Evaluation of torsional strength and torque presentation of coated rectangular stainless steel archwires, an in vitro study.

Abstract

An in vitro experimental study was performed to evaluate the torsional strength and torque released by esthetic coated archwires. A total of 52coated (study group) and 52stainless steel (control group) rectangular archwires from two manufacturers (brandI: Gestenco International AB, Gothenburg, Sweden and brandII: Ortho Technology, Lutz, FL, USA) in two sizes (0.019 × 0.025 and 0.017 × 0.0250-inch) were evaluated. The straight parts on both ends of each preformed archwire were cut in 30 mm segments. Aspecially designed experimental device was attached to the universal testing machine (Model Z020, Zwick Roell, Ulm, Germany) to measure torsional strength and to calculate the clinically significant torque interval. The groups were compared based on their brand, presence of coating and size using three-way analysis of variance (ANOVA) test at asignificance level of 5%. The results revealed that coating of the wires of brand1 resulted in asignificant reduction of torsional strength in both wire sizes (P-value = 0.0001). For the wires of brand2, coating of the 0.017 × 0.025-in wire resulted in asignificant reduction in torsional strength. However, for the 0.019 × 0.025 in wire size, the presence of coating significantly increased the torsional strength (P-value = 0.0001). Coating did not affect the measured clinical torque interval of the analyzed wires when atorque between 5and 20 Nmm was applied (P-value = 0.062). Mechanical behavior of coated archwires depends mainly on the thickness of their inner core alloy. Reduction in the diameter of the inner alloy resulted in reduced torsional strength. Despite lower mean torsional strength, in the settings of this study, coated and conventional wires demonstrated comparable torque angles if loaded in the typical range of activation.