Evaluation of fracture resistance and fracture pattern of roots following canal preparation by hand and rotary instrumentation

Abstract

The present in-vitro study was undertaken to compare fracture strength of roots
following canal preparation by hand (step-back) and rotary (ProTaper)
instrumentation and, further, to determine the direction of fracture lines.
Twenty freshly extracted human mandibular premolars were randomly divided
into two groups of 10 teeth each. In Group I, canals were prepared with step-back
technique using standardized nickel-titanium K-files. In Groups II, canals were
prepared with crown-down technique using ProTaper rotary files. After
instrumentation, a vertical load was applied by means of a spreader attached to the
Instron testing machine and inserted into the canal until fracture occurred. The roots
were subsequently examined under a stereomicroscope with 10X magnification to
determine the direction of fracture lines. The results were statistically analyzed using
paired t-test.
The Mean fracture load was 10.420 ± 3.451 kg for K-files and 12.40 ± 4.064 for
ProTaper files, the differences between the two groups were not statistically
significant (p>0.05). Most of the fracture lines observed were in bucco-lingual
direction, followed by proximal and compound fractures.
Increased canal taper by ProTaper instrumentation technique did not increase the
fracture susceptibility of mandibular premolars any more than conventional step-back
K-file preparations and may even increase the fracture resistance.