Obstructive sleep apnea (OSA) is a common disorder, affecting approximately 17% of adult women and 34% of adult men. The underlying problem is the repeated collapse of the throat during sleep, leading to impaired airflow or even complete cessation of breathing.
This process triggers a series of chain reactions: the body repeatedly experiences brief periods of oxygen deprivation during the night, drastic fluctuations in chest pressure, continuous tension in the nervous system, and constant sleep interruptions.
Therefore, OSA poses a wide range of health risks. Patients often experience excessive daytime sleepiness, fatigue, and difficulty concentrating, leading to a decreased quality of life and an increased risk of accidents at work and while driving due to lack of energy.
In the long term, it is also a significant risk factor for metabolic problems, hypertension, and cardiovascular diseases (such as coronary heart disease and stroke), and is associated with a higher risk of mortality.
Obstructive sleep apnea (OSA) has a high prevalence and can lead to a range of health problems and socioeconomic burdens; therefore, effective management of this chronic disease is crucial.
For patients with moderate to severe obstructive sleep apnea (OSA), the standard treatment is continuous positive airway pressure (CPAP). This device delivers gentle positive air pressure during sleep, acting like a “pneumatic splint” to support the throat and prevent it from collapsing.
Although CPAP is highly effective in eliminating sleep apnea, its actual effectiveness is often significantly reduced due to poor user experience and patients’ difficulty in adhering to the treatment long-term.
In this context, oral appliances are becoming an increasingly valued non-surgical treatment option. They are particularly suitable for patients with mild to moderate OSA who prefer oral appliances, cannot tolerate or adapt to CPAP therapy, or for whom CPAP therapy has failed. This device works by advancing the mandible or tongue, helping patients maintain an open airway during sleep.
Types of Orthodontic Appliances
Based on their mechanisms of action, orthodontic appliances are mainly divided into the following three categories:
1.Soft Palate Elevator
These devices aim to reduce snoring by directly lifting the soft palate and uvula to minimize their vibration. However, evidence of their effectiveness in treating obstructive sleep apnea (OSA) is currently limited.
2.Tongue Retaining Device (TRD)
A tongue retaining device (TRD) is a device that uses negative pressure suction to hold the tongue in a forward position. It continuously pulls the tongue forward during sleep, preventing it from falling back and obstructing the pharyngeal airway.
3.Mandibular Advancement Device (MAD)
This is one of the most commonly used types of oral appliance in clinical practice, with common names including mandibular advancement appliance (MAA), mandibular repositioning appliance (MRA), or mandibular advancement splint (MAS). It works by gently advancing the mandible during sleep, indirectly moving the tongue forward and thus widening the upper airway.
Mandibular advancement devices (MADs) are one of the most commonly used types of oral appliances for the clinical treatment of obstructive sleep apnea (OSA).
Their core working principle is to gently move the mandible forward during sleep, simultaneously advancing the tongue, thereby increasing the space in the upper airway, reducing airway obstruction, and improving breathing.
Based on their manufacturing method, MADs (Mandibular Advancement Devices) are mainly divided into two types: custom-made and prefabricated.
Custom-made devices are tailored by a professional dentist based on the patient’s dental model and bite pattern, resulting in a better fit and comfort.
Prefabricated (also known as thermoplastic) devices are a more economical option; they are softened with hot water and then molded directly in the mouth, a simple and quick process, but with relatively limited precision.
Existing clinical studies, particularly a randomized controlled trial comparing the efficacy of two types of devices, have shown that custom-made mandibular advancement devices (MADs) are significantly more effective than prefabricated devices in reducing the severity of obstructive sleep apnea (OSA). Therefore, custom-made devices are generally recommended as the preferred treatment option in clinical practice.
Furthermore, the design concept of MAD (mandibular advancement device) has evolved from the early “one-piece” structure, where the upper and lower jaws were rigidly connected, to the currently prevalent “two-piece” structure.
The one-piece MAD has a rigid connection between the upper and lower jaw sections, which restricts the physiological movement of the mandible, potentially causing discomfort in the temporomandibular joint in some patients.
In contrast, the currently used adjustable MAD consists of two separate parts for the upper and lower jaws, but they are dynamically connected through an adjustable linkage structure, allowing for precise adjustment of the mandibular advancement.
A randomized controlled trial showed that adjustable mandibular advancement devices (MADs) made of thermoplastic material were not inferior to custom-made acrylic MADs in terms of short-term effectiveness.
Therefore, these thermoplastic adjustable MADs can serve as a simple, economical, and readily available screening tool to initially identify patients who may benefit from long-term MAD treatment.
The amount of mandibular advancement is a key factor in determining the effectiveness of MAD (Mandibular Advancement Device) therapy.
However, a greater degree of advancement does not always lead to better results; therefore, it is necessary to determine the individualized “optimal” advancement position for each patient and make fine adjustments during use based on tolerance and effectiveness.
Currently, there is a lack of universally accepted standard methods to determine this optimal position accurately.
Most studies rely on “subjective titration protocols,” which involve adjusting the device based on the physiological limits of the patient’s mandibular advancement and changes in subjective symptoms such as snoring and daytime sleepiness.
However, this improvement based on subjective perception may be biased, and sometimes temporary symptom relief can lead to premature cessation of titration, thus affecting the final efficacy. Therefore, current MAD titration is essentially still a “trial and error” process.
In recent years, a device called a “remote-controlled mandibular positioner” has been used for nocturnal sleep monitoring. Â During monitoring, it automatically and gradually advances the mandible whenever a respiratory event occurs, thus objectively and dynamically finding the optimal position.
Studies have shown that the individualized anterior mandibular position determined using this method is significantly more effective in reducing the severity of OSA than traditional subjective titration methods.
Side Effects and Risks
In the early stages of MAD treatment, patients often report some mild and transient side effects. Short-term discomfort may include dry mouth, excessive salivation, tooth sensitivity, tenderness of the masticatory muscles, temporomandibular joint discomfort, myofascial pain, and gum irritation.
These symptoms are mostly temporary and usually subside gradually after a few days to weeks of use, as the patient adapts and the appliance is properly adjusted.
However, in a few cases, these symptoms may be more pronounced or persistent, potentially leading to treatment discontinuation.
In the long term, the main adverse effect of MAD treatment is the possibility of minor changes in the occlusal relationship, but existing studies show that this change usually does not directly lead to patients discontinuing treatment.
Conversely, its impact on bone structure or facial morphology is generally negligible.
Effectiveness and Impact
Mandibular advancement devices (MADs) do not eliminate the underlying cause of obstructive sleep apnea (OSA), but they can effectively reduce airway collapse and improve ventilation by mechanically expanding and stabilizing the upper airway through mandibular advancement. This is a treatment method that requires long-term use.
It is important to emphasize that the effectiveness of any medical device depends on correct and consistent use.
Therefore, when evaluating the overall therapeutic effect of MADs, both their objective effectiveness (such as the degree of reduction in respiratory events) and patient adherence to long-term use must be considered.
1. Validity
Mandibular advancement devices (MADs), as a treatment modality, demonstrate their effectiveness through the therapeutic benefits achieved when used correctly.
In the treatment of sleep apnea, effectiveness is typically assessed by the degree of reduction in the apnea-hypopnea index (AHI).
Overall, MAD treatment is effective in reducing snoring and improving sleep monitoring parameters such as AHI.
Specifically, among patients receiving MAD treatment, approximately one-third achieve complete remission of OSA (i.e., AHI < 5 events/hour during treatment), another one-third experience a reduction in AHI of more than 50%, while the remaining one-third show no significant improvement.
Overall, although both continuous positive airway pressure (CPAP) and MAD therapy have been shown to reduce the severity of OSA, several studies encompassing patients with mild to severe OSA have demonstrated that CPAP is more effective than MAD therapy in reducing the apnea-hypopnea index (AHI).
2. Health Effects
Mandibular advancement devices (MADs) have been shown to slightly but significantly lower both systolic and diastolic blood pressure.
Studies comparing MADs with continuous positive airway pressure (CPAP) have found that both treatments provide similar clinical benefits in lowering blood pressure and reducing the risk of cardiovascular death.
This result may be due to the fact that, although CPAP is more effective in improving nocturnal respiratory parameters, patients’ actual adherence to its use is generally lower than with MAD, thus leading to similar long-term clinical outcomes for both treatments.
Conclusion
Oral appliance therapy is increasingly becoming a common non-invasive treatment option for patients with obstructive sleep apnea (OSA).
Currently, the recommended treatment involves custom-made, adjustable mandibular advancement devices (MADs), which allow for gradual adjustment of the mandibular protrusion position.
Recent studies show that although continuous positive airway pressure (CPAP) is more effective than MADs in reducing the severity of OSA (such as the AHI index), both treatments are comparable in improving long-term health outcomes for patients (such as blood pressure control and cardiovascular risk).
This is likely related to the generally higher patient adherence to nighttime use of MAD compared to CPAP. In unselected OSA patients, most experienced a reduction in disease severity after MAD treatment, but approximately one-third showed no significant improvement.
Therefore, identifying patients suitable for MAD treatment is crucial to improving the overall success rate of this therapy. Although several predictive models and tools have been proposed, there is still a lack of thoroughly validated methods that can accurately and reliably identify ideal candidates for MAD treatment before treatment begins.
