Of Jaw-Clenching, and a Remark on Open Bite

Then the king told the attendants, ’Tie him hand and foot, and throw him outside, into the darkness, where there will be weeping and gnashing of teeth.’

– Matthew 22:13 –

The normal complaint of bite-problem patients is that they say they don’t get any rest for their jaw muscles. They are resigned and miserable and they try to stay alert to follow the good advice of deliberately keeping their jaws apart, their teeth separated. However, they constantly find themselves clenching and gnashing their back teeth. That’s human nature.

The jaw does not just hang out there all day long, waiting for meal times to provide for bits to chew on. The swallowing reflex is another important business of the occlusion system. Every 30 seconds, or so, we do a swallowing reflex and that’s when the teeth make contact.

Initially in jaw-closing, the mandible may be hanging freely to the left or right, front or back, according the tilt of your head. Normally, the jaw closing muscles bring the mandible slightly forward so that the initial cautious contact between the upper and lower dental arches happens in the front teeth area. Excess force on a single front tooth slows down the jaw-closing and the mandible is steered to a more convenient position with more and more evenly distributed tooth-to-tooth contacts. Whenever the back teeth sense first contact, once again the jaw-closing muscles go more active. As soon as the back teeth make their first initial contact, it is very hard to deliberately stop the jaw-closing.  After the teeth are set together in the maximum intercuspal position, the power thrust of the closing-in muscles reaches the maximum. The tissues yield to tooth contact forces. The teeth are bent in their sockets; the periodontal ligaments of the teeth are squeezed. The bony structures in general, are bent. Even the teeth themselves undergo torsion and strain. Thus, the power of the jaw muscles becomes exerted to the front teeth, that yield under pressure. This is the moment after which, the forceful action of the jaw -closing muscles is suddenly repealed. The increasing sensory afferent information from the yielding front teeth stopped the clenching activity of the temporal and masseter muscles. Now, the deglutition reflex can proceed on. The jaw-closing muscles can relax and get their half a minute’s rest until the next oral phase of the swallowing cascade.

Unless, you happen to belong to the unfortunate patients that have been doomed to be outside in the darkness, weeping and gnashing your teeth. What went wrong?

Clenching one’s teeth is a disturbance where the sensory information from teeth fail to guide our muscular reflexes. There is a fundamental qualitative difference in the resultant muscular activity depending whether the sensory information to the motor ganglia of the trigeminal nerve is coming from the front or the back teeth. If your front teeth fail to give a signal to stop closing-in activity, you are bound to continue biting hard. The back teeth don’t differentiate what they are chewing on. They don’t give in. They go tough against anything hard. They do the same thing, no matter whether you are biting on a piece of carrot or your own tooth. The back teeth continue biting tough and hard, trying to find a position for the mandible where the power of the muscles becomes targeted to the front teeth. They go on and on waiting for this signal to end the closing-in activity of the masseter and temporalis muscles.

In my practice, I find it easy to help my patients who complain of restlessness of their muscles and jaw-clenching. Almost always, either one or both of their upper and lower canine teeth pairs are not in contact with each other in the maximum intercuspal position. I normally correct the unevenness by adding a little composite to the palatal of the upper canines and then adjust the bite with bite foil and diamond bur, little by little, by making the patient tap freely until all the teeth occlude simultaneously. The clenching will be cured right away.

There is another interesting aspect of the deglutition reflex that I have met with individuals with open bite. People with open bite can’t stop the back-teeth-closing-in sensory input, because the front teeth do not meet at all. How can they stop clenching? How can they swallow at all? No worries, Nature has a plan for that. In the swallowing reflex, simultaneous to the power-clenching phase of deglutition, a cascade of events happens with the tongue. The tip of the tongue moves against the front teeth. The tip of the tongue adds the thrust against the incisor teeth. Individuals with open bite need to thrust their tongue much harder against the front teeth to make them yield enough so that a sufficient sensory signal can happen from the front teeth. The swallowing process turns into a vicious cycle where the tongue tip must be thrusted hard against the front teeth. The dysfunctional tongue activity happens every 30 seconds, and in the long run, it pushes and moves the front teeth further apart and makes it even harder for the anterior teeth to switch off the back tooth sensory input in the cascade of swallowing process.

The resilient yielding of tissues undergoing strain from muscles of mastication is a crucially important factor that determines the functional dynamics of the occluso-muscular complex. The tissue-yielding-factor can’t be accounted for in studies employing mechanical articulators and stone-cast models of dentition. Even modern-day three-dimensional computer-created imaging of occlusion dynamics fail to account for the impact that the minute tissue-yielding can have for the resultant sensory information coming from the teeth. The Tscan system, however, provides the clinician dentist with an insight of events that happen in vivo. Perhaps, the tissue-yielding-factor has not been an easy and obvious thing to demonstrate on dried skull bones in the study-rooms of anatomy departments, where hypotheses of mastication dynamics have been contemplated. I can’t resist the temptation to finish this article with another biblical quote about the dry bones:

Thus says the Lord GOD to these bones: Behold, I will cause breath to enter you, and you shall live.

– Ezekiel 37:5 –

 

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