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Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry
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Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2015.03.015, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry
A. Moroi, Y. Ishihara, M. Sotobori, R. Iguchi, A. Kosaka, H. Ikawa, K. Yoshizawa, K. Marukawa, K. Ueki Department of Oral and Maxillofacial Surgery, Division of Medicine, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan
A. Moroi, Y. Ishihara, M. Sotobori, R. Iguchi, A. Kosaka, H. Ikawa, K. Yoshizawa, K. Marukawa, K. Ueki: Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry. Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx. # 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. This study aimed to evaluate the postoperative changes in masticatory function in patients with jaw deformities with or without asymmetry treated by orthognathic surgery. Thirty female patients who underwent a Le Fort I osteotomy with sagittal split ramus osteotomy (SSRO) were enrolled. The patients were divided into symmetry and asymmetry groups. The bite force, occlusal contact area, and bite force balance were measured before and at 1, 3, and 6 months and 1 year after surgery; these measurements were compared statistically within and between the two groups. In the symmetry group, there was a significant difference in the preoperative bite force and the 1 month postoperative bite force (P = 0.0033). In the asymmetry group, the bite force before surgery was significantly different from that at 1 month (P = 0.0375) and at 1 year (P = 0.0353) after surgery. Significant differences in the bite force were also observed between the following time points: 1 month and 1 year (P = 0.0003), 3 months and 1 year (P = 0.0034), and 1 month and 6 months (P = 0.0486). The occlusal contact area, bite force, and occlusal balance tended to change after Le Fort I osteotomy with SSRO, with a significantly improved bite force in patients with asymmetry before surgery.
The important goals of surgery for jaw deformity are improved masticatory function and facial aesthetics. The sagittal split ramus osteotomy (SSRO) is one of the preferred surgical procedures for correcting various forms of mandibular prognathism. The Le Fort I osteotomy is also used very frequently with SSRO (double-jaw surgery) in orthognathic surgery. 0901-5027/000001+06
Numerous studies have investigated masticatory function before and after orthognathic surgery. One study reported a temporary decrease in the bite force and occlusal contact area immediately after surgery, with an improvement in both parameters over time.1 Another reported no differences in either parameter after SSRO or intraoral vertical ramus osteotomy
Keywords: bite force; osteotomy; asymmetry. Accepted for publication 24 March 2015
(IVRO) with or without Le Fort I osteotomy.2 However, no study has reported the changes in masticatory function after surgery in patients with various types of jaw deformity. Many studies have investigated occlusal problems. Occlusal instability, midline discrepancy, right–left differences in molar relationship, and inclination of the
# 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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frontal occlusal plane have been considered important occlusal characteristics in patients.3,4 Differences in the heights of the right and left rami have also been suggested as important skeletal problems associated with temporomandibular joint (TMJ) pathologies.5 A similar tendency has been identified in patients with mandibular prognathism accompanied by asymmetry.6 A study reported that the occlusal contact area and occlusal force were lower in patients with asymmetry than in individuals with a normal skull shape,7 with a shift in the occlusal balance to the deviated side in the former group.8 This study aimed to evaluate the postoperative changes in masticatory function in patients with jaw deformities with or without asymmetry treated by Le Fort I osteotomy with SSRO.
Materials and methods Patients
This retrospective study included 30 female patients (mean age 27.33 years, range 15–49 years). Only female patients were included in this study as there are marked differences in bite force between males and females. The study patients were diagnosed with mandibular prognathism and underwent Le Fort I osteotomy with SSRO between November 2007 and August 2013. As there were clear differences between patients with mandibular prognathism and patients with an open bite in the bite force and bite force balance, the patients with an open bite were excluded from this study. Informed consent was obtained from all patients in accordance with the Declaration of Helsinki, and the study was approved by the ethics committee of Yamanashi University Hospital.
Surgical procedure
The patients underwent a standard Le Fort I osteotomy, with a periodontal incision in the anterior region and a vestibular incision in the posterior region to prevent postoperative scar formation in the labial gingival tissue. The maxillary segment was then repositioned with an intermediate occlusal split and fixed with miniplates, 16 monocortical screws, and four L-type plates (four-hole, unsintered hydroxyapatite/poly-L-lactic acid; Super FIXSORB MX, Takiron Co. Ltd., Osaka, Japan). The SSRO was performed according to the method described by Trauner and Obwegeser.9 The mandibular segment was then repositioned with an occlusal split and fixed with miniplates, eight monocortical screws, and two straight plates (four-hole). All patients underwent pre- and postoperative orthodontic treatment, with the latter beginning at 1 month after surgery and completed within 1 year. Immediately after surgery, intermaxillary fixation (IMF) with elastic bands was performed to maintain an ideal occlusion in the same manner in all patients. There was no difference in the duration of IMF between the patients with and without asymmetry. Cephalometric analysis
Lateral and frontal cephalograms were taken for all patients before and at 1 year after surgery for the skeletal analysis. Cephalograms were obtained using a standardized cephalometric technique and were analyzed using CephaloMetrics AtoZ software (Yasunaga Computer Systems Inc., Fukui, Japan) on a Microsoft computer. The skeletal occlusion in all patients was classified as class III on the basis of
Fig. 1. Maxillomandibular (Mx–Md) midline angle from the frontal cephalogram. ANS, anterior nasal spine; Me, menton.
the lateral cephalometric analysis, with asymmetry taken into account for accurate frontal or axial cephalometric analysis. On the frontal cephalogram, the angle between the anterior nasal spine–menton line and the line perpendicular to the bilateral zygomatic frontal suture line was defined as the maxillomandibular (Mx–Md) midline angle. A positive Mx–Md midline angle represents mandibular deviation to the left, and a negative value represents mandibular deviation to the right (Fig. 1).10 The Mx–Md midline angles were given positive values in all patients so that all consecutive measurements could be attributed to either the deviated or the undeviated side. The patients were divided into two groups based on the Mx–Md midline angles. The asymmetry group included patients in whom the Mx–Md midline angle was greater than 3.58 (n = 15), while the symmetry group included patients in whom the angle was less than 3.58 (n = 15). One skilled observer performed all digitization so that errors in the cephalometric analyses were small and acceptable for the purposes of this study. Error analysis by digitization and re-measurement of all cases generated an average error of less than 0.4 mm for linear measurements and 0.58 for angular measurements. Measurements
A pressure-sensitive system to measure the occlusal bite force and occlusal contact area was used in this study. The pressuresensitive system comprised a pressuresensitive sheet (Dental Prescale; Fuji Photo Film Co., Tokyo, Japan) and an analysis apparatus (Dental Occlusion Pressuregraph FDP-705; Fuji Photo Film Co.) connected to a personal computer (LaVieC, LC50H/3, NEC, Tokyo, Japan) (Fig. 2A–C). The reproducibility of these devices has been determined in previous studies.11–13 Each patient was seated with her head in an unsupported natural position and a forward gaze. The Frankfort horizontal plane was maintained approximately parallel to the floor. The pressure-sensitive sheet was placed between the maxillary and mandibular arches, with the centre of the sheet between the central incisors. The patient was instructed to bite as forcefully as possible for approximately 3 s. The test was performed three times per subject, and the data were recorded as the mean of the three values. The sheet was read and analyzed by the Dental Occlusion Pressuregraph and the results were entered into the
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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Fig. 2. (A) The pressure-sensitive system (Dental Prescale; Fuji Photo Film Co., Tokyo, Japan). (B) Analysis apparatus (Dental Occlusion Pressuregraph FPD-705; Fuji Photo Film Co.). (C) The result displayed on the computer monitor.
computer and visualized on the display screen. They represented the bite force, occlusal contact area, and bite force balance. The bite force balance was defined as the distance from the line passing through the centre of the left and right areas on the sensitive sheet to the centre of gravity of the bite force (Fig. 3). The centre of gravity was calculated as follows:
P rc ¼
Fig. 3. Computer display. ‘A’ indicates the distance of the bite force balance from the centre line of right and left. Bite force balance defines the distance ‘A’ value. ‘B’ indicates the centre line of the right and left.
i mi r i M
where rc is the centre of gravity, m is each bite force, r is the position of the bite, M is the amount of bite force, and i is the total number of bite points. The bite force balance was thus given a positive value so that all consecutive measurements could be attributed to either the right or the left side. The bite measurement was measured just before surgery and at 1, 3, and 6 months and 1 year after surgery.
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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Table 1. Changes in cephalogram analysis from preoperative to 1 year postoperative in the symmetry and asymmetry groups; repeated measures ANOVA. Measurements Symmetry group SNA SNB FMA Gonial angle Occlusion plane angle Mx–Md midline Occlusal cant Mx midline Asymmetry group SNA SNB FMA Gonial angle Occlusion plane angle Mx–Md midline Occlusal cant Mx midline
Preoperative (8)
1 year postoperative (8)
P-value
77.8 77.4 31.4 125.9 12.1 1.8 1.1 1.3
79.2 76.7 30.9 130.5 10.6 2.2 2.5 1.1
0.443 (NS) 0.7579 (NS) 0.8809 (NS) 0.1526 (NS) 0.4555 (NS) 0.3606 (NS) 0.0867 (NS) 0.8173 (NS)
79.3 75.2 30.0 121.7 13.0 7.6 0.9 3.3
79.0 75.1 31.6 126.8 11.8 2.5 2.2 1.1
0.8275 (NS) 0.9302 (NS) 0.4985 (NS) 0.0815 (NS) 0.609 (NS) 0.0003 (S) 0.015 (S) <0.0001 (S)
Statistical analysis
The bite force, occlusal contact area, and bite force balance values were analyzed statistically using StatView version 4.5 software (Abacus Concepts Inc., Berkeley, CA, USA). Differences between the two groups were analyzed using an unpaired t-test. Time-dependent changes were examined using repeated-measures analysis of variance (repeated ANOVA). Results
ANOVA, analysis of variance; SNA, sella–nasion–A point; SNB, sella–nasion–B point; FMA, Frankfort mandibular plane angle; Mx–Md, maxillomandibular; Mx, maxillary; NS, not significant; S, significant.
Fig. 4. Change in occlusal contact area (mm2) in the symmetry and asymmetry groups.
Fig. 5. Change in bite force (N) in the symmetry and asymmetry groups.
In the symmetry group, the mean setback was 3.4 4.4 mm on the right side and 3.8 4.9 mm on the left side, while the corresponding values in the asymmetry group were 3.7 0.8 mm and 2.7 1.1 mm, respectively. There were no significant differences in setback values between the two groups. With regard to the cephalometric parameters, there were no significant differences between the preoperative and 1 year postoperative parameters in the symmetry group (Table 1), while in the asymmetry group, significant differences were observed between the preoperative and 1 year postoperative values for the Mx– Md midline angle and occlusal cant (Table 1). There were no significant time-course changes in the occlusal contact area among subjects, although there were significant changes within subjects (between subjects: F = 2.746, df = 1, P = 0.1087; within subjects: F = 6.672, df = 4, P < 0.0001) (Fig. 4). A similar trend was observed for the bite force (between subjects: F = 1.125, df = 1, P = 0.2979; within subjects: F = 10.640, df = 4, P < 0.0001) (Fig. 5) and bite force balance (between subjects: F = 0.554, df = 1, P = 0.4630; within subjects: F = 3.491, df = 4, P = 0.0100) (Fig. 6). There were no significant differences regarding the bite force balance, bite force, or occlusal contact area among the two groups at each observation time point (Table 2). In the symmetry group, there was a significant difference in the preoperative bite force and the 1 month postoperative bite force (P = 0.0033). There were no significant differences in the bite force, occlusal contact area, or bite force balance at the other observation points in this group. In the asymmetry group, significant differences were observed in the bite force between the following time points: before surgery and 1 month postoperatively
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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Fig. 6. Change in bite force balance (mm) in the symmetry and asymmetry groups.
Table 2. Results of the comparison of differences between the symmetry group and asymmetry group at each time point; non-paired t-test.
Preoperative Symmetry Asymmetry P-value 1 month postoperative Symmetry Asymmetry P-value 3 months postoperative Symmetry Asymmetry P-value 6 months postoperative Symmetry Asymmetry P-value 1 year postoperative Symmetry Asymmetry P-value
Occlusal contact area (SD), mm 2
Bite force (SD), N
Bite force balance (SD), mm
8.7 (5.3) 5.9 (5.0) 0.1473 (NS)
366.2 (180.2) 269.0 (149.3) 0.1189 (NS)
7.6 (5.7) 6.8 (6.6) 0.7361 (NS)
5.6 (2.7) 4.1 (2.7) 0.0668 (NS)
242.7 (122.9) 192.7 (106.5) 0.1158 (NS)
7.5 (7.6) 7.4 (6.1) 0.8385 (NS)
5.9 (2.2) 4.2 (2.3) 0.0534 (NS)
286.0 (112.7) 229.2 (105.7) 0.1659 (NS)
6.1 (4.0) 5.1 (4.1) 0.5260 (NS)
6.9 (3.4) 6.7 (3.3) 0.9145 (NS)
329.7 (171.3) 339.8 (145.9) 0.8643 (NS)
4.5 (3.7) 4.0 (2.8) 0.6695 (NS)
8.3 (3.1) 8.2 (2.7) 0.9650 (NS)
390.5 (139.7) 422.3 (119.7) 0.5088 (NS)
4.3 (3.5) 3.4 (3.0) 0.4663 (NS)
SD, standard deviation; NS, not significant.
(P = 0.0375), preoperative and 1 year postoperatively (P = 0.0353), 1 month and 1 year postoperatively (P = 0.0003), 3 months and 1 year postoperatively (P = 0.0034), and 1 month and 6 months postoperatively (P = 0.0486). The occlusal contact area was significantly different between the 1 month and 1 year postoperative time points (P = 0.0323) and the 3 months and 1 year postoperative time points (P = 0.0384). Discussion
There are several methods of examining the occlusal contact area, bite force, and the centre of the bite force. Articulating paper, wax, and silicone rubber impression materials have been used. It is not possible to simultaneously evaluate the
bite force and occlusal contact area using these materials. T-scanning enabled the measurement of the bite force and the distribution of contacts in the dental arch.11 With the T-scanning system, it is difficult to perform a quantitative analysis. The Dental Prescale system can provide constant values.1,2,12,13 This system comprises a sheet including a layer of microcapsules containing a colour-forming material and a layer containing a colourdeveloping material. The microcapsules in the sheet are of various sizes and strengths, and they are broken according to a given pressure. When the subject bites into the sheet with all teeth, the microcapsules break according to the degree of occlusal pressure and release the colour-forming material, which is absorbed by the colour-developing material to produce red
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areas on the sheet. A computer is then used to analyze and assess the intensity of the redness of each pixel, and the occlusal pressure and occlusal force are then calculated. The pressure-sensitive sheet is very flexible, and its measured values are unaffected by velocity, duration of pressure, or temperature.14 This device is considered to be more useful and reliable than the other available devices. As described previously, the bite force differs between males and females. Xu et al. reported that the masseter muscle area was 570 mm2 in males and 487 mm2 in females,15 while Ando reported these values to be 381–399 mm2 in males and 288–293 mm2 in females.16 Subsequently, Harada et al.12 and Nagai et al.13 reported that the mean bite force in control subjects was 721.0 N and 677.5 N, respectively, for males and 530.7 N and 625.2 N, respectively, for females. These results indicate that males have a greater bite force than females and that gender affects bite force values. To eliminate these gender differences, only female patients were included in the present study. Several studies have reported a significant decrease and gradual recovery in the bite force and occlusal contact area during orthodontic treatment in patients who have undergone orthognathic surgery.17,18 The decrease resulted from the pain and discomfort and the positional instability of the TMJ caused by the surgery. Another study suggested that the bite force was primarily affected by two factors: the amount of masticatory muscle force and the length of their moment arms.16 However, mechanical advantages pertaining to the bite force were not found to differ between set back surgery and advancement surgery.17 Therefore, some of the patients with asymmetry who underwent setback surgery on one side and advancement surgery on the contralateral side could be compared with the symmetry group in this study. The asymmetry group tended to exhibit a delay in bite force recovery compared with the symmetry group. The movement of bone fragments in orthognathic surgery for patients with asymmetry is so complex that the influence of soft tissues such as muscles or ligaments is increased. The large changes in bone and soft tissue consequently delay bite force recovery. Maxillary stability after a Le Fort I osteotomy to correct an asymmetric skeletal morphology and an inclined occlusal cant does not differ from that after conventional Le Fort I osteotomy. In other words, there are no differences in timecourse changes in cephalometric values
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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during the immediate postoperative period.19 In this study, all patients underwent IMF with elastic bands to maintain an ideal occlusion for 4–5 months after surgery. This period overlaps with the period when functional parameters change (1–3 months). By stabilizing bone fragments during this period, postoperative bone morphogenetic changes can be prevented. Therefore, preoperative and 1 year postoperative cephalometric values can be compared. Some reports have mentioned that patients who undergo orthognathic surgery have a lower bite force and occlusal contact area immediately after surgery.20,21 Goto et al. reported that patients with skeletal mandibular asymmetry who exhibited a lateral midline shift in the mandible had their bite balance shifted to the deviated side.8 However, no study has measured the bite force and bite occlusal contact area before and after orthognathic surgery or evaluated improvements in bite force balance after surgery in patients with asymmetry. As mentioned previously, Harada et al.12 and Nagai et al.13 reported that the mean bite force in control subjects was 721.0 N and 677.5 N, respectively, for males and 530.7 N and 625.2 N, respectively, for females, while that in patients with prognathism before surgery was 293.2 N and 183.7 N, respectively, for males and 208.5 N and 120.3 N, respectively, for females. It was obvious that the bite force of patients with mandibular prognathism was lower than that of controls (normal occlusion patients). Furthermore, the values for patients with skeletal mandibular asymmetry were lower than those for individuals with a normal skull shape, a normal occlusion in the occlusal contact area, and a normal occlusal force.7 In this study, there were no significant differences between the symmetry and asymmetry groups in each evaluated parameter before surgery, however there were significant differences between the preoperative and 1 year postoperative bite force values in the asymmetry group. Furthermore, there were significant differences in the preoperative and 1 year postoperative Mx–Md midline angle and values in the asymmetry group. These results indicate that the improvement in asymmetry of bone morphogenetics influences the improvement in the bite force. In conclusion, this study showed that the occlusal contact area, bite force, and occlusal balance in patients with jaw deformities with or without asymmetry tended to change after Le Fort I osteotomy with SSRO, with a significantly improved bite force after surgery in patients with asymmetry.
Funding
None. 11.
Competing interests
None declared. 12.
Ethical approval
Yamanashi University 1125. Patient consent
13.
Not required. References 1. Iwase M, Ohashi M, Tachibana H, Toyoshima T, Nagumo M. Bite force, occlusal contact area and masticatory efficiency before and after orthognathic surgical correction of mandibular prognathism. Int J Oral Maxillofac Surg 2006;35:1102–7. 2. Ueki K, Marukawa K, Shimada M, Nakagawa K, Yamamoto E. Changes in occlusal force after mandibular ramus osteotomy with and without Le Fort I osteotomy. Int J Oral Maxillofac Surg 2007;36:301–4. 3. Solberg WK, Bibb CA, Nordstro¨m BB, Hansson TL. Malocclusion associated with temporomandibular joint changes in young adults at autopsy. Am J Orthod 1986;89:326–30. 4. Fushima K, Inui M, Sato S. Dental asymmetry in temporomandibular disorders. J Oral Rehabil 1999;26:752–6. 5. Trpkova B, Major P, Nebbe B, Prasad N. Craniofacial asymmetry and temporomandibular joint internal derangement in female adolescents: a posteroanterior cephalometric study. Angle Orthod 2000;70:81–8. 6. Ueki K, Nakagawa K, Marukawa K, Takatsuka S, Yamamoto E. The relationship between temporomandibular joint and stress angulation in skeletal class III patients. Eur J Orthod 2005;27:501–6. 7. Thomas GP, Throckmorton GS, Ellis III E, Sinn DP. The effects of orthodontic treatment on isometric bite forces and mandibular motion in patients before orthognathic surgery. J Oral Maxillofac Surg 1995;53:673–8. 8. Goto TK, Yamada T, Yoshiura K. Occlusal pressure, contact area, force and the correlation with the morphology of the jaw-closing muscles in patients with skeletal mandibular asymmetry. J Oral Rehabil 2008;35:594–603. 9. Trauner R, Obwegeser HL. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Part I. Surgical procedures to correct mandibular prognathism and reshaping of the chin. Oral Surg Oral Med Oral Pathol 1957;10:677–89. 10. Ueki K, Marukawa K, Hashiba Y, Nakagawa K, Degerliyurt K, Yamamoto E. Changes in the duration of the chewing cycle in patients
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with skeletal class III with and without asymmetry before and after orthognathic surgery. J Oral Maxillofac Surg 2009;67:67–72. Maness WL, Benjamin M, Podoloff R, Boblick A, Golden RF. Computerized occlusal analysis: a new technology. Quintessence Int 1987;18:287–92. Harada K, Kikuchi T, Morishima S, Sato M, Ohkura K, Omura K. Changes in bite force and dentoskeletal morphology in prognathic patients after orthognathic surgery. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;95:649–54. Nagai I, Tanaka N, Noguchi M, Suda Y, Sonoda T, Kohama G. Changes in occlusal state of patients with mandibular prognathism after orthognathic surgery: a pilot study. Br J Oral Maxillofac Surg 2001;39:429–33. Hirasawa T, Hirano S, Sugita H. Dental application of pressure measuring sheet. J Jpn Soc Dent Appl Mater 1978;19:298. Xu JA, Yuasa K, Yoshiura K, Kanda S. Quantitative analysis of masticatory muscles using computed tomography. Dentomaxillofac Radiol 1994;23:154–8. Ando T. Observation of the masticatory muscles and buccal fat pad on the CT images. J Natl Med Coll 1991;16:30–41. Proffit WR, Turvey TA, Fields HW, Phillips C. The effect of orthognathic surgery on occlusal force. J Oral Maxillofac Surg 1989;47:457–63. Kim YG, Oh SH. Effect of mandibular setback surgery on occlusal force. J Oral Maxillofac Surg 1997;55:121–6. Ueki K, Hashiba Y, Marukawa K, Yoshida K, Shimizu C, Nakagawa K, et al. Comparison of maxillary stability after Le Fort I osteotomy for occlusal cant correction surgery and maxillary advanced surgery. Oral Surg Oral Med Oral Pathol 2007;104:38–43. Ellis III E, Throckmorton GS, Sinn DP. Bite force before and after surgical correction of mandibular prognathism. J Oral Maxillofac Surg 1996;54:176–81. Iwase M, Sugimori M, Kurachi Y, Nagumo M. Changes in bite force and occlusal contacts in patients treated for mandibular prognathism by orthognathic surgery. J Oral Maxillofac Surg 1998;56:850–5.
Address: Akinori Moroi Department of Oral and Maxillofacial Surgery Division of Medicine Interdisciplinary Graduate School of Medicine and Engineering University of Yamanashi 1110 Shimokato Chuo Yamanashi 409-3898 Japan Tel.: +81 55 273 9673; Fax: +81 55 273 8210 E-mail: [email protected]
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx http://dx.doi.org/10.1016/j.ijom.2015.03.015, available online at http://www.sciencedirect.com
Clinical Paper Orthognathic Surgery
Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry
A. Moroi, Y. Ishihara, M. Sotobori, R. Iguchi, A. Kosaka, H. Ikawa, K. Yoshizawa, K. Marukawa, K. Ueki Department of Oral and Maxillofacial Surgery, Division of Medicine, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan
A. Moroi, Y. Ishihara, M. Sotobori, R. Iguchi, A. Kosaka, H. Ikawa, K. Yoshizawa, K. Marukawa, K. Ueki: Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry. Int. J. Oral Maxillofac. Surg. 2015; xxx: xxx–xxx. # 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Abstract. This study aimed to evaluate the postoperative changes in masticatory function in patients with jaw deformities with or without asymmetry treated by orthognathic surgery. Thirty female patients who underwent a Le Fort I osteotomy with sagittal split ramus osteotomy (SSRO) were enrolled. The patients were divided into symmetry and asymmetry groups. The bite force, occlusal contact area, and bite force balance were measured before and at 1, 3, and 6 months and 1 year after surgery; these measurements were compared statistically within and between the two groups. In the symmetry group, there was a significant difference in the preoperative bite force and the 1 month postoperative bite force (P = 0.0033). In the asymmetry group, the bite force before surgery was significantly different from that at 1 month (P = 0.0375) and at 1 year (P = 0.0353) after surgery. Significant differences in the bite force were also observed between the following time points: 1 month and 1 year (P = 0.0003), 3 months and 1 year (P = 0.0034), and 1 month and 6 months (P = 0.0486). The occlusal contact area, bite force, and occlusal balance tended to change after Le Fort I osteotomy with SSRO, with a significantly improved bite force in patients with asymmetry before surgery.
The important goals of surgery for jaw deformity are improved masticatory function and facial aesthetics. The sagittal split ramus osteotomy (SSRO) is one of the preferred surgical procedures for correcting various forms of mandibular prognathism. The Le Fort I osteotomy is also used very frequently with SSRO (double-jaw surgery) in orthognathic surgery. 0901-5027/000001+06
Numerous studies have investigated masticatory function before and after orthognathic surgery. One study reported a temporary decrease in the bite force and occlusal contact area immediately after surgery, with an improvement in both parameters over time.1 Another reported no differences in either parameter after SSRO or intraoral vertical ramus osteotomy
Keywords: bite force; osteotomy; asymmetry. Accepted for publication 24 March 2015
(IVRO) with or without Le Fort I osteotomy.2 However, no study has reported the changes in masticatory function after surgery in patients with various types of jaw deformity. Many studies have investigated occlusal problems. Occlusal instability, midline discrepancy, right–left differences in molar relationship, and inclination of the
# 2015 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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frontal occlusal plane have been considered important occlusal characteristics in patients.3,4 Differences in the heights of the right and left rami have also been suggested as important skeletal problems associated with temporomandibular joint (TMJ) pathologies.5 A similar tendency has been identified in patients with mandibular prognathism accompanied by asymmetry.6 A study reported that the occlusal contact area and occlusal force were lower in patients with asymmetry than in individuals with a normal skull shape,7 with a shift in the occlusal balance to the deviated side in the former group.8 This study aimed to evaluate the postoperative changes in masticatory function in patients with jaw deformities with or without asymmetry treated by Le Fort I osteotomy with SSRO.
Materials and methods Patients
This retrospective study included 30 female patients (mean age 27.33 years, range 15–49 years). Only female patients were included in this study as there are marked differences in bite force between males and females. The study patients were diagnosed with mandibular prognathism and underwent Le Fort I osteotomy with SSRO between November 2007 and August 2013. As there were clear differences between patients with mandibular prognathism and patients with an open bite in the bite force and bite force balance, the patients with an open bite were excluded from this study. Informed consent was obtained from all patients in accordance with the Declaration of Helsinki, and the study was approved by the ethics committee of Yamanashi University Hospital.
Surgical procedure
The patients underwent a standard Le Fort I osteotomy, with a periodontal incision in the anterior region and a vestibular incision in the posterior region to prevent postoperative scar formation in the labial gingival tissue. The maxillary segment was then repositioned with an intermediate occlusal split and fixed with miniplates, 16 monocortical screws, and four L-type plates (four-hole, unsintered hydroxyapatite/poly-L-lactic acid; Super FIXSORB MX, Takiron Co. Ltd., Osaka, Japan). The SSRO was performed according to the method described by Trauner and Obwegeser.9 The mandibular segment was then repositioned with an occlusal split and fixed with miniplates, eight monocortical screws, and two straight plates (four-hole). All patients underwent pre- and postoperative orthodontic treatment, with the latter beginning at 1 month after surgery and completed within 1 year. Immediately after surgery, intermaxillary fixation (IMF) with elastic bands was performed to maintain an ideal occlusion in the same manner in all patients. There was no difference in the duration of IMF between the patients with and without asymmetry. Cephalometric analysis
Lateral and frontal cephalograms were taken for all patients before and at 1 year after surgery for the skeletal analysis. Cephalograms were obtained using a standardized cephalometric technique and were analyzed using CephaloMetrics AtoZ software (Yasunaga Computer Systems Inc., Fukui, Japan) on a Microsoft computer. The skeletal occlusion in all patients was classified as class III on the basis of
Fig. 1. Maxillomandibular (Mx–Md) midline angle from the frontal cephalogram. ANS, anterior nasal spine; Me, menton.
the lateral cephalometric analysis, with asymmetry taken into account for accurate frontal or axial cephalometric analysis. On the frontal cephalogram, the angle between the anterior nasal spine–menton line and the line perpendicular to the bilateral zygomatic frontal suture line was defined as the maxillomandibular (Mx–Md) midline angle. A positive Mx–Md midline angle represents mandibular deviation to the left, and a negative value represents mandibular deviation to the right (Fig. 1).10 The Mx–Md midline angles were given positive values in all patients so that all consecutive measurements could be attributed to either the deviated or the undeviated side. The patients were divided into two groups based on the Mx–Md midline angles. The asymmetry group included patients in whom the Mx–Md midline angle was greater than 3.58 (n = 15), while the symmetry group included patients in whom the angle was less than 3.58 (n = 15). One skilled observer performed all digitization so that errors in the cephalometric analyses were small and acceptable for the purposes of this study. Error analysis by digitization and re-measurement of all cases generated an average error of less than 0.4 mm for linear measurements and 0.58 for angular measurements. Measurements
A pressure-sensitive system to measure the occlusal bite force and occlusal contact area was used in this study. The pressuresensitive system comprised a pressuresensitive sheet (Dental Prescale; Fuji Photo Film Co., Tokyo, Japan) and an analysis apparatus (Dental Occlusion Pressuregraph FDP-705; Fuji Photo Film Co.) connected to a personal computer (LaVieC, LC50H/3, NEC, Tokyo, Japan) (Fig. 2A–C). The reproducibility of these devices has been determined in previous studies.11–13 Each patient was seated with her head in an unsupported natural position and a forward gaze. The Frankfort horizontal plane was maintained approximately parallel to the floor. The pressure-sensitive sheet was placed between the maxillary and mandibular arches, with the centre of the sheet between the central incisors. The patient was instructed to bite as forcefully as possible for approximately 3 s. The test was performed three times per subject, and the data were recorded as the mean of the three values. The sheet was read and analyzed by the Dental Occlusion Pressuregraph and the results were entered into the
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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Fig. 2. (A) The pressure-sensitive system (Dental Prescale; Fuji Photo Film Co., Tokyo, Japan). (B) Analysis apparatus (Dental Occlusion Pressuregraph FPD-705; Fuji Photo Film Co.). (C) The result displayed on the computer monitor.
computer and visualized on the display screen. They represented the bite force, occlusal contact area, and bite force balance. The bite force balance was defined as the distance from the line passing through the centre of the left and right areas on the sensitive sheet to the centre of gravity of the bite force (Fig. 3). The centre of gravity was calculated as follows:
P rc ¼
Fig. 3. Computer display. ‘A’ indicates the distance of the bite force balance from the centre line of right and left. Bite force balance defines the distance ‘A’ value. ‘B’ indicates the centre line of the right and left.
i mi r i M
where rc is the centre of gravity, m is each bite force, r is the position of the bite, M is the amount of bite force, and i is the total number of bite points. The bite force balance was thus given a positive value so that all consecutive measurements could be attributed to either the right or the left side. The bite measurement was measured just before surgery and at 1, 3, and 6 months and 1 year after surgery.
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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Table 1. Changes in cephalogram analysis from preoperative to 1 year postoperative in the symmetry and asymmetry groups; repeated measures ANOVA. Measurements Symmetry group SNA SNB FMA Gonial angle Occlusion plane angle Mx–Md midline Occlusal cant Mx midline Asymmetry group SNA SNB FMA Gonial angle Occlusion plane angle Mx–Md midline Occlusal cant Mx midline
Preoperative (8)
1 year postoperative (8)
P-value
77.8 77.4 31.4 125.9 12.1 1.8 1.1 1.3
79.2 76.7 30.9 130.5 10.6 2.2 2.5 1.1
0.443 (NS) 0.7579 (NS) 0.8809 (NS) 0.1526 (NS) 0.4555 (NS) 0.3606 (NS) 0.0867 (NS) 0.8173 (NS)
79.3 75.2 30.0 121.7 13.0 7.6 0.9 3.3
79.0 75.1 31.6 126.8 11.8 2.5 2.2 1.1
0.8275 (NS) 0.9302 (NS) 0.4985 (NS) 0.0815 (NS) 0.609 (NS) 0.0003 (S) 0.015 (S) <0.0001 (S)
Statistical analysis
The bite force, occlusal contact area, and bite force balance values were analyzed statistically using StatView version 4.5 software (Abacus Concepts Inc., Berkeley, CA, USA). Differences between the two groups were analyzed using an unpaired t-test. Time-dependent changes were examined using repeated-measures analysis of variance (repeated ANOVA). Results
ANOVA, analysis of variance; SNA, sella–nasion–A point; SNB, sella–nasion–B point; FMA, Frankfort mandibular plane angle; Mx–Md, maxillomandibular; Mx, maxillary; NS, not significant; S, significant.
Fig. 4. Change in occlusal contact area (mm2) in the symmetry and asymmetry groups.
Fig. 5. Change in bite force (N) in the symmetry and asymmetry groups.
In the symmetry group, the mean setback was 3.4 4.4 mm on the right side and 3.8 4.9 mm on the left side, while the corresponding values in the asymmetry group were 3.7 0.8 mm and 2.7 1.1 mm, respectively. There were no significant differences in setback values between the two groups. With regard to the cephalometric parameters, there were no significant differences between the preoperative and 1 year postoperative parameters in the symmetry group (Table 1), while in the asymmetry group, significant differences were observed between the preoperative and 1 year postoperative values for the Mx– Md midline angle and occlusal cant (Table 1). There were no significant time-course changes in the occlusal contact area among subjects, although there were significant changes within subjects (between subjects: F = 2.746, df = 1, P = 0.1087; within subjects: F = 6.672, df = 4, P < 0.0001) (Fig. 4). A similar trend was observed for the bite force (between subjects: F = 1.125, df = 1, P = 0.2979; within subjects: F = 10.640, df = 4, P < 0.0001) (Fig. 5) and bite force balance (between subjects: F = 0.554, df = 1, P = 0.4630; within subjects: F = 3.491, df = 4, P = 0.0100) (Fig. 6). There were no significant differences regarding the bite force balance, bite force, or occlusal contact area among the two groups at each observation time point (Table 2). In the symmetry group, there was a significant difference in the preoperative bite force and the 1 month postoperative bite force (P = 0.0033). There were no significant differences in the bite force, occlusal contact area, or bite force balance at the other observation points in this group. In the asymmetry group, significant differences were observed in the bite force between the following time points: before surgery and 1 month postoperatively
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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Fig. 6. Change in bite force balance (mm) in the symmetry and asymmetry groups.
Table 2. Results of the comparison of differences between the symmetry group and asymmetry group at each time point; non-paired t-test.
Preoperative Symmetry Asymmetry P-value 1 month postoperative Symmetry Asymmetry P-value 3 months postoperative Symmetry Asymmetry P-value 6 months postoperative Symmetry Asymmetry P-value 1 year postoperative Symmetry Asymmetry P-value
Occlusal contact area (SD), mm 2
Bite force (SD), N
Bite force balance (SD), mm
8.7 (5.3) 5.9 (5.0) 0.1473 (NS)
366.2 (180.2) 269.0 (149.3) 0.1189 (NS)
7.6 (5.7) 6.8 (6.6) 0.7361 (NS)
5.6 (2.7) 4.1 (2.7) 0.0668 (NS)
242.7 (122.9) 192.7 (106.5) 0.1158 (NS)
7.5 (7.6) 7.4 (6.1) 0.8385 (NS)
5.9 (2.2) 4.2 (2.3) 0.0534 (NS)
286.0 (112.7) 229.2 (105.7) 0.1659 (NS)
6.1 (4.0) 5.1 (4.1) 0.5260 (NS)
6.9 (3.4) 6.7 (3.3) 0.9145 (NS)
329.7 (171.3) 339.8 (145.9) 0.8643 (NS)
4.5 (3.7) 4.0 (2.8) 0.6695 (NS)
8.3 (3.1) 8.2 (2.7) 0.9650 (NS)
390.5 (139.7) 422.3 (119.7) 0.5088 (NS)
4.3 (3.5) 3.4 (3.0) 0.4663 (NS)
SD, standard deviation; NS, not significant.
(P = 0.0375), preoperative and 1 year postoperatively (P = 0.0353), 1 month and 1 year postoperatively (P = 0.0003), 3 months and 1 year postoperatively (P = 0.0034), and 1 month and 6 months postoperatively (P = 0.0486). The occlusal contact area was significantly different between the 1 month and 1 year postoperative time points (P = 0.0323) and the 3 months and 1 year postoperative time points (P = 0.0384). Discussion
There are several methods of examining the occlusal contact area, bite force, and the centre of the bite force. Articulating paper, wax, and silicone rubber impression materials have been used. It is not possible to simultaneously evaluate the
bite force and occlusal contact area using these materials. T-scanning enabled the measurement of the bite force and the distribution of contacts in the dental arch.11 With the T-scanning system, it is difficult to perform a quantitative analysis. The Dental Prescale system can provide constant values.1,2,12,13 This system comprises a sheet including a layer of microcapsules containing a colour-forming material and a layer containing a colourdeveloping material. The microcapsules in the sheet are of various sizes and strengths, and they are broken according to a given pressure. When the subject bites into the sheet with all teeth, the microcapsules break according to the degree of occlusal pressure and release the colour-forming material, which is absorbed by the colour-developing material to produce red
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areas on the sheet. A computer is then used to analyze and assess the intensity of the redness of each pixel, and the occlusal pressure and occlusal force are then calculated. The pressure-sensitive sheet is very flexible, and its measured values are unaffected by velocity, duration of pressure, or temperature.14 This device is considered to be more useful and reliable than the other available devices. As described previously, the bite force differs between males and females. Xu et al. reported that the masseter muscle area was 570 mm2 in males and 487 mm2 in females,15 while Ando reported these values to be 381–399 mm2 in males and 288–293 mm2 in females.16 Subsequently, Harada et al.12 and Nagai et al.13 reported that the mean bite force in control subjects was 721.0 N and 677.5 N, respectively, for males and 530.7 N and 625.2 N, respectively, for females. These results indicate that males have a greater bite force than females and that gender affects bite force values. To eliminate these gender differences, only female patients were included in the present study. Several studies have reported a significant decrease and gradual recovery in the bite force and occlusal contact area during orthodontic treatment in patients who have undergone orthognathic surgery.17,18 The decrease resulted from the pain and discomfort and the positional instability of the TMJ caused by the surgery. Another study suggested that the bite force was primarily affected by two factors: the amount of masticatory muscle force and the length of their moment arms.16 However, mechanical advantages pertaining to the bite force were not found to differ between set back surgery and advancement surgery.17 Therefore, some of the patients with asymmetry who underwent setback surgery on one side and advancement surgery on the contralateral side could be compared with the symmetry group in this study. The asymmetry group tended to exhibit a delay in bite force recovery compared with the symmetry group. The movement of bone fragments in orthognathic surgery for patients with asymmetry is so complex that the influence of soft tissues such as muscles or ligaments is increased. The large changes in bone and soft tissue consequently delay bite force recovery. Maxillary stability after a Le Fort I osteotomy to correct an asymmetric skeletal morphology and an inclined occlusal cant does not differ from that after conventional Le Fort I osteotomy. In other words, there are no differences in timecourse changes in cephalometric values
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015
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during the immediate postoperative period.19 In this study, all patients underwent IMF with elastic bands to maintain an ideal occlusion for 4–5 months after surgery. This period overlaps with the period when functional parameters change (1–3 months). By stabilizing bone fragments during this period, postoperative bone morphogenetic changes can be prevented. Therefore, preoperative and 1 year postoperative cephalometric values can be compared. Some reports have mentioned that patients who undergo orthognathic surgery have a lower bite force and occlusal contact area immediately after surgery.20,21 Goto et al. reported that patients with skeletal mandibular asymmetry who exhibited a lateral midline shift in the mandible had their bite balance shifted to the deviated side.8 However, no study has measured the bite force and bite occlusal contact area before and after orthognathic surgery or evaluated improvements in bite force balance after surgery in patients with asymmetry. As mentioned previously, Harada et al.12 and Nagai et al.13 reported that the mean bite force in control subjects was 721.0 N and 677.5 N, respectively, for males and 530.7 N and 625.2 N, respectively, for females, while that in patients with prognathism before surgery was 293.2 N and 183.7 N, respectively, for males and 208.5 N and 120.3 N, respectively, for females. It was obvious that the bite force of patients with mandibular prognathism was lower than that of controls (normal occlusion patients). Furthermore, the values for patients with skeletal mandibular asymmetry were lower than those for individuals with a normal skull shape, a normal occlusion in the occlusal contact area, and a normal occlusal force.7 In this study, there were no significant differences between the symmetry and asymmetry groups in each evaluated parameter before surgery, however there were significant differences between the preoperative and 1 year postoperative bite force values in the asymmetry group. Furthermore, there were significant differences in the preoperative and 1 year postoperative Mx–Md midline angle and values in the asymmetry group. These results indicate that the improvement in asymmetry of bone morphogenetics influences the improvement in the bite force. In conclusion, this study showed that the occlusal contact area, bite force, and occlusal balance in patients with jaw deformities with or without asymmetry tended to change after Le Fort I osteotomy with SSRO, with a significantly improved bite force after surgery in patients with asymmetry.
Funding
None. 11.
Competing interests
None declared. 12.
Ethical approval
Yamanashi University 1125. Patient consent
13.
Not required. References 1. Iwase M, Ohashi M, Tachibana H, Toyoshima T, Nagumo M. Bite force, occlusal contact area and masticatory efficiency before and after orthognathic surgical correction of mandibular prognathism. Int J Oral Maxillofac Surg 2006;35:1102–7. 2. Ueki K, Marukawa K, Shimada M, Nakagawa K, Yamamoto E. Changes in occlusal force after mandibular ramus osteotomy with and without Le Fort I osteotomy. Int J Oral Maxillofac Surg 2007;36:301–4. 3. Solberg WK, Bibb CA, Nordstro¨m BB, Hansson TL. Malocclusion associated with temporomandibular joint changes in young adults at autopsy. Am J Orthod 1986;89:326–30. 4. Fushima K, Inui M, Sato S. Dental asymmetry in temporomandibular disorders. J Oral Rehabil 1999;26:752–6. 5. Trpkova B, Major P, Nebbe B, Prasad N. Craniofacial asymmetry and temporomandibular joint internal derangement in female adolescents: a posteroanterior cephalometric study. Angle Orthod 2000;70:81–8. 6. Ueki K, Nakagawa K, Marukawa K, Takatsuka S, Yamamoto E. The relationship between temporomandibular joint and stress angulation in skeletal class III patients. Eur J Orthod 2005;27:501–6. 7. Thomas GP, Throckmorton GS, Ellis III E, Sinn DP. The effects of orthodontic treatment on isometric bite forces and mandibular motion in patients before orthognathic surgery. J Oral Maxillofac Surg 1995;53:673–8. 8. Goto TK, Yamada T, Yoshiura K. Occlusal pressure, contact area, force and the correlation with the morphology of the jaw-closing muscles in patients with skeletal mandibular asymmetry. J Oral Rehabil 2008;35:594–603. 9. Trauner R, Obwegeser HL. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. Part I. Surgical procedures to correct mandibular prognathism and reshaping of the chin. Oral Surg Oral Med Oral Pathol 1957;10:677–89. 10. Ueki K, Marukawa K, Hashiba Y, Nakagawa K, Degerliyurt K, Yamamoto E. Changes in the duration of the chewing cycle in patients
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Address: Akinori Moroi Department of Oral and Maxillofacial Surgery Division of Medicine Interdisciplinary Graduate School of Medicine and Engineering University of Yamanashi 1110 Shimokato Chuo Yamanashi 409-3898 Japan Tel.: +81 55 273 9673; Fax: +81 55 273 8210 E-mail: [email protected]
Please cite this article in press as: Moroi A, et al. Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry, Int J Oral Maxillofac Surg (2015), http://dx.doi.org/10.1016/j.ijom.2015.03.015