Inhibition of ALP by Root Canal Sealers in Human Osteoblasts

Objectives: Histological investigations have demonstrated that root canal sealers can induce mild to severe bone resorption. Alkaline phosphatase (ALP) is a membrane-bound glycoprotein, which is one of the osteogenic differentiation markers considered to indicate the formation of new bone. The aim of this study was to investigate the effects of root canal sealers AH26, Canals, and N2 on the expression of ALP in human osteoblast cell line U2OS cells. Methods: Freshly mixed materials were filled in glass rings (4 mm height and 10 mm in diameter) and eluted in 10 ml of culture medium for 1 day. Subsequently, various dilutions (final dilution: 1/2, 1/4, and 1/8) of these extraction media were prepared for this study. Cytotoxicity was measured by the almar blue dye assay. Gene expression of ALP was examined using reverse transcription-polymerase chain reaction. ALP activity was further examined using substrate assay. Results: The results showed that AH26, Canals, and N2 were cytotoxic to U2OS cells in a concentration-dependent manner (p<0.05). The exposure of U2OS cells to root canal sealers resulted in the down-regulation of ALP mRNA gene expression (p<0.05). ALP activity was also significantly suppressed by root canal sealers (p<0.05). The rank of ALP decreased in an order of AH26 > N2 > Canals. Conclusions: Taken together, the inhibition of ALP expression may play an important role in the pathogenesis of root canal sealers-induced periapical bone destruction. This study was supported by NSC 97-2314-B-040-0xx.