Abstract
Bilateral sagittal split ramus osteotomy (BSSO) is widely used to treat mandibular prognathism. Several methods have been described for fixation of the bony segments. This study compared two methods of rigid fixation (bicortical screws and monocortical miniplates) to identify differences in postoperative masticatory function and neurosensory disturbance after 5 years of mandibular set-back correction. 77 women who had undergone BSSO for Class III malocclusion were reviewed, and masticatory functions and neurosensory recovery were examined with the appropriate indicators pre- and postoperatively (at approximately 1 month, and 1, 2, 3, 4, and 5 years). Masticatory function exhibited similar recovery patterns in both groups. Orthognathic surgery improved occlusal force and occlusal contact area, but longer than 4 years after surgery may be required for postoperative occlusal functions in prognathic patients to reach the level of healthy subjects. The groups showed no significant differences in the recovery of parameters of masticatory functions and neurosensory disturbance even 5 years after surgery. In the evaluation of temporomandibular joint function using the Helkimo index, the score was significantly higher for the screw group than for the miniplate group. This suggests that BSSO fixed with miniplates may offer a relatively safe and reliable procedure yielding adequate results and high patient satisfaction.
Bilateral sagittal split ramus osteotomy (BSSO) is probably the most common procedure currently used to correct mandibular deformities. Various benefits have been reported, including better masticatory function, improved facial aesthetics, and more stable results in severe discrepancies. Prevention of relapse after this operation is important. Several studies of BSSO have found the two methods of internal rigid fixation (bicortical screws or monocortical miniplate fixation) offer similar skeletal stability and their use depends on the preference of the surgeon.
One of the main objectives of orthognathic surgery is to improve masticatory function, but the literature contains little comparative information on postoperative jaw functional recovery measured at given intervals. The authors have previously reported that statistical analysis of masticatory function showed no significant difference between the two fixation methods for 1 year postoperatively. The purpose of the present study was to compare bicortical screws and miniplate fixation in terms of masticatory function and neurosensory disturbance 5 years after BSSO in patients who had undergone surgical correction of Class III malocclusion.
Materials and methods
77 consecutive women who underwent BSSO for Class III malocclusion between 1996 and 2004 were studied in this retrospective study. All patients were selected according to the criteria in Table 1 . All patients were fitted with the usual pre- and postoperative orthodontics with fixed appliances. The lower third molars were removed several months before surgery to allow safe splitting of the mandible.
| 1. No craniofacial syndromes |
| 2. No history of jaw trauma or local nerve injury |
| 3. Normal preoperative labiomental sensation |
| 4. No additional osteotomies (such as genioplasty or maxillary osteotomy) |
| 5. No TMJ surgery before and after the bilateral sagittal split set-back osteotomy |
In Group A ( n = 36; mean age 23.1 years; range 16–40 years), subjects received one miniplate on each side and four monocortical screws. A miniplate with monocortical screws on the lateral surface was used to fixate the proximal and distal fragments. In Group B ( n = 41; mean age 21.3 years; range 16–36 years), two bicortical screws were inserted above the inferior alveolar nerve (IAN) in the retromolar area using a transcutaneous approach ( Fig. 1 ). None of the patients exhibited a severe tear or cut of the IAN during surgery.
In each analysis, patient groups (Groups A and B) were also compared with a group of controls (24 women). The mean age of the control group was 18.7 years (range 18–23 years). All controls showed Class I skeletal and dental relationships without any orthodontic treatment or surgery.
A bilateral sagittal split set-back osteotomy was performed in all patients according to T rauner & O bwegeser , as modified by D al P ont , H unsuck and E pker . Briefly, a vertical osteotomy was made in the region of the second molar. No patients showed any complications in splitting the mandible or nerve position after splitting. After osteotomy and removal of an appropriate amount of bone from the proximal segment, the teeth were placed in their planned position with maxillomandibular fixation (MMF) using stainless steel wire. The distal fragment was set back and the desired occlusion was fixed in two different ways, as described above. The 3 surgeons involved in this study were selected because they were experienced with and regularly performed both fixation techniques.
The MMF was released after mandibular fixation, and occlusion and position of the condyles were checked. The wounds were closed using resolvable sutures. The jaws were placed in MMF with stainless steel wires. MMF was removed after 7–20 days.
Postoperative orthodontic treatment started within 1 month after surgery. Patients were examined clinically and radiographically after surgery. The clinical examination was used to evaluate changes in masticatory function and sensory disturbance in patients who had undergone BSSO, from preoperatively to 5 years postoperatively. The following indices were assessed: occlusal contact area; occlusal force; Helkimo index; and sensation. All examinations were performed preoperatively and 1 month and 1, 2, 3, 4 and 5 years postoperatively.
The Dental Prescale system ® (FUJIFILM, Tokyo, Japan) was used to measure occlusal contact area and occlusal force. These measurements were made with the subject seated with the head upright, looking forward, in a natural position. The subject was instructed to bite as forcefully as possible. Maximum contact area and contact force were recorded on Dental Prescale ® . Data were scanned and analyzed using an OCCLUZER 709 (GC Corporation, Tokyo, Japan).
The Helkimo index is based on evaluation of the following five groups of symptoms: impaired range of mandibular movement, impaired function of the temporomandibular joint (TMJ), pain on mandibular movement, pain in the TMJ, and pain in the masticatory muscles. For clinical sensory testing of the lower labiomental area, standardized Semmes-Weinstein monofilaments (Smith & Nephew Rolyan Inc, Milwaukee, WI, USA) were used and differences in degree of sensory disturbance during the recovery period were analyzed statistically (S-W sensory test).
Some data were unavailable because of absence of samples, technical problems with analysis, and loss of patients to follow-up. Missing data were considered randomly lost and complete case analysis was applied. Statistical analysis was performed on the recovery period for each parameter. Occlusal contact area and occlusal force were compared between groups using Student’s t -test. Statistical calculations were performed using the Mann–Whitney U -test on other parameters. Values of p < 0.05 were considered indicative of statistical significance. Statistical analysis was performed using SPSS ® 15.0 for Windows (SPSS; Chicago, IL, USA).
Results
Operation time, blood loss, extent to which the mandible was retracted, and duration of MMF are presented in Table 2 . The two groups did not differ significantly in terms of age. Both groups showed similar morphological changes after surgery. Mean operation time was significantly longer for Group B (199 ± 45.7 min) than for Group A (165 ± 30.7 min; p < 0.05), but blood loss tended to be only slightly greater in Group B (259.7 ± 151.4 ml) than in Group A (222.8 ± 141.8 ml; p > 0.05). For Group A, mean movement in the horizontal direction was 7.3 mm on the right side, and 6.1 mm on the left side; compared with 7.0 mm and 7.0 mm, respectively, in Group B. Duration of MMF did not differ significantly between groups.
| Group A (plate) | Group B (screw) | |
|---|---|---|
| Operation time (min) | 165.0 ± 30.7 | 199.0 ± 45.7 * |
| Blood loss (ml) | 222.8 ± 141.8 | 259.7 ± 151.4 |
| Set back value | ||
| Right (mm) | 7.3 ± 3.0 | 7.0 ± 2.8 |
| Left | 6.1 ± 3.6 | 7.0 ± 3.1 |
| Duration of MMF(days) | 12.2 ± 2.6 | 14.9 ± 3.1 |
Masticatory function exhibited a similar recovery pattern in both groups. Measurements decreased immediately postoperatively, and minimum values were reached by 1 month after surgery. A significant increase occurred from 1 month after surgery, and masticatory function by around 1 year after surgery was greater than that observed preoperatively.
Briefly, 1 month after surgery, occlusal force and occlusal contact area had fallen to approximately half of the preoperative value or less ( Figs. 2 and 3 ). By 1 year postoperatively, a significant increase of approximately 1.2-fold was evident. Neither occlusal contact force nor occlusal area differed significantly between Groups A and B by 5 years after surgery. Although preoperative occlusal contact area and occlusal force were approximately half or less compared with values in the control group, these parameters reached the control group average by at least 4 years after surgery.
Changes in mean Helkimo index are shown in Fig. 4 . The trend in Group A was comparatively stable, and always < 0.5 for 5 years. The score did not differ significantly between pre- and postoperative values. Group B reached a nadir in scores (approximately 2 points) by 1 month after surgery. Scores had recovered by 1 year after surgery but this score increased again from 4 years after surgery. A significant difference was apparent between types of fixation by 5 years after surgery.
