Evaluation of Polymerization Shrinkage and Corresponding Microleakage Using mCT

Objectives: The goal of this study was to develop a quantitative nondestructive method for evaluating polymerization shrinkage and subsequent microleakage in clinically relevant cavity geometries with spatial resolution. Methods: X-ray microcomputed tomography (mCT) was used to assess polymerization shrinkage and microleakage of a commercial dental composite (TPH, Dentsply Caulk) in a series of model cavities (made of polymethyl methacrylate) designed with different volumes, configuration factors (C-factors, defined as the ratio of bonded to unbonded area), and shape. For cylindrical samples, three different volumes with the same C-factor (volume = 16, 31, or 54 mm³, and C-factor = 3.5) and three different C-factors with the same volume (C-factor = 2.5, 3.5, or 5.9, and volume = 31 mm³) were applied. Using mCT, the polymerization shrinkage of a dental composite in model cavities was calculated, and the position of each sample before and after polymerization was compared. Gaps between composites and walls of the cavities were determined and attributed to microleakage. Microleakage was also evaluated using dye penetration for comparison. Results: The polymerization shrinkage was 2.73 ± 0.17 % for the unconstrained geometry, and ranged between 2.61 ± 0.23 to 2.90 ± 0.24 % for constrained geometries with varying sample volumes or C-factors. Shrinkage occurred primarily on the top and bottom surface of the composites, and leakage was distributed unevenly throughout the sample, although it depended on the sample geometry. Conclusions: The polymerization shrinkage of composites with different volumes and C-factors was not statistically different (p-value < 0.05, one-way ANOVA) with those determined under unconstrained geometries. Microleakage and its distribution evaluated using mCT agreed well with data obtained from the dye penetration method. A new nondestructive method to evaluate microleakage in three dimensions using mCT has been developed and tested. Support: NIDCR/NIST Interagency Agreement Y1-DE-7005-01.