Abstract: Objective: To investigate the effects of bulk-fill resin-based composite type on gingival adaption of class Ⅱ cavities. Methods: Twenty-eight extracted human third molars were collected. Two class Ⅱ cavites (2x3x4 mm) were prepared on mesial and distal surfaces of each tooth. Class Ⅱ cavities were randomly divided into 7 groups (n=8), and the cavities were restored by 2 low viscosity, 3 high viscosity bulk-fill resin-based composites or 2 conventional resin-based composites, respectively. Acoustic emission (AE) signals were recorded from the beginning of light-curing of resin composite and lasted for 1000 s. The percentage of microleakage formation (M%) were calculated using optical coherence tomography (OCT). Data obtained from AE and OCT were statistically analyzed using one-way ANOVA. Results: Two low viscosity bulk-fill resin-based composites generated significantly less AE events (15.7; 17.6) and lower M% (16.1; 14.1) (P<0.05). Pearson correlation coefficient was 0.941 between AE test and OCT (P＜0.05). Conclusion: The low-viscosity bulk-fill resin composites demonstrate better internal adaption in class Ⅱ resotorations. AE and OCT can be used to assess the marginal integrity of resin composites.

Key words: Bulk-fill resin composite, Microleakage, Acoustic emission, Optical coherence tomography, Class Ⅱ