Impact of Access Cavity Design and Root Canal Taper on Fracture Resistance of Endodontically Treated Teeth: An Ex Vivo Investigation

Introduction. The susceptibility of endodontically treated teeth (ETT) to fracture is mainly associated with the loss of tooth structure. This study evaluated the effect of the access cavity design and taper preparation of root canals on ETT fracture resistance of maxillary molars. Methods: For tapering assessment, 30 sound distobuccal roots of maxillary molars were randomly assigned to 1 of 3 groups (n = 10): a .04 taper, a .06 taper, or a .08 taper. Endodontic canal preparations were performed using the Twisted Files rotary system (Kerr Co, Glendora, CA). In addition, 48 intact maxillary first and second molars were randomly assigned to 1 of 3 groups (n = 16) for cavity preparation approaches: intact teeth, traditional access cavity (TAC), or conservative access cavity (CAC). Fracture resistance was tested using a universal testing machine. For statistical analysis, the level of significance was P <= .05. Results: The .04 taper instrumentation had the highest fracture resistance (259.61 +/- 52.06), and the .08 taper had the lowest (168.43 +/- 59.63). The .04 and .06 groups did not differ significantly (P > .05); however, these groups differed significantly from the .08 group (P <= .05). Regarding the cavity preparation approaches, the 3 groups of intact teeth, CAC, and TAC showed fracture resistance mean values of 2118.85 +/- 336.97, 1705.69 +/- 591.51, and 1471.11 +/- 435.34, respectively, with no significant difference between the CAC and TAC groups (P >.05). Conclusions: Increasing the taper of the root canal preparation can reduce fracture resistance. Moreover, access cavity preparation can reduce resistance; however, CAC in comparison with TAC had no significant impact.