[Three dimensional finite element analysis of the upper incisor with different levels of periodontal support].

Purpose: To study the stress variation and distribution of the periodontium and the tooth initial displacement when the lingual fixate forces were applied to the depressed periodontal height.

Methods: Spiral CT (SCT) scanning technology, digital image transfer and transcription were used to obtain the initial 3-D data of the upper central incisor. The 3-D finite element models at six periodontal support heights were created by reducing the height of periodontal support tissues.

Results: With the loss of the alveolar height, the maximum equivalent stress and the principle stress of the upper central incisor periodontium increased. The maximum draw stress located on the lingual apex, while the maximum compressive stress located on the lingual crest of the ridge. The increment of periodontium stress was not proportional to the horizontal alveolar loss.

Conclusions: With the horizontal alveolar loss, the rotation center moved toward the apex and the capacity of periodontal support decreased significantly. In orthodontic treatment, the force should be decreased in proportion to retain the physiological movement and to avoid further injury of the support tissues.