Department of Orthodontics, Provincial Hospital affiliated with Shandong University, Jinan, China.
Am J Orthod Dentofacial Orthop. 2010 Jan;137(1):100-7. doi: 10.1016/j.ajodo.2008.01.025.
Miniscrews often loosen during orthodontic treatment, especially in teenage patients. The purposes of this study were to explore the differences of the pullout strengths of miniscrews placed in the anterior mandibles of adolescent and adult dogs and the structural parameters of peri-miniscrew bone, and to analyze the correlation between the pullout strengths and the variables of the peri-miniscrew bone structure.
Eight adult beagles and 8 young beagles with early permanent dentitions were used as experimental subjects. Two miniscrews were symmetrically placed in the anterior mandible of each dog several minutes before death. The bone density, relative bone volume, and cortical bone thickness were evaluated by micro-computed tomography, and the pullout strength of the miniscrew was tested with a testing machine. Regression analyses were used to study the relationship between pullout strength and bone density, relative bone volume, and cortical bone thickness.
The values of bone density, relative bone volume, cortical bone thickness, and pullout strength were 781.94 + or - 21.46 mg of hydroxyapatite per cubic centimeter, 0.62 + or - 0.33, 1.14 + or - 0.11 mm, and 218.40 + or - 24.50 N for the adult dogs; and 713.61 + or - 13.08 mg of hydroxyapatite per cubic centimeter, 0.57 + or - 0.20, 1.07 + or - 0.86 mm, and 130.82 + or - 2.20 N for the young dogs, respectively. All pairs of pullout force and bone structural parameters had significant correlation coefficients. The pullout force showed the strongest correlation with bone density and the weakest with cortical bone thickness.
The values of bone density, relative bone volume, cortical bone thickness, and the pullout strength of the adult group were higher than those of the young group. Furthermore, bone density is more sensitive in terms of showing pullout force compared with relative bone volume and cortical bone thickness.
微型种植钉在正畸治疗过程中经常松动，尤其是在青少年患者中。本研究旨在探讨青少年和成年犬前下颌微型种植钉的拔出强度差异及种植钉周围骨的结构参数，并分析拔出强度与种植钉周围骨结构变量之间的相关性。
8 只成年比格犬和 8 只早期恒齿期的年轻比格犬作为实验对象。在每只犬死亡前几分钟，在其前下颌对称放置 2 枚微型种植钉。通过微计算机断层扫描评估骨密度、相对骨量和皮质骨厚度，用试验机测试微型种植钉的拔出强度。采用回归分析研究拔出强度与骨密度、相对骨量和皮质骨厚度的关系。
成年犬的骨密度、相对骨量、皮质骨厚度和拔出强度值分别为 781.94 ± 21.46 毫克每立方厘米羟磷灰石、0.62 ± 0.33、1.14 ± 0.11 毫米和 218.40 ± 24.50 牛；年轻犬分别为 713.61 ± 13.08 毫克每立方厘米羟磷灰石、0.57 ± 0.20、1.07 ± 0.86 毫米和 130.82 ± 2.20 牛。所有拔出力和骨结构参数对的相关系数均有显著差异。拔出力与骨密度的相关性最强，与皮质骨厚度的相关性最弱。
成年组的骨密度、相对骨量、皮质骨厚度和拔出强度值均高于年轻组。此外，骨密度在显示拔出力方面比相对骨量和皮质骨厚度更敏感。
