Faculty of Dentistry, Mansoura University, ElDakahlia, Egypt.
Int J Oral Maxillofac Implants. 2013 May-Jun;28(3):e143-50. doi: 10.11607/jomi.2467.
The aim of this study was to evaluate the effect of cantilevered bar length on strain produced around two implants supporting a mandibular overdenture.
Two root-form implants were placed bilaterally in the canine region of an edentulous acrylic resin mandibular cast and connected with a resilient bar/clip attachment. Four linear strain gauges were bonded to the acrylic resin at the mesial and distal surfaces of each implant. Each gauge was wired separately into a 1/4 Wheatstone bridge of a multichannel digital bridge amplifier. Strains were measured without cantilevered bar extensions (control group) and with the following lengths of cantilevered bars: 11 mm (group 1), 9 mm (group 2), and 7 mm (group 3). For each cantilevered bar length, strains were measured using clips placed on the cantilevers and attached to the overdenture (bar-clip contact) and without clips (bar-acrylic resin contact). Strain measurements were performed under central and unilateral loading using a loading device.
The bar with cantilevers (either with or without clips) demonstrated a significant increase in strain compared to the bar without cantilevers. The 11-mm cantilever length generated the highest peri-implant strain values, while the 7-mm length recorded the lowest. For all cantilevered bar lengths, the strains significantly decreased with bar-clip contact compared to bar-acrylic resin contact. Under central loading, distal and mesial peri-implant strains were the highest and the lowest values, respectively, while under unilateral loading, the highest strain was recorded at distal sites of the loading side and the lowest was recorded at distal sites of the nonloading side. A positive correlation was found between the recorded strain and the cantilevered bar length.
The 7-mm cantilevered bar with clips placed on the cantilevers was recommended when two implants were used to support mandibular overdentures, as it demonstrated the lowest magnitude of strains with no significant differences between peri-implant sites.
本研究旨在评估悬臂梁长度对两个种植体支撑下颌覆盖义齿时产生的应变的影响。
将两个根形种植体分别放置在无牙丙烯酸树脂下颌模型的犬齿区域，并通过弹性杆/夹附件连接。将四个线性应变计粘贴在每个种植体的近中和远中表面的丙烯酸树脂上。每个应变计分别连接到多通道数字桥放大器的 1/4 惠斯通电桥。在没有悬臂梁延伸（对照组）和具有以下悬臂梁长度的情况下测量应变：11mm（组 1）、9mm（组 2）和 7mm（组 3）。对于每个悬臂梁长度，使用放置在悬臂上并连接到覆盖义齿的夹子（梁夹接触）和没有夹子的情况下（梁-丙烯酸树脂接触）测量应变。使用加载装置在中心和单侧加载下进行应变测量。
带有悬臂梁（带或不带夹子）的梁与不带悬臂梁的梁相比，应变明显增加。11mm 悬臂长度产生的种植体周围应变值最高，而 7mm 长度记录的应变值最低。对于所有悬臂梁长度，与梁-丙烯酸树脂接触相比，梁夹接触的应变显著降低。在中心加载下，近中和远中种植体周围的应变最高和最低，而在单侧加载下，加载侧的远中部位记录的应变最高，非加载侧的远中部位记录的应变最低。记录的应变与悬臂梁长度之间存在正相关关系。
当使用两个种植体支撑下颌覆盖义齿时，建议使用带有夹在悬臂上的 7mm 悬臂梁，因为它在种植体周围部位之间没有显著差异的情况下表现出最低的应变幅度。
