Multilevel Oral Appliance Treatment for Obstructive Sleep Apnea

SUMMARY

Obstructive sleep apnea (OSA) is caused by repeatedly choking on the base of the tongue, and sometimes also surrounding loose tissues.  The problem 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, but compliance is poor. Existing oral appliances are more tolerable than CPAP; but, as single level treatments, they are also less effective.  Jaw protrusion (mandibular advancement) appliances can create space for the tongue to shift into anteriorly, but can't actually shift the tongue anteriorly, so their effectiveness at eliminating the problem is never more than about 50%.  The tongue stabilizing device (TSD) uses a rubber suction bulb to grasp the tip of the tongue and hold it all the way out beyond the lips, but it cannot control the base of the tongue where the choking occurs.  Soft palate elevators can help draw the distal end of the soft palate antero-superiorly away from the area of obstruction, and tongue rear depressors can push the tongue base inferiorly away from the obstruction; but these modalities are rarely effective when used alone.  

All of these diverse oral appliance modalities are synergistic in many ways, but previously they could not be combined, because the hardware they required was incompatible.  Dr. Summer has developed a new tongue holding device that enables combining all these treatment modalities in a single oral appliance.  The Tongue Trap is entirely made of dental acrylic so it can be easily attached to a titrated jaw protrusion appliance in order to hold the tongue anteriorly with the mandible.  An adjustable tongue base controller and an optional soft palate elevator are included to deal with obstructions in the nasopharynx.  These  modalities can be added to an oral appliance one at a time if needed as determined by home sleep testing to ensure the patients receive only the modalities they need.   With the ability to clear obstructions at every level of the pharynx, such multi-level oral appliance treatment guided by home sleep testing is likely to become a first line treatment for OSA.

PATHOPHYSIOLOGY OF SLEEP APNEA

There is a lot of evidence that the base of the tongue is the primary obstacle in obstructive sleep apnea (OSA).  Surrounding soft tissues such as the distal end of the soft palate and the peri-tonsillar tissues can fill in around the tongue to help create a seal, but the muscular tongue base is the only object in the area large and rigid enough to resist forceful inspiration. Some researchers, especially those who promote soft palate stiffeners, refer to collapse of the pharyngeal airway, and the pharynx is indeed a collapsable tube, but in OSA it usually gets plugged rather than collapsed.   Other researchers, especially those who promote genioglossus muscle stimulators, blame relaxation of the genioglossus and other muscles of the area, but muscles normally relax during sleep.  Monkey studies show that these muscles get recruited during sleep if the airway is obstructed, and therefore an increase of genioglossus tension can be expected in response to OSA, but blaming muscle hypotension for OSA seems misplaced.  

Imaging has shown that the particular location of the obstruction is too variable to provide a basis for targeting treatment.  It occurs most frequently in the lower (oral or retroglossal) pharynx where the back of the tongue directly contacts the posterior pharyngeal wall and 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 OSA is rarely the result of one clearly identifiable obstruction. 

CPAP 

CPAP (continuous positive airway pressure) keeps the whole pharynx ballooned out (pneumatic splinting) and therefore makes it too large to get plugged by the tongue at any level.  CPAP is usually effective if the pressure is high enough. However, compliance is poor, because many people find it difficult to tolerate.

SURGERY

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, UPPP, hyoid suspension, and soft palate stiffeners.  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 one modality - mandibular protrusion. Because the mandible surrounds the airway in front and on both sides, protruding it creates a space for the tongue to posture more anteriorly. However, the mandible and the tongue are attached by muscles, which lose tonus during sleep. Thus even extreme mandibular protrusion in many cases cannot prevent the tongue from falling back into the airway.  For that reason, the hundreds of studies of mandibular protrusion appliances used for OSA treatment that have been performed in the last two decades all show that they are never more than about 50% effective at eliminating the problem.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 due to age and continued apnea events. 

The tongue stabilizing device (TSD), also marketed as the tongue retaining device (TRD) and now the MPowRX, employs a silicone rubber suction bulb to grasp the tongue tip and hold it out in front of the lips, but it cannot control the base of the tongue where the choking occurs.  As a result, it is not much more effective than jaw protrusion.  In some cases, it can even increase the severity of the OSA by pulling a larger portion of the tongue base up into the area of obstruction.   In addition, the extreme tongue protrusion it requires is difficult for most people to tolerate. 

A tongue rear depressing appliance has reportedly 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 the tongue base down and away from an obstruction in the nasopharynx, but it may increase obstruction down lower in the oropharynx or hypopharynx. 

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.  However soft palate elevators that were used previously were modifications of palatal obturators, and they employed a tissue contacting portion of hard acrylic supported by a relatively heavy wire that cannot move easily during swallowing, making them uncomfortable. They have been occasionally effective for snoring, but they have rarely been effective for OSA when used alone.

COMBINATION TREATMENT

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 that work together to clear the lower pharynx.  Protruding the body of the tongue makes its base more accessible for mechanisms which extend behind the tongue base in order to push that area anteriorly, and pushing the tongue base anteriorly away from contact with the end of the soft palate is most effective in combination with mechanics that draw the end of the soft palate anteriorly and superiorly away from the tongue base.  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 that is entirely made of dental acrylic and allows combining all these modalities in one oral appliance.  Clinically the modalities are added one at a time with home sleep testing after the addition of each modality to ensure that the patients get only the modalities they need.  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. 

STAGE ONE - TELESCOPIC MANDIBULAR PROTRUSION

Clinically treatment begins with titrating a dual-arch jaw protrusion appliance.  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 most commonly used telescopic appliance, the Herbst, 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. 

 

A number of other jaw protrusion appliances can be used as the base appliance.  These include Herbst, Somnomed, Oasys, and EMA appliances.  After the patient has titrated the appliance to find the maximal tolerable amount of jaw protrusion, it must be tested to evaluate its effectiveness.  

STAGE TWO - ADDING A TONGUE HOLDING DEVICE

If the OSA persists, we add a tongue holding device (called a Tongue Trap) which employs thousands of forward slanted bristles to hold the tongue forward together 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 tongue trap, but it cannot be pulled backward out of it without opening the mouth widely enough to release the tongue.

A single trans-palatal orthodontic elastic (dashed lines in the figure below) continually pushes the upper tongue gripping surface down into the dorsal surface of the tongue to maintain the 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). 

RESILIENT SUSPENSION OF TONGUE GRIPPING SURFACESTongue Release smaller.jpg

 

The tongue can be held 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.  It should be in the same position in the morning.  Rarely does the tongue need to be held far enough forward to break the user's lilp seal.  It just needs to be prevented from retruding.   

STAGE 3 - ADDING MECHANICS TO CLEAR THE UPPER PHARYNX

If follow-up home sleep testing shows that the patient's OSA still persists in spite of tongue and mandible protrusion, the remaining airway blockage occurs in the upper (naso) pharynx where the distal end of the soft palate and adjacent loose soft tissues get sucked into the space between the back of the tongue and the posterior wall of the upper pharynx, as illustrated below.

trd_2.jpg

To relieve this problem, the Tongue Trap employs an adjustable tongue base controller and a soft palate elevator to shift the tissues bordering the obstruction in opposite directions.The adjustable tongue base controller allows the location of contact with the tongue base to be extended gradually further downward and backward while gag reflexes learn to accomodate it.  While the tongue base is shifted further anteriorly and inferiorly away from its obstructive contact with the back of the soft palate, a soft palate elevator draws the loose tissues at the back of the soft palate anteriorly and superiorly away from its obstructive contact with the tongue base.  The soft palate elevator contacts the midportion of the soft palate where there are no gag reflexes using a silicone rubber ball suspended on a lightweight arm extending from the posterior end of the oral appliance to tent the soft palate and thereby draw its posterior end anteriorly and superiorly.  The soft palate can be elevated about 1/2 inch in most people without discomfort, and using a flat flexible arm to elevate it allows it to move easily up and down during swallowing, when the airway closes temporarily anyway.  

trd_1.jpg

CONFOUNDING FACTORS

There are also a number of confounding factors which sometimes complicate the treatment of OSA.  These factors can be a cause or a result of the problem.  They include mouthbreathing and various dental and TMJ conditions.

MOUTHBREATHING

Mouthbreathers are either obligate or habitual.  These two conditions are treated differently.

Obligate mouthbreathers have a nasal airway that is too small to allow adequate airway flow.  Their lips are always slightly parted to allow an oral airway.   Many people become obligate mouthbreathers occasionally due to rhinitis or allergies.  These people need an oral appliance that permits mouthbreathing.  The tongue trap 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.

Some obligate mouthbreathers can be cured of their mouthbreathing and converted to nasal breathing 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.  It can help relieve OSA by creating space for the tongue to rest more anteriorly and superiorly, but its effect on OSA in adults is likely to be minimal, because the airway obstruction in OSA occurs in the pharynx, not in the nasal cavity.

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, thick foam cervical collars, or incorporating interarch elastics into a dual arch oral appliance that is made for sleep apnea and fits tightly on the teeth. 

TMJ DISORDERS

TMJ disorders are rarely insurmountable problems in the treatment of OSA.  They can make protrusion of the mandible problemmatic temporarily, but usually these problems can be overcome by time.  TMJ disorders affect mostly young women, and the symptoms almost always resolve naturally by middle age when people start to develop OSA, and those that do not resolve naturally just need minimal treatment.  Thus, although authorities who advocate centric relation dentistry believe that mandibles can only be stable in their maximally retrusive positions and therefore that holding them in protrusion is likely to exacerbate a pre-existing TMJ disorder, clinical experience shows that the mandible can be moved gradually into a position of significant protrusion, even in people with pre-existing TMJ disorders, because the TMJs at that age are no longer vulnerable to the slightly increased intrajoint pressure created by mandibular protrusion.  

OCCLUSAL DISRUPTION

One common sequelae of nightly mandibular protrusion sustained over years 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.  The mandible is designed to elongate slowly throughout adulthood in order to compensate for the continual occlusal wear that also took place throughout adulthood.   Nightly mandibular protrusion is one factor that can accelerate its growth.  Subsequently reversing the growth that has already occurred is much more difficult than adjusting the occlusion to accomodate this growth. 

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 $1200.  We will also be marketing the THD to dentists and dental labs who want to add it to jaw protrusion appliances.   Our charge for an adult telescopic jaw protrusion appliance is $1900.

FOOTNOTES

 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.