Ho-Jin Kim, Hyung-Kyu Noh, Hyo-Sang Park

Differences in facial soft tissue deviations in Class III patients with different types of mandibular asymmetry: A cone-beam computed tomography study.

- Korean J Orthod 2023;53:402-419

I appreciate the authors’ hard work on the study. I have some questions in this study, and would be grateful to gain additional insights from the authors.

Q1. The authors mentioned that the mandible is affected in 74% of facial asymmetric patients, the influence of mandibular asymmetry on the facial soft tissue might be crucial. It seems moderate to severe maxillary asymmetry have influence on the facial soft tissue. Is there any consideration of the maxillary asymmetry in the exclusion criteria?

Q2. The authors mentioned that internal skeletal asymmetry was rather masked by the soft tissue. There seems to be a difference in soft tissue thickness depending on the patient’s body mass index (BMI). According to the thickness or volume of the soft tissue, the degree to which internal skeletal asymmetry is masked by the soft tissue asymmetry seems to vary. Is there a reason for not considering the patient’s BMI?

Q3. The authors mentioned that mandibular yaw correction, including more setback movement at the NDv and less setback or advancement at the Dv, would be required during skeletal Class III jaw surgery. Is the overcorrection, more setback or less setback, imperative in the skeletal Class III jaw surgery? Isn’t enhanced the symmetry of the face, without the overcorrection?

Q4. After orthognathic surgery, the degree to which soft tissues follow the changes in hard tissues is unclear, and there is the possibility of postoperative relapse. Considering these things, when should it be recommended to perform rhinoplasty in patients with yaw-dominant mandibular asymmetry (before or after orthognathic surgery)?

Questioned by

Chahee Park

Blooming Smile Orthodontic Clinic, Suncheon, Korea

We would like to appreciate our reader’s interest and valuable questions.

A1. Generally, mandibular asymmetry is predominant to facial asymmetry compared to maxillary asymmetry.1,2 Regarding the transverse deviation of the jaws and dentitions, the maxilla demonstrated the least amount of deviation, followed by the maxillary dentition, mandibular dentition, and mandible.1,3 The extent of asymmetry tends to increase from the superior part to the inferior part of the face. In addition, the vertical maxillary asymmetry and transverse occlusal cant might be compensations closely associated with the mandibular roll. Collectively, maxillary asymmetry is likely a compensatory manifestation caused by mandibular asymmetry, thus indicating a relatively low influence on the facial soft tissue.4 For this reason, this study analyzed facial soft tissue asymmetry based not on the maxillary asymmetry but on the mandibular asymmetry types.

A2. The BMI shows a significantly positive correlation with the facial soft tissue thickness.5 That is, underlying skeletal asymmetry might be more camouflaged by thicker soft tissue in patients with a higher BMI compared to those with a normal or lower BMI. We checked and found that there was no obese patient in this study, and thus, the effect of individual BMI might be insignificant in the current results.

A3. As the overlying facial soft tissue can compensate for the degree of underlying skeletal asymmetry,1 the extent of soft tissue change is generally less than that of corresponding skeletal change after jaw surgery.6 Therefore, in some cases, the overcorrection of jaw surgery might be required and helpful in achieving the symmetry of facial soft tissue. However, from a clinical perspective, the over-decompensation of the tooth position, which is mandatory to obtain the overcorrected jaw position, is unlikely to be achievable, particularly before surgery, due to opposite soft tissue pressure. Therefore, the asymmetry of the facial soft tissue remained even after symmetrical repositioning of the jaws could be further corrected by the following: additional mandibular guidance using resin bonded on the tooth,4 intermaxillary elastics between the microimplants placed in each jaw,4 or adjunctive facial procedures such as lower border osteotomy, chin augmentation/reduction, or graft surgery.7

A4. The upper dental midline needs to coincide with a philtrum, and the transverse position of the upper anterior teeth can be influenced by rhinoplasty. If rhinoplasty is planned, the upper teeth need to be moved to the planned midline of the nose during decompensation pre-surgical orthodontic treatment. If it is not planned, the upper dental midline needs to be compensated. In essence, rhinoplasty should be determined based on a three-dimensional diagnosis during initial treatment planning and can be performed simultaneously with orthognathic surgery.7 Otherwise, if an undesired or unexpected nasal deviation is perceived during the postoperative evaluation, rhinoplasty can be additionally planned and executed with plate removal surgery.8

Replied by

Ho-Jin Kim, Hyung-Kyu Noh, Hyo-Sang Park

Department of Orthodontics, School of Dentistry, Kyungpook National University, Daegu, Korea