Investigation of the effect of photobiomodulation therapy with different wavelengths on nerve regeneration: an experimental study

This study aims to evaluate the effects of photobiomodulation therapy (PBMT) applied with laser (light amplification by stimulated emission of radiation) and laser-LED light on nerve healing in crush-type inferior alveolar nerve (IAN) injuries.

Twenty-four rats were divided into 4 groups: Sham/control (n = 8), P1 (n = 8), and P2 (n = 8). The right IANs of the rats were exposed, and crushed nerve injuries were done with micro forceps for 30 s. P1 group received PMBT (a combination of 904 nm, 22 mW GaAlAs infrared laser, and 650 nm, 10 mW InGaAlP LEDs, 9 J) for 14 sessions, once every two days. The P2 group received a 940 nm InGaAsP diode laser in the same manner. The sham-control group received a placebo treatment with the laser probe turned off. On the 28th post-operative day, samples were taken from the damaged nerve areas and analyzed by histomorphometric methods.

Axon number, axon area, and myelin thickness were analyzed to assess the IAN regeneration. The maximum number of axons (4438.2) was observed in the sham-control group. The axon area (8.63 µm²) and myelin sheath thickness (2.21 ± 0.30 μm) were measured the most in the control group. No significant difference was found when the axon area/myelin thickness ratio was analyzed between the groups (p>0.05). While P1 and P2 did not differ significantly, both outperformed the sham-control group in axon number and axon area (p≤0.05).

The analyses showed that PBMT positively affected the regeneration and maturation of the crush-injured inferior alveolar nerve. These findings support further investigation into PBMT's potential clinical role in accelerating nerve repair after crush injuries.