DENTAL MATERIALS NOTES

(reference www.pgdoctors.com)
solidification shrinkage of gold alloys 1.25-1.65%... where as of base metals--- 2-3%


most commonly used titanium alloy for medical and dental puposes...,--- Ti6Al4V


Yield strength of austentite phase of ni-ti alloys is 560Mpa

mechanical properties of enamel vary acc to its histological structure. that of dentin r independent of its structure. dentin is stronger in tension n more resilient than enamel. fracture toughness of dentin varied by a factor of 3 as a function of enamel rod orientation.

physical attraction is negligible after 0.7 mm distance

lattice pattern of most of dental materials is cubic pattern

stress Internal force resisting applied External load in unit area

poisson ratio for isotrophic material is 0.5 and for metals is 0.3

yield strength it is strength required to produce particular offset

shear modulus is 0.38 times the young modulus

resilience amount of energy absorbed by structure when it is stressed not to exceed its proportional limit. It is total area under stress strain graph .

A restorative material should have high elastic modulus and low resilience

TOUGHNESS energy required to fracture a material . It is total area under stress strain graph up to break point

ductility ability of material to withstand permanent deformation under tensile load without rupture

malleability ability of material to withstand deformation without rupture under compression

stress at elastic limit - yield strength
strain at elastic limit - flexibility

ductility represent ability of material to sustain large permanent deformation under tensile load before it fracture. Measured by
percent elongation
reduction in area
cold bend test

Ductility decrease with increase in temperature and malleability increases with increase in temperature. Ductility is measured in percent elongation and is measure of brittlness.

Hardness is ability to withstand permanent deformation on form of indentation load

Macrohardness test : the mnemonic is RAB (GOD )
R for Rockwell & B for Brinell

so vicker and knoop hardness test are micro hardness test with load less than 9.8 N

vicker used for dental cast gold alloy and hardness of tooth structure. .

Flexibility is strain that occur when material stress to its proportional limit



biting forces :
molarregion 100-200 pound premolar : 50 to 100 pound cuspid : 30 to 75 pound
incisor 20 to 55 pound

cold bend test : ductility of material

newtonian fluid fluid demonstrate shear stress proportional to strain n =1 mnemonic is newton was a ideal person

pseudo plastic the viscosity decreases with increasing strain rate

dilant rigidity increase as rate of deformation increases

mnemonic the dilant or dil so the mnemonic is when i see a beautiful gal my heart beat increases )

thixotropic material ( the viscosity decreases due to increase in PRESSURE .

linear coefficient of thermal expansion change in length of material when its temperature is raised or lowered through 1 degree centigrade . Linear coefficient of thermal expansion is inversely proportional to melting temperature and directly proportional to stiffness acrylic resin have higher coefficient of thermal expansion the higher the thermal conductivity greater ability to transmit energy latent heat of fusion amount of heat required to change 1 g of substance from solid to liquid . 1 gm of water freeze 80 calories heat generated sublimation solid transfered into gas BENZOLD BRUCKE EFFECT ( PGI -2011 change in color due to change in brightness ) hue specific color produced by specific wavelength. Dominant color of an object value or brilliance the dark and light shade property of color. Lighter shade are with high value. Degree of saturation of hue is chroma like some teeth appear more yellow than others. Colour has property of scattering and absorption cohesion the molecule are of same kind adhesion two different molecule for adhesion solid have high surface energy and completely wetted by liquid the hydrophilic material ( agar alginate polyether have contact angle of 30 to 35 degree. And hydrophobic polysulfide addition and condensation silicone have water contact angle 95 degree. So for complete wettability angle is zero .

impression material are classified into elastic and non elastic elastic material are reversible - agar irreversible - alginate elastomer - poly sulphid etc inelastic impression material are impression compound , plaster of paris , zinc oxide eugenol paste and wax impression compound contract 0.3 percent to 0.4 percent from passing mouth to room temperature. It should be placed at temperature of 45 c in mouth glass transitional temperature 39 c and fusion temperature 43.5 c flow (ADA NO.3 ) 6 percent at 37 C and not less than 85 percent at 45 C carnuaba wax in impression compound regulate flow. Stearic acid plasticizer and rosin main ingredient. Zinc oxide eugenol produce RIGID impression with high acuracy and good detail base paste in zinc oxide eugenol has zinc oxide and mineral oil. It is white in color. EBA can be used substitute of eugenol colloid emulsion formed by dispersion of droplet of liquid in other liquid colloid suspension solid in liquid

composition of agar mnemonic is wah bai wah chak te phatte (wax, borate ,water, thixotropic mat, potasium sulphate ) with agar as basic constituent potassium sulphate help in proper setting of gypsum model and borate provide strength. Tempering temperature is 63 c, tray material should be condition at temperature of 46 c. Highest shelf life in impression material seen in agar impression material. Tempering time of agar is 3 minute to increase viscosity. Alginate impression material (Ada no 18 ) anhydro beta d mannuronic acid. Water powder ratio of alginate 15 g of powder mixed with 38 mL of water. Alginate are made dustless by addition of GLYCERINE. Recently fifthtly added class of elastomeric impression material is light curable poly ether urethane dimethacrylate.

Polysulphide composition ::
it has base paste with polysulfide polymer and inert filler . The accelerator paste is lead dioxide (60 to 68 percent ) act as oxidizing agent. And dibutyl phtalate (30 percent ) plasticizer

setting reaction is ::
mercaptan + lead dioxide give polysulfide + water

so , lead dioxide is cross linking agent and it cause chain lengthening by oxidation of terminal SH GROUP. Oleic acid is retarder.
Setting time 8 to 12 minutes with high curing shrinkage. It has highest permanent deformation . It has good flexibility. 7 percent . And 2mm spacing required for impression making. It can be electro plated with silver or copper. Butyl rubber dissolved in chloroform is used as adhesive when making impression with polysulfide.

So it has longest setting time. It has unpleasant odour and colour. Discomfort to patient. Highest permanent deformation. Highest tear strength. Hydrophobic in nature. Causes lowest bell death count so BIO COMPATIBILITY IS GOOD. Contains lead dioxide with characterstic of brown color.

Also called as first dental elastomer thiokol mercapton impression material. aking impression with polysulfide.

So it has longest setting time. It has unpleasant odour and colour. Discomfort to patient. Highest permanent deformation. Highest tear strength. Hydrophobic in nature. Causes lowest bell death count so BIO COMPATIBILITY IS GOOD. Contains lead dioxide with characterstic of brown color.

Also called as first dental elastomer thiokol mercapton impression material.

condensation silicon or room temperature silicone. They have highest curing shrinkage. Due to evaporation of ethyl alcohol by product. It has base accelerator , poly dimethyl siloxane orthoethyl silicate as cross linking agent, colloidal silica stannous octate as catalyst spacing impression tray for condensation silicone should be 3 mm. Setting reaction :: di methylsiloxane + ortho ethyl silicate = silicone rubber + ethyl alchohol. . Handling with latex glove is contra indicated

addition silicone or pseudo plastic impression material or poly vinyl siloxane No Volatile product lowest curing shrinkage cast poured after several hour shows least setting time of all best dimensional stability hydrogen gas byproduct platinum accelerator paladium hydrogen absorber polyether hydrophilic spacing of 4mm in tray. More shelf life. Only hydrophilic elastomer with disadvantage of high modulus of elasticity and rigidity but minimal permanent deformation

brittle material have tensile strength very less than compressive strength

flouride decrease surface energy of enamel and dentin so retain less plaque

brinell hardness number : hard steel ball
rockwell conical diamond point
vicker diamond having square based pyramid. Modified for elastic recovery material and used for brittle material eg. Tooth
knoop rhombic diamond

strain hardening or work hardening or cold working slip of molecule along the slip -planes due to stresses metal become stronger harder and decrease in ductility and corrosion resistance

annealing reversal of cold working. It occur in wrought metal only. Occur by three stage recovery recrystalization and grain growth

when gypsum cast is placed in water it linear dimension decreases by0.1 percent for every 20 minute. At 70 percent humidity gypsum absorb water from atmosphere and reaction starts

volume expansion of impression compound 1.38 to 2.29 percent. And linear contraction of compound from mouth temperature to room temperature =0.3 to0.4 percent

zinc oxide eugenol compressive strength =7 Mpa

Japanese Alginate contain soluble and insoluble carbonate ( instead of phosphate )
alginate reactor : caso4
reactor first react with retarder . Compressive strength =49.8 psi

agar can be placed in mouth for 10 minutes and it show no distortion but if alginate for more than 3 minute it show distortion

alginate can not produce surface detail as accurately as agar also cast with alginate is of inferior quality so not used for fpd impression

water of reaction is same for all gypsum product 18.6 mL BUT GAUGING water differ with type of gypsum product for type1 it is 45 ml type 3 30 ml and type 4 it is 20 ml the base paste of condensation poly silicone has low molecular weight di methyl siloxane with terminal group mercapton gp hydroxyl gp silane gp vinyl gp answer is b . Condensation silicon polymer terminate in hydroxy terminatd poly dimethyl siloxane group

condensation polymerization involves combining of two dis similar molecule into third entirely different product . It is a step growth polymerization addition polymerization when similar molecule are combined the reaction is addition polymerization copolymer is resin formed by combining of monomer that are chemically different acrylic resin is derivative of ethylene and has vinyl group structural formula. Manipulation of denture base resin can be done by compression moulding or injection moulding color stability of self cure is less because of oxidation of tertiary amine. The proportion polymer to monomer used in fluid resin technique is 2:1 to 2:5:1 boiling point of monomer 100.8 c . Thermo setting resins are epoxy resin.polymerization in epoxy resins is cross linked polymerization 21 percent polymerization shrinkage occur when methyl meth acrylate is polymerized. But when poly methyl meth acrylate and MMA are mixed shrinkage is 7 percent. Cold cure acrylic activator is dimethyl para toluidine and initiator is benzoyl per oxide fit of cold cure appliance is better than heat cure because of absence of curing stress. Denture repair is done by cold cure as heat cure tend to warp denture resin shrink toward area of greatest bulk and toward the ridge portion of denture so tensile stress occur in thinner region palate. And right and left posterior teeth are pulled toward each other and hence increase vertical dimension of occlusion. Resin with high degree of color stability are activated by sulfinate system acrylic resin is softest of all restorative material . khn=15

composite resin develop in late 1950 and early 1960 chemical cure has initiator benzoyl peroxide and activator is tertiary amine. (n dimethyl paratoludine ) And light cure activator is camphoroquinine. Light activated resin are visible light and ultraviolet light. The inhibitor is butylated HYDROXY TOLUDINE the chemical activated shrink toward centre of bulk of material and light activated shrink toward light source type of composite conventional - 8 to 12 micro meter small particle - 1 to 5 micro meters hybrid -0.6 to 1 micro meter microfilled -0.04 to0.4 micro meter micro filled is resin of choice for aesthetic restoration of anterior teeth in non stress bearing area . And small and hybrid composite are used in stress bearing areas. Bond strength of etched enamel is 18 to 22 Mpa . Enamel tags are formed at dept of 20 to 30 micron . Size of filler conventional 1 to 100 micro micro .04 to .06 micrometer hybrid 1to 5 micro meter peritectic system : limited solid solubility of two metal. Eutectic : partial solid solubility but complete liquid solubility. It has on solidification range but solidify at constant temperature. Brittle and donot appear in alloy of <8.8 percent cu.

particle size of amalgam is 15 to 35 micron

evidence of secondary caries in amalgam 12 percent

hg vapour from amalgam 1.7 microgram per day.

application of lost wax technique for cast inlay taggart

coring induction of non homogenous structure as solid alloy solidifies

pure gold is one thousand fine

age hardening 200c to 450 c for 15 to 30 minutes . It decreases ductility and softening heat treatment at 700 c for 10 minute . Ductility is decrease here.

Cobalt chrome alloys can be cold worked but cannot be heat hardened while gold can be heat hardened but not cold worked

higher melting alloy tend to have greater shrinkage and that is base metal alloy have high casting shrinkage 2.3 percent than gold alloys 1.5 percent

the carbon steel are sup at high speed and used for cutting enamel and stainless steel at low speed used for cutting dentin

specific gravity for noble metal higher than base metal

tempering decrease hardness and increases toughness

memory effect for steel at 482 c

sensitisation on heating stainless steel to 400 to 900 c there is loss of corrosion resistance due to precipitation of chromium carbide. This can be prevented by reducing carbon content

ing dentin

specific gravity for noble metal higher than base metal

tempering decrease hardness and increases toughness

memory effect for steel at 482 c

sensitisation on heating stainless steel to 400 to 900 c there is loss of corrosion resistance due to precipitation of chromium carbide. This can be prevented by reducing carbon content

MARTENSITE THE MNEMONIC IS MAR THEY CAN KILL YOU. So THEY ARE USED IN CUTTING EDGES OF INSTRUMENT AND ARE BRITTLE LEAST CORROSION RESISTANCE AUSTENITE ARE LIKE FACE BOOK. SO HAVE FACE CENTERED CUBIC STRUCTURE AND ARE MORE POPULAR SO USED IN WIRE AND WELDING AND ARE MOST CORROSION RESISTANCE AND CAN BE STRAIN HARDENED .

thermal diffusion through material depend on its thermal conductivity and latent heat of fusion melting thickness coefficient of thermal expansion thickness correct answer is d

the total area under stress strain graph represent resilience flexibility modulus of elasticity toughness answer is toughness area under stress strain graph below proportional limit give resilience while area under entire graph up to breaking point give toughness of material which of following test are conducted on human beings group 1 group 2 group 3 none of above answer is 3 brinel hardness number of pure gold 25 10 50 150 answer is a knoop hardness of heat cure acrylic resin 2 to 30 50 to 60 75 to 100 125 to 150 answer a solubility of dìhydrate is0.2 and hemi hydrate is0.9. So solubility of hemi hydrate is more than dìhydrate. So water solubility of plaster will be more than gypsum.

setting expansion in gypsum is result of outward thrust of growing crystal. When water is present in between crystal the thrust can not be created. So setting expansion of plaster will decrease with higher water powder ratio

the most effective way of controlling setting time in gypsum is addition of accelerator and retarder and not the alteration of water powder ratio

increase in compressive strength within practical limit result from all of following except
decrease W /P ratio
increased spatulation time within limit
addition of accelerators
none of above

answer is c
addition of impurities may alter the strength of set product.

stearic acid in impression compound reduce plasticity reduce brittleness reduce flow none of above answer is b shellac stearic acid and guta percha are added to improve plasticity and workability. They are referred as plasticizer . .

which of following deteriorate rapidly
polyether
polysulphide
additional silicone
condensation silicone

answer is d.

Stannous octate is responsible for bad odour of condensation silicone. Ethyl alcohol is byproduct. The evaporation of it lead to contraction of condensation silicone

which of following are tried as light cure impression material
polyether
silicone
poly sulphide
none of above

answer is a

maximum permanent deformation is for type 1 and type 2 elastomer should not exceed
2%
2.5%
4%
5%
the correct answer is b.

Material causing minimum tissue distortion is
polysulphide
silicone
impression plaster
zinc oxide eugenol paste

answer is c

advantage of rubber base impression over agar bias is
reduced necessary armentarium
easily displaced soft tissues
more acurate reproduction of detail
can be poured even today after impression made

answer is a

which of following co polymer is characterized by one monomer chain as back bone of other
rapid
block
graft
all of above
answer c

last stage of addition polymerization is
inducer
chain propagation
chain transfer
termination
answer c

liquid bottle acrylic resin turn milky due to
exhaustion of inhibtor
partial polymerization
opening of double bond in methylcrylate
all of above
answer d

which of following is added to reinforce polymethyl methacrylate in high impact strength resin
vinyl resin
butadiene stryrene
urethane di methacrylate
answer is b

for each 1 percent increase in weight of denture base by water sorption denture base expand linearly by
0.2%
0.4 %
0.5%
answer is a

the recommended powder liquid ratio for fluid resin technique is
3:1
2:1
4:1
the answer is b

which of following etching pattern is optimal for bonding
type 1
type 3
type 2
answer1
type 1 etched enamel in which center of enamel rod is dissolved with periphery intact
type 2 peripheral dissolution
type 3 combination of type 1 and type 2

which of following generation of bonding agent is single component system
generation 1
generation 2
generation 4
generation 5
answer d

the minimum come strength for proper adhesion should be 20 Mpa for restoration and 5 mpa for ortho dontic bracket .

degree of conversion for light cure BISGMA is 20-30 percent 30-40 percent 40-50 percent 50-60 percent the degree of conversion refer to degree of amount of monomer that is polymerized. Answer is d .

type 4 zinc oxide eugenol is used mainly for cavity liner permanent cementation temporary filling of material temporary cementation answer a type 1 temporary cement type 2 permanent cementation type 3 temporary filling type 4 cavity liner

working time of amalgam----- jst 3-4 minutes!!

condensation force of amalgam---- 3-4lb/ 13-18 N

ELASTIC MODULOUS OF AMALGAM-- 21Gpa

tensile sterngth of amalgam--- 48-70 Mpa

DENTAL MATERIALS

---

1. The knoop hardness number of which one of the following materials is closest to that of dentin (KHN 65)? a) Tooth enamel. b) Amalgam. c) Pure Gold. d) Silicate cement.

2. KHN of enamel is: a) 90-100. b) 100-150. c) 300.@@@ d) 600.

3. Which of the following impression materials is elastic? a) Impression compound. b) Polyether rubber base.@@ c) Zinc oxide – Eugenol paste. d) Wax.

4. Which one of the following is the safest and most reliable method of regulating setting time of gypsum products? a) Altering the water and powder ratio. b) Speed of hand spatulation. c) Controlling the temperature of water to be used for mixing.@@ d) Adding salt in mixing.

5. Which of the following impression materials can be electroplated without risk of distortion? a) Polysulphide.@@ b) Condensation silicone. c) Addition silicone. d) Hydrocolloid impressions.

6. Which of the following statements relates best regarding cavity varnish? a) Varnishes are synthetic resins dissolved in acetone.@@@ b) Varnishes are calcium hydroxide in a resin base. c) Varnishes are used to insulate the pulp thermally. d) Varnishes are base of ZnO engenol.

7. Setting expansion of casting investment is approximately: a) 0.1-0.2%. b) 0.1-0.5%.@@ c) 0.8-1%. d) 1.1-1.7%.

8. Stiffness refers to a) Resistance to elastic deformation.@@@ b) Degree of elastic deformation. c) Expandability on heating. d) Shrinkage on cooling.

9. What is trituration a) Surface discoloration of metal. b) Mixing of amalgam alloy with mercury.@@ c) Same as erosion. d) Same as corrosion.

10. The dental amalgam alloys and mercury are mixed in ratio of: a) 1:1@@ b) 2:1 c) 1:2 d) 1:3

11. Most common drawback of amalgam restoration is: a) Secondary expansion. b) Porosity. c) Marginal break-down.@@ d) Contraction on setting.

12. What are the consequences of prolonged heating of a dental casting investment? a) Disintegration of the investment. b) Rough moulds of investment. c) Contamination of the alloys. d) Any of the above.@@@

13. Regarding dental Amalgam: a) It is a mixture of silver alloy and mercury.@@@ b) It is be composed of spherical tin and mercury. c) It is a mixture of irregular particles of silver and tin. d) Amalgamation process is formed during heating of silver-mercury.

14. Which part of an amalgam restoration has the highest mercury concentration? a) Marginal area.@@@ b) Centre of the restoration. c) Pulpal area. d) Proximal surface of restoration.

15. What is the maximum level of occupational exposure considered safe with regard to mercury vapors? a) 5 µg of mercury b) 50 µg of mercury@@ c) 35 µg of mercury d) 25 µg of mercury

16. The cement which has antibacterial property is: a) Copper oxide cement.@@@ b) Glass informer cement. c) Polycarboxylate cement. d) Zinc phosphate cement.

17. Cement extensively used for attachment of orthodontic brackets to teeth is. a) Silicate cement. b) Resin cement.@@@ c) Glass ionomer cement. d) Copper oxide cement.

18. Cement not irritant to pulpal tissue is. a) Calcium hydroxide cement.@@ b) Silicate cement. c) Copper cement. d) Glass ionomer cement.

19. The main resin constituent of polishable composite resin is: a) Polymethymethacrylae b) Polycarbonate c) Cyanoacrylate d) Urethane@@@

20. Fillers are added to composite resin to: a) Increase working time. b) Increase coefficient of thermal expansion. c) Inhibit matrix deformation. d) B+C.@@

21. Activating compound for visible light curing system: a) Hydroquinone. b) Ubiquinone. c) Camphoquinone.@@ d) Benzoin methyl ether.

22. In light cure system the wavelength of radiation is in excess of: a) 100 nm. b) 200 nm. c) 300 nm. d) 400 nm.@@@

23. In UV curing system, the activator employed is: a) Benzoin methyl ether.@@@ b) Methylmethacrylate. c) Hydroquinone. d) Dibutylphthalate.

24. The stainless steel loses its resistance to corrosion if heated to a high temperature because: a) Precipitation of chromium carbide@@@ b) Precipitation of carbon carbide c) Precipitation of iron carbide d) Precipitation of nickle carbide

25. What is the function of feldspar during preparation of dental porcelain of a metal ceramic Crown? a) It decreases viscosity of ceramic material so that it can be applied on the metal substructure with ease b) Feldspar forms a glassphase that is able to soften and flow slightly at porcelain firing temperature@@@@ c) Feldspar due to its particle size interrupts crack propagation in the dental porcelain d) Feldspar forms a carbon layer that flows at porcelain firing temperature

26. The firing temperature of high fusing porcelain lies in the range of: a) 1600-1950° F b) 2000-3400° F c) 2350-2500° F@@@@@ d) 1000-1500° F

27. Dicor is: a) Ceramic material with unusual strength. b) Ceramic material with excellent esthetics. c) Ceramic material which is castable.@@ d) New type of restorative resin with minimum porosity and excellent esthetics.

28. Regarding Glass ionomers: a) The powder is methyl methacrylate. b) The powder is an aluminosilicate glass@@@. c) They release mercury. d) They are highly irritant to pulp.

29. Which of the following cements bonds to tooth structure,has an anticariogenic effect, has a degree of translucency and does not irritate the pulp? a) Polycarboxylate cement b) Resin cement c) Silicate Cemenet d) Glass ionomer cement@@

30. What is the purpose of addition of orthoethoxy benzole acid to zinc oxide eugenol cement? a) To improve compressive strength of the cement@@ b) To limit oral solubility of the cement c) To render the cement light curable d) To improve tensile strength of the cement

31. Which of the following is best for ‘cermet’ cement: a) Cermet cement is glass ionomer cement with porcelain ceramic fillers. b) Cermet cement is glass ionomer cement with silver amalgam alloy particles in it.@@ c) Cermet cement is a mixture of glass ionomer and resin cements. d) Cermet cement is light curable glass ionomer cement.

32. Which of the following possesses anticariogertic property? a) ZnPO4 cement. b) Glass ionomer cement.@@ c) Poly carboxylate cement. d) ZnO Eugenol cement.

33. Regarding zinc phosphate cements: a) Powder and liquid are mixed on cold glass slab.@@ b) Powder and liquid are mixed on hot glass slab. c) Zinc phosphate cements have endothermic reactions. d) Retention is via chemical bonding.

34. Which of the following is used for pickling of casting made with gypsum bonded investments except ? a) 100% hydrochloric acid. b) Sulphuric acid. c) Ultra sonic devices with 100% hydrochloric acid. d) Hydrogen per oxide.@@@

35. With respect to acid etching: a) It creates a microscopically rough enamel surface.@@@ b) The eTchant is usually 20% phosphoric acid. c) The eTchant is usually applied for one minute. d) Following etching the eTchant should be washed away with phosphoric acid.

36. Which one of the following elastomeric rubber impressions is most likely to deform following in compression? a) Addition silicone b) Condensation silicone c) Polyeth. d) Polysulfide.@@@

37. How soon after contamination by moisture does a zinc containing amalgam restoration start expanding? a) 24 hours b) 1-2 days c) 3-5 days@@ d) One week

38. Creep value of which of the following is highest? a) LOW copper amalgam alloy@@ b) Admix alloy c) Single composition alloys d) Creep value of all the above mentioned alloys is same

39. Regarding alginate impression material: a) Alginate impression material contains sodium phosphate to act as an accelerator. b) The set alginate impression is a hydrocolloid gel.@@@ c) The impression is stored in water to prevent inhibition. d) Alginate impression is powered after 2 hours.

40. Gold based metal ceramic alloys are best cast Lg which of the following? a) Gypsum investment. b) Phosphate bonded investment with carbon.@@@ c) Phosphate bonded investment without carbon. d) Silica bonded.

41. Regarding base metal alloys: a) The casting shrinkage of base metal alloys is less than that of gold alloys. b) Chromium added to base metal alloy acts as a solid solution hardner.@@@ c) Carbide precipitation to a certain extent decreases strength of the alloys. d) Manganese and silicone are added to base metal alloys to act as accelerator.

42. Hardness of which of the following abrasives is maximum? a) Sand b) Emery c) Boron carbide@@ d) Silicone carbide

43. Regarding dental implant materials? a) Titanium substructure is coated with tricalcium phosphate to act as disinfectant. b) Ceramics are used as implant materials because of their aesthetics. c) Co-Cr alloys (63% with other metals is- often used due to their outstanding strength. d) Calcium hydroxyapetite crystals are bonded to titanium for better adhesion to bone.@@@

44. Which of the following gases used for soldering purposes has the highest temperature? a) Hydrogen. b) Natural gas. c) Acetylene.@@@ d) Oxygen.

45. What must be added to steel in order to render it‘stainless’? a) Chromium 12-30%@@@ b) Carbon less than 1.2% c) Chromium oxide 3-20% d) Flouride 2-3%

46. The agent of choice for final finishing of amalgam is a) Dry polishing powder b) Wet abrasive powder in paste form@@@ c) Commercially available dry polishing paste d) None

47. After insertion silicate restoration should not be finished for at least a) 24 hours@@@ b) 48 hours c) 72 hours d) 96 hours

48. Powder liquid ratio for glass ionomer cement is a) 1:3 b) 3 :1@@@ c) 2 :4 d) 4 :2

49. Lead dioxide cured poly sulphide material is effectively retarded by a) Phosphoric acid b) Eugenol c) Oleic acid@@@ d) Sulphuric acid

50. Diffusible gases used for reduction of voids in porcelain is a) Helium b) Hydrogen c) Steam d) All@@@