Postoperative mandibular stability after orthognathic surgery in patients with mandibular protrusion and mandibular deviation

Wenli Lai, DDS, PhD Lecturer Department of Orthodontics West China College of Stomatology Sichuan University Chengdu, China Kazuhiro Yamada, DDS, PhD Lecturer Division of Orthodontics Department of Oral Biological Science Kooji Hanada, DDS, PhD Professor and Chair Division of Orthodontics Department of Oral Biological Science Iyad M. Ali, DMD PhD Student Division of Orthodontics Department of Oral Biological Science Ritsuo Takagi, DDS, PhD Professor and Chair Division of Oral and Maxillofacial Surgery Department of Oral Health Science Tadaharu Kobayashi, DDS, PhD Assistant Professor Division of Reconstructive Surgery for Oral and Maxillofacial Region Takafumi Hayashi, DDS, PhD Associate Professor Division of Oral and Maxillofacial Radiology Department of Tissue Regeneration and Reconstruction Course for Oral Life Science Niigata University Graduate School of Medical and Dental Sciences Niigata, Japan Reprint requests: Dr Kazuhiro Yamada Division of Orthodontics, Department of Oral Biological Science Course for Oral Life Science Niigata University Graduate School of Medical and Dental Sciences 2-5274 Gakkocho-dori Niigata 951-8514, Japan Fax: +81-25-223-5230 E-mail: kazuhiro@dent.niigata-u.ac.jp Int J Adult Orthod Orthognath Surg Vol. 17, No. 1, 2002 Postoperative mandibular stability after orthognathic surgery in patients with mandibular protrusion and mandibular deviation Skeletal stability and temporomandibular joint (TMJ) signs and symptoms were analyzed in 23 patients in whom mandibular protrusion and mandibular deviation had been corrected using bilateral sagittal split ramus osteotomy (BSSRO group, n=10) and unilateral SSRO and intraoral vertical ramus osteotomy (USSRO+IVRO group, n=13). Miniplate fixation was used in SSRO but no fixation was used in IVRO. The ratio of condylar bony change was 30.4% (7/23) and all condylar bony changes were seen on the deviated side. All preoperative signs and symptoms of TMJ disorders (4/13 patients in the USSRO+IVRO group and 2/10 patients in the BSSRO group) disappeared after surgery. Comparing the USSRO+IVRO group and the BSSRO group, in patients without condylar bony change, the mandible in both groups was stable anteriorly and horizontally after surgery, even though there was a larger horizontal mandibular movement in the USSRO+IVRO group during surgery. Comparing patients with condylar bony change versus no condylar bony change in the USSRO+IVRO group, postoperative horizontal mandibular displacement was significantly larger in the condylar bony change group than in the no condylar bony change group. These results support the idea that USSRO+IVRO can be useful in correcting mandibular deviation as well as improving signs and symptoms of TMJ disorders. However, it also seems important to be aware of the possibility of horizontal mandibular relapse in patients with condylar bony change. (Int J Adult Orthod Orthognath Surg 2002;17:13 22) Bilateral sagittal split ramus osteotomy (BSSRO) is the method most frequently used in correcting a prognathic or retrognathic mandible. This procedure involves the rigid fixation of proximal and distal bone segments, in order to shorten postoperative maxillomandibular fixation time. 1 Also, in patients with mandibular asymmetry, fixation (such as with a miniplate) has been used for fixation of rotated mandibular segments. 2 On the other hand, intraoral vertical ramus osteotomy (IVRO) with setback has also been used to correct mandibular protrusion and achieve mandibular stability. 3,4 In the surgical correction of mandibular deformities (ie, mandibular protrusion) there is little difference in the usefulness of sagittal split and vertical ramus osteotomies. However, the 13 vertical ramus osteotomy caused less rotational displacement of the proximal segment in asymmetric mandibles. 3,5,6 USSRO on the nondeviated side, combined with IVRO on the deviated side, might bring stable postoperative results without condylar displacement in surgically correcting mandibular asymmetry. 5 On the other hand, imaging studies have reported a relationship between condylar bony change and jaw deformity, and have shown that mandibular retrusion and mandibular asymmetry were related to condylar bony change and TMJ symptoms. 7 10 Concerning postoperative condylar bony change after IVRO, Matsushita et al 11 reported the presence of double contour lines in the posterior part of the condyle. They interpreted this bony

14 Lai et al change as a sign of adjustment to the new functional environment of the TMJ after surgery. The aims of the present study were to compare USSRO+IVRO and BSSRO, with reference to postoperative mandibular stability; to elucidate whether condylar bony change is related to postoperative stability in USSRO+IVRO; and to investigate the changes between preoperative and postoperative incidence of signs and symptoms of TMJ disorders. Subjects and methods Subjects The subjects comprised 23 skeletal Class III malocclusion cases (15 female and 8 male) with mandibular deviation (with or without open bite), who were surgically corrected by various surgeons in the First and Second Departments of Oral and Maxillofacial Surgery, Niigata University. Prior to their acceptance for orthognathic treatment, these patients underwent a computed tomography (CT) scan to elucidate bony structures and directions of nerve and vessels as well as condylar bony changes, after their informed consent was obtained. From the study of Beyer and Lindauer, 12 the mean threshold for acceptable dental midline deviation was 2.2 mm. According to this suggestion, using their frontal cephalograms at first visit, patients who had 2 mm or more midline deviation from the menton to the craniofacial vertical midline were included in our study. The cases had complete information, including lateral and frontal cephalograms at different treatment times. No cases of cleft palates or other craniofacial syndromes were included. The mean age at surgery was 20.9 years (range: 17 to 32 years). The average mandibular plane angle was 38.3 degrees; the average SNA and SNB angles were 81.6 degrees and 82.6 degrees, respectively. Thirteen patients had open bite and 14 patients had crossbite; the average overbite was 0.3 mm and the average overjet was 1.7 mm. As for the kind of mandibular osteotomy, bilateral sagittal split ramus osteotomy (BSSRO group) was performed in 10 cases (6 female and 4 male); unilateral sagittal split ramus osteotomy combined with intraoral vertical ramus osteotomy (USSRO+IVRO group) was performed in 13 cases (9 female and 4 male). In selecting the surgical method, we considered not only the direction of mandibular nerves but also any signs and symptoms of TMJ disorders, as well as the possibility of excessive horizontal movement (over 5 mm) of a proximal segment during surgery. IVRO was chosen for patients with signs and symptoms of TMJ disorders and/or potentially excessive rotation of a proximal segment. All patients had preoperative and postoperative orthodontic treatment. Surgery methods In the BSSRO group, SSRO was bilaterally performed with the modifications advocated by DalPont, 13 in which the split osteotomy is made at the region of the first or second molar and the teeth placed in their planned positions without an interocclusal wafer following the mandibular split. Each condylar segment was not fixed rigidly (ie, bicortically with several screws) but fixed flexibly with a miniplate. These titanium miniplates were applied intraorally on each side using four 2.0-mm-diameter monocortical titanium screws. Maxillomandibular fixation was maintained for a mean of 17.5 days. The duration of postorthodontic treatment after surgery ranged from 6 to 29 months, with an average of 15 months. In the USSRO+IVRO group, IVRO was performed on the deviated side and SSRO with miniplates (as above) was performed on the nondeviated side. In IVRO, the masseter muscle was detached from the lateral surface of the mandibular ramus, which was cut vertically using a reciprocating saw. Following this, the inferior part of the medial pterygoid muscle was also detached from the condylar segment. We performed neither repositioning nor fixation of the condylar segment. After surgery, the maxillomandibular fixation was maintained for a mean of 21 days. The duration of postorthodontic treatment after surgery ranged from 6 to 30 months, with an average of 12 months.

Table 1 Cephalometric measurements Angular lateral cephalometric measurements S-N-B SNB angle (SNB) SN-MeGo Mandibular plane angle (Mp) Linear lateral cephalometric measurements Overbite Vertical overlap of central incisors Overjet Horizontal overlap of central incisors Posterior mandibular movement Horizontal distance from point B to the line through sella perpendicular to FH plane Linear anteroposterior cephalometric measurements Mandibular deviation Me-M (deviation is positive on deviated side) Changes in measurements Surgical change Postoperative measurements preoperative measurements Postoperative change Measurements at beginning of retention postoperative measurements Imaging studies In order to assess the stability of surgery, posterior-anterior (PA) and lateral cephalograms were used. The CT at first visit was also used to diagnose condylar bony change. Cephalometric analysis The changes in mandibular position were evaluated on lateral and frontal cephalograms, which were obtained with vertically adjustable head holders. 14 All cephalograms were taken with the patients teeth in intercuspal position and traced by the same researcher. Cephalometric measurements are presented in Table 1. As for the lateral cephalograms (Fig 1), the Frankfort horizontal line through porion and orbitale was used as the x axis. Perpendicular to this, the line through sella was used as the y axis. Cephalograms taken just before surgery (T1), 1 week after surgery (T2), and at the beginning of the retention period (over 6 months after operation, T3) were superimposed according to these 2 lines. The following variables were measured: overbite, overjet, mandibular plane angle (SN-MeGo), and SNB angle. The Int J Adult Orthod Orthognath Surg Vol. 17, No. 1, 2002 15 projection on the x axis of the displacement of point B between T1 and T2, and T2 and T3 was used to measure the surgical and the postoperative mandibular movements. As for the frontal cephalogram, the perpendicular distance between the menton to the frontal midline was represented as the mandibular deviation (Fig 2). All angular and linear measurements were recorded and differences between these 3 time periods were evaluated. CT diagnosis The preoperative condylar morphology was diagnosed using computed tomography (CT; Somatom DR3, Siemens, Erlangen, Germany) taken parallel to, and at 45 to 60 degrees to, Reid s baseline with 2 mm width/interval, and with the mandible in intercuspal position (mouth closed and mouth open). The morphology of the condyle was analyzed with the bone display mode (super-high resolution mode, window with 4094HU/window level 1 000HU). The basis for the diagnoses of the condylar bony changes were flattening, erosion, and deformity. Erosion was not found in the present study. Typical images of flattening and deformity are shown in Fig 3.

16 Lai et al Fig 1 Planes and landmarks in lateral cephalogram. The reference points nasion (N), porion (Po), and sella (S) were determined, and the Frankfort horizontal line through porion (Po) and orbitale (Or) was used as the x axis. A perpendicular line through sella was used as the y axis.the mandibular plane was defined as the line between gonion (Go) and menton (Me). Fig 2 (right) Planes and landmarks in frontal cephalogram. LOL = the line joining points Lo and Lo ; M = the line through C and perpendicular to LOL; Lo, Lo = the intersection of right and left orbital margins with the greater wing of the spheroid; C = the midpoint of Lo and Lo on LOL; Me = menton. a Fig 3 Typical images of condylar bony change in TMJ X-ray CT in axial section. Arrows show flattening (a) and deformity (b). Measurement error and statistical analysis Errors in landmark localization during tracing were evaluated by retracing each of the lateral and PA cephalograms. Means and standard deviations were calculated for the differences in measurement, landmark location, and tracing. The standard error for all measurements averaged 0.5 mm or 0.5 degrees. Descriptive statistics were calculated for continuous parameters for the following b time intervals: preoperatively to 1 week postoperatively (T1 to T2) and postoperatively to setting of retainer (T2 to T3). This was done for the total sample, as well as comparatively for condylar bony change versus no condylar bony change, and again comparatively for USSRO+IVRO versus BSSRO surgery type. The Mann-Whitney rank sum t test was performed to evaluate a possible significant difference between these different groups. Differences with a P value <.05 were regarded as significant.

Results Signs and symptoms of TMJ disorders Four (30.8%) of the 13 in the USSRO+ IVRO group, and 2 (20%) of the 10 in the BSSRO group had signs and symptoms of TMJ disorders before treatment, such as clicking and/or pain, which disappeared after treatment (Table 2). However, after treatment, 1 preoperatively asymptomatic patient in the USSRO+IVRO group developed TMJ clicking. Condylar bony change Seven (30.4%) of the 23 patients had unilateral condylar bony change (5 joints with deformity, 2 joints with flattening): 2 (20%) of the 10 in the BSSRO group and 5 (38.5%) of the 13 in the USSRO+IVRO group. All the patients exhibited a lateral shift of the menton toward the condylar bony change side (Table 2). Changes in frontal and lateral cephalometric measurements for the entire sample Surgical changes (T1 T2). The mean lateral and frontal changes of the measurements at different treatment times (T1, T2, and T3) are shown in Table 3. In the lateral cephalograms, the mean mandibular setback of point B was 5.43 mm. The mean SNB decreased from 82.64 degrees to 79.52 degrees during surgery. The mandibular plane rotated clockwise, as indicated by the mean 1.73 degree change. The mean changes in overbite and overjet were 2.71 mm and 5.61 mm, respectively. In the frontal cephalogram, the mean mandibular deviation decreased 4.37 mm after surgery. Postoperative changes (T2 T3). In the lateral cephalogram, the mean postoperative skeletal relapse in the SNB and SN- MeGo plane angles were 0.16 and 0.39 degrees, respectively.the mean postoperative relapse in overbite and overjet were 0.09 and 0.55 mm, respectively. The mean postoperative relapse in point B was 0.25 mm anteriorly. In the frontal cephalogram, the mean postoperative horizontal relapse in mandibular deviation was 0.04 mm. Int J Adult Orthod Orthognath Surg Vol. 17, No. 1, 2002 17 USSRO+IVRO versus BSSRO. The mean changes in measurements for the 2 subgroups (USSRO+IVRO versus BSSRO) in patients without condylar bony change are displayed in Table 4. They include 8 patients who had BSSRO, and 8 patients who had USSRO+IVRO. In the lateral cephalogram, the change in overjet during surgery was significantly larger in the BSSRO group than that of the USSRO+IVRO group. In the frontal cephalogram, although there was no (calculation revealed) statistically significant difference in change in menton deviation between both groups, this deviation was nevertheless larger in the USSRO+ IVRO group than that of the BSSRO group during surgery. Concerning the postoperative changes in the lateral and frontal cephalograms, there were no significant differences between the USSRO+IVRO and BSSRO groups, and mandibular position was stable anteroposteriorly (or horizontally) in both groups. Bony change versus no bony change. The mean changes for the 2 subgroups, as determined by the presence or absence of condylar bony change in the USSRO+IVRO group, are displayed in Table 5. Comparing the lateral cephalograms of the condylar versus no condylar bony change groups, there was no significant difference in lateral displacement of the mandible during surgery, nor in postoperative relapse. In the measurement of the frontal cephalograms, although there were no statistically significant differences during surgery between these condylar bony change and no condylar bony change groups, the postoperative relapse in mandibular deviation was significantly larger in the condylar bony change group than that of the no condylar bony change group. Discussion USSRO+IVRO and BSSRO with miniplates The results indicated skeletal stability for both BSSRO and USSRO+IVRO. Concerning the comparison of surgical method in patients with mandibular protrusion and no condylar bony change, postoperative anterior relapse of point B and overjet were

18 Lai et al Table 2 Data summary for the 23 patients Difference of Condylar bony change Surgical method TMJ sounds TMJ pain Mandibular mandibular Patient No. Gender Age (y) deviation side Right side Left side setback (mm) IMF* (d) Right side Left side Preop Postop Preop Postop 1 Male 32 Right Flattening No 10.0 20 IVRO SSRO + 2 Male 17 Right No No 8.0 22 SSRO IVRO 3 Female 17 Right No No 4.0 11 SSRO SSRO 4 Male 19 Right No No 7.0 21 IVRO SSRO + 5 Female 18 Right No No 2.0 20 SSRO SSRO 6 Female 19 Left No No 3.0 21 SSRO SSRO 7 Male 21 Left No No 8.0 21 SSRO SSRO + 8 Female 17 Left No No 3.0 21 SSRO SSRO 9 Female 18 Left No No 8.0 28 SSRO IVRO 10 Female 21 Right Deformity No 7.0 14 SSRO IVRO + 11 Female 26 Right No No 5.5 20 SSRO SSRO 12 Female 28 Left No Deformity 4.5 18 SSRO SSRO 13 Male 27 Right Deformity No 2.0 14 SSRO SSRO + + 14 Female 17 Right Deformity No 6.0 20 IVRO SSRO 15 Male 22 Right No No 1.5 14 SSRO SSRO 16 Female 22 Right Flattening No 9.0 22 IVRO SSRO 17 Female 20 Left No No 4.5 22 SSRO IVRO 18 Female 17 Left No Deformity 6.0 18 SSRO IVRO 19 Female 20 Left No No 6.0 21 IVRO SSRO 20 Female 17 Left No No 6.5 22 SSRO IVRO 21 Male 17 Left No No 7.0 14 SSRO SSRO 22 Female 18 Left No No 4.5 21 SSRO IVRO + 23 Male 30 Left No No 6.0 22 SSRO IVRO + *IMF = intermaxillary fixation.

Table 3 Values (mean ± SD) for the whole sample (n = 23) Int J Adult Orthod Orthognath Surg Vol. 17, No. 1, 2002 19 Beginning Surgical Postoperative Preoperative Postoperative of retention changes changes (T1) (T2) (T3) (T2 T1) (T3 T2) Lateral cephalogram SNB (deg) 82.64 ± 4.04 79.52 ± 3.95 79.68 ± 3.81 3.11 ±1.80 0.16 ± 1.11 SN-MeGo (deg) 38.30 ± 6.37 40.02 ± 6.10 40.41 ± 5.84 1.73 ± 2.00 0.39 ± 1.56 Overbite (mm) 0.27 ± 1.37 2.43 ± 0.93 2.34 ± 0.84 2.71 ± 1.45 0.09 ± 1.10 Overjet (mm) 1.73 ± 3.05 3.89 ± 0.83 3.34 ± 0.73 5.61 ± 3.06 0.55 ± 0.65 Posterior 5.43 ± 3.38 0.25 ± 1.80 mandibular movement Frontal cephalogram Mandibular 8.09 ± 3.31 3.72 ± 2.75 3.67 ± 2.19 4.37 ± 1.96 0.04 ± 1.75 deviation (mm) Table 4 Comparison of surgical and postoperative changes in cephalometric measurements in patients without condylar bony change: USSRO + IVRO (n = 8) vs BSSRO (n = 5) Surgical change (T2 T1) Postoperative change (T3 T2) USSRO + IVRO BSSRO P USSRO + IVRO BSSRO P Lateral cephalogram SNB (deg) 2.94± 1.27 4.3 ± 1.79 NS 0.44 ± 0.86 0.44 ± 0.50 NS SN-MeGo (deg) 1.88 ± 2.10 1.50 ± 1.17 NS 0.19 ± 1.56 0.13 ± 1.25 NS Overbite (mm) 2.63 ± 1.19 3.06 ± 1.74 NS 0.19 ± 0.75 0.25 ± 0.93 NS Overjet (mm) 5.06 ± 2.13 7.88 ± 2.80 * 0.69 ± 0.59 0.56 ± 0.56 NS Posterior mandibular 5.75 ± 1.95 6.44 ± 4.73 NS 0.56 ± 1.43 0.94 ± 1.05 NS movement Frontal cephalogram Mandibular 5.00 ± 2.05 3.13 ± 1.55 NS 0.44 ± 0.98 0.75 ± 2.12 NS deviation (mm) *P <.05.

20 Lai et al Table 5 Comparison of surgical and postoperative changes in cephalometric measurements in patients with USSRO + IVRO: No condylar bony change (n = 8) vs condylar bony change (n = 5) Surgical change (T2 T1) 0.56 mm (9.7%) and 0.69 mm (13.6%), respectively, in patients with USSRO and IVRO, and 0.94 mm (14.6%) and 0.56 mm (7.1%), respectively, in patients with BSSRO. These findings were similar to previous papers on bilateral IVRO 15 and BSSRO 16 in patients with mandibular protrusion. Kobayashi 16 suggested that significant anterior relapse potential might exist when the amount of correction exceeded 10 mm in BSSRO with miniplates. Since in our department, orthognathic patients who need over 10 mm mandibular setback receive both maxilla and mandibular (ie, bimaxillary) surgery (which therefore excluded them from this study), and the mean mandibular setback in the present study was only 5.23 mm (range 3.0 to 8.5 mm) due to only mandibular surgery being performed, our ratio of anterior postoperative relapse might be relatively low. As for the horizontal postoperative relapse in patients with mandibular protrusion and deviation, there was a possibility of a horizontal relapse of the mandible, not only due to the difference of right and left setback, but also due to the mediolateral displacement in the posterior margin of the distal bone segment when the mandibular dentition was rotated to correct its deviation. In the present study, the Postoperative change (T3 T2) No condylar Condylar No condylar Condylar bony change bony change P bony change bony change P Lateral cephalogram SNB (deg) 2.91± 1.27 2.10 ± 1.39 NS 0.44 ± 0.86 0.10 ± 0.22 NS SN-MeGo (deg) 1.88 ± 2.10 2.20 ± 3.11 NS 0.19 ± 1.56 0.40 ± 1.52 NS Overbite (mm) 2.63 ± 1.19 2.10 ± 1.52 NS 0.19 ± 0.75 0.10 ± 1.64 NS Overjet (mm) 5.06 ± 2.13 3.50 ± 2.92 NS 0.69 ± 0.59 0.30 ± 0.98 NS Posterior mandibular 5.75 ± 1.95 4.10 ± 2.41 NS 0.56 ± 1.43 0.10 ± 0.65 NS movement Frontal cephalogram Mandibular 5.00 ± 2.05 5.60 ± 1.82 NS 0.44 ± 0.98 1.30 ± 1.72 * deviation (mm) *P <.05. ratio of horizontal postoperative relapse was low (0.9%, 0.04 mm) in all subjects. Comparing the surgical method in patients without condylar bony change, in the USSRO+IVRO, in spite of the significantly large horizontal movement at surgery compared to that in the BSSRO, postoperative horizontal movement did not show a relapse. These results suggest that USSRO+IVRO is effective in correcting mandibular deviation, due to its avoiding a mediolateral displacement of the distal bone segment. Mediolateral displacement of the mandibular segment at surgery might give rise to a rotational axial movement of the distal bone segment, with the rotational axis at the posterior molar area on the deviated side. When SSRO is done on the rotational movement side (ie, the deviated side), the proximal bone segment is pushed aside by the posterior border of the displaced distal bone segment, which may lead to a postoperative mandibular relapse and TMJ dysfunction upon the fixation of the proximal and distal bone segments. Therefore, in patients with severe mandibular deviation, IVRO is done on the rotational axial side (ie, the deviated side) and SSRO with miniplate is done on the nondeviated side.

Condylar bony change and relapse Int J Adult Orthod Orthognath Surg Vol. 17, No. 1, 2002 21 There have been a few reports on the relationship between condylar bony change and mandibular deviation, 8 10 which suggested that condylar bony change might be responsible for the mandibular deviation. The present study also showed that condylar bony change was seen on the deviated side, which was consistent with the above reports. As for the condylar bony change after IVRO in patients with mandibular deviation, some researchers have reported a double contour line in the posterior-superior part of the condyle. 11,17 They interpreted this bony change as a sign of adjustment to the new functional situation. Bell and Yamaguchi 18 reported that the condyle was consistently positioned anteriorly and inferiorly just after IVRO, but after that the condyle tended to return to its preoperative position. The condyle seems to possess great adaptability to positional changes of the mandible after IVRO. Long-term occlusal and functional stability are contingent on such adaptive changes. 18 The findings of the present study showed that there were no significant differences in anterior relapse between the condylar bony change and the no condylar bony change groups in patients with USSRO+IVRO, and the ratios of postoperative anterior relapse in both these groups were low. On the other hand, although there was a significant difference of the postoperative horizontal relapse between the 2 groups, the amount of this relapse in the condylar bony change group was still quite low (1.30 mm, 23.2%). This low relapse might be due to the occurrence of functional remodeling in the condyle after surgery, in response to the repositioning of the mandible. However, since the standard deviation for this relapse in the condylar bony change group was large, this relapse indicated a difference in adaptive capacity in this group. Since it has been reported that condylar bony change in adult patients with mandibular deviation is usually toward stability 9,10 and the condylar bony change found in the present study also showed stability (creating conditions such as flattening and deformity), the postoperative mandibular position is stable in adult orthognathic surgery patients with unilateral condylar bony change. However, there is a possibility that stable condylar bony change could transform into unstable condylar bony change, such as erosion, after surgery. Future studies with a greater number of subjects will be needed to investigate the postoperative condylar bony change and postoperative mandibular stability. Signs and symptoms of TMJ disorders Signs and symptoms of TMJ disorders have been used as parameters to assess the influence of surgical changes on function after orthognathic surgery. 16,19 21 Yamada et al 22 reported a high incidence of signs and symptoms of TMJ disorders in patients with mandibular deviation (55.6% TMJ sounds, 33.3% TMJ pain, 14.8% difficulty of mouth opening). In the present study, the ratio of signs and symptoms of TMJ disorders at first visit was 26.1% (30.8% in the USSRO+IVRO group and 20% in the BSSRO group), which was lower than the previous report of Yamada et al. 22 This difference might be due to patient selection, because the subjects in this study included only those cases in which mandibular surgery was done (not bimaxillary surgery, which is applied to patients with a large deviation and setback). After surgery, signs and symptoms of TMJ disorders from all patients from both groups disappeared. Only 1 preoperatively asymptomatic patient in the USSRO+IVRO group developed TMJ clicking after surgery. Similar results, ie, improvement in signs and symptoms of TMJ disorders, have been reported in mandibular protrusion patients with BSSRO using miniplates, 16,19 21 bilateral IVRO, 23 26 and USSRO+IVRO. 6 These results suggest that both USSRO+IVRO and BSSRO are effective in improving signs and symptoms of TMJ disorders. Concerning the disc position after IVRO, there has been debate about the position of the articular disc after surgery; namely, whether it is recaptured (normal position) 27 or not (displaced position). 11 Regardless of disc position, however, the

22 Lai et al postoperative disappearance of signs and symptoms of TMJ disorders has been reported. 11,23,25,26 Bell et al 25 reported that the success of this procedure was contingent on producing a more functional articular disc-condylar relationship in consequence of the anteroinferiorly repositioned condylar segment. Based on these findings, a critically contributing factor for improving signs and symptoms of TMJ disorders seems to establish a widely spread joint space. References 1. Kawamura H, Nagasawa H, Sato S, Motegi K, Sugawara J, Mitani H. Sagittal split ramus osteotomy combined with titanium mini-plate internal fixation. Jpn J Jaw Deform 1991;1:105 112. 2. McL Davis Jr W. A method to facilitate placement of screws for sagittal ramus osteotomy. Oral Surg Oral Med Oral Pathol 1987;64:536 538. 3. Nwoku AL, Palomero-Rodriguez R, Horch HH. The problems of correction of asymmetric mandibular prognathism. Int J Oral Surg 1974;3:229 233. 4. Hall DH. 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