The Dental cosmos . ars. Fig. 19 is a deciduous tooth brushedwith a. gritty tooth-powder. It showsa fairly deep wedge-shaped defect atthe neck and two circumscribed deepdefects of the enamel separated fromeach other by a bridge. It is sometimesdifficult to understand why certain spotsare picked out. but such is the case. Itmay be accounted for in part by the MILLER — EXPERIMENTS AND OBSERVATIONS, ETC. 1 1 1 presence of weak spots in the enameland in part by the particular directiongiven to the bristles by the configurationof the neighboring teeth or gums. Then,again, the whole surface of the e
The Dental cosmos . ars. Fig. 19 is a deciduous tooth brushedwith a. gritty tooth-powder. It showsa fairly deep wedge-shaped defect atthe neck and two circumscribed deepdefects of the enamel separated fromeach other by a bridge. It is sometimesdifficult to understand why certain spotsare picked out. but such is the case. Itmay be accounted for in part by the MILLER — EXPERIMENTS AND OBSERVATIONS, ETC. 1 1 1 presence of weak spots in the enameland in part by the particular directiongiven to the bristles by the configurationof the neighboring teeth or gums. Then,again, the whole surface of the enamelmay be worn down until it breaksthrough at some particular more promi-nenl spol ; then, the dentin being exposed, more energetically than is the case in themouth. In those experiments in whicha strip of pink gutta-percha was fixedparallel with the alveolar border, thebristles, being prevented from spreadingout freely on the corresponding side,cut especially deep. Then again, on brushing the facial snr- Fic. I. Action of sediment from a tooth-paste containing tale, on glass. the abrasion extends rapidly from thatparticular point, and considerable pro-gress may be made in a. comparativelyshort time. In the present case theenamel is much thinned down over lhewhole surface of the tooth. In my experiments I have found agreater tendency toward the cutting bythe brush into the neck of the teeth thanwe find usually in the mouth in severeeases of erosion. Phis may be dm1 inpart, I think, to the fact that only onerow of teeth is brushed at a time, andthere being no sensitive gums to ward offthe brush as well as no gums to protectthe necks of the teeth, thev are rubbed faces of our teeth we naturally close orvery nearly close the month and brushboth rows at the same time. The bristlesspread out on tin1 surfaces of the teethand only tin1 very outside row- reach thenecks of the1 teeth. Or again, if themouth is not completely closed] so thaia space remains between the two rows offront
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