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Wear behavior of precision attachments.

PURPOSE
The purpose of this article was to compare the wear behavior of precision attachments with plastic inserts to conventional metal-alloy precision attachments.


MATERIALS AND METHODS
In a comparative study attachments of various designs were subjected to alternating load cycles in a wear simulator. In addition to conventional adjustable attachments with metal-alloy matrix and patrix elements, attachments with female elements that are lined with plastic inserts were investigated for the first time. In each wear test 10,000 separating and joining movements were performed in an axial direction under a continuous spray of artificial saliva at 37 degrees C.


RESULTS
The attachments with metal surfaces showed a rapid loss of approximately 60% of the required separating/joining forces during the first 1,000 cycles; after a further 9,000 cycles these forces fell to 25% and 35%, respectively, of the initial value. The attachments with plastic inserts, by contrast, showed only a 4% and 8% loss, respectively, of the required separating/joining forces even after 10,000 wear cycles. With one attachment type a reproducible 20% increase of retention occurred during the testings.


CONCLUSION
The precision attachments with plastic female inserts showed only negligible amounts of wear and the most consistent retentive force in comparison with conventional precision attachments consisting of metal-alloy matrix and patrix components.