Fracture behaviour patterns of cusp-replacing fibre strengthened composite restorations

Abstract

OBJECTIVES : To investigate and compare, in vitro, the fracture behaviours of three types of cusp-replacing posterior composite resin restorations. METHODS : Standard preparations for posterior composite restoration of the mesio-lingual cusp were cut on seventy- five extracted lower left first and second molars and restorations placed. Group A (control, n =25) with a conventional posterior composite resin, Group B (n=25): resin reinforced with nano-scale electrospun glass fibres Group C (n=25) :resin reinforced with a fibre substructure. Specimens were thermocycled for 500 cycles between 5°C and 55°C with a dwell time of 30 seconds, then embedded in plastic cylinders in acrylic resin. The specimens were loaded in a universal testing machine at a 30° angle to the long axis of the tooth until fracture occurred. Fracture patterns were highlighted by staining, studied under a microscope and classified as favourable (restorable) or unfavourable (non-restorable). Sub-classification included adhesive and cohesive failures. RESULTS : Group C exhibited significantly more “restorable” fractures. Group B displayed significantly more “nonrestorable” fractures. Fracture patterns differed significantly between the two fibre-strengthening techniques. (Fisher’s Exact Test p = 0.05) CLINICAL SIGNIFICANCE : Resin restorations reinforced with glass-fibre substructures are more readily repaired after fracture, saving tooth structure, and reducing costs to the patient.