Appliance Fit and Thickness
SUMMARY
The excessive tightness and unnecessary thickness of all commercially made oral appliances today, including those made by your dentist through a dental lab, can exacerbate some of the same problems they are intended to solve. The tightness produces pressure on the teeth, which reflexively increases jaw muscle tension. The bulkiness causes the tongue to shift down and back into the airway space, which pulls back on the mandible. To prevent these problems, we make all of our appliances with a passive fit, minimal thickness, and a large carved out space for the tongue tip just behind the upper front teeth to promote healthy tongue posture.
EXCESSIVE TIGHTNESS occurs in oral appliances, because plastics shrink when they set, which squeezes the teeth inward, especially the front teeth in the middle of the horseshoe shaped dental arch. The resulting pressure on teeth increases jaw muscle tension, because noxious sensory signaling from any joint automatically increases the tension in the muscles which cross that joint in a reflex effort to stabilize it to protect it, and the jaw muscles cross the TMJs. Therefore, pressure on teeth or a TMJ causes automatic protective jaw muscle tension, just as a swollen ankle causes automatic protective leg muscle tension, which we see as limping. The increased background tightness caused by such jaw muscle "limping" adds to the jaw muscle tightness caused by an inflamed TMJ or an unstable bite.
Even slight pressure on teeth can trigger jaw muscle tension, because each tooth at rest is delicately suspended in a sophisticated hydraulic shock absorbing mechanism 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 teeth remain in the middle of their sockets all night, these tissues remain passive. When a tooth is held on one side of the socket all night, it triggers adaptive responses designed to make the socket once again fit the tooth position. One of those responses is protective jaw muscle tension.
In addition to having a central resting position in the middle of its socket, each tooth has a range of motion within its socket up-and-down, side to side, and even mesio-distally (front to back) against the adjacent teeth. That range of motion helps drain the socket of waste products. An appliance that "hugs" a tooth restricts its range of motion and thereby also its circulation. Tightness is not required for appliances to stay in, comfort is. An appliance only needs to be tight enough to resist the forces of gravity.
Some appliances that have been worn for many years can become passive, because the teeth have moved to fit the appliance. At first, the teeth rebound every day, shifting back and forth between daytime and nightime positions, but over time they can shift permanently. This accidental orthodontics makes the appliance more comfortable, but it also tips the front teeth inward, which increases the steepness of the overbite, which is part of the root cause of your problem.
Some dentists try to avoid complaints of tightness by making their oral appliances fit on the lower teeth, which are much less sensitive to pressure than the upper teeth; because the lower teeth are all housed in one thick piece of cortical bone, while the upper teeth are housed in two thin membrane bones connected by a long pressure-sensitive suture. However, lower appliances worn at night can destabilize bites by confining the forces of nocturnal bruxing to the back teeth, which drives them back into the bone and makes them too low, leaving you to bite mostly on the premolars or even the front teeth.
Dental companies have failed to compensate for the shrinkage of acrylic. Some companies market an acrylic that can be softened in hot water just before placing it in the mouth, which reduces the pain on initial insertion, but doesn't reduce the pressure on teeth all night or the adverse orthodontics it can cause. Other dental companies market a plastic that has an inner layer of rubber. The rubber lining allows the individual teeth at least a slight range of motion, which feels more comfortable; but it often delaminates, and it requires additional thickness, which also works against our goals by interfering with healthy tongue posture, as described in the section on excessive thickness below.
We use a special block-out process during the fabrication of each appliance to create a perfectly passive fit. As soon as the appliance is in place, it should apply no pressure to the teeth. It should almost feel like there is nothing in your mouth. Soon dental labs will be able to use digital scanning and milling or 3D printing to create appliances with a perfectly passive fit, but not yet in 2024.
EXCESSIVE THICKNESS, especially at the front of the palate, shifts tongue posture backward to avoid the bulk, which also shifts lower jawbone posture backward, because the lower jawbone is the bone for the tongue. In monkeys, cementing a block of acrylic in the front of their palates caused them to grow long narrow faces, because they acquired a lowered tongue posture to avoid the block, which caused the mandible to grow in that direction. In humans, when the tongue lowers, the mandible rotates backward as well as downward. Backward lower jawbone posture then restricts airway passage, which causes forward head posture as an airway-preserving adaptation. However, nearly all currently made appliances have a great deal of unnecessary acrylic in the front of the palate, because commercial dental labs make their appliances thick for strength, because they worry about breakage for which they may be held responsible. We don't need to make our oral appliances any thicker than necessary, because our in-house dental lab enables us to repair breaks during a single office visit for a small lab fee. Most people would rather have their oral appliance thin enough to be as comfortable and effective as possible rather than thick enough to withstand accidentally sitting or stepping on it. In addition, we carve out the front of each appliance to fit the tip of the tongue (tongue tip hollow) so the tongue can maintain a healthy posture during sleep.
