Frictional and Mechanical Properties of Surface Modified Nickel-Titanium Orthodontic Archwires

Abstract

The purpose of this study was to investigate the surface hardness, frictional force and load-deflection characteristic of three types of nickel-titanium archwires; DLC-coated, CH4-PBII and CF4-PBII NiTi orthodontic archwires. The NiTi wires were deposited with DLC films and were implanted with CH4 and CF4 using Plasma-Based Ion Implantation and Deposition (PBIID) method. These archwires and upper canine brackets with slot dimension of 0.022-inch were used in this study. Surface hardness of three types of surface modified NiTi orthodontic archwires was measured using atomic force microscopy (AFM). Frictional resistance was determined using a Universal Testing Machine with a load cell of 50 N. The custom-fabricated friction-testing device was designed and bonded each bracket in an accurate position. Load-deflection characteristic was evaluated by conducting the three-point bending test with universal testing machine. The results showed that DLC-coated NiTi wires had the lowest mean of frictional force followed by CH4-PBII, CF4-PBII and conventional NiTi wires. DLC-coated NiTi wires had the highest mean of surface hardness and there was no significant difference in the unloading force at 0.5, 1.0, 2.0 and 3.0 mm of the load-deflection graphs between different types of NiTi orthodontic archwires. The results can be concluded that the surfaces of nickel-titanium orthodontic archwires can be successfully modified by the PBIID method to increase surface hardness and reduce frictional force between stainless steel brackets and NiTi archwires. The load-deflection characteristics of three types of surface modified archwires remain unchanged.