Purpose: A triangular gap between the keeper and magnetic assembly caused by the inclination might weaken the attractive force of the overdenture. Furthermore, the load supporting ability may be compromised with a change in the position of the fulcrum line when occlusal force is loaded on the outer side of the occlusal surface.
Therefore, in this study, the influence of a triangular gap in the magnetic attachment for implant-retained overdentures on load supporting ability was evaluated by tensile test and 3-D geometric analysis.
Methods: The inclined angle of the gap was set at 0 to 10.0 degrees with aluminum foil to measure the attractive force when triangular gaps existed, and the maximum tensile strength of magnetic attachment was measured. Based on these results, overdentures on four implants placed at bilateral first molar and canine regions on an edentulous model of the upper jaw were simulated, and the load supporting ability of implant-retained overdentures was calculated with 3-D geometric analysis.
Results: The attractive force decreased with an increase in the angle of inclination. The attractive force decreased remarkably from 0 to 1.0 degrees, and it was reduced to half at 2.0 degrees and showed a moderate decrease thereafter.
When there was a gap on the palatal side, the load supporting ability decreased depending on the inclined angle, however when the gap was on the buccal side, it decreased to 1/3 on incisor loading and 1/7 on molar loading compared to that with no gap.
Conclusion: Attractive force decreased significantly when a triangular gap existed in the magnetic attachment, and in particular, it clearly caused a large decrease of load supporting ability when the gap was on the buccal side.
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