

3 main types of tissue retraction

Answer 284

Mechanical Chemomechanical Surgical

Question 285

Discuss mechanical methods of tissue retraction

Answer 285

Retraction Cord - aim: sulcus enlargement, physically displace gingiva away - disadv: sulcular haemorrhage -> moisture control + poor impression Cu Ring - aim: displace gingiva, carry impression material to ensure margins captured - disadv: traumatic, efficacy + impression accuracy

Question 286

Discuss use of impregnated retraction cord for soft tissue retraction

Answer 286

Chemomechanical method Retraction cord soaked in astringent Combine - packing of retraction cord (sulcus enlargement) - + chemical action (control haemorrhage) - = accurate impression Chemicals - iron sulphate 15% - potassium alum - aluminium sulphate

Question 287

Discuss duel cord technique for tissue retraction

Answer 287

Pack 2 impregnated retraction cords into sulcus Method - thinner cord packed 1st + remains in sulcus during impression - larger cord placed on top: follow normal steps — wait 4 mins, wash, remove, dry, take impression Aim: thinner cord red. risk gingival cuff recoiling and displacing impression Disadv: inc. inflammation + tissue damage

Question 288

Discuss use of retraction paste for soft tissue retraction

Answer 288

``` Chemomechanical method Used to create space b/w prep + sulcus - some medicated w/ AlCl - viscous + maintains rigidity — displace gingiva w/o causing trauma ``` Method - express around prep directly into sulcus - wait 2 mins, wash, dry, take impression Adv: quick, easier Disadv: technique sensitive

Question 289

Discuss rotary curettage + crown lengthening methods of soft tissue management

Answer 289

Surgical methods Rotary Curettage - aim: limited removal of sulcular epithelium w/ rotary while prep margin - adv: quick - disadv: trauma, haemorrhage, poor healing, inc. PD destruction ``` Crown Lengthening - bone removal + gingival re-contouring - adv: inc. crown height + retention, create supra margin, aesthetic - disadv — discomfort — furcation involvement; poor cleaning — margins in cementum: difficulty bonding — inc. crown:root ratio — allow T for healing ```

Question 290

Discuss electrosurgery for soft tissue management

Answer 290

Aim - controlled destruction by current from small cutting electrode — high current + temp @ tip - high freq. current cuts +/- coagulates tissues Use - when retraction cord alone not feasible; hyperplastic gingiva - sulcus widening, coagulation, gingivectomy Contraindications - Cardiac pacemakers - topical anaesthetics + flammable aerosol

Question 291

Rationale for blocking out undercuts pre-impression and where they commonly occur

Answer 291

Rationale - addition silicone + polyether rigid once set - may flow into undercuts + become lodged once set Areas - B sulcus - PD bone loss - large interdental space - beneath BP Method: soft wax (ribbon wax)

Question 292

Types of impression trays

Answer 292

Stock - adapted stock Special Triple

Question 293

Discuss use of stock and adapted stock trays for impression taking

Answer 293

Stock - sized according to average curvature of arch; S-XL - rigid plastic; flexible bend under load + distort impression - commercially available + cheap Adapted Stock - impression of last molar — difficult as material drags D; not well supported — modify D using acrylic/green stick/putty to create post. dam - arch wider than stock — warm + soften tray using flame free heater — mould post. B flange out — if doesn’t work use special

Question 294

Discuss use of special and triple trays for impressions

Answer 294

Special - use — shape of arch/tooth alignment/anatomical feature prevent seating of stock —- repaired cleft palate, much wider arch — clearance allows even layer of impression around tooth - disadv: additional lab procedure + cost - don’t use w/ heavy body for crown; in undercuts = v difficult to remove Triple - impression of prep, opposing + occlusion in 1 - use: single preparation w/ stable O + opposing teeth - disadv — dynamic O + guidance movements for whole arch not replicated — less accurate morphology; more O adjustment @ fit

Question 295

Importance of moisture control during impression taking and how this is achieved

Answer 295

Why - pt comfort - improved vision - impression accuracy: silicones are hydrophobic How - 3-in-1, aspirator, saliva ejector - RD - cellulose pads - cotton wool rolls in B/L sulcus

Question 296

Define copy and replica denture

Answer 296

Copy - similar to original denture - some modifications made Replica - exact replica of original w/o modification - v elderly/frail difficulty adapting to new

Question 297

Indications for copy dentures

Answer 297

Previously satisfactory denture - v old, now loose - req. many repairs due to failing material - O worn - poor aesthetics Elderly: allow some changes from idea to allow easier adaptation Less clinical T + pt keep denture used to

Question 298

Rationale on whether to make changes on old or new dentures

Answer 298

Old - all changes easily tested in mouth - easily removable to get original back New - old denture not altered; no matter if intolerable - changes not easily tested - need another replica of changes made after

Question 299

Techniques available for copying dentures

Answer 299

Soap box - most commonly used as cheap + easy - poor results as box flexible Dundee: stock tray + putty - rigid putty must be used to prevent distortion - more expensive cf alginate (£10 vs 8p) Murray Wolland: metal modified flasks - can use alginate - not flexible, good impression w/ no distortion

Question 300

Describe clinical + lab stages in copying denture

Answer 300

Clinic - complete modifications, check pt happy - attach greenstick/thick rolled wax (unnecessary Murray/Dundee) - fill 1/2 copy box, insert denture teeth down, set - apply Vaseline thinly to impression material - fill other 1/2 box, leave some to fill fit surface, close tightly - set, remove, return denture Lab - molten wax poured into teeth, set - self cure acrylic poured into mould, set - wax teeth removed individually, replaced w/ denture teeth Clinic - try in: aesthetics, occlusion — good: closed mouth impression w/ light body — seat U 1st, seat L, close into O Lab: remove excess, FPF

Question 301

Dis/advantages of copy dentures

Answer 301

Adv - less clinical T - pt adapt quickly; used to polished surface Disadv - cost - more lab T

Question 302

Classify luting cements

Answer 302

H2O based - ZnPO - Zn polycarboxylate - GI - RMGI Resin - composite - compomer - RMGI Temp: ZOE/non-eugenol

Question 303

Req. of luting cements

Answer 303

``` Biocompatible Aesthetic Insoluble Adequate mechanical properties Good marginal seal Retention Easy handle Radiopaque Low film thickness ```

Question 304

Composition of ZnPO luting cement

Answer 304

``` Powder - ZnO 90% - others — MgO 10%: hardens, whitens — Al2O3, SiO2: reinforcement — SnF2: short-term F- release - Zn/MgO heat Tx red. reactivity ``` Liquid - phosphoric acid 45-63% aqueous solution - + H2O accelerate set

Question 305

Dis/advantages of ZnPO luting cement

Answer 305

``` Adv - compressive: 40-140MPa; sufficient - bond strength: 0.5-1.5MPa — fairly retentive via mechanical interlocking - elastic modulus: 12Gpa; similar dentine - film thickness: <25microm — adequate if mixed properly — unreacted ZnO 8microm - low H2O solubility once set ``` ``` Disadv - tensile: 5-7MPa; brittle - difficult handle - linear shrinkage: 0.5%; micro-leakage - low pH, slow neutralise — irritation, inflammation, painful set - solubility — 0.04-3% H2O initially — lactic acidosis attack soluble ```

Question 306

Composition of Zn polycarboxylate luting cement

Answer 306

``` Powder - ZnO: heat Tx - others — MgO, SnO 10% — Al2O3, SiO2: reinforcement — bismuth salts: modify set — SnF2: easier mix, strength ``` Liquid - polyacrylic acid 30-40% — freeze dried — liquid = H2O

Question 307

Dis/advantages of Zn polycarboxylate luting cement

Answer 307

``` Adv - film thickness: similar cf ZnPO - bond strength: 1-2MPa — chemical adhesion to tooth + some metal - low pH3-4, neutralises rapidly — high MWt PAA prevent diffusion — less irritation - solubility — H2O: 0.1-0.6% — acid soluble: less cf ZnPO -resistance bacteria ingress ``` Disadv - compressive: 55-85MPa; weaker - tensile: 8-12MPa; better - elastic modules: 4-6GPa - difficult handle

Question 308

Composition of GIC

Answer 308

``` Powder - ion leachable glass - basic: SiO2, Al2O3, CaF2 - other — AlPO4, NaF — Sr3+, Ba2+: radiopacity ``` ``` Liquid - polycarboxylic acid: PAA 50% — copolymer acrylic + itaconic acid - tartaric acid 10% - free dried; liquid = H2O ```

Question 309

Dis/advantages of GIC

Answer 309

``` Adv - film thickness: low, = ZnPO - F release - bond strength: 3-5MPa — chemical adhesion — same ZnPC - compressive: 100-160MPa — inc. w/ age - elastic modulus: 10GPa - solubility: lower cf ZnPO/PC ``` Disadv - tensile: 4-5MPa; brittle - H2O sensitive: protected after placement - difficult handle

Question 310

Composition of RMGIC

Answer 310

Powder - ionomer glass - photosensitiser: DHPT ``` Liquid - PAA, tartaric acid - H2O compatible vinyl monomer (HEMA) — OR PAA w/ pendant methacrylate groups - photoinitator: camphorquinone ```

Question 311

Dis/advantages of RMGIC

Answer 311

Adv - compressive: 40-140MPa; sufficient - bond: 5-10MPa; chemical - tensile: 13-24MPa; better - F- - less H2O soluble - handle Disadv - residual monomer: toxic - polymerisation shrinkage - swell in H2O: PHEMA hydrogel

Question 312

Composition of composite luting cement

Answer 312

Monomers - bisGMA - UDMA - diluent: TEGDMA, EDGMA Fillers: ground quartz, colloidal silica - aesthetics, red. shrinkage, radiopacity - less + smaller size (<20microm) — thinner film thickness Additives - hydroquinone: shelf-life - DHPT/BP: RC - DHPT/Camphorquinone: LC - optical brightener, pigments

Question 313

Special component of self-adhesive resin cement

Answer 313

Adhesion promoting resin: 4-META, MDP Phosphate (MDP) + carboxyl (4-META) promote bond to Ca2+ (tooth) and metal oxide (ceramic/metal alloy) - no direct bond to precious metal - phosphate v susceptible to O2 inhibition Some req. primer to bond tooth, self-adhesive don’t

Question 314

Compare composition of P/L and 2 paste self adhesive resin luting cements

Answer 314

P/L - PMMA powder - MMA liquid - tributyl borane: catalyst - 4-META 2 paste - resin + 4-META (secure, Parkell Inc) - resin +MDP (panavia)

Question 315

Properties of adhesive resin cements

Answer 315

``` Compressive: 180-260MPa Tensile: 40MPa Bond - aesthetic: 15-20MPa - self 20-30MPa Insoluble High film thickness Residual monomer O2 inhibition ```

Question 316

Discuss composition of compomer cements

Answer 316

Powder/Liquid - powder: silica, strontium based glass powders - liquid: UDMA/bisGMA, acid resins 2 paste: mix of glass/silica fillers + resins

Question 317

Discuss bonding to ceramics; how it is achieved and when can’t be used

Answer 317

Tech with hydrofluoric acid - only acid to dissolve silica glass - v harmful to tooth Silane Tx (same as comp filler) Can’t use: high strength alumina/zirconia cores - acid won’t dissolve - silane won’t bond (no silica) - use self-adhesive

Question 318

Compare how to bond to base and precious metals

Answer 318

Base: etch, grit blast Precious: Sn plating, silica coating, metal primer

Question 319

Discuss tin plating, silica coating and metal primers

Answer 319

Sn Plating - cover surface noble metal in Sn - bond strength: improvement depend on alloy used — effective for self-adhesive resin, less so for comp - technique sensitive Silica Coating - silica coating + heat OR silica blasting - bond strength: enhance for any alloy - technique sensitive Metal Primer - bond strength: v effective for precious metal + resin - simple

Question 320

Discuss resin-resin bonding

Answer 320

Use: comp inlay, fibre reinforced bridges, endo posts Problem - bonding uncured -> cured difficult Micromechanical - grit blast remove surface layer - HF etch dissolve silica filler Chemical - silanation of surface filler or surface-embedded silica

Question 321

Req. of metal alloy for fixed appliance

Answer 321

``` Biocompatible: technician, pt Corrosion resistance: degradation, ion release Tarnish resistance Mechanical - high modulus - high yield stress - not brittle Easy handle/casting - low melting range - high density Cheap ```

Question 322

Composition of high Au alloys

Answer 322

``` Main - Au - Ag — hardening: solution + precipitation — whitens — red. tarnish resistance - Cu — hardening: solution + order (if >11%) — dec. MPt ``` ``` Minor - Pd/Pt — hardening: solution + precipitation — inc. MPt — corrosion resistance - In, Ir, Re, Ge: fine grain size - Zn: scavenger ```

Question 323

Properties of high Au which make it easy to cast

Answer 323

Low casting temp High density Low shrinkage: 1.4%

Question 324

Compare general properties of T1,2,3,4 Au alloys

Answer 324

T1 - burnished: improve marginal fit, inc. hardness (cold working) - use: small, well supported inlay (low stress) T2 - burnished - use: larger inlay; not thin section T3 - can he hardened — 400degree 10min for CuO, bonds adhesive resin luting - burnishing difficult - use: in/onlay, FGC, short span bridge, cast cores + posts T4 - can he hardened - not burnishable - use: high stress; removable denture + clasps, long span bridge

Question 325

Composition of medium Au alloy

Answer 325

Au: 40-60% Ag: 25% Cu: 12% Pd: 5% - all form solid solution w/ Au Single phase structure

Question 326

Composition of low Au alloy

Answer 326

Ag: 40-55% Pd: 20% Au: 10-20% Cu: 8-14 OR In: 16-18%

Question 327

Colour of low Au alloys, effect of Cu and In on this

Answer 327

Usually white | Cu-free containing In are yellow

Question 328

Properties and use of med/low Au alloys

Answer 328

Properties: similar cf T3 - hardness: 170-285VHN - yield: 340-380MPa - modulus: 75-90GPa - elongation: 4-10% - cheaper - heat harden: sufficient Cu Use: T3; in/onlay, FGC, short span bridge, cast posts + cores

Question 329

Composition of Ag-Pd alloys

Answer 329

``` Ag: 47-70% Pd: 25-40% Some - Cu: dec. MPt, harden - Zn: scavenger - In: grain size refiner ```

Question 330

Properties of Ag-Pd alloys

Answer 330

Termed white golds Cheaper Difficult cast: high MPt, low density Tarnish: presence of Ag Work harden: limited adjustment Hardness: 55-310VHN Yield: 500-940MPa Elongation: 3-33% High Pd similar to T4

Question 331

Properties of Ni-Cr alloys

Answer 331

Ni: allergen Be: carcinogenic High casting shrinkage Hardness: 400VHN Yield: 500MPa Modulus: 200GPa Elongation: 2%

Question 332

Dis/adv of Ti and alloys

Answer 332

Adv - biocompatible - low density (good for RPD) - corrosion resistance - fatigue limit: highest for alloy Disadv - difficult cast: low density (fixed) - high MPt: 1700 - high casting shrinkage 3.5% - react w/ investment

Question 333

Additional req. of metal-ceramic alloys

Answer 333

``` Good bond to porcelain Not react adversely w/ porcelain Melting range > firing temp - would melt otherwise Thermal expansion slightly > porcelain - when cooling metal retract more - compressive force on porcelain = good bond Low creep/sag ```

Question 334

Composition + properties of high Au ceramo-metal alloy

Answer 334

Au: 85% Pt/Pd: inc. MPt + In, Sn: oxide layer (bond porcelain) No Cu: red. MPt + greening of porcelain Strong bond Melting range low enough to cause sag Modulus: low; min. coping thickness 0.5mm

Question 335

Composition + properties of low Au Ceramo-metal alloys

Answer 335

Au: 50% Pd: 30% Ag: 10% In/Sn: 10% Castability, accuracy of fit, corrosion resistance similar cf high Au Cheaper Higher MPt; inc. Pd

Question 336

Composition + properties of Ag-Pd metal-ceramic alloys

Answer 336

Pd: 60% Ag: 30% In and/or Sn: 10% Cheaper alternative to high fusing gold alloy Improved modulus Difficult cast: high MPt High Ag: discolour porcelain

Question 337

Composition + properties of high Pd alloy

Answer 337

Pd: 80% + Cu, Ga, In, Sn No Ag Cu doesn’t discolour porcelain; unlike in Au containing Poor sag resistance due to creep

Question 338

Properties of Ni-Cr metal-ceramic alloy

Answer 338

Highest modulus of PFM alloy: coping thickness 0.3mm High MPt, no sag High casting shrinkage, poor castability Poor porcelain bond: adhesive failure - Cr (form passive oxide layer) only on surface - thus only bonding to surface and not bulk material Ni allergy Co-Cr can be used - stronger, harder - similar casting problems

Question 339

Discuss Ti metal-ceramic alloys

Answer 339

cpTi, Ti6Al4V High MPt, no sag Passive oxide layer: porcelain bond

Question 340

Advantages of ceramics

Answer 340

``` Aesthetics Relatively inert High MPt Low thermal expansion (similar cf tooth) High elastic modulus ```

Question 341

General composition of dental porcelains

Answer 341

Feldspar: soda (albite), potash (orthoclasej - melt 600-1000degree; form glass on cooling SiO2: glass former - MPt 1700degree; remains unchanged Al2O3: intermediate Na2O, K2O: modifier

Question 342

Discuss use of fluxes in ceramics and boric oxide

Answer 342

Fluxes - added to red. fusing temp - incl. glass modifiers (Na2O, K2O) added as carbonates Boric Oxide - glass former - add ~6% act as flux - red. fusing temp., doesn’t inc. thermal expansion

Question 343

Composition of feldspathic porcelain

Answer 343

Feldspars: 73-85% - Na:K important: K dec. fusing temp., less affect on viscosity Quartz: 13-25% Kaolin (Clay) <4%: only high fusing temp. type

Question 344

Composition of feldspathic glass

Answer 344

``` SiO2: 63%; former Al2O3: 17%; intermediate Boric oxide: 7%; former Potash (K2O): modifier Soda (Na2O): modifier Other oxides - Co: blue - Cr/Sn or Cr/Al: pink - Ti/Zr: opacity - rare earth metals: fluorescence ```

Question 345

How to minimise firing shrinkage of ceramics? Compare firing in air and reduced pressure

Answer 345

Use 3 different particles sizes w/ 7 fold size difference Firing in Air - large particle size range - slow fire, allows air to escape - few, large porosities ~6% Firing in Reduced Pressure - not total vacuum - mix large and small particles - small pores - helps prevent porosity ~0.6%

Question 346

Properties of feldspathic ceramic

Answer 346

Low strength: flexural 60-70MPa - low stress areas unless used w/ high strength support Brittle Highly translucent: aesthetic Ultraconservative prep

Question 347

Discuss strengthening of feldspathic ceramics

Answer 347

Prevent formation + propagation of cracks Generally, compressive force applied to surface to close cracks Inc. strength, red. aesthetics

Question 348

Discuss ion exchange toughening of feldspathic ceramic

Answer 348

Exchange surface Na+ -> K+ - K+ 35% larger Put in compression due to ion crowding Prod. ion exchange coating for ceramics 50-100% inc. strength depending on original composition

Question 349

Discuss dispersion strengthening

Answer 349

When high strength, elastic, crystalline grains added to glass matrix there is inc. strength if thermal expansion match Strength inc. w/ inc. crystal content + dec. crystal size

Question 350

Types of reinforced ceramic cores

Answer 350

Aluminous porcelains Glass infiltrated crystalline structure Pure Zr/Al2O3 cores

Question 351

Discuss aluminous porcelains

Answer 351

Al2O3 reinforced feldspathic core - up to 50%wt fused alpha-alumina - 25microm Crystals act as crack stoppers: similar thermal expansion cf glass Surface defects left critical, glazing has little effect on strength Can cause opacity

Question 352

Discuss glass infiltrated ceramics

Answer 352

Ceramic/glass interpenetrating phase composite ``` Porous crystalline (70%) infiltrated by glass (30%) Glass enters pores = denser material ```

Question 353

Compare In-Ceram Spinell, Alumina, Zirconia

Answer 353

Glass infiltrated crystalline ceramics Spinell - weakest: flexural 200-400MPa - best aesthetics: high translucency Alumina - flexural: 400-600MPa - dec. aesthetics: poor translucency due to refractive index differences Zirconia - strongest: flexural 600-800MPa - poor aesthetics: opacity - transformation strengthening from ZrO2

Question 354

Discuss pure alumina and zirconia cores

Answer 354

Type of reinforced ceramic cores Both polycrystalline Pure alumina - formed by dry pressing - CAD/CAM Pure zirconia - crown + bridge - higher flexural, lower modulus cf Al2O3

Question 355

What is transformation strengthening?

Answer 355

Unique property of zirconia Highly localised stress at crack tip causes load induced transformation of tetragonal -> monoclinic - 3-5% expansion; squeeze crack closed

Question 356

Discuss glass ceramics

Answer 356

Glass made to crystallise by heating in presence of seed crystals/nuclei - crystalline content 30-100% Dispersion Strengthening: through crystal growth - not added (reinforced ceramics) Properties depend on size + vol. crystals - controlled by selection of heat Tx regime

Question 357

3 main crystalline phases in glass ceramics

Answer 357

Fluoromica Leucite Lithium disilicate

Question 358

Discuss fluoromica glass ceramics

Answer 358

Based on growth of tetrasilicic fluoromica crystals Fluorescence - SiO2, Al2O3, MgO - K2O, ZrO3, fluorides Cast as glass, heat Tx produce needle like crystals Flexural 2x greater cf feldspathic porcelain

Question 359

Discuss lithium disilicate glass ceramics

Answer 359

Crystalline phase in SiO2-Li2O glass ceramic system Needle like crystals (70%): highest vol. fraction of crystalline phase Inc. strength + toughness; sufficient for all ceramic bridge

Question 360

Compare leucite containing and leucite reinforced glass ceramics

Answer 360

Leucite Containing - glasses heat Tx produce leucite crystals (35-50%) — tetragonal RT; cubic >625 - use: PFM w/ matching thermal expansion w/ alloy - low flexural, higher aesthetics cf leucite reinforced ``` Leucite Reinforced - on cooling: compressive stresses inc. around crystals as > thermal expansion cf glass — crystals crack, prod. round ended #s — both strengthen - high flexural, low aesthetics - use: single ant. unit, veneer ```

Question 361

Why are colouring systems req. for glass ceramics? Compare methods for leucite and lithium disilicate ceramics

Answer 361

All glass ceramics req. external colour for aesthetics - addition of surface layer or surface staining Leucite: layer powdered leucite reinforced ceramic sintered on surface Disilicate: req. new apatite glass layer system due to differences in thermal expansion

Question 362

Discuss porcelains for PFM/CMC

Answer 362

Low fusing porcelain containing leucite crystals High thermal expansion - ideally slightly < metal alloy - inc. glass modifier (alkali) content Leucite content controlled to give req. thermal expansion

Question 363

Discuss mechanisms of metal-porcelain bond

Answer 363

Compression (main) - thermal expansion: glass < metal - cooling: metal shrinks faster, porcelain compressed - gripped by metal Mechanical - good wetting of metal oxide by porcelain - surface roughness of metal oxide (sandblasting) Molecular: metal oxide layer - all PFM have metal oxide layer - bond via oxides in porcelain VDW’s Forces (adhesion)

Question 364

Discuss Captek

Answer 364

Core for PFM - porous Au-Pt-Pd infiltrated w/ pure Au No oxide layer used - porcelain bonder of Pt and Au micro-filaments - gives micromechanical bonding Good aesthetics Expensive

Question 365

Composition of alginate

Answer 365

``` Na/K alginate Diatomaceous earth: filler CaSO4: cross-linker Na3PO4/Na2CO3: retarder Na fluorosilicate/fluorotitinate: pH controller MgO: pH controller ```

Question 366

Composition of agar

Answer 366

``` Agar Borates: strength Potassium sulphates: accelerator Wax: filler H2O: dispersion medium ```

Question 367

Composition of poly(dimethyl siloxane)

Answer 367

Condensation silicone Base paste - silicone polymer w/ terminal OH - inert filler Catalyst - tetraethoxy orthosilicate: cross-linker - dibutyl tin dilaurate: catalyst - inert filler

Question 368

Composition of poly(vinyl dimethyl siloxane)

Answer 368

Addition silicone Base - silicone polymer w/ terminal vinyl - inert filler Catalyst - silicone oligomer w/ Si-H: cross-linker - Pt salt catalyst - inert filler

Question 369

Composition of polyether

Answer 369

Base - polyether polymer: terminal ethylene-imine - filler: rigidity, dimensional stability - plasticisers: adjust viscosity - pigments, flavourings - triglycerides: intrinsic viscosity Catalyst - sulphonium tetra borate salt: cationic starter - filler, pigment, plasticiser

Question 370

Composition of polysulphide

Answer 370

Base - polysulphide polymer: thiokol S-S - TiO2/ZnS: filler - phthalate ester: plasticiser Catalyst - PbO2: cross-linker - S - stearic/oleic acid - filler, plasticiser

Question 371

Rationale for using elastomer impression materials for fixed pros

Answer 371

Strength + dimensional stability better cf hydrocolloid | Best accuracy

Question 372

Problems associated w/ direct composites

Answer 372

Placement T consuming Difficulty ensuring good tooth-tooth contact Polymerisation shrinkage + marginal adaptation Incomplete cure due to limited DoC

Question 373

Uses of indirect composites

Answer 373

In/onlay Veneer Fibre reinforced composite Suited for - multiple post. restorations in single Q - large restoration mass

Question 374

Advantages of indirect composites

Answer 374

Full DoC: 100% monomer conversion not achieved (better cf direct) Red. polymerisation shrinkage as more polymerisation Improved physical properties + wear resistance cf direct Less abrasive cf ceramic inlay Repairable Cure: light, heat, pressure or combination

Question 375

Disadvantages of indirect composites

Answer 375

Luting cement req. - high shrinkage stresses = bond failure - flash = gingival irritation Effective cure: few unreacted methacrylate groups left - req. polishing to improve bond Highly technique sensitive Micro-leakage, recurrent caries X-ray marginal diagnosis difficult: less radiopaque cf metals Less wear resistant + durable cf ceramics Longevity: long term studies req.

Question 376

Dis/advantages of veneers

Answer 376

Adv: colour stability cf veneering resins Disadv - pre-cured comp + freshly applied resin cement = weakest porting - aesthetics: leakage @ weak interface, stain more (cf ceramic) - req. repair

Question 377

What are fibre reinforced composites? Uses?

Answer 377

Resin composites containing fibres to improve strength and stiffness Use: splint, bridge, crown, removable denture

Question 378

Types of fibres for reinforcing composite

Answer 378

Carbon Glass Polyethylene: UHMPE Aramid

Question 379

Compare mesh/woven and unidirectional fibres

Answer 379

Mesh/woven: better general and multidirectional support Unidirectional - short + long fibres, distributed in many ways in resin matrix - allow construction long span bridges

Question 380

Discuss carbon and glass fibres for reinforcing composite

Answer 380

Carbon - unaesthetic - inc. modulus: strain to failure dec. - conduct electricity Glass - req. binding for easy processing - coupling agent req. to improve interfacial bond - hazardous — careful handle: salts, oils, grease damage — respiratory problems

Question 381

Discuss aramid reinforced composites

Answer 381

V low resistance to axial compression - poor transverse properties - low longitudinal shear modulus Break into small fibrils Hygroscopic Degrade in UV

Question 382

Discuss UHMPE reinforced composites

Answer 382

Excellent modulus and strength:weight properties Lower density cf aramid Excellent biocompatibility Better impact strength cf all others Low MPt: 150 Low surface energy + poor adhesion

Question 383

Dis/advantages of fibre reinforced composites

Answer 383

Adv - high fibre content + good fibre wetting + coupling by resin = (cf particulate resin) — high flexural — high modulus — impact resistance - lighter, translucent, non-corrosive cf metal Disadv - correct bonding system critical to success - lack clinical experience

Question 384

Define temporary and provisional crown, how long must they last?

Answer 384

Temporary: cover prep. whilst definitive crown manufactured; few wks Provisional: test changes in shape/colour during function; few mnths

Question 385

Rationale for temporaries

Answer 385

Protect dentine tubules from micro-leakage Maintain O relationship Maintain aesthetics Maintain interdental space + contacts Prevent gingival hyperplasia @ margins + maintain health Confirm enough O red. + B+L Confirm retention

Question 386

Rationale for provisional crowns

Answer 386

As w/ temporaries + - check changes in O acceptable - check: aesthetics, phonetics, mastication

Question 387

5 methods for constructing temporaries/provisional

Answer 387

``` Overimpression: alginate/putty indices Vacuum formed matrix: created on cast pre-prep. Al Crown: molars Celluloid Crown former: ant. Polycarbonate crown: ant. + premolar ```

Question 388

Discuss overimpression technique

Answer 388

Impression taken in mouth or on cast - tooth broken: wax build up on model prior Complete prep., fill index w/ low exotherm resin, fit in mouth Allow set to rubbery phase - don’t set hard as difficult to remove (undercuts) Trim margin w/ soflex disc Add resin/flowable as req.

Question 389

Discuss vacuum formed matrix method of making temporaries

Answer 389

Stone cast of prep. + 2 teeth either side Resin sheet heated in vacuum forming machine, pressed into place Formed trimmed around teeth Putty index made over formed in position on cast Direct: complete prep., fill w/ low exotherm resin, set Indirect: best marginal fit - complete prep., alginate impression - quick set stone cast, temp. made on this cast - allows higher acrylics + comps to be used

Question 390

Discuss polycarbonate crown formers for making temporaries

Answer 390

Prefabricated tooth shapes for ant., fit where touch unless adapted - 1 colour, expansion, req. lots of adjustment - last resort Choose fit interdental space + roughly correct height Trimmed to correct height - usually cut interdental space to correct shape Crown filled w/ low exotherm resin, adapted to fit Trimmed/polished as before

Question 391

Discuss aluminium and celluloid crown formers for temporaries

Answer 391

Aluminium - anatomical or flat O surface - size as close fit as possible, trim margins - pt bite to form - fill w/ low exotherm resin, set - finish Celluloid - clear crown formers; useful for # tooth, req. temp. quickly - crown approximated w/ crown shearers, pp - fill w/ low exotherm resin, set - finish/polish

Question 392

Discuss TB: aetiology, transmission, risk, Dx, prevention, Tx

Answer 392

``` Leading fatal infectious disease WW Aetiology: mycobacterium tuberculosis Transmission: contaminated, airborne droplet - eradicated by immune system - 1ry TB - lay dormant Dx: Mantoux tuberculin test; ZN stain; sputum culture Prevention: BGC Tx: antimycobacterial 6/12, up to 24/12 ```

Question 393

Clinical signs and oral manifestations of TB

Answer 393

Clinical - pulmonary TB: chest pain, fever, haemoptysis, weight loss, fatigue, productive cough - extrapulmonary: LNs, meninges, pericarditis, skin, GIT - disseminated: enter bloodstream, affect any organ, usually fatal Oral: orofacial TB 2ry, disseminated from lungs - deep, punched out ulcers w/ peri-ulcer swelling + erythema - cervical lymphadenopathy, gland/bone involvement - tongue + gingival lesions — painful, solitary, well-demarcated red papule -> chronic atrophic plaque - cartilage (ear, nose): completely destroyed

Question 394

Discuss sarcoidosis: progression, aetiology, resolution, Tx

Answer 394

Multisystem granulomatous disease Aetiology: unknown - interaction b/w environmental factors + genetic determinant - not autoimmune: immune alteration/dysregulation - red. immune response: inc. infection + cancer Affects: lungs, LN, mouth, salivary glands Progression: slow, symptoms subtle Resolution: spontaneous (mnths/yrs), relapse common Tx - symptomatic - steroid/sparing immune modulator: azathioprine, methotrexate - lung transplant only long term solution in red. vital capacity pt

Question 395

Clinical signs and oral manifestations of sarcoidosis

Answer 395

Clinical - nonspecific: fever, apatite loss, fatigue, cough - respiratory: cough, dysponea, chest pain - skin — lupus pernio: chronic, infuriated papule, mid-face (ala of nose) — rash, erythema nodosum Oral - multiple, asymptomatic submucosal nodules; P, B, L mucosa - gingival + tongue: indurated swelling - FOM: ranula (mucocele from sublingual gland) - X-ray: ill-defined radiolucencies in alveolar bone - parotid: bilateral, painless swelling w/ or w/o xerostomia

Question 396

What is Wegener’s Granulomatosis? Limited vs severe? Aetiology, pathogenesis, mortality, Tx

Answer 396

Rare, necrotising anti-neutrophil cytoplasmic Ab-associated vasculitides - affects: S-M sized vessels Aetiology: unknown Pathogenesis: interaction b/w immune system + environmental factor w/ genetic predisposition Limited: restricted to U+L RT; Severe: additional multi-system manifestation Mortality: high; >90% 2yr in unTx Tx: corticosteroids + cyclophosphamide (immunosuppressant), surgery (repair damage)

Question 397

Clinical signs and oral manifestations of Wegener’s granulomatosis

Answer 397

Clinical - nonspecific: fever, night sweats, lethargy, apatite loss,arthralgia - chronic sinusitis, rhinitis, epistaxis - pulmonary: cough, haemoptysis, dysponea, stridor, wheeze - ocular: conjunctivitis, scleritis, uveitis, proptosis - skin: purpura, ulcers Oral - strawberry gingivitis/hyperplasia: granular enlargement + erythema - bone resorption, tooth loss - painful/less ulcers: B mucosa +/- P

Question 398

Discuss amyloidosis, clinical signs + oral manifestations

Answer 398

Fatal disease, deposition of EC and/or IC insoluble amyloid interfering w/ normal function of organ Clinical - kidney: nephritic syndrome (haematuria, proteinuria, hypertension) - skin: wash papules, plaques anogenital/eyelids/neck - nails: dystrophic, brittle - heart: myocardial insufficiency (fatal) Oral - localised, soft, elastic papules - macroglossia (20%), firm, loss of mobility — lat. ridging due to indentation from teeth - dysgeusia, hyposalivation, submandibular swelling

Question 399

Clinical signs + oral manifestations of anaemia

Answer 399

Clinical - fatigue, breathlessness - inc. infection - pale skin + nail beds, conjunctiva pallor Oral - pale mucosa - inc: glossitis, recurrent apthae, angular stomatitis, candidiasis

Question 400

Oral signs of leukaemia

Answer 400

Pale mucosa Spontaneous gingival bleeding + haemorrhages Painless gingival hyperplasia Ulcerative necrotic lesions

Question 401

Discuss Crohn’s disease: aetiology, Tx

Answer 401

Common inflammatory bowel disease Patchy, full thickness ulcers involving any part GIT - discontinuous involvement = skip lesions Mortality + complications inc. w/ duration Aetiology: unknown; genetic + environmental provoking factor Tx: no cure, symptomatic, diet exclusion; steroids + surgery

Question 402

GI and extra-intestinal signs of Crohn’s

Answer 402

GI - abdominal pain - anal fissures, perianal fistula, abscess (30%) - malabsorption, weight loss, vit deficiency - diarrhoea, stone formation - child: stunted growth, delayed puberty + development Extra-intestinal - rheumatological: ankylosing spondylitis, psoriatic/reactive arthritis, sacroilitis, joint/hip/back pain - skin: erythema nodosum, pyoderma gangrenosum - ocular: recurrent iritis/uveitis - GU: kidney stone, renal amyloidosis

Question 403

Discuss orofacial granulmatosis

Answer 403

Orofacial Crohn’s; can occur separately from Crohn’s Signs - lymphoedema - multiple, non-caseating giant cell granulomas - cobble stoned mucosa: tags, fissures, hyperplasia - tongue: enlarged, fissures - recurrent aphthous stomatitis,p - aphthous-like ulcers - uni/bilateral LMNL: recurrent -> permanent (Melkersson-Rosenthal syndrome) - granulomatous cheilitis -> angular cheilitis (lip swelling)

Question 404

Discuss ulcerative colitis; aetiology, Tx

Answer 404

Idiopathic chronic inflammatory bowel disorder Affects part/whole colon Sub/mucosa not full thickness Aetiology - enhanced reactivity against Ag of normal intestinal flora + certain dietary products - +ve family history Tx: aminosalicylates + corticosteroids, colectomy (cures)

Question 405

Clinical signs + oral manifestations of ulcerative colitis

Answer 405

Clinical - intermittent pattern of acute episodes - bloody diarrhoea, abdominal pain - nutritional deficiency, weight loss, failure to thrive - extra-intestinal: finger clubbing, uveitis, iritis - rheumatological: ankylosing spondylitis, sacroilitis, arthritis - skin: erythema nodosum, pyoderma gangrenosum Oral: less common cf CD - mucosa: erythematous w/ scattered pustules, haemorrhagic ulcers, abscesses - pyostinatitis vegetans: multiple friable pustules; varying severity + pain

Question 406

Discuss coeliac disease; aetiology, Tx

Answer 406

Debilitating chronic inflammatory disease of GIT Aetiology: sensitivity to gliadin Tx: diet restriction, corticosteroids

Question 407

Clinical signs + oral manifestations of coeliac disease

Answer 407

Clinical - diarrhoea: oily, foul smell - indigestion, malabsorption: weight loss, nutritional deficiency — delayed development, failure to thrive, weakness, fatigue - skin: dermatitis herpetiformis: symmetrical, itchy stinging small papules - bleeding: prothrombin deficiency (impaired VitK absorption) - hypocalcaemia: muscle weakness, paraesthesia Oral - glossitis, tongue fissuring, depapillation - ulceration (similar aphthous stomatitis) - candidiasis