Long-Term Clinical Performance of Posterior Composite Restorations After Nearly Three Decades: A Clinical Follow-Up Study

Background/Objectives: Long-term clinical data on direct posterior composite restorations are scarce, particularly beyond simple survival outcomes. This study aimed to characterize the long-term functional, esthetic, and biological behavior of posterior composite restorations after nearly three decades of service using selected FDI criteria and to assess changes across available follow-up examinations, including within a predefined sub-cohort. Methods: This observational follow-up involved 21 patients with 57 posterior composite restorations placed in 1995–1996 at the Department of Operative Dentistry, Goethe University Frankfurt, by undergraduate dental students under supervision. The 2025 follow-up used FDI criteria to assess functional, aesthetic, and biological properties, classifying outcomes as clinically acceptable, intervention needed, or failure. Descriptive analyses were applied to the entire cohort. Longitudinal analyses were conducted on a sub-cohort of 14 patients with 27 restorations at three time points. Exploratory analyses assessed associations with restoration factors, caries experience, and gingival health. Results: In 2025, 54.4% of restorations were clinically acceptable, 28.1% required intervention, and 17.5% were failures. Functional criteria remained mostly acceptable, though form and contour showed the highest mean values. In the longitudinal sub-cohort, significant changes over time were observed in anatomical form and occlusal wear. Retention, marginal adaptation, proximal contact, and surface luster did not change significantly. Biologically, restorations available for direct assessment had low incidences of secondary caries, hard-tissue defects, and postoperative sensitivity or pulpal issues. Conclusions: Posterior composite restorations can function for nearly three decades but gradually deteriorate in certain aspects. Long-term changes mainly involve cumulative functional aging of the anatomical form and occlusal wear, rather than widespread biological failure. These findings underline the importance of differentiated long-term assessment and support conservative management approaches where clinically feasible before replacement is undertaken.