Effects of Incremental Maxillomandibular Advancement on Airway Resistance and Facial Morphology

Abstract Body : Introduction and Objective – Obstructive sleep apnea (OSA) is a breathing disorder affecting millions of individuals worldwide with severe impacts on patients’ physiological and psychological health, and quality of life. Maxillomandibular advancement (MMA) is an effective treatment for OSA which involves mandibular and maxillary osteotomies which mobilize portions of the jaw bones. These mobilized portions are advanced to pull attached soft tissue of the pharynx forward, mitigating OSA resulting from airway collapse. Airway resistance (AR) decreases with MMA due to enlargement of the pharyngeal airway, indicating reduced impediment to breathing. Patients’ facial structure also changes with MMA at greater magnitudes of advancement, which may be perceived positively or negatively. Despite good clinical success treating OSA, there is little mechanistic investigation correlating AR and facial appearance with MMA. The objective of this study was to define the relationship between MMA, AR, and facial morphology.

Materials and Methods – A cadaveric study was performed using typical MMA procedures with fresh-frozen cadavers (n = 6, 3F). During surgery, devices were installed bilaterally on the maxilla and mandible permitting incremental advancements (KLS Martin, Jacksonville, FL). Cadavers were ventilated and facial 3D scanning was undertaken at 2 mm increments from 0 mm (baseline) to a maximum of 14 mm. Airway pressure was recorded during ventilation (LTV 1000, Vyaire, CA) with each cadavers’ estimated resting tidal volume (6 mL/kg body weight) using a minimum of 10 end-inspiratory holds enabling calculation of AR. Average AR at each increment was normalized to the AR at 0 mm advancement to calculate percent changes from baseline (%∆). Surface scanning was performed with a handheld 3D laser scanner (Space Spider, Artec, CA). The resultant 3D scans were compared with baselines to enumerate alterations to facial geometry and selected cephalometric landmarks.

Results – Resting tidal volume simulated ventilation was achieved on all cadavers. As MMA increased, average %∆ in AR decreased with an overall slope of -3.27 (R² = 0.9620), indicating a reduction in resistance of -3.27% per mm of advancement. Between 0 – 6 mm of advancement, %∆ was -1.70%/mm (R² = 0.8205), %∆ in AR between 6 – 10 mm was -5.03%/mm (R² = 0.9718), and between 10 – 14 mm %∆ was -3.07%/mm (R² = 0.9925). Preliminary analyses of facial changes (n = 1) show movement at soft tissue surface landmarks lag that of the maxilla and mandible at smaller MMA but match the rate of bony movement at greater advancements.

Conclusion – Results indicate the greatest change to AR occurs between 6 – 10 mm of advancement, while after 10 mm the %∆ in AR is reduced. These findings suggest advancement beyond 6 mm may be necessary for optimal therapeutic effect, but beyond 10 mm may produce diminished functional benefit while increasingly impacting appearance due to persistent movement of cephalometric landmarks.

Significance – This is the first study to investigate incremental changes to airway resistance during MMA surgery in a cadaveric model using breath-by-breath analysis. The relationship with MMA magnitude altering resistance and facial landmarks allows clinicians to optimize treatment of OSA for functional benefits while balancing changes to facial appearance, leading to greater patient satisfaction.