Evaluation of Force Degradation of the Niti Open Coil Spring After Exposure to High and Low Temperatures, in Vitro Study

Abstract

Open coil springs are designed to provide expansion force, as indicated in the opening spaces. The super elasticity of Niti arch wires and springs allows the orthodontist to apply almost continuous light force with larger activations, resulting in reduced tissue trauma. However, indirect factors like high or low temperature should be monitored as an essential part of applying any force using open coil springs. These temperature differences may influence the springiness, corrosion, and efficacy of Niti coil springs over time. The aim of this study was to evaluate the force rate of NITI open coil springs compressed from 15.0 mm to 8.5 mm after exposure to high (45 ± 3 °C) and low temperature (10 ± 3°C). Forty-five samples of 15.0 mm long Niti springs were divided into 3 groups (n = 15). Group A was immersed in artificial saliva at 37º C for 21 days. Group B was immersed in hot water (45± 3 °C). Group C was immersed in cold water (10± 3 °C). The springs were then subjected to a compression test using a Manual Digital Force Gauge at 43% of the initial size (pre-stretched). Subsequently, the springs were compressed from 15.0 mm to 8.5 mm, and the data were recorded at Day 0, 1, 10, and 21. The analysis of variance revealed p-values below 0.05 for the four-time frames: initial test (0.046), after 24 hours (0.007), after 10 days (0.082), and after 21 days (0.038), indicating significant differences in the force rate of Niti open coil springs when immersed in different temperatures. Additionally, significant differences were found among the different pairings of the three tested groups. The force rates of open coil springs with low temperature were statistically different across different time frames. However, high temperature affected the coil springs more significantly than low temperature. There were significant differences in the force rate of Niti open coil springs when immersed in different temperatures.