Impact of Minimal Root Canal Taper on the Fracture Resistance of Endodontically Treated Bicuspids

Objective: Minimal invasive endodontics preserve coronal and radicular tooth structure to increase the fracture resistance of teeth. The aim of this study was to assess the influence of final preparation taper on the fracture resistance of maxillary premolars. Materials and Methods: Sixty maxillary premolars were selected and divided into 2 groups: 30 were shaped with a final apical diameter 30 and a 4% taper and 30 with 6% taper using iRaCe (R) instrument (FKG dentaire, Switzerland). All root canals were irrigated with sodium hypochlorite and final rinse with ethylenediaminetetraacetic acid. All canals were filled with gutta-percha single-cone filling technique and AHPlus (R) sealer (Dentsply-Maillefer, Baillagues, Switzerland) and access cavity restored with resin composite. Roots were wax coated, placed in an acrylic mold and loaded to compressive strength fracture in a mechanical material testing machine recording the maximum load at fracture and fracture pattern (favorable/restorable or unfavorable/unrestorable). Fracture loads were compared statistically, and data examined with Student t-test with a level of significance set at P = 0.05. Results: No statistically significant difference was registered between the 4% taper of preparation (270.47 +/- 90.9 N) and 6% taper of preparation (244.73 +/- 120.3 N) regarding the fracture resistance of the endodontically treated premolars tested (P = 0.541), while more favorable restorable fractures were registered in the 4% taper group. Conclusions: Continuous 4% preparation taper did not enhance the fracture resistance of endodontically treated maxillary premolars when compared to a 6% taper root canal preparation. More fractures were registered in the 4% taper group.