Influence of instrument taper on the resistance to fracture of endodontically treated roots

The aim was to compare the force required to fracture uninstrumented and instrumented canines and to investigate the root-reinforcing capability of AH Plus sealer. Study design. In groups 1-3 (n = 24) canals were instrumented with either GT files, FlexMaster, or stainless steel hand instruments. Twelve teeth from each group were obturated with lateral compaction using gutta-percha and AH Plus. Group 4 (n = 12) acted as uninstrumented controls. The force required to fracture the roots was measured. ANOVA, Scheffe, and t test were used for statistical analysis. Results. The intact roots were significantly stronger than all groups with instrumented and unobturated roots (P < .05). Roots enlarged with GT files were significantly weaker (P < .05) than those instrumented with FlexMaster or hand instruments. Between the obturated and unobturated roots there were no significant differences (P > .05). Conclusions. The roots were significantly weakened by the preparation with greater taper instruments. An obturation with AH Plus did not increase the fracture resistance.