Study on Magnetic Attachment for Implants
Accuracy and Required Tightening Torque of Keeper
2004 Volume 17 Issue 1 Pages 13-21
Details
2004 Volume 17 Issue 1 Pages 13-21
Purpose: This study examined the accuracy of fit, aiming to increase the preloading of the keeper of a magnetic attachment for implants, and to improve an appropriate tightening torque.
Materials and methods: The keeper for the magnetic attachment newly developed for 3i, the Nobel Biocare (hereafter, NB), and the ITI system was evaluated.Two kinds of attachment were prepared (type A and type B with different shape). The accuracy of fit was examined with SEM and a microscope. The 3i and the NB system measured the space between the abutment ring and the keeper during the fixture and the abutment ring in type A. The ITI system measured the space between the fixture and the keeper. In type B, the keeper of 3i and NB was shared. Therefore, the space was measured with the 3i fixture by using a similar method to that used for type A. The space in the abutment of each system was measured as a control. An appropriate tightening torque of the keeper screw to prevent the screw from becoming loose was assumed to be 70% of the destruction value that had been obtained from the tightening examination. Five materials were used for each examination.
Results: The distance was 4.40 μm (SD:1.37) between the keeper and the abutment in type A for 1.19 μm (SD:0.65) for 6.01 μm (SD:2.03) for 3i and NB and ITI, and meanwhile, it was one side and 10.6 μm (SD:1.98) in the control for 13.4 μm (SD:1.40) for 1.33 μm (SD0.447) for 3i and NB and ITI. They were 4.66 μm (SD1.35) between the abutment ring and the keeper and 5.96 μm (SD:2.83) between the fixture and the abutment ring in type B for 3i. Then, it was 1.72μm (SD:1.01) between the fixture and the keeper for ITI.
Discussion: An appropriate tightening torque is 50-70% of the maximum tightening power at which the screw was destroyed. The proper tightening torque calculated
referring to this was 15 Ncm, and, then, 20 Ncm in type A then for ITI for 3i and for NB. Both 32 Ncm was possible in type B.
Conclusion: Appropriate agreement was obtained, and an increase in preloading was obtained by improving the tightening torque according to the improvement. As a result, it is thought that keepers for preventing magnetic attachment from becoming loose could be improved.
