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Treating All Four OSA Phenotypes with an Oral Appliance

This article is written by TAP inventor Dr. Keith Thornton and featured in the May issue of Sleep Review.

Many individuals commonly assume all oral appliances are designed the same and placed in a one-size-fits-all category due to their attachment to the teeth and their mandibular protrusion. However, this is not the case with TAP® devices, most notably flexTAP® (custom) and myTAP® (non-custom). With many patients demanding alternative therapies, you can trust that TAP appliances can address all four OSA phenotypes, but first, let’s explain why. With the addition of the Mouth Shield, flexTAP and myTAP can effectively treat all four phenotypic traits or “OSA endotypes.”

Nasal Breathing

Breathing through the nose affects the chemical balance in our bodies. Opting for nasal breathing helps regulate the levels of CO2 in our blood, balances acidity, and allows for better oxygen absorption by our blood cells. Additionally, nasal breathing facilitates the release of nitric oxide, a beneficial gas produced in the nasal passages. Nitric oxide plays a crucial role in vasodilation, which helps to increase blood flow to various body parts, including the lungs and brain.

Calm breathing finds its rhythm through the nose, regulating the pace of respiration. Ultimately, this practice contributes to improved sleep quality and serves as a filtration mechanism for the body. In addressing the four distinct phenotypes, the key lies in chemical control. Once a patient’s airway is effectively opened, attention can shift toward addressing their specific phenotype.

The four phenotypes we will define and discuss are:

  1. Impaired airway anatomy
  2. Arousal threshold
  3. Muscle function
  4. Loop gain


The understanding of sleep-disordered breathing has evolved, revealing a spectrum of phenotypes that contribute to its complexity. At the core of this spectrum lies SPVI, or sleep pharyngeal-ventilatory instability, a condition characterized by the instability of the pharynx during sleep. This instability stems from anatomical factors and the tendency for the jaw to fall open, leading to relaxed muscles. Additionally, dysfunction in CO2 regulation exacerbates the condition, highlighting the interaction between physiological and anatomical factors in the manifestation of sleep-related breathing disorders.

Phenotype #1 – Impaired Airway Anatomy

The first phenotype focuses on compromised airway structure. All phenotypes exhibit limited airway dimensions, a purely anatomical characteristic. Most individuals exhibit a constricted upper arch and high palate, leading to a smaller oral cavity, less room for the tongue, deviated septum, and, ultimately, airway narrowing. The size of the tongue might exceed the capacity of this upper arch. To compensate for that, we first must move the tongue out of the airway by moving the jaw forward. Then, we can address any additional non-anatomical contributors to the patient’s OSA.

Eckert asserts that “70% of people with OSA also have problems with one or more of three non-anatomical contributors to OSA.”1 These non-anatomical contributors are all related to the chemical control of breathing and the management of CO2 and O2 in the body.2

Phenotype #2 – Arousal Threshold

The second phenotype pertains to the arousal threshold. Termed in my practice as the “twitchy, skinny women’s disease,” this phenotype encompasses mouth breathers who arouse quickly. Hyperactive, skinnier people with airway constraints awaken fast and endure heightened stress. Nevertheless, this phenotype does not escape anatomical airway issues. Airway dimensions for this phenotype are commonly compared to that of a straw. While sleep apnea may not be prevalent within this group, disrupted sleep patterns are common. Additionally, people with a low threshold for arousal are more likely to fail CPAP therapy.2

Phenotype #3 – Muscle Function

The third phenotype revolves around muscular function. Regrettably, relaxation in this context proves detrimental. Individuals categorized under this phenotype lack activated muscles during sleep. Breathing through the mouth induces muscle relaxation, whereas nasal breathing enhances muscle engagement, with CO2 facilitating this process.

Phenotype #4 – Loop Gain

The fourth and final phenotype delves into high loop gain. Those exhibiting high loop gain are sensitive to CO2, prompting accelerated mouth breathing and subsequent CO2 release. The brain detects the surplus CO2, signaling a reduced breathing pace. As a result, breathing halts, lowering oxygen levels and heightening CO2 levels. This triggers a resumption of breathing, perpetuating a cycle identified as loop gain. Individuals embodying this phenotype typically lean toward older age and higher body weight.

Mechanism Comparison: Midline vs. Bilateral

With bilateral adjustment oral appliances, hardware limits the amount of tongue space (i.e., plastic between upper and lower trays in the posterior). With our hardware tethered outside the mouth in the midline, the tongue can come up and out of the airway and expand in all directions. This dual advancement of the jaw and tongue ultimately requires less jaw advancement overall. 

Most notably, both flex TAP and myTAP prevent rotation of the jaw joint. With the trays tethered together outside the mouth, these devices allow downward movement without rotation. If the patient opens any wider, the jaw joint moves down the eminence, but the jaw doesn’t rotate. With Herbst or Dorsal designs, the jaw can come down and fall back when the patient opens their jaw.

How does TAP Address All Four Phenotypes?

  1. Initially, the focus is on creating more space for the tongue to address the impaired airway anatomy. This is accomplished by protruding the jaw and increasing interocclusal space by opening the interincisal distance without backward rotation of the mandible.

When one practices nasal breathing, it engages the tongue muscles and allows the tongue to move further forward, consequently widening the airway. With the addition of the Mouth Shield, flexTAP and myTAP efficiently manage the remaining phenotypes:

  1. In the context of the arousal threshold pattern, the Mouth Shield enforces nasal breathing and promotes patient relaxation.
  1. Managing muscle functionality entails expanding available space, which is efficiently executed by both flexTAP and myTAP hardware designs. Adding the Mouth Shield activates the tongue muscles, promoting increased muscle functionality.
  1. Concerning loop gain, the management of narrow airways and the regulation of breathing chemistry must be addressed. The Mouth Shield enhances the overall effectiveness of treatment through its capacity to regulate CO2 levels and breathing patterns.


Treatment success relies on how far the jaw can open. Since people breathe in various positions, healthcare providers need the flexibility to adjust the device according to individual patient night-to-night needs.

In the current landscape, there is a heightened demand for straightforward and efficient treatments for obstructive sleep apnea among patients. Incorporating TAP into your treatment options offers the ability to address patients’ needs immediately with a customizable and adaptable device. With 30 years of research and innovation and the most independent peer-reviewed studies, TAP stands as a validated and efficacious oral appliance for managing obstructive sleep apnea.


1 Eckert DJ, White DP, Jordan AS, Malhotra A, Wellman A. “Defining phenotypic causes of obstructive sleep apnea. Identification of novel therapeutic targets.” Am J Respir Crit Care Med. Oct 15, 2013;188(8):996-1004. doi:10.1164/rccm.201303-0448OC

2 Gray EL, McKenzie DK, Eckert DJ. Obstructive Sleep Apnea Without Obesity is Common and Difficult to Treat: Evidence for a Distinct Pathophysiological Phenotype. J Clin Sleep Med. Sep 13, 2017;13(1):81-8.

Daniel J. Levendowski MBA1, Jonathan Lown MD2, Todd Morgan DMD3, Gandis Mazeika MD1. The Impact of Incremental Increases In Vertical Dimension Of Occlusion On The Relationships Between Pre- And Post-Treatment Ahi Values And Acoustic Pharyngometer Measures. Abstract #003. http://dx.doi.org/10.15331/jdsm.7298

Daniel J. Levendowski MBA1, Jonathan Lown MD2, Todd Morgan DMD3, Gandis Mazeika MD1. A Pilot Investigation To Determine If Oral Appliances At Incrementally Increased Vertical Dimensions Of Occlusion Promotes Proportionate Changes In Osa Severity And Acoustic Pharyngometer Measures. Abstract #004. http://dx.doi.org/10.15331/jdsm.7298

Garcia, G. J. M.,  Wolf, J. J.,  Campbell, D. A.,  Bailey, R. S.,  Sparapani, R. A.,  Welzig, C. M., &  Woodson, B. T.(2023).  Mandibular Advancement Reduces Pharyngeal Collapsibility By enlarging the airway rather than affecting velopharyngeal compliance. Physiological Reports,  11, e15558. https://doi.org/10.14814/phy2.15558