Facial asymmetry revisited: Part II–Conceptualizing the management

Abstract

Management of facial asymmetry is one of the arduous and challenging task to accomplish in disciplines of orthodontics and maxillofacial surgery. This article aims to describe various treatment modalities adopted conjointly by the orthodontist and maxillofacial surgeon, taking into consideration the realistic concerns and expectations of the patient. This would help improve treatment outcomes while ensuring overall well-being of the patient.

1. Introduction

Management of facial asymmetry often presents with a challenging clinical scenario. Evolving and finalizing a treatment plan should be based on an accurate qualitative and quantitative diagnosis of the patient’s particular facial asymmetry; and a list of esthetic treatment objectives as determined from the patient’s chief complaint, extent of occlusal deformity and associated sagittal or vertical jaw imbalance. Involvement of skeletal, dental and soft tissue components in the sagittal, vertical and transverse planes usually warrant a combination of orthodontic treatment and orthognathic surgery.¹

2. Treatment considerations

Developing skeletal imbalances in growing individuals can be corrected by use of hybrid orthopaedic appliances in conjunction with orthodontic treatment. However, unpredictability of the results of growth modification treatment with functional appliances in pre-adolescent children warrants constant monitoring till completion of active growth.²

Functional mandibular shifts (laterocclusions) in growing patients are amenable to correction by occlusal adjustments, aligning malposed teeth and maxillary expansion. In cases of unilateral posterior crossbite resulting from a true mandibular asymmetry (laterognathism), surgical correction is often deemed necessary.

In adults with functional shift and associated asymmetry, Joondeph³ proposed the use of diagnostic splints to properly evaluate the presence and extent of functional shift by eliminating habitual posturing, thus allowing muscle memory ‘deprogramming’ to establish the centric relation position.

True dental arch asymmetries can usually be managed orthodontically at all ages by employing asymmetric tooth-extraction patterns including differential anchorage and asymmetric mechanics such as combination of diagonal and midline elastics.⁴ Segmented arch mechanics rather than continuous arch wire mechanics should be preferred for correction of asymmetric dental malocclusions. Dental prosthesis and/or composite build-ups may be indicated for restoring missing, decayed and deformed teeth.

Botox injections, muscle relaxants, antiseizure medications, biofeedback therapy, muscle resection and bone recontouring are different treatment approaches adopted for asymmetries related to muscle hypertrophies.

Partial or complete resolution of skeletal discrepancy through orthodontic treatment alone is dependent on the severity and nature of the skeletal asymmetry.⁴ In patients having mild skeletal problems with nonsurgical plan or preference of treatment, it is necessary to maintain the compensations and asymmetry of the axial inclinations of the teeth to prevent the production of crossbite. However, skeletal asymmetries corrected by orthodontics alone approach cannot be completely eliminated and thus, the resulting compromised outcome should be explained to the patient prior to initiation of treatment.^{4, 5}

Complex facial asymmetry is often confronted with management and prognostic challenge due to the primary or secondary involvement of hard and/or soft tissues in any combination of dimensions. The effective treatment of hard tissues brings about the dramatic improvement in facial esthetics as soft tissues generally follow underlying bones; else, isolated soft tissue deformities seen in hemifacial microsomia are usually corrected during or after skeletal correction.⁶

The classification of skeletal asymmetries (resulting from unilateral excessive mandibular growth), as either hemimandibular elongation type or hemimandibular hyperplasia type, is pertinent in determining the preoperative orthodontic tooth movements and type of orthognathic surgery required.^{5, 7} Since hemimandibular hyperplasia deformity (characterized by diffuse 3-dimensional enlargement of one half of the entire mandible) begins before puberty, develops slowly and commonly exhibits latent or continued growth, maxilla is usually involved secondary to mandible with extreme dentoalveolar compensations. Bimaxillary surgery is usually indicated in these patients. On the contrary, hemimandibular elongation caused by rapid horizontal elongation mainly of the mandibular body usually starts during puberty or shortly afterwards with minimal involvement of maxilla and slight dentoalveolar compensations due to rapid growth. However, both the deformities may occur in pure and mixed forms. Milder asymmetries can be treated with isolated mandibular surgery in conjunction with inferior border osteotomy.

The aspect of growth and development should be taken into consideration during treatment planning. Accordingly, the planning and extent of surgical correction should be customized, considering the need for secondary surgery at a later age. In cases of developmental facial asymmetry, surgical treatment is usually delayed until completion of facial growth, particularly if maxillary surgery is required.

2.1. Facial asymmetry and TMJ involvement

It has been reported that the presence of temporomandibular disorder(TMD) symptoms such as joint sounds, pain and articular disk displacement is higher in patients exhibiting skeletal Class III malocclusions due to mandibular prognathism with associated facial asymmetry.⁸

Nonsurgical TMJ treatment involving use of splints, physiotherapy, chiropratic treatment, orthodontics and medication helps in alleviation of TMJ symptoms, but without stabilization and elimination of TMJ pathologies. Hence, surgical management of TMJ pathology in facial asymmetries is mandatory to achieve predictable, stable, functional, esthetic and pain free treatment outcomes. However, stable and unchanging facial asymmetry with no evidence of TMJ pathology or symptoms is amenable to correction by orthognathic surgery without TMJ surgery.⁹

Differences in consensus do exist with regards to age-based treatment planning as condylar growth usually persist until 18–23 years of age. In cases of unilateral condylar hyperplasia, primary goal of treatment is rapid elimination of pathologically active unilateral condylar process as soon as possible in the treatment sequence to preclude worsening of the asymmetric dentofacial deformity. Unilateral high condylectomy and repositioning the articular disk using Mitek-anchor technique at 15 years of age in girls and 17 years in boys yield predictable results in arresting the hyperplastic condition on the condylar hyperplasia side.⁹

2.2. Hemifacial (Craniofacial) microsomia

Due to varied clinical presentations with different degrees of mandibular deformation on the affected side as observed in hemifacial microsomia, the type and timing of treatment depends on the degree of deformation and the philosophy of treatment. Provision of early treatment in hemifacial microsomia is aimed at optimizing facial growth and consequently minimizing secondary asymmetric development of maxilla and canting of occlusal plane. Different early treatment (at 5–7 years) modalities involve reconstruction of missing elements of the proximal parts of mandible using distraction osteogenesis(DO), reconstruction of the condyle by placement of costochondral rib graft to correct the vertical and anteroposterior dimensions, and use of asymmetric functional activator after surgery to simulate jaw function and soft tissue development, and minimize maxillary canting.¹⁰ At later age (during adolescence and late teens), definitive orthognathic surgery and soft tissue augmentation surgery are performed as two-step procedures.

2.3. “Two-patient” concept in planning orthognathic surgery¹¹

A versatile tool envisaging the concept of goal-oriented therapy involves two integral components: (1) feasibility model surgery performed in consistence with the planned surgical procedure, irrespective of the occlusion so reproduced, before initiation of orthodontic treatment, and (2) cephalometric prediction tracing done using template or tracing overlay method, demonstrating the effects of surgery prior to any orthodontic tooth movement. Both these records are viewed as a “second patient”: one who manifests the results of indicated surgery prior to initiation of active orthodontic treatment. It can help determine the goals of presurgical orthodontic treatment, the orthodontic-surgical sequencing and need for adjunctive surgical procedures.

2.4. Single jaw surgery

Isolated orthognathic surgery is usually done in cases of uncomplicated asymmetries affecting mandible only, such as in deviant prognathism. Asymmetric transverse rotational movement of the mandibular distal segments is achieved using bilateral ramal osteotomies. Sagittal split ramus osteotomy(SSRO) and intraoral vertical ramus osteotomy(IVRO) are routinely used orthognathic mandibular procedures for correction of asymmetric dentofacial deformities. SSRO is usually employed for cases having mild to moderate magnitude of asymmetry (upto 7–8 mm). IVRO is usually preferred for correction of larger asymmetries (magnitude more than 8 mm) with associated TMD symptoms. IVRO is indicated for the side that moves in a posterior direction. Additionally, IVRO offers the advantages of short rehabilitation time (being quick and safe operation in cases of asymmetric mandibular prognathism), easy and rapid correction of early occlusal instability and lower risk of permanent inferior alveolar nerve injury, when compared to SSRO.¹²

2.5. Bimaxillary (Double jaw) surgery

Successful treatment of asymmetric deformities involving maxilla and mandible in more than two planes of space frequently require a combination of maxillary surgery, mandibular surgery including mandibular angle reduction, inferior border ostectomy, genioplasty in conjunction with bony augmentation of other areas of maxilla and mandible. The orthognathic surgical procedures include LeFort I osteotomy in maxilla; and bilateral IVRO, bilateral SSRO or a combination of IVRO and SSRO in mandible. A “single-splint” technique,¹³ is favoured by many oral surgeons. In patients with congenital syndromic deformities (hemifacial microsomia), the predetermined ideal position may require adjustments to compensate for soft tissue deformities. Intraoperative use of facebow facilitates in the positioning of the maxillomandibular complex in the midline.¹⁴

Following salient points should be taken into consideration during surgical planning and management by two-jaw orthognathics¹:

• 1)The dental and skeletal midlines should be ideally aligned to the facial midline.
• 2)Intercommissural plane should be parallel to the inter exocanthal plane.
• 3)Accurate prediction of effects of orthognathic surgery on lip position is difficult because soft tissue changes in the upper and lower lips after surgery occurs secondarily due to the movement of the underlying hard tissue, continuity of the orbicularis oris muscle, and soft-tissue tension. Therefore, changes in ramus height and improvement in parallelism of lip commissures to the orbital plane may not exhibit a 1:1 relationship.

2.6. Genioplasty (Esthetic reconstructive surgical procedure)

Correction of the transverse asymmetry of the chin is achieved via sliding genioplasty that repositions the chin toward the right and left side. A cant of the lower border of the chin can be corrected by performing vertical change at the osteotomy site (by downgrafting one side or performing ostectomy on the other), or by propeller genioplasty. Differential anterior or posterior repositioning of the chin can be done to correct anteroposterior asymmetry.¹⁰

Autogenous onlays (cranial or iliac crest bone), alloplastic onlays (porous polyethylene, hydroxylapatite and custom-fabricated medical-grade silastic) and microvascular groin flaps can be used for augmentations in esthetic reconstructive surgeries for skeletal asymmetries.¹¹

2.7. Adjunctive soft-tissue manipulation procedures

Orthognathic surgery for skeletal tissues can be combined with soft tissue contouring such as buccal fat pad and masseter muscle reduction in the same operation. Additional soft-tissue augmentation and/or soft-tissue reduction are usually performed as secondary procedures, if required. Augmentation procedures are recommended in various soft tissue deficiencies of head and neck region. These include free fat transfer for smaller contour or asymmetric soft tissue defects; free dermal fat grafts for larger soft tissue defects; and alloplastic implants (surgical grade, custom-contoured silastic and surgical grade polyethylene) for large and more complex-shaped soft tissue defects. Reduction procedures include myectomies, subcutaneous liposuction performed via open or closed techniques. Fat graft injection is another minor touch-up secondary procedure.¹¹

Additionally, miscellaneous modified surgical techniques for successful correction of varied presentations of asymmetry have also been documented in literature.^{15, 16, 17, 18}

In recent years, surgery-first approach (SFA) has gained popularity and is being routinely employed for successful management of appropriately selected cases of asymmetric dentofacial deformities, by overcoming the disadvantages and inconveniences of the time consuming preoperative orthodontic treatment.¹⁹ SFA enables almost complete elimination of presurgical orthodontic phase and offers the advantages of immediate correction of dentofacial deformities and soft tissue imbalances, overall reduction in treatment time, and addressal of chief complaint of the patient at the beginning of treatment, thus ensuring better patient compliance. Overall reduced treatment time with SFA is mainly attributed to two main factors, namely, elimination of skeletal and soft tissue imbalances that might interfere with tooth movement, and utilization of ‘regional acceleratory phenomenon’ during the most time-consuming step of dentoalveolar decompensation of dental arches. Moreover, SFA allows postsurgical tooth movements to be accomplished without any counteracting force from the investing soft tissues. However, dentitions presenting with severe malalignment and exaggerated curves of Spee present a relative contraindication to surgery-first approach.

2.8. Distraction osteogenesis (DO)

Distraction osteogenesis (DO) is a dynamic process facilitating the three-dimensional correction of asymmetric hypoplastic dentofacial deformities (hemifacial microsomia, mandibular hypoplasia, condylar hypoplasia) (Fig. 1a and b). The beneficial effects of the distraction forces on the surrounding soft tissues (distraction histiogenesis) are visualized in the form of soft tissue redraping along the newly constructed and corrected facial skeleton. Accurate placement of an osteotomy or corticotomy, selection of a distractor, vector planning, distraction device placement and consideration of the effects of the masticatory muscles and surrounding soft tissues that may deviate the tooth bearing segment toward an unexpected position are myriad factors influencing the precision and predictability of the results of distraction osteogenesis.²⁰

Fig. 1.

a. An adult patient presenting with facial asymmetry due to right sided TMJ ankyloses. b. Frontal view photograph showing restored facial symmetry at the completion of distraction osteogenesis (consolidation phase).

Multiplanar distraction osteogenesis in mandibular hypoplasia (genetically dwarfed mandible) offer the advantages of device placement in an area of limited bone stock, optimizing the location of only a single osteotomy and two pin sites, as well as allowing three-dimensional manipulation of the device trajectory during the distraction process. Moreover, multiplanar DO can also allow for bifocal distraction, permitting the distraction to be performed at twice the usual rate (1 mm activation on either limb of the distractor); and at different rates, depending on the amount of bone required, with total amount of distraction not exceeding 2 mm per day.

Extraoral semi-rigid and intraoral submerged mandibular distraction techniques can also be used in selected cases. A biomator orthopaedic appliance is recommended in growing children to simulate further mandibular development. Augmentation of the alveolar ridge in alveolar hypoplasia can be done using transport distraction osteogenesis. In DO, following age dependent overcorrection is recommended to counteract the poorer growth potential of the genetically recessive (micrognathic) mandible²¹:

Age (in years)	Magnitude of overcorrection (in mm)
4–8	5–6
8–12	3–4
>12	1–2

3. Orthodontic considerations

3.1. Occlusal considerations

Acute acquired asymmetries due to trauma or rapidly occurring excessive growth are usually not accompanied by dentoalveolar compensations. However, long standing and slowly developing asymmetries are usually associated with severe dental compensations in all three dimensions, and resulting in different arch shapes.¹¹

Following guidelines should be taken into consideration for presurgical orthodontic treatment in patients with facial asymmetry^{22, 10}:

• a)Dentition should not be compensated for skeletal disharmony.
• b)An existing occlusal cant should not be corrected. However, levelling of the dental arches can be done, while ensuring that the apical base midline and incisor midlines follow the cant.
• c)Dentoalveolar decompensation in the upper and lower arch must take into account the postsurgical position of the upper incisor and the anatomic limits of symphysis, respectively.
• d)Dental midlines should not be made to coincide but rather positioned in the midline of each jaw.
• e)Whenever facial asymmetry will be corrected by single-jaw surgery, the dental midline of the unoperated jaw should coincide with the facial midline.
• f)Whenever a unilateral open bite is created after increasing the ramus height in cases of hemifacial microsomia and temporomandibular joint ankyloses, the height should be maintained while allowing the vertical alveolar growth of maxilla.
• g)Cephalometric norms should not be strictly adhered to as the morphogenetic patterns of asymmetry patients usually results in specific abnormal bony architectures.
• h)Minimal incisor decompensation warrant upper second bicuspid extractions whereas upper first bicuspid extraction is indicated in cases where upper incisors require greater degrees of decompensation.
• i)Nonextraction approach with reproximation is preferred in minimal crowding cases requiring no dentoalveolar decompensation.

Integrated orthognathic-orthodontic treatment of dentofacial asymmetry should be aimed at fulfilment of following objectives, namely: Function, reliability, realistic, esthetics, cost-effectiveness (being economic), stability, satisfaction and health.

4. Summary

An awareness of normal craniofacial asymmetry is important when planning surgical intervention in patients with recognizable facial asymmetry. Evaluation of each case should be based on its individual merits. Patients should be cautioned beforehand about unrealistic expectations regarding perfect symmetry in human faces, and explain that it is impossible to achieve perfect symmetry with treatment. Meticulous and precise treatment planning considerations involving the bidirectional feedback and proficiency of the surgeon and orthodontist are the factors that influence the predictability of the desired outcome.

Conflict of interest

None.