Attachment systems for implant overdenture: influence of implant inclination on retentive and lateral forces

To evaluate the retentive force and lateral force of an implant with various types of attachments for overdentures in relation to implant inclination.

An implant (3.75 × 13 mm) was embedded into an acrylic resin block, simulating the edentulous ridge. Four different attachment systems were used, including: (1) Locator black and blue, (2) a ball attachment, (3) a flat-type magnetic attachment and (4) a self-adjusting magnetic attachment, which has vertical and rotational movement. All of the attachments were under a constant dislodging force with an angle of the implant at 0°, 15°, 30° and 45°, and the experiments were repeated 10 times using a universal testing machine to measure the retentive force. The lateral force to the implant was measured by strain gauges attached on the implant surface. Statistical analysis was performed by multiple comparisons with Bonferroni's correction. P<0.05 was considered statistically significant.

At 0°, the significantly highest retentive force was observed in the Locator blue, followed by the Locator black, ball, flat-type and self-adjusting magnetic attachments. The Locator blue and ball attachment maintained the retentive force until a 30° inclination; however, the lateral force increased significantly, especially with the ball attachment. The retentive force of the magnetic attachment was significantly lower at 0°, as well as the lateral force in the self-adjusting magnetic attachment.

Within the limitations of this study, we conclude that the retentive force decreases with an increase in implant inclination, whereas the lateral force increases, except for in magnetic attachments.