Verna Carlalberta, Dalstra Michel, Lee T Clive, Cattaneo Paolo M, Melsen Birte
Department of Orthodontics, Royal Dental College, University of Aarhus, Denmark.
Eur J Orthod. 2004 Oct;26(5):459-67. doi: 10.1093/ejo/26.5.459.
Microcracks and microdamage have been associated with bone remodelling. The aim of this study was to investigate the role of microcracks as a trigger for alveolar bone remodelling after the application of an orthodontic load. In 25 3-month-old male Danish land-race pigs, the lower right first molar was moved buccally with a force of 130 cN. The contralateral molar was not treated and was used as an internal control. After 1, 2, 4, 7 and 15 days of treatment, the regions containing the right and left molars were excised and en bloc stained in basic fuchsin. The presence of microcracks on the buccal and lingual sides of both treated and untreated teeth was detected and expressed as crack density (number/mm2). The buccal treated side showed significantly more cracks than the buccal untreated side at day 1. This difference was significantly larger than that observed at days 2, 7 and 15. The same side showed significantly more microcracks than the lingual treated side at day 1, and this difference was larger compared with that observed at days 4 and 15. The presence of more microcracks on the treated side than on the untreated side suggests a role for microcracks in the initiation of bone remodelling after orthodontic loading. The increased presence of microcracks on the side towards which the tooth was moved, and where bone resorption is usually observed, suggests that microcracks could represent the first damage induced by orthodontic force that has to be repaired by bone remodelling. Finally, the strain levels in the alveolar bone during the orthodontic load transfer in the experiment were examined by finite element (FE) analysis. Although this showed that the strains were very low (10-100 microstrain), it should be noted that occlusal loading was not taken into account. In addition, high-resolution microtomography of the alveolar bone/periodontal ligament (PDL) interface revealed that the actual surface of the alveolar bone was very rough, predisposing it to high local stress/strain peaks.
微裂纹和微损伤与骨重塑有关。本研究的目的是调查微裂纹在正畸负荷施加后作为牙槽骨重塑触发因素的作用。在25只3月龄的丹麦长白公猪中，以130 cN的力将右下第一磨牙颊向移动。对侧磨牙未作处理，用作内部对照。在治疗1、2、4、7和15天后，切除包含左右磨牙的区域，并用碱性品红进行整体染色。检测处理和未处理牙齿颊侧和舌侧的微裂纹存在情况，并以裂纹密度（数量/平方毫米）表示。在第1天，处理侧的颊侧显示出比未处理侧的颊侧明显更多的裂纹。这种差异明显大于在第2、7和15天观察到的差异。在第1天，同一侧显示出比处理侧的舌侧明显更多的微裂纹，并且与在第4和15天观察到的差异相比，这种差异更大。处理侧比未处理侧存在更多微裂纹表明微裂纹在正畸负荷后骨重塑的起始中起作用。在牙齿移动方向一侧以及通常观察到骨吸收的部位微裂纹的增加存在表明，微裂纹可能代表正畸力诱导的必须通过骨重塑修复的初始损伤。最后，通过有限元（FE）分析检查了实验中正畸负荷传递过程中牙槽骨的应变水平。尽管这表明应变非常低（10 - 100微应变），但应注意未考虑咬合负荷。此外，牙槽骨/牙周膜（PDL）界面的高分辨率显微断层扫描显示，牙槽骨的实际表面非常粗糙，使其易于出现高局部应力/应变峰值。
