Effect of Mechanical and Thermal Aging on the Retention Stability of Attachment Systems for Mandibular Implant Overdentures

Background/Objectives: This descriptive pilot in vitro study characterized changes in retentive force in four attachment-specific overdenture specimens for a four-implant mandibular overdenture model following mechanical and thermal aging and across different force-application geometries. Methods: Four parallel implants were placed in the interforaminal region of an edentulous polyurethane mandibular model. One attachment-specific overdenture specimen was fabricated for each condition: distal extension bar, ball/O-ring, Locator R-Tx, and TC-Snap with Retention.sil 600. Retentive force was measured at four unilateral and three bilateral dislodgement points at baseline, after 540 and 1080 insertion–removal cycles, and after 5000 and 10,000 thermal cycles. Ten consecutive pull-out measurements at each test point and measurement interval were obtained from the same specimen and treated as technical replicates rather than independent experimental units; the data were summarized descriptively. Results: After 1080 insertion–removal cycles, proportional retention losses were 32.50% for the distal extension bar specimen, 17.18% for the ball/O-ring specimen, 16.06% for the Locator R-Tx specimen, and 16.91% for the TC-Snap specimen. After 10,000 thermal cycles, the corresponding losses were 47.42%, 30.11%, 30.78%, and 28.02%, respectively. The tested distal extension bar specimen maintained the highest absolute retentive-force values but showed the greatest proportional loss. Point-specific and unilateral–bilateral retention patterns varied across the four tested specimens. Conclusions: Within the limitations of this descriptive pilot design, absolute retentive force and proportional retention loss represented distinct aspects of the retention behavior observed in the tested specimens, while force-application geometry was also associated with different descriptive retention patterns.