Effects of Long-term Thermocycling On Marginal Gaps of Zirconia Frameworks

Objective: To compare the marginal gaps of zirconia frameworks cemented with two resin cements before and after thermocycling. Methods: Thirty maxillary premolars were randomly divided into two groups (n=15) according to the resin cements: a self-etch resin cement (Panavia™F2.0; Kuraray Medical, Japan) and a self-adhesive resin cement (RelyX™U100; 3M ESPE, USA). The teeth were prepared with deep chamfer and the 6°convergence angle. The zirconia frameworks were fabricated using DCS® CAD/CAM. The marginal fits of zirconia frameworks were evaluated under a microscope (30x magnification) at the following sequences: before cementation, after cementation and after 20,000 thermocycles. The differences in the marginal gaps (after and before cementation: delta diff1, after thermocycling and after cementation: delta diff2) between two resin cements were analyzed using Student's t-test and Mann Whitney U test. The differences between two processes in each group were tested with paired t-test and Wilcoxon signed-rank test (p<0.05). Results: After cementation, the marginal gaps of two resin cements were significantly higher than before cementation (p<0.001). Slight differences were found in mean of delta diff2 (self-etch: 0.88 µm, self-adhesive: 0.26 µm). The marginal gaps of zirconia frameworks cemented with self-adhesive resin cement were significantly smaller than self-etch resin cement both after cementation and after thermocycling (p<0.05). Conclusion: Long-term thermocycling had no clinical effect on the marginal fit. The type of resin cements influenced the marginal fit. The marginal gaps achieved by both resin cements were within clinically accepted standards (<120 µm). Acknowledgement: This study was supported by Faculty of Dentistry, Mahidol University Scholarship.