Management of facial asymmetries — true skeletal or functional shift

Drs. Jamie Y. Kim, Chung How Kau, and Ahmet A. Celebi show a patient’s progress through treatment

The presentation of a unilateral posterior crossbite is usually accompanied by a mandibular shift producing a lower midline deviation toward the crossbite side.^1,2 Bilateral posterior crossbites often involve true basal skeletal discrepancies in the transverse relationships of the maxilla to the mandible that usually reflect a severe maxillary skeletal constriction rather than mandibular enlargement.

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Generally, there are no dental midline and facial midline discrepancies in full-occlusion and at-rest positions with any obvious functional deviations observed upon closure in bilateral posterior crossbites.³ Mandibular asymmetries have been the source of multiple debates and significant research. A question frequently addressed in the literature is the source of the asymmetry: Is it predominantly skeletal, dento-alveolar, or a combination of both? Many causes of facial asymmetry have been reported in the literature, as genetics, condylar fractures, condylar hyperplasia or hypoplasia, tumors or ankylosis in the temporomandibular region, prepubertal asymmetries, and asymmetric condylar positioning.⁴

Asymmetric condylar positioning and asymmetric mandibular growth

Many studies have reported that asymmetric condylar positioning associated with mandibular shifts can be demonstrated on tomograms and transcranial radiographs in the majority of posterior crossbite patterns that present in children.^5,6

In the skeletally immature patient with severe asymmetry, the option to treat with maxillary expansion appliances might be the most appropriate choice. In a study, 22 children with a functional posterior crossbite were corrected with maxillary expansion at a mean age of 8.5 years. The condyle on the non-crossbite side was positioned more anterior prior to treatment and moved posteriorly and superiorly after treatment.⁷ In another study, authors compared condylar and ramal asymmetries in 81 patients with unilateral posterior crossbites to 75 normal occlusive subjects. The results showed patients with unilateral posterior crossbites had more asymmetric condylar positions than the controls. Moreover, the condylar, ramal, and condylar-ramal heights on the crossbite side were smaller than the non-crossbite side.⁷

Asymmetric malocclusions can be complicated and challenging to correct, especially when there is an underlying skeletal component.⁴ Orthodontic treatment alone is a difficult choice in this situation.⁸ The treatment of patients with an asymmetry that is moderate to severe and with no significant functional limitations may be delayed until skeletal maturity is reached for a definitive orthodontic and/or surgical correction. Despite this, an attempt can be made to control and modify asymmetric growth in patients with active growing time.⁹ An attempt at early treatment is always the choice as functional shifts establish mal-occlusions and musculo-skeletal function. Often, the latter is difficult to unestablish.

In this report, we present the orthopedic and orthodontic treatment of a facial asymmetry and unilateral posterior crossbite with severe midline discrepancy in a growing patient.

Case report

Diagnosis and etiology

The patient was a 13-year-old African-American male who visited Department of Orthodontics in The University of Alabama at Birmingham for orthodontic consultation. The chief complaint was posterior crossbite on the right side. No specific medical problems or temporomandibular joint symptoms were observed. The clinical exam revealed that he had a Class I molar on the right and a half-step Class III molar on the left. The upper incisors were in negative overjet. In addition, the upper dental midline was deviated 2 mm to the left while the lower dental midline was deviated 4 mm to the right from the midsagittal plane (Figures 1 and 2). Even though a CR-CO shift was suspected, it was impossible to de-program the patient fully at the clinical exam. A CBCT radiograph (Carestream 9500) was taken to verify if a true skeletal mandibular asymmetry was present. A mildly retrusive maxilla and a prognathic mandible contributed to a Class III skeletal relationship (ANB = -2.5). His mandibular plane angle was normal (SN-MP = 35.9°) (Figure 3 and Table 1). The maxilla was skeletally narrow in the transverse dimension. Mild crowding of less than 3 mm existed in the maxillary and mandibular arches. There was Bolton discrepancy with large upper lateral incisors. His facial profile was slightly concave with a normal chin-throat distance and normal nasolabial angle. He showed mild facial asymmetry with deviation of mandible to the right side.

Treatment objectives

The treatment objectives for the dentition were correction of the right posterior cross-bite, to make the maxillary, mandibular, and facial midlines coincident. The treatment objectives for the skeleton and soft tissue were to improve the facial asymmetry, including the deviation of the chin, to correct the transverse discrepancy, and to improve the facial profile by reducing the lower lip protrusion. Thus, facial symmetry, normal overjet and overbite, and Class I canine-to-molar relationships could be obtained.

Treatment progress

The treatment plan included two phases. During the first phase of treatment, a removable diagnostic bite plate was used. The design included maxillary first molar clasps, no labial bow, an anterior bite ramp, and an acrylic plate covering the palate with an expansion screw embedded in the acrylic. The anterior bite ramp disoccluded his dentition for deprogramming of the jaw. The patient was instructed to wear the appliance full time for 23 days without any expansion. Upper metal brackets from canine-to-canine were bonded, and the expansion was initiated (1 turn/day). A 5.5 mm expansion was achieved by 22 turns, and the posterior crossbite was successfully corrected. The remaining upper and lower teeth were bonded. After 5 months of treatment, the anterior bite plate was removed, and the mandible appeared to be in the new position (Figure 4). During the second phase, treatment continued with fixed orthodontic treatment. The upper archwire progressed to 0.016 x 0.022 Niti, and the lower archwire progressed to 0.020 SS wire. At this time, Class III elastics were worn full time. The wire progression continued to 0.019 x 0.025 SS upper archwire and 0.017 x 0.025 SS reverse Curve of Spee wire on the lower arch to level the Curve of Spee. After 16 months of total treatment, appliances were removed. Maxillary and mandibular retention was performed with fixed retainers.

Figure 7: Posttreatment cephalometric radiograph; Figure 8: Cephalometric superimposition before and after treatment

Results

Intraoral photographs obtained after the first phase of treatment are presented in (Figure 4). The final records show that the unilateral posterior crossbite was resolved, and dental midlines were coincident with each other and with the facial midline. (Figures 5 and 6). The skeletal facial asymmetry was corrected by the correction of mandibular shift. Intraorally, a Class I canine and molar relationship with optimal overbite and overjet was achieved. In the comparison of the dental casts before and after treatment, maxillary inter-molar widths increased by 4 mm. Cephalometric superimposition showed A point moved back slightly due to upper anterior lingual torque. Maxillary incisors were proclined and moved forward. Mandibular incisors were slightly retroclined (Figures 7 and 8). A straight profile was achieved with improvement of lower lip to E-line. As shown in the CBCT, deviation of the mandible asymmetry resolved after treatment (Figure 9). Diode laser (NV^® Microlaser, DenMat) was used to recontour hyperplastic gingiva (Figure 10). Posttreatment panoramic radiographs showed acceptable root parallelism and developing third molars (Figure 11).

Conclusion

Facial asymmetry with a unilateral crossbite and functional shift of the mandible was treated in a growing patient, due to the expansion of the maxilla and symmetrical repositioning of the mandible. Consideration of a hidden functional shift is important for treatment planning for these patients. Orthognathic surgery may not be necessary in growing patients with functional asymmetries. Minimally invasive treatment can be treatment planned for patients exhibiting unilateral posterior crossbites possessing transverse discrepancies.[/userloggedin]
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