Fracture strength and fracture behaviour patterns of cusp-replacing fibre reinforced composite restorations.

Abstract

Objectives: This in vitro study investigated and compared the fracture strength and behaviour patterns of a conventional posterior composite resin, a composite resin reinforced with nano-scale electrospun glass-fibres and a conventional composite resin placed on a fibre substructure, all used in cusp-replacing posterior composite resin restorations. Methods: Seventy-five extracted, lower, left, first and second molars were prepared to accept standardized restorations replacing the mesio-lingual cusp. The specimens were randomly divided into 3 groups of 25 each: Group A (control) was restored with a conventional posterior composite resin, Group B was restored with the composite resin reinforced with nano-scale electrospun glass fibres and Group C was restored with a conventional posterior composite resin reinforced with a fibre substructure. All restored specimens were thermocycled for 500 cycles between 5° C and 55° C with a dwell time of 30 seconds, then imbedded in plastic cylinders in acrylic resin. The specimens were loaded at a 30° angle to the long axis of the tooth, using a jig mounted in a universal testing machine until fracture occurred. Fracture strength was recorded and specimens were then stained to highlight fracture patterns and subsequently studied under a microscope. Fractures were classified as restorable/non-restorable. Sub-classification included adhesive and cohesive failures. Results: Compared to Group A both techniques of fibre inclusion significantly strengthened the cusp-replacing composite restoration (ANOVA p = 0.05) Compared to Groups A and B the group of restorations placed on a fibre sub-structure (Group C) exhibited significantly more fractures that were classed as restorable. Compared to Group A and C the group restored with the composite resin reinforced with nano scale electrospun glass fibres (Group B) displayed significantly more fractures that were classed as non-restorable (Fisher s Exact Test p = 0.05). Conclusion: Both fibre inclusion techniques significantly strengthened cuspreplacing posterior composite restorations. Fracture behaviour patterns differed significantly between the two fibre-strengthening techniques.