1. DMS Flashcards

Question

``` Amalgam vs hybrid composite - which is higher: Compressive strength Tensile strength Elastic modulus Hardness ``` ``` Relationship between amalgam, dentine and enamel for: Compressive strength Tensile strength Elastic modulus Hardness ```

Answer 1

Amalgam Amalgam Amalgam Amalgam Amalgam > dentine > enamel Dentine > amalgam > enamel Enamel > amalgam > dentine Enamel > amalgam > dentine

Answer 2

Less tissue removed, sound tooth tissue retained, more challenging, further pit and fissure caries treatment may be required Very retentive, treats pit and fissure caries, destroys tooth tissue Increase retention in large, non-retentive cavities Removing all caries, smooth lines, angles and margins Reduces strength and increases creep, porosity and corrosion Recreate cavity walls, allows creation of proximal form, allows adequate condensation, confines amalgam to cavity Produces matrix adaptation (temporary tooth separation), prevents excess material gingivally, aids proximal wall contour, prevents movement of matrix band

Answer 3

Passage of fluid and bacteria in micro gaps between restoration and tooth Pulpal irritation, infection, discolouration, secondary caries Expel excess mercury Eliminates voids Inferior mechanical properties Detrimental change in amalgam character due to reactions in the mouth (associated with gamma 2 phase) Marginal ridge breakdown Copper incorporation

Answer 4

Liners, temporary/permanent restorations Tartaric acid, polyacrylic acid (both control setting characteristics) Glass powder - silica, alumina, CaF, AlF, AlPO4, NaF Increase radiopacity More silica, more translucent MO.SiO2 + H2A --> MA + SiO2 + H2O Acid added to solution, H ions interact and attack glass surface. Glass ions (Ca, Al, Na, F) leach out, leaving silica gel around unreacted glass Initial set due to Ca ion crosslinking with polyacrylic acid (chelation with COO- groups) --> Ca polyacrylate (Ca ions bivalent - not ideally, can chelate with two COO- groups in same molecule) Trivalent Al ensures good crosslinking, increasing strength

Answer 5

Chelation between COO- in cement and Ca2+ on tooth surface, H bonding/metallic ion bridging to collagen Al diffusion out --> excessive drying --> water loss --> saliva absorption --> contamination --> material failure Varnishes, resins (DBAs/EBAs, unfilled Bis-GMAs), greases/gels (vaseline) Poor tensile strength, lower compressive strength, poorer wear resistance, lower hardness, higher solubility F release - act as F reservoir (absorb/recharge F from toothpaste) Stable chemical bond to tooth, low microleakage, good thermal properties Brittle, poor wear resistance, poor aesthetics

Answer 6

To overcome GI brittleness Adding silver to glass, increasing toughness/wear resistance No evidence

Answer 7

Fluoro-alumio-silicate glass, barium glass, vacuum dried polyacrylic acid, K persulphate (redox catalyst), ascorbic acid HEMA, polyacrylic acid with pendant methacrylate groups, tartaric acid, photo-initiators Acid/base (as GIC) on mixing and occurs for several hours; light-activation - free radical methacrylation occurs Acid/base (as GIC) on mixing and occurs for several hours; light-activation - free radical methacrylation occurs; redox reaction initiated 5 mins after mixing (final hardening with aluminium polyacrylate can take days) Better physical/mechanical properties, lower solubility, better aesthetics Polymerisation contraction, exothermic setting reaction, swelling due to water uptake, monomer leaching

Answer 8

Produce an accurate replica of surface and shape of hard and soft oral tissues Mucostatic (fluid materials, slightly displace soft tissues) and mucocompressive (record impression of mucosa under load - displace soft tissue) or elastic and non-elastic When removed, material reaches maximum amount of strain almost instantly. This is held during removal. When fully removed, material instantly returns to original strain and pre-removal shape When removed, strain increases gradually to just below the maximum amount. This is held during removal. When fully removed, the material quickly returns to just above its original strain, resulting in a permanent deformation

Answer 9

Hydrocolloids (alginate - irreversible), elastomers (polyethers, silicones) Impression compound, impression paste Flow, setting changes, removal, storage, decontamination Viscosity, setting mechanism, thermal expansion coefficient, hydrophobic/hydrophilic, elasticity, tear strength Non-toxic, non-irritant, acceptable taste/smell, short setting time, simple, convenient working/setting times, can be decontaminated 2-phase system - fine particles of one phase dispersed in another phase - hydrocolloid (in water)

Answer 10

Alginic acid, CaSO4, trisodium PO4, fillers, modifiers, flavourings, chemical indicators Long crosslinking fibrils entangling undissolved particles Trisodium phosphate preferentially reacts with Ca in CaSO4 to delay the set; sodium alginate then reacts with Ca ions 2Na3PO4 + 3CaSO4 --> Ca3(PO4)2 + 3Na2SO4 Correct powder/liquid ratio, water 18-24C, perforated tray/adhesive Non-toxic, non-irritant, relatively easy to use, adequate setting time, acceptable taste/smell Water release Water uptake

Answer 11

Polyethers, addition silicones Give off water during curing, affecting dimensions Viscosity/flow, surface detail (ISO - 50-75um), surface wetting, elastic recovery, stiffness, tear strength, mixing time, working time 5-6mins 2-4mins 98-99.5% 1.8-9MPa

Answer 12

Replace function of normal teeth, fits well in mouth, dimensionally accurate, high softening temperature, unaffected by oral fluids Non-toxic, non-irritant, low thermal conductivity, low mechanical properties, good colour, low density, high softening temperature, dimensionally accurate, stable in use Limit at which material will return to its original shape if distorted High YM, PL and EL

Answer 13

Free radical addition polymerisation of a methacrylate monomer (chemical union of two molecules to form a larger molecule without the elimination of a smaller molecule) Activation (of initiator - benzoyl peroxide - giving 2 free radicals), initiation (free radicals break monomer C=C and transfer of free radicals), propagation (growing polymer chain), termination (of polymerisation)

Answer 14

Initiator, PMMA, pre-polymerised beads, plasticiser, pigments, co-polymers Methacrylate monomer, co-polymers, initiator Dough-like material reduces heat of reaction and minimises polymerisation shrinkage Efficient polymerisation (to give high polymer molecular weight) During cooling, the mould and acrylic have different thermal expansion coefficients Slow cooling

Answer 15

Decreased strength, warping Reduced mechanical properties, free monomer Gaseous porosity Contraction porosity Granularity Strength, appearance, saliva absorption (absorbs saliva) When curing temperature exceeds 100C, the monomer boils and small bubbles are formed Voids due to polymerisation shrinkage - too much monomer, insufficient excess material, insufficient clamp pressure

Answer 16

Study casts Positive replica (created from impression) of patients dentition Record position/shape of teeth, aid manufacture of prostheses Plaster (B-hemihydrate - larger, porous irregular crystals), stone (a-hemihydrate - non-porous regular crystals), improved stone/densite (compact smoother crystals) (CaSO4)2.H2O + 3H2O --> 2CaSO4 + 2H2O Hemihydrate dissolves, dihydrate forms. Dihydrate crystals precipitate on impurities as crystals Impurities act as nuclei for crystallisation Initial set - dehydrate crystals come into contact, expansion starts, weak solid formed. Final set - strength continues to develop On completion of setting, water evaporates and voids are produced

Answer 17

Medium/high compressive strength, low hardness, Increased spatulation - breaks down growing crystals, decreasing setting time, increasing expansion Increased powder - more nuclei of crystallisation per unit volume, faster set/greater expansion Temperature - as temperature increases, rate of diffusion of ions increases and solubility of hemihydrate decreases Chemical additives - KSO4 produces sygenite - crystallises rapidly, decreasing setting time; borax forms Ca borate, delaying setting process Convenient setting time, dimensionally accurate and stable Low tensile strength, poor abrasion resistance, very brittle

Answer 18

Aggregate of atoms in a crystalline structure Combination of metal atoms in a crystalline structure Amount of plastic deformation prior to fracture Crystalline structure, grain size/imperfections Atoms act as nuclei of crystallisation. Crystals grow to form dendrites and grow until they impinge on other crystals Regions where grains make contact Equi-axed grains (crystal growth of equal dimension in each direction), radial (molten metal cooled quickly in cylindrical mould), fibrous (wire pulled through die) Fast cooling/quenching, slow cooling Fast cooling - has more nuclei so produces more grains, produces small fine grains Impurities/additives that act as foci for enhanced crystal growth

Answer 19

Small, fine grains High EL, increased UTS, increased hardness, decreased ductility Small bulk, heat metal/alloy just above melting temperature, mould, quench

Answer 20

Imperfections/defects in crystal lattice --> alteration of lattice shape and structure. Weak points SLIP - due to propagation of dislocation. Involves rupture of only a few bonds at a time Grain boundaries because they cannot move from one grain to another Grain boundaries, alloys, cold working - increases EL, UTS and hardness and decreases ductility and impact resistance

Answer 21

Work being done on metal/alloy (bending, rolling, swaging) at low temperatures SLIP A stronger, harder material and internal stresses

Answer 22

Lattice instability leading to distortion over time - undesirable Through annealing - heating metal/alloy so that greater thermal vibrations alloy migration/re-arrangment of atoms Stress relief annealing - allows atoms to rearrange within grains Recrystallisation - spoils benefits of cold working Occurs when heated, leading to smaller, equi-axed grains Lower EL, UTS and hardness and increased ductility Repeating recrystallisation and cold work Greater amount of cold work Large grains replace small grains --> poorer mechanical properties

Answer 23

Improved properties, lower melting point Steel, amalgam, gold alloy, NiCr Physically distinct homogenous structure Homogenous mixture at an atomic scale Common lattice structure containing two metals that are soluble in one another Intermetallic compound (insoluble), solid solution (soluble)

Answer 24

Substitutional - atoms of one metal replace the other metal in lattice/grain. Can be random or ordered (regular lattice). Interstitial - atoms markedly different in size; smaller atoms are located in spaces in lattice/grain structure of larger atoms

Answer 25

Crystallisation of metal (one temp) or alloy (temp range - TL to TS) TL - temperature at which alloy begins to crystallise at different compositions TS - temperature at which alloy has completely crystallised Ensures grain composition is homogenous by allowing metal atoms to diffuse through lattice Results in larger grains Generates small grains, impeding dislocation movement and improving mechanical properties Results in coring as composition varies through the grain because atoms have not diffused through lattice Rapid cooling of liquid state, liquidus and solidus must be separate May reduce corrosion resistance of solid alloy

Answer 26

Homogenising annealing Reheat alloy after coring to allow atoms to diffuse through lattice causing grain composition to become homogenous Keep below recrystallisation temperature otherwise grain structure will be altered

Answer 27

Distorted grain structure Impedes dislocation movement and improves mechanical properties

Answer 28

Defect rolls over atoms in lattice plane. Little energy/force is required for defect to move along slip plane Defect falls into larger space existing between large and small atoms. More energy/force is required for defect to overcome different-sized atoms and move along to the grain boundary Greater stress is required to move dislocation in a solid solution (alloys are solid solution), causing a greater fracture resistance than metals

Answer 29

Contain metals that are soluble as liquids but insoluble as solids Complete insolubility between the metals composing the alloy Liquidus and solidus coincide, where grains of individual metals are formed simultaneously Hard, brittle, poor corrosion resistance Excess metal crystallises, liquid reaches eutectic composition, both metals crystallise

Answer 30

a-phase (mostly a-rich), B-phase (mostly B-rich) Dashed line on phase diagram - indicates the range of compositions of metals that are not possible Grains of a and b (not a 50/50 grain composition) Precipitation hardening Due to solution hardening, order hardening and precipitation hardening Annealing

Answer 31

Rigid, strong, hard, ductile, precise casting (no shrinkage), low density Gold, zinc, copper, silver, palladium, platinum Cobalt, chromium, nickel, molybdenum, others (carbon, zinc, aluminium)

Answer 32

Solid solution in all proportions, solution hardening, order hardening, reduced melting point, no coring, red colour, reduced density, increased corrosion Solid solution in all proportions, solution hardening, precipitation hardening (with Cu), tarnishing, absorbs gas when molten, whitens alloys Solid solution (with gold), solution hardening, fine grain structure, coring Similar to platinum but cheaper, less coring, coarser grains, absorbs gases when molten (porous casting) Scavenger - oxidises preferentially Increases hardness and wrought strength Fine grain structure

Answer 33

Wires, surgical implants, cast partial dentures (connectors) Forms solid solution with Cr, increased hardness, rigidity and strength, coring possible Forms solid solution with Co, increased hardness, rigidity and strength, coring possible, forms passive layer (improves corrosion resistance) Replaces some Co - improves ductility, slight reduction in strength, nickel allergy/sensitivity Undesirable, carbide grain boundaries, hard, brittle Reduces grain size, increases strength Increases PL Scavenger - oxidises preferentially to avoid unfavourable redox reactions of other metals

Answer 34

Investment material (1200-1400C - silica/PO4 bounded), melting (electric induction preferred - avoids C pickup), casting (centrifugal forces required; overheating --> coarse grains; cooling too fast/slow --> brittle carbides) Sandblast, electroplate, abrasive wheel, polishing buff Harder - improved wear, but time-consuming finishing or polishing Amount of strain a material can experience before failing in tensile testing - lower elongation, less ductile CoCr has low elongation and therefore low ductility Precision casting

Answer 35

Implants, partial dentures, crowns and bridges, maxillofacial implants Electric arc melting, specialised investment/casting ``` Biocompatible, good corrosion resistance Absorbs gases (when molten) ```

Answer 36

SS >Ti > CoCr > gold Gold > CoCr Ti > CoCr > gold Ti > SS = CoCr > gold SS > CoCr > Ti > gold SS > Ti > CoCr > gold Au = Ti > CoCr > SS CoCr > SS > Ti > gold

Answer 37

Amalgam - traditional - Ag3Sn + Hg --> Ag3Sn + Ag2Hg3 + Sn7Hg9 Amalgam - copper-enriched - dispersion modified - G + Hg --> G + G1 + G2 G2 + AgCu --> Cu6Sn5 + G1 Amalgam - copper-enriched - single composition - AgSnCu + Hg --> AgSnCu + G1 + Cu6Sn5 GIC - MO.SiO2 + H2A --> MA + SiO2 + H2O Dissolution, gelation, maturation Alginate - 2Na3PO4 + 3CaSO4 --> Ca3(PO4)2 + 3Na2SO4 Trisodium phosphate preferentially reacts with Ca in CaSO4 to delay the set Gypsum - (CaSO4)2.H2O + 3H2O --> 2CaSO4 + 2H2O Increased spatulation, increased powder, temperature, chemical additives Fee radical addition polymerisation of a methacrylate monomer Stages - activation , initiation, propagation, termination Camphorquinone in composite resins - photo-activator catalyst that initiates resin polymerisation when activated by blue light (430-490nm)

1. DMS Flashcards

(61 cards)