Evaluation of polymerization contraction of experimental composites using laser interferometry

Objectives: The contraction of composite materials is a consequence of monomer cross-linking during polymerization. The contraction is especially expressed in materials with low filler load, such as bioactive composite resins with amorphous calcium phosphate (ACP) as filler. These materials have shown to remineralize carious lesions in aqueous environment. The aim of this study was to determine if the addition of inactive fillers reduces the polymerization shrinkage of ACP materials. Methods: Four composites were tested: ACP control containing only ACP (40%) and the experimental hydrophilic resin (60%) ; two composites containing 40% ACP, 10% silanized fillers [silica (12μm) or barium glass (0.7μm)] and 50% hydrophilic resin and commercial control- nano creamic material (CeramX, Dentsply Caulk, Germany) with approximately 85% barium-glass and silica fillers. Composite disk specimens (10/group) were light-cured for 30s in high power curing mode (Bluephase G2, Ivoclar Vivadent, Liechtenstein). Linear dimension change was recorded during each second of the polymerization process and 30s after polymerization using laser interferometry. The results were analyzed by ANOVA and Tukey post-hoc test was used in order to find significance levels. Results: The initial expansion and consecutive contraction were observed for all materials. There was no statistically significant difference among the materials regarding the expansion. Commercial control had statistically lower shrinkage (1.01%) than any other tested material (p=0.01). ACP composite with no inert fillers had the statistically higher polymerization contraction (1.43%) than the ACP material containing 10% barium-glass (1.13%) or the ACP composite containing silica fillers (1.17%) at the 0.01 significance level. Conclusions: The addition of silanized fillers has reduced the polymerization contraction of experimental remineralizing composite resins. In order to further diminish the dimensional changes, higher filler load should be included in the formulation of ACP composites. This study was supported by MZOS (065-0352851-0410), Croatian Foundation for Science, Forschungsgemeinschaft Dental and NIDCR (DE13169).