PCD Spring 2024 Exam 1

PCD Spring 2024 Exam 1 Indications of RBC Caries lesions (small to moderate) Esthetics (tooth color) Conservative (outline, shallow, round) Replacements of composites (questionable) Advantages of RBC Esthetics Conservative Adhesion to tooth structure Low thermal conductivity Elimination of galvanic issues Alternative to amalgam? What is necessary in amalgam preps? 90 degree CSM Reverse curve Adequate depth Buccal/lingual convergence Rounded internal line angles Retention form What is necessary in composite preps? Bonding (needs a dry field) Maintaining as much tooth structure as possible What do amalgam preps have that composite preps don't? Retentive features Groove extensions Convergent walls Dovetail Reverse curve Axial wall The internal wall that runs parallel to the long axis of the tooth Gingival floor floor of the prep that is closest to the gingiva Axial wall height is determined by Proximal contact Rubber dam isolation is used to Isolate/define the operating field by isolating one or more teeth from the oral environment Advantages of rubber dam Moisture control Access and visibility Harm prevention Contamination Conditions that may prevent the use of a rubber dam Teeth that are not erupted enough Malpositioned teeth 3rd molars Pts that cannot breathe through nose Psychological reactions Properties of ceramics Esthetics ++ Brittle Properties of metals Not esthetic Strong Properties of polymers Esthetics + Versatile What is polymethyl methacrylate and what is it used for? A polymer Denture bases Temp crowns What is polyvinylsiloxane used for? Impression materials What things are resin with ceramic filler? Resin composite restoratives Adhesives Cements Type of bonds in polymers Covalent bonding Covalent bonding Sharing of electrons Equal tendencies to donate or accept electrons What elements are involved in covalent bonding? Carbon and silicon What are the primary bonds in polymers? Covalent + crosslinking What are the secondary bonds in polymers? Van der waal Hydrogen bonds Thermoplastic a material that softens when heated and hardens again when cooled Thermoset when exposed to high temperatures, bonds are set, can't be unlocked Resistant to change in shape with heating Example of thermoplastic polymer material The plastic material used to make bleaching trays/athletic mouthguards Polymethyl methacrylate (PMMA) is an... Acrylic resin Is PMMA thermoset or thermoplastic? Thermoset Heat curing mode activator and initiator No activator Initiator: benzoyl peroxide Chemical curing mode activator and initiator Activator: amine Initiator: benzoyl peroxide Light curing mode activator and initiator Activator: camphoroquinone Initiator: DMAEMA (amine) Steps in polymerization Initiation Propagation Termination Why can't we use PMMA as a restorative material? It is not easy to handle It can't handle light (not esthetic) It absorbs water, coffee, tea, etc. Shrinkage Mechanical properties Composite A compound of two or more distinctly different materials with properties that are superior or intermediate to those of the individual constituents Composite structure has what two phases? Dispersed phase Matrix phase Dispersed phase= Glass fiber Matrix phase= Epoxy resin Three components of dental resin composite Dispersed phase Matrix phase Coupling agent Coupling agent= Silane Filler loading The volume percent of filler particles vs resin matrix in the composite material The mechanical properties and clinical characteristics of dental resin composite materials are primarily determined by the Volume percent of filler loading As the % filler vs resin increases... It gets stronger It gets thicker, less flow More wear resistant What happens to the coefficient of thermal expansion as the filler % vs resin increases? It is lower the more filler you have More filler=less substance will change shape when ex: eat cold ice cream or drink hot coffee What happens to shrinkage as the % of filler vs resin increases? Decreases Resin continuum: materials from lowest to highest filler content Bonding resin Sealant Flowable composite Universal restorative composite Low filler content= High flow Low strength High shrinkage High filler content= High strength Low shrinkage Low flow Sealant function Seals occlusal grooves to prevent caries Resin cement use Cementation of ceramic crowns and veneers Flowable composite use Small restorations or as the first increment in class II restoration Flowable composite adapts well to ______ of cavity prep Irreguarities What determines the inherent properties of the composite material? Filler size Loading What single operator variable most significantly affects the clinical performance of the composite material? POLYMERIZATION Polymerization critical components for clinical success degree of conversion depth of cure polymerization shrinkage Degree of Conversion The percent of carbon-carbon double bonds that are converted into polymeric single bonds during polymerization More double bonds that are converted to single bonds = _______ degree of conversion Increased Greater DOC= Higher strength Higher stiffness Less water sorption What is the degree of conversion for common composites? About 70% DOC is proportional to the amount of _____ applied Energy Applied energy is affected by Distance Thickness of material Path of light Energy density= Power(mW/cm2) x time (sec) Depth of Cure the thickness of composite that is cured by a light source Polymerization shrinkage The bulk volumetric shrinkage that occurs as the formation of covalent bonds brings molecules closer together and reduces intra-molecular space How much shrinkage occurs when you place composite and cure? ~3% Polymerization shrinkage = ______ Stress You have ruptured of dentin bond, marginal gaps, microleakage, post-op sensitivity, and recurrent decay Coefficient of Thermal Expansion Measure of tendency of a material to change its shape, area, volume, and density in response to a change in temp ______ + ________= leakage Shrinkage + thermal expansion Dentin CTE 8 Tooth (crown enamel) CTE 11 Resin composite CTE 14-50 Pit and fissure sealant CTE 85 How do we contend with shrinkage? By adhesive bonding and using an incremental placement technique (divides the stress into portions that can be resisted by the bond) What makes the increments stick together? -air inhibited layer (greasy layer on the surface of the composite) -unreacted free radicals (allows composite to attach)