dental materials 93 Flashcards

Question

critical surface energy

Answer 1

the surface tension of a liquid that will just spread on the surface of a solid

Answer 2

a liquid must have a lower surface energy than the surface it is being placed on to flow and then stick lower SE liquid will flow onto a higher SE substrate = lower SE as a whole Wet Dentine has a lower SE than Composite filling materials * Therefore this has to be reversed so that the Wet Dentine has a Higher SE than composite * **DBAs increase surface energy of dentine surface to allow composite to flow and stick**

Answer 3

Adhesive absorbed onto surface but also into interior of dentine due to good wetting/surface energies * absorbed component can polymerise * polymer meshes with substrate- molecular entanglement = high bond strength * phosphate-calcium bonds formed \*can be hydrolysed by saliva/dentinal fluid = weakened bonds

Answer 4

dentine conditioner (acid e.g. phophoric 37%) primer bond

Answer 5

acid - phophoric 37% * removes smear layer * opens dentine tubules by removing smear plugs * decalcifies upper layer of dentine * etch washed off with water * collagen network in this top 10μm

Answer 6

**\*!Adhesive part of agent!\*** * Hydrophilic end bond to dentine (think of philic and wetted dentine surface) * Hydrophobic Methycrylate end bond to composite Molecule has to have a spacer group to allow it to be flexible in bonding for all sites Has a solvent (acetone, ethanol or water) to dissolve primer agent

Answer 7

Resin that penetrates into dentine surface attaching to primers hydrophobic surface * Mixture of resins (Usually Bis-GMA and HEMA) * Predominantly Hydrophobic * May contain filler and camphorquinone * forms micromechanical bond within tubules and exposed dentine collagen- Hybrid layer (collagen and resin)

Answer 8

* Overetching can cause collagen to collapse so no resin can penetrate * Overetching can mean the depth of etch is too much for the resin to penetrate fully leaving areas of unsupported collagen * Moisture dependence- too dry (dentine collapses) too wet (primer dilutes- reduced strength)

Answer 9

Self Etching primer + Seperate adhesive * DO NOT remove the smear layer- instead incorporate into bonding matrix * not washed off! * not as technique sensitive in terms of moisture but bond itsef not as good Usually found as a one bottle solution (Self etch and adhesive)

Answer 10

primary caries abrasion erosion failed restorations (secondary caries) trauma

Answer 11

smooth surface finsih/polishable technique sensitive low setting shrinkage (bonding agents and good technique to maintain this)

Answer 12

thermal expansion coefficient pretty poor compared to amalgam and GI under cold stimulus the composite can shrink away from cavosurface margins

Answer 13

biocompatible - generally ok (unreacted monomer can be issue) anticariogenic - gennerally not but some release F

Answer 14

filler particles resin camphorquinone low weight dimethycrylate silane (coupling agent)

Answer 15

conventional * glass/quartz microfilled * microfine silica hybrid * combination of both

Answer 16

decreased thermal expansion coefficient

Answer 17

* improve mechanical properties of material * lower polymerisation contraction * some fillers are radiopaque * greater strength etc

Answer 18

BISGMA * Bisphenol-A * Glycidyle Methacrylate * difunctional molecule - free radicals in teh resin facilitate C=C cross linking (free radical additon polymerisation)

Answer 19

initiator blue light activation -\> releases free radicals * free radicals bond to BIS-GMA resin **confers increased molecular weight and so greater viscosity and strength** converts between 35-80% resin * toxic unreactd monomer left potential reacts with blue light at 44nm - depth of cure 2mm approx

Answer 20

TEGOMA - triethylene glycol dimethycrylate inc proportion of TEGOMA = dec. viscosity * almost like pain thinner

Answer 21

coupling agent acts as a wingman for glass to allow it to preferentially bond to resin and glass rather than water * water would normally adhere to glass particles preventing resin bonding to glass silane methoxy groups do the following: * bind to absorbed water * bind to OH groups in filler

Answer 22

benzoyl peroxide and aromatic tertiary amine 2 pastes, react together to break C=C bonds and release free radicals

Answer 23

procelain fused alloys * porcelain on outside with a metal substructure

Answer 24

porcelain - good aeshtetic but microcracks form at the fitting surface = mechanincal failure alloys - good mechanical properties

Answer 25

fracture within porcelain itself

Answer 26

stress needed to cause fracture

Answer 27

stress/strain ratio - i.e. stress needed to cause a change in shape

Answer 28

dimensional change expereinced before fracture

Answer 29

resistance of a surface to indent or abrasion

Answer 30

hard strong rigid brittle (i.e. low tensile strength - can form defects, liable to fracture)

Answer 31

hard strong rigid ductile

Answer 32

Metal Oxide sandwiched between porcelain and alloy Metal Oxide also helps to eliminate cracks and defects on porcelain surface Alloy acts as a support and limits the strain porcelain experiences

Answer 33

* thermal expansion coefficient * form good bond to porcelain * avoid discoloration of porcelain * mechnical * melting

Answer 34

its important that the alloy has a similar thermal expansion coefficient to the porcelain REDUCES STRAIN

Answer 35

will allow the restoration to have longevity and maximises supporting property of alloy

Answer 36

porcelain chose for aesthetics silive in AgPd can produce a green discoluration copper not used with High Gold due to discolouration

Answer 37

bond strength * Gold (H/L), AgPd and CoCr all adequate (NiCr not) hardness * all adequate (NiCr too hard) elastic modulus * high (rigif) to support porcelain and prevent fracture * NiCr best

Answer 38

recrystallisation temp of alloy must be harder than fustion temp of porcelain or creep will occur

Answer 39

* Match Thermal exp. * Increased melting pt * Forms oxide (Bonding) * Biocompatible v good * Cu presence can cause green discolourisation of porcelain * Melting range too low * Youngs modulus too low (Elastic)

Answer 40

* Increased melting temperature * Slightly better mech. props * Biocompatible good

Answer 41

High melting point Care needed in casting

Answer 42

* High melting pt * High YM * Chromium forms oxide for bonding * High casting shrinkage * Not v biocompatible * Lowish bond strength

Answer 43

* High melting point * Minimal casting shrinkage * High YM * High tensile strength * High hardness * Lowish bond strength * Questionable Biocompatability

Answer 44

Slight differences in thermal contraction coefficient lead to compressive forces which aid bonding

Answer 45

May be electron sharing in oxides During firing porcelain flows and oxides in the metal oxide coating migrate

Answer 46

polymethylmethacrylate

Answer 47

* replaces function of natural teeth * goes in pt mouth * seen by others - aesthetics * has to be cost effective * dimensionally accurate and stable in use - fit and be retained * high softening temp (Tg) * must not distorrt when eating or cleaning * unaffected by oral fluids over time * non-toxic/non-irritant * easy to repair * radiopaque * helps with detection of inhaled or ingested fragments if broken and swallowed

Answer 48

* dimensionally accurate and stable in use - fit and retained * high softening temp (Tg) - must not distort when eating or cleaning * unaffected by oral fluids over time * high hardness and abrasion resistance

Answer 49

* high YM * high proportional limit - only large stresses will cause permanent deformation * high transverse strength - upper denture has 3pt loading (2 lateral and 1 middle downward force) * high fatigue strength - can withstand low stresses over a long time (design dependent) * high impact strength - withstand large stresses applied rapidly e.g. dropping onto hard surface - may form hairline fractures

Answer 50

* artificial tooth - avoid internal stress on cool * high thermal conductivity - so don't burn throat due to not being able to sense hot liquids

Answer 51

low aids retention - simple gravity law

Answer 52

free radical addition polymerisation - adding two molecules of either same or different form to make a bigger molecule without elimination of smaller molecule (i.e. breaking C=C bonds)

Answer 53

activation initiation propagation termination

Answer 54

heat to 72^oC or more releases radical molecules from symmetrical benzoyle peroxide molecule

Answer 55

free radicals break down C=C bond in methacrylate monomer and transfer free radical

Answer 56

growing polymer chain

Answer 57

of polymerisation chain stops growing

Answer 58

powder liquid

Answer 59

* initiator - Benzoyl Peroxide * PMMA particles - pre-polymerised beads * plasticiser - allows quicker dissolving in monomer liquid * co-polymers - improve mechanical properties

Answer 60

* Methacrylate monomer - dissolves PMMA beads and polymerises * Inhibitor - hydroquinone - prolongs shelf life by reacting with free radicals * co-polymers - improve mechanical properites

Answer 61

increased molecular weight = better mechanical properties

Answer 62

* free monomer - irritant * low molecular weight - poor mechanical properties

Answer 63

* gaseous porisity * voids in acrylic caused by monomer boiling * polymerisation shrinkage * monomer shrinks 20% due to poor packing, lack of excess material * contraction porosity

Answer 64

fine cracks forming in material

Answer 65

aggregate of atoms in crystalline structure

Answer 66

combination of metal atoms in a crystalline structure (metals are the building blocks of these)

Answer 67

fracture strength

Answer 68

maximum strength without plastic deformation

Answer 69

ultimate tensile strength

Answer 70

amount of plastic deformation prior to fracture

Answer 71

upward curve - molten metal flat line - liquid\>solid lower descending curve - cooling

Answer 72

body centred cubic

Answer 73

face centred cubic

Answer 74

atoms at these sites act as nuclei of crystallisation crystals grow to form dendrites (3D branched lattic network) crystals (or GRAINS) grow until they impinge on other crystals region where grains make contact is called a GRAIN BOUNDARY

Answer 75

equi-axed grains radial grains fibrous grains

Answer 76

if crystals growth of equal dimension in each direction

Answer 77

molten metal cooled quickly in cylindrical mould

Answer 78

wire pulled through die cold worked metal/alloy

Answer 79

fast cooling more nuclei, small fine grains

Answer 80

few nuclei, large coarse grains

Answer 81

impurities or additives act as foci for crystal growth

Answer 82

each grain is a single crystal (lattice) with atoms orientated in given directions (dendrites)

Answer 83

change in orientation of the crystal planes (impurities concentrate here)

Answer 84

high elastic limit increased UTS and hardness decreased ductility

Answer 85

forces applied and defect moves along (propagation) * when defect reaches grain boundary the lattic changes into new shape to free defect dislocations - imperfections in crystal lattic increases * elastic limit * UTS * hardness decreases * ductility * impact resistance

Answer 86

* grain boundaries (hence the fine grains) * different alloys have different atom sizes * when cold working builds up at grain boudaries

Answer 87

* down at low temp - _below recrystallisation_ temperature so some changes can be made * causes _SLIP_ - dislocations collect at boundaries * results in stronger harder material * improves * elastic limit * UTS * hardness * decreases * ductility * corroision resistance * impact resistance RESULTS IN INTERNAL STRESSES

Answer 88

not in perfect position - causes instability in the lattic * results in distortion over time (undesirable!) releived by annealing process

Answer 89

heating metal/alloy to cause thermal vibrations * vibration cause migration of atoms re-arrangement of atoms within grains * doesn't change mechanical properties or grain structure as a whole care has to be taken as if temp too high causes grains to swell and poorer mechnical properties

Answer 90

spoils cold work benefit but allows further cold working continue bouts of cold work and recrystallisation until desired shape acheived _greater amount of cold work the lower recrystallisation temp_

Answer 91

combination of 2 or more metals or metals with a metalloid (Si, C) better mechanical properties than an individual metal lower melting point than individual metal

Answer 92

physically distinct homogenous structure (can have more than one component)

Answer 93

homogenous mixture at an atomic scale

Answer 94

grains consising of metal A only

Answer 95

individual grains of metal A+B in lattic network (distinct)

Answer 96

one phase but metal A+B in homogenous mixture (solid solution)

Answer 97

be insoulble, no common lattic (2 phases) intermetallic compound - with specific chemical formulation e.g. Ag₃Sn be soluble and form a solid solution (3 types)

Answer 98

_subsititution_ - atoms of one metal replace the other metal in the crystal lattic/grain * random substition * ordered substition _interstitial_ - atoms of markedly different in size - small atoms located in spaces in lattic/grain structure of a larger atom e.g. FeC

Answer 99

crystallisation begins

Answer 100

crystallisation ends

Answer 101

temperature the alloy begins to crystallise

Answer 102

temperature where it solidifies (completely crystallised)

Answer 103

at single temperature

Answer 104

over a temperature range

Answer 105

**must cool molten alloys slowly** allows metal atoms to diffuse through lattice * ensure grain composition is homogenous downside is it has hard grains - so poor mechanical properties

Answer 106

rapid cooling of alloys causes a concentration gradient to form * different proportions of metal with one starting in low conc and increasing and the other metal antithesis of this coring helps improve mechanical properties by reducing dislocation movement and resulting in small grains

Answer 107

gentle heat and vibrate atoms, helps atoms to diffuse (below recrystalistallisation temperature) to reduce the coring but not altering the grain structure allowing a more homogenous proportion of metal right the way through its depth

Answer 108

in metals the defect rolls smoothly over the lattic along the slip plane in alloys the defect has to 'fall' into the space between the large and small atoms and climbs over the atoms alonge the grain boundary but requires a great degree of effort to do so * instead of flying over a crowd of people you have to climb over them because you cant get through them* * Requires more stress to move dislocations in a solid solution = inherently better mechanical properties

Answer 109

alloy melts at a temperature higher than that of its individual metals (together = stronger)

Answer 110

physically distinc grains soluble in liquid state insoluble in solid state unusual in that it is an alloy which cools at a single temperature not over a range

Answer 111

produce an accurate replica of the surface and shape of hard and soft oral tissues

Answer 112

negative reproduction of tissues

Answer 113

e.g. ZOE, low viscosity alginates fluid materials that displace the soft tissues slightly - i.e. give an impression of the undisplaced mucosa

Answer 114

e.g. impresion compound, high viscosity alginates/elastomers viscous materials that record an impression of the mucosa under load i.e. give impression of displaced soft tissue

Answer 115

it is advantageous to wait for a time T_F - T_L after removing the L tray before you pour the cast - so as to minimise permanent strain (deformation) remove the tray with a sharp pull to minimise permanent deformation

Answer 116

hydrocolloid - alginate elastomers

Answer 117

A colloid is a 2 phase system of fine particles (1-200nm) of one phase dispersed in another phase (water is dispersing medium in hydrocolloid) e. g. irreversible alginate * reversible agar (no longer used as cross infection)*

Answer 118

irreversible hydrocolloid 2 Na_nAlg + _nCaSO₄ ——\> _nNa₂SO₄ + Ca_nAlg Cross linking with Calcium allows the alginate to set * intermediate reaction between sodium to calcium stage allows a delay in setting * Use perforated tray with adhesive for alginate! * remove tray with a sharp pull * large bulk reduces strain on material

Answer 119

Sodium alginate (reacts w/ calcium ions) Calcium Sulphate (provides calcium ions) Trisodium sulphate (delays gel formation) Filler (increases cohesion and strength) Modifiers, flavourings, chemical indicators (surface, taste, pH)

Answer 120

polysulphides polyethers (impregum) silicone

Answer 121

monophase impression material can break stock trays - must make special tray made of prepolymer, catalyst and filler undergoes addition polymerisation type reaction

Answer 122

impression compound impression paste

Answer 123

low viscosit wetting ability

Answer 124

immediate - on setting (contraction), on removal (deformation, viscoelasticity, rigidity) long term

Answer 125

strength tear resistance

Answer 126

accuracy dimensional stability handling characteristcs cost taste colour

Answer 127

wash under running water soak in perform for min 10 mins wash under running water again bag in moist tissue

Answer 128

potassium perozomonsulphate/sodium benzoate

Answer 129

need to be rigid esp for single stage imp techniques involving putties

Answer 130

acrylic - cold cure or light cure chairside silicone can be modified with green stick

Answer 131

allows material to latch onto tray to prevent separation occuring (alginate) non perforated trays used with compound

Answer 132

helps direct impression material square - dentate pt oval/rounded - edentulous

Answer 133

72% iron 19% chromium 8% nickel 1. 7% Titanium 0. 3% carbon

Answer 134

main constituent and when combined with carbon forms steel

Answer 135

lowers the temperature at which martensitic SS forms i.e. main component of hard SS used in ortho

Answer 136

lowers critical temp that the austentite breaks down on cooling improve the corrosion resistance of the alloy improves strength

Answer 137

prevents precipitation of chromium carbides at the grain boundaries

Answer 138

allotropic - undergoes 2 solid state phase changes 1) Temp \>1400^oC - Body centred cubic lattice with low carbon solubility (0.05%) 2) Temp \> 900-1400^oC - Face centred cubic lattice with higher carbon solubility (2%) 3) Temp \> \<900^oC - Back to form in stage 1with temperature

Answer 139

Austenite * Interstitial solid solution * face centred cubic which exists at \>720^oC Ferrite * Very dilute solid solution, exists at low temp Cementite * Fe₃C, exists at low temp Pearlite * Eutectoid (minimum transformation temp between solid solution and simple mixture) * mix of ferrite and cementite (i.e because they are both at low temp)

Answer 140

martensite

Answer 141

formed because there is no time for diffusion of carbon through the lattice has a distorted BCC lattice is very brittle but this can be lessened by tempering

Answer 142

Heating at 450^oC following quenching, helps to control poor mechanical properties

Answer 143

\>13% chromium

Answer 144

corrosion resistance due to chromoium oxide layer in SS but can be attacked by chlorides Lowers the Austenite to Martensite temperature Lowers the Austenite to Martensite transition rate Decreases the % of carbon which forms a Eutectoid

Answer 145

12-13% Chromium + little carbon Heat hardenable (tempering process) dental instruments often mate of

Answer 146

contains sufficient Chromium and Nickel to suppress austenite to martensite transition i.e more than normal amounts of these metals Used in * sterilisable instruments which don’t have a cutting edge * Ortho wire, due to them being readily cold worked and their corrosion resistance * Sheet form for denture bases Corrosion resistance is more important than strength and hardness

Answer 147

manipulated by cold working i. e. are drawn into wire shape e. g. ortho wire and partial denture clasps

Answer 148

* high springiness/ Elastic Modulus (YM) * stiffness (High Young's Modulus) * high ductility * easily joined without impairing properties i.e. soldered or welded * corrosion resistant

Answer 149

ability of a material to undergo large deflection (to form arc) without permanent deformation i.e. returns to its original shape

Answer 150

occurs at 500^o-900^oC chromium carbides build up at grain boundaries alloy becomes brittle * less chromium in central region of solid solution * periphery more susceptible to corrosion solution -\> low carbon steel, stabilised stainless stel with small amounts of titanium which forms carbides preferentially and not at grain boundaries

Answer 151

* much thinner than acrylic * lighter * fracture resistant * corrosion resistant * polishable * high thermal conductivity * high impact strength - won't fracture when dropped * high abrasion resistance

Answer 152

* dimensional inaccuracy during die process * elastic recovery of steel can lead to inaccuracy * damage of die under hydraulic pressure * loss of fine detail * difficult to ensure uniform thickness

Answer 153

vitreous phase fusion firing (sintering)

Answer 154

formed by a flux i.e. Feldspar, this breaks the terahedral structure of silica forms an amorphous 2D structure feldspar lowers the fusion and softening temperature of the glass during firing it forms a solid mass around the other components

Answer 155

feldspar reacts with the outer layers of silica known as Kaolin - melding the particles together and forms leucite at 1150-1500^oC molten mass then is quenched and ground to a fine powder known as frit this stage that you incorporate opacifiers, metal oxides and crystalline alumina for colouring and strengthening

Answer 156

heating leads to sintering occurs just above the glass transistion temperature glass phase will soften and the particles coalesce causes contraction of the material by about 20%

Answer 157

feldspar silica kaolin metallic oxides

Answer 158

potassium aluminium silicate and sodium aluminium silicate potash - PAS soda - SAS

Answer 159

formed by tetrahedra when reacting it forms an amorphous high melting point glass which bonds to the feldspar

Answer 160

china clay confers opacity on porcelain and contributes to the formation of the glass matrix becomes sticky when mixed which allows the porcelain to be worked to shape a crown

Answer 161

small amounts of metallic oxides provided blended with unpigmented frit

Answer 162

aesthetics chemical stability thermal properties dimensional stability mechanical properties

Answer 163

colour stable retain surface very well without staining smooth surface and have great optical properties

Answer 164

very stable unaffected by the pH changes and ranges in the mouth doesn't stain good biocompatability

Answer 165

similar to tooth subtance similar thermal expansion coefficient to dentine thermal diffusivity low too

Answer 166

20% shrinkage when fired but in the mouth literally no change

Answer 167

very hard can damage opposing teeth if not glazed high compressive strength very low tensile strength

Answer 168

static fatigue surface micro-cracks slow crack growth together mean feldspathic ceramics can only be used in anterior region

Answer 169

decrease in strength over time in the absence of any applied load, thought to be due to hydrolysis of Si-O groups within the material over time in an aqueous ennviroment

Answer 170

can occur during manufacture, finsihing or due to occlusal wear

Answer 171

cyclic fatigue under occlusal forces in a wet environment over time

Answer 172

metal copings (porcelain fused to metal alloy) alumina core zirconia core

Answer 173

core material in Porcelain Jacket Crowns better flexure strength than feldspathic porcelain alumina particles stock cracks propagating however its opaque so can't be used as a restorative material

Answer 174

zirconium dioxide * zirconia powder doesn't sinter unless heaated at over 1600^oC * pure zirconia can crack on cooling * zirconia is a monoclinical structure * Ytrria stabilisation - allows zirconia to be used as a bridge * zirconia goes through manufacturing process and is veneered with feldspathic porcelin to produce the final restoration

Answer 175

zirconia contains small amounts of Yttria Yttria has a tetragonal structure (zirconia is monoclinical) crack starts, tip of crack causes the yttria to reach a critical stress level and causes it to convert to the monoclinical structure like the rest of zirconia which will manifest as the crack is healing over allows it be used for bridges

Answer 176

great aesthetics because of cores opacity excellent fit

Answer 177

expensive equipment initial but material is cheap porcelain can debond from core inert fitting surface so cannot etch or bond

Answer 178

lithium disilicate/reinforced glass is the ceramic used in this wax up restoration invested cast from ceramic ingot undergoes ceraming i.e. reheating it once cast to improve crystal structure and produce crack inhibiting crystals

Answer 179

1 - crystals formed: max no. nuclei formed 2 - crystal growth: max physical properties

Answer 180

any silica containing crowns can be etched with hydrofluric acid to produce a retentive surface * this surface can be bonded to using a silane coupling agent and then bonded to the tooth using an appropriate agent Zirconia crowns are inert so cannot be ethced, howevere strong enough to be self supporting and can be bonded with a traditional cement

Answer 181

milled crowns have consistent physical properties meaning they are better overall

Answer 182

* viscosity/film thickness * ease of use * radiopaque * marginal seal * biocompatibility * mechanical properties

Answer 183

dependent on size of powder/filling particles must be low to allow seating of restoration without interference viscosity increases as the material sets - highlighting the importance of seasting it quickly and with pressure 25 micro-metres thickness ideally

Answer 184

easy to mix working time should allow seating of restoration should have short setting time

Answer 185

some ceramic crowns are radiolucent radiopacity allows marginal breakdown to be illicited on radiographs

Answer 186

ideally should bond chemically to the tooth and form an inpenetrable bond

Answer 187

non toxic low thermal conductivity pulp friendly

Answer 188

high compressive strength high tensile strength high hardness YM similar to tooth

Answer 189

zinc oxide - main reactive ingredient magnium dioxide - gives white colour and compressive strength other oxides (alumina, silica) - improve physical properties and alter shade of material

Answer 190

phosphoric acid - aq solution aluminum oxide - ensures consistency of set material zinc oxide - retardant to reaction giving bettern working time

Answer 191

acid/base * ZnO + 2H₃PO₄ -\> Zn(H₂PO₄) + H₂O hydration reaction * ZnO + Zn(H₂PO₄) + 2H₂O -\> Zn₃(H₂PO₄)₂ . 4H₂O * makes Hopiete

Answer 192

prevents crystallisation leading to an amorphous glassy material glassy matrix of acid salt surrounding unreacted ZnO powder Matrix is almost insoluble but is porous and contains free water from the setting reaction the cement matures and binds to the water leading to a stronger less porous material

Answer 193

Low initial pH of 2 can cause pulpal irritation Exothermic setting reaction Not adhesive to tooth or restoration - acts almost like grout - just filling in spaces Not cariostatic final set takes 24 hrs brittle opaque

Answer 194

Similar material to Zinc Phosphate cement but instead of Phosphoric acid it is replaced with Polyacrylic acid Bonds to tooth surfaces a bit like GIC Less exothermic pH is low to begin with but returns to normal faster, long chain acids less damaging to the dentine cheap but * difficult to mix * difficult to manipulate * soluble in oral environment at low pH * opaque * lower modulus and compressive strength

Answer 195

* low shrinkage/stablity * relativly insoluble once fully set * aesthetically better than ZnPhos * self adhesive to tooth substance * F release * cheap * highly soluble

Answer 196

* composite bonds to composite * micromechanical bonding occurs on the rought internal surface of the composite inlay * bond is also chemical to remaining unbroken C=C bonds on the inlay surface * using a dual curing cement as light penetration using conventional cement wouldn't work

Answer 197

is brittle and is required to be bonded to tooth to prevent fracture untreated porcelain is smooth and non-retentive can be treated with HF to etch the surface (v.toxic) produces a rough retentive surface but is still not hydrophobic and compatible with composite resin luting agents **requires a surface wetting agent - silane coupling agent** thin porcelain - light cure composite can be used thick porcelain - dual cure needed

Answer 198

allows a strong bond to form between the silcon group in the porcelain and the base carbon as part of the composite monomer

Answer 199

like porcelain, composite doesn't directly bond to metal metal surface needs roughened - etching or sandblasting electrolytic etching (beryllium alloys best) need a dual cure luting agent

Answer 200

use carboxylic/phosphoric acid derived materials MDP and 4-META both molecules have an acidic C=C end, this reacts with the metal oxide and renders the surface hydrophobic

Answer 201

change to precious allow composition to allow oxide formation increase copper content and head to 400^oC sulphur based bonding agent

Answer 202

acid groups bind with calcium in HPA forming a stabilising attachement between tooth and resin ions from dissolution of filler neutralise the remaining acidic groups forming a chelate reinforced methacrtylate network limited removal of smear layer or significant infiltration into the tooth suface (only a couple of microns) good bond strength to dentine

Answer 203

enamel * lower than dentine * should be etched with acid prior to application dentine * better than to enamel * no need to etch ceramics * brand specific - RelyX unicem bonds quite weel to sandblasted Zirconia metal * better to non-precious metal * not good enough for ortho brackets

Answer 204

dont fully set and remain soft so can be removed easily prep must be physical base * ZnO * start * mineral oil accelerator * resins * eugenol or ortho EBA * carnuaba wax wax weakens the structure of the set cement and makes it easier to remove material can be modified to make it weaker still by incorporating petroleum jelly into the mixture eugenol not used when permenanet cement willl be resin as it inhibits set

Answer 205

N.B Contain PDS but some of the methyl groups replaced by Hydrogen and Vinyl hence termed PS instead of PDS Base paste * polydimethylsiloxane - some methyl (CH3) groups replaced by hydrogen * filler - variations change viscosity Catalyst paste * polydimethylsiloxane - some methyl groups replaced by vinyl (CH2 =CH) * filler - variations change viscosity * platinum catalyst eg chloroplatinic acid Base Paste ((PDS (Hydrogen)) + Catalyst ((PDS) Vinyl)) + Chlorplatinic acid ——\> Cross linked Polymer formed (NO BYPRODUCTS) Hydrophilic Silicones * incorporate non-ionic surfactant * wets tooth surface * more easily wetted by water containing die materials

Answer 206

TYPE 1 reaction * Silicone Polymer + Organhydrogen Siloxane (cross linking agent) ——\> Cross linked Silicone Polymer + Hydrogen Evolved TYPE 2 reaction * Silicone Polymer (Double OH) + Alkoxy orthosilicate (cross linking agent) + Silicone Polymer (Single OH) —-\> Cross Linked polymer + Alcohol * within the monomer rather than the ends of chains

Answer 207

base paste * amine terminated prepolymer for cross linking * inert filler (viscosity and strength) catalyst * ester derivative of aromatic sulphonic acid initiates polymerisation * inert oils and filler form paste polyether + sulphonate ester -\> cross linked material

Answer 208

1) Activation \> Sulphonate Ester ionises and provides cations (+) to the reaction 2) Initiation \> Cations then open up Epimime rings in the prepolymer which releases a further cation 3) Propagation \> The chain reaction of cation release continues and the now ionic prepolymers join to form a larger chain as the ions are passed along

Answer 209

viscosity surface wetting contact angle

Answer 210

determines a materials potential for making close contact with soft tissue surfaces = recording surface detail

Answer 211

must make intimate contact with teeth/mucosa

Answer 212

determines how well the material envelopes hard/soft tissue surfaces

Answer 213

reproduction of surface detail - should reproduce at least 50μm of detail viscoelasticity/elastic recovery- withdrawing impression quickly, less permanent deformation from strain

Answer 214

flow under pressure - shark fin test tear tensile strength on removal rigidity on removal

Answer 215

should be low setting shrinkage thermal expansion/contraction should be low - due to the disparity in temp from the oral cavity to the outside environment storage - some materials undergo synersis or imbibition causing dimensional change

Answer 216

abrupt changes in shape of a file that leads to a higher stress at that point aka a notch in the file

Answer 217

when elastic limit is significantly higher than that of conventional metals, will deform when heated returb to its original shape

Answer 218

permanent bond displacement occuring when elastic limit is exceeded

Answer 219

the point in which a plastically defomed file breaks

Answer 220

freely rotating in a curvature generaton of tension and compression cycles cyclic fatigue failure

Answer 221

when the load is suddently revered i.e. turning the file in the opposite direction to which has been

Answer 222

moving a substance by external vibration to allow said substance to fill a space

Answer 223

smear layer formed during preparation * organic pulpal material and inorganic dentinal debris * superifical 1-5μm with packing into tubules * bacterial contamination, substrate and interferes with disinfection * also prevents sealer penetration removal of smear layer * 17% EDTA * 10% citric acid * MTAD (mixture of a tetracylic isomeer, an acid and detergent) * sonic and ultrasonic irrigation * watch apical control

Answer 224

should never be in the canal at the same time because the EDTA neutralises the effectiveness of the NaOCl also forms papachloanailine which is cytotoxic and carcinogenic

Answer 225

* easily manipulated with ample working time * seals the canal laterally and apically * non-irritant * impervious to moisture * unaffected by tissue fluids * inhibits bacterial growth * radiopaque * does not discolour tooth * sterile * easily removed if necessary

Answer 226

natural rubber and GP are polymers of the same monomer - transpolyisoprene comes in 2 forms: * α - used in themoplastic manipulation techniques, the natural occuring form and when heated above 65^obecomes amorphous * β - more commonly used in cold lateral compaction - rapidly cooled and recrystalised alpha, used in commercially produced GP GP formulations are 60-75% Zinc Oxide inc a variety of other agents to allow them to be radiopaque on radiographs

Answer 227

* exhibit tackiness to provide good adhesion * establishes a hermitic seal * radiopacity * easily mixed * no shrinkage on setting * non-staining * bacteriostatic or does not encourafe growth * slow set * insoluble in tissue fluids * soluble on retreatment

Answer 228

* ZOE * GI sealers * resin sealers * calcium silicate sealers * medicated sealers

Answer 229

* effective antimicrobial * offers cytoprotection * resin acids are 90% of the colophony (Rosin) in the material and these are strongly antimicrobial and cytotoxic * altough toxic may be overall beneficial with longlasting antimicrobial effect and cytoprotection * formation of eugenolate consititutes hardening, this is accelerated by CaOH so this must be removed from the canals * remaining eugenol can act as an irritant * lose volume with time due to dissolution - resins can modify this

Answer 230

* advocated due to dentine bonding properties * removal upon retreatment is difficult * minimal antimicrobial activity * not enough data yet

Answer 231

AH plus Epiphany EndoRez

Answer 232

* long history of use - development of AH26 * epoxy resin * paste-paste mixing * slow setting - 8 hrs * good sealing ability * good flow * initial toxicity declining after 24hrs

Answer 233

dual cure dental resin composite sealer - used with Resilon * BisGMA * Ethoxylated BisGMA * Urethane-dimethacrylate UDMA * hydrophillic difucntional methacrylates * fillers of calcium hydroxide, barium sulphate, barium glass and silica requires self-etch primer

Answer 234

UDMA resin-based sealer * hydrophillic * good penetration into tubules * biocompatible * good radio-opacity

Answer 235

* high pH (12.8) during intial 24hrs of the setting * hydrophillic * enhanced biocompatibility * does not shrink on setting * non-resobable * excellent sealing ability * quick set - 3-4hrs - requires moisture * easy to use

Answer 236

sealers containing paraformaldehyde not acceptable lead and mercury components removed severe adn permanent toxic effects on periradicular tissues sargenti paste, endomethasone, SPAD

Answer 237

wax pattern made (e.g. crown, inlay etc) investment material poured around wax pattern and allowed to set (mould) wax then eliminated (boiled out) molten alloy is then forced into the cavity left by the wax via sprues prepared in the investment material

Answer 238

refractory - silica (quartz/tridymite/crisotbalite) binder - gypsum/phosphate/silicate modifiers - change physical properties

Answer 239

Supplied as powders and mixed with water and silica and calcium sulphate hemihydrate with other components that control setting time * quartz withstands high temps and gives expansion _Thermal inversion_ is when the silica is heated so that it undergoes a phase transformation and expands (alpha \> beta quartz) Above 320^oC there is contraction of the investment material which causes water loss, this can be reduced by modifiers like sodium chloride and boric acid Heat Soaking * \> 700^oC * CaSO₄ + 4C ——\> CaS + 4CO * (THEN) 3CaSO₄ + CaS ——\> 4CaO + 4SO₂ * Allow heat soaking to complete to allow gases to escape Chemical stability * \<1200^oC satisfies requirements * \>1200^oC problems with sulphur trioxide production - causes corrosion and porosity in alloy castings * Therefore only allots with melting point of \<1200 allowed

Answer 240

Powder * Silica * Magnesium Oxide * Ammonium Phosphate Liquid * Water * Colloidal Silica (increases strength, undergoes _hygroscopic_ expansion) Magnesium Oxide + Ammonium Phosphate + Water/Colloidal Silica —— \> Magnesium Ammonium Sulphate Type 1 PBMs * Inlays, crowns and other fixed restorations Type 2 PBMs * RPDs and other cast removable restorations * Don’t require outer casting ring

Answer 241

* Powdered Quartz/Cristobalite bonded with silica gel * Silica gel becomes Silica and is a tightly packed mass of particles * Binder is usually Ethyl Silicate with Hydrochloric acid and Industrial spirit * the ethyl silicate is hydrolysed releasing alcohol and forming silica gel * the Hydrolysis and gelation can be accelerated by Piperidine but this causes alot of shrinkage * Ethyl silicate mediated materials dont dimensionally change on setting because they are _Thermal expanders_ * their linear expansion = their linear thermal expansion unlike gypsum/phosphate

Answer 242

* polyacrylic acid (ionic monomers) * copolymers of acrylic and itaconic acid * or Acrylic and maleic acid * tartaric acid * added to control the setting characteristics of material

Answer 243

* silica * alumina * calcium fluoride * aluminium fluoride * alumonium phosphate * sodium fluoride adding Strontium + lithium salts increase radiopacity but dont take part in reaction

Answer 244

* dissoluion * gelation * hardening

Answer 245

MO.SiO2 + H2A -\> MA + SiO2 + H2O M=metal A=polyacid glass + acid -\> salt + silica gel

Answer 246

Acid into Solution H+ ions attack the glass surface Ca, Al, Na and F ions are released Leaves silica gel around the unreacted glass

Answer 247

Inital set due to Ca2+ ions cross linkinh w/ polyacid by chelation with carboxyl groups Bivalent so can bind to two carboxyl groups Chelation can happen twice on same molecule of polyacid (gels toonmuch?) At this point the material will appear hard in the mouth (after a fewminutes) caused by formation of calcium polyacrylate

Answer 248

Trivalent Aluminium increases crosslinking Formation of Aluminium Polyacrylate 30 mins to a week to happen - Helps mechanical properties greatly

Answer 249

Must be moisture and dessication free *i.e not too wet or dry* This is most important during the hardening phase if not achieved aluminium will leach out- less cross linking, water lost from matrix if dessicated, saliva contamination causes excess water absorption = A WEAK MATERIAL

Answer 250

* Varnishes * Copal ether * Acetate * Resins * Dentine/Enamel bonding agents * Unfilled Bis-GMA resins * Greases/Gels * Vaseline (not great as removed quickly by lips and tongue)

Answer 251

Can bond to enamel and Dentine w/o use of intermediate material Bond strength pretty poor (5-20 MPa) Poor Tensile strength Lower compressive strength than composite (less than 50%) Higher solubility than composite due to unprotected material during gelation phase Usually seals well Fluoride release (for short time) Bonding\*\* * Carboxyl (COO groups) in cement bond to Ca in the enamel! * In addition there is Hydrogen bonding and metallic ion bridging to the collagen in enamel too * IT IS CONDITIONED NOT ETCHED!! W/ POLYACRYLIC ACID!!

Answer 252

* Fluro-Alumino-Silicate glass * Barium glass (provides radiopacity) * Vacuum dried polyacrylic acid * Pottasium persulphate (redox catalyst - cures resin in the dark) * Ascorbic acid * Pigments (vary in shade for aesthetics)

Answer 253

* HEMA (water miscible resin) * Polyacrylic acid with pendant methyacrylate (undergo acid/base reactions and polymerisation) * Tartaric Acid (speeds up setting reaction) * Water (allows reaction between polyacid and glass) * Photoinitiators - ALLOW LIGHT CURE

Answer 254

dual curing tri curing

Answer 255

On mixing proceeds like the normal GIC (dissolution) Light activation causes free radical methycrylate reaction to occur = resin matrix formed Acid Base reaction occurs for several hours afer

Answer 256

On mixing proceeds like the normal GIC (dissolution) Redox reaction begins Light activation- resin matrix formed Redox reaction continues for 5 mins after initial mix Acid base reaction occurs for several hours Final hardening may take days

Answer 257

Better physical properties Lower solubility Fluoride release Better translucency/aesthetics Better handling

Answer 258

* prevents gaps * acts as a protective barrier e.g in Amalgam Cavity base lining placed in bulk to block undercuts for metal restorations lining for exposed dentine- promotes pulpal health

Answer 259

1. chemical stimuli - unreacted chemicals in filling material/pH of filling material 2. thermal stimuli - exothermic setting of composite#heat conduction amalgam/gold 3. bacteria + endotoxins - microleakage (against oral fluids and bacteria and their toxins ingressing between material and cavosurface margins)

Answer 260

therapeutic role in calming down pulpal inflammation and promote healing palliative reduce symptoms in pts with irreversible pulpitis

Answer 261

should be command set workable easy to mix

Answer 262

how well heat energy is transferred through a material Heat flow through a cylinder of unit cross sectional area with a temp difference of 1^oC between both ends Cavity lining should have as low thermal conductivity as possible!!

Answer 263

change in length per unit length for a rise of 1\*C (in ppm\*C-1) Liner should match thermal coefficient of tooth! GIC has better TEC than RMGI

Answer 264

similar to conductivity measured in cm2/sec Liners have similar or lower thermal diffusivity than enamel Amalgam much higher than tooth tissue- hence use of liner

Answer 265

High compressive strength allows placement of filling without breakage similar modulus to dentine Radiopaque Marginal seal low solubulity Cariostatic (fluoride release/ antibacterial) Biocompatability (non toxic, pH neutral, not exothermic)

Answer 266

calcium hydroxide liner (dycal, life) zinc oxide cements resin modified zoe GIC/RMGIC

Answer 267

dycal, life Components * Base- Calcium Hydroxide, Zinc Oxide Filler, Plasticiser * Catalyst- Butylene glycol Disalicylate (reactive element), filler, radiopaquer Setting reaction * Butylene glycol disalicylate + Zinc Oxide filler = chelation and at pH 12 Mode of action * irritates odontoblast layer- forms reparative dentine, calcium from pulp helps to form a bridge between pulp and dentine, high alkaline content is bactericidal

Answer 268

Zinc Oxide Eugenol- used as a cavity liner, PD dressing and root canal sealer Eugenol can have obtundant effect (reduce dentine sensation) and reduce pulpal pain \*inhibits set of composite resin material!! shouldn’t be used! Zinc Oxide + Eugenol= Zinc Oxide Eugenolate + Water (Base) + (Acid) = (Salt ) + (Water)

Answer 269

adds resin to the ZnO/Eugenolate matrix to reduce solubility

Answer 270

can actually bond Amalgam to tooth as the bond goes Tooth—RMGI—Amalgam (it bond to rest.material) Palliative cements- Base (seldom used)

Answer 271

50% by weight - mainly silver, tin and copper * Silver and Tin- intermetallic compound Ag3Sn * Copper- increases strength & hardness * Zn - scavenger during production - preferentially oxidises & slag formed / removed - some zinc free * \*Hg in powder - (few materials)– “pre-amalgamated” alloys - react faster

Answer 272

* Hg (50% by weight) triple distilled (very pure) – reacts with other metals

Answer 273

lathe cut (coarse medium or fine) - formed by filing ingots spherical/spheroidal - range of particle sizes, formed by sparying molten metal into inert atmosphere

Answer 274

Silver/Tin Powder reacts with Liquid Mercury Some unreacted Silver/Tin Powder remains Silver Mercury (y1) and Tin Mercury (y2) form amalgam matrix Modern amalgam sets with a small amount of contraction (due to a solidsolution of mercury forming in with the Silver/Tin (only -0.2% contraction so very small)

Answer 275

Zn + H20 (saliva) -\> ZnO + H2 (gas) Hydrogen gas causes pressure expansion of amalgam downward pressure = pulpal pain upward pressure= sitting proud of surface - chipped off ∴ Zinc free materials!

Answer 276

Amalgam strength usually ok after 24 hrs however is decreased by the following * Undermixing * Too high Hg content after condensation * poor condensation pressure * slow rate of packing- increments dont bond * corrosion by oral fluid

Answer 277

y2 most electronegative (tin and mercury) this weakens amalgam particularly at the margins orrosion products may actually hep with sealing margins reduce corrosion by * copper enriched materials * polishing margins * avoiding galvanic cells (stops random redox reactions from occuring due to two different metals with different electronegavity contacting)

Answer 278

* Gives higher early strength * Less creep * Higher corrosion resistance * Increased durability of margins either * single composition formulations * dispersion modified setting reaction

dental materials 93 Flashcards

(310 cards)