Multilevel Oral Appliance Treatment for Obstructive Sleep Apnea
SUMMARY
Obstructive sleep apnea (OSA) occurs when the pharyngeal airway gets plugged by the tongue base; sometimes with soft tissues such as the distal end of the soft palate filling in the space between the tongue base and the pharyngeal wall to complete the seal that functions as the stopper in the nasopharynx; and sometimes with the epiglottis functioning as the stopper in the hypopharynx. Because the obstruction usually occurs at multiple levels of the pharynx, surgery is only predictably effective if it is multi-level. CPAP is usually effective, because it prevents the negative pressure during inspiration from sucking the tongue back into the pharynx, and ballooning out the pharynx makes it too large to get obstructed at any level above the epiglottis; but compliance with CPAP is poor, and it is likely to interfere with glymphatic drainage. Mandibular advancement is more tolerable than CPAP; but it's not always effective, because the mandible is only loosely attached to the tongue. Now ineffective mandibular advancement appliances can be amended with easily tolerated mechanical devices that directly control the tongue and the soft palate. In dentate patients, the first stage of treatment includes moderate mandibular advancement and a soft palate elevator, the second stage includes "pinning" the tongue against the advanced mandible, and the third stage includes adding tongue base titraters to the sides of the tongue holding device to gradually pry the tongue base off the pharyngeal wall. In denture wearers, tongue holding is especially effective, because the tongue gripping surfaces can extend all the way out to the cheeks, and the light steady pressure on the denture base plates from the cushioning of the tongue keeps the denture base plates comfortably seated. However, any advancement would apply pressure to the edentulous ridges, therefore the tongue is simply held against the upper denture base plate to prevent it from dropping back into the pharynx. The FDA clinical study in denture patients with untreated obstructive sleep apnea will run from April 2024 until April 2025. The combination of soft tissue controls and mandibular advancement could make oral appliances effective enough to become a first line treatment for OSA.
PATHOPHYSIOLOGY - OSA has complex anatomic, physiologic, and sensorimotor aspects; but the obstruction event at its core is choking on the tongue base and/or epiglottis - the only pharyngeal structures with the physical features necessary to form a stopper capable of plugging the airway. In the oropharynx, the tongue base can directly contact the pharyngeal wall to plug the airway. In the nasopharynx, loose soft tissues can fill in the narrow gap between the tongue base and the pharyngeal wall like a gasket. In the hypopharynx, the weight of the tongue base can close the epiglottis like closing a trap door (floppy epiglottis), which may not respond to CPAP.
Some researchers blame OSA on “collapse” of the pharyngeal walls, and they cite the model of a Starling resistor, in which the rate of flow through a collapsible tube within a pressurized chamber depends on the pressure in the chamber; and the flow through the tube stops if the pressure in the chamber is greater than the pressure in the tube. However, in this case, the pressure in the chamber is the weight of the soft tissues surrounding the pharynx, which is much less than the negative pressure produced by a diaphragm desperately trying to inhale. Endoscopic viewing make some obstructions appear concentric, with the airway surrounded by a circle of tissues that seems to keep becoming smaller until the airway flow stops completely; but loose pharyngeal tissues cannot just tighten around the airway like a noose, because plugging the airway requires a stopper. People don't choke on loose tissues, they choke on a piece of meat. The "collapse" that occurs when supplied air pressure drops below a threshold level is the soft tissues getting sucked into the narrow gap between the tongue base and the pharyngeal wall like a gasket.
Other researchers blame OSA on an inadequate neuromuscular arousal mechanism - commonly described as the muscles relaxing too much during sleep. The patency of the unsupported portion of the pharyngeal airway is maintained by the tonus of the pharyngeal dilator muscles, which increases as much as necessary during inspiration. Experimental airway obstruction in monkeys causes the genioglossus to pulse in synchrony with inspiration.1 Similarly, airway obstruction in humans triggers a rapid increase in tonus of the pharyngeal dilator muscles (loop gain) until the arousal threshold is reached and breathing is restored. Researchers have found that some people with high loop gain over-react, which destabilizes the ventilatory system, leads to more disturbances, and prevents the return of normal breathing; and those researchers have found medications that can prevent such destabilization by reducing loop gain. Researchers have also found that some people with low arousal thresholds have their sleep repeatedly disturbed by events that are not associated with desaturation, suggesting that a portion of their limbic system may have become sensitized to partial obstructions of the pharynx and then over-reacts, much like a pain pathway that has undergone central sensitization; and they have found medications that can increase arousal thresholds to minimize their sleep disturbances. While medications that alter the neuromuscular response to obstruction may be useful in managing some OSA patients, an inadequate neuromuscular response cannot be considered the cause of the problem, because muscles normally relax during sleep.
IMAGING - has found the location of the obstruction too variable to provide a basis for targeted treatment.2 Studies using drug induced sleep videoendoscopy (DISE) have found that, when all muscle tonus is eliminated, the obstruction occurs most frequently in the velum (nasopharynx), but it also occurs frequently in the oropharynx, behind the tongue, and at the epiglottis. It can even seesaw back and forth between these locations at different times.
MEDICAL TREATMENT - Minor surgeries include genioglossus advancement, suspending the tongue base along with the hyoid bone (hyo-mandibular suspension) from a suture tethered to a bone screw in the front of the mandible,3-4 implanting an electrical stimulator in the hypoglossal nerve to dilate the pharynx by activating the genioglossus and geniohyoid muscles,5 and UPPP to cut off the distal end of the soft palate or barbed pharyngoplasty to also reposition it; but it's difficult to predict which patients are likely to respond. Predictable success surgically requires multi-level treatment, usually involving bone reconstruction, such as maxillo-mandibular advancement; but even such an extensive structural correction only brings AHI to under 5 in 43% of patients.6 Also, the advancement of the jawbones can wane over time if not accompanied by a supportive change in the activity of the jaw muscles.
Most OSA patients are treated with CPAP, because it is usually effective in those who can tolerate it; but compliance is poor. In addition, continuous positive pressure is bound to inhibit the intermittent negative pressure that powers the nightly drainage of cerebrospinal fluid from the cranium through glymphatic circulation.7-12
ORAL APPLIANCES - are mainly used just to advance the mandible, which is only attached to the tongue by muscles, which naturally lose tonus during sleep. As a result, even extreme mandibular advancement cannot prevent the tongue base from falling back into the airway - it just has a little further to fall; and mandibular advancement only solves the problem for about half of the patients treated, as shown by a remarkable similarity of results in hundreds of studies. Attempts to identify anatomical features that indicate which patients are likely to respond well to mandibular advancement have been generally unsuccessful, so the high failure rate makes mandibular advancement appliances a hard sell.
There are a few oral appliances that attempt to control some of the soft tissues involved in the obstruction; but, as solo treatments, they have not been very effective. The rubber tongue holding appliances (Tongue Stabilizing Device, Tongue Retaining Device, and Good Morning Snore Solution) employ a silicone rubber squeeze bulb that uses suction to grasp the tongue tip and hold it out in front of the lips, and they can be used in denture wearers; but the tongue tip is far from the tongue base where the choking occurs, so the treatment is only about as effective as mandibular advancement, and the extreme tongue advancement it requires is difficult for most people to tolerate.13 Soft palate lifters raise the whole soft palate, which can move it away from an obstruction located inferiorly, but their unnecessary force is also difficult for most people to tolerate. The Full Breath Solution Appliance’s "posterior tongue restrainer" pushes downward on the middle of the tongue base, which can move it away from an obstruction located superiorly, but into an obstruction located inferiorly; and the device has limited posterior reach, because it contacts the tongue base in its midline, where the main gag reflexes are located.
Combining these oral appliance treatment modalities (advancing the mandible, advancing the tongue, elevating the soft palate, and depressing the tongue base) has the potential to make them all more effective without making them less tolerable, because they are mutually supportive interventions. The mandible functions as the bony support for the tongue (and hyoid), therefore advancing the tongue and mandible together is easier than advancing either one alone. Advancing the body of the tongue makes its base more accessible for mechanisms which push that critical area down and away from an obstructive contact with the distal end of the soft palate, which is most effective when combined with mechanisms that elevate the middle of the soft palate to draw its distal end up and forward away from the tongue base. Also, mandibular advancement has synergistic effects on all these modalities by repositioning the origins of the suprahyoid and genioglossus muscles anteriorly, stretching the palatoglossus and palatopharyngeal muscles, repositioning the pharyngeal arches laterally, and shifting the hyoid bone anteriorly and superiorly (although there is wide variation in this response).
Previously it was not possible to combine these oral appliance treatment modalities, because the technologies and materials they require are incompatible. For example, the silicone rubber used for the tongue holding bulbs does not attach to acrylic; and the Full Breath Solution and Soft Palate Lifter are designed as single arch appliances.
Now new technologies enable combining the oral appliance treatment modalities as needed by adding improved and compatible versions of them, one at a time, to a mandibular advancement appliance or set of denture baseplates until the OSA is eliminated. The suggested clinical treatment sequence is described below.
DENTATE PATIENTS
Treatment for dentate patients with a healthy dentition involves three stages.
STAGE 1 – includes moderate mandibular advancement and elevation of the soft palate midline; because both modalities have very little downside, and the short-term effectiveness of the two treatments combined is better than the short-term effectiveness of either one alone. Elevating the soft palate midline "tents" that flap-like structure and thereby draws its distal end (the gasket) antero-superiorly away from the obstruction in the nasopharynx to provide short-term clearance of the airway passage, while mandibular advancement changes the functional environment that led to the obstruction. Simply elevating the soft palate to remove the gasket without also making changes in the functional environment invites relapse due to reproduction of a gasket by other loose soft tissues, and simply changing the functional environment by slightly advancing the mandible may not produce enough change to restore airway flow without removing the gasket.
MANDIBULAR ADVANCEMENT - can be performed with a variety of currently available oral appliances. Dorsal fin, EMA, and Herbst appliances that are made of acrylic (rather than nylon) can also be used for the subsequent stages of multi-level treatment. Monobloc and TAP appliances cannot be used for subsequent stages of multi-level treatment, because they limit mouth opening.
Herbst appliances have the longest history of effective treatment for OSA and the best control of mandibular position; but the bolted connectors of previous Herbst appliances are unnecessarily bulky, and they restrict lateral mandibular movements, which leads to frequent breakage. In addition, their downward vector of push on the mandible can open the lips and lead to habitual mouth breathing. To solve those problems, Dr. Summer's high push Herbst appliance has a lower profile, freely moveable connectors that cannot bind or restrict lateral movements, and a more upwardly directed vector of force on the mandible. The new high push Herbst appliance is almost unbreakable, allows unlimited lateral range of movement (it cannot bind), and can be adjusted on each side in 1/3 mm increments by sliding the rod out of the tube, rotating the tubing assembly on the externally threaded connector arm (which connects it to the upper base appliance), and re-inserting the rod into the tube to lock in the adjustment.
COMPONENTS SEPARATED COMPONENTS ASSEMBLED
INTERNALLY THREADED TUBING FOR ADJUSTMENTS
BEFORE ADVANCING AFTER ADVANCING
Palate expansion can be included with a high push Herbst appliance by using removeable offset connectors. The upper member of the appliance (the palatal expander with embedded anchors) can be worn by itself all day. Then, every night before bed, the patient can hook on the offset connectors and attached tubing assemblies attached to the lower member of the appliance. Some dexterity is required, but most people acquire the needed skills rapidly. After the expansion, the components will no longer need to be separated, and the offset connectors can be crimped in place for use at night.
There is good evidence that titrating the mandibular advancement to a position of maximal tolerable benefit improves effectiveness, therefore mandibular advancement devices should be adjustable. For people with a history of TMJ problems, treatment should begin with almost no advancement. To maintain support anteriorly for the mandible as it advances, the bite platform should extend anteriorly well beyond the labial surfaces of the upper anterior teeth, as shown in the photos below; because loss of anterior support when the mandibular anterior teeth advance past the bite platform greatly increases the forces applied to the posterior connectors and can thereby lead to breakage of any Herbst appliance.
We rarely employ extreme mandibular advancement, because holding the tongue against a slightly advanced mandible is likely to be a safer and more effective way to shift the tongue base away from the pharyngeal wall. In addition, the beneficial effects of extreme mandibular advancement on the structure of the airway diminish over time, because the forces that advance the mandible will be gradually accommodated by osseous remodeling to reduce the forces on the tissues.
ELEVATING THE SOFT PALATE MIDLINE – “tents” that flexible flap-like structure in order to draw its distal end antero-superiorly out of the narrow gap between the tongue base and the pharyngeal wall to pull the gasket away from the stopper. The "tenting" action requires so little force that patients are unaware of its presence, and the arm's flexibility enables it to easily accommodate the functional movements of the soft palate during swallowing, when breathing stops anyway. The soft silicone rubber bulb in the center of the soft palate is easily tolerated, because there are no gag reflexes there. The gag reflexes in the soft palate are all located in its distal end.
The elevation of the center of the soft palate can be seen in the X-rays below, where the black arrows mark the top of the soft palate and the thin white line in the right side X-ray is the metal arm of the soft palate elevator.
BEFORE INSERTING THE SOFT PALATE ELEVATOR AFTER INSERTING THE SOFT PALATE ELEVATOR
Elevating the center of the soft palate also tightens the nearby soft tissues, as was demonstrated below in a patient who had previously undergone UPPP, after horizontal lines were stamped on the pharyngeal wall with gentian violet. Inserting the device caused the straight purple lines on the left side photo to become curved on the right side photo. Such tensioning of the pharyngeal wall makes the soft tissues there less easily sucked into the pharynx or vibrating during snoring.
Whatever type of mandibular advancement appliance is used for stage one treatment, its effectiveness should be tested after titration. Even a 50% reduction in AHI can feel like successful treatment to the patient, but such limited improvements often do not last, because the remaining incidents keep stretching out the pharyngeal tissues until they reform a gasket that once again obstructs the airway. Multi-night home sleep testing eliminates any first night effect and the normal night-to-night variability in results.14
STAGE 2 – ADVANCING THE TONGUE BODY AND BASE
The next stage of multi-level treatment for dentate patients is to "pin" the tongue against the advanced mandible between specialized upper and lower tongue gripping surfaces that each contain thousands of forward-slanted acrylic pin points (tongue velcro).
The lower tongue gripping surface is a sheet of up to 10,000 (depending on size) accupuncture needle sized points (shown left) in a carpet of "tongue velcro" that has been shaped to fit the patient and then bonded to the lower base appliance, as shown below right. The tiny points grip the sensitive tissues on the underside of the tongue like a non-skid surface.
STEEL MODEL FOR MOLD FOR LOWER TONGUE GRIPPING SURFACE LOWER BASE APPLIANCE
The 4,000 points on the upper tongue gripping surface are sized to fit between the filiform papillae that cover the dorsal surface (top) of the tongue, as shown below left. The upper tongue gripping surface is shown below right on an upper base appliance.
UPPER TONGUE GRIPPING POINTS UPPER TONGUE GRIPPING SURFACE ON UPPER BASE APPLIANCE
. 
FILIFORM PAPILLAE
For dentate patients, the upper tongue gripping surface is spring-mounted on the upper base appliance to maintain its grip during partial opening and other submaximal mandibular movements, such as nocturnal bruxism. In the illustration below, the top figure shows the mouth fully closed and the tongue gripped, the middle figure shows the tongue still gripped during partial opening, and the bottom figure shows the tongue released during wide opening.
FULLY CLOSED
FULLY OPEN
The tongue gripping surfaces are added together with bite stops, small flat stable plateaus of acrylic located over the terminal molars where they absorb all bite forces before those forces can hurt the tongue. In the photo below, the upper bite stops are made of yellow acrylic, and the lower bite stops are made of green acrylic.
EDENTULOUS (DENTURE) PATIENTS - Generally cannot tolerate mandibular advancement; therefore treatment for OSA in this population involves just "pinning" the tongue against an upper denture base plate to prevent it from dropping back into the pharynx, and then adding a soft palate elevator if necessary.
Tongue gripping is especially effective in edentulous patients, because the tongue gripping surfaces can extend almost all the way to the cheeks, and the cushioning force from light compression of the tongue keeps the base plates fully seated on the edentulous ridges. However, the goal of treatment is not advancement, which would apply pressure to the soft tissues. The goal of treatment is just to hold the tongue against the upper denture base plate to prevent it from dropping back into the pharynx.
In most edentulous patients, resilient mounting of one of the tongue gripping surfaces to produce a cushioned grip is unnecessary, because the increase in vertical dimension that results from wearing the denture base plates together with the tongue gripping surfaces produces enough passive stretch of the jaw closing muscles to hold the tongue. The amount of passive stretch that the appliance produces depends on its vertical dimension, which can be easily controlled.
If a cushioned grip is needed to prevent tongue release during submaximal opening, the lower tongue gripping surface, (rather than the upper tongue gripping surface as in dentate patients), is "spring loaded". It is attached to the lower denture base plate by a polyester mesh anterior tether and a pair of 3/8” long orthodontic elastics on each side that connect a cleat on the posterior portion of the lingual flange of the lower tongue gripping surface with a ball clasp on the buccal side of the posterior portion of the lower denture base plate. The elastics bias the lower tongue gripping surface continually upward into the underside of the tongue. The bias is maintained until the cleats reach the same plane as the bite table. Any further opening releases the tongue. The release point is controlled by the location of the cleats on the lingual flanges.
ELASTICS BOTTOM ENDS ON CLEATS TOP ENDS ON BALL CLASPS ELASTICS SUSPEND LOWER TONGUE GRIPPING SURFACE
If the lower denture base plate is too unstable to function as a base from which the lower tongue gripping surface can be pushed upward into the underside of the tongue, both the upper and lower tongue gripping surfaces are bonded to the upper and lower denture base plates, and the base plates are connected by interarch elastics attached to buttons, cleats, or ball clasps on their buccal walls. Then, if the mandible drops out of the unstable lower denture base plate, the tongue stays gripped, and the airway remains protected.
THE FINAL STAGE - TONGUE BASE TITRATERS
In both dentate and edentulous patients, if further treatment is needed, tongue base titraters are added to the upper tongue gripping surface of the tongue holding device to gradually pry the tongue base off the pharyngeal wall in progressive 1.3 mm increments as the patient gets used to them. The upper tongue gripping surface, which has been stabilized by gripping the tongue body and bracing the mandible against the bite stops, provides good anchorage from which to titrate the position of the tongue base. The tongue base titraters have the flexibility to accommodate the natural movements of the tongue base during swallowing, when breathing stops anyway.
BEFORE SHIFT AFTER SHIFT
The tongue base titraters can depress the tongue base in a range of directions that can be varied by up to 25 degrees, as illustrated below.
BEFORE ADJUSTMENT ADJUSTED DOWN-AND-BACK ADJUSTED DOWN-AND-FORWARD
Shifting the tongue base titraters down-and-back can move the tongue base away from an obstruction in the oropharynx, as shown below in X-rays of a patinet's tongue painted with a radiopaque paste before (top) and after (middle) inserting a tongue control device; and then after (bottom) using the tongue base titraters to shift the tongue base further down-and-back. The small white radiopaque puddle in the foramen cecum in the top X-ray has been replaced by a larger white V shape where the tongue has curled around the end of the upper tongue gripping surface in the middle X-ray. However, in the middle X-ray, the airway is still restricted in the lower oropharynx and upper hypopharynx. In the bottom X-ray, the tongue base titraters have shifted the tail segments of the device and thereby also the tongue base further down-and-back, which has shifted the white V-shaped area marking the end of the upper tongue gripping surface and the end of the wire framework of the tongue base titrater in the same direction and has further increased the sagittal width of the airway space, seen between the arrows.
HYPOPHARYNX
A hypopharyngeal obstruction is treated by using the tongue base titraters to first shift the tail segments down-and-back to get them as far as possible behind the tongue base (below left), and then rotate them forward (below right) in two steps to pry the tongue base anteriorly off the lower pharyngeal wall and away from the epiglottis. The photos below show this rotation of the tail segment adjusters from down-and-back to down-and-forward. The green acrylic build-ups over the third molars are the bite stops.
TAIL SEGMENTS DOWN AND BACK TAIL SEGMENTS DOWN AND FORWARD
The photos below show one tail segment rotated down-and-back and the other rotated down-and-forward.
CLINICAL CONSIDERATIONS
GROWTH EFFECTS
While short-term treatment success requires simply reopening the airway, long-term treatment success also requires directing the slow facial growth of adulthood horizontally to gradually increase the size of the airway passage and decrease resistance to airway flow, just as muscles naturally become weaker with age, in order to maintain resting airway flow. Many people have an adult facial growth pattern that slowly but continuously rotates the mandible down and back into the space needed for the pharyngeal airway, thereby increasing resistance to airway flow. This growth can be redirected horizontally by expanding the upper jawbone and advancing the lower jawbone.
VERTICAL DIMENSION, the height of an oral appliance, affects both its effectiveness and the direction in which it influences subsequent facial growth; but the effect of increased vertical dimension on the patency of the airway varies greatly with facial form. For most patients with a normal facial form, their appliance should be no taller than necessary to ensure its structural integrity. Appliances that are tall enough to engage the passive stretch of the jaw closing muscles can produce sustained compressive forces that can damage the dentition or the TMJs.
For patients with very strong jaw muscles and short anterior faces, especially in the presence of deep overbite, their mandibular advancement appliance should include a front flat bite plate (extending from canine to canine for stability) in order to lower nocturnal bruxism forces to prevent the jaw muscles from further reducing facial height and redirect them to gradually reduce the overbite that inhibits mandibular advancement. Including the canines in the front flat bite plate provides stability, while preventing contact between the posterior teeth reduces the forces used in nocturnal bruxism by about half.
For patients with very weak jaw muscles and long anterior faces (usually accompanied by difficulty maintaining a lip seal at rest), their jaw muscles may need to be stretched and rehabilitated before they can tolerate even a 2 mm increase in vertical dimension continuously for eight hours. Also, in these people, any reduction of the vertical dimension that can be achieved by selectively grinding down teeth will make appliance wear more comfortable.
MOUTH BREATHING - is detrimental to health. It prevents the nose from moistening, filtering, and warming the air before it hits the throat - making mouth breathers prone to upper respiratory problems. It prevents the release from the paranasal sinuses into the lungs of nitric oxide, which has antibacterial properties, a vasodilating effect, and a role in ensuring good endothelial health. It also impairs the effectiveness of respiration, because the nose is so vascular that it acts like a little lung. In one study, volunteers who wore nose clips to force mouth breathing for a couple of hours developed lowered arterial oxygen levels.
Obligate mouth breathers have nasal cavities that do not allow adequate resting nasal airway flow, and they must keep their lips slightly parted to maintain an oral airway passage. Many people with a nasal cavity that is barely large enough to allow adequate airway flow become obligate mouth breathers whenever a mild allergy or rhinitis causes nasal swelling that slightly reduces the cross-sectional diameter of the nasal cavity. In obligate mouth breathers, palate expansion can be employed at any age to widen the nasal airway and raise tongue posture.16 The expansive force triggers adaptive remodeling throughout the midface. The resulting increase in nasal airway size can be maintained post-treatment by wearing a retainer nightly and stabilizing the bite to function as a daytime retainer. Changing from mouth breathing to nose breathing can improve many sleep parameters including respiration, but it rarely relieves OSA, because the expansion occurs so far from the obstruction.17
Habitual mouth breathers use an oral airway despite having an adequate nasal airway. Frequently the habit arises from an open-mouth resting posture due to a framework of bones and teeth at the front of the face that has grown too long to be comfortably covered by the drape of relaxed soft tissues hanging down from the front of the cranium, causing the lips to part when the facial muscles are at rest. During swallowing, the perioral muscles show visible strain trying to form a lip seal. During sleep, the parted lips create an oral airway passage that offers less resistance than the nasal airway passage, and it can become the habitual route for breathing.
Mouth breathing then sustains itself due to its influence on facial growth, because it lowers mandibular posture, and postural forces provide the light steady forces that shape bones. The lowered mandibular posture makes the face grow vertically long and narrow, which prevents the nasal cavity from growing wide enough to create an adequate nasal airway passage, which leads to more mouth breathing. Monkeys forced to mouth breathe by experimentally plugging their nostrils grew long narrow faces, because their mandibles acquired a lowered posture to maintain an oral airway. Humans forced to mouth breathe by a restricted nasal airway grow long narrow retrusive faces, because lowering the human mandible also rotates it down and back.
Habitual mouth breathing can be triggered by wearing an oral appliance that increases the vertical dimension far enough to part the lips, and it can usually be eliminated in these cases by almost any way of holding the mouth closed and restoring the lip seal; including chin straps, medical tape (mouth taping), thick foam cervical collars, or interarch orthodontic elastics attached to orthodontic ball clasps, cleats, or buttons on upper and lower appliances that fit on the teeth tightly enough to resist being pulled off by the weight of the mandible.
NOCTURNAL BRUXISM - is a side effect of normal sleep, when the brain sends motor signals to the jaw muscles, usually during arousals that mark a transition to a lighter sleep stage; and it reflects no particular bite condition.18 It cannot be caused by bite problems or eliminated by bite treatment,19-20 and it is not correlated with TMJ disorders.21-27 In some people, nocturnal bruxism may be an adaptive response that prevents OSA by bracing the mandible to prevent it from slipping back into the pharynx. In other people, nocturnal bruxism can be a result of OSA, because the obstructions trigger sympathetic activity to stimulate bodily movement to restore breathing, and bruxism is one of those movements. Therefore oral appliances should be designed to withstand bruxism in patients treated for OSA.
TMJ DISORDERS - usually resolve by middle age when OSA begins, so they are rarely significant barriers to gradual mandibular advancement or other oral appliance treatments for OSA. The bite destabilization that results from mandibular advancement can cause increased jaw muscle tonus, just as instability in any joint reflexively increases tonus in the muscles crossing that joint, because the bite is wired like a joint between the jawbones. In such cases, the bite can be easily restabilized by extending it anteriorly, as described below.
BITE CHANGES - The posterior open bites that frequently result from mandibular advancement can reduce chewing effectiveness and confound dentists, so they are treated as an adverse side effect that can even warrant discontinuing the treatment; but they can be easily managed in a way that restores chewing ability and increases the long-term effectiveness of the treatment. The posterior open bites that commonly result from mandibular advancement are often blamed on pathologies such as contracture of the superior lateral pterygoid muscles or inflammation in the TMJs; but the cause is not pathological. Advancement of the mandibular corpus throughout life is the natural pattern of adult human facial growth. In our ancestors, it helped compensate for the tooth wear that they also experienced throughout life; and it was stimulated by bite forces, so that individuals who chewed extensively and experienced more tooth wear also underwent more jawbone growth to compensate for that wear.26-27 Today, advancement of the mandibular corpus may be accelerated by the bite forces produced by an oral appliance that is tall enough to create passive stretch of the jaw closing muscles or by the distraction osteogenesis created by holding the mandible down and forward all night.
The loss of the previous central bite position has been difficult for dentists to accept, because it tramples on a deeply held belief system in dentistry that the center of all biting activity and the reference point for all clinical dental work should be the rearmost mandibular position. To prevent loss of this reference point, many dentists who use mandibular advancement appliances today have their patients chew on hard gum or small wedges (morning occlusal guides) every morning to create an "occlusal return" or "reprogramming" process that forces the mandible back towards its previous central bite position. Such forced mandibular retrusion can trigger regressive remodeling that enables the condyles to seat more posteriorly than they otherwise would, but simply adjusting the bite forward is much easier than trying to reverse growth that has already occurred or prevent further growth in a functional environment that stimulates it.
In addition, shifting the bite anteriorly can facilitate long-term treatment, because it shifts the mandibular postural position anteriorly, which facilitates airway passage in upright posture and can also reduce dependency on the appliance by preventing the mandible from dropping all the way back and causing sleep to deteriorate to pre-treatment levels right away if the mandibular advancement appliance is not worn for a short time, such as during a nap. In the OSA population, esthetics is rarely a barrier to mandibular advancement; and most peopleonly need enough bite stability to chew comfortably, not a perfectly located and precisely defined centric position.
THICKNESS - The unnecessary bulk, especially in the anterior regions, of nearly all current oral appliances can exacerbate airway problems by distalizing tongue posture. A study of growing monkeys showed that a block of acrylic cemented in their palates lowered their tongue and mandibular posture to avoid the block, which redirected facial growth vertically, causing them to grow long narrow faces. Humans have a shorter ramus and a more inferior center of rotation, therefore lowering tongue and mandibular posture also rotates the front of the mandible (the corpus containing the teeth) down and back into the pharyngeal airway space. To avoid impinging on tongue posture, all upper oral appliances should include a space hollowed out to fit the tongue tip (tongue tip hollow) just beneath the anterior bite table at the front of the palate behind the maxillary incisors, as shown below.
TIGHTNESS - Nearly all acrylic dental appliances force the upper teeth inward (palatally) due to the shrinkage of acrylic, especially on the labial wall of the anterior region at the center of that shrinkage. In a healthy dentition at rest, each tooth is suspended in the middle of a dynamically hyperactive socket; which contains so many blood vessels that it exhibits an individual arterial pulse and such an extensive network of sensory nerves that it occupies an oversize portion of the brain. When the teeth remain in the middle of these sockets all night, the tissues lining the sockets remain passive. Displacement of a tooth from its rest position triggers a collection of adaptive responses designed to make the socket once again fit the tooth's rest position. One of those responses includes an increase in jaw muscle tonus, because noxious afferent input from any joint triggers increased tonus in the muscles which cross that joint, the periodontium is wired like a joint between the tooth roots and their sockets, and the jaw closing muscles cross that joint. As a result, pressure on the teeth automatically increases tonus in the jaw muscles; which can add to the jaw muscle tightness caused by increased central nervous system stress or an appliance with a vertical dimension that produces passive stretch of the jaw closing muscles.
Even if a dentist could obtain a perfectly accurate impression of the dentition in its resting state and fabricate an oral appliance which perfectly fit the model made on that impression, the tight fit would impair the functional circulation to the teeth and their supporting tissues by limiting their functional ranges of motion. From its rest position, each tooth should have a range of motion of about 1/4 mm vertically and bucco-lingually and about a tenth of that distance mesio-distally in the presence of adjacent teeth. The movement of the teeth throughout their ranges of motion enhances periodontal circulation during functional activities like chewing by flushing out blood with each compression and then allowing arterial circulation to replenish it with each rebound. An appliance that "hugs" a tooth restricts its range of motion and thereby also its functional circulation.
What assures compliance in appliance wear is not tightness that makes an appliance difficult to remove but comfort that makes the patients not want to remove it. An appliance only needs enough mechanical retention to resist the forces of gravity. It can fit around an undercut for retention; but, once fully seated, it should apply no pressure to teeth, leaving each tooth in its natural rest position and allowing at least a slight range of motion.
FOOTNOTES
1) Miller A, Vargervik K. Neural control of oral respiration in the rhesus monkey. P 133-156 in Muscle Adaptation in the Craniofacial Region. Carlson D and McNamara JA, eds. Monograph 8, Craniofacial Growth Series 1978.
2) Lee CH, Hong SL, Rhee CS, Kim SW, Kim JW. Analysis of upper airway obstruction by sleep videofluoroscopy in obstructive sleep apnea: a large population-based study. Laryngoscope. 2012 Jan;122(1):237-41.
3. Mickelson SA. Hyoid advancement to the mandible (hyo-mandibular advancement). Operative Techniques in Otolaryngology. 2012:23, 56-59.
4. Handler, E, Hamans E, Goldberg AN, Mickelson S. Tongue suspension: an evidence-based review and comparison to hypopharyngeal surgery for OSA. Laryngoscope, 2014; 124(1): 329-336.
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