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.
