SUMMARY

Obsructive sleep apnea (OSA) occurs when the tongue drops back into the throat and obstructs the pharyngeal airway temporarily but repeatedly during sleep. In millions of people, these recurrent intermittent airway obstructions occur frequently enough to become a serious health problem. Studies have shown that surgery for OSA is only predictably effective 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. The standard medical treatment for OSA is CPAP (continuous positive air pressure) which uses an air compressor to balloon out the entire pharynx. CPAP is effective, but many find it difficult to tolerate. Nearly half of those who are given a CPAP machine do not use it regularly. Dentists use a variety of oral appliances to treat OSA, but each of them only operates at one level of the pharynx, and consequently none of them have been effective enough to cure most people. The vast majority of these oral appliances work by protruding the lower jawbone. Since the lower jawbone surrounds the airway on three sides (the cervical spine forms the fourth), protruding it creates more space for the airway in the pharynx. However, since the lower jawbone is only loosely attached to the tongue, protruding the lower jawbone still cannot prevent the tongue from falling back into the throat. There is an oral appliance which uses a rubber suction bulb to grasp the tongue and hold it out between the lips, but it is not much more effective than jaw protrusion, and it is less well tolerated. There is also an oral appliance which uses a long arm to hold down the back of the tongue, and it has also shown some success, but it also protects only one level of the pharynx and therefore will not by itself be effective enough to cure most OSA. We have developed a novel tongue holding device (THD) which enables combining all three of these oral appliance treatment modalties. The THD is made of dental acrylic so it is easily attached to almost any type of jaw protrusion appliance, and a portion of the THD already extends to the rear of the tongue so is easily extended to depress the rear of the tongue. Clinical tests of this first multilevel oral appliance (ML-OA) are underway, but early reports indicate that it will be significantly more effective than previous oral appliances.

PATHOPHYSIOLOGY OF SLEEP APNEA

Obstructive Sleep Apnea (OSA) occurs during sleep when the tongue drops back into the throat and obstructs the pharyngeal airway, causing patients to literally choke on their tongues.  Further attempts at breathing then suck the surrounding soft tissues in around the rear portion of the tongue, forming a seal which prevents all breathing until the resultant decrease of oxygen levels and increase of carbon dioxide levels  trigger an adrenalin release which causes a gasp that temporarily restores the airway.  In millions of people, these recurrent intermittent airway obstructions last long enough and occur frequently enough to become a serious health problem.

The location of the obstruction in the pharynx has been studied during sleep in OSA patients by ultrafast dynamic MRI, optical coherence tomography, nasopharyngoscopy, cephalometry at rest and during inspiration, videoradiography, computer assisted videoendoscopic airway analysis, fiberoptic nasopharyngoscopy, fluoroscopy, CT scanning, multisensory catheters to measure airway flow and pressure, acoustic pharyngometry, and anatomical optical coherence tomography.  Generally these studies show that the obstruction occurs about twice as frequently in the retro-palatal area (where the tongue contacts the soft palate in front of the uvula) as in the retro-glossal area (where the tongue contacts the back of the pharynx behind the uvula), but it usually occurs in both areas in people with moderate or severe OSA, and it frequently extends down to the hypopharynx behind the tongue base.  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.  Consequently, attempts to use imaging to identify one favorable target area for treatment in individual cases have been generally unsuccessful.

MEDI CAL TREATMENT

A variety of surgeries can be used to treat the problem.  The retro-palatal area can be treated by radiofrequency ablation, palatal implants and uvulopalatopharyngoplasty (UPPP). The retro-glossal area can be treated by radiofrequency ablation of tongue base, genioglossus skeletal advancement, tongue base suspension sutures and hyoid suspension. Orthognathic surgery can be used to advance upper and lower jaws. Each of these surgical procedures has had some success, however each treats only one level of the pharynx, so none has proven effective in most OSA patients.  Combining surgeries to increase airway space at multiple levels of the pharynx (multi-level surgery) is more effective than single level surgery, but also compounds the chances of undesireable side effects.  Thus surgical options remain inadequate.

CPAP (continuous positive airway pressure) is currently the primary medical treatment of OSA.  It uses an air compressor to balloon out the whole upper airway. In this way it provides multi-level treatment, and it is effective in most people with OSA.  However many patients hate it, so long term compliance is poor.  Almost half of those fiven a CPAP machine do not use it regularly.

DENTAL TREATMENT

Oral appliance treatment has until now only been available as a single level therapy, and thus it has been unable to eliminate the problem in most OSA patients. . Oral appliances have been used to either protrude the tongue, protrude the lower jawbone, or depress the rear portion of the tongue.  Each of these treatment modalities protects a different level of the pharynx, but they have  never been combined in a multi-level approach, because the technologies which produce the therapeutic effects have been incompatible.  For example the silicone rubber monobloc used for tongue protrusion cannot be attached to the dental acrylic used for jaw protrusion appliances and is too flexible to support tongue rear depression.  Thus a dentist making an oral appliance to treat OSA in a patient must choose from among three oral appliance treatment modalities with very little information about which is most likely to provide relief for that patient.

Jaw protrusion is the treatment modality used by the vast majority of dentists to treat OSA.  The lower jawbone surrounds the airway on three sides and forms the base of operation for the tongue, so moving it forward increases the amount of space for airway in retro-glossal portion of the pharynx, creates forward traction on the base of the tongue via the genioglossus and suprahyoid muscles, and may also reduce the collapsibility of portions of the pharynx by stretching the palatoglossal and palatopharyngeal arches. Studies have found that protrusion of the lower jawbone is most effective when the effect is maximized by gradually increasing the amount of  protrusion to find the most protrusive jaw position which can be tolerated (a process called titration).  As a result, most new jaw protrusion appliances are patient adjustable.  

However there are problems with jaw protrusion as a single treatment.  The extreme jaw protrusion used to try and create sufficient airway flow can cause bite disruption and other dental problems.  In addition, even extreme jaw protrusion is not able to provide adequate relief for most OSA patients.  Its success rate in reducing AHI to less than 10 is about 65%, but its success rate in reducing AHI to less than 5 is only 42%.  One reason for this limited effectiveness is that, although the most common location of obstruction is retro-palatal, jaw protrusion is more effective in the retro-glossal area.  Another reason is that, since the jawbone and the tongue are only attached by muscles, which lose tonus during sleep, even extreme jaw protrusion can’t always prevent the tongue from falling back into the pharynx - it just has a little further to fall before it can obstruct the pharyngeal airway.  Jaw protrusion appliances can even make the OSA worse by forcing the tongue to acquire a retrusive posture to avoid the hardware at the front of the palate.  This mechanism was demonstrated experimentally in growing monkeys after cementing a block of acrylic to the front of their palates caused their tongues to relocate downward and backward and in turn caused them to grow excessively loD also produces an increased AHI in some patients.  

Tongue Rear Depression was recently introduced in the form of a Full Breath Solution (FBS) appliance, which employs a rigid transpalatal bar to support a smooth tail-like bulb that holds down the back of the tongue and thereby prevents it from contacting the soft palate. In the first and still the only published study of posterior tongue depression, the FBS appliance was also about as effective as titrated jaw protrusion appliances.  However tongue rear depression in the FBS appliance can only be adjusted (titrated) by a dentist, and, even if well titrated by repeated visits to the dentist, it still only functions in the retro-palatal area.  Thus tongue rear depression as a single therapy also has only limited potential.

Combining lower jawbone protrusion, tongue protrusion, and tongue rear depression can increase the effectiveness and tolerability of each because the anatomical effects of these three modalities are synergistic .  The lower jawbone provides the base of operation for the tongue, so holding the lower jawbone forward helps hold the tongue forward, and holding the tongue forward helps hold the lower jawbone forward.  A barrier behind the rear of the tongue helps hold the body of the tongue forward, and protruding the tongue makes its rear portion more accessible for tongue depressing mechanics and less prone to collapsing into the pharynx or contacting the soft palate.  At the same time, discomfort may be diminished by combining the three modalities, because their complementary nature preserves rather than further limits functional spaces for soft tissues in the area.  For example, holding the lower jawbone in protrusion creates more space for the tongue to rest in a protrusive position.

An even more compelling reason for combining all three oral appliance treatment modalities is that it can result in multi-level treatment which protects the whole pharyngeal airway and thus provides a much greater level of effectiveness than possible in previous oral appliances.  For that reason, we have combined the three modalities in the first multi-level oral appliance (ML-OA) seen below.

Tongue holding in the ML-OA is accomplished by a novel tongue holding device (THD) which is entirely made of dental acrylic, so it can be easily added to almost any OA, and includes a resiliently suspended upper tongue gripping surface which provides an ideal platform for applying tongue rear depression. The THD prevents retrusion of the tongue by  gently squeezing it between upper and lower tongue gripping surfaces, each containing thousands of miniature forward-slanted bristles which act like directional velcro. The 4,000 bristles on the upper tongue gripping surface are sized to fit between the filiform papillae which cover the top of the front of the tongue.  The 11,000 miniature bristles on the lower tongue gripping surface engage the mucous membrane on the underside of the tongue like a bed of nails.  The tongue can easily slide into the space between the tongue gripping surfaces, but it cannot be pulled back out of that space (shown below right) without opening the mouth widely enough to activate the tongue release mechanism.

As seen below, wide opening releases the tongue because the force compressing the tongue is provided by a trans-palatal orthodontic elastic which pushes the upper tongue gripping surface down into the top surface of the tongue only until the lower jawbone and tongue drop down far enough to bring the middle of the elastic, attached to the upper tongue gripping surface, into the same horizontal plane as the ends of the elastic. At that point compression from the elastic stops and any further opening separates the tongue from the tongue gripping surfaces.  A single orthodontic elastic provides sufficient compression to prevent the patient from being able to remove the tongue from the grasp of the tongue gripping surfaces without first opening wide.

RESILIENT SUSPENSION OF TONGUE GRIPPING SURFACES

Preliminary testing of the THD device was performed at the request of the FDA after Dr. Summer sent them a sample of the first generation device.  In this study of eleven subjects, the new tongue protrusion device was shown to be safe and well tolerated by patients.  

Jaw protrusion in the ML-OA is produced by mounting the THD on a micro-adjustable telescopic jaw protrusion appliance. Telescopic jaw protrusion has been used successfully in OSA patients for decades, and the location of the telescopic hardware on the outside surfaces of the back teeth makes telescopic jaw protrusion especially compatible with tongue protrusion. However, the only widely used telescopic jaw protrusion appliance, the Herbst appliance, was designed a half century ago for orthodontic bite jumping in children, and it is unnecessarily bulky and restrictive for adults with OSA. To solve that problem, the ML-OA uses telescopic components with a lower profile for more comfort, free range of motion laterally for continued TMJ health, and micro-adjustability over a range of ½” without tools.  Flat rods and tubes better fit the buccal vestibule (the space between the teeth and the cheeks) and prevent unwanted rotation of the parts when they are engaged. After sliding the rod out of the long tube, the double tubing assembly can be rotated one turn to shift it .014” forward or backward on the threaded metal hook which attaches it to the metal loop at the back of the upper dental appliance, and then the rod and long tube can be re-engaged to lock in the adjustment.

Tongue rear depression in the ML-OA is produced by an adjustable arm fixed to the back of the upper tongue gripping surface. This surface is an ideal platform for applying forces that depress the rear of the tongue; because it already extends to the rear of the tongue, its resilient bias allows it to move with the tongue during swallowing when there is no airway flow and therefore no need to maintain the tongue rear depression, and there is considerable space available for hardware beneath the underside of the hard palate.

Safety in the ML-OA is assured by covering all the teeth of both arches to maintain dental stability, telescopic components which can be precisely adjusted by the patient to quell any TMJ disorder symptoms which arise, and the use of a small number of interconnected parts to mitigate the danger of aspirating a part if anything breaks.  The full coverage upper and lower dental bases act as retainers to prevent unwanted tooth movement, which is one of the recognized dangers of jaw protrusion appliances. The ability to easily adjust the length of each telescopic assembly individually without tools allows patients who begin to experience TMJ disorder symptoms to immediately “walk back” the telescopic assembly on the affected side until comfort is achieved.  All the mechanical features are connected so that, if any breakage occurs, no single part can separate from the others.  For example, the enlarged head of the connecting arm in the tongue rear depressor prevents the possibility of turning the plastic hemispheres far enough to disengage the connecting arm from the bracket, the telescopic components of each side are connected by a continuous wire, and the orthodontic elastic which pushes the upper tongue gripping surface down into the tongue engages tapered slots in the cap of the acrylic tubing of the tongue rear depressor so that breakage of the elastic would not result in a piece being released.

Titration of each of the three modalities in the ML-OA can be performed separately so each patient can gradually customize his or her ML-OA to suit personal needs.  For example, some people with TMJ problems may have to minimize jaw protrusion, while people who gag easily may have to minimize tongue rear depression. Ideally, the titration of each modality can be used together with home monitoring devices which assess the severity of the OSA so that effectiveness as well as comfort can be maximized by adjusting each modality.

Severe OSA is such a danger that it should be treated immediately with the most effective means available - currently CPAP.  In severe OSA, the ML-OA may be used together with CPAP in order to reduce the pressures required to keep the airway inflated and thereby make the mask more comfortable to wear.

Once you've gotten used to your ML-OA, a follow-up sleep study should be performed to find out if it is effective.  We’ll send you home with home monitoring equipment which will be used by a sleep expert to analyze your sleep.  If you are still having OSA with the appliance, you need to either further titrate the treatment modalities in the ML-OA or change to CPAP.