Anders Nattestad

Mandibular autorotation in orthognathic surgery: a new method of locating the centre of mandibular rotation and determining its consequence in orthognathic surgery

Rotation of the mandible is simulated through the centre of the condyle in planning orthognathic surgery. Previous studies have suggested that the initial mandibular movement is better characterized as multiple parts of the segments of a circle with the average centre located below and behind the centre of the condyle. This paper describes a method of locating the centre of mandibular rotation by computer-analysis of two lateral cephalograms with different degrees of opening. The method was used on 10 normal individuals showing an average centre of mandibular rotation 14.9 mm below and 5.0 mm behind the superior midsurface of the condyle for movements from occlusion to an opening of 10 mm. The implications of the located centre of rotation on orthognathic surgery was determined by simulating a closure of a 9.5 mm open bite. An error of up to 9.3 mm in the horizontal position of the maxilla would occur if the centre of the condyle was used. A retrospective study on 10 patients with increased anterior facial height was undertaken and a mean centre of rotation 8.4 mm behind and 25.1 mm below the centre of the condyle was found. Simulating the rotation of the mandible through the centre of the condyle would have resulted in a difference between the predicted and actual horizontal position of the maxilla ranging from 0.4-10.4 mm. It was concluded that using the centre of the condyle as the centre of mandibular rotation in the planning of superior maxillary movement with a Le Fort I osteotomy may cause considerable error in the horizontal position of the maxilla in most cases.

The Significance of an Erroneous Recording of the Centre of Mandibular Rotation in Orthognathic Surgery

The effect of post-operative jaw position of an error in locating the true centre of mandibular rotation was evaluated using a computer-simulation model and a mock surgery model. The centre of the condyle serves as a reference point in surgical procedures involving the maxilla. The purpose of this study was to describe the amount of malpositioning of the jaws at surgery due to a discrepancy between a simulated true centre of rotation and the centre of the condyle. The results showed, that a 20 mm error in location of the true centre of rotation could result in a 3 mm horizontal malpositioning of the maxilla.

Pulp sensibility and pulp necrosis after Le Fort I osteotomy

A longitudinal study comprising 617 teeth in 51 patients was carried out to determine the frequency of pulp necrosis and loss of pulpal sensibility after Le Fort I osteotomy. A negative pulpal sensibility was found in 39 (6%) teeth after an average follow-up period of 28 months, range 11-59 months. Development of pulp necrosis, determined by pulp testing and periapical radiolucency, was only demonstrated in 3 (0.5%) teeth. The extent of horizontal or vertical displacement of the maxilla had no influence on pulpal sensibility. Teeth adjacent to a vertical interdental osteotomy showed a significantly higher frequency of negative reactions compared to the group without an interdental osteotomy (p = 0.002). The canines demonstrated a significantly greater number of teeth with a negative sensibility reaction compared to the other tooth types. A close relationship between the apex of the canines and a wire osteosynthesis was demonstrated to have significant importance for pulpal sensibility.

BONE RESORPTION AFTER ADVANCEMENT GENIOPLASTY : PEDICLED AND NON-PEDICLED GRAFTS

The influence of soft tissue attachment in augmentation genioplasty on the amount of postoperative bone remodelling was studied in 29 patients. The soft tissue was completely detached from the advanced genial segment in 15 patients and the lingual soft tissue was maintained in 14 patients. The advancement of the chin and postoperative bone remodelling was analysed by measuring linear distances and areas on lateral cephalograms. The genial segments with a soft tissue pedicle underwent significantly less resorption than the free grafts (p less than 0.01). The difference in postoperative infection between the two groups (p less than 0.05) indicates that the likelihood of postoperative infection is significantly reduced by maintaining the soft tissue pedicle. Considerably less variation in amount of bone resorption was also observed in the patients with a pedicled graft.

Pitfalls in orthognathic model surgery. The significance of using different reference lines and points during model surgery and operation.

The planning of orthognathic surgery usually involves a simulation of jaw movements in a semi-adjustable articulator. The use of vertical and horizontal references during model surgery and operation have previously been described in great detail. The purpose of the present study was to quantify the errors resulting from using different reference lines and points in model surgery and operation. The results indicate that clinically significant differences between the planned and surgical jaw movement can result from the erroneous transfer of reference lines and points between model surgery and operation. Solutions to some of the problems discussed are suggested.

Soft tissue changes after advancement genioplasty performed as pedicled or free transplants

The influence of soft tissue attachment in augmentation genioplasty on postoperative soft tissue changes was studied in 25 patients. The soft tissue was completely detached from the advanced genial segment in 14 patients and lingual soft tissue was maintained in 11 patients. The patients were followed for a minimum of 1 year after operation and the soft tissue and bone changes were analysed by measuring linear distances and areas on lateral cephalograms. The result indicated that the soft tissue changes after surgery were significantly different between the two types of graft. In the free grafts there was found to be an increased risk of creating a larger interlabial gap and exposure of the labial surface of mandibular incisors. The higher correlations between hard and soft tissue changes in the pedicled grafts indicated that the predictability is better with this operative technique.