SESSION III ORAL MOTOR BEHAVIORS AND DENTAL PROBLEMS IN AGING Chairperson: Patricia S. Bryant Health Science Administrator Pain Control and Behavioral Studies Program Branch Extramural Programs National Institute of Dental Research Bethesda, Maryland 20205 Principles of Motor Control and Their Application to Dental Problems A.T. Welford The study of movement falls mainly within the province of psychlogy rather than physiology because the limitations on almost all everyday movements, whether in work or in leisure activities, are not imposed by muscular strength or endurance but are concerned with accurate modulation and control. Until the last few years, however, movement has been very much a cinderella within psychology. A few researchers in the 1890's and the early years of this century were concerned with the speed and accuracy of hand movements (e.g. Bryan, 1892; Woodworth, 1899; Peters and Wenbourne, 1936), and with their integration into sequences (Bryan and Harter, 1897, 1899; Book, 1908), but further developments had to wait until the 1950's when they were prompted by problems of machine control in equipment for the armed services and industry. More recently they have expanded greatly in connection with sports and athletics, these have become big business and vehicles of international prestige. as What has been done so far is of little or no direct relevance to dentistry. Some of what is known is, however, challenging in dental contexts. The purpose of this paper, therefore, will be to survey briefly the present state of knowledge concerning the control of movement, and then to apply such understanding of it as we have to two areas, both of which are rich in human experience but almost totally unexplored scientifically: namely, the use of dentures and the performance of dental operations. Psychological studies of movement Most of the movements studied have been those of the whole arm over distances from one or two inches to one or two feet. Fast movements typically show a period of rapid acceleration followed by one of decelaration as the agonist and antagonist muscles come respectively into play, so that if position reached is plotted against time, the curve is Sshaped, as in figure 1. Distance The form of the curve is that which would be expected from a sudden burst of neural impulses to the agonist followed slightly later by a burst to the antagonist, acting on a limb possessing appreciable inertia (Crossman and Goodeve, 1963). When the movement is aimed at a target, the form is modified in one of two ways. If the movement is fast and the target in a line perpendicular to the direction of the movement, there is typically a single S-shaped impulse which lands close to the line; either a little too near or too far, followed by one or more minor oscillations to settle on the line as shown in figure 2. Time Figure 2. The typical course of a rapid movement aimed to terminate on a line. Target Line If, on the other hand, the movement is slower or the target is an area within which the movement has to terminate, it consists of a series of impulses each covering less than the last of the distance between starting point and target, so that the movement becomes slower as it approaches the target, as in figure 3. The impulses tend to run into each other so that they are often difficult to detect individually, but can be seen from a plot of velocity, also as shown in figure 3. Velocity Position Time Figure 3. The typical course of a slower |