Morphology and Morphometry of Distal Root Canal System in Mandibular Molars: An Observational Study

To evaluate the morphology and morphometry of the distal root canal system in mandibular molars with special emphasis on apical anatomy and curvature assessment using different techniques.

The distal root of 600 extracted permanent mandibular molars was selected. Radiographs were taken after inserting size 10-15 K-files into the distal root canals were then examined. The radiographic findings were digitized on a computer, the root canal morphology, including the number and type of canals based on Vertucci's classification, was evaluated, and the three different curvature angles were measured from drawings of the same root canal and compared statistically in mesiodistal and buccolingual planes using Schneider, Weine, and long axis (LA) methods. After that clearing technique was performed to evaluate the apical third morphology, including the number of apical foramens, interorifice distance, and presence of isthmus at the level of 2, 4, and 6 mm by using a stereomicroscope with 30× magnification.

A single canal was most common (56.5%), with Vertucci's type I (55.5%) and type II (33.8%) being predominant. Most teeth had 1 (82.8%) or 2 (14.4%) apical foramina. The apical foramen was located short of the anatomical apex (mean deviation 0.869 mm). Isthmuses were most frequent at 2 mm from the apex. Curvature analysis revealed significant differences among methods (p < 0.001): LA axis showed the highest curvatures in the mesiodistal plane (27.7°), while Weine's method recorded the highest in the buccolingual plane (16.2°). Schneider's method consistently underestimated apical curvatures.

Mandibular molar distal roots are most frequently type I or II, but considerable anatomical variability exists in apical anatomy and curvature. Schneider's method may underestimate curvatures, whereas the LA axis and Weine's methods provide more accurate apical assessment.

Understanding the curvature of the root canal system, particularly in the distal roots of mandibular molars, is crucial for achieving successful endodontic outcomes. Curvatures, especially in the apical third, increase the risk of procedural errors such as ledging, transportation, and instrument separation. This study highlights the variations in curvature measurements based on different radiographic techniques, underscoring the need for clinicians to select the most appropriate method for assessing canal complexity. Techniques like the LA axis and Weine methods provide better insight into apical curvatures and may assist in proper instrument selection, accurate working length determination, and safer canal preparation. These findings can improve treatment predictability and reduce intraoperative complications.