Abstract
As the importance in the management of obstructive sleep apnea and other obstructive upper airway disease continues to increase, the effect of orthognathic surgery on the upper airway in correction of both dentofacial deformities and obstructive sleep apnea has become a prominent component of treatment planning in recent decades. Applied correctly, orthognathic surgery can have a dramatic and life-changing effect on decreasing nocturnal obstructions through expansion of the upper airway. Large advancements of the maxillomandibular complex allows for three-dimensional upper airway expansion to nocturnal obstruction that diminish the deleterious effects of obstructive sleep apnea. This paper will discuss the orthognathic surgical techniques that are essential in the treatment planning to achieve the desired results of relief of nocturnal upper airway obstructions.
Introduction
Obstructive sleep apnea (OSA) is serious medical condition characterized by repeated collapse of the upper airway during sleep which leads to airway resistance and obstruction, snoring, fatigue, and daytime sleepiness. This condition may have a significant impact on cognitive behavior, occupational disability, and worsen medical comorbidities, such as cerebrovascular and cardiovascular disease. Prior to 1985, OSA was a disease researched and treated exclusively by the medical specialties of otolaryngology and pulmonary medicine. Each passing year its prevalence grew alarmingly swift as more patients were diagnosed and the effect of this obstructive airway disease on the cardiovascular system, social issues associated with chronic daytime sleepiness, increased mortality rates, such as nocturnal sudden death, made it a public health threat that demanded immediate attention. At the time, through nocturnal and awake endoscopic studies the airway collapse was known to occur at multiple areas along the upper respiratory pathway. Continuous positive airway pressure (CPAP) is the recommended solution but compliance has been a significant issue. Tracheostomy was the only procedure available and was designed to bypass the entire upper airway but had its obvious social and physiologic problems. The uvulopalatopharyngoplasty (UPPP) showed initial promise, but was eventually found to have no more than a 40% successful and this only in mild obstructive cases.
Robert Riley and Nelson Powell, both dual otolaryngologists and oral and maxillofacial surgeons from Stanford University, began using orthognathic surgical procedures designed for the correction of craniofacial deformities for the treatment of OSA. The mandible and its attached anatomy, such as the genial tubercle attachment of the genioglossus muscle, were advanced forward to help relieve base of the tongue obstruction from the posterior pharyngeal wall. Along with Christian Guilleminault of the Stanford Sleep Disorders Clinic, these three men developed a two-phase plan for the surgical treatment of OSA. Phase 1 surgery consisted of multiple procedures to address obstructive areas all along the upper respiratory tract; nasal and palatal procedures for the nasopharynx, genioglossus advancement procedures for oropharynx, and hyoid suspension procedures for hypopharynx and Phase 2 surgery was maxillomandibular advancement and became known as the Stanford Protocol of Surgical Management of OSA. According to the Stanford Protocol, Phase I surgery was completed first and the patient re-evaluated 6 months later. In the situation of an insufficient response to Phase 1 surgery as determined as an AHI/RDI reduction by 50% or less than 5, Phase 2 surgery would then be recommended. Early clinical papers using reduction in the apnea-hypopnea index (AHI) or respiratory disturbance index (RDI) and nadir (lowest) oxygen saturation (nO2) levels from overnight sleep studies revealed a stunning success in the phase 2 with a greater than 90% success. This was a game changing event that eventually resulted in maxillofacial surgeons, orthodontist and the entire profession of dentistry becoming primary movers for the surgical treatment of OSA.
It was apparent from the beginning that orthognathic surgery for dentofacial deformities and OSA had only the technical procedures in common. Many of the earlier OSA surgical patients reported in the literature had no orthodontic input at all for their surgery due to the urgency of the situation and patient refusal to undergo such a time consuming and expensive procedure. Maxillomandibular advancement (MMA) for these patients had no real guidelines except to advance the maxillofacial complex as far forward as the enveloping musculature would permit with a simple goal of returning the patient to his or her original functional occlusion as long as the airway expansion was accomplished.
Orthodontists who got involved with OSA patients found the following differences from conventional orthognathic surgery:
- 1.
The extreme advancement of the lower facial skeleton (maxilla and mandible) tend to experience more instability. This may be due to increase soft tissue stretch of the face and mandibular musculature or the reduced boney interface for stability.
- 2.
The importance of planning the final esthetic facial outcome becomes far less important than the functional requirements of OSA correction.
- 3.
These patients not only represent a different age group on the average, but also tend to have more missing teeth and periodontal problems. Therefore, coordination with surgeons, periodontists, and restorative dentists is essential to successful treatment in these patients.
- 4.
Due to the poor medical condition of these patients and the urgency of correction, surgery first to advance and align the arches followed by post-surgical occlusal adjustment or formal banding may be the best option.
The orthodontist and the surgeon must understand that ideal treatment plans and esthetic considerations that are a major part of conventional orthognathic surgery may have to take a back seat to the medical needs of these very compromised patients.
The soft tissue reaction to conventional orthognathic surgery, while very important and predictable, remains secondary to the intended correction of the functional goals of occlusal and hard tissue balance. In orthognathic surgery for the OSA the soft tissue reaction of the oro-pharyngeal complex is the primary goal of all orthognathic movements.
The following report will discuss the advances in technique, the long-term stability and the present-day state of the art that have resulted from the last twenty years of applying these orthognathic principles to the treatment of OSA.
Upper airway and craniofacial anatomy in OSA
Various dynamic and static methods have been used to determine the single or multi-level source of upper airway obstruction in OSA. The primary challenge with radiograph interpretation of the upper airway is that it is accomplished on awake patients and occasionally in a sitting or standing upright position. While providing important anatomical visualization and information, these challenges are generally seen in static methods of upper airway radiographic interpretation such as cone beam CT (CBCT) digital or conventional panoramic and lateral cephalometric radiographs. Dynamic methods of evaluation of the upper airway may be better visualized with such techniques as dynamic sleep magnetic resonance imaging (MRI) and drug-induced sleep endoscopy (DISE). Sleep MRI allows for simultaneous evaluation of upper airway obstruction and respiratory events in real time during natural sleep. This allows for respiratory and desaturation events to be directly correlated with polysomnogram results and anatomic site of obstruction. DISE is a combined endoscopic and anesthetic procedure that attempts to mimic natural sleep through deepening of general anesthesia until a patient begins to obstruct in order to observe the upper airway on flexible endoscopy.
Evaluation of the anatomical levels of upper airway sleep obstruction have been shown by dynamic sleep MRI to be positively correlated with OSA severity. Specifically, severe OSA patients have significantly more lateral pharyngeal wall collapse as compared to BMI-matched mild OSA patients. , Airway obstructions visualized on sleep MRI during natural sleep ranged from isolated retropalatal and retroglossal obstruction to multi-level combined obstruction. DISE showed that obstruction may be observed in three dimensions: anteroposterior, transverse and circumferential. DISE is able to visualize various anatomical structures that can induce obstruction during sleep such as the retrovelar area (includes the soft palate, mucosal velum, and uvula); the oropharyngeal area (includes the palatine tonsils and pharyngeal walls); the hypopharyngeal area (includes the tongue base, lingual tonsils and lateral pharyngeal walls); and the laryngeal area (includes the epiglottis and arytenoids). DISE findings tend to indicate multiple levels of upper airway obstruction particularly in the retropalatal and lateral pharyngeal walls. While individual anatomical obstruction during sleep will vary, findings from dynamic upper airway observation in real time indicate that majority of nocturnal obstruction are multilevel and occur primarily in the lateral pharyngeal wall, retropalatal and retroglossal areas.
Static imaging of the upper airway such as static MRI, three-dimensional computed tomography (3D-CT), and lateral cephalometry is a valuable screening tool for OSA. OSA patients, compared to non-OSA patients, tend to have compromised three-dimensional upper airway to include compromised total airway volume and minimum cross-sectional area. Upper airway length has been shown to have a positive correlation and predictor to the OSA severity, , while lateral/retroglossal anteroposterior dimension ratio shows an inverse correlation with the OSA severity , These radiographic measures may be a good screening tool that will allow for further advanced techniques to determine the location of obstruction. Cephalometric evaluation, compared to the non-OSA population, reveals significant deviations in the OSA population that may one or more of the following: shorter dimension of cranial base; shorter maxillary length; maxillo-mandibular retrognathia related to Nasion perpendicular plane (N perpendicular FH) despite normal angles of prognathism; mandibular retrognathia; increased anterior lower facial height and mandibular plane angle; reduced size of bony pharynx; inferiorly positioned hyoid bone at C4-C6 level.
Effect of orthognathic surgery for dentofacial deformities on the upper airway
Correction of dentofacial deformities (DFD), such as skeletal Class III malocclusion, have now taken on a different perspective with consideration of upper airway obstruction. Corrective mandibular surgery affects the hyoid bone and tongue position which may influence pharyngeal airway dimensions. A decrease in pharyngeal airway from this movement may cause the development or worsening of OSA and must be taken into consideration in treatment planning. Skeletal Class III dentofacial deformity generally may be treated with mandibular setback procedures alone to correct the malocclusion without any consideration for the potential deleterious effects on the upper airway. Single-jaw mandibular setback osteotomies have been shown to reduce pharyngeal airway dimensions significantly due to posterior positioning of the hyoid bone and decreased posterior airway space. , Compared to mandibular setback surgery alone for the correction of skeletal Class III deformities, bimaxillary surgery to treat this condition produces a less compromised post-surgical pharyngeal airway with significantly less decreased cross-sectional area of the upper airway. However, while mandibular setback procedures have been shown reduce pharyngeal airway dimensions, a possible predisposing factor in the development of OSA, patients tend to adapt quickly and, while there are some initial reduced respiratory parameters with some surgeries, there has not been much significant evidence to confirm post-surgical OSA development. These studies, however, have been performed on young and healthy adolescents and the effect of aging and changes in body habitus are not taken into consideration. Many decades later the alteration in posterior airway may contribute any alteration of the posterior airway space due to orthognathic surgery should be considered during orthodontic and presurgical treatment planning. Therefore, contemporary orthognathic surgery treatment planning for correction of DFD should also seek to expand the facial skeleton and thus the upper airway to alleviate, prevent, or decrease the risk of future development of OSA.
Correction of skeletal Class II malocclusions with mandibular advancement surgery alone and without genioplasty provides significant enlargement of the upper airway at the level of oropharynx. The improvement is achieved through repositioning of the hyoid bone and vallecula into a more superior and anterior position which has shown long term stability.
Maxillary only orthognathic surgery may also effect the upper airway and OSA. These tend to be most effective when correcting maxillary hypoplasia through advancement and/or expansion in individuals requiring this procedure to correct and existing DFD. However, correction of vertical deficiencies does not appear to be as effective as correction of vertical maxillary excess does not show a significant change in upper airway volume or subjective patient excessive daytime sleepiness.
Maxillomandibular advancement
Maxillomandibular advancement (MMA) utilizes the principles of orthognathic surgery to simultaneously advance both the upper and lower jaws specifically to treat OSA through advancement and expansion of the facial skeleton. MMA has been successfully performed for several decades and, other than tracheotomy, is the most effective and predictable surgical procedure in the management of adult OSA. , , MMA advances the maxillomandibular complex with a LeFort I maxillary and bilateral sagittal split mandibular ramus osteotomies, with or without genioglossus advancement, and application of rigid internal fixation. Through the subsequent expansion of the facial skeleton, the resultant increase in upper airway pharyngeal volume is intended to decrease the risk of pharyngeal collapse from negative pressure inspiration due to obstruction during sleep to ostensibly relieve or decrease the severity of OSA. In a multi-center prospective study to comprehensively determine the effectiveness and safety of MMA for the treatment of OSA, Boyd et al. found MMA to be a highly effective and safe treatment with predictable improvements in sleepiness, quality of life, sleep-disordered breathing, and neurocognitive performance, and a reduction in cardiovascular risk as measured by decrease in blood pressure. MMA is the only surgical procedure, outside the tracheotomy, that can effectively treat severe OSA. ( Figs. 1–7 )
