Dental composites are subjected to abrasive action that can wear away the contact surface of a restored tooth. In molar teeth this problem is greatest where occlusal forces are maximum. The wear behavior of composites have been evaluated in many respects however the role of the many different polymers used has not been fully investigated. Currently, polymers of varying visoelastic properties are used in formulating composites. The hypothesis of this proposal is that the wear of composites are related to the glass transition temperature (Tg) of the polymer(s) used in composites; specifically wear is hypothesized to be lowest when the polymer's service temperature corresponds to its glass transition, temperature. The overall goal of this proposal is to gain knowledge about several inter-related mechanical properties that influence wear and the structure of different polymers used in dental composites. This proposal will synthesize several polymers under controlled conditions and measure their glass transition temperatures using a Metravib viscoanalyzer. The sophisticated viscoanalyzer is also capable of measuring modulus of elasticity on macro composite samples over a range of frequencies and temperatures. The polymers to be synthesized are homopolymers and copolymers of BIS-GMA, triethylene glycol dimethacrylate and urethane dimethacrylate. Mechanical properties of compressive strength, tensile strength and coefficient of friction of the copolymers will be measured at several temperatures relative to their Tg and service temperature of 35oC. The Tg values, modulus of elasticity and coefficient of friction for these copolymers are not available and will be useful in later model and theoretical studies. Correlation of coefficient of friction to glass transition temperature and wear will also help understand the wear process of these copolymers. Wear of the polymers will be measured using a National Institute of Standards test at several temperatures relative to the Tg and service temperature. Experimental design methodology will be used to identify formulas having optimum mechanical properties. The interrelationship of these variables will be modeled using an advanced design and statistical data treatment program (RS/1-Discover). With this knowledge formulation of composites, which have minimum wear can occur. Further evaluation of the interaction of polymer and filler may then proceed and the placement of aestetic restorations having longer service life may be anticipated.
