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

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 ).

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
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Dec 14, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Maxillary advancement versus mandibular setback in class III dentofacial deformity: are there any differences in aesthetic outcomes?
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