BACKGROUND: The conicity of the root canals of primary teeth is an important measure for endodontic therapies. However, determining this conicity depends on the methods employed, which requires further investigation.
OBJECTIVE: The aim of this study was to determine the conicity of the root canals of the upper and lower primary second molars using nanotomography (nCT).
METHODS: An in vitro study was performed using nine primary second molars, both upper and lower, subjected to nCT. Comparisons between the diameters of root canals were performed between the thirds (cervical-D0, middle-D5, and apical-D7). The conicity (%) was determined for each root canal from cervical to apical. Data were statistically analyzed with a significance level of 5%.
RESULTS: The conicity ranged from 2% to 8% for the upper primary second molars. Significant differences in root canal diameter between the thirds (D0, D5, and D7 points) were observed in the mesio- and distobuccal roots (p < .05), but not in the palatal roots (p > .05). For the lower primary second molars, the conicity ranged from 2% to 17%, as well as significant differences in root canal diameter between the thirds (D0, D5, and D7 points) were observed in all roots (distal, mesiobuccal, and mesiolingual; p < .05).
CONCLUSIONS: The conicity of the upper primary second molars was different from that of the lower ones, which showed a greater variability.

OBJECTIVE: The objective of the study was to estimate the conicity of the root canals of maxillary central and lateral incisors by computed nanotomography (Nano-CT).
METHODS: This in vitro study included nine extracted primary maxillary central incisors and 12 maxillary lateral incisors, which were subjected to Nano-CT analysis. The resulting images of each tooth were reconstructed using the OnDemand3D software, and root canal area, volume, and taper analysis were performed using the free FreeCAD 0.18 software for the 3D computer-aided design (CAD) model. Data were statistically analysed using the Stata v14.0 software, adopting a significance level of 5%.
RESULTS: The results presented the mean value of the diameter and area of the root canal of primary central and lateral incisors. In addition, the taper values for both dental groups between points D0-D5, D5-D7, and D7-D10 were determined. Considering the diameters obtained over the entire length of the root, with a length of 12 mm, a conical model was constructed.
CONCLUSIONS: Detailed knowledge of root morphology of maxillary central and lateral incisors of primary dentition by means of Nano-CT is important to achieve faster, more accurate, and efficient endodontic treatments.