WHY do many elderly people, especially those missing teeth, diaplay a chewing motion?

Dr John Rutkauskas of the American Society for Geriatric Dentistry consulted with two of his geriatric dentistry colleagues, Dr Saul Kamen and Dr Barry Ceridan, adtold Imponderables that his chewing motion is found almost exclusively in people who have lost teeth. On rare occasions, certains tranquilisers or antidepressants (in the phenothiazine family) may cause a side effect called tardive dyskinesia, an inability to control what are ordinarily voluntary movements. These movements are as likely to involve the nose as the mouth or jaws,though.

In most cases, Rutkauskas believes that the chewing motion is a neuromuscular response to the lack of teeth: an attempt by the oral cavity to achieve some from equilibrium. In particular, sufferers can't position their upper and lower jaws properly. With a full set of ivories, the teeth act as a stop to keep the jaws in place.

Of course, most people who lose teeth attempt to remedy the problem by wearing dentures. And most people adapt well. But 

Ike House, a dentist and Imponderables reader (we're sure he is prouder of the first qualification), told us that a significant number of elderly people have lost the ability to wear dentures at all because of an excessive loss of bone:

"They can close their mouth much fuller than they would with teeth present, resulting in the "nose touching skin" appearance of many elderly people. Since the normal "rest position" of about 2 or 3  mm between the upper and lower natural or artificial teeth is not able to be referenced, they may be constantly searching for this position"

Many elderly people who wear dentures feel that the prostheses just don't feet normal and restlessness leads to 'chewing in the air', as House amplifies : 

"If you had two objects in your hands, such as two coins, you would probably manipulate them in some way. When not using a pen or pencil, for example, but holding it passively, we usually move it in our hand. It may be that people wearing dentures constantly manipulate them in some way just because objects being held but not used are often moved by unconscious habit. 

I have a great -uncle who lets his upper teeth fall down between words and pushes them back up against his palate. This is a most disconcerting habit to his family!

I know some elderly patients cannot tolerate dentures in their mouth unless they are eating because they can't leave them alone."

Barnet B Orenstein, Associate Clinical Professor of Dentistry at New York University's College of Dentistry, told Imponderables that the tongue is often the culprit in creating the chewing motion:

"Elderly people often display a constant chewing motion because, having lost their lower teeth, their tongue is no longer confined to the space within the dental arch. The tongue spreads out and actually increases in size. What appears to be chewing motion is actually a subconscious effort to find a place for the tongue."

The last time we were at the Imponderables staff's official dentist, Phil Klein, we asked him to wrestle with this mystery while he mauled our molars (and we pondered whether we could deduct the office visit from our income tax as a the research as well as medical expense). Much to our relief, Dr Klein concurred with the theories stated above but raised the possibility of a few others, including rare neurological condition and grinding of teeth to the point where the lower and upper jaws can't mesh comfortably.

Klein also mentioned that problems with salivation, and particularly dryness, is a constant problem for numerous elderly people, and many with this problem move their mouth and jaw in response to the dryness. 

And then he told us we had no cavities.