Effect of polyethylene fiber reinforcement on marginal adaptation of composite resin in Class II preparations.

The aim of this study was to evaluate the effect of polyethylene fibers incorporated in a composite resin matrix on the gingival marginal adaptation of Class II slot restorations. Sixty Class II slot cavity preparations were divided into 2 groups. A fiber-reinforced resin (FRR) group received restorations of composite resin mixed with strips of polyethylene fiber, and an unreinforced resin (UR) group was restored with only composite resin. The groups were subdivided on the basis of the adhesive system (etch-and-rinse or self-etch) that was used. Shrinkage stress was evaluated by placing a strain gauge at the buccal surface of the teeth. A scanning electron microscope was used to evaluate marginal adaptation in terms of a continuous margin (CM) at the gingival margin. Statistical analysis included a 2-way analysis of variance with the Holm-Sidak correction for multiple comparisons at a significance level of 0.05. The mean strain value was significantly smaller in the FRR group (185 [SD 37] µm/m) than in the UR group (295 [SD 21] µm/m). The FRR group presented with a mean CM value of 80.2% (SD 4.6%), which was significantly higher than that of the UR group, which had an overall CM value of 64.4% (SD 4.2%). There was no statistically significant difference between the adhesive subgroups with regard to strain or percentage of CM. The results showed that the incorporation of polyethylene fibers in a composite resin matrix can help to improve gingival marginal adaptation in Class II cavities.