The change of stress distribution on the condyle after mandibular setback surgery

• Published in: European journal of orthodontics Vol. 28; no. 5; pp. 433 - 439
• Main Authors: Ueki, Koichiro, Nakagawa, Kiyomasa, Takatsuka, Shigeyuki, Yamamoto, Etsuhide
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.10.2006; Oxford Publishing Limited (England)
• Subjects: Adult; Bite Force; Case-Control Studies; Female; Humans; Male; Mandible - diagnostic imaging; Mandible - surgery; Mandibular Condyle - diagnostic imaging; Osteotomy; Prognathism - surgery; Radiography; Statistics, Nonparametric; Stress, Mechanical; Weight-Bearing
• ISSN: 0141-5387; 1460-2210
• DOI: 10.1093/ejo/cjl003

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.