Effects of Mandibular Advancement Device (MAD) on Airway Dimensions Assessed With Cone-Beam Computed Tomography

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Upper airway constriction is an important contributing factor to obstructive sleep apnea (OSA), which may be treated in a palliative manner with mandibular advancement devices (MADs) to increase patency of the airway. It may be the treatment of choice for affected individuals who cannot use a continuous positive airway pressure device or who are not candidates for surgical correction of OSA. The specific distance applied during mandibular advancement, however, is often arbitrarily determined. This project uses cone beam computed tomography imaging in patients with OSA to determine a quantifiable relationship between airway patency and mandibular advancement. This correlation may be the basis to create an ideal technique to diagnose and treat patients having OSA. Twenty-six subjects successfully treated for OSA with a MAD received 2 cone beam computed tomography scans; 1 with and 1 without the MAD. Volumetric, cross-sectional, and cephalometric measurements were gathered from these scans. With the use of linear regression statistical analysis, specific predictor parameters have been identified for volumetric and cross-sectional airway information. An average oropharyngeal volume increase of approximately 2800 mm3 was achieved with MAD therapy.

Section snippets

Overview of OSA

Sleep apnea is defined as a decrease in respiration, yielding hypoxia and hypercapnia during sleep. It can be caused by many factors, including those of either neurologic origin or physical blockage of the airway. This study focused on the latter, more common, OSA. OSA physically limits the amount of air that a person can inhale during sleep. It occurs in 4% of men and 2% of women. Many authors agree that polysomnographic data are needed for definitive diagnosis of OSA; however, there are

Continuous Positive Airway Pressure (CPAP)

The general aim of all treatment modalities in sleep-breathing disorders is to facilitate breathing and thereby reduce the risk of increased morbidity. Because there can be many causes of OSA, there are also several different treatment types. They all focus on preventing collapse of the lumen of the pharynx during sleep. The gold standard for initial treatment is home use of a device called CPAP18 because it seems to be somewhat of a “cure-all” OSA treatment. No matter where the obstruction in

Cephalometrics in OSA Imaging

The imaging of the upper airway space has traditionally been accomplished with the use of lateral cephalometric radiography (Fig 4). An advantage of this type of imaging is that it is widely used and readily available. It also uses a relatively low radiation dosage. However, images taken from a lateral viewpoint give only 2D information. This information is valuable because the AP dimension is that which is most likely to be changed with mandibular protrusion. It is not an ideal imaging

Radiation Dosage

A main advantage of using CBCT to image the oropharynx is the relatively low dosage of radiation. Several studies have been done to determine the exact radiation dosage to different parts of the body of different types of radiography.36, 37, 38 It has been found that the general dosage of CBCT dosimetry is up to 50 times less than spiral CT. CBCT uses only minimal radiation, equal to 7 panoramic exposures, or approximately 3.5 days of background exposure. This is a huge reduction from spiral

Methods

Twenty-six patients diagnosed with OSA who had been previously treated with mandibular advancement device (MAD) therapy by a general dental practitioner with advanced training in the diagnosis and treatment of OSA patients (J.M.) were recruited for the study following guidelines designated by the intuitional review board of the University of Louisville. There were 17 men and 9 women in this study group. Each subject underwent polysomnography to diagnose their OSA, defined as an AHI greater than

Cephalometric Measurements

The lateral cephalogram simulated image allowed the measurement of classic cephalometric measurements with the Dolphin Program. A custom cephalometric analysis was created for the purpose of this study. The measurements were tested by measuring the same image on another cephalometric analysis package, RMO Joe (Rocky Mountain Orthodontics, Inc., Denver, CO), and found to be the same.

Two series of cephalometric measurements were made. The first series described the anatomy of the subject on the

Results

The linear regression showed that there were 6 dependent, or “outcome,” variables measured on the volumetric scan that were found to be predictable by independent variables. These outcome variables were Volume of the oropharynx, largest cross-sectional area (LgCa), the cross-sectional area at C2 (C2Ca), the lateral linear dimension of the cross section at C2 (L-C2Ca), the AP linear dimension of the cross section at C2 (AP-C2Ca), and the ratio of these 2 linear dimensions (L:AP-C2Ca). One

Discussion

This study was the first to show a sample of OSA patients successfully treated with a removable MAD in 3D imaging. The authors of previous work with MAD and 3D imaging46, 50 used subjects who only snored or had untreated OSA patients with conventional CT, and MRI.

This was also the first study to use CBCT volumetric imaging of OSA patients. Previous 2D studies were limited to cephalometrics, whereas previous CT and MRI studies were limited to cross-sectional area and linear measurements. These

Conclusion

Lateral airway dimensions of the cross-section at C2, total volume, and cross-sectional area gained in the oropharynx can be predicted from the amount of mandibular forward movement. The saddle angle was a predictor of the linear anterior-posterior dimension, while the facial axis predicted the ellipticality of the airway at C2. With the placement of a MAD appliance, the smallest airway cross-section may move to an unpredictable position, superiorly or inferiorly along the length of the

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    The present study is currently under IRB approval at the University of Louisville as of April 20, 2006. It has undergone 2 annual reviews and is not due for another annual review until April 21, 2009. Risk to the subjects is from radiation exposure using a FDA/CDRH approved device. The short and long-term risks of somatic and genetic damage at the level used in this study are considered negligible.

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