VIBRATION CHARACTERISTICS OF THE ROTATING DENTAL INSTRUMENT

¹ School of Dentistry, University of Michigan, Ann Arbor, Mich.

Since the results described in this paper represent a portion of the work done on the problem, and since the study is still actively in progress, this should be considered as a preliminary or progress report. The results described were obtained by using the conventional handpiece and rotating dental instruments to cut ivory. The data presented are considered to be applicable only for the test conditions described and, while they perhaps show a trend to be expected when operating on teeth in the mouth, studies will be made to verify the mouth conditions.

In this study certain characteristic trends were observed, and while some specific exceptions were also noted, the prevailing observations justify the establishment of the trends. Throughout the study the fundamental vibration wave has occurred at the speed of rotation of the handpiece shaft and changes with operating speed. The fundamental vibration wave, which is larger than any harmonic, is modified by different operating speeds and pressures, as well as by the choice of cutting instrument employed. In general, the amplitude of the fundamental vibration decreases as the pressure is increased when the bur is driven in the forward direction. When operating with light pressures there is the tendency for the amplitude of vibration to decrease as the speed is increased. This tendency prevails, but is less pronounced when operating at heavier pressures. In general, the slower speeds and lighter pressures have given the larger amplitude to the fundamental vibration wave, with gradually decreasing amplitudes for the second to fifth harmonics, beyond which the harmonic amplitudes are essentially the same to the tenth. While there is some tendency for larger bur sizes to show a greater vibration characteristic, more studies will be made of this relationship.