To be published in peer-reveiwed PostGranduate Dentistry, November issue, 2000
James P. Boyd, DDS
ABSTRACT: "Bruxism" historically has been
casually defined as "the clenching and/or grinding of the teeth". Since
there can be no teeth grinding without the jaws first being clenched, a
re-definition of bruxism is presented: "Jaw clenching, with or without
forcible excursive movement, where the intensity of the clenching
dictates the severity of teeth grinding". Traditional inter-occlusal splint
methods of treating bruxism have been unpredictable because their
specific design addresses lateral movement (grinding), when it is the degree
of intensity of vertical movement (clenching) which dictates severity of
symptoms. A new method and device (a simple modification of pre-existing
concepts) which suppresses clenching intensity by exploiting the nociceptive
trigeminal inhibition reflex while preventing canine and posterior tooth
occluding, is presented.
Individuals with a far less than ideal jaw relationship and/or occlusal scheme may be completely asymptomatic, while others who have ideal jaw relationships and occlusal schemes chronically suffer from debilitating headaches, face and jaw pain (TMD). Etiological research continues to show that essentially, it doesn't matter what a person has, or where it is...what matters is, what one does with what one has.(1)
Dentistry typically acknowledges that the activity responsible for these symptoms is bruxism. However, the current standard treatment for bruxism, i.e., a splint or nightguard, may not be entirely effective at resolving the patient's symptoms. The problem lies not in dentistry's mis-treatment, but of its mis-conception of the diagnosis, i.e., "bruxism". This lack of understanding of the true nature of bruxism has resulted in the current standard of care for chronic TMD: management of symptoms(1,2,3).
Dentistry has stipulated that treatment with an inter-occlusal splint will result in one of three scenarios: the patient may improve; remain unchanged; or get worse(4,5). The reality is, treatment outcome using an traditional occlusal splint alone for patients with significant myofascial pain is no better than placebo(6). When treating TMD surgically, those patients with uncontrolled nocturnal bruxism are considered to have a poor prognosis(7). After elective orthognathic surgery, some procedures fail due to previously un-acknowledged, but suddenly destructive, bruxism. A patient cannot be informed of the risk of the potential adverse outcome if the provider himself doesn't fully understand the true nature of bruxism.
To gain an upper hand on bruxism, a better understanding of the term and therefore, the condition itself, is necessary. Bruxism is not a condition of the teeth. Teeth don't cause an activity, but are merely being affected by an activity(8). Dentistry is essentially the art and science of how healthy teeth occlude with each other. Therefore, dentistry may reflexively treat a condition it is presented with by addressing the health of the teeth, and their scheme of occlusion(9). However, signs and symptoms of bruxism result from the occluding of teeth, specifically, the intensity of occluding. The resultant scheme of occlusion may modify and direct the forces generated during the occluding. Dentistry stipulates the occluding, and attempts to treat the resultant symptoms by altering the occlusion.
Bruxism is a function of clenching. The intensity of clenching dictates the severity of grinding. There is no teeth grinding unless the jaws are first clenched together. The jaws must be clenched together intensely enough to provide adequate resistance to alternating lateral pterygoid activity, which then "grinds" the teeth in excursive movement. As the intensity of temporalis contraction (clenching) increases, resistance to mandibular lateral movement is increased, thereby increasing the efforts of the lateral pterygoids and strain on the TMJs. Therefore, as the intensity of clenching increases, the ability to move the mandible laterally (grinding) decreases. Ultimately, the most intense clenching would prevent any grinding of the teeth at all, which provide a stable and protected environment for the temporomandibular joints . With this observation, the appropriate definition of bruxism becomes apparent: "Jaw-clenching, with or without forcible excursive movements". The patient who presents with severely worn teeth, obviously a result of vigorous grinding, may have no symptoms to report, because they never exert adequate clenching intensity to become symptomatic (just enough to rub the teeth together). Another with no indication of occlusal wear, but who complains of severe headaches and neck pain and has no TMD signs or symptoms, clenches intensely in centric position. Only by recognizing bruxism as a function of clenching can these patients be accurately diagnosed.
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(10). 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)(11). 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).
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 treatment 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 (13,14,15). Direct pressure stimulation of the mandibular incisor's periodontal ligament activates a reflex loop which suppresses the temporalis' contraction intensity (conversely, anesthetization of the mandibular incisors PDL's allows clenching intensity to increase (16)). Historically, an anterior deprogrammer (such as a Lucia jig) or an anterior-point-stop (17), 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 (18) 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.) (19)
Used primarily during sleep, a modified AMPS (anterior midline point stop) reduces voluntary clenching intensity to one-third of maximum (20). As described by Okesen (17), 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 (10), 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 (21).
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 (22). 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
Brown, DDS, MPS