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Changes in tongue and hyoid positions, and posterior airway space following mandibular setback surgery
ARTICLE IN PRESS Journal of Cranio-Maxillofacial Surgery (2005) 33, 107–110 r 2004 European Association for Cranio-Maxillofacial Surgery doi:10.1016/j.jcms.2004.10.005, available online at http://www.sciencedirect.com
Changes in tongue and hyoid positions, and posterior airway space following mandibular setback surgery Masayoshi KAWAKAMI, Kazuhiko YAMAMOTO, Masaki FUJIMOTO, Kazuhiko OHGI, Masahide INOUE, Tadaaki KIRITA Department of Oral and Maxillofacial Surgery (Head: Prof. Tadaaki Kirita), Nara Medical University, Kashihara Nara, Japan Available online 29 January 2005
SUMMARY. Introduction: The postural response of the tongue after mandibular setback is clinically important for maintaining normal respiration. Although the hyoid bone moves progressively to adapt physiologically to the altered orofacial configuration following such surgery, it is not clear whether repositioning of the hyoid has an effect on the pharyngeal airway. In the present study, postoperative changes in hyoid position and pharyngeal airway space were assessed retrospectively in patients who had undergone mandibular setback surgery. Material and methods: Digitized lateral cephalograms from 30 mandibular setback surgery cases taken preoperatively, and 1 month and more than 1 year postoperatively, were used to examine pharyngeal airway morphology and the position of hyoid bone. Results: A significant downward movement of the hyoid bone was found 1 month after surgery, while the pharyngeal airway dimensions at the tongue were maintained. More than 1 year after surgery, the hyoid position returned to its original position, resulting in a significant decrease in retrolingual airway dimension. Conclusion: The results indicate that mandibular setback causes airway narrowing late after surgery, while the early postoperative airway dimension is maintained. Long-term observations should be performed because of the changes of oropharyngeal configuration following mandibular setback. r 2004 European Association for Cranio-Maxillofacial Surgery
Keywords: Cephalometry; Orthognathic surgery; Pharyngeal airway; Mandibular prognathism; Hyoid bone
surgery leading to sleep-related breathing disorder and obstructive sleep apnoea (OSA) showed an association with airway narrowing after more than 18 months (Guilleminault et al., 1985; Riley et al., 1987), and both suggested that mandibular setback may contribute to further development of OSA after surgery. In the present study, changes in hyoid position and pharyngeal airway space were assessed retrospectively. Long-term adaptations of soft tissues, including the tongue base, accompanying the change in hyoid bone position were also examined.
INTRODUCTION Surgical orthodontic treatment changes orofacial skeletal and soft tissue components, though tongue position and function compensate for those changes in the oral environment (Wickwire et al., 1972). The postural response to mandibular setback is of particular interest and importance, because of its relationship to maintaining normal respiration (Proffit and Phillips, 2003). Shortly after mandibular setback the hyoid bone goes downward for physiologic adaptation to the soft tissue, including the tongue mass, and the altered tongue posture in the reduced oral cavity prevents airway obstruction. Additional observations have revealed that the hyoid bone progressively returns to its original position (Wickwire et al., 1972; Lew, 1993), while the postoperative decrease in hypopharyngeal airway space is maintained during the follow-up period (Greco et al., 1990; Enacar et al., 1994). Wenzel et al. (1989) found that the anterior–posterior distance of the upper airway was decreased at 1 year postoperatively and the patients tended to extend their head after the surgery. Since head position may camouflage morphological changes in the upper airway, it is unclear whether repositioning of the hyoid bone has an effect on the relationship of soft and hard tissues late after surgery. Two case reports of mandibular setback
MATERIAL AND METHODS Data from 30 patients (10 males and 20 females) with mandibular prognathism, who had each received orthodontic treatment prior to surgical correction were evaluted. The mean preoperative age was 22.7 years for the females and 21.5 years for the males, with an overall age range of 18–37 years. A bilateral sagittal split ramus osteotomy (SSRO) was performed in each patient using the Obwegeser–Dal Pont method to set back the mandible. Patients who underwent bimaxillary surgery and/or those with a craniofacial anomaly, such as cleft lip, alveolus and palate, were excluded. After setback of the mandible, all patients underwent bicortical fixation (between the 107
ARTICLE IN PRESS 108 Journal of Cranio-Maxillofacial Surgery Table 1 – Demographic data before surgery. Variable
Mean (SD)
Age (years)
Male Female Male Female Right Left
Body mass index (kg/m2) Mandibular setback (mm)
21.5 22.7 21.3 20.4 6.3 5.6
(1.5) (4.8) (4.0) (1.1) (3.9) (3.4)
differences found were less than 1.0 mm and 1.01, respectively. The standard error of a single measurement was calculated for each variable and the systematic error was determined using paired t-tests (Houston, 1983). No significant systemic errors and an acceptable reliability were noted. Statistical evaluation
N
S NSH Po
FH
FMA
ANB S-H
PNS D1
C2
D2
Overjet Overbite
C3 C3-H
H
IMPA Me
Mand. pl
Fig. 1 – Landmarks used for cephalometry. S: sella; N: nasion; ANS: anterior nasal spine; FH: Frankfurt horizontal plane; Me: menton; Po: porion; PNS: posterior nasal spine; C2: second cervical vertebra; C3: third cervical vertebra; H: lowest point of hyoid bone; D1: vertical distance between dorsum of the tongue and PNS on a line perpendicular to FH; D2: horizontal distance between posterior pharyngeal wall and dorsum of the tongue on a line parallel to the palatal plane that runs through C2; S–H: vertical distance between S and H; C3–H: linear distance between H and the most anterior point of C3; NSH: angle of S–H to SN plane.
distal and proximal segments). The average of mandibular setback was 6:5 2:5 mm (Table 1). Postoperative maxillo-mandibular fixation was maintained for 2 weeks with wires or elastics. Lateral cephalograms were taken preoperatively (T1), and 1 month (T2) and more than 1 year (T3) postoperatively. The subject was seated upright in the cephalostat with the Frankfurt horizontal plane (FH) parallel to the floor and the teeth in occlusion. To obtain a standardized position of the oropharyngeal structures, the cephalograms were taken at the end of expiration after swallowing. After the films were digitized, 3 serial cephalograms from each subject were traced by the same investigator, and the traditional contours and points of dentofacial structure were digitized to enable measurement of the tongue, pharynx, and hyoid positions. Linear and angular measurements were also determined according to a previous study. (Kawakami et al., 2004; Fig. 1). Evaluation of error at measuring and calculation To assess measurement error, the records of 10 subjects were re-evaluated 2 months later. The mean
Methodological errors in the cephalometric measurements were minimized by double recording. Timedependent changes of the measurements were examined by a paired t-test. Spearman’s rank was used to determine the statistical correlation between the changes in the airway space and hyoid position, and the amount of mandibular setback. Differences were considered to be significant at po0:05:
RESULTS The body mass indices [weight (kg)/height (m)2] of the subjects were within normal limits for both the male and female groups (Table 1). Preoperative, postoperative, and 1 year-follow-up changes are shown in Table 2. Significant differences of dental and skeletal parameters (overjet, overbite, and ANB) reflected the surgical changes that occurred from T1 to T2 (po0:05). No significant changes were seen from T2 to T3. However, the mandibular plane showed a slight clockwise rotation with an increase of Frankfurt horizontal–Mandibular plane–Angle (FMA) and the lower incisors became retroclined during the postoperative orthodontic treatment (IMPA—Incisor axis–Mandibular plane– Angle). Table 2 – Changes in dental and skeletal parameters measured preoperatively, postoperatively, and after the follow-up period. Variables Overjet (mm)
Overbite (mm)
ANB (degree)
FMA (degree)
IMPA (degree)
Mean (SD)
Mean (SD)
T1 T2 T3
3.4(2.8) 3.0(1.0)a 3.1(0.7)
T2–T1 T3–T2
5.8(3.1) 0.1(1.1)
T1 T2 T3
1.1(3.4) 0.5(1.0)a 0.9(1.0)
T2–T1 T3–T2
1.6(3.1) 0.3(1.3)
T1 T2 T3
2.9(3.9) 0.3(3.0)a 0.1(3.1)
T2–T1 T3–T2
3.2(2.5) 0.3(1.3)
T1 T2 T3
32.5(6.4) 32.5(7.3) 34.3(6.2)b
T2–T1 T3–T2
0.0(5.8) 1.6(3.3)
T1 T2 T3
85.5(5.2) 84.1(5.3) 82.1(5.9)b
T2–T1 T3–T2
0.7(4.5) 1.9(3.5)
FMA—Frankfurt horizontal plane–mandibular IMPA—Incisor (axis)–mandibular plane–angle. a po0:05 between T1 and T2; b po0:05 between T2 and T3.
plane–angle.
ARTICLE IN PRESS Changes in tongue and hyoid bone positions 109
The distance from sella to the hyoid (S–H) and that from C3 (third cervical vertebra) to the hyoid (C3–H) significantly increased between T1 and T2 (po0:05; Table 3). Marked vertical movement of the hyoid was also observed. However, the amount of mandibular setback did not have a positive correlation with the increase of S–H (p ¼ 0:275), or C3–H (p ¼ 0:49), although these parameters decreased from T2 to T3, in a manner corresponding with the earlier changes Table 3 – Changes in variables of tongue space and hyoid bone position postoperatively, and after the follow-up period. Variables D1 (mm) D2 (mm) S–H (mm) C3–H (mm) NSH (degree)
a
Mean S.D. T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T2 T3
10.5 10.1 9.0 15.5 15.4 13.2 120.1 125.4 120.2 40.1 41.8 39.2 88.8 89.9 89.6
(5.4) (6.0) (4.7) (4.1) (4.2) (3.1)b (6.3) (8.5)a (9.2)b (5.1) (5.1)a (4.6)b (5.6) (4.8) (4.7)
Mean S.D. T2T1 T3T2
0.4 (3.2) 1.1 (3.1)
T2T1 T3T2
0.6 (3.1) 2.2 (3.6)
T2T1 T3T2
4.8 (5.7) 5.1 (7.5)
T2T1 T3T2
1.6 (3.4) 2.6 (2.9)
T2T1 T3T2
1.1 (3.0) 0.3 (2.6)
po0:05 between T1 and T2; po0:05 between T2 and T3.
b
Fig. 2 – Diagram of immediate postsurgical changes (T2) in tongue space, hyoid bone position, and mandible.
from T1 to T2 (po0:05). The significant decreases of S–H and C3–H indicated a tendency for the hyoid to return toward its original position during the 1-year follow-up period. In contrast, the angle of NSH was not significantly altered, indicating that the direction of hyoid bone movement was maintained following surgery. The posterior vertical tongue space (distance 1— D1) and horizontal (mesopharyngeal) tongue space (D2) did not appear to change significantly from T1 to T2. But, D2 decreased markedly from T2 to T3, while D1 was changed only slightly (po0:05). The amount of mandibular setback did not correlate with the change of D2 (p ¼ 0:305). A diagram of the postsurgical changes in the soft and hard tissues is shown in Fig. 2. DISCUSSION The inferior movement of the hyoid bone seen in the present study is consistent with the findings of other studies, showing that this movement is an adaptation preventing an encroachment of the tongue into the pharyngeal airway (Tselnik and Pogrel, 2000). Another study indicated that the pharyngeal airway size is decreased shortly after setback surgery and becomes stable later (Enacar et al., 1994). Since the narrowed airway just after surgery is also a result of postoperative swelling in the soft tissue, we chose 1 month after surgery to let this settle. Our results confirmed that the vertical and horizontal spaces around the tongue were maintained postoperatively with the downward movement of the hyoid bone to compensate for the reduced oral volume caused by the mandibular setback. However, maintenance of the retrolingual space differed from the findings of previous studies and may have been a result of the bony fixation method employed. Many studies have used subjects with wire or plate fixation following a bilateral ramus splitting osteotomy (Wenzel et al., 1989; Lew, 1993; Enacar et al., 1994). The rigid bicortical fixation with screws used in the present study offers superior stabilization of bony segments when compared with wire fixation. The latter may have a different effect on the postsurgical changes of dentofacial features than bicortical screw fixation. Following screw fixation the retrolingual space was maintained. The hyoid bone returned to its original position during the follow-up period and the tongue volume encroached upon the pharyngeal airway. It was also found that the upward repositioning of the hyoid bone occurred late postoperatively and was related to the narrowed airway space at the tongue base, which explains the subsequent physiological adaptation of the dentofacial structures following surgery (Saitoh, 2004). The movement also resulted in clockwise rotation of the mandible. A reduced airway can reflect (craniofacial) morphology closely, such as open-bite related to adenoid enlargement. To preserve airway patency, the tongue encroaching on the
ARTICLE IN PRESS 110 Journal of Cranio-Maxillofacial Surgery
pharyngeal space may induce (functional) downward rotation of the mandible. A decrease in the upper airway leads to changes in head posture and, consequentially, the hyoid position. Following mandibular setback, the patient will have some short-term extension of the head, when compared with a cephalometric radiograph taken of the natural head position (Wenzel et al., 1989; Proffit and Phillips, 2003). These compensatory changes in natural head position following orthognathic surgery might mask morphologic changes in the upper airway (Nakagawa et al., 1998). Some investigators have found that the hyoid position can be assessed with reasonable accuracy by eliminating the use of cranial reference points (Bibby, 1984; Lew, 1993). In the present study, the subjects were positioned with the Frankfurt horizontal plane parallel to the floor, and all of the cephalograms were taken just after swallowing [in expiration] with light contact between the teeth to minimize unfavourable interference when determining the hyoid bone position. A reduced airway can also cause obstructive sleep apnoea (OSA). Some of the features seen after surgery indicate a change in oropharyngeal morphology, in a pattern closely resembling that seen in sleep apnoea subjects (Turnbull and Battagel, 2000) and 2 case reports have highlighted the development of sleep apnoea following surgery for mandibular prognathism (Guilleminault et al., 1985; Riley et al, 1987). Snoring worsened over the first 18 months following surgery for both patients, which supports the results of this study that demonstrated a narrowing of the airway. None of the present patients seemed to have any symptoms of OSA before or after orthognathic surgery, though one patient had an 8.5 mm reduction of D2 (horizontal pharyngeal airway space) from 18.0 mm at T1. The overall mean of D2 after follow-up was greater than 10.0 mm, which was wider than that previously reported in OSA patients (Battagel et al, 2002). A small reduction of the retrolingual space may not always develop into OSA after mandibular setback, as OSA develops progressively before it finally appears, implying that factors other than a single anatomic defect are involved (Guilleminault et al., 1985). It is believed that there may be a critical airway dimension, below which airway collapse (intermittent/complete) is much more likely. CONCLUSION The present serial cephalometric study revealed that the pharyngeal airway space was maintained shortly after mandibular setback surgery, while the hyoid bone moved inferiorly to compensate for reduction of the oral volume. Upward repositioning of the hyoid bone resulted in a significant reduction of the posterior lingual airway late after surgery. These results suggest that long-term care for the pharyngeal airway change is required following mandibular setback surgery.
ACKNOWLEDGEMENT
This study was supported in part by a Grant-in-Aid for Scientific Research (15592171) from Japanese Society for the Promotion of Science. References Battagel JM, Johal A, Smith AM, Kotecha B: Postural variation in oropharyngeal dimensions in subjects with sleep disordered breathing: a cephalometric study. Eur J Orthod 24: 263–272, 2002 Bibby RE: The hyoid position in mouth breathers and tongue thrusters. Am J Orthod 85: 431–433, 1984 Enacar A, Aksoy AU¨, S- encift Y, Haydar B, Aras K: Changes in hypopharyngeal airway space and in tongue and hyoid bone positions following the surgical correction of mandibular prognathism. Int J Adult Orthod Orthognath Surg 9: 285–290, 1994 Greco JM, Frohberg U, Sickels JEV: Long-term airway space changes after mandibular setback using bilateral sagittal split osteotomy. Int J Oral Maxillofac Surg 19: 103–105, 1990 Guilleminault C, Riley R, Powell N: Sleep apnea in normal subjects following mandibular osteotomy with retrusion. Chest 88: 776–778, 1985 Houston WJB: The analysis of errors in orthodontic measurements. Amer J Orthod 83: 382–390, 1983 Kawakami M, Yamamoto K, Noshi T, Miyawaki S, Kirita T: Effect of surgical reduction of the tongue on dentofacial structure following mandibular setback. J Oral Maxillofac Surg 62: 1188–1192, 2004 Lew KKK: Changes in tongue and hyoid bone positions following anterior mandibular subapical osteotomy in patients with Class III malocclusion. Int J Adult Orthod Orthognath Surg 8: 123–128, 1993 Nakagawa F, Ono T, Ishikawa Y, Kuroda T: Morphologic changes in the upper airway structure following surgical correction of mandibular prognathism. Int J Adult Orthod Orthognath Surg 13: 299–306, 1998 Proffit, W.R., Phillips, C., 2003. Physiologic responses to treatment and postsurgical stability. In: Proffit, W.R., White, R.P. Jr., Sarver, D.M. (eds.), Contemporary Treatment of Dentofacial Deformity. Mosby St. Louis, 646-676. Riley R, Powell N, Guilleminault C, Ware W: Obstructive sleep apnea syndrome following surgery for mandibular prognathism. J Oral Maxillofac Surg 45: 450–452, 1987 Saitoh K: Long-term changes in pharyngeal airway morphology after mandibular setback surgery. Am J Orthod Dentofac Orthop 125: 556–561, 2004 Tselnik M, Pogrel MA: Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 58: 282–285, 2000 Turnbull NR, Battagel JM: The effects of orthognathic surgery on pharyngeal airway dimensions and quality of sleep. J Orthod 27: 235–247, 2000 Wenzel A, Williams S, Ritzau M: Relationships of changes in craniofacial morphology, head posture, and nasopharyngeal airway size following mandibular osteotomy. Am J Orthod Dentofac Surg 96: 138–143, 1989 Wickwire NA, White Jr. RP, Proffit WR: The effect of mandibular osteotomy on tongue position. J Oral Surg 30: 184–190, 1972 Dr. Masayoshi KAWAKAMI, DDS, PhD Department of Oral and Maxillofacial Surgery Nara Medical University 840 Shijo-cho Kashihara Nara 634-8522 Japan Tel./fax: +81 744 29 8876 E-mail: [email protected] Paper received 23 July 2004 Accepted 14 October 2004
Changes in tongue and hyoid positions, and posterior airway space following mandibular setback surgery Masayoshi KAWAKAMI, Kazuhiko YAMAMOTO, Masaki FUJIMOTO, Kazuhiko OHGI, Masahide INOUE, Tadaaki KIRITA Department of Oral and Maxillofacial Surgery (Head: Prof. Tadaaki Kirita), Nara Medical University, Kashihara Nara, Japan Available online 29 January 2005
SUMMARY. Introduction: The postural response of the tongue after mandibular setback is clinically important for maintaining normal respiration. Although the hyoid bone moves progressively to adapt physiologically to the altered orofacial configuration following such surgery, it is not clear whether repositioning of the hyoid has an effect on the pharyngeal airway. In the present study, postoperative changes in hyoid position and pharyngeal airway space were assessed retrospectively in patients who had undergone mandibular setback surgery. Material and methods: Digitized lateral cephalograms from 30 mandibular setback surgery cases taken preoperatively, and 1 month and more than 1 year postoperatively, were used to examine pharyngeal airway morphology and the position of hyoid bone. Results: A significant downward movement of the hyoid bone was found 1 month after surgery, while the pharyngeal airway dimensions at the tongue were maintained. More than 1 year after surgery, the hyoid position returned to its original position, resulting in a significant decrease in retrolingual airway dimension. Conclusion: The results indicate that mandibular setback causes airway narrowing late after surgery, while the early postoperative airway dimension is maintained. Long-term observations should be performed because of the changes of oropharyngeal configuration following mandibular setback. r 2004 European Association for Cranio-Maxillofacial Surgery
Keywords: Cephalometry; Orthognathic surgery; Pharyngeal airway; Mandibular prognathism; Hyoid bone
surgery leading to sleep-related breathing disorder and obstructive sleep apnoea (OSA) showed an association with airway narrowing after more than 18 months (Guilleminault et al., 1985; Riley et al., 1987), and both suggested that mandibular setback may contribute to further development of OSA after surgery. In the present study, changes in hyoid position and pharyngeal airway space were assessed retrospectively. Long-term adaptations of soft tissues, including the tongue base, accompanying the change in hyoid bone position were also examined.
INTRODUCTION Surgical orthodontic treatment changes orofacial skeletal and soft tissue components, though tongue position and function compensate for those changes in the oral environment (Wickwire et al., 1972). The postural response to mandibular setback is of particular interest and importance, because of its relationship to maintaining normal respiration (Proffit and Phillips, 2003). Shortly after mandibular setback the hyoid bone goes downward for physiologic adaptation to the soft tissue, including the tongue mass, and the altered tongue posture in the reduced oral cavity prevents airway obstruction. Additional observations have revealed that the hyoid bone progressively returns to its original position (Wickwire et al., 1972; Lew, 1993), while the postoperative decrease in hypopharyngeal airway space is maintained during the follow-up period (Greco et al., 1990; Enacar et al., 1994). Wenzel et al. (1989) found that the anterior–posterior distance of the upper airway was decreased at 1 year postoperatively and the patients tended to extend their head after the surgery. Since head position may camouflage morphological changes in the upper airway, it is unclear whether repositioning of the hyoid bone has an effect on the relationship of soft and hard tissues late after surgery. Two case reports of mandibular setback
MATERIAL AND METHODS Data from 30 patients (10 males and 20 females) with mandibular prognathism, who had each received orthodontic treatment prior to surgical correction were evaluted. The mean preoperative age was 22.7 years for the females and 21.5 years for the males, with an overall age range of 18–37 years. A bilateral sagittal split ramus osteotomy (SSRO) was performed in each patient using the Obwegeser–Dal Pont method to set back the mandible. Patients who underwent bimaxillary surgery and/or those with a craniofacial anomaly, such as cleft lip, alveolus and palate, were excluded. After setback of the mandible, all patients underwent bicortical fixation (between the 107
ARTICLE IN PRESS 108 Journal of Cranio-Maxillofacial Surgery Table 1 – Demographic data before surgery. Variable
Mean (SD)
Age (years)
Male Female Male Female Right Left
Body mass index (kg/m2) Mandibular setback (mm)
21.5 22.7 21.3 20.4 6.3 5.6
(1.5) (4.8) (4.0) (1.1) (3.9) (3.4)
differences found were less than 1.0 mm and 1.01, respectively. The standard error of a single measurement was calculated for each variable and the systematic error was determined using paired t-tests (Houston, 1983). No significant systemic errors and an acceptable reliability were noted. Statistical evaluation
N
S NSH Po
FH
FMA
ANB S-H
PNS D1
C2
D2
Overjet Overbite
C3 C3-H
H
IMPA Me
Mand. pl
Fig. 1 – Landmarks used for cephalometry. S: sella; N: nasion; ANS: anterior nasal spine; FH: Frankfurt horizontal plane; Me: menton; Po: porion; PNS: posterior nasal spine; C2: second cervical vertebra; C3: third cervical vertebra; H: lowest point of hyoid bone; D1: vertical distance between dorsum of the tongue and PNS on a line perpendicular to FH; D2: horizontal distance between posterior pharyngeal wall and dorsum of the tongue on a line parallel to the palatal plane that runs through C2; S–H: vertical distance between S and H; C3–H: linear distance between H and the most anterior point of C3; NSH: angle of S–H to SN plane.
distal and proximal segments). The average of mandibular setback was 6:5 2:5 mm (Table 1). Postoperative maxillo-mandibular fixation was maintained for 2 weeks with wires or elastics. Lateral cephalograms were taken preoperatively (T1), and 1 month (T2) and more than 1 year (T3) postoperatively. The subject was seated upright in the cephalostat with the Frankfurt horizontal plane (FH) parallel to the floor and the teeth in occlusion. To obtain a standardized position of the oropharyngeal structures, the cephalograms were taken at the end of expiration after swallowing. After the films were digitized, 3 serial cephalograms from each subject were traced by the same investigator, and the traditional contours and points of dentofacial structure were digitized to enable measurement of the tongue, pharynx, and hyoid positions. Linear and angular measurements were also determined according to a previous study. (Kawakami et al., 2004; Fig. 1). Evaluation of error at measuring and calculation To assess measurement error, the records of 10 subjects were re-evaluated 2 months later. The mean
Methodological errors in the cephalometric measurements were minimized by double recording. Timedependent changes of the measurements were examined by a paired t-test. Spearman’s rank was used to determine the statistical correlation between the changes in the airway space and hyoid position, and the amount of mandibular setback. Differences were considered to be significant at po0:05:
RESULTS The body mass indices [weight (kg)/height (m)2] of the subjects were within normal limits for both the male and female groups (Table 1). Preoperative, postoperative, and 1 year-follow-up changes are shown in Table 2. Significant differences of dental and skeletal parameters (overjet, overbite, and ANB) reflected the surgical changes that occurred from T1 to T2 (po0:05). No significant changes were seen from T2 to T3. However, the mandibular plane showed a slight clockwise rotation with an increase of Frankfurt horizontal–Mandibular plane–Angle (FMA) and the lower incisors became retroclined during the postoperative orthodontic treatment (IMPA—Incisor axis–Mandibular plane– Angle). Table 2 – Changes in dental and skeletal parameters measured preoperatively, postoperatively, and after the follow-up period. Variables Overjet (mm)
Overbite (mm)
ANB (degree)
FMA (degree)
IMPA (degree)
Mean (SD)
Mean (SD)
T1 T2 T3
3.4(2.8) 3.0(1.0)a 3.1(0.7)
T2–T1 T3–T2
5.8(3.1) 0.1(1.1)
T1 T2 T3
1.1(3.4) 0.5(1.0)a 0.9(1.0)
T2–T1 T3–T2
1.6(3.1) 0.3(1.3)
T1 T2 T3
2.9(3.9) 0.3(3.0)a 0.1(3.1)
T2–T1 T3–T2
3.2(2.5) 0.3(1.3)
T1 T2 T3
32.5(6.4) 32.5(7.3) 34.3(6.2)b
T2–T1 T3–T2
0.0(5.8) 1.6(3.3)
T1 T2 T3
85.5(5.2) 84.1(5.3) 82.1(5.9)b
T2–T1 T3–T2
0.7(4.5) 1.9(3.5)
FMA—Frankfurt horizontal plane–mandibular IMPA—Incisor (axis)–mandibular plane–angle. a po0:05 between T1 and T2; b po0:05 between T2 and T3.
plane–angle.
ARTICLE IN PRESS Changes in tongue and hyoid bone positions 109
The distance from sella to the hyoid (S–H) and that from C3 (third cervical vertebra) to the hyoid (C3–H) significantly increased between T1 and T2 (po0:05; Table 3). Marked vertical movement of the hyoid was also observed. However, the amount of mandibular setback did not have a positive correlation with the increase of S–H (p ¼ 0:275), or C3–H (p ¼ 0:49), although these parameters decreased from T2 to T3, in a manner corresponding with the earlier changes Table 3 – Changes in variables of tongue space and hyoid bone position postoperatively, and after the follow-up period. Variables D1 (mm) D2 (mm) S–H (mm) C3–H (mm) NSH (degree)
a
Mean S.D. T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T2 T3
10.5 10.1 9.0 15.5 15.4 13.2 120.1 125.4 120.2 40.1 41.8 39.2 88.8 89.9 89.6
(5.4) (6.0) (4.7) (4.1) (4.2) (3.1)b (6.3) (8.5)a (9.2)b (5.1) (5.1)a (4.6)b (5.6) (4.8) (4.7)
Mean S.D. T2T1 T3T2
0.4 (3.2) 1.1 (3.1)
T2T1 T3T2
0.6 (3.1) 2.2 (3.6)
T2T1 T3T2
4.8 (5.7) 5.1 (7.5)
T2T1 T3T2
1.6 (3.4) 2.6 (2.9)
T2T1 T3T2
1.1 (3.0) 0.3 (2.6)
po0:05 between T1 and T2; po0:05 between T2 and T3.
b
Fig. 2 – Diagram of immediate postsurgical changes (T2) in tongue space, hyoid bone position, and mandible.
from T1 to T2 (po0:05). The significant decreases of S–H and C3–H indicated a tendency for the hyoid to return toward its original position during the 1-year follow-up period. In contrast, the angle of NSH was not significantly altered, indicating that the direction of hyoid bone movement was maintained following surgery. The posterior vertical tongue space (distance 1— D1) and horizontal (mesopharyngeal) tongue space (D2) did not appear to change significantly from T1 to T2. But, D2 decreased markedly from T2 to T3, while D1 was changed only slightly (po0:05). The amount of mandibular setback did not correlate with the change of D2 (p ¼ 0:305). A diagram of the postsurgical changes in the soft and hard tissues is shown in Fig. 2. DISCUSSION The inferior movement of the hyoid bone seen in the present study is consistent with the findings of other studies, showing that this movement is an adaptation preventing an encroachment of the tongue into the pharyngeal airway (Tselnik and Pogrel, 2000). Another study indicated that the pharyngeal airway size is decreased shortly after setback surgery and becomes stable later (Enacar et al., 1994). Since the narrowed airway just after surgery is also a result of postoperative swelling in the soft tissue, we chose 1 month after surgery to let this settle. Our results confirmed that the vertical and horizontal spaces around the tongue were maintained postoperatively with the downward movement of the hyoid bone to compensate for the reduced oral volume caused by the mandibular setback. However, maintenance of the retrolingual space differed from the findings of previous studies and may have been a result of the bony fixation method employed. Many studies have used subjects with wire or plate fixation following a bilateral ramus splitting osteotomy (Wenzel et al., 1989; Lew, 1993; Enacar et al., 1994). The rigid bicortical fixation with screws used in the present study offers superior stabilization of bony segments when compared with wire fixation. The latter may have a different effect on the postsurgical changes of dentofacial features than bicortical screw fixation. Following screw fixation the retrolingual space was maintained. The hyoid bone returned to its original position during the follow-up period and the tongue volume encroached upon the pharyngeal airway. It was also found that the upward repositioning of the hyoid bone occurred late postoperatively and was related to the narrowed airway space at the tongue base, which explains the subsequent physiological adaptation of the dentofacial structures following surgery (Saitoh, 2004). The movement also resulted in clockwise rotation of the mandible. A reduced airway can reflect (craniofacial) morphology closely, such as open-bite related to adenoid enlargement. To preserve airway patency, the tongue encroaching on the
ARTICLE IN PRESS 110 Journal of Cranio-Maxillofacial Surgery
pharyngeal space may induce (functional) downward rotation of the mandible. A decrease in the upper airway leads to changes in head posture and, consequentially, the hyoid position. Following mandibular setback, the patient will have some short-term extension of the head, when compared with a cephalometric radiograph taken of the natural head position (Wenzel et al., 1989; Proffit and Phillips, 2003). These compensatory changes in natural head position following orthognathic surgery might mask morphologic changes in the upper airway (Nakagawa et al., 1998). Some investigators have found that the hyoid position can be assessed with reasonable accuracy by eliminating the use of cranial reference points (Bibby, 1984; Lew, 1993). In the present study, the subjects were positioned with the Frankfurt horizontal plane parallel to the floor, and all of the cephalograms were taken just after swallowing [in expiration] with light contact between the teeth to minimize unfavourable interference when determining the hyoid bone position. A reduced airway can also cause obstructive sleep apnoea (OSA). Some of the features seen after surgery indicate a change in oropharyngeal morphology, in a pattern closely resembling that seen in sleep apnoea subjects (Turnbull and Battagel, 2000) and 2 case reports have highlighted the development of sleep apnoea following surgery for mandibular prognathism (Guilleminault et al., 1985; Riley et al, 1987). Snoring worsened over the first 18 months following surgery for both patients, which supports the results of this study that demonstrated a narrowing of the airway. None of the present patients seemed to have any symptoms of OSA before or after orthognathic surgery, though one patient had an 8.5 mm reduction of D2 (horizontal pharyngeal airway space) from 18.0 mm at T1. The overall mean of D2 after follow-up was greater than 10.0 mm, which was wider than that previously reported in OSA patients (Battagel et al, 2002). A small reduction of the retrolingual space may not always develop into OSA after mandibular setback, as OSA develops progressively before it finally appears, implying that factors other than a single anatomic defect are involved (Guilleminault et al., 1985). It is believed that there may be a critical airway dimension, below which airway collapse (intermittent/complete) is much more likely. CONCLUSION The present serial cephalometric study revealed that the pharyngeal airway space was maintained shortly after mandibular setback surgery, while the hyoid bone moved inferiorly to compensate for reduction of the oral volume. Upward repositioning of the hyoid bone resulted in a significant reduction of the posterior lingual airway late after surgery. These results suggest that long-term care for the pharyngeal airway change is required following mandibular setback surgery.
ACKNOWLEDGEMENT
This study was supported in part by a Grant-in-Aid for Scientific Research (15592171) from Japanese Society for the Promotion of Science. References Battagel JM, Johal A, Smith AM, Kotecha B: Postural variation in oropharyngeal dimensions in subjects with sleep disordered breathing: a cephalometric study. Eur J Orthod 24: 263–272, 2002 Bibby RE: The hyoid position in mouth breathers and tongue thrusters. Am J Orthod 85: 431–433, 1984 Enacar A, Aksoy AU¨, S- encift Y, Haydar B, Aras K: Changes in hypopharyngeal airway space and in tongue and hyoid bone positions following the surgical correction of mandibular prognathism. Int J Adult Orthod Orthognath Surg 9: 285–290, 1994 Greco JM, Frohberg U, Sickels JEV: Long-term airway space changes after mandibular setback using bilateral sagittal split osteotomy. Int J Oral Maxillofac Surg 19: 103–105, 1990 Guilleminault C, Riley R, Powell N: Sleep apnea in normal subjects following mandibular osteotomy with retrusion. Chest 88: 776–778, 1985 Houston WJB: The analysis of errors in orthodontic measurements. Amer J Orthod 83: 382–390, 1983 Kawakami M, Yamamoto K, Noshi T, Miyawaki S, Kirita T: Effect of surgical reduction of the tongue on dentofacial structure following mandibular setback. J Oral Maxillofac Surg 62: 1188–1192, 2004 Lew KKK: Changes in tongue and hyoid bone positions following anterior mandibular subapical osteotomy in patients with Class III malocclusion. Int J Adult Orthod Orthognath Surg 8: 123–128, 1993 Nakagawa F, Ono T, Ishikawa Y, Kuroda T: Morphologic changes in the upper airway structure following surgical correction of mandibular prognathism. Int J Adult Orthod Orthognath Surg 13: 299–306, 1998 Proffit, W.R., Phillips, C., 2003. Physiologic responses to treatment and postsurgical stability. In: Proffit, W.R., White, R.P. Jr., Sarver, D.M. (eds.), Contemporary Treatment of Dentofacial Deformity. Mosby St. Louis, 646-676. Riley R, Powell N, Guilleminault C, Ware W: Obstructive sleep apnea syndrome following surgery for mandibular prognathism. J Oral Maxillofac Surg 45: 450–452, 1987 Saitoh K: Long-term changes in pharyngeal airway morphology after mandibular setback surgery. Am J Orthod Dentofac Orthop 125: 556–561, 2004 Tselnik M, Pogrel MA: Assessment of the pharyngeal airway space after mandibular setback surgery. J Oral Maxillofac Surg 58: 282–285, 2000 Turnbull NR, Battagel JM: The effects of orthognathic surgery on pharyngeal airway dimensions and quality of sleep. J Orthod 27: 235–247, 2000 Wenzel A, Williams S, Ritzau M: Relationships of changes in craniofacial morphology, head posture, and nasopharyngeal airway size following mandibular osteotomy. Am J Orthod Dentofac Surg 96: 138–143, 1989 Wickwire NA, White Jr. RP, Proffit WR: The effect of mandibular osteotomy on tongue position. J Oral Surg 30: 184–190, 1972 Dr. Masayoshi KAWAKAMI, DDS, PhD Department of Oral and Maxillofacial Surgery Nara Medical University 840 Shijo-cho Kashihara Nara 634-8522 Japan Tel./fax: +81 744 29 8876 E-mail: [email protected] Paper received 23 July 2004 Accepted 14 October 2004