Black & white photograph
Many patients when taught the stabbing or vibratory stroke in occlusal brusing [...] tend to place the brush perpendicular to, instead of parallel with, the row of teeth (see Fig. 306). This tends to cause the omission of some teeth and the breaking or bending of the bristles. This illustration shows a method of demonstrating, to the patient, by means of the brush and any straight instrument handy, that if the two rows of posterior teeth would continue anteriorly as straight lines, they would, because of their convergence, meet directly in front of the nose. Accordingly, he is instructed to so place the brush as to have the handle in front of the nose in order to dervie maximum benefit. While this measn may not be necessary for the lower teeth, which can be seen by the patient, it often serves very practically for the upper ones.
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