Background: Fixed orthodontic retainers have numerous advantages, but it is not known whether they can exert\npathological forces on supporting tissues around the splinted teeth. The purpose of this study was to investigate\nhow the inclination of the lower anterior teeth can affect dental displacement and also change the direction of\nocclusal loads exerted to dental and its supporting tissues.\nMethods: Four three-dimensional finite element models of the anterior part of the mandible were designed. All\nthe models contained the incisors and canines, their periodontal ligament layers (PDLs), the supporting bone (both\nspongy and cortical), and a pentaflex splinting wire placed in the lingual side of the teeth. Teeth inclination was\nconsidered to be 80Ã?° (model 1), 90Ã?° (model 2), 100Ã?° (model 3), and 110Ã?° (model 4) to the horizontal plane. The\nlower incisors were loaded with a 187-N vertical force. Their displacement patterns and the stress in their PDLs\nwere evaluated.\nResults: In incisors with 80Ã?° of inclination, less than a 0.1-mm lingual displacement was seen on the incisal edge\nand a similar distance of displacement towards the labial was seen on their root apices. However, in models with\n90Ã?°ââ?¬â??110Ã?° of inclination, the incisal edge displaced labially between about 0.01 and 0.45 mm, while root apices\ndisplaced lingually instead. By increasing the angle of the teeth, the strain in the periodontal ligament increased\nfrom about 37 to 58 mJ. The von Mises stresses around the cervical and apical areas differed for each tooth and\neach model, without a similar pattern. Increasing the angle of the teeth resulted in much higher cervical stresses in\nthe incisors, but not in the canines. In the lateral incisor, cervical stress increased until 100Ã?° of inclination but\nreduced to about half by increasing the angle to 110Ã?°. Apical stress increased rather consistently in the incisor\nand lateral incisors, by increasing the inclination. However, in the canines, apical stress reduced to about half,\nfrom the first to fourth models.\nConclusions: Increasing the labial inclination can mostly harm the central incisors, followed by the lateral\nincisors. This finding warns against long durations of splinting in patients with higher and/or patients with\nreduced labial bone thickness.
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