[Effect of coronal preflaring on the instrumentation of curved premolar canals.]

To study the effect of coronal preflaring on the instrumentation of curved premolar canals.

Sixty extracted premolars, with the degree of root canal curvature from fifteen to thirty-five, were divided into fifteen sections in curvature sequence. After that, four canals of each section were randomly distributed to four different instrumentational groups. Two groups were coronally preflared with Gates Glidden drills first. Then they were instrumented by stainless steel or nickel titanium K-files from 15# to 40# with sequential preparation to working length. The other two groups were prepared directly with the above-mentioned two instruments. The standard digital radiographs were taken to record the position of the tip of the different sizes of instruments. At last, the curvature degrees were measured and the apical transportation indexes (ATI) were determined under stereomicroscope. t test or rank test for paired data was used for statistical analysis.

The curvature degree before and after instrumentation for each group was significantly different (P<0.01). The larger the files were, the greater the ATI became. The cases of root perforations in the stainless steel K-files group became fewer after coronal preflaring. The ATI of 30# for stainless steel K-files were much less after coronal preflaring, and were not significantly different with the ATI for nickel titanium instruments (P>0.05).

The effect of nickel titanium instruments was superior to that of stainless steel instruments by comparing the change of curvature degree and the ATI of preparing curved premolars root canals. Coronal preflaring should be performed first when the root canals were instrumented by stainless steel K-files or nickel titanium instruments with sequential preparation technique.