Polymerization composite shrinkage evaluation with 3D deformation analysis from μCT images

ObjectivesThe aim of this study was to develop a method to experimentally determine and visualize the direction and amount of polymerization shrinkage.MethodsWe modified a composite to include 1.5 wt% traceable glass beads. A cylindrical cavity (6 mm diameter, 3 mm height) was restored with this traceable composite, with and without dentin adhesive, and digitized with high-resolution micro-computed tomography (μCT). Image segmentation was performed to extract the glass beads from the acquired 3D μCT images (uncured and cured). Afterwards, each glass bead was subjected to local rigid registration. The resulting displacement vectors were used to examine and calculate the changes.ResultsIn unbonded restorations, the displacement vectors were oriented inwards to the center of mass, although not perfectly. Bonded restorations exhibited two contraction patterns: either toward one side of the cavity or toward the top-surface of the restoration. The displacement vector length values (mean/SD) for the bonded group (46.8 μm/10.0 μm) was significantly higher (p < 0.01) than unbonded group (31.3 μm/8.5 μm), and the histogram curve was flatter (skew/kurtosis: 0.10/−0.56) as compared to the unbonded group (skew/kurtosis: 0.03/−0.26).SignificanceThe proposed method can visualize real 3D displacement vectors generated by polymerization shrinkage. The bonding quality and cavity geometry are critical for the direction of polymerization contraction. This method has the potential to validate current models concerning the amount and orientation of shrinkage vectors.