Effects of Low Level Laser Irradiation on the Organ Cultured Mandibular Condyle of Rat

Purpose: Low-level laser therapy （LLLT）, which is known to have anti-inflammatory and pain-relieving effects, has recently been reported to be effective for treating osteoarthritis-related pain and disorders. However, no basic studies of laser irradiation on the temporomandibular joint have been conducted. Therefore, in the present study, we histologically investigated the effects of LLLT on the growth of the rat mandibular condyle in organ culture. Methods: In this experiment, the mandibular condyles on both sides of the fetus were removed from pregnant Sprague Dawley rats on the 21st day of fetal life. The mandibular condyles used for the histological search were divided into the following four groups: control group, organ culture only; F＋L－ group, organ culture with basic fibroblast growth factor （bFGF） added to the medium; F－L＋group, organ culture and LLLT; and F＋L＋group, organ culture with bFGF added to the medium and LLLT. Organ culture of the mandibular condyles was performed at 37℃ in a 5％ CO2 incubator. Serum-free BGJb medium was used as the culture medium, and the culture was performed using mediums containing bFGF （100ng/mL） and no bFGF. The culture medium was changed every 2 days. LLLT （wavelength 633nm） was then performed on the cultured mandibular condyles under the following conditions: irradiation output 250mW, irradiation time 30 seconds, and irradiation distance 10mm. LLLT began at the start of culture （day 0） and was performed five times in total up to the 4th day at 24-hour intervals. For the histological examination, a tissue section of 5μm was embedded in paraffin, stained with hematoxylin and eosin, observed with an optical microscope, and histologically searched. Results: Fibroblasts and collagen fibers were found in the superficial layer of the mandibular condyle of all groups at the start of culture. A proliferative layer, a differentiated layer, and a hypertrophied layer were sequentially observed in the lower layer. In the mandibular condyle of the control group on the 8th day of culture, the thicknesses of the proliferative and differentiated layers decreased, and the hypertrophied layer became irregular. In the F＋L＋group, the mandibular condyle was larger than that in the control group, the differentiated and hypertrophied layers were large, and the cell number was increased. The size of the mandibular condyle increased the most in the control group, followed by the F＋L－ group, F－L＋group, and F＋L＋group. In addition, in the F＋L－ and F－L＋groups, intermediate histological findings were observed between the control and F＋L＋groups. Conclusion: These results suggest that LLLT promotes cell proliferation in the mandibular condyle in the same manner as the addition of bFGF. In particular, the increase in chondrocytes was considered to cause morphological changes in the mandibular condyle. Therefore, LLLT may promote chondrocyte proliferation and differentiation in the mandibular condyle.