Effect of root-canal preparation on resistance to fracture of premolars

OBJECTIVE: To compare fracture resistance of premolars following root canal treatment, applied with 3 preparation techniques: Balanced force method using manual stainless-steel K-file, Rotary NiTi "Lightspeed" instruments and rotary NiTi "ProTaper" instruments. MATERIALS AND METHODS: 45 extracted mandibular single-canal intact first premolars were chosen and randomly divided into 3 equal groups. Access cavities were similarly prepared in all teeth and working length was measured. The root canals were endodontically treated according to the selected method for each group, dried up and sealed using gutta-percha points and sealer, according to lateral condensation technique. Later, the teeth were restored using hybrid composite and embedded in an acrylic block. All teeth were mounted on an Instron testing machine and loaded in a 30º angle over the buccal cusp, simulating the force activated during mastication. The failure load value for each tooth was recorded. RESULTS: The failure values of the 3 research groups were compared using oneway analysis of variance. Additionally, Post-hoc scheffe contrasts were used to compare 2 groups at a time. No significant differences were found between the groups in either of the statistical methods (p>0.1). Moreover, the failure characteristics was determined for each of the teeth, and the results showed that most teeth failed at the coronal third, with no significant difference between the 3 groups. CONCLUSIONS: An apical preparation adapted to the diameter of the canal can be recommended, since we have determined that the apical dentin removal has no effect on the mechanical resistance to fracture under the current research terms.