Depth-of-Cure of Bulk-Fill Flowable Composites and Hardness of Proximal Restorations Restored with a Snowplow Technique

Flowable composites improve adaptability at the gingival margin but may affect mechanical properties. This study tested the surface hardness of proximal restorations as indicator of depth-of-cure and mechanical properties. Typodont teeth with 4 mm deep disto-occlusal preparations were (a) restored with three flowable composites in 4 mm bulk, and (b) restored with a thin layer of a flowable at the gingival margin under a universal composite. For the latter, two techniques were tested: ‘pre-cure’ and ‘snowplow’. In the pre-cure technique, the flowables were cured separately; in the snowplow technique, they were cured together with the universal composite. The universal composite placed in two 2 mm increments was the control. After 24 h, the Vickers hardness of the proximal restorations was measured every 0.5 mm from occlusal to gingival. The results were statistically analyzed using ANOVA and post hoc tests (α = 0.05). The sample size was 10/group. Bulk-filled restorations having undergone 40 s of light curing were significantly harder than those cured for 20 s. The pre-cure technique decreased hardness at depths of 3 mm and greater. The snowplow technique also led to significantly lower hardness at 4 mm, but less reductions at the 3.0 and 3.5 mm depths. The fiber-reinforced flowable composite increased the overall hardness of the restorations. In conclusion, using a flowable composite in a thin layer at the gingival margin to improve adaptation affected the hardness of the restoration. The snowplow technique reduced the softening effect associated with flowable composites compared to the pre-cure technique.