Methods and physical chemistry of resin-based dental composites
The properties of dental resin composites have improved significantly since their inception, but the fundamental physics behind their properties remain to be explained or modeled comprehensively. The aim of this thesis is therefore to study the fundamental trends and relationships between the filler particles constituting these materials and the resulting properties. Photocalorimetry (pDSC) methods have been used previously to measure the degree of conversion in dental resins, but the measurement parameters have never been adequately assessed. Through systematic variations of the analysis sequence, sample mass, temperature, light intensity, and atmospheric composition, an optimized protocol was established to yield reliable and reproducible results. A series of dental composites was then formulated with spherical silica particles of graded sizes from 75 to 1000 nanometers at different loading levels. The viscosity of these composites before polymerization was measured and used to expand the classic KriegerDougherty suspension viscosity model to account for filler surface area in addition to filler loading. This extended model (EKD) was also used to model composite conversion, resulting in the first unified model of composite viscosity and conversion using only filler size and resin composition. The maximum loading and post-cure mechanical properties of these same composites were also examined. Although the maximum functional filler loading varied according to the filler size, the ultimate flexural strength of the materials depended only on the filler loading. Further tests with these composites showed that filler size was directly responsible for transparency of the materials, with opacity increasing as a function of filler size. This work pushes the boundaries of understanding in dental composites. The newly established protocol for pDSC measurements yields more reliable conversion data, and the EKD model allows for more accurate predictions of dental composite properties directly from their component parts. The guidelines established here can now be used to design new composites with the desired properties of viscosity, conversion, mechanical strength, and transparency. Keywords: photocalorimetry, pDSC technique, viscosity, loading, spherical silica, surface area, transparency, formulations, guidance, technical understanding.
Technique pDSC Formulations Photocalorimetry pDSC technique Viscosity Loading Spherical silica Surface area Transparency Guidance Technical understanding