Fracture strength of tooth roots following canal preparation by hand and rotary instrumentation.

The study aimed to determine fracture loads in tooth roots after canal preparation using different techniques. Mesiobuccal roots of 39 extracted mandibular molars were used. Three groups each of 13 roots were prepared by stainless steel hand files (K-files), and two rotary nickel-titanium techniques (Lightspeed and Greater Taper files). After obturation, a vertical load was applied by means of a spreader inserted into the canal until fracture occurred. The mean fracture load was 10.2 +/- 4.4 kg for K-files, 15.7 +/- 9.1 kg for Lightspeed and 13.2 +/- 6.1 kg for Greater Taper files, but differences were not statistically significant (p > 0.05). Most fracture lines were incomplete fractures on the buccal surface, followed by proximal and compound fractures. Greater apical enlargement (Lightspeed) or increased canal taper (Greater Taper files) did not increase fracture susceptibility of tooth roots.