Effects of light exposure time on composite resin hardness after root reinforcement using translucent fibre post

Objectives The purpose of this in vitro study was to evaluate the Vickers hardness (VHN) of a Light Core (Bisco) composite resin after root reinforcement, according to the light exposure time, region of intracanal reinforcement and lateral distance from the light-transmitting fibre post. Methods Forty-five 17-mm long roots were used. Twenty-four hours after obturation, the root canals were emptied to a depth of 12 mm and the root dentine was artificially flared to produce a 1 mm space between the fibre post and the canal walls. The roots were bulk restored with the composite resin, which was photoactivated through the post for 40 s (G1, control), 80 s (G2) or 120 s (G3). Twenty-four hours after post-cementation, the specimens were sectioned transversely into three slices at depths of 2, 6 and 10 mm, corresponding to the coronal, middle and apical regions of the reinforced root. Composite VHN was measured as the average of three indentations (100 g/15 s) in each region at lateral distances of 50, 200 and 350 μm from the cement/post-interface. Results Three-way analysis of variance (α = 0.05) indicated that the factors time, region and distance influenced the hardness and that the interaction time × region was statistically significant (p = 0.0193). Tukeyʹs test showed that the mean VHN values for G1 (76.37 ± 8.58) and G2 (74.89 ± 6.28) differed significantly from that for G3 (79.55 ± 5.18). Conclusions Composite resin hardness was significantly lower in deeper regions of root reinforcement and in lateral areas distant from the post. Overall, a light exposure time of 120 s provided higher composite hardness than the shorter times (40 and 80 s).