This paper reports on the effect of reinforcing dental resins with continuous, longitudinally oriented highly drawn linear polyethylene fibres. The mechanical properties were measured in 3-point bending, and the composites showed a very substantial improvement when compared with the properties of an unreinforced resin. The performance improves as the fibre content increases, and the type of resin does not appear to be a significant factor. It is shown that the inclusion of the reinforcement changes the mode of failure of the resin from brittle to ductile; that is, the system may be damaged but it does not disintegrate.