Marginal adaptation and internal indentation resistance of a Class II bulk-fill resin-based composite

To compare the dentin bonded external marginal integrity and the internal surface indentation hardness of bulk-fill and conventional resin-based composite (RBC) placed in both bulk and increments.

120 MO and DO cavities were prepared in 60 extracted human third molars. The teeth were randomly divided into four groups of 15 teeth per group to be restored as follows: BB (bulk-fill RBC, placed in a 4 mm bulk increment), BL (bulk-fill RBC, placed in 2 mm incremental layers), CB (conventional RBC, placed in a 4 mm bulk increment), and CL (conventional RBC, placed in 2 mm incremental layers). Marginal gaps were measured at mesial and distal dentin gingival cavosurfaces of each tooth using scanning electron microscopy of epoxy resin replicas and Knoop hardness (KHN) was measured at three different RBC depths (1.8, 2.8 and 3.8 mm). Statistical analyses included one-way ANOVA with post-hoc Tukey's HSD, and paired-sample t-test or a nonparametric Wilcoxon signed-rank test, as appropriate.

There was no significant effect of RBC restoration type on external marginal gap at the distal surface or at the mesial surface among the four groups tested (P> 0.05 in each instance), while no significant difference in external marginal gap was found between the mesial and distal surfaces within groups (P> 0.05 in each instance). The mean RBC internal surface KHN at 1.8 mm depth was significantly greater than at 2.8 mm and 3.8 mm depths in all tested groups (P< 0.05 for all instances), with a similar mean internal hardness between all groups. The bulk-fill RBC restorations demonstrated similar marginal gap formation and Knoop hardness to conventional universal RBC restorations under the conditions of this study.

Bulk-fill resin-based composite (RBC), from the perspective of marginal adaptation and internal hardness, may be a suitable alternative to conventional RBC.