Long-term fluoride exchanges at restoration surfaces and effects on surface mechanical properties

Aim. The aim of the study was to determine whether three fluoride containing resin composites could maintain fluoride release, fluoride recharge, and mechanical stability over long-term (18-month) aging. Materials and Methods. Fluoride containing composites Beautifil II, Gradia Direct X, Tetric EvoCeram, and glass ionomer Fuji IX Extra were analyzed. Specimens of each material were fabricated for two test groups: Group 1: bimonthly fluoride release/recharge analysis (n = 5); Group 2: hardness and elastic modulus analysis (n = 6). Nanoindentation was employed at 24 hours and at 1, 3, 6, 12, and 18 months. After 18 months, each specimen was immersed (recharged) in 5000 ppm NaF gel, and fluoride rerelease, hardness, and elastic modulus were measured. Results. Beautifil II and Gradia Direct X maintained fluoride release and recharge capability throughout 18-month aging (Beautifil II > Gradia Direct X > Tetric EvoCeram). The fluoride rerelease from Beautifil II following a 10-minute NaF recharge (at 18 months) was comparable to the long-term fluoride release from Fuji IX Extra. Elastic modulus and hardness did not change significantly (P > 0.05) with fluoride release, recharge, and water aging over 18 months for all three analyzed composites. Conclusions. The long-term fluoride release, fluoride recharge, and mechanical property stability of Beautifil II and Gradia Direct X render these composites suitable for load bearing restorations in high caries risk patients. Clinical Relevance. The ability for Beautifil II and Gradia Direct X to maintain fluoride release and fluoride recharge capability, despite long-term aging, raises the potential for unrestored tooth surfaces in contact with Beautifil II or Gradia Direct X restorations to demonstrate a reduced rate of caries incidence compared to unrestored surfaces adjacent to conventional nonfluoride containing composites.