Fine Structure and Elemental Analysis of the Enamel in Andrias davidianus (Cryptobranchidae) and Onychodactylus japonicus (Hynobiidae)

Abstract

Functional teeth from Andrias davidianus and Onychodactylus japonicus were prepared for transmission electron microscopy (TEM) and electron microprobe analyzer (EMPA) of the elements of the enamel layer. The enamel layer is thin and the arrangement of the enamel crystals is regular in the outer enamel layer of Onychodactylus japonicus; on the other hand, the crystals of Andrias davidianus show irregularities in different tooth regions. Based on calcium and magnesium distribution levels using electron microprobe analyzer (EMPA), the enamel layer lacks enameloid in these species. Concentrations of iron and fluoride are located in the outer enamel layer. The presence of trace elements is related to the formation and mineralization of enamel. l of Herpetology, Vol. 25, No. 2, pp. 14 46, 1991 i t 1991 Society for the Study of Amphib ans and Reptiles cture and Elemental Analysi of the Enamel in i s avidianus (Cryptobranchidae) and actylus japonicus (Hynobiidae) O,1 KAZUYUKI SHIMADA,2 ATSUYUKI YOKOI,2 The enamel layers of the amphibian tooth form prismless structures, in contrast to mammalian teeth which have rods in the enamel layer. This material is known as aprismatic enamel, and though it is very thin, it is hypermineralized, as in mammals. In mammals, the enamel crystals are chiefly composed of hydroxyapatite, with iron, fluoride and other trace elements complexed in the surface enamel layer of the tooth (Halse and Selvig, 1974; Selvig and Halse, 1975; Weatherell et al., 1975; Heap et al., 1983; Nelson et al., 1989). A number of different trace elements may be involved in the formation of the apatite crystals. The pigmented layer of rat incisor enamel contains 1-10% iron (Halse and Selvig, 1974) bound to the surface of hydroxyapatite crystals (Selvig and Halse, 1975). Trace elements may also be associated with the mineral component of amphibian enamel. Based on observations using polarizing microscopy, Schmidt (1971) reported that the enamel of Andrias japonicus contains pigments that impart a ena el layers of the amphibian too h prismles structures, in contrast to ma brown color at the tip of the tooth, which he suggested to be an iron oxide. Using transmission electron microscopy (TEM), Kawasaki and Fearnhead (1983) reported the presence of enam loid, a substance previously reported to occur only in fish, beneath the enamel layer in the teeth of the salamanders Hynobius nigrescens and Cynops pyrrhogaster. Enameloid differs from enamel in having a different embryological origin (mesoderm vs. ectoderm), and in having a much lower mineral content (Poole, 1967). The purpose of this study was to look for an interrelationship between the fine structure, concentration, and distribution of trace elements of the enamel layer in Andrias davidianus and Onychodactylus japonicus, and to ascertain the presence or absence of enameloid in these species. MATERIALS AND METHODS Thirteen adult (total length ca. 80 cm) Andrias davidianus (Cryptobranchidae) and ten adult (tocolor at the tip of the tooth, w ich he ested to be an iron oxide. Using transmiselectron microscopy (TEM), K wasaki and head (1983) reported the presence of eloid, a substance previously reported to only in fish, beneath the enamel layer in teeth of the s lamanders Hynobius nigrescens nops py rhogaster. Enameloid differs from el in having a diff rent embryological or( esoderm vs. ectoderm), and in having a lower mineral content (Poole, 1967). urpose of thi study was t look for an relationship between the fine str cture, 141 This content downloaded from 157.55.39.59 on Mon, 17 Oct 2016 04:59:01 UTC All use subject to http://about.jstor.org/terms