Purpose
Blue light has been reported to enhance the differentiation and mineralisation potential of mesenchymal stem cells. No studies have investigated the photobiomodulation effects of blue light on the odontogenic differentiation of dental pulp stem cell-containing populations. This study aimed to determine the effect of 405-nm wavelength on the mineralisation response in these cells.

Methods
Human dental pulp cells were irradiated using a calibrated 405 nm light source at an irradiance of 57.7 mW/cm2 for 35, 69, 90 and 104 s; delivering energy densities of 2, 4, 5 and 6 J/cm2. Cell proliferation was investigated on days 2 and 4. Alkaline phosphatase activity and dentine matrix protein-1 levels were investigated on days 3 and 5. Mineralised nodule formation was investigated on days 7, 4 and 21.

Results
The 405-nm blue light had significant inhibitory effects on dental pulp cell proliferation. Simultaneously, blue light irradiation enhanced the mineralisation response, as determined by the upregulation of odontogenic markers. Irradiated cultures also demonstrated a significant increase in mineralised nodule formation compared with the non-irradiated controls at all time points.

Conclusion
Data indicate that phototherapy utilising a 405-nm wavelength may have therapeutic potential in stimulating odontogenic responses of pulp cells.