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In the pursuit of this investigation we made micro-photographs of the grits commonly used in tooth powders and pastes and also combinations as found in a number of proprietary preparations. In the process of making these photographs, each powder or paste was shaken up in an excess of water, allowed to stand for about ten minutes and then filtered. The residue was then dried and mounted as for microscopical examination. The degree of enlargement is alike in all specimens, being 400 diameters.

Figures 9 to 19 inclusive include many of the abrasives commonly used, of which the most common is precipitated chalk. There are many grades and qualities of this substance, many of which contain impurities and foreign matter but the better grades have the appearance of fine round amorphous particles of uniform size. Figs. 13 and 14 show the similarity and identity of the so-called French chalk and Talc. There are many mouth preparations which appear to contain Talc in the form of thin plates of considerable size, and which because of their sharpness make them rapid cutters. Cuttle Fish and Pumice Stone are not being used by many manufacturers at the present time altho there are a few preparations on the market which still contain them. Two samples of Pumice Stone are shown in Figs. 16 and 17 for the purpose of comparing the product of the Buffalo Dental Mfg. Co. with that of ordinary stock pumice. Tin Oxide which is largely used in tooth powders to produce a high lustre to the teeth, is found on the market in several different forms. We show two varieties, Figs. 18 and 19, one a sample bought on the market out of stock and the other preparation made by Merck. It is claimed that this latter preparation is a better polisher than some other forms, which may be accounted for by the fact that it readily absorbes water, as seen in the cut, and the individual particles swell up, giving the whole mass a sticky and pasty con

sistency, which would be expected to bo a better polishing agent than the harder varieties.

In the consideration of the proprietary preparations samples were taken from stock packages of each, and an attempt was made to select a portion for our picture which was as typical of the whole as possible. We recognize the fact that it is difficult to judge a whole product by

small sample the mixture of ingredients may vary in different batches

even in two ends of the same can. In our examination we detected certain gross differences in these preparations and have attempted to obtain a true and intelligent record of each. Of the powders and pastes which were examined those which contained the coarser forms of abrasives are Pyorrhocide, Lyons Sozodont and Sanitol as shown in Figs. 20, 23, 31, and 32. Of these, Pyorrhocide contains a relatively large amount of a coarse heavy crystaline substance, two particles of which may be seen in the cut. These large substances are imbedded in a filler of a fine powder which seems to be somewhat hydroscopic. There is no evidence of soap as it does not foam on shaking with water.

Lyons contains a definite prismatic crystal with sharp corners. The filler consists of large round substances of irregular shape. which respond to the test for starch.

Among the finer powders Euthymol, Fig. 22 has a much smaller amount of sharp material than the last two, with a filler that is quite hydroscopic and an abundance of soap, while Graves, Fig. 21, contains a considerable proportion of a finer grit incorporated with granules of starch and has little soap.

Colgate, Listerine, Kolynos, Calox, Lilly, Hutax, and Pebeco, as shown in Figs. 24 to 30 are largely composed of fine grits, some of which resemble precipitated chalk and tin oxide. Many of the illustrations are misleading in their

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appearance because of the marked hydroscopic property of their particles which cause them to swell up and clump together so that they appear larger than some of the other varieties which are less hydroscopic. This is true in the cases of Hutax and Pebeco. Many of these preparations contain a high percentage of soap. This is especially true of the pastes. Those which contain little or no soap are Pyorrhocide, Graves, Calox and Listerine.

One non-proprietary preparation was examined, which was made after a formula suggested by Dr. J. W. Jungman of Cleveland. It is a powder and was made according to the following formula:

Pulv. Castile Soap Parts 34
Sacch. Alba Pulv.
Oxide Tin (Mercks)
Creata Precip.

12
Flavor Q. S.
Fig. 33 made from such

a powder shows plainly the precipitated chalk and some evidence of the hydroscopic tin oxide.

Figs. 34 to 36 are similar magnification of three products which are made use of by prophylaxis operators in polishing the teeth. It will be seen that both CarmiCleaner and Politor are largely composed of sharp particles which resemble ground silica. They are, however, quite even in their size and much smaller than those which are found in the ordinary forms of pumice stone. Carmi-Lustra is designed as a fine polishing powder but contains a considerable amount of small sharp crystaline like substances which is imbedded in a fine hydroscopic filler.

It must be clearly understood that in a comparative study of a number of preparations such as have been considered, it is not possible to judge of the cutting or abrasive qualities of each by the size and form of their grits alone. It will be found that the cutting properties are influenced by the hardness and sharpness of the particles as much or more than by their size. So that it is possible for a powder having small sharp particles to cut with greater rapidity than one con

taining large masses. The amount of soap which such preparations contain is also a factor of great importance. For instance, by the use of talc and water on the end of the finger, one may quite easily remove the glaze from a pane of glass. But if the talc, be mixt with an equal amount of powdered soap such as is used in tooth powders, it is extremely difficult to make an impression on the surface of the glass in this manner. So that it becomes evident that a large amount of soap in a dentifrice by its tendency to foam will envelope and cover up the particles of grit, thus partially or wholly preventing their action when used on the brush.

For the purpose of estimating the effect of certain dentifrices the following experiment was made. Six specimens were prepared each consisting of three perfect teeth, arranged as in the jaw and mounted in modeling compound which was carved to simulate the gums and gingival tissues. Modeling compound caps were then fitted over the incisal third of the tooth leaving the middle and gingival thirds uncovered. These sets of teeth were then brushed in a crosswise manner with a medium size tooth brush, using a different preparation in each case. They were each given 10,000 double strokes, which on the basis of 10 such strokes per day would represent the work done in about three years of use. It was recognized that this form of brushing was not ideal or proper, but was alike in all cases and not dissimilar to that which has very common acceptance among a large proportion of the public today. It must also be admitted that the work was done without the influence of mucinous material which would naturally accumulate upon

the teeth from time to time, and which would tend to diminish the abrasive action of the dentifrice. But in each case saliva was used as a lubricant and diluent of the paste or powder to be tested.

The first one of this series was brushed

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