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

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: = 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.