This long-term observational study assessed the durability and clinical performance of posterior composite restorations over a period exceeding 23 years. Twenty-two patients (13 men, 9 women; mean age 66.1 years, range 50–84) contributing a total of 42 restorations were examined during two follow-up sessions. A single clinician evaluated all restorations according to modified FDI criteria. Statistical comparisons were performed using the Wilcoxon Mann–Whitney U test and the Wilcoxon exact matched-pairs test (significance level p = 0.05), with Bonferroni–Holm correction applied. Over time, six of seven evaluated criteria demonstrated significant deterioration, except for approximal anatomical form, which remained largely stable, except in molars where it declined. No notable differences were observed based on the restorations’ jaw location or whether they were single- or multi-surface. These results indicate that posterior composite restorations show measurable clinical changes after more than two decades, underscoring the importance of further long-term evaluations at regular intervals to monitor their performance.
