EFFECT OF ENDODONTIC ACCESS CAVITY DESIGN, CANAL TAPERING, AND THERMOCYCLING ON THE FRACTURE RESISTANCE OF ENDODONTICALLY TREATED MANDIBULAR MOLARS

Introduction. This study aimed at assessing the fracture resistance of endodontically treated mandibular molars with traditional endodontic access cavity (TEC) and truss endodontic access cavity (TREC) designs and canal tapering. Materials and methods. 60 mandibular molars were randomly divided into 10 groups (n=6): intact controls without thermocycling (group 1), intact controls with thermocycling (group 2), TEC without thermocycling with canal tapering 4% (group 3), TEC without thermocycling with tapering 6% (group 4), TEC-TC with canal tapering 4% (group 5) and TEC-TC with with canal tapering 6% ( group 6), TREC without thermocycling with canal tapering 4% (group 7), TREC without thermocycling with canal tapering 6% (group 8), TREC-TC with canal tapering 4% (group 9), TREC-TC with canal tapering 6% (group 10). For the preparation of the canals of each root in 6% and 4% of the tapering group, M Pro ( #18 %9 , # 20 %4 , #25 %6 ) and iRace ( #10 %2 , #15 %4 , #20 %4 , #30 %4 ), the rotary system was used. Root canals were obturated. Access cavity was restored with composites. All teeth were then thermocycled for 480 cycles between 5 degrees C and 55 degrees C for 30 seconds, and their fracture resistance was measured on an Instron universal testing machine. Data was analyzed using t-test and oneway ANOVA and Tukey's post-hoc test. Results and discussion. TEC designs show a significantly lower fracture resistance than TREC designs (P<0.05), while canal tapering had no significant effect on the fracture resistance of endodontically treated teeth (P>0.05), so that minimum fracture resistance was noted in TEC-TC with a canal tapering 6% group. Conclusions. Under the conditions of this study, TREC enhances the fracture strength of endodontically treated teeth under thermal stresses.