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

Abstract 

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 12mm and the root dentine was artificially flared to produce a 1mm 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 40s (G1, control), 80s (G2) or 120s (G3). Twenty-four hours after post-cementation, the specimens were sectioned transversely into three slices at depths of 2, 6 and 10mm, corresponding to the coronal, middle and apical regions of the reinforced root. Composite VHN was measured as the average of three indentations (100g/15s) in each region at lateral distances of 50, 200 and 350μm 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). Tukey's 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 120s provided higher composite hardness than the shorter times (40 and 80s).

Keywords: Composite resin, Hardness, Light exposure time, Root canal, Vickers hardness number