Taming Destructive Forces Using a Simple Tension Suppression Device
James P. Boyd, DDS
Wesley Shankland, DDS, MS, PhD
Chris Brown, DDS, MPS
Joe Schames, DMD
In a study of chronic tension-type headache patients without signs or symptoms of TMD, temporalis contraction (clenching) during sleep was shown to be, on average, fourteen times more intense than in asymptomatic control subjects. Clenching in centric and balanced position maintains a stabilized TMJ environment. However, the typical patient with chronic TMD (headaches, face and jaw pain, tooth wear) will forcibly grind their teeth to an excursive position, and then clench in that position ("grinding to a clench"), placing severe and often damaging strain on the TMJ(s). There exists a dynamic relationship between the temporalis' and lateral pterygoids, from which signs and/or symptoms may result. The intensity of the temporalis activity combined with the degree of lateral pterygoid activity (if any), dictates the presentation of headache, TMD, or tooth wear. Ultimately, in order to treat and prevent bruxism, clenching intensity must be suppressed. Unfortunately, the traditional inter-occlusal splint, while decreasing resistance to lateral movement thereby relieving lateral pterygoid contraction and TMJ strain, provides improved resistance to the temporalis, allowing clenching to persist, or intensify(12).
By reducing the resistance created by tooth contacts in excursive movement (A), a splint allows the lateral pterygoids to contract less intensely. Therefore, TMJ system strain is less, thereby relieving symptoms. However, the evenly distributed occluding forces on the same splint (B) provides a more efficient clenching surface. Therefore, temporalis intensity can
maintain or increase, thereby maintaining or increasing symptoms. The success or failure of the traditional inter-occlusal splint is a function of the intensity of clenching. If clenching intensity persists or increases after using a splint, TMD reatment becomes TMD management.
Suppression of temporalis contraction (clenching) can be achieved by exploiting the nociceptive trigeminal inhibition reflex, also known as the jaw-opening-reflex . Direct pressure stimulation of the mandibular incisor's periodontal ligament activates a reflex loop which suppresses the temporalis' contraction intensity (conversely, anesthetization of the andibular incisors PDL's allows clenching intensity to increase . Historically, an anterior deprogrammer (such as a Lucia jig) or an anterior-point-stop , has been advocated to establish and record optimal condylar position (CR) and to suppress acute muscular symptoms on a short term basis. Each are effective in clenching suppression in centric positions. However, for the deprogramming jig, excursive movements of the mandible can allow for a mandibular canine to contact the device, allowing for ipsilateral near-maximal clenching and joint strain. Protrusive movement of the mandible with the anterior-point-stop allows for occluding of the posterior teeth, again allowing for high intensity clenching. Clearly, all mandibular excursive positions, not just centric, must be considered when attempting to suppress temporalis clenching. Modifying an anterior point stop by extending the point contact both anteriorly and distally provides clenching suppression in all mandibular movements (a prefabricated, retrofitable device is available commercially through NTI-TSS, Inc.) Used primarily during sleep, a modified AMPS (anterior midline point stop) reduces voluntary clenching intensity to one-third of maximum. As described by Okesen , the modified AMPS design allows for the best "musculoskeletally stable" (CR) position of the condyles, while suppressing hyperactive musculature. Additionally, by providing for no unilateral canine or posterior contacts, as can happen with a full-coverage splint due to contortion of the mandible in excursive movement, the modified AMPS allows for the least amount of potential joint strain in any excursive or protrusive movements, thereby allowing for optimal joint healing an remodeling .
Two misconceptions of a modified AMPS are not uncommon:
posterior teeth may supra-erupt, and mandibular incisor(s) may intrude. In order
for a posterior tooth to supra-erupt, it must go unopposed for a considerable
amount of time, long enough to allow bone growth at the apex (approximately
six weeks is necessary for bone growth). Since it is impossible to masticate
with a modified AMPS in place, the daily stimulation of the posterior teeth
prevent any adverse drifting or supra-eruption . As for incisal intrusion, a
constant low-grade force must be maintained for a considerable amount of time
before intrusion can occur. Even in the most extreme circumstances, clenching
forces persist for only minutes, not nearly enough time to allow for permanent
orthodontic movement or intrusion. Even in the case of the clinician's oversight,
where the discluding element of the modified AMPS (which provides the point
stop) is not perpendicular to the long axis of the mandibular incisor (it should
be), the patient will report a tenderness to the tooth immediately after the
first night of use, and will resist wearing the device until addressed by the
dentist, long before there is any orthodontic tipping movement.
Although the modified AMPS device itself does not cause any orthodontic movement, it can allow for optimal positioning of the mandible, due to its providing for the most musculoskeletally stable condylar position. This is most noticeable in the patient whose condyles happen to seat more posteriorly and superiorly in the fossa as the patient's symptoms resolve. As the condyle seats more posteriorly and superiorly, the mandible "pivots" typically at the last molars, with the anterior mandible rotating inferiorly and posteriorly. The patient's original degree of incisal overlap during CO dictates to what degree, if any, of resulting anterior open bite. Interestingly, when informed of the odds of this scenario occurring, patients are usually surprised if they perceive that the practitioner has placed the importance of their current jaw relationship above their chronic pain. Following any repositioning of the condyles, some degree of occlusal equilibration may be necessary.
Although the modified AMPS requires slightly less fabrication time than the traditional methods of splint fabrication and delivery (which typically require impressions, models, lab-fees, and the potential for numerous adjustment appointments), the commercially available pre-fabricated devices require one simple chair-side procedure where the device can be retro-fitted and delivered in a 20-minute appointment and a follow-up appointment. Compared to the bulky and often irritating traditional splint, the relatively smaller size of a modified AMPS and its secure fit provide for excellent patient compliance, while specifically addressing and suppressing the source of the patient's discomfort.
a) Prefabricated matrix
b) Retro-fitted by reline with acrylic
c) Sculpted and finished
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