传动矫治过程中后倾曲作用下上颌第一磨牙的位移及应力分析

Maxillary first molar displacement and stress analysis of transmission straight wire technique under gable bend effect

背景:随着现代矫治技术的发展,发明一种高效的矫治器,一直是正畸学者们的研究热点之一。传动直丝弓矫治器就是在这种大环境下应运而生,能快速打开咬合、缩短疗程、治疗效率高,为疑难病例的治疗提供了新的思路。目前对传动直丝弓技术治疗初期,上颌第一磨牙位移趋势及上颌骨第一磨牙区应力分布情况,尚没有进行深入的研究。目的:建立生物相似性和力学相似性较高的传动直丝弓矫治器的三维有限元模型,获得上颌第一磨牙位移趋势及上颌骨第一磨牙区应力分布情况。方法:使用64排螺旋CT扫描,得到1例安氏Ⅱ类1分类的志愿者上颌牙列、上颌骨截面的DICOM格式的影像数据。采用Ansys workbench 13.0、Mimics 10.01、Unigraphics NX 6.0和GeomagicStudio 8.0软件相结合的方法,在Windows XP Service Pack 3系统中建立包括传动直丝弓矫治器、带环、澳丝、上颌骨、上颌牙齿及牙周膜的三维有限元模型。对模型进行加载,获得上颌第一磨牙位移趋势及上颌骨第一磨牙区应力分布情况。结果与结论:实验建立了由250 929个单元数,657 766个节点组成的传动直丝弓矫治器的三维有限元模型;获得了在后倾曲作用下上颌第一磨牙的位移趋势及上颌骨第一磨牙区的应力分布情况,利于分析传动直丝弓矫治力学体系并指导临床应用和矫治器改良。说明单纯后倾弯作用下,牙根将向颊侧骨皮质靠近,导致根尖部和上颌骨颊侧骨皮质区域的应力集中;这种应力集中可能会导致上颌第一磨牙颊侧根尖区出现牙根吸收。

BACKGROUND： With the＂ development of modern orthodontics techniques, designing an efficient appliance is the focus in recent studies. Transmission straight wire appliance was invented under this background. This appliance can accelerate teeth leveling, shorten treatment duration, improve correction efficacy, and provide a novel approach to solve intractable cases. The relationship between maxillary first molar displacement and stress distribution needs further study.OBJECTIVE：.To establish three-dimensional finite element model with better biological and mechanical similarity of transmission straight wire appliance, and obtain the relationship between maxillary first molar displacement and stress distribution. METHODS： By using 64-row spiral CT scanning, the sectional image data in DICOM of TMJ, maxilla and upper tooth were acquired from a volunteer with Angle Class II division 1. With the help of Mimics 10.01, Geomagic Studio 8.0, Unigraphics NX 6.0 and Ansys workbench 13.0 sofi.wares, the three-dimensional finite element model of transmission straight wire appliance, bend, Australian Orthodontic Wire, including maxilla, upper tooth, periodontal ligament, arch wire and brackets was established in Windows XP Service Pack 3 system. The model was loading, to obtain the maxillary first molar displacement and stress distribution. RESULTS AND CONCLUSION： A three-dimensional finite element model of transmission straight wire appliance was established, which consisted of 250 929 elements and 657 766 nodes. Furthermore, the stress distribution of maxillary first molar tilt displacement trend curve under the action of maxillary first molar region was observed, which favors to analyze transmission straight wire appliance mechanical system and guide the clinical application and appliance improvements. Our findings indicate that, under the tilt bending, dental root will be close to the buccal cortical bone, leading to stress concentration at the root tip and maxillary buccal cortical areas; this stress concentration may lead to root resorption of the maxillary first molar.