Thermal Effect Shock on the Enamel-composite Restoration Interface

Aim: To study the effect of thermal shock on the enamel – composite restoration interface as compared to standard thermal cycling protocol.

Methodology: Box shaped cavities were prepared in thirty mandibular third molars, the cavities were restored using two step etch and rinse adhesive: Adper™ Scotchbond™ 1 XT (3M™ ESPE™, St. Paul, USA), and nano-hybride resin composite Filtek™ Z250 (3M™ ESPE™, St. Paul, USA). Specimens were divided in 3 groups. The first group was thermal cycled for 600 cycles, the second group was submitted to 600 thermal shock cycles using Oral B waterjet device, and the third group was a control group. Teeth specimens were evaluated for dye leakage using 2% Basic Fuchsin dye for 24 hours, all bonded teeth were subsequently sectioned perpendicularly into 0.9 ± 0.1 mm2 sticks that were loaded on universal testing machine to obtain the ultimate tensile strength. Values were analyzed with one way ANOVA post hoc Tukey HSD (SPSS version 23) with 95% confidence interval.

Results: Both thermal shock and thermal cycling groups had significantly higher dye leakage values along the interface as compared to the control group. The microtensile bond strength values were significantly lower for the thermal shock group as compared to the control group, no significant difference was found between the thermal cycling and the control group.

Conclusion: Thermal shock was shown to induce more stress on the interface, which may lead to cracks and gap formation overtime.