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Abstract
This in vitro study was performed to compare and evaluate the stress
distribution patterns and retention of two telescopic abutment designs with convergence angles 4° and 6° in implant supported overdentures using strain gauge technology.
An acrylic resin test model representing a completely edentulous lower arch was used. The distal part of the residual ridge was covered with silicon based soft liner to simulate the mucoperiosteum. Using a dental surveyor, four root shaped implants were installed in the inter-foraminal area, parallel to each other.
A prosthesis with a metal framework specially designed for loading the implants, and testing the retention, was constructed. The model was prepared to receive eight strain gauges distributed around the implants.
An index was fabricated to fix the relation between the prosthesis and the model during picking-up procedures of the telescopic caps.
Abutments with 4° convergence angle were fastened to the implants and their caps were picked up in the prosthesis with self-cured acrylic resin.
A universal testing machine was used to test the prosthesis retention. Vertical and oblique loads (50- 70) Newton was applied at the right first molar area then at the right canine area, and strains developed at the four implants were recorded. The retention and loading experiments were repeated with the 6° convergence angle replacing the 4° convergence angle abutments. Each experiment was repeated ten times then the mean values were tabulated and statistically analyzed.
The results of this study showed that the mean retention with telescope angle 4° was significantly higher than that of telescope angle 6°. When load was applied at the cantilever the most distal implant received the highest stresses.
The angle of convergence influences the transfer of stresses to the implant.
When load was applied at the cantilever, implant with Telescope angle 4°received higher stresses than with Telescope angle 6°. While when the load was applied between the implants, the angle of convergence had no effect on the amount of stresses transferred to the implants.