Abstract: The invention relates to an improved, castable, synthetic resin material, suitable for use in dental and medical restorations, as a replacement for dental enamel and hydroxyapatite bone material. This material is also useful for electrical insulation. More specifically, the invention provides a filled reinforced resin matrix comprising a castable resin; from 5 to 50% vol of fibers of 50 .mu.m or less diameter; from 10 to 35% vol of a first particulate filler having a particle size range of 0.1 to 50 .mu.m; and from 5 to 25% vol of a second particulate filler having an ultimate particle size range of 10 to 100 nm.