“In vitro” wear behavior of extracoronal precision attachments

Abstract

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 fixed/removable pairs was verified 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 artificial saliva. Weight change and retentive ability of attachments were verified at baseline, six-month, one-year, two-year, three-year, four-year and five-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 significant associations were found between attachment type and retentive ability over time (P=0.006). Metal-alloy group showed significant differences between baseline and first year (P=0.005), baseline and second year (P=0.001), and between baseline and five years (P=0.035) of insertion/removal cycles. In the plastic insert group, no significant differences were found over time. No statistically significant 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 five years. Both attachments did not show weight change after five years of simulated use.