Surgery-first approach in correcting skeletal Class III malocclusion with mandibular asymmetry

This case report describes a surgical orthodontic case that used the recently introduced surgery-first approach to correct a severe skeletal Class III malocclusion. A 19-year-old woman presented with severe mandibular prognathism and facial asymmetry; she had been waiting for growth completion in order to pursue surgical correction. After prediction of the postsurgical tooth movement and surgical simulation, 2-jaw surgery that included maxillary advancement and differential mandibular setback was performed using a surgery-first approach. Immediate facial improvement was achieved and postsurgical orthodontic treatment was efficiently carried out. The total treatment time was 16 months. The patient’s facial appearance improved significantly and a stable surgical orthodontic outcome was obtained.

Highlights

  • We treated a surgical orthodontic patient with the recently introduced surgery-first approach.

  • Postsurgical orthodontic treatment was efficiently carried out, and the total treatment time was reduced.

  • A stable surgical orthodontic outcome was obtained.

A combined orthodontic and orthognathic surgery approach is accepted as the standard of care for patients who have a severe skeletal jaw discrepancy with facial asymmetry. It is often considered the only viable treatment option for improving facial appearance and restoring normal occlusal function.

Although the conventional 3-stage surgical orthodontic approach, which includes presurgical orthodontics, surgery, and postsurgical orthodontics, has been well established as the gold standard in most cases, some disadvantages have been recognized. One drawback is the long presurgical treatment time that typically worsens facial appearance and exacerbates the malocclusion. In some countries, these disadvantages have caused patients to seek plastic surgeons who are willing to perform orthognathic surgeries without collaboration with orthodontists or consideration for the final occlusion. Subsequently, orthodontists have witnessed many instances where patients have experienced adverse functional effects resulting from clinically unacceptable occlusal outcomes.

Recently, to address patient demand and satisfaction, the surgery-first approach was introduced to overcome some disadvantages associated with the conventional surgical orthodontic approach. Several case reports have demonstrated successful outcomes with reduced treatment time and greater patient satisfaction using the surgery-first approach in surgical orthodontics. This approach demands more careful surgical planning and stronger collaboration between skilled orthodontists and surgeons to accurately predict postsurgical tooth movement and surgical movement. Therefore, previous advocates of this approach recommend only using the surgery-first approach for mild to moderate skeletal discrepancies. However, the scope of this approach has been expanding with advances in 3-dimensional (3D) imaging technology and 3D virtual surgical simulation, the use of skeletal anchorage systems, and better understanding of the biologic response after surgery.

This case report demonstrates successful surgical orthodontic treatment with a surgery-first approach in a patient with a severe Class III skeletal jaw discrepancy and facial asymmetry. See Supplemental Materials for a short video presentation about this study.

Diagnosis and etiology

A 19-year-old woman visited the orthodontic department at Chonnam National University Hospital in Gwangju, Korea. Her chief complaints were anterior crossbite and mandibular prognathism. She reported no problems in her medical history, but she mentioned being recently diagnosed with internal derangement in both jaw joints, for which she had been receiving physical and occlusal splint therapy. Her symptoms had improved, and her temporomandibular joint specialist confirmed that her joint condition was stabilized. Her oral hygiene was well maintained.

Pretreatment facial photographs showed a concave profile, an increased lower facial height, and a significant facial asymmetry with chin deviation to the left. The maxillary dental midline was coincident with the facial midline, but the mandibular dental midline deviated 9 mm to the left ( Fig 1 ). Intraoral photographs and study casts showed more than a full-cusp Class III molar relationship (−17.0 and −8.5 mm from the Class I position on the right and left sides, respectively). Her overjet was −8 to −10 mm, and her overbite was −2 mm. Anterior and posterior crossbites from the maxillary right first premolar to the left first molar were present. There was mild to moderate crowding in both the maxillary and mandibular arches ( Figs 1 and 2 ). No functional shifts and discrepancies between centric relations and centric occlusion were detected anteroposteriorly or laterally.

Fig 1
Pretreatment facial and intraoral photographs.

Fig 2
Pretreatment study casts.

All teeth, including the third molars, were present ( Fig 3 ). Her mandibular third molars were fully erupted, and her maxillary third molars had complete root formation and were erupting. No caries or pathologies were observed, and the periodontal tissues were healthy. The frontal view of the cone-beam computed tomography (CBCT) image showed the extent of the mandibular skeletal asymmetry, which involved chin deviation of 5.0 mm toward the left side. The lateral cephalometric analysis indicated a skeletal Class III pattern, which was the result of both a retrognathic maxilla and a prognathic mandible (ANB, −5°; Wits appraisal, −21 mm; SNA, 78°; SNB, 83°), and a hyperdivergent pattern (SN-MP, 43°; FMA, 29°). The proclined maxillary and retroclined mandibular incisors represented a typical dentoalveolar compensation for a skeletal Class III malocclusion (U1-SN, 110°; IMPA, 77°) ( Table ). The 3D image analysis of facial asymmetry showed that both the frontal and lateral ramal inclinations and the mandibular body length were greater on the right side than on the left side; this contributed to the mandibular deviation toward the left ( Fig 4 ). However, the maxillary and ramal heights were actually greater on the left side; this was an unexpected finding, since typically, the maxilla and the ramus on the deviated side are normal or small.

Fig 3
Pretreatment radiographs generated from CBCT: A, frontal, lateral, and lateral soft tissue views; B, panoramic view.

Table
Cephalometric measurements
Pretreatment Postsurgery Posttreament Norm ± SD
Skeletal
FH-SN (°) 13.9 13.4 13.1 6 ± 4
SNA (°) 77.7 82 81.2 82 ± 3.5
N-A (HP) (mm) −5.9 −2.5 −1.5 2 ± 3.7
Maxillary unit length (Co-ANS) (mm) 74.1 78.6 78.6 90 ± 5
SNB (°) 82.8 77.8 79.1 80.9 ± 3
N-Pg (HP) (mm) −0.6 −12.4 −5.8 −6.5 ± 5
Mandibular unit length (Co-Pog) (mm) 122.1 115.1 115.8 113 ± 8
ANB (°) −5.1 4.2 2.3 1.6 ± 1.5
Wits appraisal (mm) −20.8 −5.8 −6.5 −1 ± 1
MP-SN (°) 42.5 44.3 42.5 33 ± 6
Occlusal plane to SN (°) 26.6 26.5 24.5 14.4 ± 2.5
FMA (MP-FH) (°) 28.5 30.9 29.5 23.9 ± 4.5
Dental
U1-SN (°) 109.8 108.8 104 102.8 ± 5.5
IMPA (L1-MP) (°) 77.2 75 88.1 95 ± 7
Interincisal angle (U1-L1) (°) 130.5 131.9 125 130 ± 6
Soft tissue
Upper lip to E-plane (mm) −5.1 1.5 −2.4 −6 ± 2
Lower lip to E-plane (mm) −1.1 5.1 0 −2 ± 2
Nasolabial angle (Col-Sn-UL) (°) 91.2 81.1 98.6 102 ± 8

Fig 4
Three-dimensional image analysis of facial asymmetry: A, facial asymmetry analysis in InVivo5 (Anatomage, San Jose, Calif); B, polygonal chart demonstrating the source and magnitude of deviations in facial skeletal asymmetry.

The patient and her parents reported a family history of mandibular prognathism. The etiology of the skeletal Class III malocclusion appeared to be primarily hereditary with some potential environmental factors.

Treatment objectives

The patient was diagnosed as having a skeletal Class III jaw discrepancy with facial asymmetry that was attributed to a retrognathic maxilla and a prognathic and asymmetric mandible. The following treatment objectives were established: (1) correct the jaw discrepancy to obtain a harmonious facial appearance, (2) correct the mandibular asymmetry to achieve facial symmetry, (3) achieve a normal occlusion with Class I canine and molar relationships, (4) obtain normal overjet and overbite, (5) achieve coincident skeletal and dental midlines, (5) coordinate the maxillary and mandibular arch forms, and (6) resolve crowding and align the teeth. Because of her severe skeletal jaw discrepancy and facial asymmetry, surgical jaw correction was the only valid treatment approach for achieving these objectives.

Treatment objectives

The patient was diagnosed as having a skeletal Class III jaw discrepancy with facial asymmetry that was attributed to a retrognathic maxilla and a prognathic and asymmetric mandible. The following treatment objectives were established: (1) correct the jaw discrepancy to obtain a harmonious facial appearance, (2) correct the mandibular asymmetry to achieve facial symmetry, (3) achieve a normal occlusion with Class I canine and molar relationships, (4) obtain normal overjet and overbite, (5) achieve coincident skeletal and dental midlines, (5) coordinate the maxillary and mandibular arch forms, and (6) resolve crowding and align the teeth. Because of her severe skeletal jaw discrepancy and facial asymmetry, surgical jaw correction was the only valid treatment approach for achieving these objectives.

Treatment alternatives

An orthodontics-only approach would not be successful in correcting this severe skeletal jaw deformity. Therefore, orthognathic surgery was unavoidable. Since the mandible predominantly contributed to the severe jaw discrepancy and facial asymmetry, the possibility of having single-jaw surgery with only a mandibular setback was evaluated. After comprehensive assessment of the virtual surgical simulations for both single-jaw and 2-jaw surgeries, it was determined that both options could comparably improve facial appearance. However, the oral surgeon (H-K. O.) preferred a 2-jaw surgery approach because a mandibular setback alone would require more than 14 mm of surgical correction, which could potentially compromise the chin-throat profile and the stability of the surgical outcome.

Conventional surgical orthodontics include 3 phases: (1) presurgical orthodontics for decompensating the dentition to increase the magnitude of surgical movement, (2) orthognathic surgery, and (3) postsurgical orthodontics for finishing and detailing the occlusion. The literature has reported that the time required for presurgical orthodontics varies from 6 months to several years, but the average time is between 12 and 18 months. In collaboration with oral surgeons, conventional 3-phase surgical orthodontics have been exclusively practiced as the gold standard in providing predictable and stable results. However, the surgery-first approach concept was recently introduced, and several successful case reports have demonstrated that it can be a viable alternative approach in surgical orthodontics. By incorporating decompensational movement of the dentition into the surgical planning, the presurgical orthodontic stage is eliminated. During the postsurgical phase, all dental movements, which include alignment, incisor decompensation, and surgical relapse, are corrected. It is also well recognized that tooth movement after surgery is more effective. Therefore, the overall treatment time for a surgery-first approach is considerably shortened.

Since the patient had a strong desire to have surgery completed before leaving Korea to start college in the United States, the surgery-first approach was offered and accepted to accommodate her time constraint.

Under the condition of having orthognathic surgery, there were 2 alternative orthodontic treatment plans: nonextraction and extraction of maxillary premolars. The extraction of maxillary premolars has been most commonly used to reduce maxillary incisor proclination and to resolve crowding. However, for our patient, the following 3 factors led to a nonextraction approach: the crowding was not severe, a slight clockwise rotation of the maxilla during maxillary advancement surgery can improve the inclination of the maxillary incisors, and increasing the surgical movement was not desirable since more than 14 mm of surgical movement was already required.

After considering all alternative plans, the authors and the patient decided on a nonextraction, 2-jaw surgery-first approach: maxillary advancement surgery using a LeFort 1 osteotomy with a slight clockwise rotation and differential mandibular setback surgery using a bilateral sagittal split ramus osteotomy.

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Dec 19, 2018 | Posted by in Orthodontics | Comments Off on Surgery-first approach in correcting skeletal Class III malocclusion with mandibular asymmetry
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