NBDE Part 2- Operative Dentistry Exam Questions With Complete Solutions

NBDE Part 2- Operative Dentistry Exam Questions With Complete Solutions Composite resin restoration is NOT recommended for this (class/tooth) - Answers-Class III DL aspect of canines amalgam/direct gold indicated Composite will not maintain the MD dimension of the tooth .Amalgam is a poor/good thermal insulator - Answers-poor .What materials are used under most amalgam restorations to provide thermal protection? - Answers-CaOH or ZOE base .Ideal depth of amalgam prep and dentin remaining for adequate pulpal insulation is _____mm into dentin and _____mm remaining - Answers-0.5 2.0 .Amount of mercury remaining in a set amalgam restoration is related to - Answers-how much of the mercury-rich matrix is left in the amalgam after condensation .Mercury-rich matrix is removed by - Answers-condensing and carving amalgam after placement .Amount of mercury remaining in amalgam after condensation directly affects - Answers-- porosity - compressive strength - corrosive resistance - surface finish of restoration .Longer the trituration time (mixing time of amalgam), smaller/greater the setting expansion - Answers-smaller .Characteristics of properly triturated amalgam - Answers-Shiny, wet, smooth, homogenous .T/F Overtriturated mix is preferable to undertriturated mix - Answers-T .Discolored, corroded, superficial layer frequently seen on the surface of amalgam is most likely - Answers-sulfide .what happens when amalgam is contaminated w/ saliva? - Answers-water in saliva reacts with zinc to produce hydrogen gas --> resulting pressure from the liberated gas produces SEVERE EXPANSION of the amalgam (corrosion, post-op pain) Compressive strength also decreases .For an amalgam restoration, the tensile strength is about ______ of its compressive strength - Answers-1/5-1/8 That's why enamel is needed to support amalgam @ the margins of restorations .T/F. Amalgam is less abrasion-resistant than composite - Answers-F. More abrasion-resistant .Minimum thickness of ___mm in axial areas to ____mm in areas of occlusal contact for adequate compressive strength - Answers-0.75 1.5-2.00 .If mercury content exceeds ___%, dramatic loss in strength results - Answers-55- marginal breakdown, fracture, corrosion .Reaction between alloy particles and mercury - Answers-Silver-Tin alloy (gamma) + Mercury --> Silver-Tin alloy (gamma) + Silver- Mercury (gamma-one) + Tin-Mercury (gamma-two) .Gamma - Answers-Unreacted alloy -strongest -Corrodes the least - Forms 30% of volume of set amalgam .Gamma-one - Answers-Matrix for unreacted alloy - second strongest phase - forms 60% of volume of set amalgam .Gamma-two - Answers-- Weakest and softest - Most susceptible to corrosion - Forms 10% of the voulme of the set amalgam - Volume decreases with time due to corrosion .Low vs. High copper amalgam - Answers-- Low-copper amalgam contains gamma-two phase - Marginal defects (chipped margins) more often seen around low-copper amalgams .Smaller particle size (amalgam), lower/higher strength, lower/higher flow, worse/better carvability - Answers-higher lower better .When facial (or lingual) extension is 2/3 from primary groove toward the cusp tip, _________________ is MANDATORY for development of adequate resitsance form - Answers-reduction of the cusp for amalgam capping .Final amalgam restoration need restored cusps with minimal thickness of ____mm for functional cusps and ____mm for nonfunctional cusps - Answers-2 1.5 .T/F Gingival cavosurface margin for amalgam prep should ALWAYS be beveled. - Answers-F. ONLY if it is in the enamel .Marginal ridge fractures are due to - Answers--Not rounding axiopulpal line angle - Marginal ridge left too high - Improper occlusal embrasure form - Improper removal of matrix band - Overzealous carving of restoration .Amalgam polishing should be done - Answers-at least 24 hours after condensation Preferably longer (24-48 hours) to ensure that reactions between alloy and mercury are completed and more corrosion-resistant surface will be created .Mercury content of amalgam should be within _______% - Answers-45-53% .Basic constituents of amalgam - Answers-Silver, Tin, Mercury, Copper and (small amounts of zinc, palladium, indium) .Amalgam Creep - Answers-- Deformation with time in response to constant stress - One of the main causes for marginal fracture of amalgam - Creep is time-dependent - High copper and low mercury content DECREASES creep -Delay between trituration and condensation increases creep -Increasing condensation pressure decreases creep .Marginal leakage of restoration decreases/increases as the restoration ages - Answers-DECREASES because corrosion products are helpful in reducing marginal leakage (Tin Oxide and Tin Sulfide) .Thickness of liners, cements, bases - Answers-- liners: 5 microns - cement: 15-25 microns - base: 1-2mm .Indications for use of base - Answers-- to replace lost dentin under restorations - to provide thermal protection against metallic restorations - to increase the resistance to the forces of condensation of amalgam - to block out undercuts when taking impressions for cast restorations - most important factor for pulp protection is thickness of remaining dentin .Liners - Answers-- placed as a thin coating on the surface of prep - desired final film thickness is 5 microns - BARRIER TO CHEMICAL irritants - not used for bulk up/thermal insulation - cannot be used alone in a deep cavity .GI cements - Answers-- hybrids of silicate and polycarboxylate cements - Powder: fluoro-alumino-silicate glass - Liquid: polyacrylate - Powder/liquid to form a cement glass particles surrounded by a matrix of fluoride elements - Fluoride-releasing properties of silicate particles -Biocompatible .GI cements is a bad/good thermal insulator, low/high solubility in the mouth, and has lower/higher cement film thickness than Zinc Phosphate cements - Answers-good low Higher (disadvantage) .Disadvantages of GI cement - Answers-Low initial pH -> post-cementation sensitivity Sensitivity to moisture contamination and dessication .T/F Cements can be used as luting agents - Answers-T .Zinc Phosphate Cement - Answers-Powder: Zinc Oxide Liquid: Orthophosphoric Acid Primary use: luting agent for cementation of cast restorations .Retention of Zinc Phosphate depends on - Answers-Mechanical Interlocking (as opposed to GI and Polycarboxylate cements) .Disadvantages of Zinc Phosphate - Answers-Low initial pH -> post-op sensitivity pH goes from ~2 to neutral @ 48 hours. Can be good due to its antibacterial effect. Lack of chemical bond formation Shrinks when contact with air .Zinc Polycarboxylate cement - Answers-Liquid: polyacrylate and copolymers Powder: Zinc Oxide and Magnesium Oxide One of the first chemically adhesive dental materials .Zinc Polycarboxylate binds primarily to - Answers-enamel weaker bond to dentin