The quantification of soft tissue cervicomental changes after mandibular advancement surgery

The quantification of soft tissue cervicomental changes after mandibular advancement surgery Randy J. Hayes, DMD, MS," David M. Sawer, DMD, MS, ~ and Alex Jacobson, DMD, MS, MDS, PhD ~

Ponte Vedra Beach, Fla., and Birmingham, A/a. Surgical mandibular advancement results in many soft tissue changes. The purpose of this study was to quantify the changes seen in the cervicomental angle and the lip-chin-throat angles in responseto mandibular advancement, as well as hyoid bone positional changes. As a result of statistical analysis of hyoid bone and soft tissue linear and angular changes, prediction models are presented as to the soft tissue response to mandibular advancement in the cervicomental region. (AMJ ORTHODDENTOFACORTHOP1994;105:383-91.)

H o r i z o n t a l movements of the mandible in the orthodontic surgical correction of skeletal dysplasia produce soft tissue changes in the chin and lips that has been well documented in the orthodontic and surgical literature. The changes that occur in the chin-neck contour after orthognathic surgery have not been evaluated as closely since past studies have focused primarily on postsurgical profile changes. Predicting soft tissue changes in relation to skeletal manipulation is an important step in the treatment planning process, and because of paucity of available information, further investigation is needed to improve the reliability of this prediction. The purpose of this study was to (1) quantify soft tissue chin-neck contour response to the change in hard tissue, (2) produce mathematical prediction models for application to presurgical prediction methods, (3) quantify positional changes of the hyoid bone with mandibular advancement, and (4) evaluate long-term adaptation of the new hyoid position. LITERATURE REVIEW

Many investigators stress the analysis of dental and skeletal pattern alone offers incomplete diagnostic information because of the extensive variation th~it exists in the soft tissue drape of the dentoskeletal framework, t-4 Several soft tissue analysess9 have been developed to increase the accuracy of treatment prediction, how*In private practice, Ponte Vedra Beach. Fla. bClinieal Associate Professor, Department of Orthodontics, University of Alabama at Birmingham. 'Clinical Associate Professor, Department of Orthodontics, University of Alabama at Birmingham. Copyright 9 1994 by the American Association of Orthodontists. 0589-5406/94/$3.00 + 0.I0 8/1/3952Z

ever, focused on the region between glabella and soft tissue pogonion. The soft tissue response to anterior and posterior mandibular movement has been relatively well documented. The terms submandible-neck, chhz-neck region, cervical angle, cervicomental, and submental area are all terms that basically describe the same anatomic area. The ideal of normal cervicomental angle has been reported to be 90~ l~ Ellenbogen and Karlin t~ contend that a cervicomental angle between 105~ and 120 ~ is ideal. Sommerville et al. t4 report the ideal cervicomental angle to be 126 ~ for males and 121 ~ for females. A few investigators have included the submental region in their soft tissue surgical assessment scheme. Worms, Isaacson, and Speidel ts used the throat length and lip-chin-throat angle as part of their orthognathic analysis. Legan and Burstone t6 use the lower face-throat angle, as well as the ratio between lower face height to submental length. Both groups of investigators stress the importance of proper evaluation of the submental area when contemplating orthognathic procedures. Hyoid bone positioning after orthognathic surgery has been the focus of a number of research projects. Marino et al. so reported that the overall success of double chin correction through soft tissue surgery is dependent on the hyoid bone position. A hyoid bone that is positioned inferior to the fourth cervical vertebra tends to predispose the person to a less than ideal treatment result. Wickwire et al. t7 identified the posterior and inferior movement of the hyoid bone immediately after posterior surgical movement of the mandible. They also observed that the hyoid tended to return toward its preoperative position with time, although it did not completely regain its original position. Kajikawa t8 reported that the soft tissue profile of the 383

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submental area moves slightly backward and downward in a parallel fashion to that of the hyoid movement seen in mandibular reduction procedures. Schendel, Wolford, and Epker ~9 observed that with the surgical advancement of the mandible the hyoid responded with a forward movement, and with time tended to return toward its preoperative position. LaBanc and Epker ~~ stressed that the immediate postoperative change in hyoid position was highly variable, but tended to be anterior in nature. They likewise observed that over time the hyoid bone tended to move back toward its preoperative position. Carlson et al. 2t attributed this hyoid movement to an adaptive process that occurs at the bone-tendon interface and not to the suprahyoid and infrahyoid musculature. After adaptation the hyoid tends to reside in a position close to its preoperative location.

MATERIALS AND METHODS The data for this investigation were derived retrospectively from lateral cephalometric radiographs of 24 patients who had undergone mandibular advancement procedures. The primary selection criteria for this investigation were as follows: 1. Patients were considered to be nongrowing at the time of surgery. 2. Patients had to exhibit a Class II skeletal relationship, in which orthognathic surgery was indicated as the treatment of choice. 3. The only surgical procedure performed on each patient was mandibular advancement. No maxillary surgery or adjunctive procedure such as genioplasty or liposuction were performed. 4. The patients must not have had any previous orthognathic or cosmetic surgery involving the middle and/or lower face. Other selection criteria included: 1. Standardized cephalometric patient-to-source and film distance. 2. Cephalograms were taken in natural head position. 3. Cephalograms were taken with the teeth in contact and lips at rest. Other criteria included avai!ability of records and quality of radiographs. The following records for each patient were required: (1) Presurgei'y or TI, a period of time no more than 140 days before surgery; and (2) postsurgery or T2, a period of time at least 4.5 months after surgery. The neck portion in each cephalogram needed to extend at least 40 mm inferior to the mandibular plane (when the mandibular plane was placed on a horizontal axis). Table I depicts the basic descriptive data of the population. The final sample population was comprised of 9 males and 15 females. The average patient age at the time of surgery was 28.6 years with a range of 15.4 to 41.1 years. All patients studied in this investigation were white.

American Journal of Orthodontics and Dentofacial Orthopedics April 1994

The presurgical cephalograms were taken, on the average, 33 days before surgery, with a range of 1 day to 140 days. Postoperative cephalograms ranged from 4.7 to 31.1 months, with a mean duration of 14.1 months. The patients had no surgical splints, centric relation splints, or other factors that would cause a backward rotation of the mandible on the cephalogram. The magnification of the two cephalometric machines used in this study were standardized. In addition to the traditional cephalometric landmarks, the following land~ marks were identified: 1. Hyoid (H), a point indicating the center of the body of the hyoid bone. ~-" 2. Labrale inferius (L/), a point indicating the mucocutaneous border of the lower lip. t6 3. Soft tissue pogonion (Pog'), the most anterior point on the soft tissue chin. ~6 4. Soft tissue menton (Me'), the lowest point in the contour of the soft tissue chin.t~ 5. R point (R), the point of maximum convexity of the transition from submental to anterior neck region, Io~ cated at the intersection of lines drawn tangent to the anterior neck and submental areas. However, if this intersection is not on the soft tissue outline of the submental-neck region, a bisecting line is drawn through the angle to the soft tissue submental-neck outline. The intersecting point of the bisecting line and the soft tissue submental-neck outline is the R point (R). 6. Terminal point (T), a point located on the soft tissue outline of the anterior neck 40 mm from the mandibular plane when the mandibular plane is placed on a horizontal reference line (Fig. 1). The ccphalometric tracing was placed on a 1 mm x-y grid with the sella nasion line superimposed on the reference horizontal plane. Starting at the nearest 5 mm reference line to terminal-point (T), marks were placed at 5 mm intervals moving superior and anterior along the soft tissue neck and chin until soft tissue menton (Fig. 2). These marks were ultimately used to graphically determine the shape of the chinneck curvature. Hard and soft tissue linear and angular measurements and hard tissue to soft tissue linear measurements were made on each film. Additional measurements for graphically determining the shape of the curve of the chin-neck region were collected: The following measures were made on each cephalogram: Angular measurements: 1. Sella (S) to basion (Ba) to hyoid (H) ~7 2. Mandibular plane-sella-nasion (SN) to gonion-gnathion (GoGn) 3. Basion (Ba) to hyoid (H) to menton (Me) 4. Anterior nasal spine (ANS) to posterior nasal spine (PNS) to hyoid (H ) 5. The angle formed by intersecting the lines from labrale inferius (L1) to soft tissue pogonion (Pog') and R point (R) to soft tissue menton (Me'). This is essentially the lip-chin-throat angle as described by Worms et al. ~

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T a b l e I. Basic descriptive data for the s a m p l e population (n = 24)

Subject

I

Mandibularplane angle

M F F F M F M M F F M F F F F F M M F M F M F F

38.87 16.57 36.08 22.19 33.02 26.92 37.67 29.40 30.58 33.14 25.38 44.47 27.98 30.26 31.61 45.00 23.77 24.17 34.29 30.96 25.59 23.11 29.20 38.44

18.25 22.34 36.22 27.09 20.34 31.47 32.36 17.70 33.04 15.41 29.35 38.69 24.95 38.07 16.16 35.59 28.69 29.57 41.16 27.37 19.01 33.97 35.52 34.98

6 72 16 9 56 20 31 25 15 3 2 70 106 12 140 8 41 i 50 7 1 72 6 33

11.47 10.03 5.80 12.87 19.93 19.20 9.80 30.23 4.83 12.33 7.37 31.13 9.30 12.60 23.90 4.67 10.70 12.07 13.60 26.33 9.80 21.67 7.80 I 1.20

30.78 6.99

28.64 7.77

33.42 36.48

14. I I 7.68

i 2 3 4 5 6 7 8 9 10 I1 12 13 14 15 16 17 18 19 20 21 22 23 24 Mean Standard deviation

J

Age (yrs)

Preoperativeduration (days)

Sex

Postoperative duration

(mos)

6. Ccrvicomental angle: The angle formed by the intersection of lines drawn tangent to the soft tissue submental region and the anterior neck region, j' Linear measurements: 1. Basion (Ba) to hyoid (H) 2. Sella (S) to hyoid (H) 3. Posterior nasal spine (PNS) to hyoid (H) 4. Basion (Ba) to B point (B) 5. Basion (Ba) to pogonion (Pog) 6. Hyoid (H) to menton (Me) 7. R point (R) to soft tissue menton (Me'): similar to Worms et al. 15 throat length measurement. 8. Hyoid (H) to R point (R)

basis of sex (Table II) to determine whether any chin-neck anatomic variances existed. The population was further divided into high and low angle groups on the basis of mandibular plane angle (SN to GoGn) measurements (Table III). Those persons have a mandibular plane angle of 33 ~ or above were placed into the high angle group. Correlations of original variables, as well as correlations concerning before-to-after surgical changes, were derived. In addition, multiple regression models were regenerated for the prediction of postsurgical variables on the basis of presurgical variables.

Other measurements were recorded with a 1 mm x-y grid. The cephalometric tracing was placed on a I mm x-y grid with the SN line superimposed onto the x-axis at the y-axis value of zero. Sella was placed at the x-value = 0 and the y-value = 0 (Fig. 2). The reference marks, which were previously placed at the 5 mm intervals along the chin-neck soft tissue outline from T to ME', were then given x and y values in relation to S (x = 0, y = 0). The R point was also given an x and y value in relation to S. These measurements were recorded on a data sheet and used to determine curve shapes for the chin-ncck region and thus allow before and after surgical comparisons. To reduce investigator bias, the cephalograms were randomly traced and measured. The population was divided into two subgroups on the

A correlation analysis was p e r f o r m e d for the entire population at T I , T 2 , and T I - T 2 . T h e population was then d i v i d e d into the s u b g r o u p s previously e m p l o y e d : m a l e , f e m a l e , high angle, and low angle. Correlation analyses w e r e p e r f o r m e d for each o f the respective subgroups. T h e respective subgroups b e h a v e d in a m a n ner that f o l l o w e d that e x h i b i t e d by the entire population. Thus, stratifying the sample to find significantly different b e h a v i o r patterns a m o n g the subgroups p r o v e d unrewarding. Hyoid bone movement ( F i g . 3). A n u m b e r o f significant correlations existed b e t w e e n the respective m e a s u r e m e n t s c o n c e r n e d with hyoid m o v e m e n t . A

RESULTS Correlations

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Note:

American Journal of Orthodonticsand DentofacialOrthopedics April 1994

Ba:

Baslon

S: N:

Sella Nasion

Pns:

Posterior Na~al Spine Anterior Nasal Spine

Ans: LI.:

l-ahlal Inferius

B: Pug: Poe': (;o: (;n: Me:

B Point Poionlon Soft-tlssue Pilgtmllln {;onion (;nalhion Nlcnlon

Nle':

Soft-tissue Menton

II:

II)uld

R: T:

R Point T Point

( Ila

l'u~

1_1. I0

Pug'

Fig. 1. Technique for locating terminal point (T).

Table II. Population subgroups by sex type Sex

Male Female

]

Nztmber (24)

9 15

strong positive correlation existed between change in S-H distance and change in PNS-H distance. A strong positive correlation was also seen between the change in Ba-H distance and the change between S-H. In addition to these linear measurements, some angular measurements likewise showed high correlation values: as S-Ba-H became more acute, Ba-H-Me became more obtuse. Finally, some hyoid linear measurements showed significant correlation values with some hyoid angular measurements; as Ba-H-Me became more obtuse, the distance between hyoid and PNS decreased. The sum of the above correlations imply a mostly superior movement of the hyoid bone following mandibular advancement surgery.

Table III. Population subgroups by mandibular plane angle

Angle t~pe High (~33 ~ Low (<33 ~)

I

Number(241 9 15

{

Meanangle 38~ 27~

Soft tissue correlations (Figs. 4, 5, 6). Several significant correlations existed that relaied to soft tissue activity. As the hyoid bone moved toward seila and PNS, the cervicomental angle decreased. Another significant correlation was between the cervicomental angle and the lip-chin-throat angle. As one decreased, the other decreased. On advancing the mandible between TI and T2, the following associations were noted: (1) Superioranterior hyoid movement was shown to be associated with mandibular advancement; (2) improvement in the lip-chin-throat angle was associated with both mandibular advancement and superior-anterior hyoid movement; and (3) improvement in the cervicomental angle

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Note:

H a y e s . Sarver, a n d J a c o b s o n

Ba: S: N: Pns:

Iiasion Sr Nasion Posterior NasaISpine Anterior NasaISpine L|,: I.abial Inhrius B: B Point P~)g: Pogonion Pog': Soft-tissue Pogonitm

Ans:

(;o: (;n:

(;onion (;nalhion

~

Me: Menfon Me': Sob-tissuel%|enton II:

tl)oid R: RPoint T: TPoint

Fig. 2. Placement of marks along cervicomental region between T point and menton.

Hyoid Bone Changes 6.00 4.00 2,00 0.00 I I Ba-II

(mm)

E] S-i!

-2.00

I PNS-H

-4.00 -6.00 -8.00 -10.00 Subjects

Fig. 3. Individual measurements T1-T2 for hyoid bone changes are illustrated by Ba-H, S-H, and PNS-H.

387

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American Journal of Orthodontic.~and Dentofacial Orlhopedics April 1994

Lip-Chin-Throat Angle 5.00

0.00

-5.00

Degrees -Io.00

-15,00

-20.00

-25.00

Subjects

Fig. 4. Individual measurements T1-T2 are illustrated for lip-chin-throat angle.

Cervicomental Angle 25.00 20.00 15.00 10.00 5.00 0.00

Degrees -5.00 -10.00 -15.O0 -20.00 -25.00

-30.00 Subjects

Fig. 5. Individual measurements T1-T2 are illustrated for cervicomental angle.

was shown to be associated with improvement in the lip-chin-throat angle, as well as superior-anterior hyoid movement. Descriptive data Preoperative and postoperative angular and linear measurements between TI and T2 yielded certain trends, namely, (1) mandibular plane increased by a mean of three degrees, consistent with clockwise rotation with mandibular advancement; (2) the hyoid bone

tended to move superiorly and slightly anteriorly toward the PNS; (3) the lip-chin-throat angle tended to become more acute thereby producing a relatively less convex facial profile; and (4) the cervicomental angle be.came more acute after the mandibular advancement. PREDICTION METHODS The prediction models were designed to quantitatively relate the change in one variable with the changes in a second variable. The focus of this investigation is

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Hayes, Sar~'er, and Jacobsen

389

R point-Me' tO00 8.00 6 O0 4 O0 2.00

Degrees

o.0o .2.oo -4.00 -6.00 -8.00 -10.00

Subjects

Fig. 6. Individual measurements T1-T2 are illustrated for FI point-Me'.

Table IV. Prediction models Dependent variable

I

Constant

Independent variable

[

P-value

(~ (*)Change (~ (~ (~

in in in in in

cervicomental cervicomental cervicomental cervicomental cervicomental

angle angle angle angle angle

= = = = =

-0.77 +0.77 + 1.83 +2.13 + 1.94

• • • x •

(~ change in Ba-H-Me (o) change in lip-chin-throat angle (mm) change in Ba-H (ram) change in S-H (mm) change in PNS-H

0.0009 0.0001 0.0080 0.0004 0.0002

(~ (~ (~ (*)Change (~ (~ (~

in in in in in in in

lip-chin-tht:oat angle lip-chin-throat angle lip-chin-throat angle lip-chin-throat angle lip-chin-throat angle lip-chin-throat angle lip-chin-throat angle

= = = = = = =

+ 1.83 - 1.04 +2.09 +2.47 +2.33 - 1.81 - 1.92

x • • x • • •

(~ change in S-Ba-H (~ change in Ba-H-Me (mm) change in Ba-H (mm) change in S-H (mm) change in PNS-H (mm) change in Ba-B point (mm) change in Ba-Pog

0.0013 0.0001 0.0006 0.0001 0.0001 0.0001 0.0001

concerned with changes that occur in the chin-neck contour after mandibular advancement. Therefore the emphasis is placed on the prediction models that use either the lip-chin-throat angle or the cervicomental angle as the dependent variable. The significant prediction models that use these two measurements, as the dependent variable, are presented in Table IV. The first group of prediction models concem the cervicomenta! angle. The table shows that for each degree of increase in the Ba-H-Me angle, the cervicomental angle decreased 0.77 ~ Concerning linear measurements, for each millimeter of decrease in the Ba-H distance, the cervicomental angle decreases 1.83 ~ In addition, as the hyoid moves 1 mm toward sella or PNS, the cervicomental angle decreases 2.13 ~ and 1.94 ~ respectively.

The last significant predictor of the cervicomental angle is the lip-chin-throat angle. For each degree of reduction in the lip-chin-throat angle, the cervicomental angle decreases by 0.77 ~. Thus lip-chin-throat angle changes, as well as hyoid movement, have predictive value concerning subsequent changes in the cervicomental angle. The other soft tissue dependent variable that was used in the predictive model analysis was the lip-chinthroat angle. A 1~ reduction in the S-Ba-H angle reduces the lip-chin-throat angle by 1.83 ~ When the Ba-H-Me angle becomes more obtuse by 1~ the lip-chin-throat angle measurement decreases by 1.04 ~ On examination of linear measurements concerning hyoid, one sees that as the hyoid moves 1 mm towards Ba, S or PNS one can expect to see a decrease in the lip-chin-throat angle

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of 2.09 ~ 2.47 ~ or 2.33 ~ respectively. Thus as the hyoid moves toward the respective stable cranial landmarks, varying degrees of improvement in the lip-chinthroat angle can be expected. The final prediction models directly relate mandibular advancement to improvement in the lip-chin-throat angle. As the mandible is advanced 1 ram, as measured at Ba-B point, the lip-chin-throat angle decreases by 1.81 ~. When mandibular advancement is measured at Ba-Pog, 1 .mm of advancement yields a decrease of 1.92 ~ in the lip-chin-throat angle. Thus predictions can be made to determine how much the facial profile will be enhanced at the lip-chin-throat angle based on known amounts of mandibular movement. DISCUSSION

Between TI (presurgery) and T2 (postsurgery), the hyoid tended to move toward the PNS of the palate, that is, superiorly and slightly anteriorly. This pattern of predominantly superior movement is different from that described by Schendel et a!.,19 but corroborates the findings of Riley et al. 23The tendency was for the hyoid bone to move anteriorly with mandibular advancement and later return toward its initial location. ~9 Another investigation, by LaBanc and Epker, 2~reported a similar anterior movement tendency, however, they emphasized the "highly variable" nature of the postoperative positions of the hyoid in their subjects. Schendel et al. 19and LaBanc and Epker2~described hyoid bone as returning approximately to its original position. At the long-term postoperative point, T2, our investigation showed the hyoid bone to be located superior to its preoperative position by a mean measurement of 3.7 mm, Therefore our investigation did not detect the long-term readaptation of the hyoid toward its original position. It is possible that longer term investigation may find a return toward the original preoperative position, but our investigation showed no tendency toward this trend. This investigation revealed other significant trends. These concerned soft tissue response to hard tissue movement and involved both the cervicomental angle and the lip-chin-throat angle. When the mandible was advanced both of these angles became more acute, achieving more desirable esthetic contours. A possible explanation for this increased convexity in the cervicomental angle relies on hyoid movement. The hyoid was shown to move superiorly and the adjacent soft tissue moved with it. In this investigation, the hyoid bone moved superiorly towards PNS a mean of 3.7 ram. Concomitantly, the hyoid moved away from R point a mean of only 1.7 mm. Therefore R point fol-

American Journal of Orthodontics and Dentofacial Orthopedics April 1994

lowed hyoid superiorly approximately 2 mm. Since R point is the apex of the cervicomental angle, this superior movement tends to deepen the angle or make it more acute. In addition to the correlation analyses, curve shapes, and basic data measurements, prediction models were generated from this investigation. The prediction models allow the quantification of the relationshi p between the respective independent and dependent variables. Hyoid movement, as well as the lip-chin-throat angle, were demonstrated to be significant predictors of the cervicomental angle response to mandibular advancement. Unfortunately, the cervicomental angle change could not be directly calculated, with a statistical level of significance, when using changes in BaPog or Ba-B point as the independent variables. This was due to the large amount of variability seen in the cervicomental measurements of the population. Thus the prediction models, cervicomental angle change = - 1 . 4 7 • miilimetric change in Ba-B point, can be derived but they fail to surpass the statistical level of significance. However, in clinical terms, they do give a general idea of cervicomental response to mandibular advancement. Basically, for each millimeter that the mandible is advanced, the cervicomental angle will decrease approximately 1.5 ~ Some factors were present in this investigation that may have influenced results and were not significantly controlled. Weight gain or loss between TI and T2 measurement points could have had an impact on the profile of the cervicomental region. This weight fluctuation could mask the true soft tissue response to mandibular advancement. Variance in soft tissue tonicity is another factor that could influence the respective person's soft tissue response to mandibular advancement. In addition, the effects of swallowing on hyoid position during the taking of the cephalograms was not evaluated. Thus the development of systems that" would address these potentially confounding factors would strengthen the experimental design, and might possibly lead to more controlled results. Furthermore, it would be of interest in future studies to investigate the effects of mandibular reduction on hyoid position. CONCLUSIONS

Having described various soft tissue profile and hard tissue changes after mandibular advancement surgery, the following conclusions are presented. 1. On mandibular advancement, the hyoid bone moves toward sella, basion, and posterior nasal spine. The overall movement can be described as superior with a slight anterior component.

American Journal of Orthodontics and Dentofacial Orthopedics Volume 105, No. 4

2. O n mandibular a d v a n c e m e n t , the soft tissue cerv i c o m e n t a l angle and lip-chin-throat angle decreased. 3. A significant p o s i t i v e correlation exists b e t w e e n changes in the soft tissue c e r v i c o m e n t a l angle and the soft tissue lip-chin-throat angle after mandibular advancement. 4. B e c a u s e o f a high level o f variability in c e r v i c o m e n t a l m e a s u r e m e n t s , statistically significant prediction m o d e l s c o u l d not be generated for c e r v i c o m e n t a l angle c h a n g e as a function o f m a n d i b u l a r a d v a n c e m e n t . H o w e v e r , as a clinical aid a p p r o x i m a t e l y a 1.5 ~ decrease in the c e r v i c o m e n t a l angle can be e x p e c t e d for each millimeter of mandibular advancement. REFERENCES 1. Burstone CJ. The integumental profile. AM J ORTIIOD1958;44:125.

2. Subtelny JD. A longitudinal study of soft-tissue facial structures and their profile characteristics, defined in relation to underlying skeletal structures. AM J OR'ntOD 1959;45:481-507. 3. Park YC, Burstone CJ. Soft-tissue profile--fallacies of hardtissue standards in treatment planning. AMJ OR'ntOD1986;90:5262. 4. Holdaway RA. A soft-tissue cephalometric analysis and its use in orthodontic treatment planning. Part I. AM J OR'rltOD 1983 ;84:1-28. 5. Hershey GH, Smith LH. Soft-tissue profile change associated with surgical correction of the prognathic mandible. AM J OR'ntOD 1974;65:483-502. 6. Lines PA, Steinhauser EW. Soft-tissue changes in relationship to movement of hard structures in orthognathic surgery: a preliminary report. J Oral Surg 1974;32:891-6. 7. Robinson SW, Speidel TM, Isaacson RJ, Worms FW. Soft-tissue profile change produced by reduction of mandibular prognathism. AM J OR'roOD 1972;42:227-35. 8. Mommaerts blY, Marxer H. A cephalometrie analysis of the long-term soft-tissue profile changes which accompany the advancement of the mandible by sagittal split ramus osteotomies. J Craniomandib Maxillofae Surg 1987;15:127-31.

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9. Quast DC, Biggerstaff RH, Haley JV. The short-term and longterm soft-tissue profile changes accompanying mandibular advancement surgery. AM J ORTItOD 1983;84:29-36. 10. blarino H, Galeano EJ, Gandolfo EA. Plastic correction of double chin--importance of the hyoid bone. Plast Reconstr Surg 1963;31:45-50. 11. Millard RD, Pigott RW, Hedo A. Submandibular lipectomy. Plast Reconstr Surg 1968;41:513-22. 12. Vismes L, Souther S. The anatomic basis for common cosmetic anterior neck deformities. Ann Plast Surg 1979;2:381-8. 13. Ellenb~en R, Karlin J. Visual criteria for success in restoring the youthful neck. Plast Reconstr Surg 1980;66:826-37. 14. Sommerville JM, Sperry TP, BeGole EA. blorphology of the submental and neck region, lnt J Adult Orthod 1988;3:97-106. 15. Worms FW, Isaacson RS, Speidel Tbi. Surgical orthodontic treatment planning: profile analysis and mandibular surgery. Angle Orthod 1976;46:1-25. 16. Legan HL, Burstone CJ. Soft-tissue cephalometric analysis for orthognathic surgery. J Oral Surg 1980;38:744-51. 17. Wickwire NA, White RP, Proffit WR. The effect of mandibular osteotomy on tongue position. J Oral Surg 1972;30:!84-90. 18. Kajikawa Y. Changes in soft-tissue profile after surgical correction of skeletal Class 1I malocclusion. J Oral Surg 1979;37:16774. 19. Schendel SA, Wolford LM, Epker BN. Mandibular deficiency syndrome. Oral Surg Oral bled Oral Pathol 1978;45:364-77. 20. LaBanc JP, Epker BN. Changes of hyoid bone and tongue following advancement of the mandible. Oral Surg Oral Med Oral Pathol 1984;57:351-6. 21. Carlson DS, Ellis E, Dechow PC. Adaptation of the suprahyold muscle complex to mandibular advancement surgery. AM J OR'I'HODDEN'rOFACORTHOP ! 987;92: ! 34-43. 22. Takagi Y, Gamble JW, Proffit WR, Christiansen RL. Postural change of the hyoid bone following osteotomy of the mandible. Oral Surg Oral bled Oral Pathol 1967;23:688-95. 23. Riley R, Guilleminault C, Powell N, Derman S. Mandibular osteotomy and hyoid bone advancement for obstructive sleep apnea: a case report. Sleep 1984;7:79-82. Reprint requests to:

Dr. David M. Sarver 1705 Vestavia Parkway Birmingham, AL 35216