Micro-CT analysis of the mandibular bone microarchitecture of rats after radiotherapy and low-power laser therapy

To investigate whether low-level laser therapy (LLLT), at different times of application (immediate and late) in the region of the parotid glands, has a distance effect on the microarchitecture of the trabecular bone in mandible of rats irradiated by volumetric modular arc therapy (VMAT). Thirty adult Wistar rats were randomly divided into placebo control groups (CG, n = 2), only radiotherapy (RG, n = 2), only LPLT (LG, n = 2), and two other groups using LLLT in the immediate time (24 h) (ILG, n = 12) and late (120 h) (LLG, n = 12) to radiotherapy by VMAT in a single dose of 12 Gy. LLLT with AsGaAl laser (660 nm, 100 mW), a spot size of 0.0028 cm², was applied in three points in the region of the right parotid gland, with energy of 2 J/cm², 20 s per point, for 10 consecutive days. After euthanasia, the right hemimandibles of each animal were dissected, prepared, and analyzed by computerized microtomography (micro-CT) and histomorphometry. The different groups were analyzed by the Tukey and Bonferroni multiple comparison tests. The micro-CT analysis found statistically significant differences between the groups, especially in the LLG, which had the highest average bone volume compared to the CG (p = 0.001) and ILG (p = 0.002) and a greater number of trabeculae than the CG (p = 0.000) and ILG (p = 0.031). The ILG also had a higher number of trabeculae than the CG (p = 0.005). Trabecula separation (Tb.Sp) was lower in the LLG (p = 0.000) and ILG (p = 0.002) when compared to the CG. In the histomorphometry, there was no statistical difference between the groups in relation to all the analyzed variables. Micro-CT analysis showed that the LLLT, even applied at a distance, both in the immediate and late VMAT times, has an effect on the mandibular bone microarchitecture by increasing the volume and number of trabeculae and decreasing the spaces between them.