Effect of Differential Energy Density Laser Modulation on the Orthodontic Tooth Movement and Bone Remodeling on the Compression zone

Background: The present study aimed to investigate the differential photobiomodulation (PBM) effects of diode laser with low-level laser and high-level laser on orthodontic tooth movement (OTM) and alveolar bone remodeling on the compression zone. Methodology: A split-mouth design OTM model of rats was established. By varying the irradiation duration of a diode laser, wavelength of 650 nm, one accelerating OTM group with five different energy densities subgroups and one inhibiting OTM group with five different subgroups were obtained, respectively. The best accelerating/inhibiting efficacy of OTM was achieved by comparing the OTM distance of different subgroups with micro-CT. The osteoclastic level on the compression zone in the best accelerating/inhibiting subgroup was observed by Hematoxylin-eosin (HE) and tartrate-resistant acid phosphatase (TRAP) staining, while the expression levels of receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG), alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), and osteocalcin (OCN) were individually explored by real-time PCR and immunohistochemical staining. Results: The maximum accelerating efficiency of OTM in the 6.7 J/cm ² subgroup was 36.7%, in which the lacunae and osteoclasts of the compression side were increased on 7d,14d (P< 0.05), and the expressions of RANKL, ALP, RUNX2, and OCN were` upregulated and the expression of OPG was downregulated. The optimal inhibiting efficiency of OTM in the 106.7 J/cm² subgroup was 34.9%, in which the lacunae and osteoclasts of the compression zone were reduced on 7d, 14d (P< 0.05), and the expressions of RANKL, ALP, RUNX2, and OCN were downregulated and the expression of OPG was upregulated. Vertical alveolar bone height loss and orthodontic teeth loosening was observed in the subgroups with energy density over 123.3J/cm² (P<0.01). Conclusions: Differential energy density laser exerted a biphasic effect on OTM which optimal parameters of 6.7 J/cm² could accelerate OTM of 36.7%, and 106.7 J/cm² could decelerate OTM of 34.9%, respectively. The osteoclast/osteoblast activity on the compression zone was promoted /inhibited.