Impacts of Conservative Endodontic Cavity on Root Canal Instrumentation Efficacy and Resistance to Fracture Assessed in Incisors, Premolars, and Molars

Introduction: Conservative endodontic cavity (CEC) may improve fracture resistance of teeth but compromise the instrumentation of canals. This study assessed the impacts of CEC on both variables in 3 tooth types. Methods: Extracted human intact maxillary incisors, mandibular premolars, and molars (n = 20/type) were imaged with micro-computed tomographic imaging (20-mu m resolution) and assigned to CEC or traditional endodontic cavity (TEC) groups (n = 10/group/type). Minimal CECs were plotted on scanned images. Canals were prepared with WaveOne instruments (Dentsply Maillefer, Ballaigues, Switzerland) using 1.25% sodium hypochlorite and post-treatment micro-computed tomographic images obtained. The proportion of the untouched canal wall (UCW) and the dentin volume removed (DVR) for each tooth type was analyzed with the independent-samples t test. The 60 instrumented and 30 intact teeth (negative control, n = 10/type) were loaded to fracture in the Instron Universal Testing machine (lnstron, Canton, MA) (1 mm/min), and the data were analyzed with 1-way analysis of variance and the Tukey test. Results: The mean proportion of UCW was significantly higher (P < .04) only in the distal canals of molars with CEC (57.2% +/- 21.7%) compared with TEC (36.7% +/- 17.2%). The mean DVR was significantly smaller (P < .003) for CEC than for TEC in incisors (16.09 +/- 4.66 vs 23.24 +/- 3.38 mm(3)), premolars (8.24 +/- 1.64 vs 14.59 +/- 4.85 mm(3)), and molars (33.37 +/- 67.71 mm(3)). The mean load at fracture for CEC was significantly higher (P < .05) than for TEC in premolars (586.8 +/- 116.9 vs 328.4 +/- 56.7 N) and molars (1586.9 +/- 196.8 vs 641.7 + 62.0 N). In both tooth types, CEC did not differ significantly from the negative controls. Conclusions: Although CEC was associated with the risk of compromised canal instrumentation only in the molar distal canals, it conserved coronal dentin in the 3 tooth types and conveyed a benefit of increased fracture resistance in mandibular molars and premolars.