Retention and stability of rigid telescopic and milled bar attachments for implant-supported maxillary overdentures: An in vitro study

Purpose: This study aimed to evaluate and compare the retention and stability of rigid telescopic and milled bar attachments for implant-supported maxillary overdentures. Materials and Methods: An acrylic resin model of the edentulous maxilla without alveolar undercuts was fabricated, and four implants were inserted in the canine and second premolar areas of the model. Two experimental overdentures were constructed and connected to the model with either rigid telescopic (RTA) or milled bar (MBA) attachments. Resistance of overdentures to axial and nonaxial (anterior, posterior, and lateral) dislodging forces was measured to represent retention and stability, respectively. Measurements were made at the beginning of the study (initial retention) and after 540 cycles of denture insertion and removal (retention after wear simulation). Results: After wear simulation, MBAs recorded significantly higher retention (P < .001) and stability against anterior dislodging (P < .001) than RTAs. RTAs recorded significantly higher stability against posterior (P = .022) and lateral (P < .001) dislodging than MBAs. Initial stability of RTA against anterior (P < .001) and posterior (P < .001) dislodging was significantly higher than stability after wear simulation. Retention of RTAs (P = .020) and stability of MBAs against posterior (P = .038) and lateral (P = .020) dislodging after wear simulation were significantly higher than initial values. Conclusion: MBA was associated with increased retention of maxillary implant overdentures compared with RTA, while RTA was associated with increased stability compared with MBA.