The purpose of the present study is to examine the relationship between the formation and composition of incremental lines in tooth dentin and the role of melatonin through histological and analytical studies. In this experiment, 5, 6 and 7 day old SD rats were used. These rats were divided into three groups: i) a control group (0.5% alcohol content drinking water); ii) a low concentration group (0.5% alcohol+20 μg/ml melatonin content drinking water); and iii) a high concentration group (0.5% alcohol+100 μg/ml melatonin content drinking water). The animal protocol was approved by the Animal Care and Use Committee of Mekai University. The specimens were observed and analyzed using light microscopy, scanning electron microscopy, transmission electron microscopy, laser Raman microprobe spectrometry, and an electron-probe microanalyzer (EPMA). In the control group, two dark-staining incremental lines of hematoxylin and one light staining layer were observed in incisor dentin. In the low-melatonin concentration group, the light staining layer became narrow. In the high-melatonin concentration group, this layer disappeared. The number and size of calcospherites in predentin increased in proportion to the concentration of melatonin administered. A new incremental line was confirmed in both the incisor and molar dentin of the melatonin treated groups. In the high-concentration group, a strong expression of ALP activity was observed. In EPMA analysis, Ca and P content were increased in the melatonin treated group. By laser Raman microprobe spectrometry, the peak of PO43− was higher in the high-concentration group. It is considered that melatonin participates in the formation of incremental lines and the calcification mechanism of dentin. The work was supported by KAKENHI (23592727).
17 May 2014 - 20 May 2014