Long-term effect of pulsed Nd:YAG laser irradiation on cultured human periodontal fibroblasts

Background and Objectives: The purpose of this study was to investigate the long-term effect of Nd:YAG laser irradiation on cultured human periodontal fibroblasts (hPF). Study Design/Materials and Methods: The cultured hPF were irradiated by pulsed Nd:YAG laser. The power delivery was 50 mJ x 10 pps (pulse per second) with irradiation duration 60, 120, 180, or 240 seconds. The viability and collagen content of laser-irradiated hPF were assessed on day 5 after laser treatment. Light microscope and transmission electron microscope (TEM) were used to observe cytomorphological change. The irradiated hPF cultured in mineralizing medium for 28 days were examined by alizarin red S and Von Kossa stain. Results: The cellular viability and collagen content of hPF decreased after Nd:YAG laser irradiation. Cell damage was noted with retraction of cellular processes, loss of normal architecture, and lysis of some cells. However, survived hPF proliferated and migrated to the cell-debris-associated deposits. The electron-dense cytoplasm and amorphous organelles in laser-damaged cells was revealed by TEM. In vitro mineralization was demonstrated in the long-term laser-irradiated hPF cultured in mineralizing medium. Conclusion: Nd:YAG laser irradiation induced partial loss of cellular viability and collagen content. The coexistence of viable cells and progressive degeneration of laser-damaged cells was associated with the in vitro mineralization of hPF.