Skeletal Class III malocclusion may be categorized as an osseous discrepancy involving either maxilla, mandible, or of mixed origin¹. These discrepancies are surgically corrected by mandibular setback, maxillary advancement or a combination of both. Common surgical techniques for correcting mandibular prognathism involving the mandible are bilateral sagittal split osteotomy (BSSO), intraoral vertical ramus osteotomy (IVRO), and intraoral inverted “L” osteotomy (IILO)². Mandibular step osteotomy (MSO) is also one technique for correcting mandibular prognathism³.

When correcting mandibular prognathism, BSSO with rigid fixation has the following advantages over IVRO or IILO: (1) improved bone-to-bone contact between the segments, (2) ease of rigid fixation, (3) improved healing due to large bony interface and rigid fixation, (4) simultaneous extraction of third molars that have erupted or become impacted, (5) immediate jaw mobilization following surgery, (6) improved condylar position control, (7) improved speech during the recovery period, (8) improved ora1 hygiene, (9) simpler post-operative nutrition maintenance at first and a faster transition to a regular diet, and (10) better post-operative comfort⁴. A pre-operative antero-posterior intermaxillary discrepancy of more than 7 mm requiring a large mandibular setback tends to have severe relapse⁵. Few studies also reported that large mandibular setbacks with or without maxillary advancement, may have a tendency for collapse in the sagittal dimension of the pharyngeal airways which might lead to sleep-disordered breathing or in rare cases obstructive sleep apnoea syndrome⁶. Mandibular length shortening by setback leads to compression of soft tissue as the volume of soft tissue remains constant, leading to a double chin, deep mentolabial fold, decreased tissue strength, and ultimately early facial aging⁷. Regardless of the sella-nasion to A point (SNA) or sella-nasion to B point (SNB), limiting the mandibular setback to less than 5 mm and advancing the maxilla to correct the deficiency gives a positive aesthetic outcome at the submental region, enhances functional outcomes, and stable results⁸.

Ostectomies of the mandibular body were performed by Hullihan, Angle, Blair, and Harsha to correct mandibular prognathism. A portion of the mandibular body was removed during these fully vertical body ostectomies using a combination of extraoral and intraoral techniques⁹. In MSO, a step-cut is made in front of the mental foramen as part of the osteotomy procedure. In order to address mandibular hyperplasia, it is recommended to either close an existing edentulous space or use the space left over after a posterior tooth extraction. The step-cut design, which offers a desirable fracture pattern and optimal bone proximity, mechanically improves the stability of the osteotomy³. In 1906, von Eiselburg published the first description of the MSO procedure for correcting mandibular retrognathia, as cited in reference¹⁰. Pichler (1918) reported using MSO to treat mandibular prognathism, as cited in reference⁹. Without intending to preserve the mental nerve, they both carried out the procedure extra orally. Dingman¹¹ integrated the intraoral and extraoral methods in 1948 to treat mandibular retrusion.

An alternative to single-stage mandibular setback for correcting mandibular prognathism either by BSSO, IVRO or bimaxillary surgery in order to minimize relapse would be to adopt a two-stage surgery wherein mandibular body osteotomy with removal of a premolar tooth is first performed followed by a second surgery at a later date involving maxillary osteotomy and further mandibular setback. We present two cases of skeletal Class III malocclusion with a severely prognathic mandible requiring orthodontic treatment with concurrent two-stage surgical management.

Two female patients aged 17-years and 16-years respectively were referred to the Department of Oral and Maxillofacial Surgery with chief complaint of forwardly placed lower jaw. They were clinically examined; radiological evaluation was done using orthopantomograph, lateral and frontal cephalograph. Diagnosis of skeletal Class III malocclusion was made. Both patients presented with large discrepancies in relation to the upper and lower jaws, concave profile, anterior divergence, reverse overjet, and potentially competent lips as shown in Fig. 1. Pre-operative cephalometric analysis was done using the software CephX–cephalometric analysis software (ver. 4.02; Orca Dental AI Ltd.). A diagnosis of prognathic mandible, retrognathic maxilla, proclined upper incisors, and a Witts appraisal of –17.54 mm and –14.24 mm as mentioned in Table 1 and Table 2 respectively indicated the need for surgical correction.

Pre-operative virtual surgical planning using PROPLAN CMF software (Materialise) aided the simulation of precise bone movements and predetermination of the amount of setback and final bony position. Additionally, model surgery was also carried out and an interocclusal splint was fabricated. During the first stage of surgery, following general anaesthesia and nasal intubation both patients underwent bilateral mandibular first premolar and maxillary second premolar extraction. The mandibular vestibular region was infiltrated with 1% xylocaine and an incision was placed below the mucogingival junction from distal to first molar on one side to the opposite side. The mandibular body was exposed preserving a part of soft tissue on the midline for perfusion, avoiding injury to the mental nerve. Anterior body osteotomy with a step modification of Dingman’s technique was performed along the space created by the extraction of lower first premolar teeth. The step osteotomy was made adjacent to the mental nerve for preservation. This modification also helps attain stability between the segments of the mandible by creating good communication between the fragments. After reduction of the osteotomised segments with the occlusal splint, osteofixation was done using Synthes Matrix MANDIBLE titanium mini plates and screws (DePuy Synthes) as displayed in Fig. 2. Post-operative orthodontics was resumed 4 weeks after surgery. The patients were reviewed periodically and were scheduled for the second stage one year post the first surgery.

At the second stage, patients were taken up for bimaxillary surgery under general anaesthesia and nasal intubation, during which the titanium implants used during anterior body osteotomy were removed through a small vestibular incision. Occlusal splint fabrication by model surgery and pre-operative virtual surgical planning using PROPLAN CMF software were implemented for precise bone movement simulation and predetermine the position and amount of setback of mandible and advancement of maxilla. Simultaneously advancement of the maxilla by 4 mm in both the patients and yaw to the right by 3 mm in patient 1 and yaw to the left by 2 mm in patient 2 respectively was carried out using Le Fort I osteotomy. Mandibular setback by 6 mm bilaterally in patient 1; 6 mm on right and 7 mm CCR on left in patient 2 using BSSO to balance the severe antero-posterior skeletal discrepancies was performed. Since mandibular setback is one of the least stable movements, titanium osteofixation was used for enhanced stability after the larger amount of setback in the first stage. As there is a necessity to remove metal osteosynthesis after bone healing is complete, segment stabilization with unsintered hydroxyapatite/poly-L-lactic acid (u-HA/PLLA) bioresorbable osteosynthesis after removal of the titanium osteofixation was done.(Fig. 3) The post-operative phase was uneventful and patient was placed on MMF until the next post-operative day and was put on a liquid diet. Post-surgical orthodontics was resumed after a duration of 4 weeks. Patient 1 was reviewed 1 year and 5 years post-operatively, while patient 2 was reviewed 1 year and 2 years post-operatively. Assessment of clincial dentaloskeletal changes and cephalometric analysis of nasopharyngeal, oropharyngeal and hypopharyngeal airways (Fig. 4) was carried out. These were later compared with pre-operative and immediate post-bimaxillary phases of treatment as shown in Table 3 and Table 4 respectively.

Isolated mandibular prognathism is seen in 20%-25% of Class III patients¹². Globally, the incidence of Class III malocclusion has been reported to vary between 0% and 26.7%, with notably high frequency rates in East Asian countries. An incidence of 2.3%-14% has been observed in the Japanese population¹³. Facial disharmony has an adverse psychological impact affecting social life¹⁴. Often surgery is the last option when the growth potential of the patient ceases. According to Stellzig-Eisenhauer et al.¹⁵, Wits appraisal is the most decisive factor in differentiating between a surgical (>5 mm value indication for surgery) and non-surgical Class III group. Most orthognathic surgical procedures are performed after the age of 18 years so that no interference of growth occurs in the treated cases¹⁶.

MSO was proposed as a purely intraoral method with step designs to address a range of mandibular abnormalities¹⁷. These include the reverse step-cut for mandibular advancement and traditional step-cut for mandibular prognathism, anterior open bite closure. Bimaxillary surgery requiring maxillary advancement for correcting skeletal Class III with mandibular prognathism can be done by Le Fort I osteotomy or multi-segment osteotomies according to requirement; it is also useful in patients with severe discrepancies who need more than 6 to 7 mm advancement to make up for the required amount of maxillary advancement with mandibular setback¹⁸. Management of ramus inclination and less relapse are two benefits of bimaxillary surgery. The primary factor for the chin to migrate forward following mandible-only surgery is the recovery of the ramus inclination change, and the gonial angle is likely to be pushed posteriorly when the mandible is set back¹⁹. Long-term post-operative assessment of over 12 years revealed that more posterior movement of soft tissues occurs in females than in males as the growth pattern and mandibular rotation is more downward in females and is anterior in males. Factors such as surgical procedure, age, direction of growth as well as post-operative bone remodelling predispose to the occurrence of relapse¹².

Combining MSO and BSSO in single stage can cause a number of complications. Iatrogenic injury to neurovascular structures may predispose to altered sensation and compromised vascularity. Additionally, stability concerns arising from multi-fragment control, reduced bony contact, infection, and indeterminable healing is a cause for concern. The need for orthodontic decompensation before bimaxillary surgery was also a reason as to why we chose the two-stage technique. Both patients reported needed a large antero-posterior correction and a single stage surgery would have resulted in a disharmonious soft tissue profile¹² and an increased risk of relapse post-operatively. Factors such as surgical procedure, age, direction of growth as well as post-operative bone remodelling predispose to the occurrence of relapse¹². MSO can be used for smaller movements, but the removal of premolars bilaterally provided ample space for a larger setback in the first stage. We chose to perform BSSO concurrently with maxillary osteotomy during the second stage for completion of the orthodontic decompensation and achieve proper, stable occlusion.

Despite the fact that mandibular setback osteotomies decrease the size of the pharynx, there was no proof of post-operative obstructive sleep apnea (OSA). However, when selecting the course of treatment for specific orthognathic procedures, possible post-surgical OSA should be carefully considered. Double-jaw operations could be the preferred procedure, particularly in cases with severe dentoskeletal Class III deformity, since there is moderate evidence that they result in less impaired post-operative pharyngeal airways²⁰. The u-HA/PLLA system has demonstrated better long-term skeletal stability with regard to the mandibular advancement or setback than the titanium-fixation group²¹ which can be credited to bioactive/osteoconductive property of the material.

To avoid complications such as mental nerve paraesthesia associated with the previous techniques, step osteotomy of anterior body of mandible was performed along the first premolar teeth space, avoiding inferior alveolar nerve and mental nerves. No paraesthesia, dental stability, skeletal stability and other complications were recorded. The u-HA/PLLA system has demonstrated better long-term skeletal stability with regard to the mandibular advancement or setback than the titanium-fixation group²¹ which can be credited to bioactive/osteoconductive property of the material. From the analyses, we also infer that there was a significant improvement in nasopharyngeal airway dimensions sagittally in both the patients. There was mild to insignificant change in oropharyngeal and hypopharyngeal airway dimensions. These results suggest that two-stage mandibular setback employing modified Dingman’s mandibular body osteotomy with step for large antero-posterior dentofacial deformity correction has produced good outcomes in terms of dental and skeletal stability without affecting the pharyngeal airway dimensions and satisfactory aesthetics.

Although the overall treatment period with a two-stage surgery is longer than conventional methods, our approach is centered on stability and acceptable soft tissue profile in the long-term. As we have performed this technique on only two patients, comparison to single stage approach would render statistical evaluation impossible. We would like to conduct a formal study to assess differences between conventional techniques and our method with regard to airway volume and stability with a larger sample, follow-up period and report the outcomes.

This case report highlights the value of a two-stage orthognathic approach in the management of patients with pronounced mandibular prognathism and severe skeletal Class III discrepancies. By integrating a modified Dingman’s mandibular body osteotomy with a step cut in the first stage followed by bimaxillary surgery, a stable occlusion, improved esthetics and preservation of pharyngeal airway dimensions can be achieved along with long term skeletal/dental stability and no neurosensory complications /relapse. From a patient perspective, the combined surgical-orthodontic intervention resulted in marked improvements in function, facial balance, and psychosocial confidence underscoring the importance of individualized, phased surgical planning in complex dentofacial deformities.