1. Enamel formation in various kinds of animals have been investigated histologically in the sections stained with resorcin-fuchsin and other routin stainings, and the transference of enamel matrix substances (resorcin-fuchsin stainable substances, bereafter: R-stainable snbstances) to the other tissues than the enamel, especially the dentine, have been found in the tooth germ tissues of rats, guinea-pigs, dogs and human beings.
In this paper, the significance of such findings as the above mentioned for amelogenesis has been discussed.
2. At each stage of the pre-formative, formative, maturation stage, of enamel formation, it is found that the substances, which are able to be stained with resorcinfuchsin and supposed to be enamel matrix substances, penetrate both to the dentinal matrix and dentinal tubules, but their appearances and periods are different from one another among those various animals above mentioned.
3. In the guinea-pigs, R-stainable substances begin to penetrate to the dentine, immediately after the time when the formation of dentinal matrix begins. At first, R-stainable substances appear between the ameloblasts (inner enamel epithelium) and the dentinal matrix, and then part of them penetrates to both dentinal matrix and tubles, and moreover, to the odontoblastic zone, through the dentinal tubules (Fig. 1 and 2).
The penetration to the dentine become more and more remarkable gradually, according as it approaches to the beginning of the enamel matrix formation, and is observed continuously until the middle stage of enamel matrix formation comes (Fig. 3).
4. In the rats, R-stainable substances begin to penetrate to both the dentinal matrix and tubules of superficial zone of the dentine from the ameloblasts (inner enamel epithelium) side, some time after the dentine formation starts (Fig. 4). The degree of this penetration gradually increases, according as it approaches to the very beginning of enamel formation (Fig. 5 and 7), but on a sudden decreases prior to the commencement of the enamel matrix formation (Fig. 6 and 7). At the formative stage of enamel, R-stainable substances penetrate to nothing but dentinal tubules of superficial dentine. And then, following to enter the maturation stage, R-stainable substances begin to penetrate to the dentinal tubules of deeper zone of dentine, neighbouring the middle zone of dentine (Fig. 8 and 9). Such findings as these are continuously observed until the endstage of maturation.
5. In the human beings, in a little while after the beginning of enamel matrix formation, R-stainable substances begin to penetrate to the dentinal tubules, and frequently this substance reach the odontoblasts zone through the whole width of dentine (Fig. 10 and 11). At the same time, the reduction of stainability of enamel matrix, neighbouring dentine does occur (Fig. 10-13). Such discolouration is more remarkable at the interrod substance than the enamel rod (Fig. 12 and 13). This appearance can be distinguished from the changes of stainability of matrix usually observed after the apposition of enamel matrix in various animals, and are not artefact occured to them in process of preparation of section. Such penetrations of these substances continue for some time, and after the time when the enamel matrix has been formed about one third of the whole width, and then gradually decrease finally to disappear at all. After a time, decolouration of enamel matrix is recovered and shows similar appearance to the surrounding enamel matrix.
6. In the dogs, R-stainable substances penetrate to the dentinal tubules only in superficial layer of dentine at the endstage of preformative stage of enamel formation. This phenomenon is observed continuously during the formative stage of enamel (Fgi. 14).
7. At the beginning of penetration of R-stainable substances to the dentine of guinea pigs, the nucleus of ameloblasts just still begin to migrate to the basal side of the cytoplasms
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