Mandibular incisors were dissected from the jaw of 15- and 16-day C57BL/10 mouse embryos and cultured on agar-solidified Eagle's basal medium supplemented with fetal calf serum, an antibiotic, and glutamine, The experimental medium was the same as the control except that fluoride was added such that the final concentrations ranged from 2.0-8.0 mM NaF. Control and experimental explants were recovered after two, four and six days of incubation and studied histologically. After two days of fluoride treatment (3.0 mM NaF), cellular degeneration was observed in the dental papilla mesenchyme while the enamel organ epithelium appeared more resistant. Prolonged treatment or treatment at higher concentrations resulted in destruction of the dental papilla. The enamel organ was still present but was abnormal and reduced. Older tooth germs were less affected overal when incubated at the same fluoride dosage and time of treatment. When explants subjected to limited exposure (2 days) to fluoride were placed on control medium, the suppressed tooth germs recovered. The recovery was enhanced by grafting untreated mesenchyme to the treated explants followed by incubation on control medium. The observations indicate that NaF can suppress the development of tooth germs in vitro and that recovery from the suppresion does occur. The more severe inhibition observed in the mesenchymal component when compared to the response of the epithelial component of the treated explants suggests that fluoride may alter the ultimate morphology of the tooth crown by disrupting the normal epithelial-mesenchymal interaction which occurs during early tooth development.
Embryonic molars and incisors were dissected from mandibles of 15-day post-fertilization C57BL/10 mouse embryos and were cultured in vitro for six days on agar-solidified Eagle's basal medium. Experimental explants were cultured on medium which was the same as the control except that 50, 75 or 100 microgram/ml tetracycline was added. Treated explants of both incisors and molars were suppressed in development and reduced in size. Enamel organs and dental papillae of all tooth germs subjected to higher tetracycline concentrations were abnormal in structure and differentiation of ameloblasts and odontoblasts was inhibited. Explants treated with higher dosage levels of the drug were more severely affected than those exposed to lower concentrations. Recovery from the suppression induced by tetracycline was observed in explants transferred to control medium for four days of growth following treatment. Differentiated ameloblasts and odontoblasts observed in the recovering tooth germs indicated that the inhibition in development was temporary. The results of this study showed that tetracycline can alter dental development in vitro prior to mineralization. The observed inhibition may be related to a disruption of collagen biosynthesis which is thought to play a role in the controlling epithelial-mesenchymal interaction involved in tooth germ morphogenesis.
The dentition of mice and rats, which normally consists of one incisor and three molars per quadrant, is not generally known for the occurrence of an excess number of teeth. This report describes experimentally induced supernumerary teeth which were observed in 5 of 44 mouse molar explants.Second molar tooth germs and the adjacent third molar rudiment were dissected as one explant from the mandibles of 18-day C57BL/10 mouse embryos. Care was taken to exclude incisor tissue The explants were cultured for 2 days on agar-solidified Eagle's basal medium** supplemented with 12 % fetal calf serum,** 1I% glutamine,** and 1% Gentamicint in a humid atmosphere of 5 % CO2 in air at 37 C in order to facilitate the subsequent placement of the explants in the anterior chamber of the eyes of homologous adult hosts. After two weeks, the eyes containing the transplants were then enucleated, processed through routine histological procedures, sectioned at 10 um, and stained with hematoxylin and Biebrich's scarlet.In all 44 intraocular grafts studied, the second molar tooth germs had advanced in development as evidenced by the presence of both enamel and dentin matrix. After 2 weeks of culture as arn intraocular graft, the third molar tooth germs had attained a stage of morphodifferentiation comparable to that acquired by the same tooth in vivo after 10 to 12 days of postnatal growth (COHN, Am J Anat 101: 295, 1957) indicating that the controlling influences governing third molar development had not been disturbed. Odontoblasts and a predentin matrix were aligned opposite a single layer of differentiated columnar ameloblasts with polarized nuclei. But, overall, these teeth were smaller in size when compared to the second molars. In five cases (11 %), a supernumerary tooth had developed adjacent to the lateral aspect of the third molar. The figure illustrates an intraocular graft with a normal appearing second and third molar plus an additional tooth which was similar
The inhibitory action of tetracycline on the development of embryonic mouse incisors cultured in vitro was examined. Explants exposed to tetracycline were severely inhibited in development. In contrast, tooth germs cultured in the presence of both tetracycline and iron escaped inhibition and attained a stage of development which compared favorably with the controls.
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