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Maxillary advancement versus mandibular setback in class III dentofacial deformity: are there any differences in aesthetic outcomes?

Maxillary advancement versus mandibular setback in class III dentofacial deformity: are there any differences in aesthetic outcomes?



International Journal of Oral & Maxillofacial Surgery, 2017-04-01, Volume 46, Issue 4, Pages 483-489, Copyright © 2016 International Association of Oral and Maxillofacial Surgeons


Abstract

A retrospective evaluation of maxillary advancement and mandibular setback in class III patients was performed and their aesthetic outcomes compared. Patients with a sella–nasion–A-point angle (SNA) of 80–84° were selected. Pre- and postoperative lateral cephalograms were obtained for 34 class III patients; these were divided into two groups according to the surgical procedure performed: mandibular setback group ( n = 17) and maxillary advancement group ( n = 17). The pre- and postoperative cervical length, lip–chin–throat angle, lower/upper lip thickness, distance from the lower/upper lip to the aesthetic line, soft tissue angle, facial contour angle, and nasolabial angle of the two groups were compared. Significant differences were observed for cervical length ( P = 0.0003) and sex ( P = 0.003) when comparing maxillary advancement with mandibular setback. Although the preoperative cervical length was similar in the two groups, it increased significantly after maxillary advancement and decreased after mandibular setback. In this study, the differences in aesthetic outcomes depending on the surgical procedure performed were considered. Some aesthetically important parameters proved to be superior after maxillary advancement when compared to mandibular setback, even with the maxilla in the normal position.

Class III malocclusion is considered one of the most complex conditions in terms of diagnosis and treatment planning, and an increasing demand for surgical correction has been observed in recent years. Treatment should include the following goals: function, aesthetics, long-term stability, and the selection of the procedure with the lowest complication rate. The anatomical feasibility should also be considered.

The level of patient satisfaction is an important factor that has a significant impact on oral health-related quality of life. The facial profile comprises five main prominences: the forehead, nose, lips, chin, and the submental–cervical region. Additionally, lip thickness, lip tonicity, initial incisor inclination, and lip height affect the resulting soft tissue changes and consequently the aesthetic outcome. The final aesthetic outcome, however, is determined by the procedure performed, individual soft tissue adaptation, and achievable possible tendency. The lip and the chin are the two regions influenced by mandibular setback and maxillary advancement.

Historically, Class III malocclusions were treated by isolated mandibular setback; however, bimaxillary procedures have become increasingly frequent. One important reason for the increase in bimaxillary procedures is the achievement of stable long-term results. However, one-jaw surgery is often sufficient to correct most of the dentofacial deformity, and two-jaw surgery can increase the risk of complications. The selection of which jaw to operate on is generally based on the position of the maxilla and the mandible. Mandibular setback is generally the procedure of choice if the mandible is positioned anteriorly with the maxilla in the normal position.

Many studies have compared the aesthetic outcomes of mandibular setback surgery, maxillary advancement surgery, and combined surgery. In this study, the aesthetic outcomes of mandibular setback surgery were compared to those of maxillary advancement surgery in patients suffering from class III dentofacial deformities with the maxilla in the normal position. The hypothesis was that in patients with a class III deformity with the maxilla in the normal position, the aesthetic outcome differs between maxillary advancement and mandibular setback.

Materials and methods

The study was performed in accordance with the Declaration of Helsinki statement for medical research involving human subjects. The study protocol was reviewed and approved by the Ethics Committee of RWTH Aachen University prior to study commencement. As the patients in this study remained anonymous, the consent process was not compulsory.

A retrospective cohort study was conducted based on the clinic medical records. The patients ( n = 34) underwent combined orthodontic and orthognathic surgery and were assigned to either the mandibular setback group ( n = 17) or the maxillary advancement group ( n = 17) according to the surgical procedure performed. Although different orthodontists performed the orthodontic treatment, one surgeon performed all of the mandibular setback procedures and another performed all of the maxillary advancement procedures. The examiner in this study was blinded to the surgeon names. The study inclusion criteria were as follows: (1) non-syndromic patient with a class III dentofacial deformity and a preoperative sella–nasion–A-point angle (SNA) of 80–84° and Wits value of <0 (the Wits value is the distance between AO (perpendicular from A-point to occlusal plane) and BO (perpendicular from B-point to occlusal plane)) ; (2) the patient had completed skeletal growth; (3) the surgical treatment performed was either mandibular setback or maxillary advancement; (4) the patient had not undergone previous surgery involving the middle or lower face.

A lateral cephalogram was taken at the beginning of orthodontic treatment (T1) and at least 6–10 months postoperatively (T2), after the postoperative swelling had subsided. Patients were asked to have their teeth in occlusion and their lips in an unstrained and relaxed position to avoid muscular compensation. The changes in outcome (pre- and postoperative) were compared by means of continuous outcome distances and angles (sagittal, vertical), cervical length (Gn′–H: the distance between the soft tissue gnathion (Gn′) point and the neck point (H)), nose position, and dental, upper lip, and lower lip changes ( Fig. 1 ).

Graphic showing the mean tracing of the hard and soft tissues (gonion angle, mandible inclination, lower lip to E-line, nasolabial angle, soft tissue facial angle, nose prominence, upper lip thickness, upper lip length, lower lip length, cervical length, lip–chin–throat angle, facial contour, upper lip to E-line).
Fig. 1
Graphic showing the mean tracing of the hard and soft tissues (gonion angle, mandible inclination, lower lip to E-line, nasolabial angle, soft tissue facial angle, nose prominence, upper lip thickness, upper lip length, lower lip length, cervical length, lip–chin–throat angle, facial contour, upper lip to E-line).

Statistical analysis

To assess the differences between the two groups – mandibular setback vs. maxillary advancement – the analysis of covariance (ANCOVA) models were adjusted to the data of the 14 outcome parameters separately ( Table 1 ). Specifically, cervical length served as a dependent variable; age, sex, and treatment, as well as the (two-way) interaction between age and treatment and the (two-way) interaction between sex and treatment served as independent variables (fixed-effects). Normal errors were assumed and the validity was checked by residual and influence diagnostics. Similar models were used for the other outcome variables.

Table 1
Values of selected cephalometric variables before and after surgery (mean ± standard deviation), with Dahlberg's standard deviation of error for each variable.
Variables Before surgery After surgery Accidental error
SNA (°) 81 ± 4.15 81 ± 4.13 0.8
SNB (°) 83.9 ± 4.71 80.5 ± 4.21 0.79
Wits appraisal (mm) −10 ± 4.08 −4.1 ± 3.52 0.75
Gonion angle (°) 128.5 ± 6.32 128.17 ± 6.87 0.69
Mandible inclination (°) 34.61 ± 6.83 34.76 ± 6.44 0.78
Upper 1 inclination (°) 105.61 ± 7.61 104.88 ± 5.80 0.81
Lower lip to E-line (mm) −8.3 ± 3.31 −5.7 ± 3.71 0.51
Nasolabial angle (°) −2.5 ± 3.24 −3.4 ± 3.03 0.78
Soft tissue facial angle (°) 110 ± 12.53 100.6 ± 12.2 0.8
Upper lip thickness (mm) 18.2 ± 3.53 16.5 ± 3.32 0.51
Pg′ (mm) 13 ± 3.23 13 ± 4.23 0.7
Upper lip length (mm) 21.9 ± 3.34 23.7 ± 4.43 0.4
Lower lip length (mm) 46.5 ± 7.52 48.1 ± 6.13 0.6
Cervical length (mm) 50.6 ± 10.04 47.9 ± 10.42 0.72
Lip–chin–throat angle (°) 50.6 ± 10.14 47.9 ± 10.32 0.77
Upper lip to E-line (mm) −8.3 ± 3.32 −5.7 ± 3.72 0.74
SNA, sella–nasion–A-point angle; SNB, sella–nasion–B-point angle; E-line, aesthetic line; Pg′, soft tissue pogonion.

Using a backward selection process, the model was first reduced by removing the non-important interaction terms ( P > 0.05) and was then continued in the same way with the main effectors of sex and age. Of primary interest was the effect on the main effect treatment group in the ANCOVA models. The type 1 error rate for the multiple testing of the 14 outcome variable endpoints was controlled using Hochberg's multiple testing procedure. The results of the adjusted effects of the different treatments (adjusted for age and sex and the interaction term) on the respective outcome variables are given in Table 2 , along with the 95% confidence intervals for the mean difference, the P -values, and the (adjusted) Hochberg significance levels. The overall significance level was set to 5%. All computations were performed using SAS version 9.4 (TS1M1) (SAS Institute, Cary, NC, USA) in Windows X64 7 Pro (Microsoft, Redmond, WA, USA).

Table 2
Values of the soft tissue cephalometric index in relation to mandibular setback/maxillary advancement.
Source Least square mean 95% CI for difference P -value Hochberg significance level Comments a
Mandibular setback Maxillary advancement
Cervical length (mm) 44.439 54.618 −15.343 to −5.014 0.0003 0.0036 (1) b
Lip–chin–throat angle (°) 113.706 106.470 0.977 to 13.495 0.024 0.0071 (1)
Upper lip thickness (mm) 17.010 14.872 0.231 to 4.044 0.029 0.0107 (1)
Lower lip to E-line (mm) −5.784 −3.862 −3.716 to −0.128 0.036 0.0143 (1)
Soft tissue facial angle (°) 93.925 95.133 −3.043 to 0.6295 0.189 0.0179 (1)
Facial contour angle (°) −9.119 −11.174 −1.184 to 5.295 0.205 0.0214 (1)
Upper lip to E-line (mm) −6.414 −5.934 −2.098 to 1.138 0.549 0.0250 (2)
Upper 1 inclination (°) 106.348 105.122 −3.176 to 5.628 0.574 0.0286 (1)
Nasolabial angle (°) 106.585 102.075 −10.335 to 7.752 0.772 0.0321 (1)
Upper lip length (mm) 22.750 23.014 −2.141 to 1.6128 0.775 0.0357 (1)
Mandible inclination (°) 32.154 31.904 −1.964 to 2.463 0.819 0.0393 (1)
Lower lip length (mm) 44.387 43.965 −3.334 to 4.178 0.820 0.0429 (1)
Nose prominence (mm) 15.808 15.603 −1.627 to 2.038 0.820 0.0464 (1)
Gonion angle (°) 126.968 127.149 −3.681 to 3.319 0.916 0.0500 (1)
CI, confidence interval; E-line, aesthetic line; ANCOVA, analysis of covariance.

a (1) ANCOVA model with baseline value and treatment; (2) ANCOVA model with significant sex.

b Treatment interaction.

Results

This study included 34 patients with a class III dentofacial deformity and an SNA of 80–84°; 14 were male and 20 were female, and they ranged in age from 16 to 51 years (mean age 25 years). These patients underwent combined orthodontic–surgical treatment, and cephalograms were taken pre- and postoperatively. The mean age of the maxillary advancement group was 31 years, and the mean age of the mandibular setback group was 25 years ( t = −1.86, df = 35.7, P = 0.070). The mean mandibular setback was −7.1 mm (maximum −12.9 mm, minimum −2 mm) and the mean maxillary advancement was 4.6 mm (maximum 8.5 mm, minimum 2.4 mm).

The sella–nasion–B point angle (SNB), SNA, and Wits appraisal changed significantly depending on the procedure performed (SNB: t = −6.61, df = 27.05, P = 0.0001; SNA: t = −5.84, df = 25.97, P = 0.001; Wits: t = −1.75, df = 25.66, P = 0.008).

There was a significant difference between the maxillary advancement and mandibular setback groups with regard to sex ( P = 0.003).

The cervical length differed significantly depending on whether mandibular setback or maxillary advancement was performed ( P = 0.0003). The mean preoperative cervical length was 55.00 mm (standard deviation (SD) 7.95) in the mandibular setback group and 54.00 mm (SD 11.49) in the maxillary advancement group. The mean postoperative cervical length was 46.00 mm (SD 11.28) in the mandibular setback group and 56.00 mm (SD 10.97) in the maxillary advancement group.

The mean change in the lip–chin–throat angle was 10.47° (SD 6.5) in the mandibular setback group and −0.64° (SD 9.1) in the maxillary advancement group; the change in the lip–chin–throat angle in the mandibular setback group appeared to be significantly different to that in the maxillary advancement group ( P = 0.024), but this difference was not significant using the Hochberg procedure.

The change in upper lip thickness in the mandibular setback group was not significantly different to that in the maxillary advancement group when using the Hochberg significance level ( P = 0.029).

The distance between the lower lip and the aesthetic line in the mandibular setback group was not significantly different to that in the maxillary advancement group ( P = 0.549).

The postoperative change in the soft tissue facial angle in the maxillary advancement group (mean −0.88°, SD 2.61) was similar to that in the mandibular setback group ( P = 0.128).

The postoperative facial contour angle did not differ significantly between the groups using the Hochberg significance level ( P = 0.205).

The postoperative anterior movement of the upper lip in the mandibular setback group (mean 0.88 mm, SD 2.75) was similar to that in the maxillary advancement group (mean 1.58 mm, SD 2.93) ( P = 0.549).

The postoperative change in the upper incisor inclination in the mandibular setback group (mean 1.9°, SD 7.1) was similar to that in the maxillary advancement group (SD 8.2) ( P = 0.549).

The nasolabial angle increased after mandibular setback (SD 7.53) and decreased after maxillary advancement (SD 6.5), but the difference between the groups was not significant ( P = 0.772).

There was no significant difference between the two groups in mandible inclination ( P = 0.819) or length of the lower lip ( P = 0.820).

Although the nose prominence tended to decrease more in the mandibular setback group (mean −0.94 mm, SD 2.4) compared with the maxillary advancement group (mean −1.58 mm, SD 2.9), this difference was not significant ( P = 0.820).

The postoperative change in gonion angle of the mandibular setback group (SD 3.6) was similar to that in the maxillary advancement group ( P = 0.800).

Discussion

The purpose of this study was to compare the aesthetic outcomes of maxillary advancement with those of mandibular setback in patients with a class III dentofacial deformity but with the maxilla in the normal position (SNA of 80–84°). This should help in selecting the appropriate jaw if one-jaw surgery is planned, or in choosing the appropriate amount of movement for each jaw if two-jaw surgery is considered.

The facial appearance after maxillary advancement was more favourable than that after mandibular setback. It was observed that the cervical length increased after maxillary advancement in contrast to mandibular setback. Additionally, mandibular setback resulted in a straightening of the upper lip with a concomitant undesirable increase in the nasolabial angle.

To reduce the selection bias, the surgeons were asked for their reasons for choosing maxillary advancement or mandibular setback. The surgical procedure was chosen based on personal preference in relation to clinical findings or the position of the jaw. Mandibular setback was the main procedure performed before 2005, but maxillary advancement became the main procedure thereafter. To reduce measurement bias, all cephalograms were traced and digitized by the same examiner. The surgical approaches applied were the one-piece Le Fort I osteotomy for maxillary advancement and the bilateral sagittal split osteotomy for mandibular setback. The preoperative cervical length was similar in the two groups, but increased significantly after maxillary advancement and decreased after mandibular setback.

No increase in the incidence of double chin was observed following maxillary advancement ( Fig. 2 ) when compared to mandibular setback ( Fig. 3 ). This may explain the more favourable facial appearance in the maxillary advancement group and its impact on the chin region. There was considerable variation in the change in cervical length, which was greater in patients who had maxillary advancement, and maxilla impaction due to the autorotation of the mandible. As reported in previous studies, a straightening of the upper lip was also found after mandibular setback, with a concomitant increase in the nasolabial angle. Increasing the nasolabial angle has a negative effect on the aesthetic outcome. Although the nose prominence was decreased in the maxillary advancement group, this amount of decrease was similar to that found in the mandibular setback group ( Table 2 ).

Photographs of a patient who underwent maxillary advancement: (a) pre-treatment, (b) post-treatment.
Fig. 2
Photographs of a patient who underwent maxillary advancement: (a) pre-treatment, (b) post-treatment.

Photographs of a patient who underwent mandibular setback: (a) pre-treatment, (b) post-treatment.
Fig. 3
Photographs of a patient who underwent mandibular setback: (a) pre-treatment, (b) post-treatment.

A consciousness and perception of the attractiveness of different facial parameters may be useful in compiling the optimal treatment option. Generally, the amount of sagittal discrepancy and the position of the mandible and the maxilla vis-à-vis the skull base are decisive factors for selecting the surgical procedure. If there is a small discrepancy, one-jaw surgery will generally be sufficient to correct the deformity; in such cases, two-jaw surgery will inevitably increase the risk of complications without additional benefits. Many studies have shown that mandibular setback has a negative impact on function and can lead to a negative aesthetic outcome in the submental region. In addition, maxillary advancement increases the width of airways and improves the aesthetics of the nasolabial and submental regions. The vertical change was similar in the two groups ( Table 2 ). A minimal vertical change following maxillary advancement caused a forward movement of the mandible and increased the cervical length positively, as also reported by Proffit et al.

As recommended in a previous study, surgeons performing this operation should limit the amount of mandibular setback to less than 5 mm and correct the remaining distance by advancing the maxilla, irrespective of the SNA or SNB. This has a positive aesthetic impact on the submental region, improves the functional outcome, and shows stable, long-term results, as reported in other studies. Some authors have also reported that isolated mandibular setback is less predictable and less stable, and others have shown that maxillary advancement is a more stable component and causes larger mandible autorotation.

The nose, facial contour angle, cervical length, and facial angle are the main components of facial aesthetics, and should all be considered when planning and predicting the outcome of orthognathic surgery. Vasudavan et al. showed that the Le Fort I advancement produces an elevation of the nasal tip, as evidenced by a reduction in nasal length and nasofrontal angle, along with an increase in the nasal tip protrusion. In the present study, it was found that advancing the maxilla had a great effect on the nose (nasolabial angle and nose prominence), the cervical length, and the upper lip, as reported previously. The distance from the upper lip to the aesthetic line – depending on the patient's sex – was significantly different after maxillary advancement when compared with mandibular setback. In female patients, maxillary advancement was performed more often than mandibular setback, whereas the opposite was the case for male patients. A possible reason for this is related to the surgeon's consideration of the double chin deformity which can result from mandibular setback. This requires further investigation.

In conclusion, maxillary advancement achieved a significantly more favourable outcome when considering the cervical length in class III patients, regardless of the maxilla position. These findings should be considered when selecting the appropriate jaw for osteotomy.

Funding

No funding.

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