Basics of TMD etiology and how it relates to the NTI Therapeutic Protocol.
Temporomandibular disorders all have one perpetuating and/or causative factor in common: an excessive motor activity of the mandibular division of the trigeminal nerve, that is, excessive occluding of the teeth.
Four factors dictate the presenting signs and symptoms:
--Intensity of the occluding;
--Frequency of the occluding;
--Duration of the occluding;
--Degree of condylar rotation and direction of the pull on the condyle by the resistance encountered by the lateral pterygoids during the occluding event .
Of those four factors, the most significant is the intensity of the event. The ideal occlusal splint (below) cannot reduce the intensity of nocturnal clenching, in fact, it allows clenching to exceed voluntary maximum.
In the animation above, the condyles are "stable" during the occluding event (sometimes referred to as "posterior support for the joint). Due to the bilateral intensity of elevation, (that is, clenching), neither lateral pterygoid has the ability to translate its condyle and disclude the teeth. Only until the temporalis' relax do all the teeth disclude.
When temporalis relaxation and ipsilateral translation of the condyle occurs unilaterally (below), the remaining scheme of occluding teeth becomes an influential factor in the presenting signs and symptoms, of which, contacting canines during mandibular depression ("canine rise) is highly desirable, as it minimizes condylar translation and muscle intensity, while directing the vector pull on the condyle more anteriorly than a posterior contact. (The ideal directional pull of the LP's on the condyle is anteriorly, and the more translated the condyle is during parafunctional occluding events, the more pathologic strain on the condyle and shearing load to the disc there is)
An occluding contact, made possible by the persistence of elevation innervation (ie, clenching activity) provides resistance to the lateral pterygoids' attempts at translating the condyle (ie, open and disclude the teeth). The location of the resistance dicates the static force vector created by the isometrically contracting lateral pterygoid and the degree of strain/load experienced by the affected joint.
When lateral pterygoids bilaterally protrude the mandible (below: while teeth are still occluding, from A to B), or when there is an incisor-to-incisor contact during functional closure, clenching (elevation) intensity is minimized. The force vectors of the pull of the lateral pterygoids on the condyles brace and support the condyle anteriorly against the slope of the eminence.
Therefore, the provision of "incisal guidance" is the optimal goal of nocturnal occlusal splint therapy.
Below, an NTI device provides for incisal guidance in the centered clench and in an excursive occluding event.
It is critical to prevent the canine teeth from receiving stimulation though their long axis, as doing so allows for increased intensity of clenching events.
An NTI device is a modified, or enhanced, anterior bite stop which prevents reciprocating posterior tooth contacts, or canine contact on the device or another tooth.
During normal masticatory function, crushing (clenching) forces increase as condylar rotation decreases as the bolus gets smaller, thereby maintain stability and lack of strain on the joint
In order to keep condylar ROTATION to a minimum, the VDO of the Discluding Element (DE) needs to be minimized (excessive VDO of the DE shown in yellow below).
The NTI's design is to mimic the naturally occurring tolerable forces of mastication and incising by following two basic rules:
- Minimize clenching intensity by preventing molar or canine contact, allowing for only incisor edge contact during parafunctional occluding events during sleep in all excursive and/or protrusive positions;
- Minimize joint strain/load by minimizing condylar rotation during occluding events in all excursive and/or protrusive positions.