Masaaki Ogawa

Iron Concentration in Teeth of Tetra-odontiform Fishes and its Phylogenetic Significance

It is known that iron is deposited in the enameloid of some teleost fishes, although its biological significance has not been clarified. In the present investigation, a quantitative analysis of iron in the enameloid of fishes of a primitive suborder, the Balistoidei, and an advanced suborder, the Tetra-odontoidei, of the Tetra-odontiformes of marine teleosts was performed by means of the electron microprobe. The results indicated that the enameloid of Balistoidei contained from 0.4-13.5% iron at its surface layer, whereas that of Tetra-odontoidei was very low in iron, which could not be discriminated from the background value of the emission intensity. The enameloid of three perciform species belonging to the Acanthuridae-from which the Tetra-odontiformes are considered to have been derived-also contained high iron (2. 7 - 3.9%) throughout its entire layer. The iron concentration in the enameloid seemed to be related to the phylogeny of fishes rather than to their environmental water and feeding habits, and it is believed that the mechanisms of iron concentration into the developing enameloid have been lost during evolution from the Achanthuridae to the Tetra-odontoidei. Since a similar phenomenon has been previously observed with respect to the fluoride concentration in the enameloid of the same fishes (Suga et al., 1981a), it is speculated that the concentrations of iron and fluoride, which have originally no chemical correlation, have some special biological significance, although the timing and distribution pattern of their deposition are completely different.

Evolution of Fluoride and Iron Concentrations in the Enameloid of Fish Teeth

It is well known that the fluoride has an ability to promote precipitation and growth of apatite crystal and to make its crystallinity higher due to its incorporation into crystal lattice. On the other hand, excess uptake of fluoride during tooth development interferes with the functions of the hard tissue forming cells, especially, the enamel forming cells, and, finally, induces hypomineralization of enamel (mottled enamel). Fluoride in the teeth, especially, in human enamel, under normal and various pathological conditions, has been examined by many investigators mainly in connection with dental caries [1, 2]. On the other hand, deposition of histologically detectable amount of iron in the enamel of amphibians, reptiles and some mammals and in the enameloid of some fishes has been known for many years. It has been considered that the iron minerals act as hardening agents on the surface of enamel and enameloid [3–5].

Expression status of mRNA for sex hormone receptors in human dental pulp cells and the response to sex hormones in the cells

OBJECTIVES Sex hormone receptors are reported to be present in human dental pulp (HDP) cells. The purpose of this study was to examine the biological significance of oestrogen and androgen receptors (ER and AR, respectively) in HDP cells. DESIGN We isolated HDP cells expressing ER- and AR-mRNAs and investigated the expression status of the receptors and the response to sex hormones in the cells. RESULTS HDP cells expressing ER- and/or AR-mRNAs had the ability to form alizarin red S-positive nodules in which calcium and phosphorus were deposited in vitro and to differentiate into odontoblasts-like cells and dentine-like tissue in vivo. Individual clones isolated from HDP cells exhibited a different expression pattern of mRNA for ER and AR. Some clones expressed ERα- and/or ERβ-mRNAs and the others coexpressed ER- and AR-mRNAs. Using the Ingenuity software, we found that 17β-estradiol (E2) and dihydrotestosterone (DHT) could act directly on HDP cells through ER-or androgen signalling-mediated mechanisms. E2 or DHT stimulated the mRNA expression for genes related to odontogenesis of dentine-containing teeth and odontoblast differentiation, suggesting that ER and AR in HDP cells may be involved in dentinogenesis. CONCLUSIONS Our findings provide new insights into the biological significance of sex hormone receptors in HDP cells.

Fluoride and Iron Concentrations in the Enameloid of Lower Teleostean Fish

Our quantitative elemental analyses with the electron microprobe indicated that the fluoride and iron concentrations in the enameloid of bony fish are related to the phylogeny of fish. The enameloid of some bony fish with high F also contained high Fe. In order to clarify the phylogenetic significance of such a peculiar dual deposition of F and Fe into developing enameloid, quantitative electron microprobe analyses of these elements were made on the teeth of taxonomically lower teleosts. There were significantly different trends of F and Fe concentrations in the enameloid among various forms of lower teleosts. In the Osteoglossiformes, the enameloid of the osteoglossid species contained very low levels of F and Fe, whereas in the single representative of the Mormyroidei, the F was very low but Fe was very high. In the Elopomorpha, the enameloid of the elopiform species contained a medium level of F and high Fe, and that of the anguilliform high levels of F and Fe. In the Salmoiformes, the salmonid species had medium F and high Fe, and in a species of the Esocidae, high F and high Fe levels were found. The stomiiform fish exhibited levels of medium and high F and high Fe. The results of the present study and our previous investigations made on archaic non-teleostean and various teleostean fish indicate that the mechanisms of F and Fe concentrations into developing enameloid are independent of each other, and that the mechanisms of Fe concentration appeared earlier and disappeared later than, or concurrently with, that of the F concentration, in the course of fish evolution.

Fluoride release from fluoride-releasing orthodontic materials and the effect of saliva on etched enamel Part 2. Effect of fluoride release on etched enamel in artificial saliva

The objective of the present study, following by the previous study, was to evaluate the effect of the fluoride (F) release from each material on etched or non-etched bovine enamel in artificial saliva. In this study, a 2% NaF solution and a 6min immersion period for the rechargeable treatment were applied, and then F and Ca concentrations in the artificial saliva with etched or non-etcnhed bovine enamel were determined. Moreover, each enamel specimen was analyzed by EPMA. The results obtained are as follows: (1) F release in artificial saliva was significantly different between the products, but little F rechargeable abilities was observed. (2) A significant negative correlation was observed between F and Ca concentrations for the first two weeks. (3) EPMA analysis showed that the F uptake was increased with F release and was greater for the etched bovine enamel. These result shows that the application of F-releasing material may be beneficial for orthodontic treatment.

Fluoride release from fluoride-releasing orthodontic materials and the effect of saliva on etched enamel Part 1. Evaluations of fluoride release in de-ionized water and factors influencing the fluoride rechargeable ability

Fluoride(F)-releasing materials have been widely applied in the adhesion of orthodontic bands and brackets to prevent the development of dental enamel caries during the treatment. One of these materials, glass ionomer cement (GIC), has been considered to act as a long-term F reservoir, because it not only releases F but also has a specific F rechargeable abillity from external F agents such as F mouthrinse. The objective of the present study was to determine the F release from two fluoride-releasing orthodontic materials in de-ionized water, and to evaluate the effects of the products, the F concentration of NaF solutions (0.02, 2%) and the immersion time (3, 6min) on the F rechargeable ability, during a two week trial. The results indicated that both the F releasing and the F rechargeable abilities were significantly different between products, and the effect of NaF immersion on the rechargeable ability was greater for the F concentration of NaF solution than for the effect of immersion time.