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Soft-Tissue Changes Related to Mandibular Advancement Surgery
Soft-Tissue Changes Related to Mandibular Advancement Surgery Antony G.H. McCollum, Graham J.M. Gardener, William G. Evans, and Pieter J. Becker This retrospective study assessed the relationship between the soft-tissue contours of the lower lip and chin and the underlying hard tissues consequent to surgical advancement of the mandible in the endeavour to enhance prediction in treatment planning. Cephalometric head films of 25 cases, 7 of which had advancement genioplasties, were available at presurgical, early postsurgical, intermediate, and long-term stages. Nineteen cephalometric landmarks were located and the data measured relative to X-Y coordinates constructed on the head films and were recorded on a Kontron video plan computer (Kontron Messgerate, GmbH, Image-analysis-systems, Eching/ München, West Germany). The data were organized and tabulated with Statgraphics version 4.0 software and statistically analyzed at the Institute of Medical Biostatistics, University of the Witwatersrand. No significant differences were found in the data between the patients who had undergone advancement genioplasties and those who had not. The soft-tissue chin advanced in a 1:1 ratio with the bony chin and a significant correlation was found between the horizontal change at labrale inferius relative to the lower incisor tip with a ratio of 0.77:1, but only marginally improved when tissue thickness was incorporated into a multiple regression analysis. Vertical changes of the lower lip did not show significant correlations with any hard tissue changes. Only when presurgical tissue thickness was included into a multiple regression analysis did the vertical change at labrale inferius demonstrate a fairly good correlation with the vertical change at menton. No significant changes occurred in the upper lip, and there was no significant relapse recorded at a minimum of 12 months after surgery. (Semin Orthod 2009;15:161-171.) © 2009 Elsevier Inc. All rights reserved.
urgical advancement of the recessive mandible to improve function and esthetics in adults is reasonably routine and generally well controlled. Predicting the soft-tissue reaction of
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Department of Orthodontics, University of the Witwatersrand, Johannesburg, South Africa (A.G.H.M.). Private Practice, Southampton, UK (G.G.J.M.). Department of Orthodontics, University of the Witwatersrand, Johannesburg, South Africa (W.G.E.). Biostatistics Unit, MRC and School for Therapeutic Sciences, University of the Witwatersrand, Johannesburg, South Africa (P.J.B.). Address correspondence to Antony G.H. McCollum, BDS, HDD, MDent, PO Box 67104, Bryanston, Sandton, South Africa, 2021; E-mail: [email protected] © 2009 Elsevier Inc. All rights reserved. 1073-8746/09/1503-0$30.00/0 doi:10.1053/j.sodo.2009.03.001
the lower lip to this precise surgical movement of the bone has, however, proven a challenge. Pretreatment planning usually requires the use of cephalometric prediction tracings and, more recently, surgeons have relied on computer software programs to further assist the visualization of the projected results. It is clear that soft-tissue reactions to bone repositioning play an essential role in prediction of treatment outcome. Many studies in the literature have reported on these reactions. Most predict that the softtissue chin advances in a more or less 1:1 ratio, in concert with movement of the hard tissue chin with strong correlations between the relationship.1-9 However, considerable variation in results has been reported for the proportional
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advancement of the lower lip, measured from the lower incisor tip to labrale inferius, in relation to the forward positioning of the mandible. Reports have allocated relationships ranging from a high coordination of 0.8:1 to a low of only 0.26:1.1-14 Even studies allowing for considerable postsurgery settling, up to 3 years, have found varied relationships, ranging from 0.48:1 to 0.79: 19-13 and, in some cases, a finding of up to 30% relapse after the first year of surgery.14 Studies that rely on mean values do not explain individual variation and it has only been when many variables have been included in the analyses that stronger correlations have been identified as, for example, by Jensen et al15 (r ⫽ 0.82) and Hamada11 (r ⫽ 0.76). Veltkamps et al12 showed that the inclusion of up to 5 different variables into a multiple regression equation improved the correlation significantly (r ⫽ 0.88). The factors that contribute to the considerable variation of results include the variation in thickness of the lower lip from one individual to the other, lip tonicity, posture, muscle pull, skeletal stability,5,15,10,16 lowerlip redundancy,15,17 area of the lower lip,5,9,16,18 interlabial gap,18 influence of the maxillary incisor teeth15,19 and posture of the lips,4,16,17 and difficulty in taking the head films with the lips in a relaxed state.4 Mommaerts and Marxer4 and Mobarak et al10 found in deep bite cases a positive correlation between an increase in facial height if the lower jaw is rotated in a clockwise direction while it is advanced, with a concomitant decrease in the characteristically deep labio-mental fold. The lip becomes thinner as it unfurls, allowing a relatively reduced advancement together with vertical movement at soft tissue menton. Dermaut and de Smit6 and Mobarak et al10 recorded statistically and clinically insignificant changes to the upper lip after the lower jaw was advanced. In the present retrospective study we further explored the complex relationship between bone and soft-tissue responses by invoking an intricate statistical analysis to refine the balance between tissue movements.
Materials and Method Subjects The cephalometric records of 25 grown Caucasian patients who had had mandibular advance-
ment osteotomies (16 women, mean age of 28.2 years at surgery, ranging from 17 to 50 years, and 9 men, mean age 27 years, ranging from 17 to 48 years) from the files of a private orthodontic practice, were included in the study. Seven of these patients also had advancement genioplasties. All patients were medically fit and without any developmental syndromes and had received full fixed appliance orthodontic treatment to appropriately decompensate the incisors. The arches were stabilized 6 weeks before the mandibular advancement. Six different maxillo-facial surgeons severally performed the osteotomies according to the method described by Epker et al.20
Cephalometrics All cephalometric radiographs were taken on the same machine by the same operator. The patient held the teeth in occlusion, and the orthodontist personally ensured that the lips were in the relaxed state. Only radiographs of sufficient quality to enable accurate recording of the relevant hard and soft tissue landmarks were acceptable for the study. The radiographs had been taken at the following stages: the initial head film, presurgery—T1, 6 weeks after surgery—T2, at the completion of postoperative orthodontics (4 to 11 months)—T3, and 12 months after surgery—T4. The major period used in this study is T1–T3, which refers to the time interval between the presurgical stage to the completion of orthodontic treatment (n ⫽ 25). However, data also were also collected for the periods T2–T3 and T3–T4. The sample was divided into two groups—those who had received advancement genioplasties (n ⫽ 7) and those whose treatment included only mandibular advancement. Cephalometric tracings were completed for each radiograph on Ozatex 0.5 mm D/Matt drafting film paper (Ozalid SA, Pty. Ltd., Drawing Office Material, Spartan, Kempton Park, South Africa) with a 6-H pencil. Two locating crosses were scribed directly onto the radiographic film and were copied to the overlying film paper once it had been secured to the radiographic film. The anatomical tracing, cephalometric landmarks, and their abbreviations used in the study are illustrated in Figure 1. To locate those landmarks defined as “most ante-
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Figure 1. Typical cephalometric tracing and the abbreviations for the landmarks measured. N ⫽ nasion, S ⫽ sella turcica, PNS ⫽ posterior nasal spine, ANS ⫽ anterior nasal spine, NT ⫽ nose tip, Sn ⫽ subnasale, A ⫽ A point, A= ⫽ soft-tissue point A or superior labial sulcus, Ls ⫽ labrale superius, St ⫽ stomion, LIT ⫽ lower incisor tip, UIT ⫽ upper incisor tip, Li ⫽ labrale inferius, B ⫽ point B, B= ⫽ inferior labial sulcus, or soft-tissue point B, Pog ⫽ pogonion, Pog= ⫽ soft-tissue pogonion, Gn ⫽ hard tissue gnathion, Gn= ⫽ soft-tissue gnathion, Me ⫽ hard-tissue menton, Me= ⫽ soft-tissue menton.
rior or posterior” on curved segments of the tracing, a perpendicular effecting a one point contact immediately identified the point. In other instances the perpendicular met the curved tracing outline as an area of contact. The midpoint of this contact was used (Fig 2). Each radiograph was traced twice under the same conditions at the same occasion to diminish the error of variability.21 On the first presurgical tracing, reference axes were determined to enable the recording of the horizontal and vertical changes. An X axis was created
at a 6-degree angle to S-N and the Y axis was constructed as a perpendicular to S-N at sella turcica.22 The references axes were not determined on the second tracing but were transferred from the first presurgical tracing to the second presurgical tracing after the tracings were accurately overlaid by superimposing the 2 locating crosses which had been copied onto each tracing directly from the radiograph. This standardized the reference system for each set of presurgical tracings for each patient.
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Corporation, Rockville, MD) and analyzed at the Institute of Medical Biostatistics, a unit of the Medical Research Council of South Africa at the University of the Witwatersrand, Johannesburg.
Statistical Analysis Error of the Method
Figure 2. Definition of a point on a curved segment. A perpendicular line dropped from the X-axis, tangent to the relevant cephalometric landmark (in this case, Nose Tip).
Then, in each set of tracings the reference axes were transferred from the presurgical tracings to the post surgical tracings. This was achieved by finding the closest orientation between the two tracings by closely superimposing the outlines of sella turcica, de Coster’s lines, superior orbital rim, orbit and the fronto-nasal area structures.3 The reference axes were then copied onto the post-surgical tracing. The coordinates of every reference landmark on each tracing were sequentially computed in relation to the X and Y reference system using a digitizing program on a Kontron Messgerate, GmbH, Image-analysis-system (Eching/München, West Germany). The “X” coordinates represented the horizontal distance from the vertical axis, and the “Y” coordinates the vertical distance from the horizontal axis measured in millimeters to an accuracy of 3 decimal places. A negative value was assigned to posterior or superior displacements while a positive value was assigned to anterior or inferior changes. The coordinates for each parameter on each radiograph were measured, twice, the mean value determined thereby decreasing the error of variabitity.21 This was further decreased by completing the two sets of measurements at the same session.21 All the data were organized and tabulated with Statographics 4.0 software (Statistical Graphics
The accuracy of digitizing was tested by randomly selecting one tracing that was re digitized 9 times on separate occasions at least 24 hours apart and the coefficient of variation between these measurements calculated. Intraexaminer repeatability of landmark identification was tested by use of the duplicate set of data for each patient and applying the coefficient of repeatability as used by the British Standards Institution (Bland and Altman23), which was calculated for each landmark. A coefficient of repeatability of less than 1.5 mm was chosen as acceptable for this study.17,24,25 Interexaminer accuracy of landmark location was obtained from 10 orthodontists who traced and located 6 landmarks that were chosen as representative of the diversity of landmarks in the study. The means of these measurements for each of the 6 landmarks were digitized, a coefficient of variation was derived and the limits of agreement, as defined by Bland and Altman,23 were used to assess the agreement between the researchers’ measurements and those of the 10 orthodontists. Change During the T1-T3 Time Interval It was firstly necessary to determine whether the proportional changes of the seven genioplasty patients differed from those of the nongenioplasty patients. Simple proportional equations were calculated for the same landmarks for both groups of patients. A Student’s t test was applied and, when applicable adjusted for un-equal variances derived from Levene’s test.26 Significance was determined at the 0.05 level. Data Management Descriptive statistics were calculated for the data from the T1–T3 time and a paired Student’s t test was used to evaluate the significance of the mean change from T1 to T3 values for each landmark, measured in millimeters along each axis. The level chosen for significance was at P ⱕ
Soft-Tissue Changes Related to Mandibular Advancement Surgery
0.05. A change greater than 1.5 mm.17,24,25 was regarded as clinically relevant. The data for those hard and soft tissue landmarks for which were recorded statistically and clinically significant changes were then subjected to analysis to assess the relationship between these changes. For the changes from T1–T3, Pearson correlation coefficients were calculated between these landmarks and the coefficients of determination were assessed for each landmark. A coefficient of determination of greater than 50% indicates a good correlation, ie, r ⱖ 0.7.24 The correlation analyses were performed to evaluate the relationship of the changes which had occurred between the following corresponding hard and soft tissue landmarks in the horizontal and vertical dimensions: LIT and Li, B and B=, Pog and Pog=, Gn and Gn= and Me and Me=. In addition changes occurring at LIT, Pog and Me were each tested for correlation with changes recorded at Li, B=, Pog=, Gn=, and Me=. Multiple regression analyses were performed on the aforementioned landmarks to assess the relationship between the changes of the hard and soft tissues in the horizontal and vertical dimensions, together with an additional factor, the presurgical tissue thickness. Again the coefficient of determination was calculated. Other variables that could influence soft tissue change are facial type, elasticity of the tissue and patient stress as it influences muscle tone. From the results of these statistical analyses, it was possible to identify the best possible predictors upon which to base a forecast of new, post surgical positions of the soft tissue land marks. Statistics for the period T2 to T3 (n ⫽ 20) patients, ie, from the early (6 weeks) post surgical stage to the end of active orthodontic treatment enabled an assessment of initial surgical stability and, similarly the analysis of data from T2 to T4 (n ⫽ 19) patients, ie, from the early postsurgery stage to at least 1 year postsurgery, enabled evaluation of the skeletal, dental, and soft tissue results in the longer term.
Results Error of the Method Accuracy of Digitizing The average coefficient of variation for all the landmarks was 0.207% in the horizontal di-
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mension and 0.164% in the vertical dimension, both values well below 1%, depicting high repeatability. Intraexaminer Repeatability of Accuracy of Landmark Identification The average coefficient of repeatability in the horizontal dimension was 0.99 mm, the softtissue landmarks averaging 0.98 mm, and the hard tissue landmarks 0.99 mm. In the vertical dimension the mean coefficient of repeatability was 1.43 mm, the soft-tissue landmarks recording 1.52 mm, and the hard-tissue landmarks 1.33 mm. The following landmarks were then excluded from further analysis because their coefficients of repeatability exceeded 1.5 mm: ANS-h, A-V, A=-v, Ls-v, B-v, B=-v, Pog–v, and Pog=–v. Figure 1 h refers to horizontal and v to the vertical dimension) As a result of these exclusions the overall average coefficient of repeatability improved to 0.865 mm in the horizontal dimension and in the vertical dimension to 1.013 mm, now below the 1.5-mm accuracy level set for the study.17,24,27 Interexaminer Accuracy of Landmark Identification The average coefficient of variation for the values recorded by the 10 orthodontists in the horizontal dimension was 0.652% and in the vertical plane was 0.917%, which is a high degree of accuracy for the method of location used. The Bland and Altman23 analysis indicated a minimal bias of ⫺0.167 mm towards the researcher. Results for the Time Period T1 (Presurgical) to T3 (End of Postsurgical Orthodontic Phase) The testing for any differences between the 7 genioplasty patients and the 18 nongenioplasty patients was accomplished by the use of simple proportional relationships that were subjected to Student’s t test, adjusted for unequal variances using Levene’s test. Between the 2 groups, only the proportional change from hard tissue point B to soft-tissue point B= (Fig 1) was significant (P ⱕ 0.05). This is probably because point B is very close to the surgical site of the advancement genioplasty. With only one set of parameters demonstrating a significant difference, it
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Table 1. Descriptive Statistics and P Values for the Changes During the Time Interval T1–T3 Landmark NT NT Sn Sn A= Ls St. St. Li Li B= Pog= Gn= Gn= Me= Me= ANS A UIT UIT LIT LIT B Pog Gn Gn Me Me
h v h v h h h v h v h h h v h v v h h v h v h h h v h v
Mean Change
SD
Range, Min–Max
P Value
0.27 0.05 0.1 0.12 ⫺0.03 ⫺0.26 1.23 0.34 4.1 ⫺1.57 5.56 5.11 5.05 3.1 5.2 2.91 ⫺0.05 0.95 ⫺0.16 0.32 5.31 2.8 4.6 5.21 5.21 2.61 5.22 2.65
0.46 0.99 0.83 0.52 0.77 1.27 1.71 0.83 1.53 2.01 2.32 2.99 2.92 3.01 3.46 2.87 0.63 0.83 1.28 0.93 1.68 1.2 1.92 3.38 3.42 2.45 3.45 2.38
⫺0.75, 1.05 ⫺1.95, 2.00 ⫺2.45, 1.50 ⫺1.10, 1.15 ⫺2.10, 1.55 ⫺2.35, 2.55 ⫺1.70, 5.50 ⫺1.05, 1.95 1.15, 7.40 ⫺5.85, 3.05 1.45, 10.75 1.10, 13.65 1.35, 12.05 ⫺2.85, 10.15 0.55, 13.00 ⫺2.60, 9.25 ⫺1.05, 1.50 ⫺1.60, 1.85 ⫺2.45, 2.60 ⫺2.10, 2.05 0.50, 7.75 ⫺0.50, 7.10 0.65, 9.30 0.25, 13.65 1.40, 13.75 ⫺1.70, 10.20 0.65, 13.15 ⫺1.85, 9.55
0.008* 0.794 0.539 0.25 0.836 0.31 0.002* 0.050* 0.000** 0.001** 0.000** 0.000** 0.000** 0.000** 0.000** 0.000** 0.752 0.578 0.522 0.097 0.000** 0.000** 0.000** 0.000** 0.000** 0.000** 0.000** 0.000**
“⫺” indicates posterior horizontal (h) or vertical (v) movements. *P ⱕ 0.05; degrees of freedom ⫽ (n⫺1) ⫽ 24. **P ⱕ 0.001; degrees of freedom ⫽ (n⫺1) ⫽ 24.
was evident that the genioplasty and nongenioplasty groups could be combined into one group for the purposes of this study. Table 1 depicts the descriptive statistics and P values for the changes during the time interval T1 to T3. The matched t test identified the following hard and soft tissue landmarks as showing significant and clinically relevant changes namely: LIT—Li, B and B=, Pog and Pog=, Gn and Gn=, and Me and Me= (Fig 1). These data were subjected to simple regression analysis (Table 2). All the correlations were significant (P ⱕ 0.05) with coefficients of determination ranging from 43% to 100% in the horizontal and from 16.73% to 58.37% in the vertical dimension. For the nongenioplasty group, B–B= showed an improved coefficient of determination of 69.22% in comparison with the 43.03% recorded by the whole sample, although both values were highly significant (P ⬍ 0.001). The vertical correlation between LIT and LI demonstrated a significance of P ⫽ 0.042 but with a coefficient of determination of only 16.73%. The correlations between
the changes when P ⬍ 0.001 carry a greater emphasis than those for which P ⱕ 0.05. In Table 3, Pearson correlation coefficient analyses express the relationship between changes at hard tissue landmarks LIT, Pog and Me and the soft tissue changes at Li, and B=, Pog=, Gn=, and Me= for the period T1–T3, respectively. Strong correlations were found in the horizontal dimension between LIT-Li, Pog-Pog=, Pog-Me=, and Pog-Pog= (Fig 1). All the relationships between Pog in the vertical dimension were ignored due to poor repeatability. In the vertical dimension the only strong correlation was between Me-Me=, and Me-Gn= (Fig 1). Table 4 lists the results obtained for the multiple regression analyses, which included tissue thickness for corresponding soft and hard tissue points, and compares these results with those obtained for the correlation analysis, the latter being the equivalent of a simple regression. The relationships were improved but only by an average of 6.69% and, for LIT-h and Li-h, the coefficient of determination was only very mar-
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Table 2. Pearson Correlations, Simple Regression Equations, and Coefficients of Determination were Calculated for the Statistically Significant and Clinically Relevant Corresponding Hard- and Soft-Tissue Changes Hard to Soft Tissue Relations ⌬LIT-⌬LI ⌬LIT-⌬LI ⌬B-⌬B= ⌬Pog-⌬Pog= ⌬Gn-⌬Gn= ⌬Gn-⌬Gn= ⌬Me-⌬Me= ⌬Me-⌬Me=
Pearson Correlation (Cr)
Simple Regression Equation
Coefficient of Determination (R2 ⫻100)%
P Value
0.685 0.409 0.656 0.857 0.883 0.761 1.000 0.764
⌬LI-h ⫽ ⫺0.78 ⫹ 0.63 (⌬LIT-h) ⌬LI-v ⫽ 2.72 ⫹ 0.41 (⌬LI-v) ⌬B=-h ⫽ ⫺1.90 ⫹ 0.79 (⌬B-h) ⌬Pog=-h ⫽ ⫺1.17 ⫹ 0.76 (⌬Pog-h) ⌬Gn=-h ⫽ ⫺1.14 ⫹ 0.75 (⌬Gn-h) ⌬Gn=v ⫽ ⫺0.66 ⫹ 0.94 (⌬Gn-v) ⌬Me-H ⫽ 0.03 ⫹ 1.00 (⌬Me-h) ⌬Me=-v ⫽ ⫺0.47 ⫹ 0.92 (⌬Me-v)
46.92 16.73 43.03 73.44 77.97 57.91 100.0 58.37
0.001** 0.042* 0.001** 0.001** 0.001* 0.001** 0.000** 0.001**
h v h h h v h v
In the case of simple linear regression, r ⫽ R. ⌬ ⫽ change. *P ⱕ 0.05, degrees of freedom ⫽ (n⫺1) ⫽ 24. **P ⱕ 0.001, degrees of freedom ⫽ (n⫺1) ⫽ 24.
ginally improved. For the change at LIT-v and Li-v, the coefficient of determination (Fig 1) for vertical change was 16.73% and, when tissue thickness was added, it improved to 32.39%. To try to improve the understanding of the vertical relationships, a multiple regression analysis was used to assess the correlation between the vertical changes at Me and the vertical changes at all the relevant soft tissue landmarks (Table 5). Again the coefficient of determination showed some improvement once tissue thickness was added to the regression analysis, the greatest improvement occurring between the relationship Me and Li from 30.91% to 38.94%. In Table 6 the data summarize the simple and multiple regression equations for the changes between hard and soft tissue points which had been identified as statistically significant. The simple proportional relationships were derived directly from the mean changes occurring between T1 and T3 at the land marks but it is the regres-
sion equations that more appropriately define the relationships and it is these which may be extrapolated to mandibular advancements in general.
Results for the Period T2 (6 Weeks After Surgery) to T3 (at the Conclusion of Postsurgical Orthodontics) No landmark showed clinically relevant changes, although the vertical change at LIT demonstrated a statistical significance at P ⱕ 0.01 and the following landmarks showed statistical significance at P ⱕ 05: NT-vertical, Gn-vertical, and Me-vertical. No further statistical evaluation was performed on these data in accord with the principle that regression analyses were only undertaken when changes that had occurred had been shown to be statistically and clinically significant.
Table 3. Hard- and Soft-Tissue Correlations (r) Between 3 Hard Tissue and 5 Soft Tissue Landmarks Hard Tissue LIT-h Soft tissue Li=-h Li=-v B=-h B=-v Pog=-h Pog=-v Gn=-h Gn=-v Me=-h Me=-v
LIT-v
0.685
Pog-h
Pog-v
Me-h
0.338
0.008
0.652
0.232
0.857
0.452
0.881
0.385
0.942
0.317
0.409 0.482 0.324
Me-v
0.556
0.324 0.254 0.35 0.205
h ⫽ horizontal, v ⫽ vertical.
0.38
0.756 0.764
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Table 4. Coefficients of Determination Obtained From Correlation Analyses and From Multiple Regression Analyses for the Corresponding Soft- and Hard-Tissue Points for the Period T1 To T3 When Tissue Thickness Is Included Hard to Soft Tissue Relation
Correlation Analyses
Coefficient of Determination (R2 ⫻ 100)%
Multiple Regression
Coefficient of Determination (R2 ⫻ 100)%
⌬LIT-⌬LI h v ⌬B-⌬B= h ⌬Pog-⌬Pog= h ⌬Gn-⌬Gn= h ⌬Gn-⌬Gn= v ⌬Me-⌬Me= h v
0.685 0.409 0.656 0.857 0.883 0.761 1 0.764
46.92 16.73 43.03 73.44 77.97 57.91 100 58.37
0.688 0.569 0.69 0.867 0.886 0.804 1 0.8
47.36 32.39 47.64 75.21 78.51 64.6 100 64
In the case of simple linear regression, r ⫽ R. ⌬ ⫽ change.
Some authors in the past have challenged the use of cephalometrics as a research tool but Houston21 gave practical advice on how to minimize cephalometric variability, advice which has been incorporated into the present study. Furthermore, a method was introduced in this study for standard identification of land marks on gently curving contours which improves the accuracy of landmark identification. It was recognized that after surgery, if the soft tissue contour was superimposed over the immediate underlying bony contour this would not necessarily reflect the new contour point when the tracing is superimposed on the cranial base structure. For example, presurgical hard tissue Pogonion is closely related to soft tissue Pogonion (Pog=) but after surgery the most anterior point on the contour of the soft tissue chin may not reflect the original position of soft tissue Pog= due to clockwise rotation of the distal segment of the mandible. Acceptable limits of intra and interobserver accuracy were achieved for landmark identification. Horizontal accuracy was greater than was the vertical, thereby confirming earlier reports.3,5 To improve overall reliability any measurement having an accuracy of repeatability of more than 1.5 mm
Results for the Time Period T3 (at the Conclusion of Postsurgical Orthodontics) to T4 (at Least 12 Months After Surgery) No landmarks showed clinically important changes, although Li disclosed a statistically significant change at P ⱕ 001 and the following landmarks showed statistically significantly changes at P ⱕ 0.05, Sn-h, A=-h, Ls-h, St.-h, B=-h, LIT ⫺h, and v and Me ⫺h (Fig 1). No further statistical analysis was undertaken, and it could be concluded that these cases demonstrated no clinically relevant relapse at a minimum of 1 year after surgery.
Discussion The present study makes an attempt to clarify the relationship between hard and soft tissue changes that occur after surgical advancement of the mandible. This has an impact on the ability of the orthodontist or maxillofacial surgeon to forecast the final profile. Park and Burstone28 stated that a forecast based upon hard tissues alone will not predictably and reliably define the treatment plan. Every effort has been made to standardize the technique of land mark identification in an endeavor to achieve a degree of accuracy greater than which may have been previously possible.
Table 5. The Relationship Between Changes at Menton and Changes at Associated Soft Tissue Points Multiple Regression Analysis
Correlation Analysis
Hard to Soft Tissue Relation
(R)
(R ⫻ 100)%
(r)
(R2 ⫻ 100)%
Me-Li v Me-Gn= v Me-me= v
0.624 0.790 0.800
38.94 62.42 64.00
0.556 0.756 0.764
30.91 57.15 58.37
Note: the multiple regression analysis included tissue thickness. In the case of simple linear regression, r ⫽ R.
2
Soft-Tissue Changes Related to Mandibular Advancement Surgery
Table 6. Summary of the Simple and Multiple Regression Equations and the Mean Proportional Relationships of the Significant Hard- and Soft-Tissue Changes Simple Regression Equations ⌬Li-h ⫽ ⫺0.78 ⫹ 0.62 (LIT-h) ⌬Li-v ⫽ 2.81 ⫹ 0.47 (Me-v) ⌬B=-h ⫽ ⫺1.90 ⫹ 0.79 (B-h) ⌬Pog=-h ⫽ ⫺1.17 ⫹ 0.76 (Pog-h) ⌬Gn=-h ⫽ ⫺L. 14 ⫹ 0.75 (⌬Gn-h) ⌬Gn=-v ⫽ ⫺0.66 ⫹ 0.94 (⌬Gn-v) ⌬Me-h ⫽ 0.03 ⫹ 1.00 (⌬Me-h) ⌬Me=-v ⫽ ⫺0.47 ⫹ 0.92 (⌬Me-v) ⌬ ⫽ change
Proportional Relationships ⌬Li-h ⫽ 0.77 (⌬IT-h) ⌬LI-v ⫽ ⫺0.59 (⌬Me-v) ⌬B=-h ⫽ 1.21 (⌬B-h) ⌬B=-h ⫽ 1.07 (⌬Pog-h) ⌬Pog=-h ⫽ 0.98 (⌬Pog-h) ⌬Gn=-h ⫽ 0.97 (⌬Gn-h) ⌬Gn-h ⫽ 0.97 (⌬Pog-h) ⌬Gn=-v ⫽ 1.19 (⌬Gn-v) ⌬Gn=-v ⫽ 1.17 (⌬Me-v) ⌬LMe=-h ⫽ 1.10 (⌬Me-h) ⌬LMe=-v ⫽ 1.00 (⌬Me-v)
Multiple Regression Equations ⌬Li-h ⫽ ⫺0.10 ⫹ 0.58 (⌬LIT-h) ⫹ 0.04 (TT) ⌬Li-v ⫽ ⫺3, 29 ⫹ 0.56 (⌬LIT-v) ⫹ 0.30 (TT) ⌬Li-v ⫽ ⫺1.45 ⫹ 0.49 (⌬Me-v) ⫹ 0.20 (TT) ⌬B=-h ⫽ ⫺5.02 ⫹ 0.79 (⌬B-h) ⫹ 0.25 (TT) ⌬Pog=-h ⫽ ⫺3.07 ⫹ 0.79 (⌬Pog-h) ⫹ 0.15 (TT) ⌬Gn=-h ⫽ ⫺2.11 ⫹ 0.77 (⌬Gn-h) ⫹ 0.10 (TT) ⌬Gn=-v ⫽ 3.23 ⫹ 0.94 (⌬Gn-v) ⫺ 0.35 (TT) ⌬Me=-h ⫽ 0.04 ⫹ 1.00 (⌬Me-h) ⫺ 0.002 (TT) ⌬Me=-v ⫽ 2.26 ⫹ 0.91 (⌬Me-v) ⫺ 0.34 (TT)
was excluded. In this regard approximately onethird of the vertical parameters had to be excluded but there was still sufficient data in the vertical dimension to permit meaningful consideration. This aspect had not been considered in detail by many of the articles reviewed. The addition of seven patients who had advancement genioplasties made little difference to the data in both the vertical and horizontal dimensions except at B= point, which could be expected as it is adjacent to the osteotomy cut. The genioplasty is merely an extension of the horizontal movement of the mandible and affects the soft tissue in the same proportional manner. In general agreement with most authors,1-12 advancement of the mandible correlates with movement of the soft tissue contours of the chin from soft tissue B point (B=) to soft tissue menton (Me=) after the repositioning of the symphysis in an almost 1:1 ratio in the horizontal and vertical dimensions. Mommaerts and Marxer4
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and Mobarak10 included vertical changes at menton and reported a positive change in depth and angle of the labiomental sulcus. As menton moves caudally the sulcus angle opens and the depth decreases. Veltkamp et al12 included the vertical change at the incisor tip as the lower jaw is advanced, into a multivariate regression analysis which helped to improve the predictability of the response at labrale inferius. The present study agrees with Dermaut and de Smit,9 Mobarak et al,10 and Keeling et al.25 that changes in the upper lip are seemingly independent of soft tissue changes that occur with mandibular advancement. However, Mobarak et al10 found in hypodivergent cases that the nasolabial angle increased as the upper lip became a little more recessive 3 years after surgery. The lower lip behaves differently to the upper lip and chin as the lower jaw is advanced. In this study, Li responds to horizontal movement at lower incisor tip (LIT) in a ratio of 0.77:1, which is less than that found in the Talbot6 report of 0.85:1 but very close to that of Veltkamp et al12 at 0.79:1 and Ewing and Ross7 at 0.80:1. Other studies reported ratios that varied between 0.26:1 (Dermaut and de Smit6) and 0.67:1 (Thuer et al8). This variability could be the result of many factors, such as a failure to obtain a relaxed lip position when taking the cephalometric radiographs before and after the treatment and differing muscular patterns associated with different facial types (although Mobarak et al10 found that this made no difference). Other influences that could be considered are age-related factors, tissue thickness, type and tone of musculature, facial type and the extent of the eversion of the lower lip. In the present study, it is significant that when tissue thickness is included in the multiple regression equation (Table 4) for the relationship between LIT-h and Li-h the coefficient of determination only very slightly improved. This finding appears to indicate that other factors, such as the extent of the overjet, deep bite, and the protrusion of the lower lip ahead of the upper incisor play important roles, as indicated by Veltkamps et al.12 Mobarak et al10 found a positive correlation between increase in lower anterior facial height, decrease in tissue thickness, and decrease in the depth of the labio mental fold. They deduced that the reduction in tissue thickness was caused by the unrolling and stretching of the lower lip and found that the preoperative
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tissue thickness was significantly correlated with the net change in tissue thickness in all three of the morphologic groups they studied. Mobarak et al10 reported that the proportional advancement of the lower lip in the horizontal plane was 60% of skeletal movement in all 3 groups 3 years after surgery. This reduced relationship could be attributed to the longer time span which allowed for soft tissue adjustment and settling. At the 2 week stage after surgery there is still a significant amount of swelling of the soft tissue, which could impact on the result. Mobarak et al10 also encountered a significant amount of skeletal and dental relapse in their study, a finding which was not experienced among the cases included in the present study. In the vertical dimension, disappointingly, the only meaningful correlation found in the current study was that between the changes at labrale inferius (Li) and menton (Me), which was strengthened when tissue thickness (TT) was incorporated into the multiple regression analysis. Thus, the vertical change at Li follows the vertical change at Me according to the multiple regression equation ⌬Li-v ⫽1.45 ⫹ 0.49 (⌬Me-v) ⫹ 0.20(TT). It appears that previously reported correlations in the vertical dimension have been weak or erratic.3,5 In summary, the results of the present study compare favorably with those of previously published research. The soft-tissue changes related to mandibular advancement would appear to be fairly predictable especially for the chin area. The lower lip is more of a challenge, but the incorporation of presurgical tissue thickness into a multiple regression equation offers a partial solution to the predictability of the postsurgical change. The relative complexity of these relationships will limit their application in hand-drawn predictions and it is upon precise mathematical definitions of hard- and soft-tissue relationships that the development of computer-aided forecasting must depend. Further refinement and pooling of results is necessary to enhance the predictability of results and it would be desirable to develop prospective studies when all appropriate criteria of standardization could be met.
Conclusions We present the following conclusions: (1) The horizontal cephalometric measurements were
shown to be more reliable than vertical measurements; (2) the inclusion of data from the seven advancement genioplasty cases did not have a significant influence on the proportional changes between hard and soft tissue movements; (3) the upper lip behaved in an independent manner compared with the lower lip and demonstrated no significant changes; (4) the soft-tissue changes of the chin area follow the horizontal and vertical changes of the bony chin in a 1:1 ratio; (5) horizontal changes at LI follow the horizontal changes at LIT in a ratio of 0.77:1; (6) hard tissue menton moves vertically in an effective 1:1 ratio with soft-tissue menton and with soft-tissue gnathion; (7) consideration should be given to the presurgical tissue thickness of the lower lip when attempting to forecast soft-tissue changes; and (8) in this study, no clinically relevant relapse was noted at least 1 year after surgery.
References 1. Lines PA, Steinhauser EW: Soft tissue changes in relationship to movement of hard structures in orthognathic surgery: A preliminary report. J Oral Surg 32:891-896, 1974 2. Talbott JP: Soft tissue response to mandibular surgery (Thesis), Lexington, University of Kentucky, 1975. Cited by Quast DC, Biggerstaff RH, Haley JV: The short and long-term soft-tissue profile changes accompanying mandibular advancement surgery. Am J Orthod 84:29-36, 1983 3. Quast DC, Biggerstaff RH, Haley JV: The short term and long term soft tissue profile changes accompanying mandibular advancement surgery. Am J Orthod 84:29-36, 1983 4. Mommaert MY, Marxer HA: Cephalometric analysis of the long term soft tissue profile changes which accompany the advancement of the mandible by sagittal split ramus osteotomy. J Cranial Maxillofac Surg 15:52-62, 1987 5. Hernandez-Orsini R, Jacobson A, Sarver DM, et al: Short and long-term soft tissue profile changes after mandibular advancements using rigid fixation techniques. Int J Adult Orthod Orthog Surg 4:209-219, 1989 6. Dermaut LR, De Smit: Effects of sagittal split advancement osteotomy on facial profiles. Eur J Orthod 11:366374, 1989 7. Ewing M, Ross RB: Soft tissue response to mandibular advancement and genioplasty. Am J Orthod Dentofac Orthop 101:550-555, 1992 8. Thuer U, Ingerval B, Vuillemin T: Stability and effect on the soft tissue profile of mandibular advancement with sagittal split osteotomy and rigid internal fixation. Int J Adult Orthod Orthog Surg 9:175-185, 1994 9. Albrechtson LA, Larsen BE: Changes in lower lip cross sectional area subsequent to mandibular advancement surgery. Int J Adult Orthod Orthog Surg 12:287-296, 1997
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10. Mobarak KA, Espeland L, Krogstad O, et al: Soft tissue profile changes following mandibular advancement surgery: Predictability and long-term outcome. Am J Orthod Dentofac Orthop 101:353-367, 2001 11. Hamada T, Motohashi N, Kawamoto T, et al: Two dimensional changes in soft tissue profile following mandibular advancement in Japanese retrognathic adults. Int J Adult Orthod Orthognath Surg 16:272-279, 2001 12. Veltkamp T, Buschang PH, English JD, et al: Predicting lower lip and chin response to mandibular advancement and genioplasty. Am J Orthod Dentofac Orthop 122:627634, 2002 13. Dolce C, Hatch JP, van Sickles JE, et al: Five year outcome of soft tissue profiles when wire or rigid fixation is used in mandibular advancement surgery. Am J Orthod Dentofac Orthop 124:249-256, 2003 14. Eggensperger NM, Lieger O, Thuer U, et al: Soft tissue profile changes following mandibular advancement Surgery an average of 12 years post operatively. J Oral Maxillofac Surg 65:2301-2310, 2007 15. Jensen AC, Sinclair PH, Wolford LM: Soft tissue changes associated with double jaw surgery. Am J Orthod 53:266275, 1992 16. Burstone CJ: Lip posture and its significance in treatment planning. Am J Orthod 53:262-265, 1967 17. Hillesund E, Field D, Zachrisson BU: Reliability of softtissue profile in cephalometrics. Am J Orthod 74:537550, 1978 18. O’Reilly MT: Integumental profile changes after surgical orthoclontic correction of bimaxillary dento-alveolar protrusion in black patients. Am J Orthod Dentofac Orthop 96:242-248, 1989
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19. Moshiri F, Jung ST, Scharoff A, et al: Surgical diagnosis and treatment planning: A visual approach. J Clin Orthod 16:37-59, 1982 20. Epker BN, Wolford LM, Fish LC: Mandibular deficiency syndrome. II. Surgical considerations for mandibular advancement. Oral Surg Oral Med Oral Pathol 45:348363, 1978 21. Houston WJB: The analysis of errors in orthodontic measurements. Am J Orthod 83:382-390, 1983 22. Phillips C, Turvey A, McMillan A: Surgical orthodontic correction of mandibular deficiency by sagittal split osteotomy: Clinical and cephalometric analysis of 1-year data. Am J Orthod Dentofac Orthop 96:501-506, 1989 23. Bland JM, Altman DG: Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1:307-310, 1986 24. Mitgard J, Bjork G, Linder Aronson S: Reproducibility of cephalometric landmarks and errors of measurements of cephalometric cranial distances. Angle Orthod 44:5662, 1974 25. Wisth PJ, Boe OE: The reliability of cephalometric soft tissue measurements. Arch Oral Biol 20:595-599, 1975 26. Levene H: Robust tests for equality of variance. Contributions to Probability and Statistics (ed 1), Olkin, Palo Alto, Stanford University Press, 1960 27. Baumrind S, Frantz RC: The reliability of head film measurements. 1; Landmark identification. Am J Orthod 60:111-127, 1971 28. Park Y, Burstone CJ: Soft-tissue profile-fallacies of hardtissue standards in treatment planning. Am J Orthod Dentofac Orthop 90:52-62, 1986
urgical advancement of the recessive mandible to improve function and esthetics in adults is reasonably routine and generally well controlled. Predicting the soft-tissue reaction of
S
Department of Orthodontics, University of the Witwatersrand, Johannesburg, South Africa (A.G.H.M.). Private Practice, Southampton, UK (G.G.J.M.). Department of Orthodontics, University of the Witwatersrand, Johannesburg, South Africa (W.G.E.). Biostatistics Unit, MRC and School for Therapeutic Sciences, University of the Witwatersrand, Johannesburg, South Africa (P.J.B.). Address correspondence to Antony G.H. McCollum, BDS, HDD, MDent, PO Box 67104, Bryanston, Sandton, South Africa, 2021; E-mail: [email protected] © 2009 Elsevier Inc. All rights reserved. 1073-8746/09/1503-0$30.00/0 doi:10.1053/j.sodo.2009.03.001
the lower lip to this precise surgical movement of the bone has, however, proven a challenge. Pretreatment planning usually requires the use of cephalometric prediction tracings and, more recently, surgeons have relied on computer software programs to further assist the visualization of the projected results. It is clear that soft-tissue reactions to bone repositioning play an essential role in prediction of treatment outcome. Many studies in the literature have reported on these reactions. Most predict that the softtissue chin advances in a more or less 1:1 ratio, in concert with movement of the hard tissue chin with strong correlations between the relationship.1-9 However, considerable variation in results has been reported for the proportional
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advancement of the lower lip, measured from the lower incisor tip to labrale inferius, in relation to the forward positioning of the mandible. Reports have allocated relationships ranging from a high coordination of 0.8:1 to a low of only 0.26:1.1-14 Even studies allowing for considerable postsurgery settling, up to 3 years, have found varied relationships, ranging from 0.48:1 to 0.79: 19-13 and, in some cases, a finding of up to 30% relapse after the first year of surgery.14 Studies that rely on mean values do not explain individual variation and it has only been when many variables have been included in the analyses that stronger correlations have been identified as, for example, by Jensen et al15 (r ⫽ 0.82) and Hamada11 (r ⫽ 0.76). Veltkamps et al12 showed that the inclusion of up to 5 different variables into a multiple regression equation improved the correlation significantly (r ⫽ 0.88). The factors that contribute to the considerable variation of results include the variation in thickness of the lower lip from one individual to the other, lip tonicity, posture, muscle pull, skeletal stability,5,15,10,16 lowerlip redundancy,15,17 area of the lower lip,5,9,16,18 interlabial gap,18 influence of the maxillary incisor teeth15,19 and posture of the lips,4,16,17 and difficulty in taking the head films with the lips in a relaxed state.4 Mommaerts and Marxer4 and Mobarak et al10 found in deep bite cases a positive correlation between an increase in facial height if the lower jaw is rotated in a clockwise direction while it is advanced, with a concomitant decrease in the characteristically deep labio-mental fold. The lip becomes thinner as it unfurls, allowing a relatively reduced advancement together with vertical movement at soft tissue menton. Dermaut and de Smit6 and Mobarak et al10 recorded statistically and clinically insignificant changes to the upper lip after the lower jaw was advanced. In the present retrospective study we further explored the complex relationship between bone and soft-tissue responses by invoking an intricate statistical analysis to refine the balance between tissue movements.
Materials and Method Subjects The cephalometric records of 25 grown Caucasian patients who had had mandibular advance-
ment osteotomies (16 women, mean age of 28.2 years at surgery, ranging from 17 to 50 years, and 9 men, mean age 27 years, ranging from 17 to 48 years) from the files of a private orthodontic practice, were included in the study. Seven of these patients also had advancement genioplasties. All patients were medically fit and without any developmental syndromes and had received full fixed appliance orthodontic treatment to appropriately decompensate the incisors. The arches were stabilized 6 weeks before the mandibular advancement. Six different maxillo-facial surgeons severally performed the osteotomies according to the method described by Epker et al.20
Cephalometrics All cephalometric radiographs were taken on the same machine by the same operator. The patient held the teeth in occlusion, and the orthodontist personally ensured that the lips were in the relaxed state. Only radiographs of sufficient quality to enable accurate recording of the relevant hard and soft tissue landmarks were acceptable for the study. The radiographs had been taken at the following stages: the initial head film, presurgery—T1, 6 weeks after surgery—T2, at the completion of postoperative orthodontics (4 to 11 months)—T3, and 12 months after surgery—T4. The major period used in this study is T1–T3, which refers to the time interval between the presurgical stage to the completion of orthodontic treatment (n ⫽ 25). However, data also were also collected for the periods T2–T3 and T3–T4. The sample was divided into two groups—those who had received advancement genioplasties (n ⫽ 7) and those whose treatment included only mandibular advancement. Cephalometric tracings were completed for each radiograph on Ozatex 0.5 mm D/Matt drafting film paper (Ozalid SA, Pty. Ltd., Drawing Office Material, Spartan, Kempton Park, South Africa) with a 6-H pencil. Two locating crosses were scribed directly onto the radiographic film and were copied to the overlying film paper once it had been secured to the radiographic film. The anatomical tracing, cephalometric landmarks, and their abbreviations used in the study are illustrated in Figure 1. To locate those landmarks defined as “most ante-
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Figure 1. Typical cephalometric tracing and the abbreviations for the landmarks measured. N ⫽ nasion, S ⫽ sella turcica, PNS ⫽ posterior nasal spine, ANS ⫽ anterior nasal spine, NT ⫽ nose tip, Sn ⫽ subnasale, A ⫽ A point, A= ⫽ soft-tissue point A or superior labial sulcus, Ls ⫽ labrale superius, St ⫽ stomion, LIT ⫽ lower incisor tip, UIT ⫽ upper incisor tip, Li ⫽ labrale inferius, B ⫽ point B, B= ⫽ inferior labial sulcus, or soft-tissue point B, Pog ⫽ pogonion, Pog= ⫽ soft-tissue pogonion, Gn ⫽ hard tissue gnathion, Gn= ⫽ soft-tissue gnathion, Me ⫽ hard-tissue menton, Me= ⫽ soft-tissue menton.
rior or posterior” on curved segments of the tracing, a perpendicular effecting a one point contact immediately identified the point. In other instances the perpendicular met the curved tracing outline as an area of contact. The midpoint of this contact was used (Fig 2). Each radiograph was traced twice under the same conditions at the same occasion to diminish the error of variability.21 On the first presurgical tracing, reference axes were determined to enable the recording of the horizontal and vertical changes. An X axis was created
at a 6-degree angle to S-N and the Y axis was constructed as a perpendicular to S-N at sella turcica.22 The references axes were not determined on the second tracing but were transferred from the first presurgical tracing to the second presurgical tracing after the tracings were accurately overlaid by superimposing the 2 locating crosses which had been copied onto each tracing directly from the radiograph. This standardized the reference system for each set of presurgical tracings for each patient.
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Corporation, Rockville, MD) and analyzed at the Institute of Medical Biostatistics, a unit of the Medical Research Council of South Africa at the University of the Witwatersrand, Johannesburg.
Statistical Analysis Error of the Method
Figure 2. Definition of a point on a curved segment. A perpendicular line dropped from the X-axis, tangent to the relevant cephalometric landmark (in this case, Nose Tip).
Then, in each set of tracings the reference axes were transferred from the presurgical tracings to the post surgical tracings. This was achieved by finding the closest orientation between the two tracings by closely superimposing the outlines of sella turcica, de Coster’s lines, superior orbital rim, orbit and the fronto-nasal area structures.3 The reference axes were then copied onto the post-surgical tracing. The coordinates of every reference landmark on each tracing were sequentially computed in relation to the X and Y reference system using a digitizing program on a Kontron Messgerate, GmbH, Image-analysis-system (Eching/München, West Germany). The “X” coordinates represented the horizontal distance from the vertical axis, and the “Y” coordinates the vertical distance from the horizontal axis measured in millimeters to an accuracy of 3 decimal places. A negative value was assigned to posterior or superior displacements while a positive value was assigned to anterior or inferior changes. The coordinates for each parameter on each radiograph were measured, twice, the mean value determined thereby decreasing the error of variabitity.21 This was further decreased by completing the two sets of measurements at the same session.21 All the data were organized and tabulated with Statographics 4.0 software (Statistical Graphics
The accuracy of digitizing was tested by randomly selecting one tracing that was re digitized 9 times on separate occasions at least 24 hours apart and the coefficient of variation between these measurements calculated. Intraexaminer repeatability of landmark identification was tested by use of the duplicate set of data for each patient and applying the coefficient of repeatability as used by the British Standards Institution (Bland and Altman23), which was calculated for each landmark. A coefficient of repeatability of less than 1.5 mm was chosen as acceptable for this study.17,24,25 Interexaminer accuracy of landmark location was obtained from 10 orthodontists who traced and located 6 landmarks that were chosen as representative of the diversity of landmarks in the study. The means of these measurements for each of the 6 landmarks were digitized, a coefficient of variation was derived and the limits of agreement, as defined by Bland and Altman,23 were used to assess the agreement between the researchers’ measurements and those of the 10 orthodontists. Change During the T1-T3 Time Interval It was firstly necessary to determine whether the proportional changes of the seven genioplasty patients differed from those of the nongenioplasty patients. Simple proportional equations were calculated for the same landmarks for both groups of patients. A Student’s t test was applied and, when applicable adjusted for un-equal variances derived from Levene’s test.26 Significance was determined at the 0.05 level. Data Management Descriptive statistics were calculated for the data from the T1–T3 time and a paired Student’s t test was used to evaluate the significance of the mean change from T1 to T3 values for each landmark, measured in millimeters along each axis. The level chosen for significance was at P ⱕ
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0.05. A change greater than 1.5 mm.17,24,25 was regarded as clinically relevant. The data for those hard and soft tissue landmarks for which were recorded statistically and clinically significant changes were then subjected to analysis to assess the relationship between these changes. For the changes from T1–T3, Pearson correlation coefficients were calculated between these landmarks and the coefficients of determination were assessed for each landmark. A coefficient of determination of greater than 50% indicates a good correlation, ie, r ⱖ 0.7.24 The correlation analyses were performed to evaluate the relationship of the changes which had occurred between the following corresponding hard and soft tissue landmarks in the horizontal and vertical dimensions: LIT and Li, B and B=, Pog and Pog=, Gn and Gn= and Me and Me=. In addition changes occurring at LIT, Pog and Me were each tested for correlation with changes recorded at Li, B=, Pog=, Gn=, and Me=. Multiple regression analyses were performed on the aforementioned landmarks to assess the relationship between the changes of the hard and soft tissues in the horizontal and vertical dimensions, together with an additional factor, the presurgical tissue thickness. Again the coefficient of determination was calculated. Other variables that could influence soft tissue change are facial type, elasticity of the tissue and patient stress as it influences muscle tone. From the results of these statistical analyses, it was possible to identify the best possible predictors upon which to base a forecast of new, post surgical positions of the soft tissue land marks. Statistics for the period T2 to T3 (n ⫽ 20) patients, ie, from the early (6 weeks) post surgical stage to the end of active orthodontic treatment enabled an assessment of initial surgical stability and, similarly the analysis of data from T2 to T4 (n ⫽ 19) patients, ie, from the early postsurgery stage to at least 1 year postsurgery, enabled evaluation of the skeletal, dental, and soft tissue results in the longer term.
Results Error of the Method Accuracy of Digitizing The average coefficient of variation for all the landmarks was 0.207% in the horizontal di-
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mension and 0.164% in the vertical dimension, both values well below 1%, depicting high repeatability. Intraexaminer Repeatability of Accuracy of Landmark Identification The average coefficient of repeatability in the horizontal dimension was 0.99 mm, the softtissue landmarks averaging 0.98 mm, and the hard tissue landmarks 0.99 mm. In the vertical dimension the mean coefficient of repeatability was 1.43 mm, the soft-tissue landmarks recording 1.52 mm, and the hard-tissue landmarks 1.33 mm. The following landmarks were then excluded from further analysis because their coefficients of repeatability exceeded 1.5 mm: ANS-h, A-V, A=-v, Ls-v, B-v, B=-v, Pog–v, and Pog=–v. Figure 1 h refers to horizontal and v to the vertical dimension) As a result of these exclusions the overall average coefficient of repeatability improved to 0.865 mm in the horizontal dimension and in the vertical dimension to 1.013 mm, now below the 1.5-mm accuracy level set for the study.17,24,27 Interexaminer Accuracy of Landmark Identification The average coefficient of variation for the values recorded by the 10 orthodontists in the horizontal dimension was 0.652% and in the vertical plane was 0.917%, which is a high degree of accuracy for the method of location used. The Bland and Altman23 analysis indicated a minimal bias of ⫺0.167 mm towards the researcher. Results for the Time Period T1 (Presurgical) to T3 (End of Postsurgical Orthodontic Phase) The testing for any differences between the 7 genioplasty patients and the 18 nongenioplasty patients was accomplished by the use of simple proportional relationships that were subjected to Student’s t test, adjusted for unequal variances using Levene’s test. Between the 2 groups, only the proportional change from hard tissue point B to soft-tissue point B= (Fig 1) was significant (P ⱕ 0.05). This is probably because point B is very close to the surgical site of the advancement genioplasty. With only one set of parameters demonstrating a significant difference, it
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Table 1. Descriptive Statistics and P Values for the Changes During the Time Interval T1–T3 Landmark NT NT Sn Sn A= Ls St. St. Li Li B= Pog= Gn= Gn= Me= Me= ANS A UIT UIT LIT LIT B Pog Gn Gn Me Me
h v h v h h h v h v h h h v h v v h h v h v h h h v h v
Mean Change
SD
Range, Min–Max
P Value
0.27 0.05 0.1 0.12 ⫺0.03 ⫺0.26 1.23 0.34 4.1 ⫺1.57 5.56 5.11 5.05 3.1 5.2 2.91 ⫺0.05 0.95 ⫺0.16 0.32 5.31 2.8 4.6 5.21 5.21 2.61 5.22 2.65
0.46 0.99 0.83 0.52 0.77 1.27 1.71 0.83 1.53 2.01 2.32 2.99 2.92 3.01 3.46 2.87 0.63 0.83 1.28 0.93 1.68 1.2 1.92 3.38 3.42 2.45 3.45 2.38
⫺0.75, 1.05 ⫺1.95, 2.00 ⫺2.45, 1.50 ⫺1.10, 1.15 ⫺2.10, 1.55 ⫺2.35, 2.55 ⫺1.70, 5.50 ⫺1.05, 1.95 1.15, 7.40 ⫺5.85, 3.05 1.45, 10.75 1.10, 13.65 1.35, 12.05 ⫺2.85, 10.15 0.55, 13.00 ⫺2.60, 9.25 ⫺1.05, 1.50 ⫺1.60, 1.85 ⫺2.45, 2.60 ⫺2.10, 2.05 0.50, 7.75 ⫺0.50, 7.10 0.65, 9.30 0.25, 13.65 1.40, 13.75 ⫺1.70, 10.20 0.65, 13.15 ⫺1.85, 9.55
0.008* 0.794 0.539 0.25 0.836 0.31 0.002* 0.050* 0.000** 0.001** 0.000** 0.000** 0.000** 0.000** 0.000** 0.000** 0.752 0.578 0.522 0.097 0.000** 0.000** 0.000** 0.000** 0.000** 0.000** 0.000** 0.000**
“⫺” indicates posterior horizontal (h) or vertical (v) movements. *P ⱕ 0.05; degrees of freedom ⫽ (n⫺1) ⫽ 24. **P ⱕ 0.001; degrees of freedom ⫽ (n⫺1) ⫽ 24.
was evident that the genioplasty and nongenioplasty groups could be combined into one group for the purposes of this study. Table 1 depicts the descriptive statistics and P values for the changes during the time interval T1 to T3. The matched t test identified the following hard and soft tissue landmarks as showing significant and clinically relevant changes namely: LIT—Li, B and B=, Pog and Pog=, Gn and Gn=, and Me and Me= (Fig 1). These data were subjected to simple regression analysis (Table 2). All the correlations were significant (P ⱕ 0.05) with coefficients of determination ranging from 43% to 100% in the horizontal and from 16.73% to 58.37% in the vertical dimension. For the nongenioplasty group, B–B= showed an improved coefficient of determination of 69.22% in comparison with the 43.03% recorded by the whole sample, although both values were highly significant (P ⬍ 0.001). The vertical correlation between LIT and LI demonstrated a significance of P ⫽ 0.042 but with a coefficient of determination of only 16.73%. The correlations between
the changes when P ⬍ 0.001 carry a greater emphasis than those for which P ⱕ 0.05. In Table 3, Pearson correlation coefficient analyses express the relationship between changes at hard tissue landmarks LIT, Pog and Me and the soft tissue changes at Li, and B=, Pog=, Gn=, and Me= for the period T1–T3, respectively. Strong correlations were found in the horizontal dimension between LIT-Li, Pog-Pog=, Pog-Me=, and Pog-Pog= (Fig 1). All the relationships between Pog in the vertical dimension were ignored due to poor repeatability. In the vertical dimension the only strong correlation was between Me-Me=, and Me-Gn= (Fig 1). Table 4 lists the results obtained for the multiple regression analyses, which included tissue thickness for corresponding soft and hard tissue points, and compares these results with those obtained for the correlation analysis, the latter being the equivalent of a simple regression. The relationships were improved but only by an average of 6.69% and, for LIT-h and Li-h, the coefficient of determination was only very mar-
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Table 2. Pearson Correlations, Simple Regression Equations, and Coefficients of Determination were Calculated for the Statistically Significant and Clinically Relevant Corresponding Hard- and Soft-Tissue Changes Hard to Soft Tissue Relations ⌬LIT-⌬LI ⌬LIT-⌬LI ⌬B-⌬B= ⌬Pog-⌬Pog= ⌬Gn-⌬Gn= ⌬Gn-⌬Gn= ⌬Me-⌬Me= ⌬Me-⌬Me=
Pearson Correlation (Cr)
Simple Regression Equation
Coefficient of Determination (R2 ⫻100)%
P Value
0.685 0.409 0.656 0.857 0.883 0.761 1.000 0.764
⌬LI-h ⫽ ⫺0.78 ⫹ 0.63 (⌬LIT-h) ⌬LI-v ⫽ 2.72 ⫹ 0.41 (⌬LI-v) ⌬B=-h ⫽ ⫺1.90 ⫹ 0.79 (⌬B-h) ⌬Pog=-h ⫽ ⫺1.17 ⫹ 0.76 (⌬Pog-h) ⌬Gn=-h ⫽ ⫺1.14 ⫹ 0.75 (⌬Gn-h) ⌬Gn=v ⫽ ⫺0.66 ⫹ 0.94 (⌬Gn-v) ⌬Me-H ⫽ 0.03 ⫹ 1.00 (⌬Me-h) ⌬Me=-v ⫽ ⫺0.47 ⫹ 0.92 (⌬Me-v)
46.92 16.73 43.03 73.44 77.97 57.91 100.0 58.37
0.001** 0.042* 0.001** 0.001** 0.001* 0.001** 0.000** 0.001**
h v h h h v h v
In the case of simple linear regression, r ⫽ R. ⌬ ⫽ change. *P ⱕ 0.05, degrees of freedom ⫽ (n⫺1) ⫽ 24. **P ⱕ 0.001, degrees of freedom ⫽ (n⫺1) ⫽ 24.
ginally improved. For the change at LIT-v and Li-v, the coefficient of determination (Fig 1) for vertical change was 16.73% and, when tissue thickness was added, it improved to 32.39%. To try to improve the understanding of the vertical relationships, a multiple regression analysis was used to assess the correlation between the vertical changes at Me and the vertical changes at all the relevant soft tissue landmarks (Table 5). Again the coefficient of determination showed some improvement once tissue thickness was added to the regression analysis, the greatest improvement occurring between the relationship Me and Li from 30.91% to 38.94%. In Table 6 the data summarize the simple and multiple regression equations for the changes between hard and soft tissue points which had been identified as statistically significant. The simple proportional relationships were derived directly from the mean changes occurring between T1 and T3 at the land marks but it is the regres-
sion equations that more appropriately define the relationships and it is these which may be extrapolated to mandibular advancements in general.
Results for the Period T2 (6 Weeks After Surgery) to T3 (at the Conclusion of Postsurgical Orthodontics) No landmark showed clinically relevant changes, although the vertical change at LIT demonstrated a statistical significance at P ⱕ 0.01 and the following landmarks showed statistical significance at P ⱕ 05: NT-vertical, Gn-vertical, and Me-vertical. No further statistical evaluation was performed on these data in accord with the principle that regression analyses were only undertaken when changes that had occurred had been shown to be statistically and clinically significant.
Table 3. Hard- and Soft-Tissue Correlations (r) Between 3 Hard Tissue and 5 Soft Tissue Landmarks Hard Tissue LIT-h Soft tissue Li=-h Li=-v B=-h B=-v Pog=-h Pog=-v Gn=-h Gn=-v Me=-h Me=-v
LIT-v
0.685
Pog-h
Pog-v
Me-h
0.338
0.008
0.652
0.232
0.857
0.452
0.881
0.385
0.942
0.317
0.409 0.482 0.324
Me-v
0.556
0.324 0.254 0.35 0.205
h ⫽ horizontal, v ⫽ vertical.
0.38
0.756 0.764
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Table 4. Coefficients of Determination Obtained From Correlation Analyses and From Multiple Regression Analyses for the Corresponding Soft- and Hard-Tissue Points for the Period T1 To T3 When Tissue Thickness Is Included Hard to Soft Tissue Relation
Correlation Analyses
Coefficient of Determination (R2 ⫻ 100)%
Multiple Regression
Coefficient of Determination (R2 ⫻ 100)%
⌬LIT-⌬LI h v ⌬B-⌬B= h ⌬Pog-⌬Pog= h ⌬Gn-⌬Gn= h ⌬Gn-⌬Gn= v ⌬Me-⌬Me= h v
0.685 0.409 0.656 0.857 0.883 0.761 1 0.764
46.92 16.73 43.03 73.44 77.97 57.91 100 58.37
0.688 0.569 0.69 0.867 0.886 0.804 1 0.8
47.36 32.39 47.64 75.21 78.51 64.6 100 64
In the case of simple linear regression, r ⫽ R. ⌬ ⫽ change.
Some authors in the past have challenged the use of cephalometrics as a research tool but Houston21 gave practical advice on how to minimize cephalometric variability, advice which has been incorporated into the present study. Furthermore, a method was introduced in this study for standard identification of land marks on gently curving contours which improves the accuracy of landmark identification. It was recognized that after surgery, if the soft tissue contour was superimposed over the immediate underlying bony contour this would not necessarily reflect the new contour point when the tracing is superimposed on the cranial base structure. For example, presurgical hard tissue Pogonion is closely related to soft tissue Pogonion (Pog=) but after surgery the most anterior point on the contour of the soft tissue chin may not reflect the original position of soft tissue Pog= due to clockwise rotation of the distal segment of the mandible. Acceptable limits of intra and interobserver accuracy were achieved for landmark identification. Horizontal accuracy was greater than was the vertical, thereby confirming earlier reports.3,5 To improve overall reliability any measurement having an accuracy of repeatability of more than 1.5 mm
Results for the Time Period T3 (at the Conclusion of Postsurgical Orthodontics) to T4 (at Least 12 Months After Surgery) No landmarks showed clinically important changes, although Li disclosed a statistically significant change at P ⱕ 001 and the following landmarks showed statistically significantly changes at P ⱕ 0.05, Sn-h, A=-h, Ls-h, St.-h, B=-h, LIT ⫺h, and v and Me ⫺h (Fig 1). No further statistical analysis was undertaken, and it could be concluded that these cases demonstrated no clinically relevant relapse at a minimum of 1 year after surgery.
Discussion The present study makes an attempt to clarify the relationship between hard and soft tissue changes that occur after surgical advancement of the mandible. This has an impact on the ability of the orthodontist or maxillofacial surgeon to forecast the final profile. Park and Burstone28 stated that a forecast based upon hard tissues alone will not predictably and reliably define the treatment plan. Every effort has been made to standardize the technique of land mark identification in an endeavor to achieve a degree of accuracy greater than which may have been previously possible.
Table 5. The Relationship Between Changes at Menton and Changes at Associated Soft Tissue Points Multiple Regression Analysis
Correlation Analysis
Hard to Soft Tissue Relation
(R)
(R ⫻ 100)%
(r)
(R2 ⫻ 100)%
Me-Li v Me-Gn= v Me-me= v
0.624 0.790 0.800
38.94 62.42 64.00
0.556 0.756 0.764
30.91 57.15 58.37
Note: the multiple regression analysis included tissue thickness. In the case of simple linear regression, r ⫽ R.
2
Soft-Tissue Changes Related to Mandibular Advancement Surgery
Table 6. Summary of the Simple and Multiple Regression Equations and the Mean Proportional Relationships of the Significant Hard- and Soft-Tissue Changes Simple Regression Equations ⌬Li-h ⫽ ⫺0.78 ⫹ 0.62 (LIT-h) ⌬Li-v ⫽ 2.81 ⫹ 0.47 (Me-v) ⌬B=-h ⫽ ⫺1.90 ⫹ 0.79 (B-h) ⌬Pog=-h ⫽ ⫺1.17 ⫹ 0.76 (Pog-h) ⌬Gn=-h ⫽ ⫺L. 14 ⫹ 0.75 (⌬Gn-h) ⌬Gn=-v ⫽ ⫺0.66 ⫹ 0.94 (⌬Gn-v) ⌬Me-h ⫽ 0.03 ⫹ 1.00 (⌬Me-h) ⌬Me=-v ⫽ ⫺0.47 ⫹ 0.92 (⌬Me-v) ⌬ ⫽ change
Proportional Relationships ⌬Li-h ⫽ 0.77 (⌬IT-h) ⌬LI-v ⫽ ⫺0.59 (⌬Me-v) ⌬B=-h ⫽ 1.21 (⌬B-h) ⌬B=-h ⫽ 1.07 (⌬Pog-h) ⌬Pog=-h ⫽ 0.98 (⌬Pog-h) ⌬Gn=-h ⫽ 0.97 (⌬Gn-h) ⌬Gn-h ⫽ 0.97 (⌬Pog-h) ⌬Gn=-v ⫽ 1.19 (⌬Gn-v) ⌬Gn=-v ⫽ 1.17 (⌬Me-v) ⌬LMe=-h ⫽ 1.10 (⌬Me-h) ⌬LMe=-v ⫽ 1.00 (⌬Me-v)
Multiple Regression Equations ⌬Li-h ⫽ ⫺0.10 ⫹ 0.58 (⌬LIT-h) ⫹ 0.04 (TT) ⌬Li-v ⫽ ⫺3, 29 ⫹ 0.56 (⌬LIT-v) ⫹ 0.30 (TT) ⌬Li-v ⫽ ⫺1.45 ⫹ 0.49 (⌬Me-v) ⫹ 0.20 (TT) ⌬B=-h ⫽ ⫺5.02 ⫹ 0.79 (⌬B-h) ⫹ 0.25 (TT) ⌬Pog=-h ⫽ ⫺3.07 ⫹ 0.79 (⌬Pog-h) ⫹ 0.15 (TT) ⌬Gn=-h ⫽ ⫺2.11 ⫹ 0.77 (⌬Gn-h) ⫹ 0.10 (TT) ⌬Gn=-v ⫽ 3.23 ⫹ 0.94 (⌬Gn-v) ⫺ 0.35 (TT) ⌬Me=-h ⫽ 0.04 ⫹ 1.00 (⌬Me-h) ⫺ 0.002 (TT) ⌬Me=-v ⫽ 2.26 ⫹ 0.91 (⌬Me-v) ⫺ 0.34 (TT)
was excluded. In this regard approximately onethird of the vertical parameters had to be excluded but there was still sufficient data in the vertical dimension to permit meaningful consideration. This aspect had not been considered in detail by many of the articles reviewed. The addition of seven patients who had advancement genioplasties made little difference to the data in both the vertical and horizontal dimensions except at B= point, which could be expected as it is adjacent to the osteotomy cut. The genioplasty is merely an extension of the horizontal movement of the mandible and affects the soft tissue in the same proportional manner. In general agreement with most authors,1-12 advancement of the mandible correlates with movement of the soft tissue contours of the chin from soft tissue B point (B=) to soft tissue menton (Me=) after the repositioning of the symphysis in an almost 1:1 ratio in the horizontal and vertical dimensions. Mommaerts and Marxer4
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and Mobarak10 included vertical changes at menton and reported a positive change in depth and angle of the labiomental sulcus. As menton moves caudally the sulcus angle opens and the depth decreases. Veltkamp et al12 included the vertical change at the incisor tip as the lower jaw is advanced, into a multivariate regression analysis which helped to improve the predictability of the response at labrale inferius. The present study agrees with Dermaut and de Smit,9 Mobarak et al,10 and Keeling et al.25 that changes in the upper lip are seemingly independent of soft tissue changes that occur with mandibular advancement. However, Mobarak et al10 found in hypodivergent cases that the nasolabial angle increased as the upper lip became a little more recessive 3 years after surgery. The lower lip behaves differently to the upper lip and chin as the lower jaw is advanced. In this study, Li responds to horizontal movement at lower incisor tip (LIT) in a ratio of 0.77:1, which is less than that found in the Talbot6 report of 0.85:1 but very close to that of Veltkamp et al12 at 0.79:1 and Ewing and Ross7 at 0.80:1. Other studies reported ratios that varied between 0.26:1 (Dermaut and de Smit6) and 0.67:1 (Thuer et al8). This variability could be the result of many factors, such as a failure to obtain a relaxed lip position when taking the cephalometric radiographs before and after the treatment and differing muscular patterns associated with different facial types (although Mobarak et al10 found that this made no difference). Other influences that could be considered are age-related factors, tissue thickness, type and tone of musculature, facial type and the extent of the eversion of the lower lip. In the present study, it is significant that when tissue thickness is included in the multiple regression equation (Table 4) for the relationship between LIT-h and Li-h the coefficient of determination only very slightly improved. This finding appears to indicate that other factors, such as the extent of the overjet, deep bite, and the protrusion of the lower lip ahead of the upper incisor play important roles, as indicated by Veltkamps et al.12 Mobarak et al10 found a positive correlation between increase in lower anterior facial height, decrease in tissue thickness, and decrease in the depth of the labio mental fold. They deduced that the reduction in tissue thickness was caused by the unrolling and stretching of the lower lip and found that the preoperative
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tissue thickness was significantly correlated with the net change in tissue thickness in all three of the morphologic groups they studied. Mobarak et al10 reported that the proportional advancement of the lower lip in the horizontal plane was 60% of skeletal movement in all 3 groups 3 years after surgery. This reduced relationship could be attributed to the longer time span which allowed for soft tissue adjustment and settling. At the 2 week stage after surgery there is still a significant amount of swelling of the soft tissue, which could impact on the result. Mobarak et al10 also encountered a significant amount of skeletal and dental relapse in their study, a finding which was not experienced among the cases included in the present study. In the vertical dimension, disappointingly, the only meaningful correlation found in the current study was that between the changes at labrale inferius (Li) and menton (Me), which was strengthened when tissue thickness (TT) was incorporated into the multiple regression analysis. Thus, the vertical change at Li follows the vertical change at Me according to the multiple regression equation ⌬Li-v ⫽1.45 ⫹ 0.49 (⌬Me-v) ⫹ 0.20(TT). It appears that previously reported correlations in the vertical dimension have been weak or erratic.3,5 In summary, the results of the present study compare favorably with those of previously published research. The soft-tissue changes related to mandibular advancement would appear to be fairly predictable especially for the chin area. The lower lip is more of a challenge, but the incorporation of presurgical tissue thickness into a multiple regression equation offers a partial solution to the predictability of the postsurgical change. The relative complexity of these relationships will limit their application in hand-drawn predictions and it is upon precise mathematical definitions of hard- and soft-tissue relationships that the development of computer-aided forecasting must depend. Further refinement and pooling of results is necessary to enhance the predictability of results and it would be desirable to develop prospective studies when all appropriate criteria of standardization could be met.
Conclusions We present the following conclusions: (1) The horizontal cephalometric measurements were
shown to be more reliable than vertical measurements; (2) the inclusion of data from the seven advancement genioplasty cases did not have a significant influence on the proportional changes between hard and soft tissue movements; (3) the upper lip behaved in an independent manner compared with the lower lip and demonstrated no significant changes; (4) the soft-tissue changes of the chin area follow the horizontal and vertical changes of the bony chin in a 1:1 ratio; (5) horizontal changes at LI follow the horizontal changes at LIT in a ratio of 0.77:1; (6) hard tissue menton moves vertically in an effective 1:1 ratio with soft-tissue menton and with soft-tissue gnathion; (7) consideration should be given to the presurgical tissue thickness of the lower lip when attempting to forecast soft-tissue changes; and (8) in this study, no clinically relevant relapse was noted at least 1 year after surgery.
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