Modified Maxillomandibular Advancement Technique

1

Introduction

Orthognathic surgery has been used to treat obstructive sleep apnea (OSA) since the mid-1980s. In the classical phase II surgery for OSA described by Riley et al., 10-mm advancement of the maxilla and mandible resulted in an impressive 97% cure rate in patients who had failed phase I surgery and 91% in patients treated solely by phase II surgery. Other studies on bimaxillary advancement techniques have also shown success rates ranging from 75% to 100%, which are superior to other surgical treatments for obstructive sleep apnea syndrome (OSAS). Maxillomandibular advancement (MMA) has now been accepted as an effective treatment modality for OSAS.

Many studies that have evaluated the perceived facial changes associated with such advancement surgeries reported favorable perceived aesthetic result from the patients' viewpoint. ; however, all of these studies were done on Caucasian cohorts. There is currently no literature on the aesthetic outcome of MMA of such a large extent for the treatment of OSA in Asians. The aesthetic outcome after MMA is different between Caucasians and Far East Asians, as there is a greater incidence of bimaxillary protrusion in the Far East Asian face. These and other ethnic differences in the cephalometric parameters between the Far East Asian and the Caucasian have been previously shown. Though the soft tissue measurements like the distance from the mandibular plane to the hyoid bone, the posterior airway space, and the distance from the posterior nasal spine to the tip of the soft palate did not vary significantly, the angle measurement from the sella to nasion to point A, subspinale and the angle from sella to nasion to point B, supramentale were significantly different between the racial groups.

From a purely aesthetic point of view, profiles that are flat or slightly bimaxillary protrusive are considered more attractive in the Western sense of aesthetics than those that have extreme bimaxillary protrusion. On the contrary, in a comparative study of the perception of Chinese facial profile aesthetics by native Chinese dental professionals, students, and lay people, facial profiles that were normal or had bimaxillary retrusion were perceived to be more attractive than profiles that had bimaxillary protrusion, protrusive mandible, retrusive mandible, retrusive maxilla, or protrusive maxilla. Therefore considering the relatively greater maxillary and mandibular protrusion in the Asian population and the biased perception by the native Chinese favoring bimaxillary retrusion, the aesthetic effects of increased bimaxillary protrusion after MMA would be undesirable in the Far East Asian face.

Patients with bimaxillary protrusion may have lip seal problems due to the protrusion as evidenced by upward strain of the mentalis and increased activity of perioral muscles; this may be unfavorably increased after MMA. The increased tension on advanced maxillary and mandibular segments in a patient with bimaxillary protrusion may also affect the stability of the advancement, which may increase regression and failure rates postoperatively. The long-term stability of the advanced segments due to decreased tension after an anterior segmental setback was also a factor in the consideration of the development of the modified technique for the Far East Asian face.

2

Indications

Anterior segmental surgeries have been practiced in oral and maxillofacial surgery since the 1960s. It is generally indicated for cases of bimaxillary protrusion. This involves the posterior setback of the anterior maxilla (premaxilla) and the anterior alveolar segment of the mandible, usually after the extraction of a bicuspid from each quadrant of the dental arch. Together with the standard Le Fort I and bilateral sagittal split osteotomies, the surgery, when applied to OSAS patients, achieves the aim of increasing the posterior airway space without significant aesthetic facial alterations.

The indications for modified MMA to treat OSA are the same as for standard MMA. The modification is offered in patients with bimaxillary protrusion who do not want their facial profile and appearance altered postoperatively. These patients can be identified on physical examination by the presence of lip closure problems, excessive proclination, wide nasal alar base, excessive show of teeth or gums when smiling, and protrusive lips on facial profile examination and cephalometric measurements.

3