8. DMS

Question 1

Bonding 1

1. Describe how to bond to enamel
2. Describe the 3 types of bond to dentine
3. Why is a DBA is required
4. How do DBAs work/what do they do
5. What is the dentine smear layer
6. What is the adhesion-decalcification concept

Answer 1

1. Micromechanical. Acid etch technique, 37% phosphoric acid. Acid roughens the surface of dry enamel, allowing micro mechanical interlocking of resin-filled materials. Etching increases the surface energy of the enamel surface (improving wettability), allowing resin to adapt better
2. Mechanical (molecular entanglement), chemical, van der Waals (electrostatic interaction)
3. Dentine is hydrophilic with low surface energy. DBA required to increase the surface energy of dentine
4. Increase surface energy of dentine, allow composite resins to flow and stick to the surface. Also primer/coupling agent - bifunctional molecules with a hydrophilic end and hydrophobic end. Hydrophilic end bonds to dentine and hydrophobic end bonds to composite resins. Contain spacer groups allowing for flexibility during bonding and may contain filler particles to increase strength. HEMA, 4-META, MDP. DBAs are light-curable and form the hybrid layer of collagen and dentine
5. Adherent layer of organic debris that remain on the dentine surface after dentine prep during tooth restoration. 0.5-5um thick, can be removed/modified by dentine conditioners (phosphoric acid, EDTA) or incorporated, penetrated and infiltrated by self-etching primers
6. Interaction of bonding materials with hydroxyapatite-based tissues. Mineral exchange - minerals removed from dental hard tissues are replaced by resin which, once mineralised, mechanically interlocks in these porosities. This is molecular entanglement

Question 2

Cavity Liners 1

1. What is the difference between a cavity liner and a cavity base
2. Give 3 functions of cavity liners
3. Give 3 indications
4. Name 3 types
5. How does CaOH set, give 3 advantages and 1 disadvantage
6. Why is GIC preferred
7. Name 3 types of ZnO-based cements and give 2 advantages of each

Answer 2

1. Liner is thin coating (<0.5mm), base is thick dentine replacement
2. Protect pulp from chemical and thermal stimuli, prevent microleakage (bacteria and endotoxins) and palliative function (reduce symptoms). Protective barriers, prevent gaps/voids/air blows
3. Deep cavities (direct restorations), close to pulp, small pulp exposures, cavities close to gingival margin, pulpitis-type symptoms
4. CaOH, GI, ZnO
5. Chelation reaction between ZnO and butyl glycol disalicylate. Bactericidal, forms tertiary dentine, quick set, radiopaque, easy to use; low compressive strength, unstable and soluble in oral fluids
6. Bonds to and seals dentine, releases fluoride
7. ZnPO4 - cheap, easy to use, non-adhesive, non-cariostatic
   Zn polycarbozylate - ZnPO4 but bonds to tooth
   ZOE - low strength, highly soluble
   RMZOE - increased compressive strength, reduces solubility
   EBAZOE - reduced solubility, increased strength

Question 3

Ceramics 1

1. Define dental ceramic
2. What is feldspar
3. How are feldspathic ceramics formed
4. Define sintering
5. Give 8 features of conventional feldspathic ceramics
6. What is static fatigue
7. What is the function of a metal-cored ceramic
8. How are metal cores bonded
9. Name 2 types of alloys and 6 ideal properties for MCC metals/alloys

Answer 3

1. Solid material comprising of inorganic compound of metal, non-metal or metalloid atoms primarily held in ionic and covalent bonds
2. Fluxing agent that lowers fusion and softening temperature of glass
3. Form leucite when heated to 1150-1500C (powder of known physical and thermal properties). Powder melts together to form crown. Powder and water mixed and applied to die, heaters in furnace causing sintering
4. Ceramic particles begin to fuse into a single mass. Occurs above glass transition phase. Glass phase softens and fuses, followed by controlled diffusion and solid ceramic mass formed. 20% material contraction
5. Best aesthetics, smooth surface, stable, high compressive strength, high hardness, low tensile strength, low flexural strength, very low fracture toughness
6. Time dependent reduction in strength even in absence of applied load. Likely due to hydrolysis of Is-O groups within the material over time in aqueous environments
7. Increase fracture resistance and toughness
8. Metal oxides - helps eliminate defects/cracks on the porcelain surface, micro mechanical, chemical bonds, stressed skin effect
9. CoCr, NiCr, AgPd, high gold alloy, low gold alloy. High bond strength, high hardness, high elastic modulus, similar thermal expansion coefficient to porcelain, should avoid discolouring porcelain

Question 4

Ceramics 2

1. Give 3 features of alumina cores
2. What do alumina particles act as
3. Where can alumina cored MCCs be used
4. What type of zirconia is used and describe the benefit of this type
5. Give 3 properties of zirconia cores
6. Where can zirconia cored MCCs be used
7. How are silica-containing ceramics luted to teeth
8. How are zirconia-cored ceramics luted

Answer 4

1. Strong, opaque, excellent aesthetics, relatively cheap
2. Crack stoppers, preventing cracks propagating through material and causing fracture
3. Single posterior crowns
4. Yttria-stabilsied zirconia. Normal zirconia monoclinic crystal at room temp. If crack begins when stress at crack tip reaches critical level, the crystal transforms to a monoclinic structure. Causes slight expansion of materials and closes up crack tip
5. Very hard, strong, tough, best aesthetics
6. Crowns and bridges throughout mouth
7. Etched with HF to produce a retentive surface. Etched surface can be bonded to using a silane coupling agent and bonded to the tooth using a bonding agent
8. No silica and not affected by acid (inert fitting surface), strong enough to be self-supporting and can be luted with conventional cements

Question 5

Impression Materials 1

1. Define impression material
2. Difference between mucostatic and mucocompressive
3. 5 ideal properties
4. Describe ideal elastic behaviour
5. Describe observed elastic behaviour
6. Name 3 problems with impression taking

Answer 5

1. Material used to produce an accurate negative replica of the surface and shape of hard and soft oral tissues
2. Muscostatic - displace soft tissues slightly and give an impression of undisplayed mucosa
   Mucocompressive - materials that record an impression of mucosa under load and give an impression of displaced soft tissue
3. Accuracy, low viscosity, good surface detail, good surface wetting, able to be disinfected, non-toxic, non-irritant, complete elastic recovery, easy to use, high tear strength, low setting shrinkage, flexible, low stiffness
4. Upon removal, material reaches max amount of strain almost instantly. Max strain held during removal. When fully removed, material instantly returns to original strain and returns to pre-removal shape
5. Upon and during removal, material strain gradually increases to just below the max amount of strain. When fully remove, materials quickly returns to almost the initial strain. Results in permanent strain/deformation and a permanent change in dimension
6. Poor bond to tray (no adhesive), lack of occlusal detail (inadequate seating), ledges, drags, air blows, voids, delimitation, seating error, surface inhibition, inconsistent mixing and surface contamination

Question 6

Impression Materials 2

1. What type of material is alginate
2. Give 5 features
3. Give 3 components and describe the setting reaction
4. Name an example of a polyether
5. What other elastomeric impression material can be used
6. How are elastomers formed
7. Give 3 features of polyethers

Answer 6

1. Irreversible hydrocolloid, elastic, mucostatic
2. Non-toxic, non-irritant, adware setting time, easy to use, adequate flow, good elastic recovery, poor tear strength, poor storability
3. Sodium alginate, trisodium phosphate, filler, flavourings, calcium sulphate
   2NanAlg + nCaSO4 -> nNa2SO4 + CanAlg
4. Impregum
5. Addition silicones
6. Polymerisation with cross-linking of polymer chains, generating elastic properties
7. Adequate tear resistance, hydrophilic, adequate elasticity, good dimensional stability

Question 7

Investment Materials 1

1. Define investment material
2. Name 3 types
3. Name 3 ideal features
4. What are the 2 main components and what do they do
5. 2 indications for gypsum-bonded investment
6. 3 types of gypsum-bonded investment
7. 3 features of gypsum-bonded investment
8. 3 factors that decrease setting time of gypsum-bonded investments
9. Setting reaction
10. Describe hydroscopic expansion and 4 features that increase it

Answer 7

1. Refractory material used to surround the wax pattern during the procedure of fabricating the metallic permanent restoration. Forms the mould into which the alloy is cast after the wax has been eliminated
2. Gypsum-bonded, phosphate-bonded, silica-bonded
3. Expand, porous, strong, smooth surface, chemically stable, easy to remove from cast, easy to use, cheap
4. Binder (form coherent mass), refractory component (withstands high temp, gives expansion)
5. Create study models and casts, record position and shape of teeth, treatment planning, diagnostic wax up, prostheses construction
6. Plaster, stone, improved stone (densite)
7. Low hardness, low strength, very brittle, porous, dimensionally adequate, stable, adequate for fine detail reproduction, convenient setting time
8. Increased powder, spatulation, impurities, temperature, chemical additives (potassium sulphate; borax increases setting time)
9. (CaSO4)2.H2O -> 2CaSO4.2H2O
10. Water molecules attracted between crystals by capillary forces, forcing crystals apart. Increased by low powder/water ratio, increased silica content. higher water temp, longer immersion time

Question 8

Investment Materials 2

1. 3 features of phosphate-bonded investments
2. 3 features of silica-bonded investments
3. Lost wax technique description

Answer 8

1. Increased strength, easy to use, porous, chemically stable
2. Sufficient strength, complicated manipulation, not porous
3. Sprue, wax pattern, invest, set, wax burnt out leaving space, expansion, motel alloy cast under pressure, trapped gases escape, cooling to room temp, alloy shrinkage, de-vestment

Question 9

Luting Agents

1. 3 types
2. 5 ideal features
3. 3 indications for composite luting agents
4. 3 indications for GIC luting agents
5. 3 indications for dual-cure composite luting agent
6. 1 indication for anaerobic cure composite luting agent
7. 1 indication for light-cure composite luting agent

Answer 9

1. Conventional cements (ZnO based), GIC, composite resins, self-adhesive composite resins
2. Low viscosity, easy to use, radiopaque, good marginal seal, good aesthetics, low/no solubility, biocompatible, cariostatic, good mech properties
3. Indirect composites, porcelain, metal, non-precious metals, precious metals
4. MCC, metal posts, zirconia crowns, gold restorations
5. Fibre posts, composite inlays, porcelain inlays
6. Adhesive bridges
7. Veneers

Question 10

Metals and Alloys 1

1. 2 types of cooling and what the lead to
2. Why are small fine grains more advantageous
3. Describe dislocations
4. What does impeded dislocation movement cause
5. Describe cold working
6. What does cold working do to mechanical properties of metals

Answer 10

1. Quenching/fast cooling - more nuclei, more grains, small and fine grains
   Slow cooling - fewer nuclei, fewer grains, large coarse grains
2. High elastic limit, increased UTS and hardness, decreased ductility
3. Imperfections/defects in the crystal lattice. Weak points which lead to an alteration of lattice structure and shape. Resistable, occur due to slip. Cannot move from one grain to another and therefore accumulate at grain boundaries
4. Increases elastic limit, UTS, hardness and decreases ductility and impact resistance
5. Work hardening/strain hardening. Work been been on metal/alloy at low temperature (below recrystallisation temperature - bending, rolling, swaging). Causes slip, leading to stronger harder metal. Strengthening of metal by plastic deformation. Dislocations interact and create obstructions in crystal lattice. Resistance to dislocation formation develops
6. Increases elastic limit, UTS, hardness and decreases ductility, impact strength and corrosion resistance

Question 11

Metals and Alloys 2

1. Describe annealing
2. Describe stress relief annealing
3. Describe recrystallisation
4. Give 2 advantages of alloys
5. Define solid solution
6. Describe the 2 types of alloy cooling
7. Describe homogenising annealing

Answer 11

1. Heating of metal/alloy so that greater thermal vibrations allow migration of atoms and atoms rearrange
2. Eliminates internal stresses caused by cold work by allowing atoms to rearrange within grains
3. Occurs when metal/alloy is heated. Leads to smaller, equi-axed grains, reducing EL, UTS, hardness and increasing ductility. Spoils benefits of cold work but allows for further cold work
4. Improved mechanical properties, lower melting points
5. Common lattice structure containing two metals that are soluble in one another. Can be substitutional (atoms of one metal replace the other in the crystal lattice; random or ordered) or interstitial (when atoms are markedly different in size and smaller atoms are located in spaces in the lattice of larger atoms)
6. Slowly - metal atoms diffuse through lattice, ensuring grain composition is homogenous, but large grains
   Rapidly - prevents atom diffusion through lattice, causes coring as composition varies throughout the grain (undesirable) - smaller grains which impede dislocation mo emend, improving mechanical properties
7. Reverses coring. Reheats alloy to allow atoms to diffuse and cause grain composition to become homogenous

Question 12

Metals and Alloys 3

1. What is the composition and function of components of 18/8 stainless steel
2. What makes steel stainless
3. Give 5 advantageous properties of stainless steel
4. Give 4 causes of stainless steel wire fracture
5. Describe weld decay

Answer 12

4. 72% Fe (forms steel), 18% Cr (chromium oxide layer increases corrosion resistance), 8% Ni (improves UTS and corrosion resistance), 1.7% Ti (corrosion resistance), 0.3% C (forms steel)
5. Cr >13%
6. Light, fracture resistant, strong, corrosion resistance, high thermal conductivity, impact strength, abrasion resistance, often thin in cross-section
7. Overworked, mechanical abrasion, fatigue, weld decay
8. Intergranular corrosion created by overheating the alloy that occurs between 500-900C. Causes chromium carbides to precipitate at grain boundaries

Question 13

PMMA

1. Describe PMMA setting reaction and stages
2. Give 2 powder and 2 liquid constituents of PMMA
3. Give 8 properties of PMMA
4. Describe 2 types of porosity
5. Describe why granularity occurs
6. Describe why residual monomer occurs
7. What is another issue with denture bases/PMMA
8. Name 2 types of finishing techniques

Answer 13

1. Free radical addition polymerisation reaction
   Activation (of initiator to provide free radicals), initiation (free radicals break C=C bond in monomer and transfer free radical), propagation (growing polymer chain), termination (of polymerisation)
2. Powder - benzoyl peroxide initiator, pre-polymerised PMMA beads, co-polymers, pigments, plasticiser
   Liquid - MA monomer, inhibitor, co-polymers
3. Adequate thermal expansion, high softening temperature, high thermal conductivity, rigid, high flexural strength, good abrasion resistance, good colour, low fracture toughness, insoluble in oral fluids, high hardness, cheap, easy to repair, non-irritant, non-toxic
4. Gaseous - monomer boiling/rapid cooling causing gaseous bubbles in PMMA in thicker parts of base plate
   Contraction - insufficient pressure during processing, too much monomer, insufficient excess material, causing voids due to polymerisation shrinkage where acrylic dough is not sufficiently packed all over the baseplate
5. Rough granular surface due to too little monomer, found all over baseplate
6. Due to insufficient terminal bill and/or under-curing
7. Crazing
8. Dough-packing, injection moulding

Question 14

Amalgam

1. Give 3 constituents
2. Name 2 types of amalgam and which is better and why
3. Name and describe 2 types of amalgam particles
4. Describe setting reaction for both types
5. What does the gamma-2 phase show and how is it removed
6. 2 indications
7. 4 contraindications
8. 5 advantages
9. 5 disadvantages
10. Why are materials now zinc-free

Answer 14

1. Mercury, silver, tin, copper, other metals, zinc
2. Traditional
   Copper-enriched - increased strength and hardness
3. Lathe-cut
   Spherical (less mercury, higher tensile and early compressive strengths, less sensitive to condensation, easier to carve)
4. Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9
   Copper enriched:
   AgSnCu + Hg -> AgSnCu + gamma-1 + Cu6Sn5
5. Weak strength, poor corrosion resistance. Copper-enriched removes gamma-2 phase, making it stronger and causing less creep
   Silver copper is mixed with gamma-2 to make it stronger and less corrosive. Other methods to reduce corrosion includes polishing margins and avoiding galvanic cells
6. Moderate and large-sized cavities in posterior teeth, ability to seat matrix and wedges around tooth, moisture control not brilliant
7. Anterior teeth, aesthetics paramount, mercury sensitivity, inability to produce retentive cavity, pregnant, child
8. User-friendly, strong, durable, good LT clinical performance, radiopaque, high elastic modulus, high hardness, cheap
9. Poor aesthetics, no bond to tooth, high thermal diffusivity, destructive prep, marginal breakdown, tooth discolouration, ditching (LT corrosion at margin), lichenoid reactions, amalgam tattoo
10. Zinc is a scavenger during production – preferentially oxidises and slag formed/removed.
    Materials are now zinc-free due to the reaction of zinc with saliva/blood: Zn + H2O -> ZnO + H2
    Bubbles of hydrogen gas is formed within amalgam. Pressure build-up causes expansion. Downward pressure causes pulpal pain. Upward pressure causes the restoration to sit proud of the surface/protrude

Question 15

Composite

1. 3 types, which is best and why
2. 5 components, describe each and give an example of each
3. 5 indications
4. 3 contraindications
5. 5 advantages
6. 5 disadvantages

Answer 15

1. Conventional, microfine, hybrid (best - compromise)
2. Filler particles - improve mechanical properties, aesthetics, abrasion resistance, reduce PCS. Glass silica/quartz
   Resin - bifunctional molecules that undergo free radical addition polymerisation - bis-GMA
   Light activator - photo-active atom catalyst that initiates polymerisation of resins when activated by blue light (430-490nm) - camphorquinone
   Low weight dimethacrylates - adjust viscosity and reactivity of resin monomer. TEGDMA
   Silane coupling agent - bifunctional molecule binding resin and filler particles
3. Anterior teeth, where aesthetics important, cores, veneers, indirect inlays/onlays, luting agents, class III, IV, V restorations,
4. Moisture control impossible, limited tooth structure remaining, posterior teeth with limited finances
5. Good aesthetics, conservative prep, support for remaining tooth tissue, good bond to tooth, low thermal conductivity, good LT clinical performance, no galvanism
6. PCS (causing micro leakage, etc.), marginal integrity, post-op sensitivity (due to PCS, contraction, insufficient cure - prevent by <2mm increments), low fracture toughness, high elastic deformation, technique sensitive, hydrolytic breakdown, limited depth of cure, high thermal expansion coefficient

Question 16

GIC

1. 2 types
2. 4 components
3. Describe setting reaction, including each stage
4. 5 indications
5. 2 contraindications
6. 5 advantages
7. 5 disadvantages
8. How does GIC bond

Answer 16

1. GIC, RMGIC
2. Polyacrylic acid, tartaric acid, silica, alumina, CaF, AlF, AlPO4, NaF
3. MO,SiO2 + H2A -> MA + SiO2 + H2O
   Phase 1 – dissolution. Acid added to solution; hydrogen ions interact and attack the glass surface, causing glass ions to be released/leached out. This leaves silica gel around unreacted glass
   Phase 2 – gelation. Initial set. Calcium ions crosslink with the polyacid by chelation with the carboxyl groups, forming calcium polyacrylate. Calcium ions are bivalent, so can react with two molecules
   Phase 3 – maturation/hardening. Trivalent aluminium ions ensure good crosslinking with an increase in strength
4. Temporary restoration, luting agent, shallow cervical restorations, where moisture control difficult, dressing, FS, ortho cement, cavity base/liner
5. Definitive restoration of large posterior cavities, where composite can be placed
6. Relatively good aesthetics, fluoride release/reservoir, stable strong bond to enamel and dentine, low micro leakage, good thermal properties, no setting contraction
7. Brittle, poor wear resistance, initial moisture susceptibility, poor handling characteristic s, not excellent aesthetics, susceptible to acid attack and drying out over time
8. Ion exchange with calcium in enamel and dentine and hydrogen bonding with collagen in dentine

Question 17

RMGIC

1. 4 components of RMGIC
2. 2 types of RMGIC materials
3. 3 RMGIC advantages vs GIC
4. 3 RMGIC disadvantages vs GIC
5. 2 RMGIC advantages vs composite
6. 2 RMGIC disadvantages vs composite

Answer 17

1. Fluoro-alumino-silicate glass, barium glass, potassium persulfatd, ascorbic acid, poly acrylic acid, HEMA, tartaric acid, photo-initiators
2. Dual cure - acid base, light activation
   Tri cure - acid base, light activation, redox reaction
3. Better aesthetics, better handling properties, better strength
4. PCS, exothermic setting reaction, reduced strength if unreacted monomer (if not light cured)
5. Easier to use, less moisture sensitive, fluoride reservoir
6. Reduced strength, worse aesthetics