Effects of the photobiomodulation using different energy densities on the periodontal tissues under orthodontic force in rats with type 2 diabetes mellitus

Abstract To evaluate the impact of the GaAlAs diode laser with energy densities of 160 J/cm2, 320 J/cm2, and 640 J/cm2 on the periodontal tissues under continuous orthodontic force application and on the rate of orthodontic tooth movement in rats with type-2 diabetes mellitus. The intensity of primary alveolar bone formation was also investigated through the immune-positive osteocytes for OPN antibody. Forty adult male Wistar rats were divided into eight groups of 5 rats: normoglycemic (N), 160 J-laser-normoglycemic (160 J-LN), 320 J-laser-normoglycemic (320 J-LN), 640 J-laser-normoglycemic (640 J-LN), diabetic (D), 160 J-laser-diabetic (160 J-LD), 320 J-laser-diabetic (320 J-LD), and 640 J-laser-diabetic (640 J-LD) rats. Diabetes mellitus was induced by a single intravenous injection of 40 mg/kg monohydrated-alloxan. An orthodontic force magnitude of 20cN was applied. The laser parameters were continuous emission of 780-nm wavelength, output power of 20mW, and fiber probe with a spot size of 0.04 cm in diameter. Radiographic, histomorphological, and immunohistochemical analysis were performed after a period of 21 days. The photobiomodulation using the energy density of 640 J/cm2 strongly stimulated the alveolar bone formation and contributed the reorganization of the soft periodontal tissues, followed by the 320 J/cm2. Extensive alveolar bone loss, intense infiltration of inflammatory cells, and degradation of the PDJ tissue were mainly found in the D and 160 J-LD groups. The rate of orthodontic tooth movement was represented by the interdental distance between the cementoenamel junctions of the right mandibular first and second molars . This distance was larger in the diabetic groups (D: 39.98±1.97, 160 J-LD: 34.84±6.01, 320 J-LD: 29.82±1.73, and 640 J-LD: 35.47±4.56) than in the normoglycemic groups (N: 21.13±1.19; 160 J-LN: 22.69±0.72, 320 J-LN: 22.28±0.78, and 640 J-LN: 24.56±2.11). The number of osteopontin-positive osteocytes was significantly greater in the 640 J-LD (14.72 ± 0.82; p &lt; 0.01) and 640 J-LN (13.62 ± 1.33; p &lt; 0.05) groups than with D (9.82 ± 1.17) and 160 J-LD (9.77 ± 1.10) groups. Therefore, the energy density of 640 J/cm2 provided the best maintenance and integrity of the periodontal tissue microarchitecture under continuous orthodontic force when compared with the other dosages, mainly in the uncontrolled diabetic rats. The interdental distance was greater in the D and 160 J-LD groups due to presence of severe periodontitis caused by diabetes plus the mechanical stress generated by continuous orthodontic forces, implying, thus, an insufficient biostimulatory effect for the dosage of 160 J/cm2.摘要：本研究旨在评估能量密度分别为160 J/cm²、320 J/cm²及640 J/cm²的GaAlAs二极管激光（GaAlAs diode laser），对持续正畸力作用下的牙周组织，以及2型糖尿病大鼠正畸牙移动速率的影响。同时通过骨桥蛋白（OPN）抗体标记的免疫阳性成骨细胞，探究原发性牙槽骨形成的强度。 选取40只成年雄性Wistar大鼠，分为8组，每组5只：正常血糖组（N）、160 J激光-正常血糖组（160 J-LN）、320 J激光-正常血糖组（320 J-LN）、640 J激光-正常血糖组（640 J-LN）、糖尿病组（D）、160 J激光-糖尿病组（160 J-LD）、320 J激光-糖尿病组（320 J-LD）及640 J激光-糖尿病组（640 J-LD）。 通过单次静脉注射40 mg/kg一水合四氧嘧啶构建糖尿病模型。施加20 cN的正畸力。激光参数设置为：波长780 nm连续发射模式，输出功率20 mW，光纤探头光斑直径0.04 cm。 于实验周期21天后，进行影像学、组织形态学及免疫组织化学分析。 结果显示，能量密度为640 J/cm²的光生物调节作用可显著促进牙槽骨形成，并有助于牙周软组织重构，效果优于320 J/cm²剂量组。糖尿病组（D）及160 J激光-糖尿病组（160 J-LD）主要表现为广泛牙槽骨丢失、炎症细胞重度浸润及PDJ组织降解。 正畸牙移动速率以右侧下颌第一、第二磨牙牙骨质牙釉质界之间的牙间距离表征。糖尿病各组[D: 39.98±1.97、160 J-LD: 34.84±6.01、320 J-LD:29.82±1.73、640 J-LD:35.47±4.56]的牙间距离均大于正常血糖各组[N:21.13±1.19；160 J-LN:22.69±0.72、320 J-LN:22.28±0.78、640 J-LN:24.56±2.11]。 骨桥蛋白阳性成骨细胞数量在640 J-LD组（14.72 ± 0.82; p < 0.01）及640 J-LN组（13.62 ± 1.33; p < 0.05）中显著高于D组（9.82 ± 1.17）及160 J-LD组（9.77 ± 1.10）。 综上，与其他激光剂量相比，640 J/cm²的能量密度在持续正畸力作用下，可最优维持牙周组织微结构的完整性，该效果在未控制的糖尿病大鼠中尤为显著。糖尿病组及160 J-LD组的牙间距离更大，原因为糖尿病引发的重度牙周炎联合持续正畸力产生的机械应力共同作用，这也提示160 J/cm²剂量的生物刺激效果不足。