Effect of Irradiation with Different Wavelengths on Fibroblasts and Oral Micro-organisms

Objectives: To investigate the effect of irradiation with light of different wavelengths on the proliferation of immortalized mouse fibroblasts (3T3, DSM ACC59), primary human gingival fibroblasts (HGF), Strep. sobrinus (Ss, NCTC 10921), Strep. mutans (Sm, DSM 20523), and L. acidophilus (La, DSM 20079). Methods: 3T3 and HGF were grown in 96-well plates for 24 h. Microorganisms were grown in trypticase-soy and de Man-Rogosa-Sharpe broth, respectively. Light from diode lasers (cw) was emitted at 633 nm, 660 nm resp. 760 nm with an output energy of 242 mW. The energy density varied between 1 J/cm² and 40 J/cm². After irradiation, fibroblasts growth were determined by XTT assays (mitochondrial metabolic activity). Bacterial cell suspensions were diluted and spreaded over Columbia agar plates with 5 % sheep blood or MRS agar plates. The plates were incubated under microaerophilic conditions for 48 h. Bacterial growth was measured by performing colony counts. All experiments with each six replicates were reproduced ten times. Experimental plates were compared to untreated controls (cell growth = 100 %). Results were statistically evaluated by ANOVA. Results: Standard deviations in the experimental groups were higher than those in the control groups. A significant stimulation of bacterial growth was found in Ss and Sm after irradiation with 760 nm and energy densities = 20 J/cm². In all other groups, the proliferation was inhibited with increasing radiation dose. The influence on growth was more pronounced in bacteria than in fibroblasts. Conclusions: From the results we conclude that the influence on proliferation varies between the cell species; fibroblasts are less susceptible than La, Ss, and Sm. Our results differ from biostimulation effects achieved with lower energy densities that are described in the literature. The proliferation of Ss and Sm can be stimulated with irradiation of 760 nm. Partly supported by CeramOptec GmbH, Bonn, Germany.