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

OBJECTIVES: An in vitro experimental study was performed to evaluate the torsional strength and torque released by esthetic coated archwires. MATERIALS AND METHODS: A total of 52 coated (study group) and 52 stainless steel (control group) rectangular archwires from two manufacturers (brand I: Gestenco International AB, Gothenburg, Sweden and brand II: Ortho Technology, Lutz, FL, USA) in two sizes (0.019â€¯× 0.025 and 0.017â€¯× 0.0250-inch) were evaluated. The straight parts on both ends of each preformed archwire were cut in 30 mm segments. A specially 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 a significance level of 5%. RESULTS: The results revealed that coating of the wires of brand 1 resulted in a significant reduction of torsional strength in both wire sizes (P-value = 0.0001). For the wires of brand 2, coating of the 0.017â€¯× 0.025-in wire resulted in a significant reduction in torsional strength. However, for the 0.019â€¯× 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 a torque between 5 and 20 Nmm was applied (P-value = 0.062). CONCLUSIONS: 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.

Effect of esthetic coating on surface roughness of orthodontic archwires.

BACKGROUND AND AIM: Esthetic wires are commonly used in orthodontic treatments. Surface roughness is an important factor in the friction and bacterial adhesion in these wires. Surface roughness of esthetic wires has not been assessed, except in a few recent (mostly qualitative esthetics) studies. The aim of this study was to quantitatively compare the surface roughness of 4 coated esthetic wires with that of a conventional orthodontic wire. MATERIALS AND METHODS: In this in vitro trial, 25 coated and uncoated orthodontic archwires were studied, including: NiTi Memory wire (American Orthodontics, USA) as a control group; Orthocosmetic Elastinol (Ortho Organizers, USA); Perfect (Hubit, Korea); Imagination (Gestenco, Sweden); EverWhite (American Orthodontics, USA). All were .016×.022" rectangular maxillary wires. Fifteen millimeters of wire was cut off at the posterior end and a surface area of 2000×2000nm was probed using a Scanning Probe Microscope (DS95-50E/DME, Denmark) to determine the surface roughness values. The roughness parameters of Sa, Sdq, Sv and Sy were measured and statistically compared by Kruskal-Wallis and Mann-Whitney U tests. RESULTS: The average range of the 4 parameters was the highest for the uncoated Ni-Ti Memory wire (control group) while the Perfect coated wire showed the lowest values. The differences were significant for parameters Sa and Sy (P<0.02 and P<0.023) and non-significant for Sv and Sdq. Significant differences existed between uncoated and coated wires regarding Sa and Sy values (P<0.01), being higher for the uncoated wires. CONCLUSION: Taking into account the study limitations, the surface roughness values of NiTi uncoated archwires were significantly higher than those of the coated wires.