The European Journal of Orthodontics Advance Access originally published online on May 5, 2006
The European Journal of Orthodontics 2006 28(5):433-439; doi:10.1093/ejo/cjl003
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The change of stress distribution on the condyle after mandibular setback surgery
Department of Oral and Maxillofacial Surgery, School of Medicine, Kanazawa University, Japan
Address for correspondence Koichiro Ueki, Department of Oral and Maxillofacial Surgery, School of Medicine, Kanazawa University, 13-1 Takaramachi, Kanazawa 920-8941, Japan. E-mail: kueki{at}med.kanazawa-u.ac.jp
The rigid-body spring model (RBSM) theory was incorporated into a model as a discrete method for analysing problems of limit, such as the stress distribution on the condyle. The purpose of this study was to evaluate the two-dimensional RBSM for determining stress on the temporomandibular joint (TMJ) in patients after orthognathic surgery. Thirty-two patients (five males and 27 females, mean age 21.4 ± 4.9 years) with mandibular prognathism underwent bilateral sagittal split ramus osteotomy (SSRO) and setback; 48 subjects were recruited as controls. Anatomical landmarks were traced from pre- and post-operative lateral cephalograms and the information was processed using the Fortran analysis program. The force vector on the condyle, its degree, its direction, and the displacement co-ordinates (x, y) and rotation (q) at the gonial angle were calculated.
When muscular power was assumed to be 1, the post-operative degree of the force vector was higher than the pre-operative value (P < 0.05). The X co-ordinate, x, and rotation, q, of the displacement vector in the pre-operative patients with mandibular prognathism were significantly higher than those in the control subjects (P < 0.05). There were still significant differences between the displacement values post-operatively between the patients and controls (P < 0.05).
The results suggest that the degree and direction of the force vector and the resulting displacement co-ordinates can be used as parameters in a surgical model. The RBSM may also be useful in evaluating the pre- and post-operative skeletal morphology of jaw deformities.