Abstract Objectives Secondary caries and restorative fracture are the two main reasons for restoration failures. Fluoride ion (F) release can help inhibit caries. Plaque pH after a sucrose rinse can decrease to a cariogenic pH of 4–4.5. The objective of this study was to investigate the effects of solution pH and immersion time on the mechanical properties and F release of restorative materials. Methods Three resin-modified glass ionomers (Viremer, Fuji II LC, Ketac Nano), one compomer (Dyract Flow), and one composite (Heliomolar), were tested. Flexural strength and elastic modulus were measured before and after 84 d of immersion in solutions of pH 4, 5.5, and 7. F release was measured as a function of pH and immersion time. Results Immersion and material type had significant effects on mechanical properties. Vitremer had a flexural strength (mean ± sd; n = 6) of 99 ± 25 MPa before immersion; it decreased to 32 ± 9 MPa after 84 d of immersion ( p < 0.05). In comparison, Heliomolar had a smaller strength loss, decreasing from 99 ± 9 MPa to 65 ± 7 MPa ( p < 0.05). Solution pH had little effect on mechanical properties. For example, Fuji II LC had a strength of 63 ± 15 MPa at pH 4, similar to 61 ± 30 MPa at pH 5.5, and 56 ± 22 MPa at pH 7 ( p > 0.1). In contrast, solution pH had a significant effect on F release. F release at 84 d for Fuji was 609 ± 25 μg/cm 2 at pH 4, much higher than 258 ± 36 μg/cm 2 at pH 5.5, and 188 ± 9 μg/cm 2 at pH 7. Significance The restoratives tested were able to greatly increase the F release at acidic, cariogenic pH, when these ions are most needed to inhibit caries. However, mechanical properties of these F-releasing restoratives degraded significantly in immersion. Efforts are needed to develop F-releasing restoratives with high levels of sustained F release, as well as improved durability of mechanical properties for large stress-bearing restorations.