Effects of different photobiomodulation therapy doses on cell viability after bacterial and ionizing radiation–induced stress: a pilot in vitro study

Purpose Photobiomodulation therapy has proven to be effective in accelerating cell proliferation, migration, and transcription. The study aimed to analyze the cell viability effects of different parameters of PBMT in a cultured cell line of human gingival fibroblasts after bacterial and ionizing radiation–induced stress. Methods Explant technique was used to produce a primary cell culture. Cells were grown in Dulbecco’s modified Eagle’s medium with 10% fetal bovine serum until stressful condition induction with lipopolysaccharide of Escherichia coli , Porphyromonas gingivalis protein extract, and ionizing radiation. Laser irradiation was carried out in four sessions set with 660 nm wavelength, an output power of 30 mW and 40 mW and energy density of 2, 3, 4, and 5 J/cm 2 . Results After 24 h from the last laser irradiation session, the groups outputted in 30 mW of power maintained the cell viability while operating with 2, 4, and 5 J/cm 2 . However, 3 J/cm 2 dose significantly decreased cell viability ( p < 0.05). When the laser irradiation session was set in a higher power (40 mW), cell viability was reduced using 2, 3, and 5 J/cm 2 doses, with statistical significance for 5 J/cm 2 ( p < 0.001). In addition, operating the same energy using lower power seems to be superior to a higher power, being statically significant for 5 J/cm 2 dose ( p < 0.001). This pattern followed with all different groups, except by 3 J/cm 2 . Conclusions The present study showed that delivering 2, 4, and 5 J/ cm 2 of density of energy with 30 mW and more time of exposure presented better results on cell viability compared to the same density of energy with output power of 40 mW. Further studies comparing density energy should be conducted.