Secondary caries and restoration fracture remain the two most common problems in restorative dentistry. Release of fluoride ions (F) could be a substantial benefit because F could enrich neighboring enamel or dentin to combat caries. The objective of this study was to incorporate novel CaF(2) nanoparticles into dental resin to develop stress-bearing, F-releasing nanocomposite. CaF(2) nanoparticles, prepared in our laboratories for the first time, were combined with reinforcing whisker fillers in a resin. Flexural strength (mean+/-sd; n=6) was 110+/-11 MPa for the composite containing 30% CaF(2) and 35% whiskers by mass. It matched the 108+/-19 MPa of a stress-bearing, non-releasing commercial composite (Tukey's at 0.05). The composite containing 20% CaF(2) had a cumulative F release of 2.34+/-0.26 mmol/L at 10 weeks. The initial F release rate was 2 microg/(hcm(2)), and the sustained release rate after 10 weeks was 0.29 microg/(hcm(2)). These values exceeded the reported releases of traditional and resin-modified glass ionomer materials. In summary, nanocomposites were developed with relatively high strength as well as sustained release of fluoride ions, a combination not available in current materials. These strong and F-releasing composites may yield restorations that can reduce the occurrence of both secondary caries and restoration fracture.