Impact of torsional and bending inertia on root canal instruments.

The laws of applied mechanics can be used to analyze and predict the behavior of mechanical parts subjected to strain and distortion, such as endodontic instruments. Simple mathematical formulas can be used to represent the impact of torsional and bending inertias on stresses in endodontic instruments being used in root canals. The boundary integral method was applied to two theoretical models with the same diameters but different cross-sections to evaluate quantitatively and qualitatively the stresses produced in orthogonal cross-sections. The results confirmed the mathematical deduction concerning the impact of torsional and bending stresses. The results indicate that clinical protocols based on the torsional and bending properties of endodontic instruments must be strictly followed, and endodontic instrument manufacturers must adopt standardized criteria for describing these properties.

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.

Corrosion susceptibility of titanium covered by dental cements.

OBJECTIVES: The aim of this study is to determine the influence of acidic fluorinated cements (as glass ionomer (GI) cements) on the passivation of titanium, using electrochemical investigations. METHODS: We realized experimental electrodes that associate titanium and dental cements. Polarization resistance of titanium electrodes has been determined for uncovered metal and electrodes covered with three dental cements. Student's t-tests proved the reproducibility. We also compared successive voltammograms for uncovered titanium and GI covered titanium. RESULTS: Correct passivation was observed with zinc eugenate, but fluorinated GI or zinc phosphate coverage increased the corrosion susceptibility. SIGNIFICANCE: However there is no evidence of titanium depassivation when covered with cement. No clinical contraindication can be held.