Conical Seal Design™ is the original and scientifically documented conical connection of the Astra Tech Implant System™, creating a strong and stable fit between implant and abutment. Below you will find many references that primarily address the technical questions related to Conical Seal Design.
Implant-abutment interface:
biomechanical study of flat top versus conical
Purpose: The aim of this study was to determine the impact of having a conical versus a flat-top fixture-abutment connection on the induced stress patterns within the bone surrounding an implant with a microthreaded portion, via finite element analysis.
Material and Methods: The finite element method is a very powerful mathematical tool used to calculate the stresses in a structure.
An axisymmetric finite element model of the mandible was used, with previously established parameters for elastic constants. The bone and titanium were assumed to be isotropic, having the same elastic properties in all directions. The implant was modeled to represent a 3.5 mm diameter implant with either an 11-degree internal connection or a flat-to-flat con-nection. Axial stiffness decreased at the apical end to simulate the macrothreads of an implant reducing the overall wall thickness compared to the microthreaded region.
Axial loads of 1000 N were applied to both systems, with either an even load distribution over the surface or concentrated on selective nodes.
Principal stresses in the bone and the interfacial shear stress were calculated on the assumption that there was no fusion between implant and bone, such that the interface could not resist tensile stress. Interlocking between implant and bone was modeled by connecting interfacial implant and bone nodes in a vertical direction resisting shear.
Results: Peak interfacial shear stresses measured between 44 and 100 MPa for the flat-to-flat connection becoming progressively worse when the load applied was modeled only on a lateral node contact.
For the conical connection the stresses ranged from 26 to 32 MPa, when applying the same load. In addition the stress distribution patterns were markedly different with load being concentrated at the most coronal margin for the flat-to-flat connection but being more evenly distributed and at a deeper level, on the implant surface in the bone, for the conical connection.
A similar pattern was noted for the principle stresses which ranged from -32.4 to -277.7 MPa and from -8.5 to -103.3 MPa for the two connections respectively. These stresses were compressive in nature.
Discussion: While the principal stresses recorded were higher than the interfacial shear stress recorded for both connections, the forces were compressive in nature, which is well tolerated by cortical bone. In this respect the shear stress is considered to be of greater significance.
Furthermore while clinical function of implant supported prostheses will lead to a variety of vectorial loads and moments, it is likely that only the axial loads will result in interfacial shear stresses, and these can be most destructive if the shear strength of the interface is exceeded, leading to slip and fracture of the interfacial tissues.
In the current finite element analysis it was apparent that the induced stresses were reduced by application of the axial load along the internal conical surface of the implant. This also resulted in a more even and deeper distribution of the stress taking it away from the more delicate marginal region. This would indicate that an implant with a conical interface can theoretically resist a bigger axial load before triggering bone resorption. In general terms the results also indicate that a favorable stress distribution can be accomplished by a more central and deeper application of the axial load.
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