An investigation on the repair bond strength of different thermal cycles applied on zirconia-based restorations

Objective: The aim of this study was to investigate the effect of different thermal cycles applied on zirconia-based restorations on the repair strength of composite resins. Method: In order to imitate porcelain crown fractures with zirconia based; porcelain, zirconia and porcelain-zirconia specimens (7 mm in diameter, 3 mm in height) were prepared with 60 pieces in each group. Specimens were divided into 4 subgroups as control and 3000, 6000, 12.000 thermal cycling groups (n=15). The control group specimens were stored in distilled water at 37 ° C for 24 hours. The specimens to be thermally cycled were placed in apparatus prepared for the thermal cycler device and thermal cycling was performed. After the surfaces of the specimens were roughened with a diamond bur, the materials in the repair kit were applied in the order and manner recommended by the company. Composite resin was applied to all surfaces using tygon tubes (3 mm in diameter and 3 mm in height) and polymerized. The shear bond strength test was performed using a universal testing machine (0.5 mm/min). Failure types were analyzed under a stereomicroscope. Two-way ANOVA and Bonferroni test were used for statistical analysis. Results: The bond strength values of zirconia specimens were statistically significant and higher than porcelain and porcelain-zirconia specimens in control, 3000 and 6000 thermal cycling groups (p<0,05). When 12.000 thermal cycles were applied, the highest value was found in zirconia specimens but there was no statistically significant difference between porcelain and porcelain-zirconia specimens (p>0.05). It was observed that the bond strength values of porcelain and porcelain-zirconia specimens were not statistically significant in the control group and when the same thermal cycle was applied (p>0,05). Porcelain specimens exhibited cohesive failure types, zirconia specimens exhibited adhesive failure types and porcelain-zirconia specimens exhibited predominately mixed failure types. Conclusion: The increase in thermal cycle applications has an effect on repair bond strength. Key words: zirconia , thermal cycling, porcelain repair systems