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Changes in the temporomandibular joint after mandibular setback surgery in monkeys: intraoral vertical versus sagittal split ramus osteotomy
Changes in the temporomandibular joint after mandibular setback surgery in monkeys: intraoral vertical versus sagittal split ramus osteotomy Qiang Zhao, DDS, MS,a Jing Hu, DDS, PhD,b Dazhang Wang, DDS,b and Songsong Zhu, DDS,a Chengdu, Sichuan SICHUAN UNIVERSITY
Objective. This study was to investigate the changes in condylar position and structure of the temporomandibular joint (TMJ) after mandibular setback using 2 forms of the ramus osteotomy. Study design. Twelve adult male rhesus monkeys were randomly divided into groups A (n ⫽ 6) and B (n ⫽ 6) for mandibular setback surgical procedure. An intraoral vertical ramus osteotomy (IVRO) was performed in group A, whereas a sagittal split ramus osteotomy (SSRO) was performed in group B. Changes in condylar position were quantified by computed tomography (CT) preoperatively and postoperatively. All animals in groups A and B were killed at 12 weeks after surgical procedure. The TMJ specimens were harvested and processed for histological examination. Results. In group A, the CT examinations showed a significant anteroinferior displacement of the condyle after surgical procedure. In group B, slight posterior displacement and lateral tilting of the condyle were noted after surgical procedure. Thickened cartilage layer and endochondral ossification were seen in the condyles of group A, but only minimal alteration in articular cartilage was found in group B. Conclusions. Both SSRO and IVRO can be biologically sound procedures for correction of mandibular prognathism. Intraoral vertical ramus osteotomy procedure leads to condylar adaptive remodeling, which may have favorable effects on TMJ, and it could be considered as a preferred surgical treatment for those patients with preoperative TMJ disorders. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:329-37)
The intraoral vertical ramus osteotomy (IVRO) and sagittal split ramus osteotomy (SSRO) are the main surgical procedures used to correct mandibular excess. Although IVRO is a faster, easier, and arguably stable procedure for the treatment of mandibular prognathism, SSRO has been performed more often because of the ability to apply rigid fixation. In the correction of mandibular excess, SSRO has several more advantages than IVRO, including better bony interface between the segments, easier use of rigid fixation, and quicker recovery of oral function. However, in addition to a much lower incidence of neurologic injury, IVRO1,2 or modified condylotomy 3 has been reported to be favorable to the temporomandibular joint (TMJ) because of anterior-inferior repositioning This research was supported by a grant from Trans-Century Training Program Foundation for the Talents, Ministry of Education of China (grant no. 2002-48 to J.H.). a Research Fellow, Key Laboratory of Biomedical Engineering, Sichuan University, Chengdu, China. b Professor, Department of Oral and Maxillofacial Surgery, West China College of Stomatology, Sichuan University, Chengdu, China. Received for publication Oct 15, 2006; returned for revision Dec 10, 2006; accepted for publication Dec 29, 2006. 1079-2104/$ - see front matter © 2007 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2006.12.024
of the condyle and the increase of the joint space, with a chance of improved symptoms of the joint. Conversely, in SSRO rigid fixation of the mandible may create a greater change in the position of the condyle and a higher incidence of TMJ dysfunction compared with nonrigid fixation.4,5 Although the advantages and disadvantages of these 2 techniques have been frequently discussed, there are still controversy over which is the preferred treatment for mandibular prognathism.6,7 There are some skeletal class III malocclusion patients who have preoperative TMJ symptoms, which also remains a problem during selection of surgical procedure for setback of their mandible. A number of clinical investigations have reported the influences of various surgical techniques on the TMJ8-11; however, no animal study about the differences in TMJ changes after IVRO and SSRO for mandibular setback exists. The purpose of this study was to observe the changes in condylar position and the histology of TMJ by using different mandibular ramus osteotomies through a primate model. MATERIAL AND METHODS Animals Twelve adult male rhesus monkeys weighing 8 to 10 kg were randomly divided into group A (n ⫽ 6) and group B (n ⫽ 6). The animal care was in accordance 329
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Fig. 1. Photographs of surgical procedures. A, Intraoral vertical ramus osteotomy (IVRO). The condylar segment was placed laterally to the distal segment. B, Sagittal split ramus osteotomy (SSRO). The miniplate with monocortical fixation was performed. C, The custom-made interocclusal wafer. D, Intermaxillary fixation was carried out by wire fixation.
with the guidelines of the Animal Center for Medical Experiments at Sichuan University. All monkeys were kept indoors under the supervision of the veterinarian staff. Presurgical protocol Similar to the method described by Ellis and colleagues12,13 the upper and lower anterior teeth (including the canines) were extracted under anesthesia 4 weeks before surgical procedure. This was necessary to facilitate setback of the mandible and feed during a period of intermaxillary fixation (IMF). The upper and lower dental impressions were taken after extraction of the teeth. The dental models were prepared and articulated. Model surgical procedure was done to create a mandibular setback of 2 molar cusps (approximately 5-6 mm). Then, an acrylic interocclusal splint was fabricated for locking the remaining teeth into the new position.
Surgical procedures The monkeys were premedicated with ketamine hydrochloride (10 mg/kg intramuscularly), an oroendotracheal intubation was performed, and they were anesthetized with pentobarbital sodium intravenously. In this animal study, IVRO was performed according to the technique of Bell and colleagues.1,2 Sagittal split ramus osteotomy was similar to the method described by Lupori et al.14 Both surgical procedures were done intraorally in all monkeys. In group A, bilateral vertical ramus osteotomies for mandibular setback were performed using an oscillating saw in 6 monkeys (Fig. 1, A). After setback of the mandible, a splint was used, and IMF was carried out with stainless steel wires (Fig. 1, C, D). The IMF was released at the sixth week after surgical procedure. During the period of IMF, the monkeys continually attempted to remove the fixed wires; we often trimmed their fingernails and tightened the wires. The IMF was
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found to be loose in 4 animals at 3 weeks after surgical procedure, but repeat fixation of wiring the jaws together was never required. In group B, bilateral sagittal split ramus osteotomies were performed in 6 animals. After separation of the proximal and distal segments, the mandible was moved backward and placed in the planned occlusion by using the interocclusal wafer. The ramus had the proximal and distal segments fixed with a miniplate and 4 titanium screws (2 mm in diameter and 6 mm in length) for monocortical osteosynthesis (Fig. 1, B). Intermaxillary fixation was applied for only 1 week after surgical procedure. A senior surgeon (J.H.) performed all surgical procedures, with the same surgical instruments, on the monkeys. The monkeys received 1 600 000 units of penicillin daily for 7 days after surgical procedure. In the period of IMF in both groups, the animals were given the same mash diet through the anterior dental gap that resulted from the extraction of upper and lower anterior teeth before surgical procedure. The animals in groups A and B were supplied this soft food for another 3 weeks after the release of the IMF and then were given the normal diet. Radiographic examinations Under general anesthesia, computed tomography (Somatom; Sensation 4, Siemens Medical Solutions, Erlangen, Germany) was used for assessment of each pair of TMJs, with images taken of axial slices at every 1.0 mm. The teeth of the animals were kept in occlusion during CT examination. Three-dimensional CT scanning films were taken under standardized conditions preoperatively and at 12 weeks postoperatively. Images of midcondylar slices of the sagittal and coronal plane scanning were acquired for assessment of changes in the position of the condyles. In the sagittal images, some reference points and lines were selected to evaluate the position of condyle (Fig. 2). The measurements used in this study were the distance A-C and P-D; the mean of the right and left sides was recorded for statistical analysis. The reference points on the CT scan were digitized with Syngo software (Somaris Medical Solutions, Forchheim, Germany). The accuracy was set at 0.1 mm for the liner measurements. The angle (␣) between the condylar long axis and the Frankfort horizontal plane was measured in the coronal images for evaluation of tilting of the condyle (Fig. 3). The accuracy was set at 0.1° for the angular measurement. Each parameter was read 3 times, and the mean was calculated for the statistical evaluations. The difference in preoperative and postoperative measurements was statistically assessed by the Student t test.
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Fig. 2. Reference points and lines at occlusion in the sagittal scan images. P, the inferior point of postglenoid spine; T, the inferior point of tuberculum; x-axis, P-T line; D, intersection between posterior condyle and x-axis; A, most cranial point on curvature of glenoid fossa; y-axis, a line was drawn from point A perpendicular to x-axis; C, intersection between the superior curvature of condyle and y-axis.
Fig. 3. The angle (␣) between the condylar long axis and the Frankfort horizontal plane was measured in the coronal scan images.
Histological examination All monkeys in group A and B had CT examinations at 12 weeks after surgical procedure, and then they were killed with overdose of pentobarbital. The jaw was in occlusion when the animal was killed. The common carotid arteries were perfused with a mixture
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Fig. 4. Postoperative three-dimensional reconstruction films. A, Twelve weeks after IVRO. Note minor bone resorption in the tip of proximal segment (arrow), and minimal open bite occurring. B, Twelve weeks after SSRO.
of 4% paraformaldehyde and 0.5% glutaraldehyde in phosphate buffer at pH 7.4. Both sides of the TMJ were harvested en bloc. The specimens were fixed in 10% neutral buffered formalin for an additional 2 days and then decalcified in 0.5 mol/L ethylene-diamine-tetraacetic-acid. Each condyle was divided sagittally into 3 blocks (lateral, middle, and medial thirds) and embedded in paraffin. Five sagittal sections (5-m thickness) were obtained from each block and stained with hematoxylin and eosin for examination under light microscopy. Two additional nonoperated monkeys having similar age and weight were used as controls. The control animals were treated with similar diet, and their condyles were harvested and prepared in the same manner. In each condyle, 1 of the 5 sagittal sections per block (lateral, middle, and medial) was chosen at random and examined on the anterior, superior, and posterior aspects. In addition to general histological observation, a histomorphometric analysis was performed on these sections to measure the thickness in the fibrous and cartilage layers by a computer system with image analyzing software Image-Pro Plus, version 4.5 (Media Cybernetics, Inc., Silver Spring, Md). The mean thicknesses were obtained from group A (IVRO), group B (SSRO), and control animals. For statistical analysis, data from each group were averaged and compared statistically using the Student t test. The differences were considered significant at P values less than .05. RESULTS All animals tolerated the operative procedures well. There were no wound infections. In the SSRO group, all monkeys showed an obvious retruded lower jaw and good stability in occlusion during the whole experimen-
tal period. In the IVRO group, anterior open bite (3-4 mm) was seen in all 6 monkeys at release time of IMF. It disappeared in 4 animals at 12 weeks after surgical procedure, but minimal open bite still existed in the other 2 monkeys. In the three-dimensional reconstruction films, bony osteosynthesis between the proximal and distal segments was observed in both groups. However, in group A some signs of bone resorption were seen in the tip of the proximal segment of 3 monkeys (Fig. 4). At killing, the TMJ specimens had intact condylar and fossa morphology. There were no gross differences in the shape and appearance of the TMJs between group A and group B. Radiographic analysis The changes in condylar position after IVRO (group A) and SSRO (group B) are shown in Table I. In the sagittal images, the measurements for A-C and P-D in group A were found to be increased (P ⬍ .05) after setback of the mandible, which means the condyles were displaced anteroinferiorly after IVRO. In group B, there was no significant difference in the measurements for A-C and P-D before and after surgical procedure (P ⬎ .05), which means the condyle was not displaced significantly in the sagittal plane after SSRO (Fig. 5). In the coronal images, the angle (␣) between the condylar long axis and the Frankfort horizontal plane was decreased in group A and increased in group B after surgical procedure. Although this angle did not show significant difference before and after surgical procedure in both groups (P ⬎ .05), the condyle was rotated somewhat clockwise (medial tilting) to the preoperative position in the IVRO monkeys, and somewhat counter-
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Table I. Average changes in the condylar position before and after intraoral vertical ramus osteotomy and sagittal split ramus osteotomy A-C (mm)
Preoperatively Postoperative week 12
␣ (degree)
P-D (mm)
IVRO
SSRO
IVRO
SSRO
IVRO
SSRO
1.6 ⫾ 0.3 2.6 ⫾ 0.5
1.7 ⫾ 0.3 1.6 ⫾ 0.4
2.8 ⫾ 0.8 3.6 ⫾ 0.8
2.7 ⫾ 0.7 2.4 ⫾ 0.7
8.3 ⫾ 2.0 7.9 ⫾ 2.0
8.2 ⫾ 1.8 8.4 ⫾ 1.9
All values are mean ⫾ SD. IVRO, intraoral vertical ramus osteotomy; SSRO, sagittal split ramus osteotomy.
Fig. 5. In the sagittal images, anteroinferior displacement of the condyle was obvious after IVRO, and the change in the position of the condyle was not evident after SSRO. A, Before IVRO. B, After IVRO. C, Before SSRO. D, After SSRO.
clockwise (lateral tilting) to the preoperative position in the SSRO animals (Fig. 6). Histological findings Histological changes in TMJs after IVRO and SSRO are shown in Fig. 7. Data regarding the mean thickness of fibrous and cartilage layers are shown in Table II. In group A, the fibrous layer of the condyle was somewhat thinner than that in the control specimens (P ⬎ .05).
The cartilage layer showed a significant increase in thickness over that in the control specimens (P ⬍ .05). Furthermore, hypertrophic chondrocytes and active osteoblasts in the area of the cartilage/bone interface were remarkable. New bone deposition (endochondral ossification) in the region underneath the cartilage layer was also observed. The posterosuperior aspect of the condyle was more involved within these adaptive changes. In group B specimens, although a decreasing
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Fig. 6. In the coronal images, slight medial and lateral tilting of the condyles to the preoperative position were noted in the IVRO and the SSRO monkeys. A, Before IVRO. B, After IVRO. C, Before SSRO. D, After SSRO.
trend in fibrous layer and an increasing trend in cartilage layers were found after SSRO, the differences did not reach statistical significance when compared with the control specimens (P ⬎ .05). New bone formation was not obvious in the region underneath the cartilage layer. In addition, the mean thickness of the cartilage layer was 244 m for the IVRO group and 195 m for the SSRO group. This difference was statistically significant (P ⬍ .05). DISCUSSION Orthognathic surgery, especially mandibular ramus osteotomies, may cause changes of condylar position and produce beneficial or adverse effects on TMJ. The changes in the position of the condyle TMJ after vertical ramus osteotomy and sagittal split ramus osteotomy have been described in several clinical investigations.2,8,9,13 The earliest reports of changes in condylar position were noted after oblique or vertical ramus osteotomy. In 1974, Hollender and Ridell,15 in a radio-
graphic study of 36 joints subjected to oblique ramus osteotomies, found a distinct double contour in the posterior part of the condylar head of 30 joints with anterior and inferior displacement of the condyle. Similar results were observed by subsequent studies.16-20 Using a three-dimensional CT superimposition technique, Kawamata et al.21 evaluated postoperative condylar displacement in orthognathic patients and found that in SSRO patients, lateral tilting was predominant, and in IVRO patients, medial tilting was predominant. In the current study, anteroinferior displacement and lateral tilting of the condyles were observed after vertical ramus osteotomy in monkeys. This finding is consistent with previous clinical investigations. In addition to the possible effect of intracapsular edema and manipulation of the fragments, condylar sag (anteroinferior movement of the condyle) and the medial tilting of the condyle might be expected from the direction of pull of the lateral pterygoid muscle and the pterygomasseteric sling to the proximal segment.
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Fig. 7. Histological photomicrographs of the condyles. A, Normal control condyle (hematoxylin-eosin, original magnification ⫻40). B, A condyle in group A demonstrating adaptive remodeling in the temporomandibular joint. Note the thickened cartilage layer and hyperplastic chondrocytes with new bone formation in the zone of the cartilage/bone interface (hematoxylin-eosin, original magnification ⫻100). C, A condyle in group B. Although minor adaptive remodeling was seen, overall the characteristics of the photomicrograph resemble the histological characteristics of the normal control (hematoxylin-eosin, original magnification ⫻100).
Table II. The measurement for thickness of fibrous and cartilage layers in the condyles
Fibrous layer (m) Cartilage layer (m)
Control (n ⫽ 4)
Group A (n ⫽ 12)
Group B (n ⫽ 12)
65.8 ⫾ 20.6
50.9 ⫾ 18.0
59.0 ⫾ 21.5
173.3 ⫾ 32.6
243.7 ⫾ 60.5
194.7 ⫾ 50.3
All values are mean ⫾ SD.
The adaptive changes in TMJ as a result of condylar displacement have been discussed in the previous studies.14,21,22 A double contour of the condylar head or the glenoid fossa was the specific radiographic finding, indicating remodeling activity. However, it was difficult to provide the direct evidence by radiographic analysis to demonstrate postoperative remodeling of the TMJ. Based on histological examination, our ani-
mal study showed that the condylar displacement after IVRO was associated with histological changes in the articular cartilage and bone structure. An increase in the cartilage thickness and obvious endochondral ossification were found in the area of the cartilage/bone interface. The anteroinferior condylar displacement may induce fibrocartilage to enter an activated state. The proliferation of chondrocytes and osteoblasts in the condyle is indicative of adaptive remodeling, which may help the TMJ to finally adjust to an altered biomechanical environment and not cause a significant change in occlusion. Temporomandibular joint symptoms and internal derangement are commonly found in patients with dentofacial deformities. In a majority of those patients, the improvement or resolution of joint symptoms following orthognathic surgical procedure, especially in IVRO, has been observed. The exact mechanism for improvement of TMJ symptoms after IVRO is still unclear. An
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explanation for this outcome is based on the hypothesis that the disk-condyle relationship will be altered favorably by anterior and inferior condylar movement.1,2 A slight condylar displacement subsequent to IVRO may allow repositioning of the condyle to a more functional position within the joint and resolve symptoms in the patients with TMJ dysfunction.10 In 1995, Werther et al.3 reported that the articular disk was reduced using modified condylotomy in 79% of disk displacement joints. The author emphasized the differences between standard IVRO and the modified condylotomy. The latter, although a modification of the IVRO, is really an indirect arthroplasty designed to increase joint space for disk reduction and does not alter the occlusion. Condylar sag is the objective in modified condylotomy. In the present study, anterior open bite was found in all 6 monkeys at IMF release after IVRO, which may be related to the “condylar sag” following the IVRO procedure. It is noteworthy that the open bite did not exist in 4 animals at 12 weeks after surgical procedure; the other 2 monkeys still had minimal open bite. With time relapse, the gradual remodeling in TMJ morphology could have contributed to the disappearance of open bite. On the other hand, anterior vertical elastic is advisable to maintain the ideal occlusion after release of maxillomandibular fixation. Furthermore, the modified condylotomy as described by Werther et al.3 may be a better approach for patients with preoperative TMJ symptoms and internal derangement. There are inconsistent data about the change in the position of the condyle after SSRO. Freihofer and Petresevic,23 in a radiographic analysis of 38 patients who had SSRO for mandibular advancement, found 10 of 26 condyles were positioned anteriorly in the glenoid fossa. Will et al.24 found both condyles to be positioned superiorly, and the left condyle also moved posteriorly in the patients who received SSRO. Using CT, Harris et al.25 found the condyles were displaced medially, posteriorly, superiorly, and angled medially after mandibular advancement with SSRO. For mandibular setback procedure by SSRO, Lee and Park,26 in a threedimensional CT evaluation of the condylar position in 30 Korean patients who underwent SSRO for mandibular setback, found the condyle tends to move inferiorly and rotate inward on the axial view and backward on the sagittal view. Our previous study19 also showed that a posterior displacement of the condyle after mandibular setback using SSRO. Ueki et al.20 completed a study that evaluated condylar and TMJ disk positions after SSRO and IVRO for mandibular setback. Their results suggest that SSRO does not improve anterior disk displacement, IVRO improves anterior disk displacement in the initial postoperative period, and both procedures may improve TMJ symptoms.
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The aforementioned variations in the condylar position after SSRO could be attributable to the differences in race, skeletal morphology (Class II or III), and evaluation method used. The use of rigid fixation in SSRO may be another important factor that produces the displacement of the condyle. Ellis and Hinton,13 in an animal study for mandibular advancement using SSRO, found the monkeys who underwent IMF showed a tendency for anterior movement of the condyle; the monkeys that underwent rigid fixation (bicortical osteosynthesis) showed a tendency for posterior condylar position. At 6 weeks after surgical procedure, the animals that had posterior displacement of the condyles showed evidence of resorption of the posterior surface of the condyles. Kundert and Hadjjanghelou,27 in a clinic investigation, found that SSRO with rigid fixation caused an increase in condylar displacement compared with IMF procedure. Freihofer and Petresevic23 reported an increase in postoperative joint clicking in a study of 38 patients who underwent SSRO with rigid fixation. However, some other studies comparing these 2 fixation methods do not support the aforementioned conclusions.5,8,24 In this animal study, SSRO with monocortical screw fixation was performed in 6 monkeys. A slight posterior displacement and lateral tilting of the condyle (no significant statistical difference to preoperative) was noted after setback procedure. Simultaneously, only minimal adaptive remodeling in the condyle was observed. It suggested that SSRO with monocortical osteosynthesis procedures did not cause a distinct displacement of the condyle and exert an adverse effect on the TMJ. Rigid fixation may lead to condylar displacement because the fixation with lag screws tends to eliminate the gaps between the proximal and the distal segments, which are normally generated with mandibular movement in any direction. However, Hackney et al.8 and Spitzer et al.28 suggest that the use of screw fixation seems to cause no major malposition of the condyle and does not change intercondylar angle or intercondylar width. Therefore, if a fixation using simple positional screws is examined carefully, significant medial or lateral condylar displacement can be prevented. Furthermore, the TMJ has an adaptive capacity to adjust to the altered position of the condyle. Slight movement of the condyle (within physiological limit) after mandibular osteotomies can induce an adaptive remodeling in the condyle and the glenoid fossa, which may not only prevent the occurrence of TMJ disorders, but also the occurrence of postoperative malocclusion. Mandibular ramus osteotomies may lead to changes in condylar position and cause TMJ dysfunction to develop. However, the variations in direction and magnitude of condylar displacement may have different
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effects on the TMJ. For example, anterior displacement of condyle could be more beneficial than the opposite situation. In the current study, the monkey that underwent IVRO with IMF showed an anteroinferior displacement of the condyle, which induces a significant adaptive remodeling in the TMJ; the animals that received SSRO with rigid fixation showed no obvious positional and histological changes in the condyle. This experimental study suggested that both SSRO and IVRO can be biologically sound procedures for correction of mandibular prognathism, but IVRO could be considered as a preferred surgical treatment for those patients with preoperative TMJ disorders. REFERENCES 1. Bell WH, Yamaguchi Y, Poor MR. Treatment of temporomandibular joint dysfunction by intraoral vertical ramus osteotomy. Int J Adult Orthod Orthognath Surg 1990;5:9-27. 2. Bell WH, Yamaguchi Y. Condyle position and mobility before and after intraoral vertical ramus osteotomies and neuromuscular rehabilitation. Int J Adult Orthod Orthognath Surg 1991;6:97-104. 3. Werther JR, Hall HD, Gibbs SJ. Disk position before and after modified condylotomy in 80 symptomatic temporomandibular joints. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:668-79. 4. Paulus GW, Steinhauser EW. A comparative study of wire osteosynthesis versus bone screws in the treatment of mandibular prognathism. Oral Surg 1982;54:2-6. 5. Timmis DP, Aragon SB, Van Sickels JE. Masticatory dysfunction with rigid and nonrigid osteosynthesis of sagittal split osteotomies. Oral Surg 1986;62:119-23. 6. Ghali GE, Sikes JW Jr. Intraoral vertical ramus osteotomy as the preferred treatment for mandibular prognathism. J Oral Maxillofac Surg 2000;58:313-5. 7. Wolford LM. The sagittal split ramus osteotomy as the preferred treatment for mandibular prognathism. J Oral Maxillofac Surg 2000;58:310-2. 8. Hackney FL, Van Sickels JE, Nummikoski PV. Condylar displacement and temporomandibular joint dysfunction following bilateral sagittal split osteotomy and rigid fixation. J Oral Maxillofac Surg 1989;47:223-7. 9. Feinerman DM, Piecuch JF. Long-term effects of orthognathic surgery on the temporomandibular joint: comparison of rigid and nonrigid fixation methods. Int J Oral Maxillofac Surg 1995;24:268-72. 10. Ueki K, Marukawa K, Nakagawa K, Yamamoto E. Condylar and temporomandibular joint disc positions after mandibular osteotomy for prognathism. J Oral Maxillofacial Surg 2002;60: 1424-32. 11. Kerstens HCJ, Tuinzing DB, vander Kwast WAM. Temporomandibular joint symptoms in orthognathic surgery. J Craniomaxillofac Surg 1989;17:215-8. 12. Ellis E III, Reynolds S, Carlson DS. Stability of the mandible following advancement: a comparison of three postsurgical fixation techniques. Am J Orthod Dentofac Orthop 1988;94:38-49. 13. Ellis E III, Hinton RJ. Histologic examination of the temporomandibular joint after mandibular advancement with and without
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rigid fixation: an experimental investigation in adult Macaca mulatta. J Oral Maxillofac Surg 1991;49:1316-27. Lupori JP, Kewitt GF, Van Sickels JE. Bilateral sagittal split osteotomy advancement and setback. In: Fonseca R, editor. Oral and maxillofacial surgery. Philadelphia: Saunders; 1999. p. 297-303. Hollender L, Ridell A. Radiography of the temporomandibular joint after oblique sliding osteotomy of the mandibular rami. Scand J Dent Res 1974;82:466-9. Wisth PJ, Tornes K. Radiographic changes in the temporomandibular joint subsequent to vertical ramus osteotomy. Int J Oral Surg 1975;4:242-50. Sund G, Eckerdal O, Astrrand P. Changes in the temporomandibular joint after oblique sliding osteotomy of the mandibular rami. J Maxillofac Surg 1983;11:87-91. Rotskoff KS, Herbosa EG, Nickels B. Correction of condylar displacement following intraoral vertical ramus osteotomy. J Oral Maxillofac Surg 1991;49:366-72. Hu J, Wang D, Zou S. Effects of mandibular setback on the temporomandibular joint: a comparison of oblique and sagittal split ramus osteotomy. J Oral Maxillofac Surg 2000;58:375-80. Ueki K, Marukawa K, Nakagawa K, Yamamoto E. Condylar and temporomandibular joint disc positions after mandibular osteotomy for prognathism. J Oral Maxillofac Surg 2002;60:1424-32. Kawamata A, Fujishita M, Nagahara K, Kanematu N, Niwa KI, Langlais RP. Three-dimensional computed tomography evaluation of postsurgical condylar displacement after mandibular osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85:371-6. Eckerdal O, Sund G, Astrrand P. Skeletal remodeling in the temporomandibular joint after oblique sliding osteotomy of the mandibular rami. Int J Oral Maxillofac Surg 1986;15:233-9. Freihofer HPM, Petresevic D. Late results after advancing the mandible by sagittal splitting of the rami. J Maxillofac Surg 1975;3:250-7. Will LA, Joondeph DR, Hohl TH, West RA. Condylar position following mandibular advancement: its relationship to relapse. J Oral Maxillofac Surg 1984;42:578-88. Harris MD, Van Sickles JE, Alder M. Factors influencing condylar position after the bilateral sagittal split osteotomy fixed with bicortical screws. J Oral Maxillofac Surg 1999;57:650-4. Lee W, Park JU. Three-dimensional evaluation of positional change of the condyle after mandibular setback by means of bilateral sagittal split ramus osteotomy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:305-9. Kundert M, Hadjjanghelou O. Condylar displacement after sagittal splitting of the mandibular rami. J Maxillofac Surg 1980;8:278-87. Spitzer W, Rettinger G, Sitzmann F. Computerized tomography examination for the detection of positional changes in the temporomandibular joint after ramus osteotomies with screw fixation. J Maxillofac Surg 1984;12:139-42.
Reprint requests: Jing Hu, DDS, PhD Department of Oral and Maxillofacial Surgery West China College of Stomatology Sichuan University Chengdu, Sichuan 610041, China [email protected]
Objective. This study was to investigate the changes in condylar position and structure of the temporomandibular joint (TMJ) after mandibular setback using 2 forms of the ramus osteotomy. Study design. Twelve adult male rhesus monkeys were randomly divided into groups A (n ⫽ 6) and B (n ⫽ 6) for mandibular setback surgical procedure. An intraoral vertical ramus osteotomy (IVRO) was performed in group A, whereas a sagittal split ramus osteotomy (SSRO) was performed in group B. Changes in condylar position were quantified by computed tomography (CT) preoperatively and postoperatively. All animals in groups A and B were killed at 12 weeks after surgical procedure. The TMJ specimens were harvested and processed for histological examination. Results. In group A, the CT examinations showed a significant anteroinferior displacement of the condyle after surgical procedure. In group B, slight posterior displacement and lateral tilting of the condyle were noted after surgical procedure. Thickened cartilage layer and endochondral ossification were seen in the condyles of group A, but only minimal alteration in articular cartilage was found in group B. Conclusions. Both SSRO and IVRO can be biologically sound procedures for correction of mandibular prognathism. Intraoral vertical ramus osteotomy procedure leads to condylar adaptive remodeling, which may have favorable effects on TMJ, and it could be considered as a preferred surgical treatment for those patients with preoperative TMJ disorders. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:329-37)
The intraoral vertical ramus osteotomy (IVRO) and sagittal split ramus osteotomy (SSRO) are the main surgical procedures used to correct mandibular excess. Although IVRO is a faster, easier, and arguably stable procedure for the treatment of mandibular prognathism, SSRO has been performed more often because of the ability to apply rigid fixation. In the correction of mandibular excess, SSRO has several more advantages than IVRO, including better bony interface between the segments, easier use of rigid fixation, and quicker recovery of oral function. However, in addition to a much lower incidence of neurologic injury, IVRO1,2 or modified condylotomy 3 has been reported to be favorable to the temporomandibular joint (TMJ) because of anterior-inferior repositioning This research was supported by a grant from Trans-Century Training Program Foundation for the Talents, Ministry of Education of China (grant no. 2002-48 to J.H.). a Research Fellow, Key Laboratory of Biomedical Engineering, Sichuan University, Chengdu, China. b Professor, Department of Oral and Maxillofacial Surgery, West China College of Stomatology, Sichuan University, Chengdu, China. Received for publication Oct 15, 2006; returned for revision Dec 10, 2006; accepted for publication Dec 29, 2006. 1079-2104/$ - see front matter © 2007 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2006.12.024
of the condyle and the increase of the joint space, with a chance of improved symptoms of the joint. Conversely, in SSRO rigid fixation of the mandible may create a greater change in the position of the condyle and a higher incidence of TMJ dysfunction compared with nonrigid fixation.4,5 Although the advantages and disadvantages of these 2 techniques have been frequently discussed, there are still controversy over which is the preferred treatment for mandibular prognathism.6,7 There are some skeletal class III malocclusion patients who have preoperative TMJ symptoms, which also remains a problem during selection of surgical procedure for setback of their mandible. A number of clinical investigations have reported the influences of various surgical techniques on the TMJ8-11; however, no animal study about the differences in TMJ changes after IVRO and SSRO for mandibular setback exists. The purpose of this study was to observe the changes in condylar position and the histology of TMJ by using different mandibular ramus osteotomies through a primate model. MATERIAL AND METHODS Animals Twelve adult male rhesus monkeys weighing 8 to 10 kg were randomly divided into group A (n ⫽ 6) and group B (n ⫽ 6). The animal care was in accordance 329
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Fig. 1. Photographs of surgical procedures. A, Intraoral vertical ramus osteotomy (IVRO). The condylar segment was placed laterally to the distal segment. B, Sagittal split ramus osteotomy (SSRO). The miniplate with monocortical fixation was performed. C, The custom-made interocclusal wafer. D, Intermaxillary fixation was carried out by wire fixation.
with the guidelines of the Animal Center for Medical Experiments at Sichuan University. All monkeys were kept indoors under the supervision of the veterinarian staff. Presurgical protocol Similar to the method described by Ellis and colleagues12,13 the upper and lower anterior teeth (including the canines) were extracted under anesthesia 4 weeks before surgical procedure. This was necessary to facilitate setback of the mandible and feed during a period of intermaxillary fixation (IMF). The upper and lower dental impressions were taken after extraction of the teeth. The dental models were prepared and articulated. Model surgical procedure was done to create a mandibular setback of 2 molar cusps (approximately 5-6 mm). Then, an acrylic interocclusal splint was fabricated for locking the remaining teeth into the new position.
Surgical procedures The monkeys were premedicated with ketamine hydrochloride (10 mg/kg intramuscularly), an oroendotracheal intubation was performed, and they were anesthetized with pentobarbital sodium intravenously. In this animal study, IVRO was performed according to the technique of Bell and colleagues.1,2 Sagittal split ramus osteotomy was similar to the method described by Lupori et al.14 Both surgical procedures were done intraorally in all monkeys. In group A, bilateral vertical ramus osteotomies for mandibular setback were performed using an oscillating saw in 6 monkeys (Fig. 1, A). After setback of the mandible, a splint was used, and IMF was carried out with stainless steel wires (Fig. 1, C, D). The IMF was released at the sixth week after surgical procedure. During the period of IMF, the monkeys continually attempted to remove the fixed wires; we often trimmed their fingernails and tightened the wires. The IMF was
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found to be loose in 4 animals at 3 weeks after surgical procedure, but repeat fixation of wiring the jaws together was never required. In group B, bilateral sagittal split ramus osteotomies were performed in 6 animals. After separation of the proximal and distal segments, the mandible was moved backward and placed in the planned occlusion by using the interocclusal wafer. The ramus had the proximal and distal segments fixed with a miniplate and 4 titanium screws (2 mm in diameter and 6 mm in length) for monocortical osteosynthesis (Fig. 1, B). Intermaxillary fixation was applied for only 1 week after surgical procedure. A senior surgeon (J.H.) performed all surgical procedures, with the same surgical instruments, on the monkeys. The monkeys received 1 600 000 units of penicillin daily for 7 days after surgical procedure. In the period of IMF in both groups, the animals were given the same mash diet through the anterior dental gap that resulted from the extraction of upper and lower anterior teeth before surgical procedure. The animals in groups A and B were supplied this soft food for another 3 weeks after the release of the IMF and then were given the normal diet. Radiographic examinations Under general anesthesia, computed tomography (Somatom; Sensation 4, Siemens Medical Solutions, Erlangen, Germany) was used for assessment of each pair of TMJs, with images taken of axial slices at every 1.0 mm. The teeth of the animals were kept in occlusion during CT examination. Three-dimensional CT scanning films were taken under standardized conditions preoperatively and at 12 weeks postoperatively. Images of midcondylar slices of the sagittal and coronal plane scanning were acquired for assessment of changes in the position of the condyles. In the sagittal images, some reference points and lines were selected to evaluate the position of condyle (Fig. 2). The measurements used in this study were the distance A-C and P-D; the mean of the right and left sides was recorded for statistical analysis. The reference points on the CT scan were digitized with Syngo software (Somaris Medical Solutions, Forchheim, Germany). The accuracy was set at 0.1 mm for the liner measurements. The angle (␣) between the condylar long axis and the Frankfort horizontal plane was measured in the coronal images for evaluation of tilting of the condyle (Fig. 3). The accuracy was set at 0.1° for the angular measurement. Each parameter was read 3 times, and the mean was calculated for the statistical evaluations. The difference in preoperative and postoperative measurements was statistically assessed by the Student t test.
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Fig. 2. Reference points and lines at occlusion in the sagittal scan images. P, the inferior point of postglenoid spine; T, the inferior point of tuberculum; x-axis, P-T line; D, intersection between posterior condyle and x-axis; A, most cranial point on curvature of glenoid fossa; y-axis, a line was drawn from point A perpendicular to x-axis; C, intersection between the superior curvature of condyle and y-axis.
Fig. 3. The angle (␣) between the condylar long axis and the Frankfort horizontal plane was measured in the coronal scan images.
Histological examination All monkeys in group A and B had CT examinations at 12 weeks after surgical procedure, and then they were killed with overdose of pentobarbital. The jaw was in occlusion when the animal was killed. The common carotid arteries were perfused with a mixture
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Fig. 4. Postoperative three-dimensional reconstruction films. A, Twelve weeks after IVRO. Note minor bone resorption in the tip of proximal segment (arrow), and minimal open bite occurring. B, Twelve weeks after SSRO.
of 4% paraformaldehyde and 0.5% glutaraldehyde in phosphate buffer at pH 7.4. Both sides of the TMJ were harvested en bloc. The specimens were fixed in 10% neutral buffered formalin for an additional 2 days and then decalcified in 0.5 mol/L ethylene-diamine-tetraacetic-acid. Each condyle was divided sagittally into 3 blocks (lateral, middle, and medial thirds) and embedded in paraffin. Five sagittal sections (5-m thickness) were obtained from each block and stained with hematoxylin and eosin for examination under light microscopy. Two additional nonoperated monkeys having similar age and weight were used as controls. The control animals were treated with similar diet, and their condyles were harvested and prepared in the same manner. In each condyle, 1 of the 5 sagittal sections per block (lateral, middle, and medial) was chosen at random and examined on the anterior, superior, and posterior aspects. In addition to general histological observation, a histomorphometric analysis was performed on these sections to measure the thickness in the fibrous and cartilage layers by a computer system with image analyzing software Image-Pro Plus, version 4.5 (Media Cybernetics, Inc., Silver Spring, Md). The mean thicknesses were obtained from group A (IVRO), group B (SSRO), and control animals. For statistical analysis, data from each group were averaged and compared statistically using the Student t test. The differences were considered significant at P values less than .05. RESULTS All animals tolerated the operative procedures well. There were no wound infections. In the SSRO group, all monkeys showed an obvious retruded lower jaw and good stability in occlusion during the whole experimen-
tal period. In the IVRO group, anterior open bite (3-4 mm) was seen in all 6 monkeys at release time of IMF. It disappeared in 4 animals at 12 weeks after surgical procedure, but minimal open bite still existed in the other 2 monkeys. In the three-dimensional reconstruction films, bony osteosynthesis between the proximal and distal segments was observed in both groups. However, in group A some signs of bone resorption were seen in the tip of the proximal segment of 3 monkeys (Fig. 4). At killing, the TMJ specimens had intact condylar and fossa morphology. There were no gross differences in the shape and appearance of the TMJs between group A and group B. Radiographic analysis The changes in condylar position after IVRO (group A) and SSRO (group B) are shown in Table I. In the sagittal images, the measurements for A-C and P-D in group A were found to be increased (P ⬍ .05) after setback of the mandible, which means the condyles were displaced anteroinferiorly after IVRO. In group B, there was no significant difference in the measurements for A-C and P-D before and after surgical procedure (P ⬎ .05), which means the condyle was not displaced significantly in the sagittal plane after SSRO (Fig. 5). In the coronal images, the angle (␣) between the condylar long axis and the Frankfort horizontal plane was decreased in group A and increased in group B after surgical procedure. Although this angle did not show significant difference before and after surgical procedure in both groups (P ⬎ .05), the condyle was rotated somewhat clockwise (medial tilting) to the preoperative position in the IVRO monkeys, and somewhat counter-
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Table I. Average changes in the condylar position before and after intraoral vertical ramus osteotomy and sagittal split ramus osteotomy A-C (mm)
Preoperatively Postoperative week 12
␣ (degree)
P-D (mm)
IVRO
SSRO
IVRO
SSRO
IVRO
SSRO
1.6 ⫾ 0.3 2.6 ⫾ 0.5
1.7 ⫾ 0.3 1.6 ⫾ 0.4
2.8 ⫾ 0.8 3.6 ⫾ 0.8
2.7 ⫾ 0.7 2.4 ⫾ 0.7
8.3 ⫾ 2.0 7.9 ⫾ 2.0
8.2 ⫾ 1.8 8.4 ⫾ 1.9
All values are mean ⫾ SD. IVRO, intraoral vertical ramus osteotomy; SSRO, sagittal split ramus osteotomy.
Fig. 5. In the sagittal images, anteroinferior displacement of the condyle was obvious after IVRO, and the change in the position of the condyle was not evident after SSRO. A, Before IVRO. B, After IVRO. C, Before SSRO. D, After SSRO.
clockwise (lateral tilting) to the preoperative position in the SSRO animals (Fig. 6). Histological findings Histological changes in TMJs after IVRO and SSRO are shown in Fig. 7. Data regarding the mean thickness of fibrous and cartilage layers are shown in Table II. In group A, the fibrous layer of the condyle was somewhat thinner than that in the control specimens (P ⬎ .05).
The cartilage layer showed a significant increase in thickness over that in the control specimens (P ⬍ .05). Furthermore, hypertrophic chondrocytes and active osteoblasts in the area of the cartilage/bone interface were remarkable. New bone deposition (endochondral ossification) in the region underneath the cartilage layer was also observed. The posterosuperior aspect of the condyle was more involved within these adaptive changes. In group B specimens, although a decreasing
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Fig. 6. In the coronal images, slight medial and lateral tilting of the condyles to the preoperative position were noted in the IVRO and the SSRO monkeys. A, Before IVRO. B, After IVRO. C, Before SSRO. D, After SSRO.
trend in fibrous layer and an increasing trend in cartilage layers were found after SSRO, the differences did not reach statistical significance when compared with the control specimens (P ⬎ .05). New bone formation was not obvious in the region underneath the cartilage layer. In addition, the mean thickness of the cartilage layer was 244 m for the IVRO group and 195 m for the SSRO group. This difference was statistically significant (P ⬍ .05). DISCUSSION Orthognathic surgery, especially mandibular ramus osteotomies, may cause changes of condylar position and produce beneficial or adverse effects on TMJ. The changes in the position of the condyle TMJ after vertical ramus osteotomy and sagittal split ramus osteotomy have been described in several clinical investigations.2,8,9,13 The earliest reports of changes in condylar position were noted after oblique or vertical ramus osteotomy. In 1974, Hollender and Ridell,15 in a radio-
graphic study of 36 joints subjected to oblique ramus osteotomies, found a distinct double contour in the posterior part of the condylar head of 30 joints with anterior and inferior displacement of the condyle. Similar results were observed by subsequent studies.16-20 Using a three-dimensional CT superimposition technique, Kawamata et al.21 evaluated postoperative condylar displacement in orthognathic patients and found that in SSRO patients, lateral tilting was predominant, and in IVRO patients, medial tilting was predominant. In the current study, anteroinferior displacement and lateral tilting of the condyles were observed after vertical ramus osteotomy in monkeys. This finding is consistent with previous clinical investigations. In addition to the possible effect of intracapsular edema and manipulation of the fragments, condylar sag (anteroinferior movement of the condyle) and the medial tilting of the condyle might be expected from the direction of pull of the lateral pterygoid muscle and the pterygomasseteric sling to the proximal segment.
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Fig. 7. Histological photomicrographs of the condyles. A, Normal control condyle (hematoxylin-eosin, original magnification ⫻40). B, A condyle in group A demonstrating adaptive remodeling in the temporomandibular joint. Note the thickened cartilage layer and hyperplastic chondrocytes with new bone formation in the zone of the cartilage/bone interface (hematoxylin-eosin, original magnification ⫻100). C, A condyle in group B. Although minor adaptive remodeling was seen, overall the characteristics of the photomicrograph resemble the histological characteristics of the normal control (hematoxylin-eosin, original magnification ⫻100).
Table II. The measurement for thickness of fibrous and cartilage layers in the condyles
Fibrous layer (m) Cartilage layer (m)
Control (n ⫽ 4)
Group A (n ⫽ 12)
Group B (n ⫽ 12)
65.8 ⫾ 20.6
50.9 ⫾ 18.0
59.0 ⫾ 21.5
173.3 ⫾ 32.6
243.7 ⫾ 60.5
194.7 ⫾ 50.3
All values are mean ⫾ SD.
The adaptive changes in TMJ as a result of condylar displacement have been discussed in the previous studies.14,21,22 A double contour of the condylar head or the glenoid fossa was the specific radiographic finding, indicating remodeling activity. However, it was difficult to provide the direct evidence by radiographic analysis to demonstrate postoperative remodeling of the TMJ. Based on histological examination, our ani-
mal study showed that the condylar displacement after IVRO was associated with histological changes in the articular cartilage and bone structure. An increase in the cartilage thickness and obvious endochondral ossification were found in the area of the cartilage/bone interface. The anteroinferior condylar displacement may induce fibrocartilage to enter an activated state. The proliferation of chondrocytes and osteoblasts in the condyle is indicative of adaptive remodeling, which may help the TMJ to finally adjust to an altered biomechanical environment and not cause a significant change in occlusion. Temporomandibular joint symptoms and internal derangement are commonly found in patients with dentofacial deformities. In a majority of those patients, the improvement or resolution of joint symptoms following orthognathic surgical procedure, especially in IVRO, has been observed. The exact mechanism for improvement of TMJ symptoms after IVRO is still unclear. An
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explanation for this outcome is based on the hypothesis that the disk-condyle relationship will be altered favorably by anterior and inferior condylar movement.1,2 A slight condylar displacement subsequent to IVRO may allow repositioning of the condyle to a more functional position within the joint and resolve symptoms in the patients with TMJ dysfunction.10 In 1995, Werther et al.3 reported that the articular disk was reduced using modified condylotomy in 79% of disk displacement joints. The author emphasized the differences between standard IVRO and the modified condylotomy. The latter, although a modification of the IVRO, is really an indirect arthroplasty designed to increase joint space for disk reduction and does not alter the occlusion. Condylar sag is the objective in modified condylotomy. In the present study, anterior open bite was found in all 6 monkeys at IMF release after IVRO, which may be related to the “condylar sag” following the IVRO procedure. It is noteworthy that the open bite did not exist in 4 animals at 12 weeks after surgical procedure; the other 2 monkeys still had minimal open bite. With time relapse, the gradual remodeling in TMJ morphology could have contributed to the disappearance of open bite. On the other hand, anterior vertical elastic is advisable to maintain the ideal occlusion after release of maxillomandibular fixation. Furthermore, the modified condylotomy as described by Werther et al.3 may be a better approach for patients with preoperative TMJ symptoms and internal derangement. There are inconsistent data about the change in the position of the condyle after SSRO. Freihofer and Petresevic,23 in a radiographic analysis of 38 patients who had SSRO for mandibular advancement, found 10 of 26 condyles were positioned anteriorly in the glenoid fossa. Will et al.24 found both condyles to be positioned superiorly, and the left condyle also moved posteriorly in the patients who received SSRO. Using CT, Harris et al.25 found the condyles were displaced medially, posteriorly, superiorly, and angled medially after mandibular advancement with SSRO. For mandibular setback procedure by SSRO, Lee and Park,26 in a threedimensional CT evaluation of the condylar position in 30 Korean patients who underwent SSRO for mandibular setback, found the condyle tends to move inferiorly and rotate inward on the axial view and backward on the sagittal view. Our previous study19 also showed that a posterior displacement of the condyle after mandibular setback using SSRO. Ueki et al.20 completed a study that evaluated condylar and TMJ disk positions after SSRO and IVRO for mandibular setback. Their results suggest that SSRO does not improve anterior disk displacement, IVRO improves anterior disk displacement in the initial postoperative period, and both procedures may improve TMJ symptoms.
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The aforementioned variations in the condylar position after SSRO could be attributable to the differences in race, skeletal morphology (Class II or III), and evaluation method used. The use of rigid fixation in SSRO may be another important factor that produces the displacement of the condyle. Ellis and Hinton,13 in an animal study for mandibular advancement using SSRO, found the monkeys who underwent IMF showed a tendency for anterior movement of the condyle; the monkeys that underwent rigid fixation (bicortical osteosynthesis) showed a tendency for posterior condylar position. At 6 weeks after surgical procedure, the animals that had posterior displacement of the condyles showed evidence of resorption of the posterior surface of the condyles. Kundert and Hadjjanghelou,27 in a clinic investigation, found that SSRO with rigid fixation caused an increase in condylar displacement compared with IMF procedure. Freihofer and Petresevic23 reported an increase in postoperative joint clicking in a study of 38 patients who underwent SSRO with rigid fixation. However, some other studies comparing these 2 fixation methods do not support the aforementioned conclusions.5,8,24 In this animal study, SSRO with monocortical screw fixation was performed in 6 monkeys. A slight posterior displacement and lateral tilting of the condyle (no significant statistical difference to preoperative) was noted after setback procedure. Simultaneously, only minimal adaptive remodeling in the condyle was observed. It suggested that SSRO with monocortical osteosynthesis procedures did not cause a distinct displacement of the condyle and exert an adverse effect on the TMJ. Rigid fixation may lead to condylar displacement because the fixation with lag screws tends to eliminate the gaps between the proximal and the distal segments, which are normally generated with mandibular movement in any direction. However, Hackney et al.8 and Spitzer et al.28 suggest that the use of screw fixation seems to cause no major malposition of the condyle and does not change intercondylar angle or intercondylar width. Therefore, if a fixation using simple positional screws is examined carefully, significant medial or lateral condylar displacement can be prevented. Furthermore, the TMJ has an adaptive capacity to adjust to the altered position of the condyle. Slight movement of the condyle (within physiological limit) after mandibular osteotomies can induce an adaptive remodeling in the condyle and the glenoid fossa, which may not only prevent the occurrence of TMJ disorders, but also the occurrence of postoperative malocclusion. Mandibular ramus osteotomies may lead to changes in condylar position and cause TMJ dysfunction to develop. However, the variations in direction and magnitude of condylar displacement may have different
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effects on the TMJ. For example, anterior displacement of condyle could be more beneficial than the opposite situation. In the current study, the monkey that underwent IVRO with IMF showed an anteroinferior displacement of the condyle, which induces a significant adaptive remodeling in the TMJ; the animals that received SSRO with rigid fixation showed no obvious positional and histological changes in the condyle. This experimental study suggested that both SSRO and IVRO can be biologically sound procedures for correction of mandibular prognathism, but IVRO could be considered as a preferred surgical treatment for those patients with preoperative TMJ disorders. REFERENCES 1. Bell WH, Yamaguchi Y, Poor MR. Treatment of temporomandibular joint dysfunction by intraoral vertical ramus osteotomy. Int J Adult Orthod Orthognath Surg 1990;5:9-27. 2. Bell WH, Yamaguchi Y. Condyle position and mobility before and after intraoral vertical ramus osteotomies and neuromuscular rehabilitation. Int J Adult Orthod Orthognath Surg 1991;6:97-104. 3. Werther JR, Hall HD, Gibbs SJ. Disk position before and after modified condylotomy in 80 symptomatic temporomandibular joints. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:668-79. 4. Paulus GW, Steinhauser EW. A comparative study of wire osteosynthesis versus bone screws in the treatment of mandibular prognathism. Oral Surg 1982;54:2-6. 5. Timmis DP, Aragon SB, Van Sickels JE. Masticatory dysfunction with rigid and nonrigid osteosynthesis of sagittal split osteotomies. Oral Surg 1986;62:119-23. 6. Ghali GE, Sikes JW Jr. Intraoral vertical ramus osteotomy as the preferred treatment for mandibular prognathism. J Oral Maxillofac Surg 2000;58:313-5. 7. Wolford LM. The sagittal split ramus osteotomy as the preferred treatment for mandibular prognathism. J Oral Maxillofac Surg 2000;58:310-2. 8. Hackney FL, Van Sickels JE, Nummikoski PV. Condylar displacement and temporomandibular joint dysfunction following bilateral sagittal split osteotomy and rigid fixation. J Oral Maxillofac Surg 1989;47:223-7. 9. Feinerman DM, Piecuch JF. Long-term effects of orthognathic surgery on the temporomandibular joint: comparison of rigid and nonrigid fixation methods. Int J Oral Maxillofac Surg 1995;24:268-72. 10. Ueki K, Marukawa K, Nakagawa K, Yamamoto E. Condylar and temporomandibular joint disc positions after mandibular osteotomy for prognathism. J Oral Maxillofacial Surg 2002;60: 1424-32. 11. Kerstens HCJ, Tuinzing DB, vander Kwast WAM. Temporomandibular joint symptoms in orthognathic surgery. J Craniomaxillofac Surg 1989;17:215-8. 12. Ellis E III, Reynolds S, Carlson DS. Stability of the mandible following advancement: a comparison of three postsurgical fixation techniques. Am J Orthod Dentofac Orthop 1988;94:38-49. 13. Ellis E III, Hinton RJ. Histologic examination of the temporomandibular joint after mandibular advancement with and without
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Reprint requests: Jing Hu, DDS, PhD Department of Oral and Maxillofacial Surgery West China College of Stomatology Sichuan University Chengdu, Sichuan 610041, China [email protected]