INTRODUCTION : Fracture of composite restorations, especially when one or more cusps are replaced, is a common reason for failure. Finite element analysis has shown that crack propagation at the tension side of the restoration signals the failure.
AIMS AND OBJECTIVES : The strengthening effect of placing a fibre substructure on the tension side was investigated and the results compared with the fracture strengths of a conventional posterior composite without a substructure (control) and of a composite reinforced with fibres incorporated within the composite.
DESIGN : The study was an in vitro experimental blind study.
METHODS : 75 extracted lower first molars were divided into three groups of 25 teeth each to allow for the comparisons and the restorations were placed. All specimens were thermocycled for 500 cycles between 5Â°C and 55Â°C with a dwell time of 30 seconds. Each restoration was subjected to loading on a Universal testing machine at a 30Â° angle to the long axis of the tooth, until fracture occurred. Maximum force before failure (Fmax in N) was recorded.
RESULTS : The results indicated a significantly higher strength for the composite resin restorations placed on a fibre substructure.
CONCLUSION : A uni-directional fibre substructure is recommended to achieve greatest strength.