Carbon Dioxide Laser Irradiation Stimulates Mineralization in Dental Pulp Cells

Abstract

Reparative dentin is formed in the dental pulp in response to various external stimuli such as caries and abrasion. Carbon dioxide laser has been used to accelerate the formation of reparative dentin on the exposed pulp surface. However, the mechanism by which carbon dioxide laser irradiation stimulates mineralization in direct pulp capping treatment is not fully understood. We examined the effects of carbon dioxide laser irradiation on mineralization in rat dental pulp cells. Rat dental pulp cells were irradiated with a carbon dioxide laser at an output power of 2 W for 20, 40, and 60 s and were cultured in media containing ascorbic acid and β-glycerophosphate. Cell viability was examined 24 h after laser irradiation by a modified MTT assay. Alizarin Red S staining was performed 10 days after laser irradiation. The amounts of collagen secreted from the cells after irradiation were quantified following Sirius Red staining. The expression levels of collagen type I and HSP47, collagen-binding stress protein, were analyzed by real-time PCR. HSP47 protein expression was examined by Western blotting. The cell viability was not affected by laser irradiation at 2 W for up to 40 s. However, it was significantly decreased by 20% at 60 s. The amount of mineralization after 10 days of irradiation at 2 W for 40 s was significantly increased in comparison to the other conditions. The extracellular collagen production was significantly increased, by 73% on day 2 and 38% on day 4, after laser irradiation. Although collagen type I gene expression was not changed by laser irradiation, HSP47 gene and protein expression was induced within 12 h and 24 h, respectively. These results suggested that carbon dioxide laser irradiation stimulated mineralization in dental pulp cells by increasing HSP47 expression.