Clinical Evidence
HIT-6 Disability ↓ | Placebo-Controlled Trial ↓ | HIT-6 Results ↓ | Clenching & Migraine ↓ | Bite-Force Study ↓ | EMG Study ↓
From Physiological Rationale to Clinical Evidence
The NTI protocol was developed around a mechanical principle: limiting forceful posterior and canine engagement may reduce the intensity of parafunctional jaw-clenching.
But a plausible mechanism is not, by itself, evidence of clinical effectiveness.
The essential question is whether modifying these mechanical conditions can produce measurable improvements in patients' lives.
That question has been investigated in published clinical research, including a randomized, placebo-controlled crossover study involving patients with chronic migraine.
Measuring Headache-Related Disability
Migraine treatment outcomes are often described in terms of headache frequency or intensity. Another important measure is the degree to which headaches interfere with everyday life.
The HIT-6 classifies headache-related disability into four categories: severe impact, substantial impact, some impact, and little or no impact.
A movement from one category to another represents a change in the patient's reported level of headache-related disability.
The NTI placebo-controlled study evaluated these changes, allowing investigators to compare outcomes associated with the active NTI device and a placebo oral appliance.
What Did the Placebo-Controlled Study Demonstrate?
In a randomized, single-blind, placebo-controlled crossover study published in BMC Neurology (2022), Blumenfeld and Boyd investigated whether an NTI device could reduce headache-related disability in patients with refractory chronic migraine.
The results revealed substantial differences between the active NTI device and the placebo appliance.
Improvement in HIT-6 Disability Categories
| Clinical Outcome | NTI Device | Placebo Device |
|---|---|---|
| At least one-category improvement | 68% | 12% |
| Two-category improvement | 36% | 0% |
While one-category improvement is the commonly desired outcome in pharmaceutical studies evaluating improvement in disability, the observation of two-category improvement is rare, if not existent.
These percentages use the 25 enrolled subjects as the denominator. Nineteen completed the full two-month crossover trial.
Among those 19 completers, 74% experienced at least a one-category improvement with the NTI, compared with 16% using placebo. A two-category improvement occurred in 47% with NTI versus 0% with placebo.
The difference in categorical improvement was statistically significant (Fisher's exact test, p = 0.00125).
Why These Findings Matter
A two-category improvement in HIT-6 represents a substantial reduction in a patient's reported headache-related disability.
The absence of two-category improvements with the placebo device is particularly noteworthy.
Although this was a small pilot study requiring confirmation in larger trials, its findings support further investigation of nocturnal jaw-clenching suppression as an adjunctive approach to chronic migraine management.
Published research: Blumenfeld AM, Boyd JP. Adjunctive treatment of chronic migraine using an oral dental device: overview and results of a randomized placebo-controlled crossover study. BMC Neurology. 2022;22:72.
https://pubmed.ncbi.nlm.nih.gov/35246048/
The Relationship Between Jaw-Clenching and Migraine
Why Investigate Masticatory Muscle Activity?
The muscles responsible for jaw closure are capable of generating substantial forces, particularly during forceful clenching.
Sensory information from the masticatory system travels through the mandibular division (V3) of the trigeminal nerve, which participates in the broader trigeminal sensory pathways involved in craniofacial pain.
This anatomical relationship provides a rationale for investigating whether excessive jaw-clenching may contribute to headache-related symptoms in susceptible individuals.
A Potentially Modifiable Source of Trigeminal Input
The NTI approach is based on a straightforward clinical proposition:
If forceful jaw-clenching contributes to a patient's cumulative trigeminal nociceptive input, reducing that activity may help reduce the overall burden.
This is a proposed physiological mechanism, not proof that jaw-clenching causes migraine.
The clinical significance lies in identifying a potentially modifiable factor that conventional migraine treatment may not directly address.
Experimental Evidence: Maximum Bite Force in Migraine Subjects
In a study published in Headache (2000), Burnett and colleagues compared masticatory muscle activity and bite force in 10 migraine subjects and 10 matched asymptomatic controls.
The investigators found that maximum voluntary bite forces were approximately twice as high in the migraine group:
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Anterior bite force: 231.9 versus 115.1
-
Posterior bite force: 455.9 versus 232.5
Both differences were statistically significant (P < .01).
The migraine group also demonstrated significantly greater absolute EMG activity in the masseter and temporalis muscles during maximum voluntary contractions.
Importantly, the investigators did not find significant differences in resting EMG activity or ordinary oral functions.
Clinical significance: These findings demonstrate that the studied migraine subjects were capable of generating substantially greater voluntary clenching forces than matched controls.
The study did not measure nocturnal clenching or establish that increased bite force causes migraine. However, the findings provide a rationale for investigating excessive masticatory loading as a potentially modifiable contributor in selected patients.
Burnett CA, Fartash L, Murray B, Lamey P-J. Masseter and temporalis muscle EMG levels and bite force in migraineurs. Headache. 2000;40:813–817.
Sustained NTI Use and Masticatory Muscle Activity
A 2019 clinical study by Boulad and colleagues evaluated electromyographic activity in 15 patients with muscular-origin temporomandibular disorders before treatment with NTI splints and after six months of use.
The investigators reported substantial reductions in muscle activity during maximum voluntary contraction:
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Masseter: 50.8% reduction in mean EMG activity
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Temporalis: 57.2% reduction in mean EMG activity
Both changes were statistically significant (p < 0.001).
These findings demonstrate that sustained NTI use was associated with markedly reduced maximum voluntary masticatory muscle activity in this patient group.
Although the study lacked an untreated control group and did not directly measure nocturnal clenching or migraine outcomes, it provides additional experimental evidence relevant to the NTI approach.
Boulad JMK, et al. Effects of Treatment with Nociceptive Trigeminal Inhibition Splints on Electromyography in Temporomandibular Joint Disorder Patients. J Contemp Dent Pract. 2019;20(5):598–602.