The influence of fibre placement and position on the efficiency of reinforcement of fibre reinforced composite bridgework

The effect of placement of ultra-high molecular weight polyethylene (UHMWPE ) fibres on the flexural properties and fracture resistance of a direct den tal composite was investigated. The UHMWPE fibres are increasingly being us ed for the reinforcement of laboratory fabricated resin composite crown and bridgework. The aim of this study was to assess the effect of a commonly u sed laboratory fabrication variable on the in vitro strength of beam shaped specimen simulating a three-unit fixed bridge. Four groups (10 specimens p er group) of Herculite XRV were prepared for flexural modulus and strength testing after reinforcement with UHMWPE fibres. Two groups of control speci mens were prepared without any fibre reinforcement. Half the specimen group s were stored in distilled water and the other groups were stored dry, both at 37 degreesC for 2 weeks before testing. The results of this study showe d that placement of fibre at or slightly away from the tensile side improve d the flexural properties of the composite in comparison with the unreinfor ced control specimen groups whilst the mode of failure differed according t o fibre position. Scanning electron microscope (SEM) investigation revealed that placement of the fibre slightly away from the tensile side favoured c rack development and propagation within the resin bridging the interfibre s paces in addition to debonding parallel to the direction of fibre placement . Laboratory fabrication variables may effect the strength of fibre reinfor ced bridgework significantly.