Effects of Excessive Implant Angulation on Retention of Two Types of Overdenture Attachments during Cyclic Loading

This study investigated the effects of implant angulation and cyclic dislodgment on retention of Locator and Dalbo Plus attachments.

Fifty pairs of acrylic blocks for five implant angulations (0, 10, 20, 30 and 40 degrees) and two attachment systems (locator and Dalbo Plus®; n = 5) were fabricated. In each pair, one block contained two implant analogs connected to their attachments, and the other block contained matrix parts of the attachments. 1440 cycles of insertion and removal were implicated on specimens after mounting the blocks in the universal testing machine. The retention was registered at cycle numbers 1, 120, 360, 720, and 1440. Data were analyzed using one-way analysis of variance (ANOVA) and Duncan's multiple range test (p ≤ 0.05).

Data analysis showed that implant angulation had significant effects on retention of both attachments at all different angles (p ≤ 0.05). Dalbo Plus showed no significant differences between 30 and 40 degrees (p ≥ 0.05), but between 0 and 30 degrees, differences were significant (p ≤ 0.05). Moreover, cyclic loading had significant effects on retention of both attachments at all different loading cycles (p ≤ 0.05). On evaluating combined effects of cyclic loading and implant angulation on retention, a significant decrease in retention was noted for both Locator and Dalbo Plus attachments at angulations of 0, 10, 20 degrees after 1440 cycles (1 year of clinical use; p ≤ 0.05).

Both angulation and cyclic loading have negative effects on implant-supported overdentures and decrease retention over time. Furthermore, as the angle between implants increases, decrement of retention becomes more significant.

Inter-implant angulation could play a significant role in overdenture retention Keywords: Dental implants; Dental prosthesis; Implant angula-tion; Implant-supported Overdenture; Retention.