PubMed · 8510864
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M A Toomajian. 1993. Unconvinced.. https://pubmed.ncbi.nlm.nih.gov/8510864/
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AIM: The aim of this study was to compare canal preparations completed with Hedstrom and K-files of ISO size 15 - 40, made of nickel-titanium (Ni-Ti) and stainless steel (SS). METHODOLOGY: Eighty simulated canals with 200 and 30 degrees C curvatures were prepared using the step-back technique and quarter turn/pull instrument manipulation. Middle and apical level canal sections were taken using computed tomography. RESULTS: No significant difference was found between any of the file types at either level with respect to canal curvature (20 degrees or 30 degrees). At the middle level, the stainless steel files caused more enlargement toward the inner part, compared to nickel-titanium files. At the apical level, nickel-titanium canal files caused more enlargement toward the inner part, whereas more outward enlargement was caused by stainless steel instruments. No significant difference could be observed at the middle level (P > 0.05) related to the enlargement toward the outer side of the canal curvature. Transportation at both levels was significantly less (P < 0.001) for the Ni-Ti files than the SS ones. Centring ratios of the file types at the middle level were low, but not significantly different (P > 0.05), whereas at the apical level the centring ratios were significantly higher for the Ni-Ti files (P < 0.001). CONCLUSIONS: Ni-Ti instruments produced preparations with adequate enlargement, less transportation, and a better centring ratio.
AIM: The aim of this study was to evaluate the efficacy of ultrasound in cleaning the surface of stainless steel and Ni-Ti endodontic instruments. METHODOLOGY: Twenty nickel-titanium instruments (10 Quantec files and 10 Nitiflex) and 20 stainless steel K-files (10 Maillefer-Dentsply and 10 Moyco Union Broach) were removed from their original packages and evaluated using a scanning electron microscope. Scores were given for the presence of residues on the surface of the instruments. The instruments were then cleaned in an ultrasonic bath containing only distilled water or detergent solution for 15 min, and re-evaluated, using scanning electron microscopy. RESULTS: Before cleaning, a greater amount of metallic debris was observed on the nickel-titanium Quantec instruments (P < 0.05), when compared to those made of stainless steel. Statistical analysis showed that the use of ultrasound was effective for cleaning the instruments, regardless of the irrigating solution or the instruments type (P < 0.05). CONCLUSIONS: The use of ultrasound proved to be an efficient method for the removal of metallic particles from the surface of stainless steel and Ni-Ti endodontic 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.