Impact of two theoretical cross-sections on torsional and bending stresses of nickel-titanium root canal instrument models.

The use of nickel-titanium in the manufacture of endodontic instruments has given rise to continuous-rotation canal preparation techniques. These techniques involve unidirectional torque, meaning that files are under constant stress and strain when operating. The study presented herein compares torsional and bending stresses in triple U and triple helix models. This was done by applying the boundary integral method to theoretical cylindrical models. The two theoretical models underwent very different torsional stresses, both in terms of intensity and distribution. Bending stresses were much more similar, but to obtain the same curvature, bending moments had to be different. The results of the mathematical calculations indicated that triple U and triple helix instruments should be used for different operating procedures.