Apical morphology of the palatal roots of maxillary molars by using micro-computed tomography.

INTRODUCTION The apical constriction (AC) has been a traditional landmark as an end point of canal preparation and obturation. However, the morphology and incidence of this structure have not been definitively determined. The purpose of this study was to determine these factors by using a noninvasive technology, micro-computed tomography. METHODS Forty extracted maxillary molar palatal roots were separated and mounted. Each root was scanned with micro-computed tomography. Slices from the scan were computer reconstructed by using special software. This rendered each root three-dimensionally "transparent." Roots were rotated, and the apical canal region was selected. In 2 sessions, trained evaluators identified the AC as to (1) presence (single and tapered) or (2) absence (flaring, parallel, and delta). Evaluator agreement was assessed by Cohen's kappa. Descriptive frequencies were determined for apical constriction presence and morphology. RESULTS Interagreement and intra-agreement of evaluators were good. In regard to frequency of occurrence, most (65%) canals did not demonstrate an AC. The morphology, in order of most to least, was parallel 35%, single 19%, flaring 18%, tapering 15%, and delta 12%. CONCLUSIONS From the noninvasive evaluation of our sample it was concluded that an AC was usually not present and that this apical canal region was variable. If this is true with other tooth groups, the AC should not be used as an anatomical marker for preparation and obturation.