Holberg Christof, Winterhalder Philipp, Rudzki-Janson Ingrid, Wichelhaus Andrea
Department of Orthodontics, University of Munich, Bavaria, Germany
Department of Orthodontics, University of Munich, Bavaria, Germany.
Eur J Orthod. 2014 Oct;36(5):550-6. doi: 10.1093/ejo/cjt023. Epub 2013 Apr 18.
Loosening and loss rates of monocortical mini-implants are relatively high, therefore the following null hypothesis was tested: 'The local bone stress in mono and bicortically-anchored mini-implants is identical'.
Anisotropic Finite Element Method (FEM) models of the mandibular bone, including teeth, periodontal ligaments, orthodontic braces, and mini-implants of varying length, were created. The morphology was based on the Computed Tomography data of an anatomical preparation. All mini-implants with varying insertion depths (monocortical short, monocortical long, bicortical) were typically loaded, and the induced effective stress was calculated in the cervical area of the cortical bone. The obtained values were subsequently analysed descriptively and exploratively using the SPSS 19.0 software.
The null hypothesis was rejected, since the stress values of each anchorage type differed significantly (Kruskal-Wallis Test, P < 0.001). Therefore, the lowest effective stress values were induced in bicortical anchorage (mean = 0.65MPa, SD = 0.06MPa) and the highest were induced in monocortical (short) anchorage of the mini-implants (mean = 1.79MPa, SD = 0.29MPa). The Spearman rank correlation was 0.821 (P < 0.001).
The deeper the mini-implant was anchored, the lower were the effective stress values in the cervical region of the cortical bone. Bicortical implant anchorage is biomechanically more favourable than monocortical anchorage; therefore, bicortical anchorage should be especially considered in challenging clinical situations requiring heavy anchorage.
单皮质微型种植体的松动和丢失率相对较高，因此对以下原假设进行了检验：“单皮质和双皮质固定微型种植体的局部骨应力相同”。
创建了下颌骨的各向异性有限元模型，包括牙齿、牙周韧带、正畸矫治器和不同长度的微型种植体。形态基于一具解剖标本的计算机断层扫描数据。对所有不同植入深度的微型种植体（单皮质短、单皮质长、双皮质）进行典型加载，并计算皮质骨颈部区域的诱导有效应力。随后使用SPSS 19.0软件对获得的值进行描述性和探索性分析。
原假设被拒绝，因为每种锚固类型的应力值存在显著差异（Kruskal-Wallis检验，P < 0.001）。因此，双皮质锚固诱导的有效应力值最低（平均值 = 0.65MPa，标准差 = 0.06MPa），而微型种植体的单皮质（短）锚固诱导的有效应力值最高（平均值 = 1.79MPa，标准差 = 0.29MPa）。Spearman等级相关性为0.821（P < 0.001）。
微型种植体锚固越深，皮质骨颈部区域的有效应力值越低。双皮质种植体锚固在生物力学上比单皮质锚固更有利；因此，在需要强锚固的具有挑战性的临床情况下，应特别考虑双皮质锚固。
