Sleep-related bruxism (SRB) is a primary cause of headaches. It is one of the most commonly reported symptoms in patients 25-35.
Headaches tend to be centered in the temple regions but can affect the entire head. They are severe in nature and can be debilitating.
Why do these occur?
In SRB, there is a mutation in a gene on chromosome 13 called the HTR2A gene. In SRB there are multiple copies of this gene. The purpose of this gene is to produce receptors in the brain and the stomach for serotonin, a neurotransmitter, that suppresses activity.
We have protective reflexes like gagging, coughing, sneezing, etc. One such reflex, the masseter inhibitory reflex (MIR) protects the teeth from damage when eating.
If you bite into a hard food unexpectedly, you immediately stop chewing, remove the offending item, and slowly resume chewing. Otherwise, you could break a tooth! This is the MIR in action. It activates in as little as 1 millisecond!
In SRB, the increased number of serotonin receptors suppresses the MIR, allowing the patient to grind and clench with 100% of their bite force!
This is the cause of damage to the teeth discussed elsewhere.
Fatigue and damage to the chewing muscles occur over time and headaches associated with these muscles result.
Tension headaches have been shown to also be associated with the HTR2a mutation similar to SRB. There is suppression of the MIR and extreme clenching and grinding forces.
Figure 1 Suppression of the MIR in SRB
There are two stages of the MIR. The first, called exteroceptive 1 phase or ES1, occurs very quickly and the second phase, ES2, is slightly later. In image 1 above, the top tracings show the normal ES1 and ES2 reactions.
The middle tracing, mild SRB, the ES2 phase is shortened allowing the patient to clench and grind much harder than normal.
The last tracing, severe SRB, the ES2 phase is completely missing with a complete loss of protection.
This is all a result of the Masseter Inhibitory Reflex being suppressed.
Figure 2: Comparing tracings of sleep-related bruxism and tension headaches of the MIR
IN figure 2 above, the upper tracing is of a severe SRB patient, the lower is of a tension headache patient. They are almost identical!
SRB and tension headaches are intimately related. Tension-type headaches are one of the most commonly reported symptoms of SRB and it is possible that it could be due to a concurrent tension headache. These two are very closely related and very often occur in the same individual.
