Forum Implantologicum 13 (2017), No. 1 8. June 2017
Forum Implantologicum 13 (2017), No. 1 (08.06.2017)
Treatment Options for the Posterior Edentulous Jaw: A Note on the Mechanics of Screw-Fastened Implant Connectors
Implant connectors are intricate pieces of machinery that are designed to withstand functional loads during mastication. In mechanical terms these loads take the form of continuous streams of back and forth stress applications. yet while the vast majority of implant-borne restorations bear these stresses without any detrimental effects, in some instances (in the order of a few percent) screw loosening and/or fracture will occur. hence one may reasonably ask why such mishaps take place and how they can be prevented. The answer lies in a thorough understanding of the way a screw-fastened connector works - more specifically what a clinician should do or be careful of when screw-tightening a restoration onto an implant.
The primary function of a screw is not to bear all the stresses applied. To the contrary, by virtue of its clamping action, the screw should distribute the load onto carrier surfaces. Screw mechanics in dynamic environments center on the concepts of 'pretension' (inside the screw) and the corresponding 'preload' (of the surfaces) as well as how they decay over time once the connector is placed in function. The essential objective of any connector design is to minimize not the absolute value but the stress amplitude during cyclic loading consequent to mastication.
Therefore, for the clinician, the objective is to permit the connector - the screw - to function under optimal conditions. This translates into establishing tight contact between the carrier surfaces machined into the implant head and that of the prosthetic component. Further, these surfaces must be firmly clamped so that the force transfer between them is maximized and the stress inside the screw is relieved.
Keywords: Implant, connector, screw, fatigue, stress, fracture, screw loosening