Alternative methods for determining shrinkage in restorative resin composites

Abstract

Resin composites (Filtek Z250, Z350 and P90/3M ESPE, Esthet-X, TPH Spectrum/Dentsply 4 Seasons, Tetric Ceram/Ivoclar-Vivadent) polymerization shrinkage was evaluated by 3 different methods: coordinate measuring machine (CMM), optical coherence tomography (OCT) and the application of a well-known method, such as Archimedes Principle. The null hypothesis tested: (1) there are no differences between the materials tested; (2) there are no differences between the methods used for polymerization shrinkage measurements. For CMM measurements, specimens were made in a cylindrical Teflon mold (7×2 mm). The difference between the volume of the mold and the volume of the specimen was calculated. OCT evaluations were performed using cylindrical specimens (7x0.5mm). Images were obtained before and after photoactivation, and thickness variations were measured. Density variations were also registered and volumetric changes were measured using Archimedes Principle of buoyancy (n=5). Statistical analysis of the data was performed with one-way ANOVA, Games–Howell test and Pearson’s Correlation. The results varied according to the method used. When methods were compared to Archimedes principle, a positive but regular correlation was found (CMM -0.57/ OCT -0.49).