Schematic Analysis and Fiducial Point of Tooth for Root Canal Therapy

Objectives To identify schematic relationships between root canal axis, the cementoenamel junction (CEJ), and the contour of the clinical crown’s facial surface in maxillary central incisors. Materials and Methods 72 radiographic images of extracted maxillary central incisors with previous root canal treatment were collected. Angles (tangent angle) between the root canal axis and lines tangent to fiducial points on the facial surface 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, and 5.5 mm cervical to the incisal edge were measured using ImageJ software. Facial-palatal CEJ widths were measured and divided into facial and palatal CEJ by the root canal axis. Generalized linear models were used to assess any relationship between CEJ widths and the constructed tangent angles. The Paired Difference T-test was performed to determine the ratio of palatal CEJ to facial CEJ widths. Results The correlation between CEJ width and angle measurements was statistically significant except at 3.5 mm (P < .05). The tangent angle values decreased from the most incisal point (22.8°) to the most cervical point (18.4°). The average value of total CEJ widths was 7.44 mm. Palatal CEJ was on average 0.22 mm greater than facial CEJ widths (P = 1.61e-6). Conclusions Using CEJ width and tangent angle of fiducial point, the root canal axis of the maxillary central incisor can be predicted. Clinical relevance Crown morphology can be applied to design a standardized endodontic access stent to aid in root canal therapy in maxillary central incisors when the canal is difficult to identify.