INMP Department of Social Dentistry and Gnathological Rehabilitation, University of Rome Tor Vergata, Rome, Italy.
J Prosthet Dent. 2013 Jan;109(1):9-21. doi: 10.1016/S0022-3913(13)60004-9.
Complete-arch restorations supported by fewer than 5 dental implants can induce unbalanced load transfer and tissue overloading, leading to excessive bone resorption and possible clinical failure. This is primarily affected by the cantilever length, the implant design and positioning, and the morphology and properties of the bone.
The purpose of this study was to compare 2 different restorative techniques for complete-arch rehabilitations supported by 4 implants. The primary purpose was to highlight the possible risks of excessive stress and unbalanced load transfer mechanisms and to identify the main biomechanical factors affecting loading transmission.
Three-dimensional (3D) numerical models of edentulous maxillae and mandibles restored with 2 techniques using 4 implants were generated from computed tomography (CT) images and analyzed with linear elastic finite-element simulations with 3 different static loads. The first technique used 2 vertical mesial implants and 2 tilted distal implants (at a 30 degree angle), and the second used vertical implants that fulfilled platform switching concepts. Bone-muscle interactions and temporomandibular joints were included in the mandibular model. Complete implant osseous integration was assumed and different posthealing crestal bone geometries were modeled. Stress measures (revealing risks of tissue overloading) and a performance index (highlighting the main features of the loading partition mechanisms) were introduced and computed to compare the 2 techniques.
Dissimilar load transfer mechanisms of the 2 restorative approaches when applied in mandibular and maxillary models were modeled. Prostheses supported by distally tilted implants exhibited a more effective and uniform loading partition than all vertical implants, except in the simulated maxilla under a frontal load. Tilted distal implants reduced compressive states at distal bone-implant interfaces but, depending on bone morphology and loading type, could induce high tensile stresses at distal crests. Overloading risks on mesial periimplant bone decreased when the efficient preservation of the crestal bone through platform switching strategies was modeled.
Numerical simulations highlighted that the cantilever length, the implant design and positioning, and the bone's mechanical properties and morphology can affect both load transmission mechanisms and bone overloading risks in complete-arch restorations supported by 4 implants. Distally tilted implants induced better loading transmission than vertical implants, although the levels of computed stress were physiologically acceptable in both situations.
全口义齿修复仅由少于 5 个牙种植体支撑会导致不平衡的负荷转移和组织过载，从而导致过度的骨吸收和可能的临床失败。这主要受悬臂长度、种植体设计和定位、骨骼的形态和特性影响。
本研究旨在比较两种不同的全口义齿修复技术，这些修复技术均由 4 个种植体支撑。主要目的是突出过度的应力和不平衡的负荷转移机制的风险，并确定影响负荷传递的主要生物力学因素。
从 CT 图像生成无牙颌上颌和下颌的三维（3D）数值模型，并使用线性弹性有限元模拟分析在 3 种不同静态载荷下进行分析。第一种技术使用 2 个近中垂直植入物和 2 个倾斜远中植入物（成 30 度角），第二种技术使用满足平台转换概念的垂直植入物。下颌模型中包括骨-肌相互作用和颞下颌关节。假设完全植入物骨整合，并对不同的愈合后牙槽骨几何形状进行建模。引入并计算了应力测量值（揭示组织过载的风险）和性能指标（突出负载分配机制的主要特征），以比较两种技术。
当应用于下颌和上颌模型时，两种修复方法的不同负荷传递机制被建模。与所有垂直植入物相比，远端倾斜植入物支撑的修复体具有更有效的和均匀的负载分配机制，除了在前负荷下模拟的上颌中。远端倾斜植入物降低了远端骨-植入物界面的压缩状态，但根据骨骼形态和加载类型，可能会在远端嵴上引起高拉伸应力。通过平台转换策略有效地保留牙槽嵴骨时，近中种植体周围骨的过载风险会降低。
数值模拟强调了悬臂长度、种植体设计和定位、骨骼的机械性能和形态都可以影响全口义齿修复的负载传递机制和骨过载风险，这些修复由 4 个种植体支撑。与垂直植入物相比，倾斜植入物可更好地传递负荷，但在两种情况下计算出的应力水平都是生理上可接受的。
