[Three-dimensional finite element analysis of four-implants supported mandibular overdentures using two different attachments].

Objective: To compare the biomechanical characteristics of four-implants mandibular overdentures supported by Locator attachment or bar-clip attachment under different mechanical loads using three-dimensional finite element analysis method. Methods: Two different models of four-implants supported mandibular overdentures using Locator attachment and bar-clip attachment (hereinafter called Locator model and bar-clip model) were established. Each model was subjected to five different mechanical loading conditions: 100 N vertical loading in central incisor (vertical load of incisor), 100 N vertical loading or oblique loading in canine (vertical or oblique loads of canines), 100 N vertical or oblique loading in mandibular first molar (vertical or oblique loads of mandibular first molar). The stress distributions in implants, peri-implant bone and mucosa were recorded under the above five conditions to evaluate the effects of different attachments on the biomechanical properties of implant-supported mandibular overdentures. Results: Regardless of loading conditions and types of attachments, the stress concentration in implants were located at the neck of implants, and the stress concentration in peri-implant bone was located in the cortical bone. The stress values in mucosa were always much smaller than those in implants and cortical bone. Regardless of loading positions (on canine or on mandibular first molar), the maximum stress at the bone interface around the implant under lateral loading was much higher than that under vertical loading. Under various loading conditions, the stress in implants and cortical bone of the Locator model (the highest von Mise stress value was respectively 79.5 and 22.3 MPa) were lower than that of bar-clip model (the highest von Mise stress value was 110.3 and 28.7 MPa respectively) while the maximum compressive stress in mucosa (0.198 MPa) in Locator model was slightly higher than that in the bar-clip model (0.137 MPa). Conclusions: In clinical practice, the lateral force applied to the implant-retained overdenture should be minimized to avoid complications caused by pathological loads. Under the same loading condition, the stress distributions in overdenture using Locator attachment are more dispersed, which is more conducive to long-term stability of implants.目的： 采用三维有限元法分析下颌4枚种植体支持的Locator和杆卡附着体覆盖义齿的生物力学特点。 方法： 建立下颌4枚种植体支持的Locator和杆卡附着体覆盖义齿的三维有限元模型（简称Locator模型和杆卡模型），每个模型分别加载5种载荷：100 N垂直载荷加载于下颌中切牙（切牙垂直载荷）、100 N垂直或斜向载荷加载于下颌尖牙（尖牙垂直或斜向载荷），100 N垂直或斜向载荷加载于下颌第一磨牙（磨牙垂直或斜向载荷），分析种植体、种植体周围骨及黏骨膜应力分布情况。 结果： 无论何种载荷下，应力均集中于种植体颈部及周围骨皮质，黏骨膜受力均远小于种植体及骨皮质。无论尖牙还是磨牙加载，斜向载荷下相同模型种植体及骨皮质最大von Mise应力均远大于垂直载荷。Locator模型种植体及其周围骨的受力（最大von Mise应力分别为79.5和22.3 MPa）均小于杆卡模型（最大von Mise应力分别为110.3和28.7 MPa），而Locator模型黏骨膜的最小主应力（0.198 MPa）略大于杆卡模型（0.137 MPa）。 结论： 临床中应尽量减小种植覆盖义齿的侧向力；相同载荷下，Locator附着体覆盖义齿的应力分布更有利于种植体的长期稳定。.