Phẫu thuật sai khớp cắn loại iii trên bệnh nhân có ngưng thở khi ngủ tắc nghẽn Orthognathic surgery for skeletal class iii malocclusion in a patient with obstruCTive sleep apnea

Obstructive sleep apnea (OSA) is commonly associated with craniofacial patterns involving mandibular retrusion and skeletal Class II malocclusion. However, OSA can also occur in patients with skeletal Class III deformities.

This becomes particularly relevant in orthognathic surgery because a treatment plan that appears appropriate from an occlusal and aesthetic perspective may not necessarily be optimal if the proposed skeletal movements could adversely affect the upper airway.

This case illustrates that consideration.

A seemingly straightforward skeletal Class III case

The patient was a woman in her thirties who presented with a skeletal Class III malocclusion and concern regarding her prognathic facial appearance.

Following the initial assessment, combined orthodontic and orthognathic treatment was recommended. Presurgical orthodontics was performed to position the teeth appropriately over their skeletal bases, after which the patient returned for surgical planning.

From a purely skeletal and occlusal perspective, this initially appeared to be a relatively conventional Class III case: maxillary advancement combined with a degree of mandibular setback could establish a Class I occlusion while improving facial balance.

However, one finding on the lateral cephalogram prompted a reconsideration of this conventional strategy.

When the airway becomes part of surgical planning

The patient's posterior airway space appeared relatively narrow on the lateral cephalogram, measuring approximately 9 mm according to the method used during the assessment.

A two-dimensional airway measurement cannot diagnose obstructive sleep apnea. Nevertheless, in combination with the patient's clinical characteristics, this finding raised sufficient concern to warrant formal sleep assessment before determining the final skeletal movements.

The patient therefore underwent polysomnography.

The study demonstrated an apnea–hypopnea index (AHI) of 10.7 events per hour, consistent with mild obstructive sleep apnea.

This information substantially changed the surgical strategy.

A conventional mandibular setback could potentially have an unfavorable effect on the retrolingual airway. In a patient with pre-existing OSA, this possibility needed to be incorporated into the treatment plan rather than considered only after surgery.

Changing the jaw movements to account for the airway

Instead of setting the mandible back, an alternative skeletal strategy was selected.

The mandible was slightly advanced, while the maxilla was advanced to a greater extent to achieve the required maxillomandibular relationship and establish a Class I occlusion.

Correction of the Class III deformity was therefore no longer based on the conventional concept of “maxillary advancement plus mandibular setback.” The movements were individualized around three simultaneous objectives:

occlusion – facial aesthetics – airway.

Genioplasty and mandibular angle contouring were also incorporated into the overall surgical plan to further refine the lower facial contour.

Three-dimensional planning and patient-specific surgical guidance

The skeletal movements were simulated preoperatively in a three-dimensional virtual environment, allowing the relationship between the maxilla, mandible, chin, occlusion, and facial profile to be evaluated before the final surgical strategy was selected.

Once the plan had been established, patient-specific cutting and positioning guides were digitally designed and manufactured using metal 3D printing.

These guides assisted in transferring the planned skeletal movements from the virtual environment to the operating room, particularly in a procedure involving several independently controlled movements.

OSA is not exclusive to patients with mandibular retrusion

Obstructive sleep apnea is a complex disorder with multiple potential levels and mechanisms of upper airway obstruction. Its anatomical contributors vary considerably between individuals.

The retrolingual region is one of the areas that may contribute to airway obstruction. This helps explain why treatments that advance the mandible or the maxillomandibular complex can improve the airway in appropriately selected patients with OSA.

Conversely, mandibular setback may reduce airway dimensions in some patients, making its potential airway consequences particularly relevant when pre-existing sleep-disordered breathing has already been identified.

This does not mean that every patient with skeletal Class III malocclusion requires a sleep study, nor does it mean that mandibular setback inevitably causes OSA. The important principle is to identify patients whose symptoms, anatomy, or risk profile justify further evaluation.

Beyond correction of the bite

This case demonstrates an important principle in orthognathic surgery:

A successful surgical plan should not simply position the jaws to create an ideal occlusion. It should balance occlusion, facial aesthetics, function, and the individual patient's overall clinical condition.

Had the patient's OSA not been identified before surgery, a skeletal plan that appeared entirely reasonable from an occlusal perspective might not have been the most appropriate strategy for her.

Sometimes, a relatively subtle finding during preoperative assessment can change the entire direction of surgical planning.