Effect of aging on marginal and internal adaptation of bulk-fill resin composites with different viscosities in class II restorations

Aim To evaluate and compare the effect of thermocycling and water storage on the marginal and internal adaptation of bulk-fill resin composites with different viscosities (No-cap low viscosity, thermoviscous, sonically activated, and conventional bulk-fill) in Class II restorations using scanning electron microscope. Materials and methods Fifty-six sound molars were prepared with standardized class II cavities (occlusal depth:3.0 mm, bucco-lingual width: 3.0 mm, depth, proximal box: 3.0 mm bucco-lingual width, 1.5 mm axial depth, and gingival margin extended 1-mm below CEJ). They were assigned into four groups according to the material used ( n = 14). For the marginal and internal adaptation test, half of the specimens in each group were tested after one week, however the remaining half were tested after 12 months of water storage and exposure to 10,000 thermal cycles between 5 and 55 °C. Replicas were made and evaluated for marginal and internal adaptation using a scanning electron microscope at different magnifications. Continuous margin percentage values (%CM) and Maximum gap width values (MGW) were statistically analyzed. Results Aging did not significantly affect external % CM, internal % CM, or external MGW ( p > 0.05). However, internal MGW values were significantly lower in immediate specimens compared with aged ones ( p < 0.05). Among the tested composites, no significant differences were observed in external or internal % CM or external MGW ( p > 0.05). Nevertheless, at the dentin gingival margin, lower-viscosity bulk-fill composites generally showed numerically lower internal MGW values than the high-viscosity bulk-fill composite. However, after Bonferroni adjustment, statistically significant differences were observed only between Flowable and Tetric and between SonicFill and Tetric ( p < 0.05). Furthermore, a strong correlation was detected between external and internal adaptation parameters (%CM and MGW) ( p < 0.05). Conclusion Aging did not adverse effect %CM or external MGW but significantly increased internal MGW. Some lower-viscosity bulk-fill composites showed lower internal MGW values at the gingival margin than the high-viscosity composite under the conditions of this in vitro study.