Elkholy F, Mikhaiel B, Repky S, Schmidt F, Lapatki B G
Department of Orthodontics, Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
Private practice, Wolfschlugen, Germany.
J Orofac Orthop. 2019 Nov;80(6):315-326. doi: 10.1007/s00056-019-00193-7. Epub 2019 Oct 8.
Derotation of rounded teeth has proved difficult for aligners to achieve. In this study, we investigated the effect of aligner attachment geometry on the three-dimensional (3D) force and moment (F/M) values exerted during derotation of a mandibular canine.
The experiment setup comprised an acrylic mandibular arch model with a separated right canine (tooth 43) mounted on a hexapod via a 3D F/M sensor. Polyethylene terephthalate glycol (PET‑G) aligners with thicknesses of 0.5, 0.625, and 0.75 mm were tested in combination with quarter-sphere, vertical-ellipsoid, and pyramidal attachments bonded to tooth 43. The experimentally measured movement consisted of mesio- and distorotation of tooth 43 in 1° steps up to ±15° in each direction.
Compared with no attachment, vertical-ellipsoid and quarter-sphere attachments increased the rotational moment by a median factor of 1.5-12.3. Moment increases for pyramidal attachments were significantly smaller (Mann-Whitney U‑test, p < 0.05). Quarter-sphere attachments inhibited the intrusive forces up to 6.07° distorotation, whereas the intrusion prevention range for most aligner attachment combinations was significantly smaller (2.95° for vertical-ellipsoid and 2.88° for pyramidal attachments; Mann-Whitney U‑test, p < 0.05). None of the attachment geometries could completely prevent intrusive forces during mesiorotation.
The quarter-sphere geometry had the best overall mechanical properties because it induced relatively high rotational moment increases and counteracted unwanted intrusive forces most effectively of all three geometries. The determined maximum attachment dislodgement and intrusion prevention angles of approximately 6° provide a guide to determining setup increments for mandibular canine derotation.
事实证明，利用矫治器实现圆弧形牙齿的扭转很困难。在本研究中，我们调查了矫治器附件几何形状对下颌尖牙扭转过程中所施加的三维（3D）力和力矩（F/M）值的影响。
实验装置包括一个丙烯酸树脂下颌牙弓模型，其上有一颗分离的右侧尖牙（43号牙），通过一个三维F/M传感器安装在一个六足平台上。测试了厚度分别为0.5、0.625和0.75毫米的聚对苯二甲酸乙二醇酯（PET-G）矫治器，这些矫治器与粘结在43号牙上的四分之一球体、垂直椭球体和金字塔形附件组合使用。实验测量的移动包括43号牙在每个方向上以1°步长进行近中扭转和远中扭转，最大可达±15°。
与无附件相比，垂直椭球体和四分之一球体附件使扭转力矩增加了1.5至12.3倍。金字塔形附件的力矩增加明显较小（曼-惠特尼U检验，p<0.05）。四分之一球体附件在远中扭转达6.07°时可抑制侵入力，而大多数矫治器附件组合的防侵入范围明显较小（垂直椭球体为2.95°，金字塔形附件为2.88°；曼-惠特尼U检验，p<0.05）。在近中扭转过程中，没有一种附件几何形状能够完全防止侵入力。
四分之一球体几何形状具有最佳的整体力学性能，因为在所有三种几何形状中，它能使扭转力矩增加相对较高，并且最有效地抵消了不必要的侵入力。确定的最大附件脱位和防侵入角度约为6°，为确定下颌尖牙扭转的就位增量提供了指导。
