Abstract: PURPOSE: To detect the mechanical conditions of short root teeth during stepwise and overall retraction in extraction cases of Class I malocclusion patients, and help clinicians better understand the force distribution of short root teeth under different retraction methods. METHODS: CBCT was used to scan the maxillofacial and oral condition of the volunteers. The obtained CBCT data were imported into Mimics 20.0 software for processing. Modelings were conducted using Geomagic Studio 2014 reverse engineering software and NX1911 software. The three-dimensional finite element software Ansys Workbench 2019 was employed to simulate stepwise and overall retraction using an invisible correction model for extraction cases. The displacement trends, stress magnitudes, and stress distribution in the periodontal ligament of maxillary short root teeth were investigated. RESULTS: During the retraction of short root teeth, the stress in the roots appeared on the labial surface. When the canine was first distally moved into position, and then 2-2 retraction by 0.2 mm (condition 2), equal effect force value of the central incisor was the largest. The maximum values of the minimum principal stress and hydrostatic pressure in the periodontal ligament of the central incisor appeared on the labial surface of the cervical root. Among them, the force value was the smallest under the condition of 3-3 overall retraction by 0.2 mm (condition 1). In terms of displacement, the short root teeth exhibited elongation during retraction, with the maximum movement distance in the Y direction observed under condition 1. CONCLUSIONS: The forces on the root and periodontal ligament of the short root teeth are the lightest, and there is a slight root resorption under condition 1. Short root teeth are easy to tipping movements and elongation, with a greater amount of tipping and elongation observed under condition 1.

Key words: Short root tooth, Individual retraction, Overall retraction movement, Finite element analysis