In Vitro Study of Retention of Paired Press-Stud Overdenture Component Attachments

Objectives: Mandibular two-implant overdentures have become widely used for edentulous patients. Loss of retention of the stud attachment assemblies presents maintenance problems to both patient and dentist. The objective of this study was to investigate effects of repeated separation/reunion cycles on the retention of paired overdenture stud attachment assemblies set in acrylic resin.
Methods: Two analogues for stud attachments (ITI®Straumann) were secured vertically in the first acrylic block, and the attachments were secured in the second acrylic block. A removable rod, attached to the second block, acted as a seating guide during cycling. Specimens in one group had the pairs of stud attachments set vertically and parallel, and specimens in the other group had one attachment set vertically and the second set at 15°. Each specimen was placed in a Universal Testing Machine, the guidance rod removed, and the separating force recorded after each 100 separating/uniting cycles, up to 1000 cycles. Repeated-measures ANOVA was employed for data analysis.
Results: After adjustment, specimens in the parallel group displayed consistently higher separating force compared to the tilted group; both groups showed consistently equivalent values before tightening. The statistical analysis indicated that the overall model was significant (p=0.0043), along with factors of group (p≤0.0001) and specimen (p≤0.0001). Before and after tightening was significant (p≤0.0001), with minimal significant interactions for group before and after adjustment, and between group and before/after tightening. The effect of measurement over time was significant (p=0.0004); there was significant interaction between measurements over time and group (p=0.02).
Conclusions: No appreciable difference in retention was evident between the group with parallel attachments and the group with an attachment converging at 15°, before adjustment. The first group showed greater retention after adjustment. The majority of the significant effect for the factor group was attributed to disparity between the two groups following tightening.