Effects of LED-Irradiation on Calcified Nodules Formed in HDP Cells

Objectives: When pulp tissue is irritated by mechanical, thermal, or bacterial irritants, inflammatory reactions occur in the pulp and produce, in particular, pro-inflammatory cytokines. Pulp repair characterized by dentin bridge formation is known to occur after direct pulp-capping of exposed pulp by using calcium hydroxyl products. Although this direct pulp-capping technique is practiced widely, hard tissue formation often does not progress smoothly toward a cure, necessitating pulpectomy. The clinical use of LED has increased, and LED are now employed frequently even for conservative treatment. We have been studied the anti-inflammatory effect of 405nm-LED irradiation when used as an adjuvant to accelerate hard tissue formation. However, issues such as cell-propagated signaling immediately after LED irradiation and calcified nodules formation have received little attention. We investigated the effects of 405nm-LED irradiation on the calcified nodules formed of human dental pulp (HDP) cells.

Methods: The cells were cultured in alpha-MEM containing 10%-FCS, and 405nm-LED irradiation for 0, 1, 2.5, 5 or 10min. After LED-irradiation, the cells were incubated with culture medium supplemented with mineral-inducing factors comprising 50µg/ml ascorbic acid and 10mM ß-glycerol-phosphate. Production of OPN was measured using ELISA technique. ALPase activity was measured using ALPase activity kit. Calcified nodule formation was determined by Alizarin red S staining and von Kossa staining, and the amount of calcium was then measured.

Results: Calcified nodule formation was increased on 30days in 5min LED-irradiation group. Amount of calcium was also highest in the 5min LED-irradiation (p<0.01). ALP activity in the LED-irradiated and control groups increased in a time-dependent manner and peaked on 15days. ALPase activity was significantly highest in the 5min LED-irradiation (p<0.01). Production of OPN in conditioned medium was also highest in the 5min LED-irradiation (p<0.01).

Conclusion: These results suggested that HDP cells calcification ability is enhanced by LED-irradiation.