Effect of access cavity design on canal instrumentation efficiency and fracture resistance in mandibular molars: A cone-beam computed tomography study

Abstract Introduction: This study evaluated the impact of access cavity designs on canal instrumentation efficiency and fracture resistance in mandibular molars using cone-beam computed tomography (CBCT). Materials and Methods: Thirty extracted mandibular molar teeth were divided into three groups ( n = 10 per group) as follows: Group 1: Traditional endodontic access cavity (TEC); Group 2: conservative endodontic access cavity (CEC); and Group 3: “Truss” access cavity (TAC). CBCT scanning was performed before and after canal instrumentation. The canals were instrumented using the ProTaper ® Next file system. All samples were obturated and loaded to fracture. The teeth’ pre- and postinstrumentation images were compared, and dentin thickness was evaluated. Variance analysis of variance and Tukey’s post hoc tests were analyzed. A significance level of 0.05 was used. Results and Discussion: Among the three designs, TEC demonstrated the greatest reduction in remaining dentin thickness (RDT) across all root regions, particularly in the apical third, where significant differences were observed compared to TAC. The CEC design demonstrated a moderate reduction in RDT and fracture resistance, with values falling between TEC and TAC. TAC was the most conservative design, showing the lowest decrease in RDT and the highest fracture resistance among all groups. Conclusion: While TEC provides superior canal access, it significantly compromises fracture resistance, whereas CEC and TAC demonstrate better preservation of dentin and structural integrity at the expense of complete canal instrumentation. Clinicians must carefully evaluate the different options and prioritize long-term treatment outcome considerations, recognizing the importance of individualized cavity design tailored to the specific clinical case and scenario.