The aim of this study was to investigate the effects of low-energy laser irradiation on differentiation to osteoblasts of human mesenchymal stem cells (hMSC). Alkaline phosphatase (ALP) activity and osteocalcin release were measured from irradiated-hMSC. The expressions of core binding factor a1 (Cbfa1) and osterix (Osx) were also examined by RT-PCR.
Low-energy laser irradiation (Ga-Al-As semi-conductor laser, output 50 mW) was applied to hMSC for 3 min (9.33 J/cm²/min: 27.99J/cm²), at 24 h intervals during the culture period of 28 days.
The laser irradiation groups showed significantly greater both ALP activity during experimental period and osteocalcin release on days 14 to 28 in comparison with the control group. RT-PCR results also showed that the expressions of Cbfa1 and Osx were up-regulated on days 3 and 7. The present results suggest that low-energy laser irradiation facilitates differentiation to osteoblasts of hMSC via Cbfa1 and Osx expressions.

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The subgingival dental calculi of people in their twenties and that of people over forty were compared to examine changes in structure and composition. The calculus samples of the older group were green, gray, and dark brown in contrast to that of the younger group. On the calculi of the older group, polygonal structures, flake-like structures, and bacillus-like structures were common. In the calculi of the younger group, small spherical structures were commonly observed. EPMA analysis revealed the composition of the calculi of the younger group contained higher levels of Na than that of the older group, while that of the older group contained higher levels of O, Ca, P, and Mg compared to the younger group. The Ca/P molar ratio was 1.75±0.39 on average in the younger group. The Ca/P molar ratio was 1.50±0.21 on average in the older group. HA was detected in the younger group, and W was detected in the older group by X-ray diffraction method. The analysis results of EPMA and the result of the X-ray diffraction method were in harmony. It is possible that the difference in crystal type and composition of subgingival dental calculi between the two groups is due to age.

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