the intrusion of the  anterior  portion of  the denture     tissue-

r e f e r e n c e s

ward。14 Clinical studies have also suggested that one of the   chief concerns of patients wearing two-implant overdentures

is denture rotation。31 Therefore, it has been recommended by some investigators that clinicians should use three or four implants when increased retention is required。15 Clinicians should also pay attention to the appropriate extension of the denture base and occlusal harmony to prevent excessive rotational  movement。31

There has been some concern that with three-implant overdentures, the strain in the bone around the middle implant may be high, especially when functioning with the posterior teeth。 Nevertheless, our results showed that during simulation of grinding food with the posterior teeth, the maximum equivalent strain in the cortical bone was located around the left implant, on the same side as the load。 Therefore, it could be concluded from our results that overdenture anchored by three implants did not cause any strain burden in the cortical bone around the middle implant。 Geckili et al。 also found that the marginal bone loss around the central implants of three- implant mandibular overdentures, when using ball or bar attachments, was lower than around the implants on the left and right sides。33 Furthermore, as mentioned above, three- implant overdenture was more stable than the two-implant model in our study。 For patients who complain about rotational movement around the fulcrum line of their two-implant mandibular overdenture, adding a third implant in the midline of the jaw could theoretically improve denture stability。

目的：本研究的目的是评估植入物骨中的应变分布，下颌覆盖义齿锚固的义齿应力和义齿稳定性不同数量的植入物在不同的载荷条件下，通过三维有限元分析（3D FEA）。

方法：建立四个下颌覆盖义齿三维有限元模型一到四个Straumann植入物与定位器附件。 三种负载应用于每个模型的义齿：左侧为100 N垂直和倾斜载荷第一磨牙和下切牙上的100 N垂直载荷。 生物力学行为记录植入物骨，植入物，基台和覆盖义齿。文献综述

结果：在下切牙上的垂直载荷下，单植入物义齿旋转在植入物的一侧到另一侧，并且在植入物中没有发现应变的明显增加骨。 在相同的装载条件下，双植入物保留义齿在穿过两个植入物的支点线周围显示更多的明显旋转，基台的最大等效应力高于其他型号。在三植入物支持的义齿中，在皮层中没有发现应变集中在三种负荷条件下，中间植入物周围的骨骼。

结论和临床意义：单植入物保留下颌覆盖义齿没有在单个植入物周围的骨骼中显示破坏性应变集中，并且可能是具有成本效益的缺齿患者的治疗方案。 第三种植入物可以放置在其间原来的两名患者由双注射过度义齿康复报告不变并且明显的义齿围绕支点线旋转。

1。介绍

近年来，治疗完全无牙的下颌骨通过植入物义齿已成为常规策略,完全无精神病患者有持续性使用常规下颌假体的问题可以从种植体义齿中获益明显

2002年，麦吉尔共识声明中表示两个植入物保留的义齿应该是第一个选择治疗无牙的下颌骨。5最近，有报道指出单个植入物是

适用于过度义齿保留，并可能导致高度成功率与覆盖义务相当多种植入物。6-11 Walton et al。 比较患者满意度和下颌覆盖义齿的假体结果一个或两个植入物保留在86名参与者一年。在这项随机临床试验中，研究人员发现较低组件成本和处理时间，具有可比性满意和维护时间，保留义齿通过一个中线植入物。然而，一些作者有报道了单种植体意外高的失败率保留下颌覆盖义齿使用立即加载方案12,13