Evaluation of the incidence of transportation after placement and removal of calcium hydroxide.

The purpose of this in vitro study was to evaluate the incidence of apical transportation after the placement and removal of Ca(OH)2 in straight and curved root canals. Twenty maxillary central incisors (group A) and 20 mesiobuccal canals from mandibular molars (group B) were instrumented at the working length to a #45 file and #30 file, respectively. Postinstrumentation radiographs were taken with the corresponding final file inserted into the canal to the working length. Afterward, the root canals were filled with a Ca(OH)2 paste using Lentulo spirals, and the teeth incubated for 7 days. The Ca(OH)2 paste was then removed up to the working length using a #45 file for group A and a precurved #30 file for group B. Final radiographs were taken with the file inserted into the canal to the working length. Postinstrumentation and final radiographs were superimposed to evaluate the incidence of transportation. As expected, in group A (straight canals) no transportation was detected, whereas in group B (curved canals) 9 of 20 canals showed apical transportation (95% confidence interval, 23.1-68.5% transportation). Statistically significant differences were observed between groups A and B (p < 0.05).