The effect of 904 nm low level laser on condylar growth in rats.

A growth center of the mandible that contributes to its length and height is the mandibular condyle. Proliferation of prechondroblasts, followed by synthesis of the extracellular matrix and hypertrophy of the cartilage cells, governs the major part of condylar growth. The sample consisted of 54 male rats, weighing between 60 g and 80 g, divided randomly into three groups. Group I was the control group, group II was irradiated bilaterally, and group III was irradiated on the right side. Laser irradiation (lambda = 904 nm, 2000 Hz, pulse length 200 ns and output power 4 mW) was performed, and the procedure was repeated after a 50-day interval. Two months later, the rats were killed. In a single blind manner the lengths of denuded mandibles and the lengths of mandibles on soft tissue were measured. The growth of the mandibles in the unilaterally irradiated group (P < 0.001) and the bilaterally irradiated group (P < 0.05) was significantly more than that in the control group. There was no significant difference between right and left condylar growth in the bilaterally irradiated group (P = 0.3). Soft tissue analysis also verified these results (P < 0.001). Histomorphometric results also revealed a significant difference between laser-irradiated groups and the control group (P < 0.01). We concluded that particular laser irradiation with the chosen parameters can stimulate condylar growth and subsequently cause mandibular advancement. These findings might be clinically relevant, indicating that low level laser irradiation can be used for further improvement of mandibular retrognathism.