Interfacial adaptation of composite restorations before and after light curing: Effects of adhesive and filling technique

Purpose: To investigate the effects of placement technique and adhesive material on adaptation of composites before and after light curing. Materials and Methods: Cylindrical cavities (3 mm diameter, 1.7 mm depth) in extracted human molars were restored in 6 groups (n = 5) using 2 adhesives - two-step self-etching Clearfil SE Bond 2 (SE2) and all-in-one Clearfil Tri-S Bond Plus (TSP) (Kuraray Noritake Dental) - and 2 composites - Estelite Sigma Quick (ESQ) and Estelite Flow Quick (FLQ) (Tokuyama Dental) - placed with three different techniques: ESQ bulk placed, FLQ lining followed by ESQ and FLQ bulk placed. Specimens were scanned twice using swept-source optical coherence tomography (SS-OCT) before and after photopolymerization of the composite. Gap formation during polymerization or the difference in floor interface (DFI%) and final unsealed interface (USI%) were measured by image coregistration and subtraction on 6 diametrical planes across each scan. Results: Two-way ANOVA suggested that both factors (adhesive and filling technique) and their interaction were significant (p < 0.001). SE2 showed significantly lower DFI% than did TSP when the composites were placed in bulk, but no difference was found when flowable lining was applied (p < 0.05). Within TSP, all filling techniques were significantly different and the lining group showed the lowest values, followed by ESQ-bulk. Overall, SE2 always showed lower UFI% than did TSP, while there was no difference among different techniques within SE2. Conclusion: SS-OCT is a unique method to observe the pre-existing interfacial defects and gaps developed during polymerization, which were found to depend on both placement technique and applied adhesive.