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Abstract
The abutment connection with the crown is fundamental to the structural stability of the implant system and to the prevention of mechanical exertion that can compromise the success of the implant treatment. The aim of this study is to clarify the difference in the stress distribution patterns between implants with internal and external-hex connections with the crown using the Finite Element Method (FEM). Material and Methods: The internal and external-hex connections of the Neoss and 3i implant systems respectively, are considered. The geometrical properties of the implant systems are modeled using three-dimensional (3D) brick elements. Loading conditions include a masticatory force of 200, 500 and 1000N applied to the occlusal surface of the crown along with an abutment screw torque of 110, 320 and 550Nmm. The von Mises stress distributions in the crown are examined for all loading conditions. Assumptions made in the modeling include: 1. half of the implant system is modeled and symmetrical boundary conditions applied; 2. temperature sensitive elements are used to replicate the torque within the abutment screw. Results: The connection type strongly influences the resulting stress characteristics within the crown. The magnitude of stress produced by the internal-hex implant system is generally lower than that of the external-hex system. The internal-hex system held an advantage by including the use of an abutment between the abutment screw and the crown. Conclusions: The geometrical design of the external-hex system tends to induce stress concentrations in the crown at a distance of 2.89mm from the apex. At this location the torque applied to the abutment screw also affects the stresses, so that the compressive stresses on the right hand side of the crown are increased. The internal-hex system has reduced stress concentrations in the crown. However, because the torque is transferred through the abutment screw to the abutment contact, changing the torque has greater effect on this hex system than the masticatory force. Overall the masticatory force is more influential on the stress within the crown for the external-hex system and the torque is more influential on the internal-hex system.
Highlights
Dental implants are a consistently accepted form of dental treatment
The first step of the modeling is to define the geometry of the implant system
This is followed by specifying the material behavior in terms of the Young's modulus, Poisson's ratio and density for the implant and componentry
Summary
Clinical research in oral implantology has led to advancements in the biom echan ical as pects of implants, implant surface features and implant componentry. These advancements in implant componentry include the modification of the external-hex connection between the abutment and crown to the currently used internal-hex (Figure 1b)). Both internal and external-hex connected implant systems are extensively used, distinctly different performances are on offer in terms of the stress characteristics produced within the crown. There are two major factors which can cause the crown and implant to fail.
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