European Journal of Cardiovascular Medicine

Evaluation of root canal curvatures is essential for endodontic research and clinical dentistry. Clinically, root canal curvatures are linked to a higher chance of iatrogenic mistakes, which can impede the root canal system's shape and ultimately result in treatment failure.1, 2 The British Endodontic Society (BES) Case Assessment Tool (British Endodontic Society, 2022) and the American Association of Endodontists (AAE) Case Difficulty Assessment Form both include root canal curvature as one of the factors that help clinicians with their preoperative assessment and management, including referral when necessary. For research purposes, evaluation of the root canal curvatures is intended to reduce selection bias, which can impact several technical outcome measures assessing endodontic instruments in laboratory studies, such as shaping ability, debris extrusion  and cyclic fatigue resistance, amongst others.^3,4

Similarly, Pruett et al.⁵ developed a novel metric for determining root canal curvature called the "curvature radius." A major clinical contributing factor to instrument breakage and canal transportation may also be the radius of curvature, which increases the load on endodontic instruments.⁶ The goals of this research were to assess and compare three distinct approaches to calculating curvature angles and to propose a new metric called the "canal access angle" (CAA), which is comparable to the Schneider angle.

In this investigation, one hundred human mandibular first and second molars were employed. Teeth with exterior resorption, very narrow canals, and incompletely developed apices were excluded, as were teeth with blocked canals that would prevent identification. Artefacts on the root surfaces were eliminated by keeping the extracted molars in distilled water after they had all been immersed in a 10% formalin solution. Following endodontic access, radiographs were acquired and a size 10 K-file was inserted into the mesiobuccal canal up to the apical foramen. The teeth were positioned such that the long axis of the root was parallel and as near to the surface of the X-ray film as possible. They were then softly waxed to Kodak Ultra-speed film (Kodak, Stuttgart, Germany).

The long axis of the root was perpendicular to the central X-ray beam, and radiographs of each root canal were taken in the buccolingual direction. All radiographs had the same exposure duration and a fixed distance of roughly 40 cm between the film and the X-ray source. The films were cleaned, dried, repaired, and developed. A computer was then used to scan the radiographs (Scanner: Agfa–Duascan, Germany). According to the Schneider method, a line is first drawn in the coronal third parallel to the canal's long axis. A second line is then drawn from the apical foramen to intersect the place where the first line departed the canal's long axis. These lines intersect at the Schneider angle. In the height of curvature (x), and the angular and linear values used in this study were plotted in a PC environment using the program Free Hand (Macromedia, Inc., San Francisco, CA), and the pertinent measurements were made using the program AutoCAD R12. The resultant values were evaluated statistically using Pearson correlation and multi- ple regression analyses.

In the curvature height (x), and the distance from A to point D is the curvature distance (AD = y). The angular and linear values used in this study were plotted in a PC environment using the program Free Hand, and the pertinent measurements were made using the program AutoCAD R12. The resultant values were evaluated statistically using Pearson correlation and multi- ple regression analyses

Figure 1. (a) Curvature angle measurement from the same root canal of a representative molar using three different techniques. (b) CAA, the angle be- tween the line from the canal entrance (A) to apex (B) and a line parallel to the long axis of the canal extending from the coronal part of canal. S: Schneider angle, AC, The distance between points A and C; CD(x), curvature height; AD(y): curvature distance. (c, d) The canal access angles of two canals with different canal geometry may differ, even if they have the same canal curvature when measured using the Schneider technique.

Table 1- The results of the second part of the investigation are summarized

Table 2- Pearson correlation analysis revealed

1. A positive correlation (r = 0.31) between the CAA and canal length (p < 0.001).
2. A positive correlation (r = 0.74) between the CAA and curva- ture height (x) (p < 0.001), and a negative correlation (r = – 0.38) between the CAA and curvature distance (y) (p < 0.001).
3. A positive correlation (r = 0.93) between the CAA and Schnei- der angle (p < 0.001).

The multiple regression analysis indicated that the values of x (p < 0.001) and y (p < 0.005) influence the CAA, i.e. change in the CAA depends on the values of x and y.