Attention has been paid to the mottled tooth since the report of Black and McKay in 1916. Thereafter the developing mechanism of mottled teeth has been made clear to some extent by many examinations and studies, but the majority of them is that of the permanent tooth and very few works have been made on the deciduous tooth. What these few works agree in their opinions with each other is that incidence of mottled deciduous teeth is lower than that of permanent ones, but the reason for this difference is still in the stage of speculation. The results of clinical and experimental studies on the mechanism of development of mottled deciduous teeth are described in this paper.
Material and Methods: The Th-Neo-Thorin Method was used for determination of fluorine. All the materials used were distilled and only the fluorine ion was isolated.
1) Numerous cases of mottled deciduous teeth were discovered when investigation of mottled teeth had been carried out in Tomita District, Tamashima City and Konko Town in Okayama Pref. in 1953.
The results obtained from the studies on the relationship between their incidence and caries of deciduous teeth and on determination of the fluorine content in drinking water are as follows:
a) Average number of the persons with mottled teeth was 47.84 per cent in the permanent teeth and 15.23 per cent in the deciduous teeth, in the ratio 3 to 1. And the degree of mottled teeth was M1 in most cases and M2 in few cases and no M3 could be found.
b) Minimal threshold of fluorine in the incidence of mottled teeth was approxiamtely 1.0 ppm. in the deciduous teeth, while 0.5 ppm. of fluorine caused mottled teeth ofdegree of M1.
c) Caries incidence of the deciduous teeth was as low as that of the permanent teeth; and caries incidence in case of mottled deciduous teeth was lower than that in case of permanent ones.
2) The following experiments were performed for the purpose of investigating the rôle the placenta played in the fluorine metabolism during pregnancy:
First, the fluorine content in the placenta of pregnant women and in the drinking water taken by them selves during the pregnancy were determined both in fluorine and non-fluorine districts.
Then oral examinations of the children of the mothers in the fluorine district were conducted. And the rationship of incidence of the mottled deciduous teeth to the content of fluorine in the placenta and in the drinking water was investigated and the fluorine content of the deciduous teeth was determined at the same time.
The results obteined were as follows:
a) When the mother took a large amount of fluoride, some of fluorine was retained in her placenta, while the rest pessed through the placenta and had an effect on the embryo.
b) The higher was the content of fluorine in drinking water, the larger was the amount of fluorine retained in the placenta.
c) A small amount of fluorine could be recognized in the control placenta taken from the non-fluorine district.
d) Incidence of mottled deciduous teeth was dependent upon the fluorine content of drinking water.
e) The larger the content of fluorine in drinking water, the more frequently seen the incidence of mottled deciduous teeth with its minimal threshold of 1.0 ppm.
f) Fluorine of 334.4 ppm. on average was contained in the mottled deciduous teeth, i.e. about one third of fluorine in the mottled deciduous teeth.
3) The following animal experiments were performed in order to confirm those results mentioned above in human:
Rabbits were used as experimental animals to investigate what amount of fluorine was retained in the placenta and to what extent it was transmitted to her embryo and, moreover, to determine whether there was any limit in the retention of fluorine within the placenta.
