Novel dental resin composites containing LiAl-F layered double hydroxide (LDH) filler: Fluoride release/recharge, mechanical properties, color change, and cytotoxicity.

Objectives: A novel LiAl-F layered double hydroxide (LDH) with a beneficial anions-exchangeable feature was developed for use as a fluoride reservoir. This study aims to investigate the fluoride release/ recharge capability of an LDH-contained dental resin composite and their effects on physical and biological properties.

Methods: 3% and 5% of LDH (R3, R5), wet-milled micro-scale LDH (R3W, R5W), or dry-milled nano-scale LDH (R3D, R5D) were added to a micro-hybrid flowable resin composite (RX). A commercial dental compomer (CC) was selected for comparison. An ion selective electrode recorded the daily fluoride release for 90 days (Daily fluoride recharging from 30th to 60th day). The flexural tests were performed according to ISO 4049. Also, the surface microhardness, color changes (L*, a*, b*), Al/Li ion leaching, and cytotoxicity were evaluated.

Results: The LDH-contained resin composites show significantly increased fluoride release and recharge capability. Among them, R3 and R5 have more stable and long-term fluoride release than R3W, R5W, R3D, R5D, and CC. The LDH filler did not induce cytotoxicity, although few amounts of Al/Li ions were detected on the first day. The LDH filler did not alter the flexural strength of RX, and the microhardness (R3, R5, R3D, and R5D) was significantly higher than the CC group (P < 0.01). The LDH filler slightly increased the color of the composite in red (a* values) and yellow (b* values).

Significance: The LiAl-F LDH can be a fluoride reservoir filler for dental resin composites that increases the anti-caries ability.