Vibration characteristics of the rotating dental instrument.

PATIENT discomfort in restorative dentistry has been attributed mainly to the two factors of heat generation and the vibration produced during the cutting operation on the tooth. A review of the literature, however, gives little information on either the extent or chief source of vibrations. Gabel reported that the chisel produced the least pain of any instrument used to cut dentin. While the reason for this is not clear, Gabel speculated that it is due in part to the lack of vibration and noise and to a small heat production.1 Braceland2 referred to the work of Best,3 in which he described the relationship of vibration to pain, and pointed out that the dental engine frequently starts painful, annoying stimuli to bring about a reaction of aversion on the part of the patient. In a direct attempt to measure the nerve reaction set up by vibratory stimuli applied to the teeth, Pfaffman made certain interesting observations.4 Electrically controlled sinusoidal waves, checked oscillographically, were applied to cats' teeth. Nerve endings were placed between plates and the nerve response recorded on the oscillograph. "Spikes" resulted as a nervous reaction on the oscilloscope, which continued after the stimulus was removed. The nerve responded faster and more intensely to high frequencies, but the nervous reaction died faster than the response to low frequency. When the initial shock was over, the nerve set up a vibration frequency identical with the impulse. This observation is of some interest in the study of vibrations produced by the rotating dental instrument. The work reported by Walsh and Symmons5 concluded that (1) the upper limit of vibration perception is about 600 C.P.S., (2) a region of "maximum unpleasantness" exists between 150 C.P.S., and 200 C.P.S. and (3) the dental engine and handpiece produce a dominant vibration at about 100 C.P.S. Their first two conclusions are interesting in that they limit the field of vibration that should be studied. The third conclusion was arrived at from data obtained from patient reaction and from values obtained by using a rigidly mounted handpiece to cut away the surface of a brass slug, mounted in a vertical cylinder. These references indicate that vibration and noise are a source of patient discomfort and show that only little work has been done on research in any aspect of the subject of vibrations resulting from dental operations. It can be demonstrated that the vibrations produced by the rotating dental bur are in part a function of the material being cut, and the harder the