Department of Oral and Maxillofacial Pathobiology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan.
Bone. 2013 Apr;53(2):497-506. doi: 10.1016/j.bone.2013.01.021. Epub 2013 Jan 19.
Root resorption is an adverse outcome of orthodontic tooth movement. However, there have been no available approaches for the protection and repair of root resorption. The aim of this study was to evaluate the effects of low-intensity pulsed ultrasound (LIPUS) on root resorption during experimental tooth movement and the effects of LIPUS in the RANKL/OPG mechanism in osteoblasts and cementoblasts in vitro. Twenty four Wistar strain male rats of 12-week-old were used in this study. The upper first molars were subjected to experimental movement in the mesial direction for 1-3weeks. Through the experimental periods, the right upper first maxillary molar was exposed to LIPUS (LIPUS group) every day for 1, 2 or 3weeks. The nature of root resorption was observed and then quantified by histomorphometric analysis. In the 2weeks period, significantly greater amount of tooth movement was observed in the LIPUS group (p<0.05). In addition, LIPUS group showed less root resorption lacunae and lower number of odontoclasts. In the period of 3weeks, LIPUS group presented significantly shorter length of root resorption lacunae and smaller amount of root resorption area (p<0.01). The number of odontoclasts and osteoclasts was also significantly lower in the LIPUS group (p<0.01 and p<0.05, respectively). However, no significant differences could be found regarding the amount of tooth movement. It is shown that LIPUS exposure significantly reduced the degree of root resorption during tooth movement without interrupting tooth movement. In vitro experiments showed that MC3T3-1 constitutively expressed higher levels of RANKL and RANTES mRNA comparing to OCCM-30. However, OPG mRNA expression was much higher in OCCM-30. LIPUS stimulation significantly increased the mRNA expression of RANKL in MC3T3-E1 at 4 (p<0.01) and 12h (p<0.05), although OPG mRNA expression was not affected by LIPUS. In contrast, the expression of RANKL and OPG mRNAs were both significantly increased by LIPUS in OCCM-30 at 12h (p<0.01). Moreover, LIPUS application suppressed the up-regulation of RANKL mRNA induced by compression force in OCCM-30, but no similar effect could be observed in MC3T3-E1. In conclusion, it is suggested that LIPUS exposure significantly reduces root resorption by the suppression of cementoclastogenesis by altering OPG/RANKL ratio during orthodontic tooth movement without interfering tooth movement. LIPUS may be an effective tool to prevent root resorption during tooth movement and is applicable to clinical use in near future.
根吸收是正畸牙齿移动的不良后果。然而，目前还没有可用的方法来保护和修复根吸收。本研究旨在评估低强度脉冲超声（LIPUS）对实验性牙齿移动过程中根吸收的影响，以及 LIPUS 在体外成骨细胞和造骨细胞中 RANKL/OPG 机制中的作用。本研究使用了 24 只 12 周龄的 Wistar 雄性大鼠。上第一磨牙向近中方向进行实验性移动 1-3 周。在实验期间，右上颌第一磨牙每天接受 LIPUS（LIPUS 组）照射 1、2 或 3 周。通过组织形态计量分析观察并定量根吸收的性质。在 2 周期间，LIPUS 组的牙齿移动量明显更大（p<0.05）。此外，LIPUS 组的根吸收陷窝较少，破牙细胞较少。在 3 周期间，LIPUS 组的根吸收陷窝长度明显缩短，根吸收面积明显减小（p<0.01）。LIPUS 组的破牙细胞和破骨细胞数量也明显减少（p<0.01 和 p<0.05）。然而，牙齿移动量没有明显差异。结果表明，LIPUS 照射在不中断牙齿移动的情况下，显著降低了牙齿移动过程中的根吸收程度。体外实验表明，MC3T3-1 细胞比 OCCM-30 细胞表达更高水平的 RANKL 和 RANTES mRNA。然而，OCCM-30 细胞中 OPG mRNA 的表达水平要高得多。LIPUS 刺激可显著增加 MC3T3-E1 中 RANKL mRNA 的表达，在 4 小时（p<0.01）和 12 小时（p<0.05）时增加（p<0.01），尽管 OPG mRNA 的表达不受 LIPUS 的影响。相反，LIPUS 刺激可显著增加 OCCM-30 中 RANKL 和 OPG mRNA 的表达，在 12 小时时增加（p<0.01）。此外，LIPUS 处理可抑制 OCCM-30 中压应力诱导的 RANKL mRNA 的上调，但在 MC3T3-E1 中未观察到类似的作用。总之，结果表明，LIPUS 照射通过改变 OPG/RANKL 比值，在不干扰牙齿移动的情况下，显著减少正畸牙齿移动过程中的根吸收，从而抑制破骨细胞的形成。LIPUS 可能是一种预防牙齿移动过程中根吸收的有效工具，在不久的将来可应用于临床。
