Numerical modeling the structural changes of Bis-GMA-based dental composites during the photopolymerization

Dental composite materials are preferably used as a filling material due to their esthetic appearances and ease of use. Dental composites are composed of three major components; an organic polymer matrix, inorganic filler particles and coupling agent. The polymer matrix is usually produced by visible-light-cured bisphenol-a-glycidyl methacrylate (Bis-GMA), diluted with triethyleneglycol dimethacrylate (TEGDMA). Inorganic fillers like barium or zinc glasses, quartz, zirconia, silica are used to reinforce the organic matrix. Polymerization shrinkage of composites arises from the formation of a polymer due to the monomer transformation which composes of organic matrix phase. Consequently, this may result in patient's teeth such failures as enamel fractures, de-bonding, microleakage and secondary caries. For this reason, investigation of shrinkage behavior during polymerization process is important to compose better composite material property. The purpose of this study was to investigate the shrinkage behavior by means of mathematical modeling the shape change and to determine the parameters influencing the shrinkage value. Dental composites were obtained experimentally by using BisGMA (Bisfenol A-glycidil methacrylate) and HEMA (Hydroxyethyl methacrylate) as the organic matrix and hydroxyapatite (HA), alumina and zirconia as the inorganic fillers with various amounts. Archimedes principle was used for determine the density of the samples before and after polymerization. Shape change of the composites was found by numerically relating to the density values of the composites and these results were compared with the results of experimental shrinkage values obtained by laser profilometer. Polymerization shrinkage and shape change results obtained by numerical modeling were found to be in good agreement with the corresponding experimental values obtained by laser profilometer.