Prolonged water immersion alters resistance to sliding of aesthetic orthodontic coated wires

OBJECTIVE

The objective of this study was to compare the resistance to sliding of aesthetic orthodontic coated wires after prolonged water immersion for up to 4 weeks.

SETTING AND SAMPLE POPULATION

An in vitro study of commercially available orthodontic appliances.

MATERIALS AND METHODS

Aesthetic coated stainless-steel wires (Parylene-coated, epoxy-coated and Teflon-coated) (0.019" × 0.025") and an uncoated control were immersed in distilled-deionized water for zero, two or four weeks at 37°C and then were subjected to resistance-to-sliding tests through a three-bracket system of sapphire ceramic brackets (0.022" × 0.028" slot) and clear-coloured elastic ligatures at a contact angle of 0° or 3°. Maximal and average resistance to sliding was analysed by a three-way analysis of variance, two general linear models and a post hoc Tukey's honest significant difference test.

RESULTS

Water immersion time, contact angle, wire group and their interactions had statistically significant effects on the resistance to sliding of tested orthodontic wires. Various coated wires had distinct timely changes in the maximal and average resistance to sliding after water immersion for 2 to 4 weeks. When compared to the uncoated control in most of the experimental conditions, epoxy-coated wires had lower or non-significant differences in resistance to sliding, while Parylene-coated wire had higher resistances.

CONCLUSIONS

Prolonged water immersion for weeks alters the resistance to sliding of aesthetic orthodontic wires coated with Parylene, epoxy or Teflon. Based on their resistance to sliding, different designs in orthodontic biomechanics should be considered for the different aesthetic orthodontic coated wires.

In vitro evaluation of the influence of velocity on sliding resistance of stainless steel arch wires in a self-ligating orthodontic bracket

INTRODUCTION

Of the variables used by in vitro studies of resistance to sliding (RS) in orthodontics, sliding velocity (SV) of the wire is often the one farthest from its clinical counterpart. We investigated whether velocity influences the RS at values approximating the orthodontic movement.

METHODS

A SS self-ligating bracket with a NiTi clip was fixed onto a custom-made model. Different shaped orthodontic SS wires of four sizes and two types (round, 0.020″ and 0.022″; rectangular, 0.016″×0.022″ and 0.017″×0.025″) were tested using an Instron^® testing machine. Wires were pulled at four velocities (1×10^-2  mm/s, 1×10^-3  mm/s, 1×10^-4  mm/s, 1×10^-5  mm/s). Shapiro-Wilk test was used to evaluate the normal distribution of the data; two-way ANOVA was performed to compare means in the RS with wire characteristics and SV. Significance level was set at P<.05.

RESULTS

RS was higher for rectangular wires, and for those with larger diameters. Lower SV was associated with lower RS, with wire type and size having an interaction effect. The RS relatively to SV can be represented as: RS ∝ α[ln(SV)]+β, where α and β are constants.

CONCLUSIONS

At very low SV and low normal forces, SV influences the RS of SS archwires in orthodontic brackets, and the proportionality is logarithmic. Although respecting these parameters in vitro is challenging, quantitative evaluations of RS should be carried out at clinically relevant velocities if aiming at translational application in the clinical scenario.

Zinc-oxide nanocoating for improvement of the antibacterial and frictional behavior of nickel-titanium alloy

AIM

To fabricate a friction-reducing and antibacterial coating with zinc oxide (ZnO) nanoparticles on nickel-titanium (NiTi) wire.

MATERIALS & METHODS

NiTi orthodontic wires were coated with ZnO nanoparticles using the chemical deposition method. Characteristics of the coating as well as the physical, mechanical and antibacterial properties of the wires were investigated.

RESULTS

A stable and well-adhered ZnO coating on the NiTi wires was obtained. The hardness and elastic modulus of the ZnO nanocoating were 2.3 ± 0.2 and 61.0 ± 3.6 GPa, respectively. The coated wires presented up to 21% reduction in the frictional forces and antibacterial activity against Streptococcus mutans. ZnO nanocoating significantly improved the surface quality of NiTi wires. The modulus of elasticity, unloading forces and austenite finish temperature were not significantly different after coating.

CONCLUSION

This unique coating could be implemented into practice for safer and faster treatment to the benefit of both patient and clinician.