Comparison between different flow application techniques: SDR vs flowable composite

To evaluate the effect of layer thickness of flowable composites on the marginal adaptation of Class II fillings after thermomechanical loading (TML).

Sixty standardized Class II box cavities were prepared under simulation of intrapulpal pressure with gingival margins located 1 mm below the cementoenamel junction (CEJ) in dentin. The samples were evenly distributed into six groups (A to F). After adhesive (XPBond) application, box preparations were filled with a first increment of either a nanohybrid composite (A, D) Ceram.X mono, or with one of two flowable materials SDR (B, E) or x-Flow (C, F). The first increments were 1 (A,B,C) or 4 mm (D,E,F) thick. All cavities were finally filled incrementally with Ceram.X mono. Replicas were prepared before and after TML (1.2 x 106 cycles; 5/50°C; maximum load 49 N). Replicas were evaluated for marginal adaptation (tooth/composite) using scanning electron microscopy (200X). The percentage of continuous margins was compared between and within groups before and after TML using ANOVA and Scheffé's post-hoc tests.

For group F before TML, adaptation of cervical margins located in dentin was compromised compared to the other groups (p < 0.05). After TML, at the same location, group F showed significantly worse adaptation compared with groups A to C and E (p < 0.05), but no difference to group D was found. The marginal integrity of all interfaces before and after TML was significantly worse in group F compared with all other groups (p < 0.05).

Different flow application techniques for Class II cavities have an influence on the marginal adaptation (before/after TML). Applying a 4-mm first increment, both Ceram.X mono and SDR showed no differences vs groups in which the first increment was 1 mm thick.