|
Cervical and facial/sinus complications arising from protrusive clenching |
|
|
|
| The inferior LP is highly active during a resisted protrusion of the mandible. The resistance is provided the the occluding of the anterior teeth, made possible by the elevation of the mandible by the anterior fibers of the temporalis.
Since the clenching is done largely on the anterior teeth (thereby limiting temporalis contraction potential) and in a protruded manner (further limiting the temporalis intensity), temporal headache is less commonly reported.
As the LPs advance the condyles, the condyles are braced in an anterior direction against the eminence (rather than strained medially as in the excursive movement). The digastric works in concert with the ILP, aiding in depression the mandible following the occluding of the teeth. Prolonged protrusive clenching activities are therefore well tolerated by the joint complex, but can be straining on the pterygoid plates of the sphenoid bone (the origin of the LPs, circled, below), causing signs and symptoms of "sinus disease" (pain, pressure of sinuses).
The animation to the right demonstrates a restricted path of parafunction, commonly mistaken as "constricted envelop of function". In actual function (mastication) all of the teeth immediately disclude upon initical contact, whereas in parafunction, perpetuating elevation maintains resistance to the LPs attempts at discluding the teeth.
|
An obligatory reaction of the trapezius during a protursive
clenching event is to counteract the influence of the digastric (which is to tilt the head forward, since the mandible isn't opening) and support the skull over the shoulders. Therefore, protrusive clenching habit usually involves a chronic cervical involvement.
The utilization of an NTI device eliminates the
resistance to protrusive clenching attempts.
|
In the animation to the right, the left lateral pterygoid (LP) is pulling in two directions: "forward" anterior/medial on the condyle, and distal/lateral on the pterygoid plate of the sphenoid bone. The intensity of the strain on the pterygoid plate is a function of the intensity of the contraction of the LP. The intensity of the contraction of the LP is a function of the resistance it encounters durings its contraction (there is typically none, since LPs serve to disclude the teeth and open the jaw). The resistance the LP encounters is a function of the clenching intensity that is maintaining the occluding of the teeth (in the example, the molars on the right)
|
|
If the slope of the occluding surface of the DE allows for increasing vertical opening upon protrusion, strain and compaction may persist at the joints.
 
If the DE's slope continues to open the vertical as protrusion procedes beyond the opposing incisors (above left), the ramp must be altered to be parallel with the maxillary plane (above right)
Clinically, for the symptomatic patient, have them protrude as far as possible on the DE and clench. If they report acute and enhanced pain, reduce the DE as shown and have the patient repeat the protrusion. Typically, the pain with be reduced or prevented. Repeat as indicated.
|
The properly made NTI device's Discluding Element creates minimal freeway space and is parallel to the maxillary occlusal plane.Although the DE may be sloped on the palatal side of the incisors to close the vertical as much as possible, the slope must return to parallel to the maxillary plane as it extends labially past the upper incisors.
|
| How seating of a condyle(s) can change the anterior bite relationship |
| If chronic clenching initated at an early age in a protrusive position, the utilization of an NTI device will allow the condyles to be seated to their optimal orientation, which may be posterior and superior to the habitual postion.
The result may be a degree of anterior open bite, in the presense of resolution of symptoms. See also: Informed Consent Reminder.
In the above example thepatient is in a left excursive movement. If the left condyle seats more posterior and superiorly, the posterior teeth will occlude prematurely, thereby preventing the previous anterior bite relationship.
|
 |
|
Education 
