Geramy Allahyar, Shahroudi Atefe Saffar
Professor, Dental Research Center Dentistry Instituted, Orthodontics Department, Tehran University of Medical Sciences, Tehran, Iran.
Assistant Professor, Orthodontics Department, Lorestan University of Medical Sciences, Khoram-abad, Iran.
J Dent (Tehran). 2014 Jan;11(1):75-84. Epub 2014 Jan 31.
Several appliances have been used for palatal expansion for treatment of posterior cross bite. The purpose of this study was to evaluate the stress induced in the apical and crestal alveolar bone and the pattern of tooth displacement following expansion via removable expansion plates or fixed-banded palatal expander using the finite element method (FEM) analysis.
Two 3D FEM models were designed from a mesio-distal slice of the maxilla containing the upper first molars, their periodontium and alveolar bone. Two palatal expanders (removable and fixed) were modeled. The models were designed in SolidWorks 2006 and then transferred to ANSYS Workbench. The appliance halves were displaced 0.1 mm laterally. The von Mises stress in the apical, crestal, and PDL areas and also the vertical displacement of the cusps (palatal and buccal) was were evaluated.
The total PDL stress was 0.40003 MPa in the removable appliance (RA) model and 4.88e-2 MPa in the fixed appliance (FA) model and the apical stress was 9.9e-2 and 1.17e-2 MPa, respectively. The crestal stress was 2.99e-1 MPa in RA and 7.62e-2 MPa in the FA. The stress in the cortical bone crest was 0.30327 and 7.9244e-2 MPa for RA and FA, respectively and 3.7271 and 7.4373e-2 MPa in crestal area of spongy bone, respectively. The vertical displacement of the buccal cusp and palatal cusp was 1.64e-2 and 5.90e-2 mm in RA and 1.05e-4 and 1.7e-4 mm in FA, respectively.
The overall stress as well as apical and crestal stress in periodontium of anchor teeth was higher in RA than FA; RA elicited higher stress in both cortical and spongy bone. The vertical displacement of molar cusps was more in removable than fixed palatal expander model.
已有多种矫治器用于腭部扩展以治疗后牙反合。本研究的目的是使用有限元法（FEM）分析，评估通过可摘式扩展板或固定带环腭扩展器进行扩展后，根尖和牙槽嵴顶骨所产生的应力以及牙齿移动模式。
从包含上颌第一磨牙、其牙周组织和牙槽骨的上颌近远中切片设计两个三维有限元模型。对两种腭扩展器（可摘式和固定式）进行建模。模型在SolidWorks 2006中设计，然后转移到ANSYS Workbench。将矫治器的两半向外侧移动0.1 mm。评估根尖、牙槽嵴顶和牙周膜区域的冯·米塞斯应力以及牙尖（腭侧和颊侧）的垂直位移。
可摘矫治器（RA）模型中的牙周膜总应力为0.40003 MPa，固定矫治器（FA）模型中的为4.88e - 2 MPa，根尖应力分别为9.9e - 2和1.17e - 2 MPa。牙槽嵴顶应力在RA中为2.99e - 1 MPa，在FA中为7.62e - 2 MPa。皮质骨嵴处的应力在RA和FA中分别为0.30327和7.9244e - 2 MPa，松质骨牙槽嵴顶区域的应力分别为3.7271和7.4373e - 2 MPa。颊侧牙尖和腭侧牙尖的垂直位移在RA中分别为1.64e - 2和5.90e - 2 mm，在FA中分别为1.05e - 4和1.7e - 4 mm。
RA中支抗牙牙周组织的总应力以及根尖和牙槽嵴顶应力高于FA；RA在皮质骨和松质骨中均引起更高的应力。可摘式腭扩展器模型中磨牙牙尖比固定腭扩展器模型中的垂直位移更大。
