The canal may even present several curvatures and, by drawing a tangent to one of them, this may not be that of the smallest radius. Moreover, the angle may change with the arc length without a variation in the radius length. In the preparation of curved canals it is important to observe the radius and not the angle of curvature since the latter does not represent the true curvature of the root canal. According to Al-Omari et al. Southard at al.
Curves having a small radius can lead to greater wear than curves with a greater radius.
In all of the samples the root canal was straightened after instrumentation, which was not proportional to the value of the radius. Root canals with a smaller radius did not always result in greater straightness. It was observed that the beginning of the curvature was displaced in the apical direction of the root canal. This can be attributed to the variation in the hardness of dentin among the tooth samples, direction and intensity of force applied by the operator, flexibility of the instrument and the localization of the beginning point of the curvature. Harder dentin has greater capacity to deflect the files, directing the wear towards the external part of the curvature of the canal.