Statement of problem

Mini implants (<3 mm in diameter) are being used as an alternative to standard implants for implant-retained mandibular overdentures; however, they may exhibit higher stresses at the crestal level.

Purpose

The purpose of this finite element analysis study was to evaluate the biomechanical behavior (stress distribution pattern) in the mandibular overdenture, mucosa, bone, and implants when retained with 2 standard implants or 2 mini implants under unilateral or bilateral loading conditions.

Material and methods

A patient with edentulous mandible and his denture was scanned with cone beam computed tomography (CBCT), and a 3D mandibular model was created in the Mimics software program by using the CBCT digital imaging and communications in medicine (DICOM) images. The model was transferred to the 3Matics software program to form a 2-mm-thick mucosal layer and to assemble the denture DICOM file. A 12-mm-long standard implant (Ø3.5 mm) and a mini dental implant (Ø2.5 mm) along with the LOCATOR male attachments (height 4 mm) were designed by using the SOLIDWORKS software program. Two standard or 2 mini implants in the canine region were embedded separately in the 3D assembled model. The base of the mandible was fixed, and vertical compressive loads of 100 N were applied unilaterally and bilaterally in the first molar region. The material properties for acrylic resin (denture), titanium (implants), mucosa (tissue), and bone (mandible) were allocated. Maximum von Mises stress and strain values were obtained and analyzed.

Results

Maximum stresses of 9.78 MPa (bilaterally) and 11.98 MPa (unilaterally) were observed in 2 mini implants as compared with 3.12 MPa (bilaterally) and 3.81 MPa (unilaterally) in 2 standard implants. The stress values in the mandible were observed to be almost double the mini implants as compared with the standard implants. The stresses in the denture were in the range of 3.21 MPa and 3.83 MPa and in the mucosa of 0.68 MPa and 0.7 MPa for 2 implants under unilateral and bilateral loading conditions. The strain values shown similar trends with both implant types under bilateral and unilateral loading.

Conclusions

Two mini implants generated an average of 68.15% more stress than standard implants. The 2 standard implant–retained overdenture showed less stress concentration in and around implants than mini implant–retained overdentures.

中文翻译：

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两个标准植入物或2个小型植入物保留下颌覆盖义齿的生物力学行为：三维有限元分析

问题陈述

微型植入物（直径<3 mm）被用作标准植入物的替代物，用于保留种植体的下颌覆盖义齿；但是，它们在地壳水平可能会显示较高的应力。

目的

这项有限元分析研究的目的是评估在单侧或双侧负重条件下保留2个标准种植体或2个微型种植体后，下颌覆盖义齿，黏膜，骨骼和种植体的生物力学行为（应力分布模式）。

材料与方法

使用锥束计算机断层扫描（CBCT）对下颌无牙且其假牙的患者进行扫描，并使用CBCT数字成像和医学通讯（DICOM）图像在Mimics软件程序中创建3D下颌模型。将该模型转移到3Matics软件程序中，以形成2毫米厚的粘膜层并组装义齿DICOM文件。使用SOLIDWORKS软件程序设计了一个12毫米长的标准植入物（Ø3.5毫米）和一个小型牙科植入物（Ø2.5毫米）以及LOCATOR凸形附件（高度4毫米）。在犬牙区域中的两个标准或2个微型植入物分别嵌入3D组装模型中。下颌骨的底部固定，并且在第一磨牙区域单侧和双侧施加100 N的垂直压缩载荷。分配了丙烯酸树脂（义齿），钛（植入物），粘膜（组织）和骨骼（下颌骨）的材料属性。获得并分析了最大冯·米塞斯应力和应变值。

结果

在2个小型植入物中观察到的最大应力为9.78 MPa（单侧）和11.98 MPa（单侧），而2个标准植入物中的最大应力为3.12 MPa（单侧）和3.81 MPa（单侧）。与标准种植体相比，下颌骨中的应力值几乎是微型种植体的两倍。对于两个植入物，在单侧和双侧加载条件下，义齿的应力在3.21 MPa和3.83 MPa范围内，粘膜的应力在0.68 MPa和0.7 MPa范围内。在双边和单边载荷下，两种植入物的应变值都显示出相似的趋势。

结论

两个微型植入物产生的应力平均比标准植入物高68.15％。2种标准植入物保留的覆盖义齿比微型植入物保留的覆盖义齿显示的应力集中小。