The majority of OA is designed to maintain the mandible and/or tongue in a protruded posture, thereby preventing upper airway obstruction during sleep. Proposed mechanisms of action of OA include increased upper airway size, decreased upper airway collapsibility, activation of upper airway dilator muscles, and stabilization of mandibular posture. Several different upper airway imaging techniques have been used to assess changes in upper airway size and function with OA in patients with OSAS. These imaging techniques include cephalometry, computed tomography, magnetic resonance imaging, and video endoscopy, but most of these studies show poor reliability in predicting treatment outcomes. Voluntary mandibular and tongue protrusions have been shown to increase upper airway size and alter upper airway shape particularly in the velopharynx in subjects with and without OSAS. Several studies have demonstrated an increase in the anteroposterior diameter of the upper airway following OA insertion (Fig. 36.2). This increase was predominant in the oropharynx and hypopharynx, but some studies have also suggested an effect on the velopharynx (Figs. 36.3 and 36.4). Almost all of these upper airway imaging studies have been performed during wakefulness, and it is unknown whether the same changes occur during sleep. Mandibular advancement OAs have been shown to increase upper airway muscle tone, which may also contribute to increased upper airway patency.

The effectiveness of OA therapy can be influenced by the patient’s body mass index, the severity of OSAS, the presence of positional OSAS, and the degree of mandibular advancement obtained with the OA. Until recently, the majority of the data concerning the efficacy of OA in the treatment of OSAS were from uncontrolled case series studies which were subject to study design issues such as regression to the mean, and selection and reporting bias. With about 18 randomized controlled trials comparing OA to placebo and/or CPAP, there is increasing evidence that OA significantly improve snoring, daytime sleepiness, quality of life, systemic hypertension, and indices of sleep-disordered breathing. A variety of prospective randomized trials have been performed to evaluate the efficacy, side effects, compliance, and preference of OA treatment in patients with OSAS. There are at least 9 randomized controlled trials comparing OA to an inactive control that demonstrate that OA improves daytime sleepiness, systemic hypertension, and indices of sleep-disordered breathing in patients with OSAS. Additional well-designed, large-scale randomized controlled trials comparing active and control OA are required to determine which groups of patients are most likely to benefit from OA treatment, how these patients can be identified, and how much benefit can be achieved and with what cost, side effects, and complications. There are at least 10 randomized controlled trials which have compared the efficacy and side effects of OA and CPAP. Although both CPAP and OA led to similar improvements in daytime sleepiness, health status, and blood pressure, conversely the magnitude of improvement in AHI was significantly more with CPAP. Some studies suggest that the higher efficacy of CPAP is counterbalanced by the higher adherence to OA (hour per night and nights per week), resulting in a similar treatment effectiveness [16]. Furthermore, it takes longer to obtain optimal treatment with an OA than CPAP, which can be a major issue in patients with excessive daytime sleepiness. Patients who responded to both treatments tend to prefer the use of an OA to CPAP. All of the randomized controlled trials have been short-term studies over 3–6 months, but there are now several non-randomized studies establishing long-term efficacy over 4–5 years.

OA design has been proposed as an important determinant of treatment success, and there have been at least 9 prospective comparative studies evaluating different OA designs. Most studies using comparable mandibular protrusion with minimum vertical opening have shown that the differences were minimal. Some studies looking at vertical opening have shown a detrimental effect of the increase in the anterior vertical opening of these devices. There were varying degrees of patients’ acceptance, but the incidence of long-term side effects with different OA is independent on the appliance design. Finally, there is one longitudinal parallel group study comparing the effectiveness of OA with uvulopalatopharyngoplasty in patients with mild to moderate OSAS over 4 years, which suggests that an OA was more effective than uvulopalatopharyngoplasty in improving indices of sleep-disordered breathing. However, the significance of this finding is questionable, as there is no definitive evidence of the effectiveness of this type of corrective upper airway surgery. OA therapy may also be indicated as an adjuvant to nasal CPAP when the patient is away from home or electrical power, or used in conjunction with CPAP, allowing patients who were unable to tolerate high CPAP pressures to use CPAP in combination with an OA with an average reduction of 2.5 cm of H₂O pressure. OAs have also been used as combination therapy in patients who have had an unsuccessful response to uvulopalatopharyngoplasty.

A variety of predictors of OA treatment success have been proposed. It has been suggested that younger, less obese patients, with smaller neck circumference and with OSAS that occurs predominantly in the supine position, may be more likely to obtain a successful response with an OA. Treatment success may be inversely related to pretreatment severity, but this relationship may just be a function of the definition of treatment success. Several upper airway skeletal and soft tissue measurements made from pretreatment lateral cephalometry have been shown to be associated with treatment success. These include a more micrognathic or retrognathic mandible and small soft palate and tongue. Upper airway fluoroscopy and, more recently, flow-volume curves and nasal resistance measurements have also been proposed as techniques to guide successful OA therapy. A primary oropharyngeal site of obstruction may be associated with a better treatment outcome. However, there is considerable overlap between good and poor treatment responses with all these variables. The utility of any treatment recommendation based on clinical features, OSAS severity, or upper airway anatomy requires prospective validation.

Self-reported treatment adherence data for up to 5 years are available for OA therapy. Self-reported treatment adherence has been reported as high as 96 % patients using OA for >75 % nights and 80 % patients using OA >75 % of each night. Treatment adherence varies between OA type and appears better with mandibular advancement rather than tongue retaining OA. Adherence rates appear to decrease with duration of use and have been reported as 60 % at one year and 48 % at two years. Previous experience with nasal CPAP suggests that self-reported treatment adherence tends to overestimate actual use. Recently, Vanderveken and colleagues (2012) have described an objective sensor to monitor OA compliance, which has recently been approved for commercialization. Future studies and clinical practice should now include objective OA compliance data.

Side effects are common, but generally minor. Excessive salivation, mouth dryness, morning-after occlusal changes, and discomfort in the gums, teeth, or jaw are common side effects in the first weeks of OA therapy, but usually resolve with time. More persistent side effects related to temporomandibular joint dysfunction and dental crown damage appear to be uncommon. Long-term common side effects include tooth movement and occlusal alteration (Video 10, Side effects). Small occlusal changes may be found in up to 80 % of patients after continuous five years of OA wear, independent of the appliance used. The clinical significance of these occlusal changes is uncertain. OA adjustment can decrease side effects by reducing pressure on the anterior teeth and excessive mandibular advancement. Side effect types vary between types of OA with tongue pain occurring in tongue retention OA and gagging associated with OAs that have a maxillary component to modify soft palate position.

The cost of OA therapy varies depending on the type of OA used and the extent and expertise of the dental supervision. Consensus opinion indicates that a prefabricated OA can range from $45 to 100 and custom-made OA ranges from $500 to over $1000. OA usually remains effective for two to three years and after that they can break and require either repair or replacement. OA treatment generally includes about ten dental appointments, and then, dentist service fees vary greatly between $200 per appointment or a fixed fee of $2500, depending on the time spent caring for the patient and geographic economic factors. Costs can equal or exceed those associated with nasal CPAP therapy. There is increasing evidence that OA is a cost-effective treatment for OSAS [10].

A Cochrane systematic review [7] recently concluded that there was increasing evidence that OA improves subjective daytime sleepiness and sleep-disordered breathing compared with control appliances. However, it recommended that until there was more definitive evidence on the effectiveness of OA compared to CPAP, OA therapy should be restricted to patients with mild symptomatic OSAS and those patients who are unwilling or unable to comply with CPAP therapy. The American Academy of Sleep Medicine [5] reviewed similar data to the Cochrane Collaboration and recommended that OAs were indicated for use in patients with mild–moderate OSAS who prefer them to CPAP, or who do not respond to, or are not appropriate candidates for, or who fail treatment with CPAP. They recommended CPAP therapy as first-line therapy for patients with severe OSAS, but OA can also be prescribed for severe OSAS if patients can not tolerate CPAP. OA can have insufficient reduction in OSAS severity and has also shown a placebo effect on sleepiness; therefore, it is important to perform follow-up sleep monitoring to verify the efficacy of OA therapy. Patients treated with OA require long-term dental follow-up to monitor patient adherence, to evaluate OA deterioration or maladjustment, to evaluate the health of the oral structures, and to monitor occlusal changes.