Although the sample size is small and the results thus preliminary
clinical observations, I believe it will be interesting to see the
nature and frequency of motor function impairments in this group.

Results

Positional stability. A useful measure of change in an oral
positional function is the labial posture index. This index is primarily
focused on the problem of labial spill of saliva, drooling. A deficiency
in control of this function is very common in older people, less so in
middle-aged individuals, and essentially absent in the younger groups
(Fig. 1). In addition to the annoyance or embarrassment drooling may
cause these individuals, it frequently results in a chronic inflammation
of the labial fornices.

Figure 1. The incidence, by subject's age, of
some motor functional impairment in labial posture
stability. The criteria used for determining impair-
ment are described under methods.

A second tool to assess positional function is the tongue stability
index. Some impairment, as indicated by positive findings here, is
reasonably common among middle-aged and older subjects (5/10 per group)
but infrequent in younger individuals (1/5, Fig. 2).

Figure 2. The incidence, by subject's age, of some
motor functional impairment in tongue posture stability.
The criteria used are described under methods.

10

Dysfunction of the tongue suspensory muscles could conceivably manifest
itself in ways which would cause discomfort in daily life. One obvious
concern would be during sleep, when the tongue, due to lack of support,
would be liable to fall on the pharyngeal airway while an individual
slept on his back. This might be a cause of one type of what is
commonly referred to as "sleep apnea." In fact, three of our subjects,
who have demonstrable alteration in tongue positional stability,
reported an inability to sleep on their back and occasional arousal from
sleep due to shortness of breath. Another concern would be an inability
to competently close the junction of the mouth and pharynx with a
resultant increase in mouth breathing especially at night.

Finally, brief mention should be made of an occasional (5/20) observation with middle-aged and older subjects, that of irregular tongue motion. A range of unsteady movement has been seen. Disorders of motoneurons innervating the tongue could hamper such activities as eating and speech as well as possibly leading to traumatic injury to the tongue itself.

Swallowing. By utilizing several diagnostic criteria, the swallowing index may provide a clinical insight into motor impairment affecting competent swallow. The frequency of observed dysfunction is again skewed toward middle-aged (3/10) and older (4/10) subjects versus younger ones (0/5, Fig. 3).

Figure 3. The incidence, by subject's age, of some motor functional impairment in swallowing. The criteria used are described under methods.

Because of the potentially "disastrous consequences" (fatal choking, laryngeal food spills, regurgitation) of perturbations in the swallowing mechanism, motor disturbances in the involved musculature should be recognized as a disturbance of normal oral physiology (Bosma, 1976).

Chewing. Almost all dentulous older individuals studied reported no difficulties in chewing their food. Occasionally a subject would comment that "it took longer to eat, that chewing was slower and could lead to some embarrassment when dining with younger individuals." Each subject was clinically evaluated for motor power associated with jaw closing as described above. Demonstrable weakness in the muscles closing the jaw was infrequently observed, though again only in middleaged (2/10) and older (3/10) subjects (Fig. 4).

Figure 4. The incidence of impaired chewing function in different aged subjects. The criterion used is described under methods.

Weakness in these muscles did not necessarily correlate with a loss of muscle mass in the masseter and temporalis muscles. This was evaluated by palpation through the skin while subjects were asked to clench their teeth. Often subjects with clearly less palpable muscle tissue still exhibited strong coordinated jaw elevations.

Speech. It is important to emphasize that impairment of the muscles of the pharyngeal palate, the intrinsic muscles of the tongue, facial muscles, etc. could affect phonation, sound resonance and errors in speech. Though a short clinical session renders it impossible to detect all but major alterations in speech, one must be aware that slow, subtle changes may occur and conceivably influence the performance of certain daily activities.

Conclusion

These clinical observations provide little insight into the reasons for the disturbances. Do the findings reflect primary age changes in the neuromuscular system or are they secondary to other physiologic changes? Might many of these findings represent changes in sensory functions which offer peripheral influences on motor function? Many oral motor behaviors can be modified by sensory input (Sessle, 1976), and purportedly changes in taste, smell, tactile discrimination, and so on accompany normal human aging. Also, salivary secretions may provide some peripheral stimuli for certain oral motor functions. With advanced age the production of parotid saliva after stimulation is significantly diminished (Franks and Hedegard, 1973).

The oral motor apparatus is an exquisitely refined system. It performs critical daily functions in a subtle and unassuming fashion. In this paper, I have attempted to describe certain disturbances in normal motor function in the aging oral cavity. Because of the importance of these functional impairments, efforts should be directed at their study.

References

Bosma, J.F.:

Sensorimotor examination of the mouth and pharynx. Front.

Oral Physiol. 2:78-107, 1976.

Brody, H.: An examination of the cerebral cortex and brainstem in aging. In Terry, R.D. and Gershon, S. (eds.). Neurobiology of Aging. New York: Raven Press, 1976.

Franks, A.S.T. and Hedegard, B.:
Scientific Publications, 1973.

Geriatric Dentistry. Oxford: Blackwell

Gutmann, E.: In Finch, C. E. and Hayflick, L. (eds.). The Biology of Aging. New York: Van Nostrand Reinhold Co., 1977.

Kaldor, G. and DiBattista, W.J.: Aging in Muscles. New York: Raven
Press, 1978.

Kawamura, Y., Okazaki, H., O'Brien, P.C., and Dych, P.J.: Lumbar motoneurons of man. Number and diameter histogram of alpha and gamma axons of ventral root. J. Neuropathol. Exp. Neurol. 36:853-860,

1977.

I.