Canal Straightening Following Overinstrumentation with Three Nickel-Titanium Rotary Instruments

The aim of the present in vitro study to compare canal straightening following shaping of curved canals with three types of new generation nickel-titanium (NiTi) rotary instruments-ProTaper Next (PTN)^®, BT RaCe (BTR)^®, and WaveOne Gold (WOG)^®- and three different levels of protrusion beyond the major apical foramen.

Forty-five extracted human maxillary and mandibular molars with at least one curved canal were distributed in three comparable groups of 15 canals each. The canals were instrumented to the major foramen and then overinstrumented with the final file 0.5 mm, 1 mm, and 1.5 mm beyond the foramen using PTN (Group PTN = 15), BTR (Group BTR = 15), and WOG (Group WOG = 15). Standardized pre- and post-instrumentation radiographs of the root canal were obtained for all groups using digital intraoral radiographs coupled with software. Differences in the degree of curvature were regarded as straightening and canal curvature was evaluated based on Schneider technique using the AmScope software for measurements and compared between groups and levels of instrumentation applying Mixed-model ANOVA. Significance was set at 0.05.

Canal curvature tended to gradually straighten out as the level of instrumentation increased in all three groups without statistically significant difference among the groups (P = 0.826).

Overinstrumentation in curved canals resulted in straightening of the canal curvature.