Effect of metal ions released from orthodontic mini-implants on osteoclastogenesis.

BACKGROUND: Orthodontic mini-implants can undergo corrosion and the release of metal ions can affect cellular behavior. Osteoclasts are involved in orthodontic tooth movement and implant stability. Osteoclasts and their precursors can be exposed to metal ions released from orthodontic mini-implants. OBJECTIVES: This study aimed to investigate the effect of metal ions released from orthodontic miniimplants on human osteoclastogenesis. MATERIAL AND METHODS: Stainless steel and titanium alloy mini-implants were separately immersed in culture media for 14 days (days 1-14), and then moved to new media for a further 14 days (days 15-28). The concentration of the released metal ions was measured. Osteoclast precursors derived from human CD14+ monocytes were cultured in these media and in a control medium without mini-implant immersion. Cell viability, the number of osteoclasts and the area of resorption were investigated. RESULTS: A higher concentration of metal ions was detected during the first 14 days as compared to the control. The concentration of these metal ions then declined after this period. The viability of osteoclast precursors was not affected by the released metal ions. There was a significant reduction in the number of osteoclasts when cultured in the medium with the titanium alloy mini-implants immersed for days 1-14. The area of resorption was also significantly reduced in this group. The media with the titanium alloy mini-implants immersed for days 15-28 and with the stainless steel mini-implants immersed for both study periods did not show statistically significant changes in the number of osteoclasts. CONCLUSIONS: Metal ions were released from orthodontic mini-implants in the early period and declined thereafter. Metal ions released from titanium mini-implants in the early period inhibited osteoclastogenesis, while metal ions from stainless steel mini-implants had no effect on osteoclast differentiation.

Mechanical stress induced S100A7 expression in human dental pulp cells to augment osteoclast differentiation.

OBJECTIVES: Mechanical injury of dental pulp leads to root resorption by osteoclasts/odontoclasts. S100 proteins have been demonstrated to be involved in inflammatory processes and bone remodeling. This study aimed to investigate the effect of mechanical stress on S100A7 expression by human dental pulp cells (HDPCs) and the effect of S100A7 proteins on osteoclast differentiation. MATERIALS AND METHODS: Isolated HDPCs were stimulated with compressive loading (2 and 6 hr), or shear loading (2, 6, and 16 hr). S100 mRNA expression and S100A7 protein levels were determined by real-time PCR and ELISA, respectively. Osteoclast differentiation was analyzed using primary human monocytes. The differentiation and activity of osteoclasts were examined by TRAcP staining and dentine resorption. In addition, the expression of S100A7 was analyzed in pulp tissues obtained from orthodontically treated teeth. RESULTS: Compressive and shear mechanical stress significantly upregulated both mRNA and protein level of S100A7. Dental pulp tissues from orthodontically treated teeth exhibited higher S100A7mRNA levels compared to non-treated control teeth. S100A7 promoted osteoclast differentiation by primary human monocytes. Moreover, S100A7 significantly enhanced dentine resorption by these cells. CONCLUSIONS: Mechanical stress induced expression of S100A7 by human dental pulp cells and this may promote root resorption by inducing osteoclast differentiation and activity.