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.  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, 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 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 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 they have never been combined, because the hardware they require has previously been incompatible.  Dr. Summer has developed a new tongue holding device (THD) that grasps the tongue from tip to base between thousands of forward slanted bristles.  It can be added to jaw protrusion appliances that were found tolerable but ineffective to hold the tongue together with the mandible in a slightly protrusive position. A tongue base adjuster and a soft palate elevator can be added if needed to clear obstructions in the nasopharynx.  These options will enable dentists to provide multi-level treatment of OSA as a first line treatment option.

PATHOPHYSIOLOGY OF SLEEP APNEA

There is a lot of evidence that the base of the tongue is the primary obstacle that plugs 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 and rigid enough to obstruct the airway. Some researchers blame collapse of the pharyngeal airway, and the pharynx is indeed a collapsable tube, but in OSA it gets plugged rather than collapsed.   Other researchers blame pendulous soft palate and peritonsillar tissues, and these tissues can get sucked into the spaces between the tongue base and the posterior wall of the pharynx, but they are much too thin and flexible to be able to resist the forces of inspiration without the rigid support of the tongue base.  Still other researchers blame relaxation of the genioglossus and other muscles of the area, but muscles normally relax during sleep.  Monkey studies show that all the head and neck muscles get recruited during sleep if the airway is obstructed, and therefore an increase of genioglossus tension can be expected in response OSA, but blaming its lack of tension 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 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 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.  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 could not 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 push that area anteriorly, and pushing the tongue base anteriorly 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 so it can be added to most jaw protrusion appliances.  This device, called a tongue trap, grasps the tongue between upper and lower tongue gripping surfaces each containing thousands of forward slanted bristles that act like directional velcro.  Biased together by a single 3/4 inch long 2 oz. orthodontic elastic, they can hold the tongue all night without discomfort.  It usually does not need to be placed very far anteriorly, it just needs to be held in slight protrusion together with the mandible. Optional tongue base adjusters and a soft palate elevator can be added if needed.  The basic technology is covered under US patents 9,801,755 B2; 9,808,371 B2; and 9,636,250 B2 with other patents applied for.  

STAGE ONE - 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 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. 

 

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. 

STAGE TWO - ADDING A TONGUE HOLDING DEVICE

If the OSA persists, we add a tongue holding device (the tongue trap) 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 tongue trap, but it cannot be pulled backward out of it without opening the mouth widely enough to release the tongue.

 The tongue trap continually pushes the upper tongue gripping surface down into the dorsal surface of the tongue with the force of a single 2 ounce trans-palatal orthodontic elastic (dashed lines in the figure below) that maintains its grip on the tongue until the mouth is opened wide enough to release it.  As a result of the resilient suspension of the upper tongue gripping surface shown below, the tongue is held in the tongue trap 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 SURFACES

 

 

 

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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.  

 

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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.

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An optional tongue base adjuster and a soft palate elevator can be added to relieve this blockage by pushing the tissues contributing to it in opposite directions.

A tongue base adjuster on each side of the upper tongue gripping surface allows repositioning of the two tail sections that engage the lateral portions of the tongue base, avoiding the gag reflexes that are mostly located in the midline.  Using a straight hemostat, the tail sections can be shifted further posteriorly and/or can be set at a steeper angle.   Studies of the tongue rear depressor indicate that the location of contact with the tongue base can be extended gradually 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 surprisingly far without discomfort, and flexible arm holding elevating it can move easily during swallowing, when the airway closes temporarily anyway.  

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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 must be 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.3 

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.