“In vitro” wear behavior of extracoronal precision attachments

The objective of this study was to evaluate the retentive ability and weight change of two extracoronal attachments after repeated insertion/removal cycles. Material and methods: Two extracoronal attachments were used, one with plastic inserts and the other one with conventional metal-alloy. Initial retentive ability was checked under a 20kgf load cell at 5mm/min. The weight of the fi xed/removable pairs was verifi ed with an electronic mass comparator. Fixed/removable pairs were tested with an insertion/removal cycling machine, for 5800 cycles (corresponding to 5 years) at a speed of 32 rpm speed. Insertion/ removal cycles were performed under artifi cial saliva. Weight change and retentive ability of attachments were verifi ed at baseline, six-month, one-year, two-year, three-year, four-year and fi ve-year time intervals. The two-way ANOVA for repeated measurements test was used to verify possible interactions between precision attachment type and retentive ability/weight change over time. Statistically signifi cant associations were found between attachment type and retentive ability over time (P=0.006). Metal-alloy group showed signifi cant differences between baseline and fi rst year (P=0.005), baseline and second year (P=0.001), and between baseline and fi ve years (P=0.035) of insertion/removal cycles. In the plastic insert group, no signifi cant differences were found over time. No statistically signifi cant associations were found between precision attachment types and weight change over time (P=0.643). Initial retentive ability can not be standardized for both attachments; the metal-alloy showed better performance than the plastic insert after fi ve years. Both attachments did not show weight change after fi ve years of simulated use.