241: Understanding Phase Separation of Photopolymerized Dental Restorations

Presenter(s)

Sarah Beth Holles

Abstract or Description

Dental restorations are complex biomaterials, as they have many requirements in terms of physical and mechanical properties. Restorations must be biocompatible, mechanically robust, have an appearance that is aesthetically pleasing to patients, and most importantly, should have long lifespans. For safety and aesthetic reasons, photopolymerized restoratives based in three-dimensional polymer networks have become more favorable in recent years. However, these materials have an incredibly high failure rate compared to previously-employed amalgam-based restorations. To try and reduce the failure rate, a deeper understanding of these materials is needed. Current research attributes restoration failure to inconsistent polymerization at the interface between the native tooth structure and the restoration. These inconsistencies can be a result of phase separation during photopolymerization, which produces a distribution of more densely cross-linked (strong) and loosely cross-linked (weak) domains. To understand this phase separation behavior and identify solutions to mitigate this challenge, our work investigates the phase behavior of photopolymerizable formulations similar to dental adhesive materials currently on the market. To determine the ultimate driving force for phase separation, the formulations are varied in terms of crosslink density, ratio of hydrophilic and acid-etching monomers, as well as the fraction of a water/ethanol co-solvent. FTIR spectroscopy and dynamic mechanical analysis (DMA) are employed to characterize phase composition, thermomechanical behavior, and extent of conversion of these model formulations. Initial results support the hypothesis that solvent fraction most significantly influences phase separation. With these findings, effective strategies to mitigate failure of these materials will be discussed.