A radically curable polyurethane composite for dental restorations, including provisional restorations, includes polyurethane dimethacrylate prepolymers that have at least one flexible unit within a polyurethane dimethacrylate backbone, and one or more dimethacrylate monomers. Composite materials made with polyurethane dimethacrylate prepolymers of the invention exhibit superior and optimal properties of flexural strength and deflection-at-break relative to conventional dental resin composites. Composite materials of the invention also provide improved melt-resistance in response to the heat of grinding or finishing, thereby improving the fit of restorations made from the composite and preserving the finishing instruments. Methods of treating a tooth using the radically curable polyurethane composite and methods of making the polyurethane dimethacrylate prepolymers with flexible units is also provided. A kit including the radically curable polyurethane composite is also described.