Effect of Temperature on Deactivation Force of Three Commercial NiTi Orthodontic Archwires

Abstract

© (2014) Trans Tech Publications, Switzerland. The purpose of this study was to investigate the transition temperature range (TTR) and the effect of temperatures at 10, 20, 30, 40, 50 and 60oC on the deactivation force of three commercially available NiTi archwires. Three different brands of NiTi archwires, NiTi OR (Ormco), NiTi GH (G&H) and NiTi H (Highland), with a cross sectional area of 0.016 x 0.022 inch2 were analysed for transformation temperature range (TTR) by using differential scanning calorimeter and load-deflection characteristics using a three-point bending test at temperatures of 10, 20, 30, 37, 40, 50 and 60oC. Descriptive analysis was used to calculate each variable and Kruskal Wallis test was performed to assess the difference in measurements among the three NiTi wires. P<0.05 was considered as statistical significant. TTR showed austenitic temperature finish (Af) at 24.45oC for NiTi OR, 27.55oC for NiTi GH and 51.5oC for NiTi H. The highest deactivation force was found in NiTi H followed by NiTi OR and NiTi GH at the temperatures below and higher than 37oC. There were siginificant differences (p<0.05) in the deactivation force of NiTi OR - NiTi H and NiTi GH - NiTi H at 10oC and 20oC, and NiTi GH – NiTi H and NiTi GH – NiTi OR at 30oC and 37oC. However, no significant difference was found among all NiTi wires at 40, 50 and 60oC, except NiTi GH – NiTi H at 60oC. A close relationship was found between temperature and unloading curves (deactivation force); increase in the temperature led to an increase in the plateau of delivery deactivation force and decrease in temperature led to a decrease in the plateau of delivery deactivation force. The TTRs of commercial NiTi archwires are variable, especially the austenitic finish temperature. The deactivation force increases in higher temperature and decreases in lower temperature.