Appliance Fit and Bulk
The excessive tightness and unnecessary bulk of commercially made oral appliances not only makes them uncomfortable, it also exacerbates some of the same problems they are intended to solve. Therefore, to make them easier to wear and more effective, we make all our oral appliances in our own lab using special techniques to ensure minimal thickness and passive fit.
Commercial dental laboratories make their appliances thick, because they worry about breakage; but thick appliances can exacerbate TMJ disorders by adversely affecting tongue posture. Since the tongue has no bone of its own, its base of operation is the lower jawbone. Consequently, anything that causes retrusion of the tongue causes retrusion of the lower jawbone. In experimental studies, placing a block of acrylic in the palates of growing monkeys caused them to grow long narrow faces, because it forced their tongues and in turn their lower jawbones to acquire lower and more retrusive resting postures. A bulky appliance can have a similar effect.
One reason we can make our appliances no thicker than necessary is because most people would rather wear an oral appliance that is thin enough to be comfortable rather than one thick enough to withstand accidentally sitting or stepping on it. In addition, if you do break your appliance, we can fix it in one appointment for a small laboratory charge.
The other reason we make our appliances no thicker than necessary is to prevent impinging on tongue posture and thereby also jaw posture. In normal tongue posture, the tip of the tongue rests against the palate just behind the upper front teeth. To facilitate normal tongue posture, we carve out a hollow for the tip of the tongue just beneath the joint protective ramp at the front of the appliance. This "tongue tip hollow" allows the tongue to maintain a normal healthy resting posture, which also allows the lower jawbone to maintain a normal healthy resting posture.
Commercial dental laboratories also make their appliances too tight, especially around the front teeth. Plastics all shrink when they set or cool, usually about 3%. Because the upper dental arch is horseshoe shaped, shrinkage of plastic in an upper dental appliance squeezes the teeth inward, especially the front teeth in the middle of the horseshoe.
The resulting pressure on teeth increases jaw muscle tension, just as any source of facial pain, including TMJ inflammation. Increases in jaw muscle resting tension are cumulative. Those caused by pain or pressure around the teeth add to those caused by an inflamed TMJ or an unstable bite. In this manner, by putting pressure on the teeth, the tightness of the appliance works against our treatment goals in TMJ disorder patients.
Eventually the pressure of a tight appliance is usually relieved by the inadvertent tooth movement it creates. At first, the teeth rebound every day, shifting back and forth between daytime and nightime positions, but over time they shift positions until they fit the appliance. This accidental orthodontics makes the appliance more comfortable, but in most people it moves the teeth in the worst possible direction, because the inward shifting of the upper front teeth increases the steepness of the overbite and can thereby increase the retrusive strain on the lower jawbone.
The dental industry has been unable to solve the shrinkage problem. Some dental companies market a plastic that can be softened in hot water just before placing it in the mouth. Heating the appliance reduces the pain of inserting it each night, but it doesn't reduce the negative effects of the tightness after the appliance returns to mouth temperature. Other dental companies market a plastic that has an inner layer of rubber, which is more comfortable against the teeth than hard plastic; but it requires additional thickness without providing additional strength, and it frequently delaminates because rubber is difficult to attach to plastic.
Some dentists try to avoid the tightness problem by making their oral appliances fit on the lower teeth, which are less sensitive to pressure than 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 and highly innervated suture. However, lower appliances worn at night can destabilize bites by confining the forces of nocturnal bruxing to the back teeth. These forces can shorten the back teeth by intruding them back into the basal bones, while allowing the front teeth to get longer by supererupting (extruding) out of the basal bones. The resulting increase in overbite can destabilize a natural bite and create the need for dental work just to re-establish a stable natural bite. For that reason, dentists should not make lower nightguards except in class 3 malocclusions.
We use a special block-out process during the fabrication of the appliance to create a passive fit. Leaving the teeth in their rest positions makes the appliance comfortable enough to wear every night on a long term basis and prevents pressure on the teeth from reflexively increasing jaw muscle resting tensions or causing adverse tooth movement.