Nociceptive Trigeminal Inhibition Reflex

TMD, Bruxism, chronic tension headaches, migraine, all are controlled and/or moderated by the Trigeminal Nerve System

The trigeminal nerve is the largest of the cranial nerves

Its name derives from the fact that it has three major branches: the ophthalmic nerve (V1), the maxillary nerve V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has both sensory and motor functions

All three divisions feed into the Trigeminal Sensory Nucleus

The current understanding of the nature of migraine is that it results froma disorder of "sensory modulation", meaning that information received by the Sensory Nucleus is misinterpreted, thereby resulting in either a disproportionate response, or an inappropriate response altogether. For example, during a migraine attack, the simple pressure changes of the fluid that surrounds the brain (resulting from the beatingof the heart), is perceived as "pounding
The therapeutic goal in migraine prevention is to limit the amount of noxious sensory input(that is, to limit your migraine "triggers") to the Trigeminal Sensory Nucleus, so that itis not perceived as nociception. Essentially, the goal is to limit as much negative inputto the Trigeminal Sensory Nucleus as possible

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 translation and direction of the pull on the condyle by the lateral pterygoid during the occluding event

Of those four factors, the most significant is the intensity of the event

The ideal occlusal splint (left) cannot reduce the intensity of nocturnal clenching, in fact, it allows clenching to exceed voluntary maximum
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 (right), 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

When lateral pterygoids bilaterally protrude the mandible (left: while teeth are still occluding), 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

In July 1998, the U.S. Food and Drug Administration (FDA) granted approval for the "NTI Clenching Suppression System" (now: "Nociceptive Trigeminal Inhibition Tension Suppression System": NTI-tss

According to the manufacturer, the NTI-tss device is indicated for the prevention and treatment of bruxism, temporomandibular disorders (TMDs), occlusal trauma, tension-type headaches and/or migraine

The NTI-tss device is a small pre-fabricated anterior bite stop which covers – in its most widely used form – the two maxillary (or mandibular) central incisors. The fit along the teeth is accomplished at the chair side by filling either an autopolymerizing acrylate or a thermoplastic material into the base of the device, which is subsequently adapted along the central incisors, thereby increasing the vertical dimension between the upper and lower jaw. Adjustments along the outer surface of the bite stop are made by the dentist to ensure that at jaw closure and during excursive movements tooth contacts are present only between the intraoral device and the incisal embrasures of the antagonistic teeth. This "miniature anterior bite appliance" is typically worn during the night, although two variations of the bite stop are offered for daytime use

Rationale

Chronic symptoms of the head and neck can often be attributed to

A) Headache -- the temporalis muscle (it closes and clenches the jaw

B) Sinus pressure and pain -- the lateral pterygoid muscles (it moves the jaw side to side and/or forward

C) Neck stiffness and pain -- trapezius muscle (it stabilizes the skull during jaw clenching and grinding

The NTI device snaps into place and fits comfortably on either the upper or lower front teeth. It is worn during sleep and prevents the intensity of muscular Para function. For migraine sufferers, there is a more discreet version for daytime use, which is usually required (in addition to nighttime device) for 6 to 8 weeks for best results

HOW DOES IT WORK

The Nociceptive Trigeminal Inhibition Tension Suppression System (NTI-tss) takes advantage of a protective reflex which suppresses the temporalis muscles from contracting with their fullest intensity

Here are a couple of examples of this protective reflex. Let's say you've just taken a candy bar out of the freezer. How do you know if it's too hard to eat? Easy, you bite on it with your front teeth. If it's so hard that your lower front teeth can barely make a dent in it without hurting, you know it needs to thaw out a bit. But what if you're really hungry and just can't wait any longer? Simple, just use your back molars and start crushing away! How about when you're eating carrots? You can nibble on the skinny ones with your front teeth, but the big fat ones need to go between your back teeth in order to break off a piece because it would hurt to use your front teeth. Or imagine you're having a bowl of thick'n'chunky beef stew. If you accidentally bite the spoon with your lower front teeth...yeow!You instantly open your mouth. What if there is a piece of bone in the stew? Unfortunately, you may discover it by chewing on it with your back teeth and splitting a molar in half

Here's what's happening. lower incisors are designed to warn you that what you're about to eat may be too hard to chew on. Whenever the lower incisors are put under moderate to severe pressure, they signal the temporalis muscles to relax before pain and damage can happen to them. This is called the jaw-opening-reflex. It is designed to prevent you from putting something too hard into your mouth that may be damaging to your back molar teeth. The back molars, on the other hand, do practically the opposite. Whenever something comes in contact with them (like frozen-solid Snickers Bars, a piece of bone, or TMJ splints), the back molars signal the jaw-closing muscles to bite down hard because they figure, since there's something between them; it must be time to chew

The NTI-tss device takes advantage of the jaw-opening reflex by only allowing contact to be made on only one or two of the lower front teeth (incisors), and never allowing any of the back teeth (or canine teeth) to touch. (The prevention of allowing canine and posterior teeth from contacting is probably just as important as the lone contact on the incisors

The reaserch shows that the contacting of either the canine or posterior teeth instantly allows a significant increase in temporalis contraction. Thus, when the mouth is being closed, a lower incisor will touch the NTI-tss appliance, suppressing the temporalis muscles' ability to contract! Of course, the NTI-tss appliance cannot be worn when actual eating and chewing are taking place

Tension headache and common migraine sufferers develop a habit of pressing some or all of teeth together when concentrating on something. They may squeeze our teeth together just a little bit or go for a full-on clench. Jaw may be lined up in the middle, or they may hold it off to the side a bit, and we have no idea we're doing it. By definition, they usually have absolutely no awareness of their habit. No one else is aware that they are doing anything abnormal because their clenching (whatever the degree) is a silent and motionless act (especially when sleeping, unlike "grinding" of teeth
There are two versions of the NTI-tss appliance, one for sleeping, and one for when awake. Daytime clenching activity by itself really doesn't cause anything, but acts as an irritant to pre-existing condition…one that was developed while asleep. Wearing the daytime appliance for a month or so (except when chewing) allows them to have a more intimate awareness of their habit and most importantly, frequently allows the signal to be sent to suppress the musculature (every time you "tap" on the device). Although clenching activity during sleep is impossible to stop, the nighttime

NTI-tss device allows for a suppressed or reduced intensity of muscle contraction (which may also by a function of not allowing for canine and posterior teeth to touch). It's important to point out that in the muscular parafunction world, it's the intensity of contraction that creates and perpetuates the symptoms
It's during certain stressful parts of the day (like during scary movies, driving, balancing your checkbook, when the sympathetic nervous system makes its presence felt.) and especially at night, when high intensity temporalis contraction occurs that the NTI-tss appliance is worn

Essentially, the NTI-tss appliance is a simple habit-breaking device for daytime, and prevents the sleep disorder of intense temporalis contraction at night

Contra indications

An anterior midline point stop (as provided by the NTI) has been shown to decrease (suppress) muscle activity, and allow the optimum musculoskeletally stable (anterior-superior) condylar position. In the event the patient’s condylar position is not optimal, the patient’s condyle may re-position more posteriorly/superiorly during resolution of their symptoms. This may result in a change of the patient’s occlusal scheme. Although this is not a result of "supraeruption", it may appear that way, due to the mandible pivoting at the distal most molar, possibly creating a lone contact which may be adjusted through equilibration

In the presense of MINIMAL INCISAL OVERLAP (for example, 1 or 2 mms, which is not uncommon following orthodontic therapy, as the mandibular incisor's brackets limit the degree of overlap), the potential for the development of an Anterior Open Bite is at its greatest
This fact should be pointed out to the patient. If they do not consent to the possibility of a change of occlusal scheme (even though symptoms have improved), this method of therapy is CONTRA-INDICATED

In the presence of advanced periodontal disease, the NTI alone should be used with caution
An opposing device should be considered

Not all occlusal schemes are compatible to the application of an NTI device without significant modifications to the device, such as in the case of severe flaring and/or rotation of the central incisors. A custom device may need to be fabricated instead

Following any apical or alveolar surgery to any of the teeth that support the NTI, discontinue use until completely healed

In the event of severely worn centrals (for example, a loss of 50% of tooth structure) an unaltered typical NTI device is contraindicated, due to lack of available undercut for retention

The device may need to be extended laterally to provide adequate retention

If the patient insists on a "more comfortable" fit, that is, not as snug, confirm that the patient CAN NOT remove the NTI without using their hands. The NTI is contra-indicated if the patient is non-compliant with the appropriate retentive adaptation

Its use is contraindicated if the supporting teeth have provisional restorations. (Use the Thermoplastic Beads instead

An unaltered NTI can not be placed in the presence of orthodontic brackets