Comparison of retention in polyvinyl siloxane matrix systems versus conventional metal housing with nylon inserts in ball-retained mandibular implant overdentures

Objective: This study compared the retentive performance of two polyvinyl siloxane (PVS) matrix systems (retention.sil 400 and 600) versus conventional metal housing with nylon inserts in ball-retained mandibular overdentures.Methods: Thirty ball-retained overdenture models were allocated into three groups based on the attachment system material (n=10): Group 1, conventional metal housing with nylon inserts; Group 2, retention.sil 400; and Group 3, retention.sil 600. A total of 1440 insertion-removal cycles, simulating one year of clinical use, were conducted at 50 mm/sec using a universal testing machine. Retention forces were measured at baseline (0 cycles) and after 360, 720, 1080, and 1440 cycles. Statistical analyses were performed using one-way ANOVA, followed by post hoc Tukey's test at a significance level of P<0.05.Results: The conventional group showed the highest retention at all cycles. There were statistically significant differences in retention between the conventional group and both PVS groups at all cycles (P<0.001), but no significant differences were found between the two PVS groups (P>0.05). Absolute retention loss was significantly greater in the conventional metal housing with nylon inserts than in the two PVS groups (P<0.001). No significant difference was found in relative retention loss among the groups (P=0.108).Conclusions: Conventional metal housing with nylon inserts provided superior mean retention compared to the retention.sil 400 and retention.sil 600 matrix systems at all cycles, with no significant difference between the two PVS materials. The relative retention loss, however, did not significantly differ between the conventional group and PVS groups.