三维有限元分析种植体支持平面型及弹性衬垫型磁性覆盖义齿在正常骨及骨质疏松状态下的应力

Three-dimensional finite element analysis of stress distributions in osteoporosis and normal mandibular dental implant-supported overdentures with flat-type and cushion-type magnetic attachments

背景:种植磁性覆盖义齿借助种植体、磁性附着体及口腔黏膜为义齿提供固位、支持和稳定,因此种植磁性覆盖义齿对无牙颌患者特别是颌骨状况不理想的患者尤为合适。目的:比较下颌骨种植体支持的平面型及弹性衬垫型磁性附着体义齿在正常骨质和骨质疏松状态下的生物力学特性。方法:选取1例符合要求的无牙颌患者下颌骨、覆盖义齿CT数据,建立包含下颌骨、种植体、磁性附着体及覆盖义齿的三维有限元模型,其中骨质状态有正常骨质与骨质疏松两种情况,磁性附着体有平面型及弹性衬垫型两种。对每种模型的覆盖义齿施加4个加载力,分别为下颌切牙的垂直向加载力、右下尖牙的垂直向加载力、右下第一磨牙的垂直向和倾斜向(颊舌向倾斜45°)加载力,加载力大小均为100 N,分析皮质骨和松质骨的最大应力。结果与结论:(1)在同一磁性附着体与加载力下,正常颌骨种植体周围皮质骨的最大应力大于骨质疏松状态下的皮质骨;当施加右下第一磨牙倾斜向加载力时,种植体周围的皮质骨应力值是垂直向加载的2倍以上;当加载条件相同时,无论是正常颌骨还是骨质疏松颌骨,平面型磁性附着体的应力值均高于弹性衬垫型磁性附着体。(2)在同一磁性附着体与加载力下,正常颌骨种植体周围松质骨的最大应力均大于骨质疏松状态下的松质骨;当施加右下第一磨牙倾斜向加载力时,种植体周围的松质骨应力值是垂直向加载的2倍以上;两种磁性附着体在垂直向力加载下,正常颌骨种植体周围松质骨的最大应力大于骨质疏松状态下的松质骨;当加载条件相同时,无论是正常颌骨还是骨质疏松颌骨,平面型磁性附着体的应力值均明显高于弹性衬垫型磁性附着体。(3)结果表明,在骨质疏松状态下,颌骨所受的低应力源于骨组织更大的弹性形变,不利于骨结合,侧向力会造成种植体周围更大的应力产生,不利于种植体的稳定性。

BACKGROUND: Implanting magnetic overdentures use implants, magnetic attachments, and oral mucosa to provide retention, support, and stability for the denture. Therefore, implanting magnetic overdentures are particularly suitable for edentulous patients, especially those with unsatisfactory jaw conditions. OBJECTIVE: To compare the biomechanical response of normal mandible and osteoporosis mandible in two implants supported with flat-type and cushion-type magnetic attachments. METHODS: The CT data of mandible and overdenture of one patient with edentulous jaw that met the requirements were selected. A three-dimensional finite element model of a two-implant-retained mandibular overdenture with flat-type and cushion-type magnetic attachments was developed and two types of bone quality(normal and osteoporosis) were prepared. Four types of load were applied to the overdenture in each model: 100 N vertical and oblique(buccal lingual inclination 45°) loads on the right first molar and a 100 N vertical load on the right canine and the lower incisors. The maximum equivalent stresses in cortical bone and cancellous bone of the models were analyzed.RESULTS AND CONCLUSION:(1) Under the same magnetic attachment and loading force, the maximum equivalent stress in normal cortical bone and cancellous bone was greater than in osteoporotic bone. When the lower right first molar was loaded with oblique loading force, the stress value of the cortical bone around the implant was more than twice that of the vertical loading. When the loading conditions were the same, whether it was normal jaw or osteoporotic jaw, the stress value of the flat-type magnetic attachment was higher than that of the cushion-type magnetic attachment.(2) Under the same magnetic attachment and loading force, the maximum stress of the cancellous bone around the normal jaw implant was greater than that of the cancellous bone in the osteoporotic state. When the right lower first molar was inclined to the loading force, the stress value of the cancellous bone around the implant was more than twice that of the vertical load. The maximum stress of the cancellous bone around the normal jaw implant was greater than that of the cancellous bone in the osteoporotic state under the vertical force of the two magnetic attachments. When the loading conditions were the same, whether it was a normal jaw or an osteoporotic jaw, the stress value of the flat-type magnetic attachment was significantly higher than that of the cushion-type magnetic attachment.(3) The results show that in the state of osteoporosis, the low stress on the jaw bone comes from greater elastic deformation of the bone tissue, which is not conducive to osseointegration, and lateral force will cause greater stress around the implant, which is not conducive to the stability of the implant.