Effect of co-precipitation plus spray-drying of nano-CaF(2) on mechanical and fluoride properties of nanocomposite.

OBJECTIVE: Fluoride (F)-releasing restoratives typically are either weak mechanically or release only low levels of F ions. The objectives of this study were to: (1) develop a novel photo-cured nanocomposite with strong mechanical properties and high levels of sustained F ion release via a two-step "co-precipitation + spray-drying" technique to synthesize CaF(2) nanoparticles (nCaF(2)); and (2) investigate the effect of spray-drying treatment after co-precipitation of nCaF(2) on mechanical properties and F ion release of composite. METHODS: Two types of CaF(2) particles were synthesized: A co-precipitation method yielded CaF(2)cp; "co-precipitation + spray-drying" yielded nCaF(2)cpsd. Composites were fabricated with fillers of: (1) 0% CaF(2) + 70% glass; (2) 10% CaF(2)cp + 60% glass; (3) 15% CaF(2)cp + 55% glass; (4) 20% CaF(2)cp + 50% glass; (5) 10% nCaF(2)cpsd + 60% glass; (6) 15% nCaF(2)cpsd + 55% glass; and (7) 20% nCaF(2)cpsd + 50% glass. A commercial F-releasing nanocomposite served as control. RESULTS: The nCaF(2)cpsd had much smaller particle size (median = 32 nm) and narrower distribution (22-57 nm) than CaF(2)cp (median = 5.25 mum, 162 nm-67 mum). The composite containing nCaF(2)cpsd had greater flowability, flexural strength, elastic modulus and hardness than CaF(2)cp composite and commercial control composite. At 84-day immersion in water, the nanocomposites containing 20% nCaF(2)cpsd had 65 times higher cumulative F release, and 77 times greater long-term F-release rate, than commercial control. CONCLUSIONS: A novel two-step "co-precipitation + spray-drying" technique of synthesizing nCaF(2) was developed. The photo-cured nanocomposite containing 20% nCaF(2)cpsd possessed strong mechanical properties and excellent long-term F-release ability, and hence is promising for dental restoration applications to inhibit secondary caries.