Assessment of the changes in retention and surface topography of attachments for maxillary 4-implant-retained overdentures

Statement of problem: Restoring the edentulous maxilla with an implant-retained overdenture (IRO) can present a challenge because of increased implant divergence and the added wear of the implant abutments and attachments. However, knowledge pertaining to the degree of implant divergence and its effects on the wear pattern of the implant attachments is lacking. Purpose: The purpose of this in vitro study was to investigate the change in the retention and wear characteristics of unsplinted abutments and attachments when used to retain a maxillary 4-implant palateless complete removable overdenture with different implant angulations. Material and methods: Three groups of specimens of 0-, 15-, and 30-degree implant angulations were evaluated, each with 7 specimens. The retention of specimens was recorded after aging cycles equivalent to 1, 2.5, and 6 years of use. The surface of the attachments was examined with light and scanning electron microscope (SEM). Results: Increasing the interimplant divergence improved the initial retention. After 1 year of use, retention of the 15- and 30-degree groups was significantly higher than that of the 0-degree group (P<.05). No significant difference in retention was found between the 15- and 30-degree groups (P>.05). After 2.5 and 6 years of use, no significant difference in retention was noted between groups (P>.05). Under light and SEM examination, the wear of the abutments and attachments was related to the interimplant divergence. Conclusions: The initial retention of single attachments increased significantly as the implant divergence increased. The retention of the 15- and 30-degree groups was significantly higher than that of the 0-degree group after 1 year of use. No significant difference in retention was found after 2.5 and 6 years, regardless of implant angulation.