In dental school, students are introduced to the temporomandibular joint (TMJ) through the hinges of an articulator. However, this tool does not naturally mimic the real TMJ. Instead of the mandible depressing and advancing as in real life, the maxillary component of the articulator is elevated and retruded by the practitioner.

Advances in education regarding the anatomy, diseases, and pathophysiology of the teeth and supporting structures continue to take place, but the insight and appreciation of the biophysics of the TMJ, how it can become strained and overloaded, and how to manage it are often left to continuing education resources.

The dental school articulator riddle has confounded many dentists throughout their careers as they navigate more specialized splint therapy and its real or supposed effects on the TMJ. In a peer-reviewed research study published this year with Dr. Andrew M. Blumenfeld, I aimed to address some of these specialized treatments through an adjunctive treatment of chronic migraines using an NTI-tss Plus^® (Nociceptive Trigeminal Inhibition Tension Suppression System) device. The following overview of the TMJ and NTI devices will focus on the functions of the TMJ, its anatomy and physiology, and the effectiveness of NTI devices in relieving severe migraine pain.

On the first day of dental school, the dental student is taught that occlusion is stipulated and that at rest, “normal” is “lips together, teeth apart.” For the teeth to remain in occlusion, the elevating musculature must be in a constant state of contracting. However, in the articulator, gravity replaces the elevating musculature. This results in a constant state of clenching of the mounted models, with the intensity of the clenching being a function of the weight of the maxillary cast model.

The most glaring misrepresentation of the articulator’s distortion of reality is the condyle-to-fossa relationship. In real life, when the persisting contraction of the elevators (clenching) ceases, the mandible depresses, with the condyle traveling down and forward along the eminence to rest position. When attempting to demonstrate rest position using the articulator, the practitioner extends the articulator’s incisal guide pin, which lifts the maxilla up to separate the teeth. Gravity continues to push the maxillary model down, which gives the practitioner the impression that the condylar ball appears to want to travel up and back along the eminence. From that opened position, due to the slope of the eminence, gravity’s influence on closure pushes the maxilla down and forward, which is interpreted by the practitioner as the mandible elevating up and back.

There are no muscles of mastication that encourage retrusive movement during functional elevation. In actual masticatory function, when incising on an object (or making contact with the anterior stop of an NTI device), the elevating musculature maintains the up-and-forward pressure of the condylar complex perpendicular against the slope of the eminence.

No matter how intensely one tries to incise an object, incisor edge contact governs innervation to approximately one-third of the maximum, with the condyle continually pressed up and forward against the eminence. It cannot move distally into the retrodiscal tissues. This is essentially how an NTI device is capable of reducing muscle contraction intensity by 70%. Based on dental students’ initial training with an articulator, it is understandable why a practitioner’s false assumption of using NTI devices is that it would cause distalization of the condyle.

In orthopedics, a splint is often prescribed to support a load-bearing joint (e.g., the knee) that has been strained or damaged. This splint is coupled with the articulating bones that comprise the joint and then assumes a portion of the purposeful ambulatory functional load. Joints that are not subject to the forces of gravity, such as the elbow, are not splinted, but are simply isolated to minimize their use.

An occlusal splint is often prescribed to minimize the strain or load on the TMJ, but the TMJ is not subject to the forces of gravity. The splint is not coupled to either the maxilla or mandible, and it is not used during purposeful functional mastication. There are many types of occlusal splints to choose from, but most are commonly used during sleep and often have no effect or influence until parafunctional activity ensues.

Not until the muscles of elevation are innervated does an occlusal splint have any effect. The splint assumes the role of the occluding surface of one of the arches. Upon contact with the splint, the occluding scheme provided by the splint then influences the parafunctional activity.

Stemming from the initial training with an articulator, the practitioner stipulates occlusion and therefore can wrongly assume that posterior interferences cause muscle hyperactivity, when in reality, the existence of a posterior contact is the result of elevator hyperactivity. Because the practitioner knows that occlusion or clenching is going to happen, the first order of business is to ensure balanced occlusion by spreading the forces resulting from the persisting elevation, such as that caused by clenching, throughout the splint to avoid traumatization of any individual teeth. During a clenching event, where the mandible is centered and the occluding contacts are spread evenly throughout the splint, there is no adverse strain or load on the TMJ.

From the centered clenching position on the splint, before the elevation innervation ceases completely and thereby ends any occluding at all, one or both of the lateral pterygoids (LPs) may contract and attempt to disclude the teeth.

For example, in a unilateral LP contraction of the right LP, the right condyle advances, shifting the mandible to the left. In normal masticatory function, if the LP is contracting, the mandible is depressing in the opening stroke of chewing with no resistance to opening. However, in parafunction, the elevator innervation, or clenching activity, persists, presenting the LP’s activity with significant and varying degrees of resistance. It is this resistance that creates the isometric contraction of the LP, which transfers considerable strain and load to its associated condylar complex.

The practitioner can then endeavor to minimize clenching intensity in the excursive positions by striving to provide for immediate posterior disclusion during the excursion. By providing posterior disclusion with a transition to incisal guidance, the practitioner best ensures that there is minimal joint strain and load during masticatory parafunction.

Even the ideal splint still allows for intense nocturnal clenching. This clenching can provide a considerable nociceptive afferent bombardment to the trigeminal sensory nucleus, which is known to be an irritant and sometimes the cause of chronic or episodic migraines.

The use of an NTI-tss Plus or NTI OmniSplint^® (an NTI device with a full-arch design) can address both issues: A migraine prevention device can minimize joint strain and load as well as jaw clenching intensity. At the initiation of nocturnal parafunction when the elevator musculature is innervated, the first and only contact is on the incisor’s edge. With an NTI device, the first contact is the anterior midline. This governs the clenching intensity, providing a positive therapeutic effect on migraine events. The discluding element (DE) of the NTI appliance provides instant incisal guidance, minimizing joint strain and load without having to pursue immediate posterior disclusion. The NTI therapeutic protocol provides parafunctional control and achieves the goals of dentists and their patients.

The most recent NTI study confirms that an NTI appliance “should be considered as a method of whether jaw-clenching is a contributing factor to ongoing migraines.”¹ When study participants used an NTI device every night for six months, maximum temporalis motor activity was reduced by over 50%.¹

The study also found that decreasing peripheral sensitization with a device like the NTI can help decrease central sensitization — a hallmark of migraines.¹ It is important to note that no adverse effects were reported by any of the subjects wearing an NTI device.

The study’s randomized, placebo-controlled, crossover methods were measured through a simple, six-question test given to the participants called the HIT-6^™ (Headache Impact Test) questionnaire. This questionnaire addresses six key areas: pain, social functioning, role functioning, vitality, cognitive functioning and psychological distress.²

In the research study, 68% of migraine sufferers saw an improvement in their HIT-6 scores with NTI appliance use.¹ This is a game-changer for the dental world. Migraines are one of the leading causes of all global disability, and dentists have the resources and supporting research to confidently prescribe their migraine patients with a proven dental solution.³

For more information about the NTI-tss Plus and NTI OmniSplint, visit glidewell.com/migraine-prevention.