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The concept in oral appliances for obstructive sleep apnea (OSA) management is protrusion of the mandible and/or tongue for structural effects on the upper airway.
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The upper airway is a muscular tube and its dimensions are enlarged with mandibular and tongue advancement.
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Protrusion of the mandible and tongue stretches the muscles, thereby reducing upper airway collapsibility with airway shape change and increase in muscle tone.
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Oral appliances are effective and evidence-based options in managing OSA.
Types of oral appliances
The primary oral appliance (OA) used in obstructive sleep apnea (OSA) treatment is the mandibular advancement device (MAD). MADs may be either an over-the-counter stock device or customized for individual patients. MADs come in various designs and materials, but most comprise upper and lower splints mounted over the dentition as either a 1-piece monoblock (Fig. 1) or a 2-piece biblock (Fig. 2). Connectors or blocks relate the upper and lower splints in a biblock to protrude the mandible in a forward position during sleep.
Tongue-retaining devices, or tongue-stabilizing devices (TSDs) (Fig. 3), are a second type of OA, which displace the tongue anteriorly and may be customized or come in different stock sizes. TSDs use negative pressure and salivary adhesion to hold onto the tongue and anterior lip shields to elongate and reposition the tongue in a more forward position independent of the mandible during sleep, thereby opening the oropharyngeal airway.
Airway imaging with cone-beam computed tomography, magnetic resonance imaging and nasal endoscopy showed anteroposterior (AP) mandibular protrusion predominantly increases the caliber of the airway at the retropalatal area via lateral expansion and displacement of parapharyngeal fat pads
Effects of mandibular advancement on upper airway dimension and collapsibility in patients with obstructive sleep apnea using dynamic upper airway imaging during sleep.
The lateral widening from AP movement is attributed to stretching of soft tissue connections between the tongue, soft palate, and lateral pharyngeal walls.
TSDs increase airway AP diameter to a greater degree than MADs, and traction on intrapharyngeal connections through the tongue base additionally increases the lateral dimension of the airway. Compared with MADs, TSDs produce greater increases in retropalatal and retroglossal cross-sectional area (CSA). This is attributed to greater anterior tongue movement with TSDs.
Electromyography shows that MADs increase activation of masseter, lateral pterygoid, genioglossus, and geniohyoid muscles. It is postulated that on top of the purely structural anatomic effects of MADs, increased neuromuscular activation contributes to upper airway patency.
The effect of a mandibular advancement splint on electromyographic activity of the submental and masseter muscles in patients with obstructive sleep apnea.
Morphologic increase in CSA, change in cross-sectional shape, decrease in airway length, and neuromuscular activation with MAD may contribute to reduced collapsibility.
Effects of mandibular advancement on upper airway dimension and collapsibility in patients with obstructive sleep apnea using dynamic upper airway imaging during sleep.
Empirically, a significant reduction in upper airway collapsibility in stage 2 and stage 3 sleep was observed with MAD use. Improvement in collapsibility was significantly greater in complete responders than in partial responders or nonresponders.
Oral appliance effects on obstructive sleep apnea compared with continuous positive airway pressure
Continuous positive airway pressure (CPAP) and MADs are chronic, noninvasive, symptomatic treatments for OSA that do not treat the underlying anatomic basis of the condition. Pneumatic splinting of the airway with CPAP is acknowledged as the gold standard for treatment of OSA, although MAD has been progressively recommended with each iteration of the American Academy of Sleep Medicine (AASM) guidelines.
even with increasing numbers of primary studies. According to the AASM/American Academy of Dental Sleep Medicine (AADSM) task force, CPAP is significantly better than MAD at reducing AHI scores (difference of 6.24 events per hour).
MADs are efficacious in improving minimum arterial oxygen saturation (Sao2), and the improvement has been reported to have a nonlinear dose-dependent relationship with degree of advancement.
Comparing subjective self-reported MAD compliance with objective recorded CPAP compliance, MAD compliance is better. The AASM/AADSM task force reported that MADs were used 0.70 more hours per night than CPAP.
A meta-analysis of 6 studies encompassing both subjective and objective MAD compliance measures reported an additional 1.1 hours per night use of MAD over CPAP.
Depending on OSA severity and total sleep time, less than ideal compliance with CPAP can substantially decrease its effectiveness. Better MAD compliance over CPAP could be why health outcomes of the 2 treatment modalities are similar despite better CPAP efficacy at reducing AHI and increasing oxygenation.
Despite better efficacy with CPAP than MADs in reducing AHI and improving Sao2, differences in ESS scores are more ambiguous. A network meta-analysis of 67 studies found that CPAP and MADs are both effective in reducing excessive daytime sleepiness as assessed by the ESS, but CPAP is likely to be more effective than MADs, with a greater reduction in ESS by an average of 0.8 points.
Comparison of the effects of continuous positive airway pressure and mandibular advancement devices on sleepiness in patients with obstructive sleep apnoea: a network meta-analysis.
Function and quality of life are commonly measured using both the sleep-specific Functional Outcomes of Sleep Questionnaire (FOSQ) and generic Medical Outcomes Study 36-Item Short Form Health Survey (SF-36). MADs are associated with improvements in FOSQ subscale and total scores as well as SF-36 scores.
with direct comparisons as well as network meta-analysis showing no significant difference in treatment outcomes between CPAP and MAD in the mental and physical components of SF-36. Other meta-analyses have also reported no difference in FOSQ or SF-36 scores.
A network meta-analysis reported that CPAP was associated with a reduction in systolic blood pressure of 2.5 mm Hg and diastolic blood pressure reduction of 2.0 mm Hg. MADs were associated with reduction in systolic blood pressure of 2.1 mm Hg and diastolic blood pressure of 1.9 mm Hg. There was no significant difference between CPAP and MADs.
Comparison of the effects of continuous positive airway pressure and mandibular advancement devices on sleepiness in patients with obstructive sleep apnoea: a network meta-analysis.
Studies on other cardiovascular markers (heart rate variability, circulating cardiovascular biomarkers, endothelial function, and arterial stiffness) were deemed heterogeneous and inconclusive.
A prospective cohort study on long-term cardiovascular mortality in 208 subjects found CPAP and MAD equally effective in reducing the risk of fatal cardiovascular events in patients with severe OSA, despite higher residual AHI for MAD compared with CPAP users (16.3 vs 4.5 events per hour). There was no difference in the cumulative cardiovascular mortality between OSA patients treated with CPAP or MAD and that of the nonapneic controls, suggesting effective symptomatic treatment with either modality despite differences in residual AHI.
This outcome, however, is from a single observational study. More longitudinal studies with better methodology are needed to answer key questions on cardiovascular morbidity and mortality outcomes.
Long-term use of OAs leads to occlusal changes. A meta-analysis reported a significant increase in lower incisor inclination by 2.07°, resulting in 0.99-mm decrease in overjet (OJ) and 1.0-mm decrease in overbite (OB). A greater decrease in OJ and OB was associated with longer treatment. There was no significant change in the upper incisor inclination or interincisal angle.
Three-dimensional computer-assisted study model analysis of long-term oral-appliance wear. Part 2. Side effects of oral appliances in obstructive sleep apnea patients.
Three-dimensional computer-assisted study model analysis of long-term oral-appliance wear. Part 2. Side effects of oral appliances in obstructive sleep apnea patients.
Transient muscle soreness and temporomandibular joint (TMJ) discomfort have been reported after MAD use, especially during the initial titration period.
A 5-year follow-up study of MAD patients found mild, temporary subjective side effects, such as muscular or TMJ discomfort, but no changes in temporomandibular disorder prevalence using the Research Diagnostic Criteria for Temporomandibular Disorders.
Effects of mandibular advancement on upper airway dimension and collapsibility in patients with obstructive sleep apnea using dynamic upper airway imaging during sleep.
Patients of female gender, younger age, smaller neck circumference, lower body mass index, lower AHI, and supine-dependent OSA are predicted to have better treatment success with MADs.
The literature lacks consensus in successful treatment outcome, with a majority of success criteria used in research not meshing with clinical definitions of OSA severity. Discordant success criteria makes comparing results of different studies difficult.
Prospective trials are under way to determine predictive potential of wakeful nasoendoscopy with Müller maneuver, drug-induced sleep endoscopy (DISE), and computational fluid dynamics.
Predicting Therapeutic Outcome of Mandibular Advancement Device Treatment in Obstructive Sleep Apnoea (PROMAD): study design and baseline characteristics.
In the meantime, careful diagnosis and patient selection can increase the chances of success.
Cephalometry
Classically, shorter soft palate length, larger retropalatal airway space, lower hyoid bone position, and a smaller mandible are associated with favorable MAD treatment response.
Anatomically based outcome predictors of treatment for obstructive sleep apnea with intraoral splint devices: a systematic review of cephalometric studies.
however, exploring cephalometric predictors for MAD response found a majority of observational studies on cephalometric predictors had flawed designs and failed to control for known confounding factors such as age, gender, body mass index, and baseline AHI. Definitions of treatment success were inconsistent, and heterogeneity in design prevented data synthesis and meta-analysis. Cephalometric parameters warranting further study included mandibular plane angle, hyoid to mandibular plane distance, and soft palate length.
Mandibular Advancement Device Design
Customized versus noncustomized
Both customized and noncustomized MADs reduce AHI in adult patients with OSA, but meta-analysis by the AASM/AADSM task force shows the improvements to be far greater in customized than noncustomized, with an AHI reduction of 13.89 events compared with 6.28 events per hour.
Both custom titratable and custom nontitratable MADs reduce AHI, improve Sao2 and reduce ESS scores, with meta-analyses by the AASM/AADSM task force showing the improvements to be approximately equivalent. Titratable MADs are recommended, however, over nontitratable MADs because the confidence interval for the effect of custom, titratable MADs is considerably smaller than for custom, nontitratable MADs.
Due to dose-dependent effects, a clinical titration can improve MAD response and increase the amount of achievable protrusion. This is only possible with titratable MADs.
Treatment response to MAD can be estimated by visualizing airway response to mandibular protrusion or tongue thrust with nasoendoscopy or MRI in awake supine patients, or in patients using DISE. An increase in velopharyngeal CSA with mandibular advancement was significantly associated with greater AHI reduction with MADs.
Müller maneuver during nasoendoscopy induced significantly greater collapse in velopharyngeal and oropharyngeal CSA in MAD nonresponders than responders. With mandibular advancement, Müller maneuver induced a significantly greater collapse at all airway levels in nonresponders.
Mandibular advancement device titration using polysomnography
Due to the dose-dependent relationship between efficacy and protrusion, increasing protrusion can increase treatment response in OSA patients. Conventional titration protocols use subjective symptoms to adjust mandibular advancement over several months and an outcome polysomnography (PSG) to confirm efficacy. There is no consensus, however, on an optimal titration protocol.
Manually increasing MAD advancement during overnight PSG can increase therapeutic efficacy of mandibular protrusion while reducing the number of titration visits required by most therapeutic protocols. After a clinical titration period, overnight MAD titration with PSG using the final MAD increased treatment response by an additional 9.9% to 30.4% of study subjects.
Disappointing outcomes were reported, however, using an interim MAD without a period of clinical titration because efficacy of the interim MAD was not translated to the final MAD.
Overnight MAD titration with PSG may require large single-night mandibular advancements to relieve respiratory events, in contrast to slow titration with conventional protocols. Significant jaw discomfort was noted with PSG titration without prior MAD use
Using remote-controlled mandibular positioners (RCMPs) for single-night titration of MADs is similar to overnight MAD titration with PSG, with the advantage of adjustment done remotely without waking the patient or removing the appliance. Sleep architecture is maintained while protruding the mandible progressively until respiratory events are eliminated.
RCMPs can determine an effective target protrusion that is correlated with successful MAD treatment, may be able to identify nonresponders early, and reduce the number of titration reviews needed compared with conventional titration protocols.
The use of remotely controlled mandibular positioner as a predictive screening tool for mandibular advancement device therapy in patients with obstructive sleep apnea through single-night progressive titration of the mandible: a systematic review.
combining the therapies using a novel hybrid appliance resulted in augmentative treatment effects. Tongue suction with 6 mm mandibular protrusion produced better treatment response than 8 mm mandibular protrusion alone.
Continuous positive airway pressure and oral appliance hybrid therapy in obstructive sleep apnea: patient comfort, compliance, and preference: a pilot study.
Patients who are generally unsuitable for MAD treatment include edentulous patients and patients with inadequate number of sound teeth, severe periodontitis, and/or history of TMJ disease. There are exceptions, and MADs can sometimes be worn successfully by edentulous patients with good dentoalveolar ridges.
Clinical titration should be followed by overnight PSG. Subjective feedback is not sufficient to determine the optimal setting of MAD. Post-PSG titration has been shown to improve MAD efficacy significantly.
Effects of mandibular advancement on upper airway dimension and collapsibility in patients with obstructive sleep apnea using dynamic upper airway imaging during sleep.
The effect of a mandibular advancement splint on electromyographic activity of the submental and masseter muscles in patients with obstructive sleep apnea.
Comparison of the effects of continuous positive airway pressure and mandibular advancement devices on sleepiness in patients with obstructive sleep apnoea: a network meta-analysis.
Three-dimensional computer-assisted study model analysis of long-term oral-appliance wear. Part 2. Side effects of oral appliances in obstructive sleep apnea patients.
Predicting Therapeutic Outcome of Mandibular Advancement Device Treatment in Obstructive Sleep Apnoea (PROMAD): study design and baseline characteristics.
Anatomically based outcome predictors of treatment for obstructive sleep apnea with intraoral splint devices: a systematic review of cephalometric studies.
The use of remotely controlled mandibular positioner as a predictive screening tool for mandibular advancement device therapy in patients with obstructive sleep apnea through single-night progressive titration of the mandible: a systematic review.
Continuous positive airway pressure and oral appliance hybrid therapy in obstructive sleep apnea: patient comfort, compliance, and preference: a pilot study.
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