"Doc! I don't like wearing my oral appliance because my jaws don't come back together in the morning." It is a well known fact that after wearing an intra-oral appliance at nighttime it can cause the jaws to feel like they do not go back together correctly in the morning. This mis-alignment if left alone could cause myofacial pain during the following days activities. I recently attended a meeting for the American Academy of Dental Sleep Medicine and heard one of the speakers explanation for this phenomenon and it left me dissatisfied. She stated that it was due to the static anterior positioning of the muscles of mastication all night in one position. She then alluded that the muscles had become stiff and needed to be exercised. Although muscle stiffness may be a small contributing factor, I felt like there was more to it than that. This type of thinking may have arisen from the practice of giving patients who experience post oral appliance therapy morning misaligment a strip of rubbery material to chew on to re-align their bite. I, myself, wear an anterior positioning obstructive sleep apnea appliance (The Moses™) and use a jaw re-positioner every morning for about 30 minutes to re-align my jaw back into a comfortable position. It is a hard thermoplastic positioner that forces my jaw back into maximum intercuspation (proper bite). I set my first alarm for thirty minutes before I need to wake up in the morning. At this time I remove my oral appliance and place into my mouth the re-positioner. If I fall back to sleep, my wife usually tells me I snored. When I wake up to the second alarm, my jaw/bite are back into a comfortable position and I feel great. So, why would the muscle of mastication have such a great affect on my bite if positioned a few millimeters anteriorly by an intra-oral appliance? My answer is it doesn't. Instead, I feel the answer lies inside the temporomandibular joint itself. With a review of the anatomical structures of the TMJ you will see that there is the joint head (condyle) inside the joint socket (condylar fossa) separated by a cartilaginous disk (meniscus). The TMJ is a true "double joint" in that it not only rotates, but it also translates. Translations is where the condyle head slides out of the condylar fossa on the disk and forward along the maxillary skull called the articular eminence. This translation and rotation of the lower jaw helps us open our mouth wide enough to eat submarine sandwiches. The synovial space above the disk is called the upper joint compartment and the space below is called the lower joint compartment. These compartments are filled with a slippery liquid called synovial fluid. The TMJ depends on where the teeth are positioned and the bite of the teeth depend on the position of the TMJ. This is where the problems occur.
Normal Synovial Function:Under normal conditions each joint in our body is lubricated by a slippery material called synovial fluid. It is continually made, absorbed and replenished by the synovial membranes lining the joint space compartments. Synovial fluid is a product of blood plasma ultrafiltrated from the synovial capillaries by what is called Starling Pressure. This pressure is the differences between the capillary plasma (blood pressure) and the synovial fluid (compartment space), minus the difference in osmotic pressure across the capillary walls. In other words, if left alone the joint compartments will automatically fill with synovial fluid on its own from the affects of blood pressure. The synovial fluid is not static and drains out through the subsynovium into the lymphatic system by intra-articular fluid pressure. This pressure is cause by the joint's movements back and forth on the synovial compartments during everyday activities. Essentially, the joint's actions are a kind of pumping mechanism for moving synovial fluids in and out of the joint.
Jaw Mis-alignment:The simple explanation for this post oral appliance therapy morning mis-aligment can be summed up by the term stiff joints after a long period of inactivity. By stabilizing the lower jaw forward in one position for an extended period of time, the upper synovial compartment is not compressed flat by the condylar head of the joint. This allows for the potential space inside the upper compartment to balloon up with synovial fluids caused by blood pressure (Starling pressure). Once the oral appliance is removed after a prolonged period of use, the joint cannot fall back into its usual place because of this ballooned upper compartment space. Therefore, the teeth cannot position themselves into the right bite as long as the joint is not in its proper place. Chewing on a rubbery strip will force the muscles of mastication to move the jaw joint back and forth aiding in the absorption of the excess synovial fluid into the lymphatic system and bring the joint back into its proper orientation inside the condylar fossa. Once the joint is in proper position the teeth will align into a comfortable bite. The jaw re-positioner that I wear in the morning simply forces my teeth into the proper bite which forces the excess synovial fluid out of the upper compartment of the TMJ.
Critical Post Oral Appliance Therapy:Although there are usually no long term TMJ complications from wearing anterior re-positioning appliances, the bite and myofacial muscle may suffer:
- Malocclusion may cause broken teeth, failing dental restorations and possibly orthodontic changes.
- Myofacial pain may accompany prolonged joint "ballooning"
- Using either a joint re-positioner for 30 minutes or chewing on a rubbery material for 10 minutes after waking will help to alleviate any "stiff joint" problems you may be experiencing.
- Consult your dentist for any unresolved problems.
- PLEASE NOTE: The posterior open bite and the forward posturing of the jaw after prolonged sleep appliance usage may be used to resolve obstructive sleep apnea (No CPAP and no sleep appliance). How's that for a bomb shell? Find out how!