Adhesive strength of cervical composite restorations

BACKGROUND: The effectiveness of universal adhesives for restorations remains a subject of debate. The long-term reliability of adhesive bonds in cervical cavities, depending on the functional role of the tooth (chewing vs. biting), has not been sufficiently studied. Numerous studies on ensuring reliable adhesion indicate that this topic remains relevant for further investigation. AIM: To assess the adhesive bond strength of composite restorations to hard dental tissues in laboratory samples of anterior and posterior teeth before and after thermocycling. MATERIALS AND METHODS: The study included extracted teeth (n = 60) obtained from elderly (60–75 years) and senile (75–90 years) patients due to periodontal indications. The teeth were divided into two groups (n = 30 each) based on the adhesive system used: Group 1, Universal Bond II; Group 2, OptiBond Solo Plus. Both groups used the flowable photopolymer EsFlow and the universal composite Point 4. Each group was further divided into two subgroups based on function: anterior (A) and posterior (P) teeth (n = 15 in each), and subsequently, into two additional subgroups based on thermocycling: (a) before thermocycling and (b) after thermocycling. Cervical cavities (5 × 5 × 3 mm) were prepared in all samples using a high-speed dental handpiece under water cooling. The specimens underwent 1000 thermocycles alternating for 30 s each (with a 30-second intermediate interval) at a temperature regime of (5 ± 2) °C and (60 ± 2) °C. The adhesive strength of the teeth was then evaluated under compressive load. RESULTS: The adhesive strength under compression in subgroups 1Aa and 2Aa was 1663.6 [1574.6; 2175.1] N and 2151.5 [967.9; 3970.3] N, respectively. The difference between them was statistically insignificant (p = 0.538), confirming group homogeneity. The adhesive strength values in subgroups 1Ab and 2Ab were 1353.3 [1219.2; 2096.8] N and 1620.7 [847.2; 2434.7] N, respectively (p = 0.868). Statistically significant differences were observed between subgroups 1Aa and 1Ab (p = 0.017) and between 2Aa and 2Ab (p = 0.017). In the posterior tooth groups, the adhesive strength in subgroups 1Pa and 2Pa was 4100.0 [2818.1; 48401.4] N and 3800.0 [2000.0; 4500.0] N, respectively (p = 0.476), indicating the effectiveness of both adhesive systems. In subgroups 1Pb and 2Pb, the adhesive strength was 3479.5 [2708.8; 3995.6] N and 1999.0 [1646.3; 3120.8] N, respectively (p = 0.153), confirming the effectiveness of adhesion and the integrity of the restoration–tooth complex. CONCLUSION: Posterior teeth withstand higher loads compared to anterior teeth. A decrease in bond strength was observed in all groups after thermocycling, which is influenced not only by the type of adhesive system but also by the anatomical characteristics of posterior teeth, including their shape, surface area, and relief.