Development of Regression Models for the Prediction of NiTi Archwire Forces in an Orthodontic Bracket System Using Response Surface Methodology

Abstract

Superelastic NiTi archwire is extensively employed in the early stage of orthodontic therapy due to its capacity to transmit constant and light force to the tooth. The archwire force prediction for orthodontic treatment planning becomes a challenging process as the generated friction at the wire-bracket interface modifies the force exerted by the NiTi archwire. If plotted, the typical force plateau behavior of the superelastic NiTi archwire now gives way to a slope. This study established regression models for estimating the magnitude of forces released by NiTi archwire when bent at various settings in an orthodontic bracket system. Four bending settings parameters were considered: archwire geometry, inter bracket distance, the magnitude of archwire deflection, and testing temperature. The relationships between the settings and the wire forces were investigated using a response surface methodology approach based on data obtained from bending simulation. The magnitude and slope of the unloading force of superelastic NiTi archwire decrease gradually as the amount of wire deflection and inter-bracket distance increase, respectively. NiTi archwires with a diameter of 0.016 inches are best used in the early stages of orthodontic therapy because of their lower unloading forces of 0.57 N to 1.71 N and lower force slope values of 0.13 N/mm to 0.72 N/mm. The developed regression models have strong R-squared values for the loading force, unloading force, and force slope of 0.996, 0.9830, and 0.9748, respectively, and may thus be used to aid the orthodontist in forecasting the amount of force being exerted on a tooth in various malocclusion conditions.