Low-level 809 nm GaAlAs laser irradiation increases the proliferation rate of human laryngeal carcinoma cells in vitro

The aim of the study was to investigate the effect of low-level 809 nm laser irradiation on the proliferation rate of human larynx carcinoma cells in vitro. Epithelial tumor cells were obtained from a laryngeal carcinoma and cultured under standard conditions. For laser treatment the cells were spread on 96-well tissue culture plates. Sixty-six cell cultures were irradiated with an 809 nm GaAlAs laser. Another 66 served as controls. Power output was 10 mW(cw) and the time of exposure 75-300 s per well, corresponding to an energy fluence of 1.96-7.84 J/cm2. Subsequent to laser treatment, the cultures were incubated for 72 h. The proliferation rate was determined by means of fluorescence activity of a redox indicator (Alamar Blue Assay) added to the cultures immediately after the respective treatment. The indicator is reduced by metabolic activity related to cellular growth. Proliferation was determined up to 72 h after laser application. The irradiated cells revealed a considerably higher proliferation activity. The differences were highly significant up to 72 h after irradiation (Mann-Whitney U test, p < 0.001). A cellular responsiveness of human laryngeal carcinoma cells to low-level laser irradiation is obvious. The cell line is therefore suitable for basic research investigations concerning the biological mechanisms of LLLT on cells.

Effects of esradiol and progesterone on the proliferation of human gingival fibroblasts

AIM

The aim of the in vitro study was to examine the effect of estradiol and progesterone on the proliferation rate of human gingival fibroblasts (HGF) derived from a healthy and a diabetic (type II) individual.

METHODS

In the first experiment, cells in the logarithmic proliferative phase were incubated with estradiol or progesterone at concentrations of 10, 50, and 100 microg/ml for 72 h. Beside the hormones, a glucose solution at a concentration of 200 mg/dl was added to the cell cultures in the second experiment in order to mimic a diabetic situation. The proliferation rate of the cells was determined by means of fluorescence activity of a redox indicator (Alamar Blue(R) Assay) added to the cell culture. Proliferation, expressed in relative fluorescence units (RFU), was determined after 24, 48, and 72 h.

RESULTS

Progesterone at concentrations of 50 and 100 microg/ml significantly (Mann-Whitney-U-Test, p<0.05) reduced cellular growth in both cultures. Estradiol did not have a significant effect on cellular growth. The effect of progesterone was slightly reduced by glucose when cells from the healthy individual were used and remained almost unchanged with the cells from the diabetic patient.

CONCLUSIONS

The results of the present study may help to understand the role of the female sex-hormones in the development of gingival and periodontal diseases during pregnancy. Further research work, however, is needed to elucidate the cellular mechanisms leading to the effects observed.

Efficacy of NaOCl/H2O2 irrigation and GaAlAs laser in decontamination of root canals in vitro

BACKGROUND AND OBJECTIVES

To investigate the bactericidal effect of an 809 nm semiconductor laser alone, and in combination with NaOCl/H(2)O(2) irrigation in root canals in vitro.

STUDY DESIGN/MATERIALS AND METHODS

A total of 72 human single-rooted teeth extracted for periodontal reasons were included. The crowns were removed, the roots shortened to a length of 12 mm, and the canals enlarged up to an apical size of #50 file. The specimens were autoclaved and incubated with a suspension of Streptococcus sanguinis (ATCC 10556). Laser irradiation was performed on a PC-controlled XY translation stage. A 200 micron optic fiber was used. Twelve specimens were irradiated at a power output of 1.5, 3.0, and 4.5 W in the cw-mode. The total irradiation time was 60 seconds per canal. Twelve specimens were rinsed with NaOCl and H(2)O(2) only, 12 were rinsed and laser treated, and 12 served as untreated controls. After laser treatment, the specimens were sonicated and the bacterial growth was examined by counting colony forming units on blood agar plates. Temperature changes at the outer root surface during irradiation were registered by means of thermocouples. Treated and control specimens were investigated by means of scanning electron microscopy.

RESULTS

Mean bacterial reductions of 0.35 log steps at a power output of 1.5 W, 1.44 at 3.0 W, and 2.84 at 4.5 W were calculated. Bacterial reduction by the NaOCl/H(2)O(2) solution alone was 1.48 and comparable to that achieved by irradiation at 3.0 W. With a log kill 2.85, the combination of rinsing and laser irradiation at 3.0 W resulted in a further significant bacterial reduction as compared to rinsing alone (P = 0.004). Irradiation did not result in excessive heat generation at the root surface. Carbonization of the root canal wall was observed in single teeth at 3.0 and 4.5 W and no controlled sealing of the dentinal tubules could be achieved in the root canal.

CONCLUSIONS

The application of the diode laser might be an adjunct to conventional endodontic treatment when used in combination with a NaOCl/H(2)O(2) solution.