Identification and management of maxillomandibular transverse width discrepancies constitute an important part of treating dentofacial deformities. Previous literature shows extensive reports of managing maxillary transverse width discrepancies that are widely accounted for. The surgical methods employed to correct a transverse width deficiency of maxilla consists of rapid maxillary expansion and its variations¹, depending on the amount of discrepancy and direction of the bony corrections. In severe cases, multiple maxillary osteotomies² at Le Fort I level^3,4 may be required. These are, however, technique-dependent procedures and carry the risk of many potential complications, such as relapse⁵, periodontal defects, prolonged intraoperative time, alterations in gingival contour, loss of tooth vitality, postoperative mobile segments, and massive hemorrhage⁶. It is feasible to adjust minor bimaxillary transverse deformities by orthodontic camouflage without surgery. Nonetheless, moderate to severe cases still need some form of surgical correction procedure to re-instate the ideal maxillary transverse width.

Though historically not a new technique, mandibular midline osteotomies have been employed to correct excess and discrepancies in the transverse dimension. When patients present with a normal maxilla and mandibular width excess, expansion of the maxilla is mostly preferred⁷. Hara et al.⁷ performed a mandibular width reduction by performing osteotomies at symphyseal and posterior mandibular regions in a bimaxillary discrepancy patient, having mandibular excess. When the maxilla presents adequate transverse width or a mild width deficit that can be corrected with orthodontics, isolated mandibular surgery may be useful in adjustment of bimaxillary problems.

In bimaxillary discrepancies wherein a normal maxilla and an abnormal mandible are observed, the standard management approach is either a mandibular surgery or a multi-segmented maxillary transverse width variation^7,8. In any case, the normal jaw with adequate dimensions should be preserved as such and any surgical correction must involve the affected jaw.

While performing the diagnosis, extra concern should be exerted to identify the presence of transverse width problems in the dentoalveolar level as well as in the skeletal level. When the transverse discrepancy is present at both levels, osteotomies for bimaxillary problems including the chin should be well-planned. The presence of other deformities and the requisite for their concomitant correction, and post-treatment stability should be considered. Here, we introduce a novel technique for the correction of bimaxillary transverse width discrepancy wherein the maxilla had normal transverse width and the mandible showed deficiency in the transverse dimension following pre-surgical orthodontic treatment.

All patients reported to the outpatient clinic at the Department of Oral and Maxillofacial Surgery, Shimane University Faculty of Medicine and underwent pre-surgical orthodontic treatment for approximately 6 to 12 months; orthodontic decompensation was achieved. Virtual surgical planning was done using the ProPlan CMF software (Materialise) (Fig. 1) and interocclusal splints were fabricated for intraoperative use. Informed consent was obtained before surgery. The same single surgical team performed all the surgeries.

To establish a stable functional occlusion, adequate correction of bimaxillary transverse discrepancies is required. Concurrent vertical and sagittal discrepancies often hide the presence of an underlying transverse problem. Common combinations seen in maxillomandibular discrepancy is: (a) narrow maxilla and normal mandible, (b) normal maxilla and wide mandible, (c) narrow maxilla and wide mandible⁹, (d) narrow maxilla and narrow mandible⁸, and (e) normal maxilla and narrow mandible¹. Studies have also evidently shown that underdeveloped maxillae often are accompanied with smaller mandibles with increased articular angle and overjet¹⁰. The surgical options include maxillary constriction/widening surgery and mandibular constriction/widening surgery or distraction osteogenesis (DO). In this study, the maxilla with adequate transverse width and constricted mandible having arch width discrepancy was indication for a surgical correction as described here. Although literature shows evidence that favours maxillary expansion via surgery or DO, it can prove to be more stressful for the patient than when bi-jaw surgery is performed⁷. As mentioned earlier, multi-piece segmental maxillary osteotomies carry the risk of a myriad of complications. There have been concerns regarding the stability after multi-piece segmental osteotomies, mainly because of soft tissue surrounding the maxilla. A recent publication noted a relapse rate of 26.3% after segmental Le Fort I osteotomy after one-year follow-up duration¹¹. Though traditional orthodontic correction/appliance expansion can be employed, neglecting the underlying skeletal issue leads to relapse and rates¹² of about 20%-30% have been noted¹³.

Vertical midline symphyseal cuts with or without augmentation are associated with complications such as large relapse, mucosal issues, and necessity for rigid fixation¹³. Modified osteotomy cuts suited to correct midline defects have also been described. Surgical midline widening is portrayed as an underused technique in orthognathic surgery due to (1) relapse concerns, (2) TMJ effects, (3) procedural unfamiliarity, and (4) no adequate address of the skeletal problem¹⁴. Besides the above-mentioned, impending complications such as (1) condylar torquing, (2) midline diastema, (3) bi-angle width control, (4) lingual flaring, and (5) vascularity compromise in multiple osteotomies often make surgical midline widening an uncommon procedure¹⁵. None of the potential complications were observed in any of our cases. Intraoperatively, when the mandible was in multiple segments, condylar torquing/positioning¹⁵, control of bi-angle width and lingual flaring were anticipated and prevented appropriately.

Osteotomy designs similar to our study have been described before; however, it was designed mainly for narrowing of the mandibular arch¹⁶ and combined with tooth-borne distraction osteogenesis¹⁷. Moreover, the combined procedure of BSSRO, genioplasty and midline symphyseal split to correct anterior mandibular asymmetry was advocated by Anghinoni et al.¹⁸. Though numerous multi-segmental mandibular osteotomies involving the midline have been described, this study is the first report of a single stage mandibular widening procedure with or without genial form alterations for bimaxillary transverse discrepancy. We did not use any rigid fixation or distraction, but the third generation bioactive bioresorbable 3D plate and screw fixation was used.

The presence of healthy periodontium surrounding teeth at the osteotomy and minimum 1 mm bone surrounding the tooth root has been followed¹⁹. Even if there is no prior divergence between the central incisor roots orthodontically, the roots should at least be parallel to each other and perpendicular to the mandibular occlusal plane¹⁴. Some authors have not noted any kind of periodontal issues if the osteotomy line runs through the PDL of one incisor root, with proper postoperative maintenance¹⁴. Palpation of the lingual side during osteotomy aids to assess saw position and depth during osteotomy, thereby preventing soft tissue injury¹⁷. Our pre-surgical orthodontic plan was set to retain sufficient space for osteotomy and posed no problem intra- and postoperatively.

We found that our technique can be successfully applied and resulted in widening of about 2-4 mm at first molar region without any stability or relapse complications. We observed gonial flaring in expansions of more than 4 mm, which requires simultaneous angle ostectomy. Previous study mentioned that widening more than 7 mm requires distraction to maintain stability¹³. As such, less stability after conventional mandibular widening have been reported, the maximum amount of mandibular widening and the degree of stability that can be achieved without distraction remains a debatable topic.

Since the posterior mandibular width decreases when the mandible is widened anteriorly, in case of large widening movements, transverse crossbite can be presented and progressively corrected postoperatively¹⁹. It has been noticed that midline widening is more difficult than narrowing mainly due to tissue resistance. Therefore, rigid fixation may be necessary in the anterior mandible to prevent torquing movement of the bony segments by muscle pull²⁰. It was recommended to use rigid fixation using bi-cortical screws or rigid osteosynthesis for some mandibular widening cases due to potential instability, however, it was not required in our study. We prefer to use bioactive/bioresorbable osteosynthesis for the patients, because titanium osteosynthesis mandates a second removal surgery and moreover, the bioresorbable systems have consistently proved to be effective²¹. The bioactive/bioresorbable 3D plating system has bio-conductive properties, thus enabling faster bone regeneration. Furthermore, application of 3D plate helped us to resist torquing of the osteotomized segments, which was especially advantageous in this study²².

We conclude that, in patients exhibiting normal maxillary width with transversely small mandibles, mandibular width expansion surgery is beneficial in correcting the existing discrepancy. Our novel techniques showed good postoperative outcomes and are highly useful to correct bimaxillary transverse width deficits. It consumes short intraoperative time, is relatively less invasive, and simple to perform.