Photobiomodulation counteracts DAMP signaling to improve Odontoblast Survival for Dentin Repair

Objectives Tooth vitality is driven by the odontoblast responses in the pulp-dentin complex. Low-dose light treatments, termed Photobiomodulation (PBM) therapy has been noted to induce odontoblast differentiation from dental pulp stem cells and promote dentin repair in a sterile, direct pulp capping approach. Its ability to direct repair in a routine clinical scenario post-infection or injury remains to be elucidated. Methods An odontoblast cell line, MDPC-23 were subjected to various stressors namely inflammation (TNF-α), bacterial infection (LPS), hypoxia (CoCl₂), nutrient deprivation (0.2% serum), and pH stress (pH 4 or 12). Cells were treated with four PBM wavelengths of 447 nm (blue), 532 nm (green), 658 nm (red), and 810 nm (near-infrared) delivered at doses of 0.03, 3, or 30 J/cm². To investigate potential mechanisms, small molecule inhibitors targeting ROS (N-Acetylcysteine, NAC), ATP (Sodium Azide, NaN₃), NFκB (BAY 11-7082), BCL-2 (anti-apoptotic), Caspase-3 (pro-apoptotic) were used. Cell viability was assessed with Alamar Blue and mitochondrial membrane potential was assessed with JC-1 fluorescence assay. Results We noted all four PBM wavelengths induced significant (n = 4, p < 0.05) odontoblast survival at 3 J/cm ² at optimal cell density. All stressors, except LPS, reduced odontoblast viability significantly (n = 4, p < 0.05) that were rescued significantly (n = 4, p < 0.05) with the red and green wavelengths most consistently. Both wavelengths were not significantly (n = 4, p > 0.05) affected by neutralization of ROS, BCL-2 or Caspase 3, but differentially affected by ATP deprivation and significantly (n = 4, p < 0.05) neutralized by NF-κB inhibition. The increased mitochondrial membrane potential to TNFα treatments were also differentially modulated by the two wavelengths significantly (n = 4, p < 0.05) suggesting there are divergences in individual signaling pathways mediating the overall PBM survival response. Conclusion These results demonstrate that discrete PBM wavelengths evoke context-dependent odontoblast proliferative responses. These findings highlight the therapeutic potential of PBM in modulating odontoblast responses to various damage stimuli that can be utilized to develop specific protocols for optimal clinical therapeutic clinical outcomes.