Chewing gum is not good for you?

Those dentists, who are oriented to treat patients suffering from bite-related problems, don’t like chewing gum. Strange, isn’t it?

One would think that a little exercise for the jaw muscles can’t be bad. Shoulder-pain-doctors, back-pain-doctors and all the rest of professionals who treat patients with any problems related to the muscle and joint function, always applause physical exercise. The common, and empirical, knowledge of almost any doctor in the jaw-closing-business is, however, that chewing gum aggravates their patient’s joint and muscle problems. What’s wrong with chewing gum? What can be unnatural in chewing? Isn’t the process of chewing the hallmark of human civilization? Convivial jaw movement in a dinner table society is a powerful social gesture. Throughout the existence of human race, the ability to effortlessly chew one’s food – as unhesitant as the rest of the dining company – has been positively determining the social status and the acceptance of an individual as a member of a social group. The inability to show the gesture of mandible movements, to chew one’s food as the others do, provokes caution in a social group. The amicable social cohesion of The Beefeaters dinner party becomes strained as soon as a member of the Beefeater club suddenly, after the soup, when the roast has been brought into the table, becomes aware of the hesitant jaw movements of a fellow member sitting on the opposite side of the dinner table.

“How come, is there something wrong with the steak?” inquires the alarmed table-mate. He had just recently recognized the same uneasy kind of chewing pattern with her daughter at his own family dinner table. To his dismay, he had learned his daughter having become succumbed to the influence of a television documentary dealing with the ethics of animal farming and animal rights.

“No worries”, replied the uneasily chewing Beefeater. The ethical aspects of meat-eating had never been his concern, the trouble was the filling his dentist had made just in the afternoon before the dinner. The filling was high and prevented him from chewing normally.

In my previous blog article: “Chewing gum. Details of the process and a remark on its social implications” I reasoned that after the food bolus has become crushed between the molar and premolar teeth, the bits and morsels are supposed to be milled by a smooth mediotrusive roll of the mandible from the working side lateral excursive position to the midline. The mediotrusive move of the mandible cannot happen, unless there is a constant sensory signal from the anterior teeth, that switches on the activity of the median pterygoid muscle, that brings the mandible medially towards the maximum intercuspal position of the dentition of the upper and lower jaws. The path of return of the mandible from lateral excursion to the midline must be unobstructed by disturbances from the back teeth. A slightest touch in the back would cause a burst in temporal and masseter muscles, and the activity of their antagonist, the medial pterygoid muscle would be stalled. This wouldn’t make a smooth mediotrusive movement, but a jagged zig-zag locomotion, where the temporal alternation of either up or medially  orientated muscle groups, depending on the amount of posterior contact interferences, would be negotiating the path of return to the midline of the mandible. Alaleuan liikesuunnat sulkemisessa osissa

The lateral excursion test is an essential part of any proper dental examination. We want to see whether our patients’ jaw glides effortlessly to the lateral. In the lateral excursion test we examine, the other way around, the same path of gliding that happens when our patient does the end phase of his/her chewing cycle. In the following illustration, I have drawn an orange arch to give an idea where the dental arch of the upper jaw lies. Pink arch gives an idea of direction of the movement of the mandible. The extent of the jaw movement in this picture is overly exaggerated. A green circle is to depict the location of the palatal surface of the maxillary cuspid tooth. The red line inside the green circle usually confines the limits of normal chewing.lateral excursion with green circle

I have learned to appreciate the following kind of a staunch red line that the occlusion foil marks to the palatal aspect of the cuspid teeth of my patients. This video shows what I do to treat patients with occlusion problems.

The points of interference in the back teeth area are very difficult to distinguish from occlusion bearing points of contact. Nevertheless, it is those almost undistinguishable wispy dots that have to be removed in order to obtain a staunch red line, the hallmark of proper canine guidance. Personally, despite my 30 years of practice, I must admit that I almost always fail to identify the right ink mark to grind unless I compare the foil marks to a Tscan movie. With an uninterrupted red line like that on the palatal surface of this young lady above, however, gives me a confidence that I have eliminated all the disturbing contacts of the back teeth area. As confirmed by a Tscan movie the lateral excursion test for this young lady showed smooth gliding of the mandible, uninterrupted by interferences. As a result, she was set free from her almost daily bouts of migraine. Clicking in her jaw joint also disappeared. I have been following the condition of her occlusion at recall visits. She still is very happy of having received the treatment a couple of years ago. The occlusal alterations that I performed have remained unaltered, as if the natural harmony of muscles and dentition would be a self-repairing system itself.

I have examined thousands of Tscan-movies of the lateral excursions of my patients. I have concluded, that would there be a slightest interference of the back teeth, a jaw-elevating reflex ensues. A minuscule tactile contact between the back-teeth during the lateral glide of mandible fires a powerful burst of activity in the masseter and temporalis muscles. The interference produces a jagged total force curve on a Tscan force vs. time graph. The activity of elevator-muscles shuts down the activity of muscles that exert lateral movements. The time required for the mandible to disclude the back teeth is prolonged.

In the natural chewing cycle the same things happen as with the lateral excursion test, but it happens vice versa, in an opposite direction. The smooth return of the mandible from lateral excursion into the midline is hampered by the slightest interference in the back-tooth area. The reflex activity of the two powerful elevator muscles ensues and the antagonistic medial pterygoid muscle is turned off. The mandible can’t glide smoothly to the maximum intercuspidation. A jagged up-lateral-up-lateral stepwise jaw-closing ensues, depending on how many times the anterior guidance of the mandibular path-of-gliding was interrupted by back-tooth interferences. The chewing doesn’t proceed smoothly, but it appears awkward and strained.

To understand the movements of the mandible, it is essential to understand the direction of the muscles involved in the process. The medial pterygoid muscle is commonly thought to belong to the “elevator” group of muscles, which I think is is a misnomer. The medial pterygoid exerts a mediotrusive direction of force which is mostly perpendicular with the direction of force of the masseter muscle. The fibers of the medial pterygoid point almost directly in the opposite direction of most fibers of the temporal muscle. The antagonistic nature of the masseter and temporal muscles in relation to the medial pterygoid is a fact of anatomy. It is misleading to put the medial pterygoid muscle together within the jaw-elevator group of muscles. Besides, even the sensory control of  its activity is emanating from an entirely different place – the sensory endings of the anterior teeth.

To resume the title of this article I would conclude that the general physical activity is no less harmful for the muscles of mastication than it is for the rest of the body muscles and joints. However, the occlusal interferences of the dentition disturb the smooth and effortless action of the jaw muscles in a similar manner as your walking would be hampered by a pebble in the sole of your shoe.

Instead of instructing our patients to stop chewing, it is a much better idea to take away the interferences of dentition and let the muscles do the thing they best want to do. Take the pebble out of the shoe. The trouble, of course, is to find out where the pebble lies in the dentition. Experienced dentists admit that it is not easy to make a filling to match perfectly to the lateral chewing movements. Traditional occlusion foil technique just does not always do the trick. Implementing digital technology into our everyday practice to detect and record occlusal contact force alterations in vivo sets the quality of dental work to a new level of standard.

 

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