The simultaneous protective effect of photobiomodulation on root resorption while accelerating orthodontic tooth...

To investigate the effect of photobiomodulation (PBM) on orthodontically induced root resorption (OIRR) while accelerating orthodontic tooth movement (OTM), and explore the possible role of periodontal ligament stem cells (PDLSCs) during this process. Thirty rats were randomly divided into 5 groups (A1-A5). The right upper first molars (UM1s) were assigned as PBM side (P), receiving different energy densities of PBM: A1-P (3.3 J/cm²); A2-P (5 J/cm²); A3-P (6.7 J/cm²); A4-P (8.3 J/cm²); A5-P (10 J/cm²). A diode laser (650 nm, 30 mW) with 0.09 cm² beam area was used to irradiate right UM1s at three points (the mesial, buccal and palatal sides) over the root and the irradiation time per point was 10 s in group A1, 15 s in group A2, 20 s in group A3, 25 s in group A4 and 30 s in group A5. The left UM1s were split-mouth control side. Bilateral UM1s were moved mesially by 50 g force for 14 days. The amount of OTM, root length (RL), total root resorption volume (T-RRV), RRV of compression zone (RRV-CZ) and RRV of tension zone (RRV-TZ) were evaluated by micro-CT, and CAP expression level of PDLSCs was analyzed by IHC staining. Groups of 5 and 6.7 J/cm² achieved significant accelerated orthodontic tooth movement (AOTM). There was no significant difference of RL, T-RRV and RRV-CZ between PBM and control sides. PBM irradiation at 5-10 J/cm² significantly reduced RRV-TZ. Moreover, the 6.7 J/cm² group achieved the largest AOTM efficiency and showed the highest reduction rate in decreasing RRV-TZ. The expression level of CAP was significantly higher on PBM side than that on control side in both compression and tension zones. Diode laser (650 nm, 30 mW) of 5-10 J/cm² had a protective effect on orthodontic tooth root by upregulating the cementoblastic differentiation of PDLSCs. Particularly, diode laser of 6.7 J/cm² exhibited the best efficiency in preventing OIRR of tension zone while accelerating OTM.