Root canals in one-rooted maxillary second molars.

The Royal Dental College, Copenhagen, houses an extensive collection of human teeth extracted in Denmark. The collection currently contains 104 one-rooted, permanent maxillary second molars. The root complex on these teeth was sectioned at the junction between the coronal and the apical halves, i.e. mid-root, and at the junction between the middle and the apical thirds, i.e. apically. Using a stereomicroscope we then registered, mid-root and apically, the following variables: canal number, canal position, and canal cross-section. Mid-root there was 1 centrally located root canal in 25.96% of the teeth examined; 2 canals were observed either mesially and distofacially, mesiofacially and distally, or facially and lingually in 34.62%; 3 canals positioned mesiofacially, distofacially, and lingually were found in 39.42%. At the same level 63.51% of the canal cross-sections were non-circular, whereas 36.49% of the canals had a circular cross-section image. The non-circular canal cross-sections could more specifically be characterized as C-shaped, Y-shaped, hourglass-shaped or the root canal had a greater faciolingual than mesiodistal extension or, respectively, a greater mesiodistal than faciolingual extension. Apically there was 1 centrally located root canal in 35.58%; 2 canals were observed with a position either mesially and distofacially, mesiofacially and distally, or facially and lingually in 37.49%; 3 canals located mesiofacially, distofacially, and lingually were found in 26.92%. At the apical level, 64.32% of the root canal cross-sections were non-circular, whereas 35.68% of the canals showed a circular cross-section. The results presented here are aimed at: clinical dentists, endodontists, and dental morphologists.