Comparison of the frictional resistance and optical properties of aluminum oxide and zinc oxide coated nickel titanium archwires – An in vitro study

Abstract

Objectives: The friction that appears during sliding mechanics poses a clinical challenge to the orthodontist. The primary focus of an ideal tooth movement is to reduce the friction created at the archwire-bracket interface. Various variables (both biological and mechanical) affect the role of friction during orthodontic tooth movement. One among the variables which play a critical role is the archwire used in fixed mechanotherapy. Nickel-titanium (NiTi) archwires are widely used in clinical conditions due to their properties such as low force delivery and wider elastic working range. Innovations in the field of material science have led to the evolution of nickel titanium archwires with coating and surface modification to enhance the esthetics and decrease friction. Esthetics is of major concern in patients undergoing orthodontic treatment. As the esthetic demand keeps rising, the need for developing an esthetically acceptable material is required and it should not compromise on the clinical performance. The study aimed to evaluate and compare the frictional resistance and optical properties of ALUMINIUM oxide and zinc oxide-coated Ni-Ti archwires. Material and Methods: The archwires were divided into three groups (n = 10), respectively: Group 1 – control group of uncoated NiTi archwires, GROUP 2 – zinc oxide coated NiTi archwires, and Group 3 – ALUMINIUM oxide coated NiTi archwires. The frictional resistance test was done using a universal testing machine, Instron, and optical properties were assessed using a colorimeter. The analysis of variance was used to determine whether a significant difference existed between the groups and a further post hoc Tukey test was used to determine the significant difference in the mean (P < 0.05). Results: The two coated archwire groups – zinc oxide and ALUMINIUM oxide archwires showed a significant decrease in frictional resistance. Of the three groups, zinc oxide showed the least frictional resistance compared to the ALUMINIUM oxide-coated group and the uncoated group. Optical properties were calculated using the formula ΔE*ab for the three groups. Of which zinc oxide coated archwires were closest to VA1 indicating that it matches the shade of the natural tooth while the other two groups did not match the tooth color implying that it is not much esthetic as that of zinc oxide coated archwires. Conclusion: The zinc oxide-coated archwire resembles tooth color as well as has less frictional resistance compared to the other archwires.