Evaluation of fracture resistance and failuremodeof thin-walled roots restored with different post systems

The objective of this manuscript was to evaluate the fracture resistance and failure mode of roots of bovine incisors with the root canal purposely enlarged, reinforced with different restorative materials and compared with intact roots restored with cast post and core. In this manuscript 75 bovine inferior central incisors were selected, being sectioned transversally and leaving only 14 mm of root. A standardized wear sequence was used to make them fragile, leaving the remaining walls with 0.5 to 0.7 mm thick in the cervical edge. In the control group (RI) the remaining walls had 2.0 to 2.5 mm thickness at the cervical edge and were restored with cast post and core. All samples received a total metallic crown. From the four experimental groups (n = 15), one group did not received internal root reinforcement (SR) and the other three were tested for composite resin (RC) or glass ionomer cement (CIV) reinforcements associated with cast post and core or composite resin in association with fiberglass post (PFV). The tests were applied in a universal test machine (Instron) with tangential compression loading, focusing on the palatal side of the crown, forming an angle of 135° with the long axis of the root, at a speed of 1 mm / min. The force average values obtained were 330.45 N; 218.58 N; 186.54 N; 275.44 N and 295.10 N for the groups RC Group, PFV Group, Group IV, SR Group and RI Group. Among the RC, SR and RI groups there was no statistical difference for the obtained average forces. The PFV and IV groups differ statistically from the mean force obtained in relation to the RC, SR and RI groups (P <0.05). However PFV and IV are statistically similar. In the PFV and IV groups, there was a higher incidence of favorable fractures, while in the other groups non-favorable fractures prevailed. Reinforcing internally a fragile root with composite resin favors the increase of fracture resistance. A greater amount of remaining dentin was responsible for a greater fracture resistance, but without statistical difference in comparison with weakened roots without reinforcement. Restored fragile roots with PFV associated to the composite resin (anatomical post) have the advantage of having favorable fractures, allowing the reuse of the root.On the other hand, when working with cast post and core we normally reach an increase in resistance, but a large incidence of non-favorable fractures is present.