Multilevel Oral Appliance Treatment for Sleep Apnea
Obstructive sleep apnea (OSA) is caused by repeated choking on their tongue and sometimes also surrounding loose tissues during sleep. It affects millions of people, but current treatment for it is problemmatic. Surgery is predictably effective only if it is performed at multiple levels of the pharynx, because most people with OSA have multiple sites of obstruction at different levels of the pharynx. CPAP is usually effective because it balloons out all levels of the pharynx and thereby makes it too large for the tongue to obstruct, but compliance is poor. Oral appliances that protrude the mandible create space into which the tongue can shift anteriorly, but they can't actually shift the tongue anteriorly, so their effectiveness is never more than about 50%. An oral appliance that uses a rubber suction bulb to grasp the tip of the tongue and hold it all the way out beyond the lips is difficult to tolerate and still can't control the back of the tongue where the choking occurs. Soft palate elevators can help draw the distal end of the soft palate away from the area of obstruction, but they are rarely effective when used alone.
These diverse oral appliance modalities are synergistic in many ways, but they have never been combined, because the hardware they require has previously been incompatible. Therefore, to improve the effectivenss of oral appliances for treatment of OSA, Dr. Summer has designed a new tongue holding device (THD), which enables combining all these treatment modalities in a single oral appliance. Because it is entirely made of dental acrylic, the THD can be added to most mandibular protrusion appliances after titration. It has springy tail sections that push the base of the tongue forward and have flexibility to move with the wave of contraction during swallowing, and it may also include a soft palate elevator to move the distal end of the soft palate away from the base of the tongue. Such multi-level treatment is likely to be the key to predictable success with oral appliances for OSA, just as multi-level treatment has proved to be the key to predictable success with surgery for OSA.
PATHOPHYSIOLOGY OF SLEEP APNEA
The back of the tongue is the primary obstacle to the airway in obstructive sleep apnea (OSA). Surrounding soft tissues such as the distal end of the soft palate and the peri-tonsillar tissues can play a role by filling in around the tongue to help create a seal, but the tongue is the only object in the area large enough to obstruct the airway. It is common to blame the problem on relaxation of the genioglossus and other muscles of the area, but muscles are supposed to relax during sleep. Monkey studies show that they can be recruited during sleep when the airway is compromised experimentally, and thus they could be expected to increase their tonus somewhat in response to the airway compromise in OSA, but blaming them for the problem seems misplaced.
Imaging has shown that the particular location of the obstruction is too variable to provide a basis for targeted treatment. It occurs frequently in the lower (oral or retroglossal) pharynx where the back of the tongue directly contacts the posterior pharyngeal wall. It also occurs frequently in the upper (nasal or retro-palatal) pharynx where the soft palate and adjacent soft tissues get sucked into the space between the back of the tongue and the posterior pharyngeal wall. In people with moderate or severe OSA, the obstruction usually occurs in both areas, and it frequently extends down to the hypopharynx. One study found multiple sites of obstruction in 72% of the subjects. Another reported seesawing obstructions and varying obstructions within the same individual. Apparently pharyngeal airway collapse in OSA is rarely the result of one clearly identifiable obstruction.
CPAP (continuous positive airway pressure) keeps the whole pharynx ballooned out and therefore makes it too large to get plugged by the body of the tongue at any level. The treatment is usually effective if the pressure is high enough. However many people find it difficult to tolerate.
Surgery for OSA is not predictably effective unless it is performed at multiple levels of the pharynx (multi-level surgery), such as combining maxillary and mandibular advancement. However compounding surgeries also compounds costs and morbidities, therefore surgical remedies remain problemmatic.
ORAL APPLIANCE TREATMENT
Oral appliance treatment for OSA also has not been predictably effective as a single level therapy. The vast majority of the oral appliances made by dentists to treat OSA use only mandibular protrusion. Because the mandible surrounds the airway in front and on both sides, protruding it creates a space for the tongue to rest more anteriorly. However, the mandible and the tongue are attached by muscles, which lose tonus during sleep. Thus even extreme mandibular protrusion cannot always prevent the tongue from falling back into the airway. For that reason, the hundreds of studies of mandibular protrusion appliances that have been performed in the last two decades all show that they are never more than about 50% effective.1 Some studies defining success as a 50% reduction in AHI show a slightly higher success rate, but almost all of those "successes" will still need further treatment as the tissues continue to stretch out due to age and continued apnea events.
The tongue stabilizing device (TSD), also known as the tongue retaining device (TRD) or the MPowRX, uses a silicone rubber suction bulb to grasp the tongue tip and hold it out between the lips. The grip on the tongue tip can be effective, but the extreme tongue protrusion required to hold it out between the lips is difficult to tolerate. In the only prospective study of a TSD, 60% of the patients dropped out because of tongue pain. In addition, the severity and frequency of blockage in the lower pharynx can be increased by pulling a larger portion of the tongue up into the area of obstruction. In one study, a TSD caused large increases in the AHI of two of the subjects. Generally these devices are reserved for people who cannot wear a jaw protrusion appliance, such as people with inadequate dental support.
A tongue rear depressing appliance has also shown some success in protecting the upper pharynx. The Full Breath Solution (FBS) appliance employs a rigid transpalatal bar to support a smooth tail-like bulb that holds down the rear portion of the tongue. Holding down the rear portion of the tongue probably helps prevent obstruction in the upper pharynx, but it may increase obstruction in the lower pharynx.
Soft palate elevators can draw the distal end of the soft palate anteriorly and superiorly away from the site of airway obstruction by tenting this very flexible structure from its midportion, where there are no gag reflexes. Soft palate elevators that were used previously had a tissue contacting portion of acrylic and were supported by a relatively heavy wire, making them uncomfortable.
Combining all these oral appliance treatment modalities offers obvious advantages in both comfort and effectiveness, because their actions are highly synergistic. The mandible provides the base of operation for the tongue (which has no bone of its own), therefore mandibular protrusion and tongue protrusion are mutually supporting modalities. Mandibular protrusion facilitates mechanics that push down and forward on the tongue rear by creating space into which the body of the tongue can shift down and forward. Pushing inferiorly and anteriorly on the back of the tongue and drawing the end of the soft palate anteriorly and superiorly work together to clear an obstruction in the upper pharynx.
However previously it has not been possible to combine these oral appliance treatment modalities, because the hardware required for each of them has been incompatible. For example, the silicone rubber of the TRD is difficult to attach to the acrylic used in mandibular protrusion appliances.
Dr. Summer has developed a new tongue holding device (THD) that enables combining all these treatment modalities to create a multi-level oral appliance treatment. The THD is is entirely made of dental acrylic so it can be added to a Herbst, SUAD, Somnomed, EMA, or Oasys appliance after the appliance has been titrated. The THD can then directly hold the tongue anteriorly with the mandible all night long.
TELESCOPIC MANDIBULAR PROTRUSION
We normally begin treatment with a telescopic mandibular protrusion appliance that has been modified for use in adults. Telescopic appliances have long proven effective in treatment for OSA, but the telescopic hardware in the commonly used Herbst and SUAD appliances was designed more than half a century ago for orthodontic bite jumping in children. When used in adults, it is unnecessarily bulky, and it can impair TMJ health by preventing lateral mandibular movements. To make the telescopic components more suitable for long term use in adults with OSA, we have flattened them to better fit the buccal vestibule, attached them flexibly in order to allow a free range of motion laterally for TMJ health, and made them micro-adjustable by the patient over a range of ½” without tools for titration of jaw protrusion.
After the patient has titrated the appliance to find the maximal tolerable amount of jaw protrusion, we use a home sleep test to evaluate its effectiveness. We use three nights of consecutive testing to minimize the effects of internight variability and the confounding factors created by initial wear of a new device during sleep.
THE TONGUE HOLDING DEVICE (THD)
If the OSA persists, we add the tongue holding device (THD), which grasps the tongue between upper and lower tongue gripping surfaces, each containing thousands of miniature forward-slanted bristles that act like directional velcro, to hold the tongue forward with the mandible. The 4,000 bristles on the upper tongue gripping surface (shown below) are sized to fit between the filiform papillae that cover the dorsal surface of the front of the tongue. The 10,000 miniature bristles on the lower tongue gripping surface engage the more sensitive unkeratinized mucous membrane on the underside of the tongue like a bed of nails. Because of the 45 degree angle of the bristles, the tongue can easily slide forward into the THD, but it cannot be pulled backward out of it without opening the mouth widely enough to release the tongue.
The upper tongue gripping surface is "spring-loaded" - continually biased into the dorsal surface of the tongue by a single 2 ounce trans-palatal orthodontic elastic (dashed lines in the figure below) so it can maintain its grip on the tongue throughout the night despite the rhythmic masticatory muscle activity (RMMA) that causes small movements of the mandible during normal sleep. The bias from the elastic is strongest when the mouth is closed (top figure), and it continues until the mouth opens wide enough to bring the middle of the elastic into the same plane as the ends of the elastic (middle figure). Any further opening separates the tongue from the tongue gripping surfaces (bottom figure). In this manner, wide opening serves as the tongue release mechanism. If the THD fits correctly, the user cannot remove the tongue without opening the mouth widely.
RESILIENT SUSPENSION OF TONGUE GRIPPING SURFACES
As a result of the gentle but persistent grip of the THD on the body and base of the tongue, the tongue can be held all night in any position desired. Generally it is placed far enough forward for its tip to maintain light contact with the lips when the device is inserted, and it will be in the same position in the morning. A preliminary study of an early version of the THD conducted for the FDA with before and after full night PSG on 13 subjects showed that, used as a single modality, the THD was safe and about as effective as other oral appliance modalities.
In addition, to control the location of the tongue base, the upper tongue gripping surface of the THD has a spring-tail section that extends further distally and posteriorly to hold the base of the tongue anteriorly away from the pharyngeal wall. These tail sections are located on the lateral portions of the dorsal surface of the tongue where there are minimal gag reflexes.
TREATMENT OF THE UPPER PHARYNX
If follow-up home sleep testing still shows OSA with the back of the tongue pulled anteriorly off the posterior wall of the lower pharynx (oropharynx), the remaining airway blockage occurs where the distal end of the soft palate gets sucked into the space between the back of the tongue and the posterior wall of the upper pharynx (nasopharynx), as illustrated below.
To relieve this blockage, we add a soft palate elevator that works together with the tail sections of the upper tongue gripping surface to move the tissues bordering the upper pharynx in opposite directions. The soft palate is elevated by a lightweight arm that contacts its midportions where there are no gag reflexes. The very flexible tissue of the soft palate can be elevated surprisingly far without discomfort by a silicone rubber tissue contacting portion mounted on an arm that is flexible enough to move easily during swallowing, when there is no need to hold the airway open anyway. Elevating the soft palate in its midsection tents the whole structure and thereby draws its distal end anteriorly and superiorly. Holding the tongue rear inferiorly while drawing the distal end of the soft palate superiorly maintains airway passage between them, as illustrated below.
Obligate mouthbreathers have a nasal airway that is too small to allow adequate airway flow, and their lips are always slightly parted to allow an oral airway. Many people become obligate mouthbreathers occasionally due to rhinitis or allergies, therefore they need an oral appliance that permits mouthbreathing. The THD permits mouthbreathing, because its upper tongue gripping surface descends with the mandible when the mouth is part way open and thereby creates an oral airway passage just under the hard palate.
Habitual mouthbreathers have developed a habit of holding the mouth open and breathing through it in spite of an adequate nasal airway passage. The problem can be corrected by holding the mouth closed using devices such as chin straps, head straps, thick foam cervical collars, or incorporating interarch elastics into a dual arch oral appliance made for sleep apnea. If interach elastics are used, the oral appliance must fit tightly on the teeth.
Some obligate mouthbreathers can be converted to nasal breathers by expanding the palate. The process can be performed gradually in adults without significant discomfort, and a change from oral to nasal breathing yields major health benefits. However any effect of palatal expansion on OSA in adults is likely to be minimal, because the airway obstruction in OSA occurs in the pharynx, not in the nasal cavity.3
One common sequelae of jaw protrusion is an inability to return to the patient's normal habitual occlusion every morning and then throughout the day. Some dentists prescribe a series of exercises to force the mandible back retrusively every morning, which may trigger remodeling that enables the joints to accept a more posterior condylar position; but in almost all these cases the mandible has simply outgrown the occlusion, and the occlusion needs to be adjusted to fit the slightly more anterior position of the mandibular corpus.
COSTS OF MULTILEVEL TREATMENT
During 2018, while we are collecting data for a study, we will be adding THDs to existing jaw protrusion appliances that were found tolerable but ineffective for $500. We will also be marketing the THD to dentists and dental labs who want to add it to jaw protrusion appliances.
1. Hoffstein V. Review of oral appliances for treatment of sleep-disordered breathing. Sleep Breath 2007;11(1);1-22.
2. Ribero AN, de Paiva JB, Rino-Neto J, Illiponti-Filho E, et al. Upper airway expansion after rapid maxillary expansion evaluated with cone beam computed tomography. Angle Orthod 2012;82(3):458-463.