Red-Light-Emitting Diode Irradiation Modulates Dental Pulp Cellular Responses

Low level light irradiation (LLLI) using lasers and light emitting diodes (LEDs) is reported to promote mineralised tissue repair processes however the cellular and molecular mechanisms involved remain unclear. Objectives: To characterise the responses of dental pulp and comparative bone marrow cells in cultures following irradiation using LED. Methods: Pulp and bone marrow cells were derived from freshly sacrificed 6-week old rats. Pulp cell cultures were established following exposure of the pulp chamber and mechanical mincing/enzyme digestion of excavated tissue. Bone marrow cells were obtained following media flushing of femora. Cells (passages 1-3) were grown on standard tissue culture plasticware in alpha-MEM medium with 2 mM L-Glutamine, 5/10% FCS and 1% penicillin/streptomycin. Proliferative responses were determined using standard cell counting and BrdU immunocytochemical labelling following LED irradiation (660nm). Mineralization in cell cultures supplemented with dexamethasone (10^-8M), ascorbic acid (0.5mg/ml) and beta-glycerophosphate (10mM) was determined using Alizarin red staining. Results: Single dose delivery of LED irradiation at 20 and 40secs increased pulp cell numbers by 7-days. Whilst bone marrow cells demonstrated a more limited growth response to single LED exposure, double exposure (60secs at days 1 and 4) increased cell numbers significantly by day 7 compared with single exposure (day 1) and control (unexposed). Similar responses to double doses of LED were also detected in pulp cell cultures. BrdU assay demonstrated cells exhibited increased proliferation following LED irradiation. Significantly increased mineralization was detected in pulp cell cultures at 15-days in response to double dose (60secs) LED irradiation at days 1 and 7 compared with non-irradiated controls. Conclusion: LLLI using either single or multiple irradiation doses from simple LEDs may offer therapeutic potential for the promotion of wound repair in mineralised tissues such as that of the dentine-pulp complex.