Sleep Apnea
Instructions For Dentists
The new add-on airway components that control the tongue and elevate the soft palate can be attached to most oral appliances and denture base plates made of dental acrylic. They cannot be attached to oral appliances made of nylon or polymers other than acrylic, such as the Narval and Panthera appliances, and they cannot function properly in appliances that do not allow opening and closing, such as TAP, EMA, Silent Night, and monobloc appliances.
ADDING MANDIBULAR ADVANCEMENT HARDWARE TO EXISTING DUAL ARCH ORAL APPLIANCES
The high push Herbst hardware can be added to maxillary and mandibular oral appliances as long as the buccal walls have sufficient structural support for the retentive anchors. Some maxillary appliances such as aligners will need support added to the labial and buccal walls to resist the posteriorly directed forces applied to them by pushing the mandible anteriorly; and some mandibular appliances will need support added to the lingual surfaces, especially from canine to canine, to resist the anteriorly directed forces applied to them by being pushed anteriorly.
When bonding the anchors onto the appliances, the loops on the upper appliance are usually located just distal to the first molars, and the loops on the lower appliance are usually located just distal to the canines. However the positions of the anchors can be altered as needed. For example, if a lower first premolar is located buccally far beyond the canine, the loop of the lower anchor can usually be placed in the interproximal area distal to the first premolar instead of the canine. Similarly, if an upper first molar is displaced buccally, the loop of the upper anchor may be located just medial to the first molar. To determine the optimal locations for the anchor loops, the path for the telescopic components between upper and lower retentive anchor loops are visualized by looking at the appliances on mounted models. If the maxillary second molars are located very close to the mandibular canines in the construction bite, single tubes would have to be cut very short, and they may be difficult to handle and adjust without accidentally coming apart due to the rods sliding out of the tubes.
ADDING TONGUE HOLDING COMPONENTS TO EXISTING DUAL ARCH ORAL APPLIANCES
If titrated mandibular advancement fails to eliminate a patient’s OSA, the next step in multi-level treatment is to advance the tongue together with the mandible.
CHOOSE THE TARGET TREATMENT POSITION - The target treatment position has a mandibular and a tongue component. The mandibular component should have been established by titration of the mandibular advancement appliance. The tongue component is included by having the patient remove the titrated mandibular advancement appliance (usually after having worn it overnight or at least for as long as possible before the appointment) and then bite down lightly on the tongue tip. In this position, with the tongue tip between the incisors, inject a thick bodied bite registration material between the molars on both sides, slightly displacing any portions of the tongue that are resting between them. After that bite registration material sets, have the patient remove the tongue tip from between the anterior teeth while maintaining the occlusion on the bite registration material between the molars, and inject more bite registration material between the premolars and anterior teeth. The construction bite for use in determining the height of the occlusal stops will be obtained by mounting the models of the patient’s teeth in this bite and then opening the articulator an additional 1-2 mm to make room for the thickness of the lower tongue gripping surface over the lower incisors.
Only very rarely does the tongue need to be held so far forward in its target position that it violates the lip seal. The lip seal keeps the tongue tip moist, prevents drooling, and sometimes helps prevent mouth breathing; but violating the lip seal poses no significant health risk, especially compared to OSA. If the tongue needs to be protruded beyond the lip seal, the patient must be able to tolerate the increase in vertical dimension needed to hold a larger part of the tongue between the incisors and must be willing to deal with the drooling or dry mouth that can result from lack of a lip seal during sleep. The patient can protect the tongue tip from drying out with coconut oil.
In edentulous patients, there is much more variability in potential target tongue positions, and the one chosen determines the forces that will be placed on the denture. The tongue is a tangle of muscles that all have resting postures, and the farther the tongue is repositioned from its resting posture, the more force it will place on the denture. Any anterior positioning of the tongue in the target position requires an upper denture with a sound anterior alveolar ridge that can resist posteriorly directed forces. If the upper denture cannot resist the posteriorly directed forces needed to hold the tongue as far anteriorly as necessary, its resistance can be increased by incorporating reverse-pull headgear connected to the upper denture using low force elastics.
The vertical dimension of the new tongue holding device is also a big variable in edentulous patients. If the vertical dimension is too low, the tongue will tend to pull inferiorly on the upper denture and can unseat it. If the vertical dimension is excessive (tall), the passive stretch of the elevator muscles can produce too much pressure on the soft tissues. IThe upper tongue gripping surface is normally left flat in a transverse plane. However, if the vertical dimension is excessive and incorporating a large tongue threatens to increase it further, the flat front portion of the upper tongue gripping surface can be curved to fit the concavity of the hard palate. The tongue in its resting posture will immediately expand to fill the available space.
IMPRESSIONS
To take an impression of the tongue top when the tongue is in its target position, while the patient protrudes the tongue as far as possible for a few seconds, quickly inject fast set PVS bite registration material onto the fork shaped piece of polyester mesh (included in the kit) resting on the tongue and extending as far back as possible on the sides of the tongue where there are few gag reflexes, as shown below left. Then, as the patient begins to pull the tongue back toward a more comfortable position, keep injecting onto the tongue body. Finally ask the patient to bite lightly on the tongue tip in the target position while the material sets as shown below right, and close the lips around the tongue tip. The mesh fork allows the impression to be removed quickly if the patient begins to gag.
After cutting it sagitally, the tongue top impression can be placed on a model and used to judge the contours of the tongue in its target position, such as where it changes its orientation from horizontal to more vertical in the area beneath the soft palate. That information can then be used to adjust the shape of the upper tongue gripping surface in order to make it closely fit the tongue in its target position, which helps keep the tongue in its target position throughout the night.
To take an impression of the floor of the mouth with the tongue in its target treatment position, while the patient raises the tongue, inject a light body VPS into the floor of the mouth and up onto the lingual aspects of the lower teeth; then have the patient place the tongue in the target position and bite down lightly on it while the VPS sets. Placing the resulting impression on a model of the lower teeth can provide a guide for shaping the lower tongue gripping surface to ensure that it does not prevent the patient from being able to protrude the tongue into the target position.
ADDING A SOFT PALATE ELEVATOR
If you want to add a soft palate elevator to a maxillary appliance, the impression of the maxillary arch should include enough posterior landmarks to enable you to identify the midline of the soft palate, where the silicone rubber bulb should push upward. The antero-posterior location of the rubber ball is much less critical than its midline location, because it can still tent the soft palate whether it is located near the front or near the back of the soft palate. Soft palate tenting devices can be easily added to upper dentures, because elevating the soft palate rarely requires enough force to cause unseating of the posterior end of the denture.
SEND TO LAB WITH PRESCRIPTION
Include the oral appliance to be amended, the components to be added, and all necessary impressions.
CHECK THE AMENDED APPLIANCE WHEN IT RETURNS FROM THE LAB
If you had high push Herbst components added to a pair of upper and lower oral appliances, check to be sure that there is adequate space for the tubes between upper and lower anchors and the acrylic covering them. When the appliances are mounted on models fully closed in the construction bite, the tubes should not be pressed against the acrylic and should be free to move around a little from side to side, as felt with fingers. If the tubes are pinched against the acrylic, articulating paper placed under the tube while the articulator is closed and moved into excursions can identify the pinch point.
If you had a biased upper tongue gripping surface added to a dual arch mandibular advancement appliance, mount the newly amended appliance in the construction bite on an articulator and ensure that there is sufficient space (about 2 mm) for the upper tongue gripping surface to move up and down relative to the appliance to be sure the tongue will not be pinched when the patient bites down on the occlusal stops. From the anterior teeth to the first molars, there should be about 2 mm of space visible between the lower tongue gripping surface and the upper teeth or the seated upper tongue gripping surface. The sides of the patient’s tongue should be able to squeeze out into this space when the patient bites on the occlusal stops.
DELIVERING AN APPLIANCE WITH A TONGUE HOLDING DEVICE
Before the patient inserts the tongue, have the patient put in the appliance and bite down on the occlusal stops to ensure the appliance is fully seated with stable bilateral support. Then explain to the patient that, after inserting the tongue, it can be released immediately anytime just by opening the mouth wide. Finally have the patient insert the tongue by opening a little, pushing the tongue tip into the space between the anterior teeth, biting down forcefully again, and closing the lips around the tongue tip. After a minute for the tongue gripping surfaces to seat into the surface of the tongue, you can check their ability to hold the tongue against retrusion by verifying that the patient cannot pull the tongue back out of the tongue holding device without first opening widely enough to release the tongue. At this time, you should also check to see that the occlusal stops have adequate height by ensuring that the patient can bite down forcefully without causing pain or redness from excessive pressure on the tongue tip.
TROUBLESHOOTING AT DELIVERY
If the patient cannot tolerate the tongue holding device without gagging, the tail sections of the upper tongue gripping surface can be trimmed, especially medially where the gag reflexes are located.
If the patient reports pain at the back of the tongue when biting down forcefully, the contour of the upper tongue gripping surface is too steep, and it can be shallowed by holding it by its tether and dipping it in boiling water for 10 seconds before bending it with the fingers. If the patient can pull the tongue back out from between the tongue gripping surfaces without first opening wide, the curve of the upper tongue gripping surface is too flat, and it can be increased by bending it with boiling water.
If the patient reports pain at the front of the tongue when biting down forcefully, check to be sure that the front portion of the tongue gripping surface can seat fully below the occlusal plane of the maxillary anterior teeth and canines on the model. For example, in the photo below, the front of the upper tongue gripping surface is not adequately seated and could pinch at the canine area.
If the patient reports pinching of the sides of the tongue when biting down forcefully, check to make sure the sides of the upper tongue gripping surface fit entirely within the palatal borders of the trough prepared in the upper appliance and below the occlusal plane, leaving room for the sides of the tongue to squeeze out between the occlusal surfaces of the canines, premolars, and first molars. When the appliance is in the patient’s mouth, you should be able to push the suspended upper tongue gripping surface slightly further upward into its seat on the upper appliance using a finger. If there is no movement of the upper tongue gripping surface possible, the upper tongue gripping surface may need to be narrowed or the portion of the appliance covering the palatal surfaces of the premolars, canines, or anterior teeth may need thinning.
You can check the fit of the upper tongue gripping surface against the tongue in its target position by injecting light bodied regular set VPS directly onto the gripping side (the tongue velcro) of the upper tongue gripping surface, quickly inserting the appliance, and having the patient close with the tongue in the target position while the VPS sets. If the fit is good, the VPS should leave a thin uniform layer. Later the VPS can be easily removed from the tongue velcro in one piece using an explorer or any sharp instrument.
If the patient seems unable to protrude the tongue into the target position, either the lingual frenum is blocked in the midline just lingual to the mandibular incisors or the lingual flanges are too long to allow the floor of the mouth to rise with the tongue. In such cases, the barrier to tongue protrusion can be identified by injecting a light bodied VPS onto the lower tongue gripping surface while the appliance is in the mouth, and then having the patient protrude the tongue and move it a little side to side, like border molding a denture.
If the patient reports any pain in the soft palate or even any sensation there when inserting the appliance, the thin flat arm of the soft palate elevator can be easily bent with a three prong pliers or even just fingers. The position of the soft palate elevator can also be easily reset after using a rotary wire wheel to release the retentive barbs from the acrylic. To check the position of the soft palate elevator in the patient’s mouth, you can take an impression of the soft palate area with the soft palate elevator in place. Simply lubricate the silicone rubber ball of the soft palate elevator lightly with coconut oil or a similar lubricant that is safe for human consumption so it does not stick to VPS, inject VPS on and around it, and insert the appliance.
Treatment For Denture Patients
Denture patients develop obstructive sleep apnea more commonly and severely than people with a normal set of teeth, because they have no bite platform against which they can prop their lower jawbone to prevent it from dropping down and back into the space needed for airway passage through the pharynx (throat). However, denture patients cannot wear the mandibular advancement appliances that are used to treat obstructive sleep apnea in people with teeth, because their gums cannot tolerate the pressure required to push the lower jawbone forward off the upper jawbone. Therefore, until now, their only options have been CPAP or surgery.
Now denture patients have a non-surgical alternative. Dr. Summer has developed and successfully tested a tongue holding device and a soft palate elevator that can be built onto denture base plates (dentures without teeth) and worn during sleep to prevent the soft tissues of the throat from plugging the airway. The soft palate elevator has already been FDA approved. The tongue holding device was found safe and effective in patients with normal teeth in a clinical study for the FDA, but not yet in denture patients. Therefore, we are conducting a clinical study involving denture patients with untreated obstructive sleep apnea. Those who qualify will receive a tongue holding device along with before and after home sleep testing to evaluate its effectiveness. If the tongue holding is not effective, a soft palate elevator will be added, followed by another home sleep test.
The tongue holding device holds the tongue body between upper and lower tongue gripping surfaces composed of thousands of tiny bristles, like tongue velcro, in sheets that are molded to fit your mouth. The tiny bristles are all slanted forward at a 45 degree angle to prevent the tongue from dropping back into the pharynx. The tongue holding technology is summarized below and described in detail in the file entitled, MULTI-LEVEL TREATMENT OF SLEEP APNEA under the FOR DOCTORS tab.
Tongue holding is especially effective in denture wearers; because the tongue gripping surfaces can extend almost all the way to the cheeks, and the denture base plates supporting them are held comfortably seated on the gums by the tongue functioning like a big long cushion between them. Therefore, very little retention is required in the denture base plates, and they can even be effective in people who cannot wear dentures for eating. However, the goal of the tongue holding treatment in denture wearers is not advancement, which would apply pressure to the gums. 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.
To create the cushioned grip that ensures comfort and prevents tongue release during submaximal opening, the lower tongue gripping surface, (rather than the upper tongue gripping surface in dentate patients), is spring-loaded to push the back of the tongue upward against the upper denture base rather than downward against the mandible. The anterior end of the lower tongue gripping surface is attached to the lower denture base plate by a polyester mesh tether, and the posterior ends of the lower tongue gripping surface are continuously biased upward into the underside of the tongue by a pair of torsion springs or 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, as shown below. The bias from the elastics 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.
BOTTOM ENDS OF ELASTICS ON CLEATS TOP ENDS OF ELASTICS ON BALL CLASPS ELASTICS SUSPEND LOWER TONGUE GRIPPING SURFACE
If tongue holding is insufficient to eliminate the obstructive sleep apnea in a denture wearer, a soft palate elevator is attached to the back of the upper denture base plate, followed by another home sleep test. The soft palate elevator is described in detail in MULTILEVEL ORAL APPLIANCE TREATMENT in detail under the FOR DOCTORS tab.
MULTILEVEL ORAL APPLIANCE TREATMENT
SUMMARY
Obstructive sleep apnea (OSA) is caused by choking on the tongue base and soft palate during sleep. The following paper describes treatment of this condition for people with a normal set of healthy teeth. Many dentists now treat OSA in these people with mandibular advancement appliances, and the appliances are well tolerated; but they are only effective in 50% of patients, because the mandible is only loosely attached to the tongue and not at all attached to the soft palate. Therefore, Dr. Summer has devised mechanisms that can be added to ineffective mandibular advancement appliances in order to also control the positions of the tongue and soft palate. For people without teeth (denture wearers), the treatments are described under the file TREATMENT FOR DENTURE PATIENTS. For people who want a detailed description of the new mechanisms and a protocal for comprehensive oral appliance treatment of OSA, the protocol and rationale can be found in the file entitled, MULTILEVEL ORAL APPLIANCE TREATMENT under the FOR DOCTORS tab.
BACKGROUND
OSA affects millions of people, but current treatment for it is problematic. Minor surgeries can be helpful but rarely curative. CPAP is usually effective if the pressure is high enough, but compliance is poor, because many people find it difficult to tolerate. Oral appliances currently used to treat the problem work by advancing the mandible, which increases the space available in front of the tongue; but it cannot draw the tongue forward into that space, because the mandible is only attached to the tongue by muscles, which naturally lose their tonus during sleep. As a result, even extreme mandibular advancement cannot prevent the tongue from falling back into the throat to block the airway, it just has further to fall, and mandibular advancement only cures about half of the people treated, as seen consistently in hundreds of studies.
New mechanical devices can now be added to ineffective mandibular advancement appliances to make them more effective by also holding the tongue to prevent it from dropping back into the throat, elevating the middle of the soft palate to draw its back end away from the obstruction, and prying the tongue base off the pharyngeal wall. To prevent unnecessary treatment, these modalities can be added one at a time until the problem is solved, as described below:
STAGE ONE
MANDIBULAR ADVANCEMENT - The first stage of multilevel oral appliance treatment for patients with natural teeth involves using an adjustable mandibular advancement appliance to gradually move your mandible further forward until you find the most advanced position that you can comfortably tolerate. A variety of oral appliances are currently available from many dentists for this "titration" process. The appliances cause bite changes, which should be treated by bite adjustment, usually by the dentist who made your oral appliance, as explained further at the end of the file entitled MULTI-LEVEL ORAL APPLIANCE TREATMENT OF SLEEP APNEA under the FOR DOCTORS tab.
Telescopic (Herbst) appliances have the longest history of success in treatment for sleep apnea and the best control over mandibular position, but the hardware they employ was designed more than a century ago for bite jumping in children, and it is unnecessarily bulky and restrictive when used in adults, leading to discomfort and breakage. To solve these problems, Dr. Summer's high push Herbst appliance has a lower profile for comfort, free lateral movement to prevent binding and breakage, an upward vector of force on the mandible to prevent mouth breathing, and unlimited adjustability without tools by just rotating the tubing assembly on the threaded connector, as shown below.
A SOFT PALATE ELEVATOR - is often added to the mandibular advancement appliance in stage one in order to open the nasopharyngeal airway by pulling the distal end of the soft palate out of the narrow gap between the tongue base and the pharyngeal wall, because the two treatments work together better than either one alone. Drawing the distal end of the soft palate away from the obstruction works like removing a gasket from a seal. It can immediately open the airway, but it cannot prevent formation of a new gasket without changing the functional environment that formed the gasket. Mandibular advancement changes the functional environment, but it may not change it enough to restore airway flow without also removing the gasket.
The soft palate elevator employs a silicone rubber bulb on the end of a thin flexible arm to “tent” the middle of the soft palate, where there are few gag reflexes, in order to draw its distal end, which is full of gag reflexes, upward and forward away from the obstruction, as shown above. The soft palate is a thin flap of tissue that has almost no tonus during sleep, and a light force is able to keep it elevated about 1/4” all night without causing any discomfort.
At the end of stage one treatment, some type of follow-up sleep testing is necessary to find out how well the treatment is working. If it's only partly effective, you'll feel better; but you'll likely relapse over time, as the remaining incidents continue stretching out the soft tissues of the pharynx.
STAGE TWO – The next stage of multi-level oral appliance treatment is to hold the tongue against the advanced mandible between specialized upper and lower tongue gripping surfaces that each contain thousands of forward slanted bristles, (AKA tongue velcro), to prevent it from dropping back into the pharynx. Their grip is so effective that a single orthodontic elastic or a lightweight spring connecting them provides enough compressive force to hold the tongue without discomfort all night in the space shown below.
A lower tongue gripping surface is shown below left and an upper tongue gripping surface is shown below right.
To prevent accidental release of the tongue during sleep, at least one of the upper tongue gripping surfaces (the upper for patients with teeth and the lower for denture patients) is mounted in a continual biasing mechanism that creates a cushioned grip which persists throughout the submaximal mandible and tongue movements that occur during normal sleep. The cushioned grip continues until the mouth is opened wide enough to release the tongue. In most people, the target position for the tongue is just far enough forward for its tip to maintain light contact with the lips closed around it, as shown below. Patients go to sleep with the tongue in this target position, and they awake with the tongue in the same target position, because the tongue cannot escape during sleep.
STAGE 3 - If follow-up sleep testing shows that the apnea persists, the remaining airway blockage probably occurs down lower in the hypopharynx, where the tongue base directly contacts the pharyngeal wall. To treat the hypopharyngeal obstruction, the tongue base is gradually pried off the pharyngeal wall by incremental adjustment mechanisms called tongue base titraters that are mounted on the back of the upper tongue gripping surface to shift its tail segments, in progressive weekly increments, further down and back as the patient gets accustomed to them.
The three rows of apertures in the tongue base titraters enable the direction of depression to be varied by 25 degrees, as shown below.
UNADJUSTED DOWN AND BACK DOWN AND FORWARD
FACTORS COMPLICATING TREATMENT
MOUTH BREATHERS - Mouth breathing is devastating to health, because the air that hits the back of the throat has not been warmed, filtered, and moistened by the nose; which leads to more frequent upper respiratory infections. Some people are obligate mouth breathers, because their nasal cavity is too narrow to allow adequate airway flow. Other people have a nasal cavity that is just wide enough to allow normal nasal airway flow, and thehy become obligate mouth breathers whenever allergies or rhinitis causes swelling of the nasal mucous membranes. Obligate mouth breathers can be converted to nose breathers after palatal expansion to widen the nasal airway. However, palate expansion rarely eliminates apnea, because the area that is widened is located far from the back of the throat where the obstruction occurs. Habitual mouth breathers use an oral airway despite having an adequate nasal airway passage, and their mouth breathing habit can usually be eliminated by almost any mechanism that can hold the mouth closed; including chin straps, lip taping, thick foam cervical collars, or interarch orthodontic elastics on an oral appliance that fits on the teeth tightly enough to resist being pulled off them by the weight of the lower jawbone.
TMJ DISORDERS - can make it difficult to advance the mandible rapidly or extensively, but they usually resolve by middle age when OSA begins, so they rarely prevent gradual mandibular advancement, and they do not even interefere with soft palate elevation or tongue holding.
BITE CHANGES - are frequent consequences of mandibular advancement due to a combination of tooth movement and jawbone growth. Patients usually find that their back teeth no longer fit well together in the morning and then throughout the day, because the upper front teeth have shifted backward, the lower front teeth have shifted forward, and the mandible has elongated. The resulting "posterior openbite" can make chewing less effective, but chewing capacity can be easily restored by having your dentist adjust your bite forward. Dentists are trained to adjust bites backward rather than forward, so it is often difficult for them to understand why they need to do it and how, but adjusting the bite forward in treatment of sleep apnea can provide important benefits. The resting posture of the mandible is controlled by its central bite position. Advancing the central bite position thus advances the resting posture of the mandible and tongue, which facilitates daytime airway flow and reduces dependence on the mandibular advancement appliance, because the mandible that gets used to being in a forward position can stay there for short periods of time, like when taking a nap.
COSTS - Many different types of mandibular advancement appliances are available from many dentists. We employ a fully adjustable (titratable) high push Herbst appliance. The fee for that appliance for stage one treatment is $2600. Stages two and three costs depend on circumstances, and they can be waived if you are participating in one of the two ongoing clinical studies to evaluate the effectiveness of the treatment using after before and after home sleep testing.
Comprehensive Oral Appliance Treatment For Sleep Apnea
Obstructive sleep apnea occurs when people choke on their tongues during sleep. Dentists make a variety of different oral appliances to treat obstructive sleep apnea, and they are tolerated by patients much better than CPAP; but they almost all work just by advancing the mandible (the lower jawbone). Advancing the mandible creates space in front of the tongue and thereby allows it to rest in a more forward (advanced) position; but advancing the mandible cannot draw the tongue forward into that new space, because the tongue and mandible are only attached by muscles, which naturally lose most of their tonus during sleep. As a result, they only cure the problem in about half of the patients treated.
To relieve sleep apnea in the people with ineffective mandibular advancement appliances and in people who wear dentures, Dr. Summer has developed new technologies that can be added to these oral appliances to also control the soft tissues that produce the actual obstruction. A tongue holding device holds the tongue and tongue base forward together with the mandible so it cannot drop back into the pharynx, while a soft palate elevator draws the end of the soft palate forward and upward away from obstruction in the nasopharynx. These components are described in detail in the file entitled, MULTI-LEVEL TREAMENT OF OBSTRUCTIVE SLEEP APNEA under the tab FOR DOCTORS.
The pilot study for the FDA submission used patients with a normal healthy set of teeth (dentate patients). The new study, beginning fall 2023, will involve only denture patients who have obstructive sleep apnea. They will receive a new denture baseplate (no teeth) containing a tongue holding device and also a soft palate elevator if needed. Multi-night home sleep testing will be used to guide treatment.
Many dentists now make mandibular advancement appliances for treatment of obstructive sleep apnea, but effective treatment for obstructive sleep apnea should consider both short-term and long-term effects. Therefore, while short-term relief can be obtained by elevating the soft palate and advancing the mandible and tongue; the slow facial growth of adulthood should also be redirected anteriorly to gradually improve the airway by including functional orthodontic mechanics into the design of the mandibular advancement appliance.