Effect of endodontic instrument taper on post retention

The purpose of this study was to evaluate the effect of various tapers of canal preparations on the retention of posts. Ninety human central or lateral mandibular incisors were prepared by removing the clinical crown at the CEJ and instrumenting the canals with instruments of varying tapers. The groups comprising 10 teeth each were divided as follows: Taper 0.02 Ni-Ti hand files (control), Taper 0.04 ProFile Series 29, Taper 0.06 ProFile Series 29, Taper 0.08 ProFile GT Rotary, Taper 0.10 ProFile GT Rotary, Taper 0.12 ProFile GT Rotary, Taper 0.08* ProFile GT Rotary 0.08 taper with #50/.12 taper in coronal third, Taper 0.10* ProFile GT Rotary 0.10 taper with #50/.12 taper in coronal third, Taper 0.12* ProFile GT Rotary 0.12 taper with #50/.12 taper in coronal third. Canals were filled with gutta-percha and AH 26 sealer using lateral condensation. Gutta-percha was removed with a heated 5/7 plugger until a level of 5 mm of gutta-percha was left in the apical segment of the root. Post channel preparation was made to the appropriate size with minimal change in canal shape with the Premier IntegraPost drill, and the corresponding IntegraPost was cemented with 3M Vitremer cement. The roots were fixed in copper rings with mounting plaster and mounted on an Instron TT machine. The posts were subjected to gradually increasing vertical tensile force until dislodgment of the post occurred. Force (lb) required to dislodge the post was obtained for each tooth, and the average force of the groups was compared using a one-way ANOVA with Tukey's multiple comparisons. The highest resistance to dislodgment was obtained with Taper 0.04 (79.10 +/- 10.73), whereas the lowest was obtained by the Taper 0.02 (18.70 +/- 13.44). No statistical difference was found between six of the groups: Taper 0.08*, Taper 0.10, Taper 0.12*, Taper 0.10*, Taper 0.12, and Taper 0.06. Taper 0.08 was statistically inferior to Taper 0.04 but not Taper 0.02. The 0.04 taper seems to be the best taper for maximal resistance to post dislodgment.