Title

Interface adhesion and abrasive wear study of polymeric dental composites

Date of Completion

January 1998

Keywords

Chemistry, Polymer|Engineering, Chemical|Health Sciences, Dentistry

Degree

Ph.D.

Abstract

Several dimethacrylate monomers were copolymerized to form the polymer matrix. The copolymerization process was studied using DSC and FTIR. The equilibrium conversion of double bonds was found to be about 60% to 86% for photo polymerization, depending on the mobility of the pendent double bonds and the network structures formed. The properties of the copolymers were characterized using DMTA, Instron tensile test and other techniques.^ A glass surface treatment method was developed by incorporating the SiCl$\sb4$ into the conventional silylation process. The $\gamma$-MPS and SiCl$\sb4$ were applied in a sequential way. The tenacity of the silane coating on the glass surface was enhanced significantly by the modified method, as demonstrated by solvent extraction, TGA and DRIFT experiments. The filler-matrix interface adhesion and durability were greatly improved by the modified silane treatment process as illustrated by SEM microphotographs and embedded single fiber fragmentation tests. The significant improvement in adhesion and stability was attributed to the presence of a highly crosslinked and strongly, perhaps chemically, bonded siloxane coating on the glass surface.^ The mechanical properties of untreated glass bead composites deteriorated dramatically when exposed to water. Most noticeably, the modulus decreased with increasing filler volume fraction. The $\gamma$-MPS/SiCl$\sb4$ treated glass bead composites, on the other hand, maintained their mechanical properties when exposure to 37$\sp\circ$C water.^ A pin-on-disk wear test apparatus was constructed through modification of a commercially available tribometer. It featured water circulation on the sliding surface, friction force measurement, stable counterface and fast measurement of the wear rate. The specific wear rates of neat resins and relative wear rates of composites were determined. The effects of various parameters on wear resistance were investigated. The failure mode on a worn surface was examined using SEM. It was found the microcutting and microcracking were the predominant mechanisms for the materials tested under the abrasive wear conditions of this research. The specific wear rate depended non-linearly with the normal load. The wear rates decreased with increasing ductility of the material, increasing filler size and decreasing the filler volume fraction. ^