Investigation of the wear of prefabricated attachments-An in vitro study of retention forces and fitting tolerances

Objective: To quantify wear processes by measuring the retention force changes and the fitting tolerance at different prefabricated attachment systems to estimate the wear constancy and applicability in clinical practice. Method and Materials: Seven prefabricated attachment systems (Dalbo-Classic, Dalbo-PLUS, Dalbo-Z, Mini-Gerber-PLUS, Stufenexzenter, SphäroLock, and Degussa-Kugelankersystem) with different construction and alloy composition were tested. Twenty samples of each system were subjected to 10,000 insertion-separation cycles in a wear simulator with a periodontium-simulating specimen holder. The simulator was designed to record the force needed to insert and to separate the attachment and the distance moved during the insertion and separation cycles. Results: All types of anchors showed wear that led to a loss or to an increase in retention force at the beginning of the wear simulation. Anchors with a plastic retention insert showed the slightest changes in retention force. The wear does not have an effect on the fitting tolerance. Conclusion: Anchor systems that possess an adjustable matrix should be preferred. They allow decreasing or increasing the retention force of an anchor if this force is changed by wear. There is no risk of a loss of support if forces in occlusal direction are exerted because there is no clinically relevant change in the fitting tolerance. Palabras clave: anchors, fitting tolerance, overdentures, prefabricated attachments, retention force changes, wear