As to the blackish-brown deposit on the teeth, th- author investigated not only the frequency of the type of its occurrence but also the relations between that deposit and the decay of teeth, and seeking after the nature of that deposit, carried out various experiments with following results.
1. The author named the sole object of his study, i. e. the deposit on the teeth blackishbrown dental deposit.
2. The frequency of occurrence of blackishbrown dental deposit. Investigating the occurrence of the deposit about 7191 persons of both sexes from 6 to 14 Years of age, the author obtained the following results:
1) As to the age and sex, that deposit occurs most frequently at the epoch when the teething of deciduous teeth or the eruption of permanent teeth is completed in both sexes.
2) As to the position, the deposit occurs most frequently at the front teeth of lower jaw in both sexes.
3. The type of occurrence of the blackishbrown dental deposit. The author divided the types into 4 types and 8 kinds according to the states of occurrence of the deposit, that is
Type I: one having the deposit on the whole set of teeth of both jaws,
Type II a: one having it on the whole row of teeth of upper jaw only,
Type II b: one having it on the whole dentition of upper jaw and on a limited part of lower jaw,
Type III a: one having it on the whole dentition of lower only,
Type III b: one having it on the whole row of lower jaw and on a limited part of upper jaw,
Type IV a: one having it on a limited part of upper jaw.
Type IV b: one having it on a limited part of lower jaw,
Type IV c: one having it on a limited part of both jaws.
4. As to the age and sex of the same age, the deposit occurs most frequently on the whole set of teeth of both jaws (type 1) independent to the age and sex,
5. Relation between the blackish-brown dental deposit and the tendency to suffer the decay of teeth.
Searching for the ratio, of the decaying of teeth about 1601 persons having this deposit and 1225 persons having no such deposit, it was found that the one having that deposit is less disposed to the decay of teeth than the one having no such deposit, independent to sex and age.
6. The author could not find any difference between the hydrogen ion concentration of the saliva of the one having blakish-brown dental deposit and that of the one having no such deposit.
7. Comparing the amylase value of saliva of the one having blackish-brown dental deposit and that of the one having no such deposit, the acthor could not find any difference between the two.
8. When compared the result of spectroscopic analysis of the saliva and serum of the one possessing blackish-black deposit to that of the one having no such deposit, the saliva of the former was found to contain Mn in addition to the constituents of saliva of the latter, but no difference could be found as of their sera.
9. Analysis of blackish-brown dental deposit,
1) Results of the analysis of blackish-brown dental deposit showed clearly that it consists of Ca, Sr, Ag, Zn, Cu, Al, Fe, Mg, Mn, (Au), P, Si, Hg, and B.
2) Analysis by X-ray diffraction method showed that blakish-black dental deposit was Ca3 (PO4) 2. H2O.
3) According to the results of quantitative analysis of b-b. dental deposit, it contains 18.9% P and 36.6% of Ca.
10. From the results of the colour dissolution test of b-b. dental deposit, it was clear that the pigment black colour was organic and soluble in antiformine.
