Orthodontic and surgical management of a patient with severe mandibular deficiency and asymmetry with condylar hypoplasia using 3-dimensional surgical planning in combination with a modified surgery-first approach

Progressive improvements in digital technology and surgical techniques have synergized the speed, predictability, and favorable outcomes for patients undergoing surgical-orthodontic treatment with handicapping dentofacial deformities. This case report will demonstrate the management of a patient with severe mandibular hypoplasia, condylar hypoplasia, and mandibular asymmetry. The dentofacial deformity, and consequently, the unaesthetic facial appearance, led to psychosocial stress, symptoms of excessive daytime sleepiness, and functional limitations, especially related to mandibular movements. A modified surgery-first approach was used, which was successfully performed using computer-assisted surgical planning. Postsurgical orthodontics was accomplished with the aid of temporary skeletal anchorage mini-plates. An additional alloplastic enhancement of the chin addressed the severe microgenia, which the osseous advancement could not achieve. This resulted in a total advancement of the pogonion by 26 mm yielding a remarkable improvement in the patient’s facial esthetics. Furthermore, a considerable improvement in mandibular function and reduction in daytime sleepiness occurred. The severe malocclusion with a discrepancy index value of 47 was treated to a successful final occlusion in 21 months of treatment time.

Highlights

  • Handicapping dentofacial deformity was addressed using a modified surgery-first approach.

  • Computer-aided surgical planning for maxillomandibular advancement with counter-clockwise rotation.

  • Early surgery promoted psychosocial and functional benefits for ensuing orthodontic treatment.

  • Skeletal anchorage mini-plates placed during initial surgery were used for cant correction.

  • Significant mandibular advancement was augmented by alloplastic grafts at the chin and mandibular angles.

Of the many dentofacial deformities necessitating combined orthodontic-surgical management, mandibular hypoplasia is one of the most prevalent. The National Health and Nutritional Estimates Survey, which was based on dental occlusion, estimates that between 5%-10% of the United States population and 0.5%-1.0% of U.S. white population is affected by mandibular deficiency that is severe enough to be handicapping.

Mandibular hypoplasia is exceedingly variable in both its clinical presentation and etiology. Its etiology could be congenital, developmental, or acquired. Although the acquired form of mandibular hypoplasia usually has a definitive etiology, developmental hypoplasia is often idiopathic in origin. Congenital mandibular hypoplasia, unilateral or bilateral, most frequently results from the underdevelopment of the first and second branchial arches. The congenital mandibular hypoplasia can either be associated with syndromes, such as occulo-auriculo-vertebral spectrum, Treacher Collins syndrome, or can occur in isolation, as in some forms of the Pierre Robin sequence. Although there is considerable heterogeneity in the phenotypic spectrum seen in these patients because of variable expressivity and reduced penetrance of the gene, mandibular hypoplasia is the most common and archetypal sign even when it occurs as a part of a craniofacial microsomia (CFM).

Nonsyndromic malformations of the mandible form a unique group by not being associated with any known syndromes. The nonsyndromic form also presents with great variability in the esthetic, skeletal, neuromuscular, occlusal, and growth characteristics and has been previously referred to as the mandibular deficiency syndrome.

Although etiology-based diagnosis and management are desirable, of greater importance is the efficient and effective management of the dentofacial deformity (DD), and its accompanying morbidity. Severe mandibular deficiency can be extremely debilitating for the patient, both in terms of functional impairment and esthetic disfigurements, thereby negatively impacting the quality of life. Therefore, orthodontics combined with surgery to rectify the skeletal discrepancy not only affords stable skeletal bases and a pleasing appearance but also restores the patients’ confidence and enhances their quality of life.

Orthognathic surgery for the treatment of patients with DD has evolved through the integrated efforts of orthodontists and surgeons during the past 50 years, which has led to refinements that ensure the delivery of efficient and predictable outcomes. Technologic advancements such as 3-dimensional (3D) imaging and computer-aided surgical planning have added to the visualization and the accuracy of both diagnosis and surgical treatment planning. Virtual surgical planning, followed by 3D printing of the splints, transfers the accuracy to the surgical table with linear differences of less than 1 mm. This is particularly useful in correction of asymmetries in which 3D planned surgeries have proved to be considerably more accurate. Another evolution for patients with DD is the surgery-first approach (SFA), which is gaining popularity because of the advantages of decreased total treatment time and affording immediate improvement in the facial esthetics and function; thereby improving the overall quality of life early on and thus enhancing patient cooperation.

The case report that follows describes the management of a patient with severe mandibular hypoplasia, condylar hypoplasia, and mandibular asymmetry, leading to an unaesthetic facial appearance accompanied by functional limitations of mouth opening and lateral mandibular movements with symptoms of obstructive sleep apnea (daytime sleepiness). This case was managed using computer-assisted surgical planning and modified SFA, followed by comprehensive orthodontics and, finally, an alloplastic enhancement of the chin. This approach resulted in a significant improvement in the patient’s facial and smile esthetics and considerable improvement in function.

Diagnosis and etiology

A 17-year-old postpubertal white male presented to the orthodontic clinic at the University of Connecticut Health Center with a chief complaint of, “I want to straighten my teeth and jaws.” His medical history revealed seasonal allergies. A history of depression was reported by his primary care physician. The patient’s mother noted that he was a mouth breather and had been snoring since infancy. The family denied knowledge of the presence of any genetic abnormalities and declined to be subjected to any testing for that reason. The dental history was noncontributory, and this was their first visit to the orthodontist. Functional examination revealed a maximum mouth opening of 27 mm and restricted lateral excursive movements.

The extraoral examination revealed down-slanting eyes and facial asymmetry with the chin deviated to the right side of the face by 4 mm. He had a convex soft tissue profile with a severely retrusive chin, 20 mm behind the vertical line dropped through subnasale. An obtuse nasolabial angle and chin-throat angle along with slight paranasal deficiency was also observed. The lower facial height was decreased, but the ratio of anterior to posterior facial heights was normal because the posterior facial height was also decreased ( Fig 1 ). On intraoral examination, the patient presented with a Class II Division 1 malocclusion, with a full cusp Class II molar relationship on the right and end-on relationship on the left. Overjet was 9.5 mm from the labial of the mandibular incisors to the most protrusive maxillary incisor ( Fig 2 ). The patient also exhibited an impinging overbite with a deep curve of Spee and a steep occlusal plane. Noticeable on occlusal and frontal examinations was canting or a “roll” of the mandibular dentition, with the left side inferior to the right side. Cephalometric analysis revealed a severe skeletal Class II relationship with a retrusive mandible, a hyperdivergent growth pattern, and a dual mandibular border. Upright maxillary incisors and flared mandibular incisors were representative of the inclinations typical for Class II dental compensations. Panoramic radiographs demonstrated bilateral condylar flattening with the right condyle more affected than the left and an asymmetrical mandibular border with a pronounced antegonial notch on the right ( Fig 3 , A ; Table ).

Fig 1
Pretreatment facial and intraoral photographs.

Fig 2
Pretreatment dental casts.

Fig 3
A, Pretreatment lateral cephalometric radiograph, tracing, cephalometric measurements, and panoramic radiograph. B, Pretreatment CBCT demonstrating bilateral condylar flattening and mandibular asymmetry.

Table
Lateral cephalometric analysis
Measurement Normal Pretreatment Posttreatment Change
SNA (°) 82.0 ± 2.0 80.0 82.5 2.5
SNB (°) 80.0 ± 2.0 68.2 75.5 7.3
ANB (°) 2.0 ± 2.0 11.9 6.9 5.0
SN-MP (°) 32.0 ± 5.0 43.0 52.0 9.0
FMA (°) 24.0 ± 4.5 35.0 43.0 8.0
U1-SN (°) 102.0 ± 5.5 99.0 102.0 3.0
U1-NA (mm) 4.3 ± 2.7 0.0 1.1 1.1
L1-NB (mm) 4.0 ± 1.8 8.0 8.6 0.6
L1-MP (°) 95.0 ± 7.0 99.0 87.4 11.6
Upper lip to E-line (mm) −6.0 ± 2.0 −0.1 −2.8 2.7
Lower lip to E-line (mm) −2.0 ± 2.0 4.1 −2.5 6.6

A preliminary assessment for a sleep disorder was done using the Epworth Sleepiness Scale in which he obtained a score of 11, indicating moderate to excessive daytime sleepiness. Based on these findings, he was referred to the Department of Pediatric Sleep Medicine at Yale University by the Plastic and Reconstructive Surgery Department for a polysomnography assessment. That assessment revealed that the patient had primary snoring associated with sleep disruption and daytime sequelae, although no evidence of significant sleep-disordered breathing was detected.

To further evaluate his condylar morphology and mandibular asymmetry, a cone-beam computed tomography (CBCT) scan was obtained. The CBCT revealed that there was bilateral condylar hypoplasia with the right condyle more hypoplastic than the left. Mandibular body asymmetry to the right was seen in addition to an asymmetric chin, which also deviated to the right ( Fig 3 , B ). A Technetium 99 m limited bone scintigraphy was acquired to test for progressive bone resorption at the condyles. The result of the scan was negative, indicating that either the condylar resorption was stabilized or that it was a primary (congenital) condylar hypoplasia. Establishing the exact etiology of the mandibular and condylar hypoplasia was difficult because the parents of the patient did not want their son to be subjected to any other testing and/or genetic testing. The American Board of Orthodontics Discrepancy Index (DI) was recorded at 47 ( Supplementary Material ).

Treatment objectives

The primary treatment objective was to improve the patient’s quality of life. This could be accomplished by addressing the compromised function; by improving the upper airway; as well as by optimizing the facial esthetics. Esthetic correction entailed: establishing facial symmetry, improving smile esthetics, and achieving a balanced soft tissue profile by addressing the chin prominence, the mentolabial angle, and the chin-throat angle along with obtaining a harmonious lip relationship. Additional objectives were to establish a stable jaw relationship, an ideal occlusal and functional relationship, and an ideal overjet and overbite.

Treatment alternatives

Based on the patient’s chief complaint, our primary objectives, and the extent of the required correction, the options suggested to the patient for the management of the severe mandibular hypoplasia were primarily a combination of surgical-orthodontic treatments.

The first option was surgical mandibular advancement and correction of asymmetry through an asymmetrical bilateral sagittal split osteotomy (BSSO) and an advancement genioplasty. Preliminary treatment simulation and soft tissue predictions for this plan were obtained using Dolphin Imaging & Management Solutions software (version 11.8.06.15 premium; Chatsworth, Calif). On analyzing the simulated outcome of the treatment, maxillary advancement was added to the surgical plan for the following reasons (1) the amount of advancement required to overcome the severity of mandibular deficiency was impaired by the limits imposed by the overjet; (2) correcting the preexisting deficiency of the maxilla—though not significant— would enhance the facial harmony; (3) signs of sleep disruption and daytime sequelae indicating upper airway problems, though not overtly diagnosed as obstructive sleep apnea, could still benefit from the bimaxillary surgery; and (4) a counterclockwise maxillomandibular rotation would aid in correcting the mandibular plane, occlusal plane and in the mandibular projection. Hence, the single-jaw surgical option was revised to a maxillomandibular advancement with counterclockwise rotation. The mandibular advancement would be asymmetric, combined with an asymmetric advancement genioplasty.

The second option was distraction osteogenesis (DO), as it has been opined that it would provide better stability because of the gradual lengthening of the bone and the surrounding soft tissue envelope. Two combinations of DO were discussed, (1) mandibular distraction combined with orthognathic surgery—LeFort I osteotomy and genioplasty, and (2) combined maxillo-mandibular distraction with an advancement genioplasty at the time of removal of the distractor. Given that, of the 2 jaws, it was the mandible that needed to be advanced by a considerable amount and was severely hypoplastic, both clear indications for DO, it was decided that the first combination might be more appropriate for the patient if DO was selected as the treatment alternative. In addition, it would be easier to incorporate the maxillomandibular counterclockwise rotation into this option.

The third option was camouflage treatment with extraction of maxillary premolars as a means to manage the dental malocclusion. This was considered as the last option and would be offered to the patient only if he did not consent to the surgery along with the explanation that this option would not address the skeletal disharmony, and therefore not lead to any substantial esthetic or functional improvements.

All 3 options were presented to the patient and his parents as well as discussed with the maxillofacial surgical team before arriving at the final treatment plan. The patient and his parents, after 6 months of consideration, consented to proceed with surgical mandibular advancement. On deliberation with the surgeons as to the superiority of the 2 surgical treatment options—orthognathic surgery and DO—the surgeons, although not rejecting DO as a possibility, favored orthognathic surgery for the following reasons (1) the need for more procedures with DO, specifically placement and removal of the device and orthognathic surgery for the maxilla and chin; (2) protracted treatment duration with DO because of the time needed to correct the severe hypoplasia, which includes the latency period, active period and consolidation period within the distraction process; and (3) stability obtained with rigid fixation in orthognathic surgery could be exceptional even in large movements. Overall, they felt that in an era of trying to limit the number of procedures that favored placing the jaws expeditiously in the ideal spot, BSSO was a better option.

After all parties had consented to go with the first option, we decided to perform the surgical-orthodontic treatment using SFA because of 2 main reasons. First, the team of orthodontists and surgeons were experienced and competent with this approach and had achieved shortened treatment times using this approach. Second, the advantages provided by this approach were well suited for this patient, such as addressing his chief complaint early in the treatment and thus improving his quality of life. It is important to note that, although the patient was motivated for the treatment, he was diffident and tense in the dental chair; this was perhaps because of the enormous effort required for him to open the mouth wide during orthodontic examinations and records. We expected that the SFA might help enhance patient cooperation, and this assumption was actualized during treatment.

Therefore, the final treatment plan chosen and executed was: limited maxillary advancement, large mandibular asymmetric advancement, and counterclockwise rotation of both jaws accompanied by an asymmetric advancement genioplasty using the SFA. The minor modification required for this approach was to bond the maxillary arch 1 month before the surgery to align and flare the maxillary incisors, and thereby eliminate any interference to the mandibular advancement.

Treatment progress

The maxillary arch was bonded with 0.022-in preadjusted edgewise appliance. A 0.016-in nickel-titanium wire followed by a 0.016 × 0.022-in nickel-titanium wire was used to flare the maxillary incisors to align them with the maxillary left central incisor. This approach was used to eliminate any interference to the mandibular advancement. Four weeks later, the mandibular brackets were bonded, after which a CBCT scan (exposure time, 14 seconds; field of view, 12-in; voxel size, 1.25 mm) was taken to construct a composite model of the facial skeleton. The virtual model was constructed using the Synthes PROPLAN CMF software (Materialise, Plymouth, Mich) ( Fig 4 ). The scan was oriented to the natural head position based on the extraoral photographs, and this position was reconfirmed by clinical evaluation. The interorbital plane matched the horizontal reference line in the natural head position. A perpendicular line bisecting the horizontal reference plane drawn between the orbits served to determine the facial midline. Dental models obtained from the patient were positioned in the desired postsurgical occlusion and digitally scanned using ProMax 3DMid (Planmeca OY, Helsinki, Finland) CBCT machine, and the stereolithographic files were incorporated into the composite model. The virtual surgical planning incorporated maxillomandibular advancement and counterclockwise rotation ( Fig 5 ). The first virtual surgery was the asymmetric BSSO of 15.1 mm on the right and 10.7 mm on the left for mandibular advancement and yaw rotation ( Fig 6 ). The mandibular counterclockwise rotation was also executed, which was then followed by the virtual LeFort I osteotomy to advance the maxilla and rotate it counterclockwise with the center of rotation close to ANS ( Fig 7 ). In addition, a 10 mm asymmetric advancement genioplasty was also planned ( Fig 8 ). To transfer the computerized plan to the patient, virtual intermediate and final splints were created. These digital files were then converted to physical splints made of hybrid epoxy-acrylate polymer using the rapid prototyping additive manufacturing process (SLA-3500 machine; 3D Systems, Rock Hill, SC) ( Fig 9 ).

Oct 7, 2020 | Posted by in Orthodontics | Comments Off on Orthodontic and surgical management of a patient with severe mandibular deficiency and asymmetry with condylar hypoplasia using 3-dimensional surgical planning in combination with a modified surgery-first approach
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