No abstract

The aim of this study was to examine the developmental aspects of the dental lamina and the tooth germ of the marsupial opossum (Monodelphis domestica), and to clarify the dental formula of this animal. Specimens were 12‐, 16‐, and 18‐d‐old opossums. 3‐D reconstructions were constructed from frontal serial sections. In these animals, the tooth germs of the deciduous maxillary and mandibular canine, deciduous third premolar and first molar, and the deciduous maxillary first incisor and second molar had a successional dental lamina and a replacement tooth germ. The tooth germ of the deciduous maxillary fourth incisor and the mandibular first incisor were reduced. The dental lamina was continuous in each jaw except for the deciduous maxillary first incisor. The first dentition (deciduous dentition) remained as the permanent dentition on the deciduous maxillary first incisor, and the deciduous maxillary and mandibular canine and first molar. The maxillary fourth incisor and the mandibular first incisor were the second dentition (successional dentition). Only the deciduous third premolars were replaced. These results showed monophyodonty caused by both deciduous and replacement tooth germ degeneration.

No abstract

Abstract:The aim of this study is to examine the developmental aspect of the dental lamina and the tooth germ, the structure of the tubular enamel and the function of the enamel tubules in the marsupial, opossum (Monodelphis domestica). The dental formula of the animal used in the present study was 5134/4134=50. In 12-, 16-, and 18-day-old opossum, the tooth germs of the upper and lower deciduous canines, third deciduous molars and first molars, and the upper first deciduous incisor and second molar had successional dental laminae and the replacement tooth germ. The tooth germs of the upper fourth deciduous incisor and the lower first deciduous incisor were reduced. The dental lamina was continued in each jaw except for the upper first deciduous incisor. This dental lamina continued with the oral epithelium in the mesial or distal region of each tooth germ, except for the lower third molar. The first dentition (deciduous dentition) remained as the permanent dentition on the upper first deciduous incisor, and the upper and lower deciduous canines and first molars. The upper fourth incisor and the lower first incisor were the second dentition (successional dentition). The third deciduous molars were replaced by the third premolars in both jaws.Tissue differentiations such as the enamel knot, enamel cord and stratum intermedium were observed as in eutherian mammals. Most enamel prisms, surrounded by interprismatic enamel, ran obliquely from the dentinoenamel junction (DEJ), and bent near the enamel surface. The enamel tubules were distributed in both enamel prisms and the interprismatic enamel near the DEJ. Several enamel tubules ran within one enamel prism. From the middle to the surface of the enamel, one enamel tubule ran in a single enamel prism.One enamel tubule continued from the DEJ to near the enamel surface, and was speculated to develop in relation to one ameloblast. The fiber of the odontoblast process continued from the dentinal tubule distribut-

The aims of this study are to clarify the structure of tubular enamel and the function of enamel tubules on the marsupial of opossum (Monodelphis domestica). Almost all enamel prisms, surrounded by interprismatic enamel, ran obliquely from the dentinoenamel junction (DEJ), and bent near the enamel surface. The enamel tubules are distributed in both enamel prisms and the interprismatic enamel near the DEJ. From the middle to the surface of the enamel, one enamel tubule ran within a single enamel prism. Most of enamel tubules continued from the DEJ to near the enamel surface. It is suggested that each enamel tubule developed in relation to one ameloblast. The fibers of odontoblastic process penetrated the DEJ from the dentinal tubules into the enamel tubules, and some branched across the enamel prisms. The odontoblastic process may be actively cross into the ameloblastic layer and may be involved in the formation of enamel tubules. After in vivo injection of tetracycline, tetracycline labeling showed that the odontoblastic tubules continued to enamel tubules. And strontium was detected in enamel tubules from the DEJ to the enamel surface, as was the dentinal tubules. In conclusion, there was active transport by the odontoblast and it's process through the enamel tubules.