Hardness of Composite Resin in Flared Root Canals After Reinforcement

Objectives: The polymerization degree of composite resin has been directly related with hardness and can affect the durability of canal reinforcement. The objective of this in vitro study was to verify the Vickers hardness (VH) of composite resin (CR) after root reinforcement, considering the light-curing time, depth and post distance.

Methods: Forty-five roots of maxillary incisors with 17mm-length were endodontically treated. After 24h, gutta-percha was removed at 12mm and the canals were overprepared with diamond tips (Vortex, #4137; KG, #717). During reinforcement, the canals were filled with RC and light cured using DT Light Post with different times: G1 (control) - 40s; G2- 80s and G3- 120s. After 24h of posts cementation, the roots were horizontally cut at 2, 6 and 10mm in depth, which correspond the cervical, middle and apical region. CR microhardness was evaluated by the average of 3 indentations (100g/15s) in each depth at lateral distances of 50, 200 and 350ìm from the cement/post interface.

Results: The three-way analysis of variance (a = 0.05) indicated that time, depth and distance influenced in hardness (p<0.001), and the time X depth interaction was significant (p<0.019). Tukey test disclosed that VH values in G1 (76.37 ± 8.58) and G2 (74.89 ± 6.28) were statistically different (p<0.05) from G3 (79.55 ± 5.18).

Conclusions: In deeper regions and in the most lateral distant areas of the post, the hardness was significantly lower (p<0.001). However, light-curing time of 120s provided greater CR hardness when compared with 40 and 80s, mainly in the apical region.