 Astra Tech
BioManagement Complex
|
 Conical Seal Design
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.
 An in vitro evaluation of the strength of an internal conical interface compared to a butt joint interface in implant design
Purpose: The aim of the study was to compare the
strength of the fixture/abutment and abutment/ bridge cylinder interfaces for implants utilizing a
butt joint and a conical joint design.
Materials and Methods: The Astra Tech implant and Branemark implant were used to represent the conical joint and butt joint designs respectively, with units being assembled according to manufacturer's recommendations.
Each implant was screwed into a metal beam at one end, with the abutment or bridge-cylinder being clamped to another beam at the opposite end. In order to assess the strength of the implant/abutment and abutment/bridge cylinder interfaces, the 3-point bending test was utilized, with the application of a known force at right angles to the interface, by means of a screw driven loading device. For each system and each interface, 6 units were tested.
Recordings were made for both the point of first plastic bending, recorded as a 0.3 mm deformation and also maximum bending to failure. The displacements were recorded on a Linear Variable Differential Trans-former (LVDT). Load and displacement were analysed using an appropriate software program.
Results: For the implant/abutment interface, the mean moments required to register the point of first plastic deformation was 1315 Nmm and 645 Nmm for the conical joint and butt joint respectively, with a mean moment force of 2030 Nmm and 1262 Nmm to cause failure of each joint. The difference between the moments was highly statistically significant (p = 0.00010 and p < 0 0010, respectively). Furthermore the coefficient of variance was low confirming the strict homogeneity of both material and design, in both systems, which would suggest that the results would be reproducible in larger sample.
In the Astra Tech system failure did not result in either elongation or abutment fracture, however it is likely that imperceptible vertical hair-line fractures did occur at the neck of the implant. For the Brkne-mark system there was a notable elongation of the abutment screw with loosening of the joint.
When testing the two systems at the abutment/ bridge cylinder interface, the mean moments required to register the first point of plastic deformation were 994 Nmm and 725 Nmm for the conical and butt joints respectively, with a moment force of 1866 Nmm and 1305 Nmm required to cause failure of each joint, which for the Astra Tech system was a fracture of the bridge screw, but for the Branemark system, the abutment screw was once again seen to be the focus of deformation. Again the differences were statistically significant (p < 0.010 and p = 0.0001, respectively).
Discussion: Biomechanical failure has become the focus of concern with a constant source of data drawing attention to the problems of screw loosening and screw fracture.
Whilst numerous efforts have been made to address this problem, in particular with the introduction of the torque driver, there has been little data published confirming the efficacy of the butt joint or other designs to resist bending moments.
This study has demonstrated that the conical joint is significantly superior to the butt joint in resisting bending moments when tested in the extreme, such as in the 3-point bending apparatus described, and that furthermore the abutment screw is the weakest point in the butt joint design and not the bridge screw, when using the Estheticone system. |
|
|
