Retention degradation of two milled bar systems versus solitary attachments for implant mandibular overdentures: An in vitro study

Abstract

ABSTRACT Purpose This in vitro study compared initial retention forces and long‐term degradation patterns of three attachment systems for mandibular implant‐retained overdentures: solitary studs, milled bars with sleeves, and milled bars with studs. Materials and Methods A simulated mandibular model with three parallel implants received overdentures incorporating each attachment system (n = 10 per group). To simulate 5 years of clinical use, specimens underwent 5400 insertion‐removal cycles. Measurement of retention forces via vertical dislodgement (5 mm/min) was checked at 12 intervals. Statistical analysis included two‐way repeated measures ANOVA and linear regression to study retention degradation patterns. Results Two‐way repeated measures analysis of variance (ANOVA) revealed significant differences in retention stability (p<0.001). Bar systems demonstrated better durability, with bar‐sleeves keeping 16.03 ± 0.22 N (86.5% loss) and bar‐studs 19.90 ± 0.97 N (82.2% loss) after 5,400 cycles, compared to solitary studs’ 5.38 ± 0.21 N (95.8% loss). Linear regression confirmed predictable degradation in bar systems (R 2 >0.84, slope: ‐7.23 to ‐7.03 N/cycle) versus erratic decay in solitary studs (R 2 = 0.46). Post‐hoc tests showed no significant difference between bar subtypes (p = 0.567). Conclusion These findings suggest that, under in vitro conditions, splinted bar attachments, regardless of interface design, offer greater long‐term retention durability than solitary systems, considering their use may be advantageous in adequate prosthodontic space. The predictable linear degradation pattern of bar systems in this in vitro model suggests a potential mechanical rationale for less frequent maintenance (e.g., clip/matrix replacement every 3–4 years), in contrast to the more rapid and erratic degradation observed for solitary studs, which would imply a need for more frequent intervention in a clinical setting.