Unevenness of the apical constriction in human maxillary central incisors.

This study examined the incisoapical extent of the apical constriction in 45 human maxillary central incisors. The null hypothesis was that the apical constriction is a flat ring. Our working hypothesis was that the constriction is actually uneven or "skewed" as it traces a path around the circumference of the canal. Teeth were split and imaged with 25x magnification, and the most apical and coronal limits of the apical constriction were identified and measured. Analysis of the data indicates that a majority (>70%) of maxillary central incisors exhibit an unevenness or "skew" of the apical constriction of greater than 100 microm in the incisoapical dimension, with a maximum measured skew of 385 microm. On the basis of the results of this study, a statistically significant (P < .05) variation in the longitudinal position of the apical constriction around its circumference was confirmed in maxillary central incisors.