Lee Jae-In, Lee Yoon, Kim Nan-Young, Kim Yu-Lee, Cho Hye-Won
Department of Prosthodontics, College of Dentistry, Wonkwang University, Iksan, Korea.
Clin Implant Dent Relat Res. 2013 Oct;15(5):735-49. doi: 10.1111/cid.12134. Epub 2013 Aug 9.
The precise fit of an implant prosthesis is considered to be a prerequisite for the success and maintenance of osseointegration. It is unknown how much static stress can be tolerated at the implant-bone interface with ill-fitting prostheses for the two different types of retention (cement vs screw).
The purpose of this study was to evaluate the stress pattern and magnitude in the supporting tissues around ITI (Straumann AG, Waldenburg, Switzerland) implants with screw- or cement-retained prostheses with marginal gaps by photoelastic analysis.
A photoelastic model of a human mandible, partially edentulous distal to the canine, was made of PL-2 resin. Three ITI implants (4.1 × 10 mm, Straumann AG, Waldenburg, Switzerland) were placed in the posterior edentulous region, and screw- or cement-retained three-unit fixed partial dentures (FPDs) were fabricated. Ill-fitting prostheses were made by placing a 100-μm gap between the abutments and the superstructures on the second premolar or the first molar. A static vertical force of 134 N was applied at three loading points on each prosthesis. Photoelastic stress analysis was carried out to measure the fringe order around the implant-supporting structures.
Even in the unloaded condition, low-level stresses were generated around the implants after screw tightening or cementing the three-unit FPDs with marginal gaps. Loading on the terminal implants developed high concentrated stresses around the loaded implant, regardless of the types of restorations or the presence of gaps. However, when the middle implant was loaded, moderate stresses were distributed to the anterior and posterior implants.
Screw-retained FPDs with gaps exhibited a wider range of stresses on the interproximal region of adjacent implants than cement-retained FPDs. However, severe misfit in the prosthesis caused the nonaxial stress transfer to the adjacent implants in the cement-retained FPDs with gaps.
种植体修复体的精确适配被认为是骨结合成功及维持的前提条件。对于两种不同固位方式（粘结与螺丝固位）的修复体，种植体-骨界面在适配不佳时能够耐受多大的静应力尚不清楚。
本研究的目的是通过光弹性分析评估采用螺丝或粘结固位修复体且存在边缘间隙的ITI（瑞士士卓曼公司，瓦尔登堡）种植体周围支持组织中的应力模式和大小。
用人下颌骨的光弹性模型，该模型在尖牙远中部分无牙，由PL - 2树脂制成。在无牙后牙区植入3枚ITI种植体（4.1×10 mm，瑞士士卓曼公司，瓦尔登堡），制作螺丝或粘结固位的三单位固定局部义齿（FPD）。通过在第二前磨牙或第一磨牙的基台与上部结构之间设置100μm的间隙来制作适配不佳的修复体。在每个修复体的三个加载点施加134 N的垂直静载荷。进行光弹性应力分析以测量种植体支持结构周围的条纹级数。
即使在未加载状态下，在螺丝拧紧或粘结有边缘间隙的三单位FPD后，种植体周围也会产生低水平应力。无论修复体类型或间隙是否存在，对末端种植体加载都会在加载种植体周围产生高集中应力。然而，当对中间种植体加载时，中等应力会分布到前后种植体上。
与粘结固位的FPD相比，有间隙的螺丝固位FPD在相邻种植体的邻面区域表现出更广泛的应力范围。然而，修复体严重不匹配会导致有间隙的粘结固位FPD中的非轴向应力传递到相邻种植体。
