 Astra Tech
BioManagement Complex
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 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.
 Assessment of cold welding properties of the internal conical interface of two commercially available implant systems
Purpose: The external butt joint is common in implant
design with joint connection being dependent on the abutment screw. Data to support this design from an
engineering perspective is scant and has been shown
to result in joint instability. By contrast the concept of a one-piece conical abutment has been shown to yield high resistance to bending moments, resulting in improved joint stability. However, concern has been expressed that such conical abutments are at risk of "cold welding" making them non-retrievable. This study set out to confirm or refute the presence of cold welding for two commercially available conical abutment designs, utilized in the ITI and Astra Tech (AT) implant systems.
Materials and Methods: 5 units of the AT 3.5 mm diameter implant, and 4.0 mm diameter implant allowed a comparison of interfacial surface area, 15.3 mm2 versus 27.9 mm2 respectively. At the same time a comparison of these AT units to 4 units of the ITI system (group 3) allowed a comparison between the 8" (ITI) and 11" (AT) tapers. Additionally all test were run dry and also with components bathed in artificial saliva at 37°c.
Two test series were performed. The low torque tests, which were deemed clinically relevant, were performed for tightening torques ranging from 4 to 50 Ncm. The high torque series was for torques greater than 100 Ncm and was employed to identify the limits of each system with 3 units eventually torqued to failure to reveal the critical zones. Additionally 2 units in this series were torqued to the maximum prior to failure and then "bench rested" for 10 and 60 minutes to determine any apparent influence of elastic recoil of the material.
Data was subject to statistical analysis to determine any correlation between tightening and loosening torque, whereby a figure exceeding 100% represented an increased torque required to remove the abutment, indicating cold welding. Additionally statistics were used to determine any significant difference between systems tested, and between dry versus wet environments.
Results: In the low torque series the trend was for all units tested within the three groups to be loosened at 80-90% of the tightening torque. One or two units exceeded 100% at isolated torque levels, however the correlation between removal torque and tightening torque was highly significant, p<0.01, confirming that overall there was no evidence of cold welding. Additionally there was no statistical difference between wet versus dry conditions (p>0.30).
For the high torque series new units were utilized. The AT 3.5 mm units failed to achieve a cold weld even at the 200 Ncm level, and even after bench resting. By contrast the AT 4.0 mm and ITI units both demonstrated cold welding of 113% and 104% respectively, as a mean at the 100 Ncm level. Above 100 Ncm the mean values for cold welding actually decreased slightly, notably after bench resting. Failure of the units occurred at a mean of 211, 307, and 200 Ncm for the AT 3.5 mm, AT 4.0 mm and ITI units respectively. The volume of data available for this series was too limited to conduct a separate statistical analysis and was therefore pooled in with the data from the low torque series.
Discussion and Conclusions: Considering clinically relevant torques of 20 to 50 Ncm, there was little variation between systems, with a removal torque approximately 85% of the tightening torque, with a strong correlation, p< 0.01. This contrasts a previous report indicating a 124% value for the ITI system at 25 Ncm. There was no difference between the results for dry components versus those bathed in artificial saliva at 37°c.
The high torque series revealed a difference between AT 3.5 mm, where a cold weld was never demonstrated, and AT 4.0 mm achieving a cold weld at 100 Ncm. This suggests that the surface area of the interface is crucial in determining cold welding. There was little difference between the AT 4.0 mm and the ITI units. It should be noted however, that this apparent cold welding might be a reflection of the difference between resting friction and gliding friction, which for metals is always higher. All components failed at levels far in excess of what is achieved clinically.
It can be concluded that for clinically relevant levels of torque, none of the units tested achieved a cold weld.
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