Wear resistance of composite repairs: Direct vs. semi-direct techniques in simulated oral aging

Wear resistance of composite repairs, especially under severe chemical-mechanical challenge, has not been investigated. This in vitro study evaluated the wear resistance of composite restorations repaired using different techniques in simulated oral aging.

Sixty human molars with direct Mesio-occluso-distal composite restorations were aged in the "Rub&Roll" device simulating two years of clinical service. The restorations were repaired using direct (n = 29) or semi-direct (n = 29) techniques. Specimens were randomly divided into three aging media for an additional two-year simulation: deionized water (control), 1% citric acid solution (chemical-mechanical challenge), and yellow millet seed solution (mechanical challenge). Wear was assessed using profilometry and 3D scan. t-test, two-way ANOVA, and multiple linear regression were used for statistical analysis. p < 0.05 was considered statistically significant.

After repair, neither repair technique significantly influenced height or volume loss of specimens. The chemical-mechanical challenge had the greatest impact on height loss (coefficient = 0.11, 95% CI: 0.06-0.17 mm, p < 0.001) and volume loss (coefficient = 0.23, 95% CI: 0.13-0.32 mm³, p < 0.001) of specimens. The effect of techniques on height loss of repaired restorations was not significant. However, challenges affected height loss, with chemical-mechanical challenge showing the highest height loss (coefficient = 0.21, 95% CI: 0.16-0.28 mm, p < 0.001).

The wear resistance of repaired composite restorations was not influenced by the repair technique. Instead, chemical-mechanical factors, were the primary determinants of wear, underscoring their critical role in the longevity of tooth-restoration complexes.