Hydroxyapatite is a biologically compatible material and a major component of dental enamel and bone tissue. Because of its biocompatibility and structural similarity to human teeth and the skeletal system, a number of dental studies have evaluated its application as a bone substitute or dental restorative material. This study was to evaluate the differences in bonding strength and resistance to demineralization between micro-hydroxyapatite and nano-hydroxyapatite added to self-cured resin-reinforced/modified glass ionomer cement. RelyX^™ was used as the base glass ionomer cement material and for the control group. 10% micro-hydroxyapatite added glass ionomer cement was named experimental group 1, and 10% nano-hydroxyapatite added glass ionomer cement was named experimental group 2. Physical tests for ISO9917-1:2007 in each group was acceptable, except the setting time of nano-hydroxyapatite added glass ionomer cement, which exceeded maximum setting time. Bonding strength was greatest in nano-hydroxyapatite glass ionomer cement, and cohesive failure was common in all specimens. When fractured surface was observed under SEM, spherical particles were observed in experimental groups containing hydroxyapatite particles, and they were more prevalent in nano-HA added glass ionomer cement group than in micro-hydroxyapatite added group. Both experimental groups exhibited greater resistance to demineralization compared to the control group, and there was no significant difference between the experimental groups. Under SEM, nano-hydroxyapatite added glass ionomer cement exhibited increased resistance to demineralization compared to micro-hydroxyapatite added glass ionomer cement.

In many studies, adult stem cells have been found in human periodontal ligament (PDL), but in most cases they were found in the permanent teeth. The aim of the present study was to characterize stem cells from the PDL of deciduous teeth (dPDLSCs) and compare them with those from the PDL of permanent teeth (pPDLSCs). Stem cell markers were examined by a flow cytometric analysis. The results of in vitro differentiation into adipogenic and osteogenic lineages were analyzed by histochemical staining and quantitative reverse transcription–polymerase chain reaction (RT-PCR). The results of in vivo transplantation were analyzed by histological staining, immunohistochemical staining, and quantitative RT-PCR. There were no significant differences in the proliferation rate, cell cycle distribution, expressions of stem cell markers such as Stro-1 and CD146, or in vitro differentiation. The pPDLSC transplants made more typical cementum/PDL-like tissues and expressed more cementum/PDL-related genes (CP23 and collagen XII) than did the dPDLSC transplants. Together, these results suggest that pPDLSCs are better candidates for use in reconstructing periodontium.