A study on the morphological changes of osteocytes in rat alveolar bone during orthodontic tooth movement

本研究的目的是：1)利用免疫组织化学方法检测正畸牙齿运动过程中大鼠牙槽骨骨细胞的形态变化；2)确定骨细胞代谢的分子标记物。本研究选用8周龄雄性Wistar大鼠。根据Igarashi等人（1998）的描述，上颌第一磨牙通过使用标称尺寸为0.012英寸的Ni-Ti丝膨胀弹簧在颊部移动。动物在牙齿运动3、6、12、24小时、2、4、7、10和14天后被杀死。实验结束后，用4%多聚甲醛加0.5%戊二醛在0.1 M PB, pH 7.4溶液中固定动物，用10% EDTA溶液脱钙，加工成石蜡包埋。6 μ m厚的切片用苏木素-伊红或骨钙素、i型、II型和X型胶原蛋白和肌动蛋白丝的抗体染色。实验结果如下：1)骨钙素前体和成熟骨钙素是检测牙槽骨和骨形成细胞代谢变化的合适分子标志物。2)正畸牙移动3小时后，第一磨牙5根牙周组织受压侧均出现透明组织。10.3 d时透明组织扩散，几乎脱色。对照组骨细胞胞浆和细胞突中肌动蛋白丝免疫组化染色强烈。尤其是年轻骨细胞染色强烈。与此相反，靠近透明组织的骨细胞细胞质在第1天染色变弱，在第4天其细胞突的染色消失。结果表明，在正畸牙齿移动早期，由于牙周组织细胞间的细胞间通讯消失，导致透明变性组织附近的骨细胞死亡。

The purposes of the present study were 1) to examine the morphological changes of osteocytes in rat alveolar bone during orthodontic tooth movement using immunohistochemistry for actin filaments and 2) to determine a molecular marker for osteocyte metabolism. Eight-week-old male Wistar rats were used in this study. The maxillary first molars were moved buccally by using a expansive spring of Ni-Ti wire with a nominal size of 0.012 inch as described by Igarashi et al. (1998). The animals were killed after 3, 6, 12, 24 hours, 2, 4, 7, 10 and 14 days of tooth movement. After experiments, the animals were fixed with 4 % paraformaldehyde plus 0.5 % glutaraldehyde in 0.1 M PB, pH 7.4, decalcified with 10 % EDTA solution and processed into paraffin embedding. Six-mu in-thick sections were stained with hematoxilin-eosin or antibodies for osteocalcin, typesI,II and X collagen and actin filaments. The results were as follows ;1) Precursor and mature osteocalcin was a proper molecular marker for examining the metabolic changes of alveolar bone and bone-forming cells.2) After 3 hours of orthodontic tooth movement, hyaline tissue appeared in the pressure side of the periodontal tissue of all five roots of the first molar. The hyaline tissue spread and almost dessapered at day 10.3) Immunohistochemistry for actin filament showed intense staining in cytoplasm and cellular processes of osteocytes in control group. Especially young osteocytes showed intense staining. In contrast, the staining of osteocyte cytoplasm adjacent to the hyaline tissue became weak at day 1 and the staining of its cellular processes disappeared at day 4.These results demonstrated that osteocytes adjacent to the hyaline degeneration tissue became cell death during early stage of orthodontic tooth movement due to the disappearance of intercellular communication between the periodontal tissue cells.