Flexural strength and fracture behaviour of cusp-replacing fibre strengthened composites

Objectives: To investigate the flexural strength (A) and fracture behaviour (B) of a composite resin (QuiXfill, Dentsply) (Group A, control), a composite resin reinforced with nano-scale electrospun glass fibres, (Group B, Aelite, BISCO) and a composite resin,(Group C, QuiXfill, Dentsply) placed on a fibre substructure (everStick fibres, Stick Tech Ltd) in cusp-replacing composite resin restorations. Methods: 75 extracted lower left 1st and 2nd molars were prepared to accept a standardized MOL restoration. The specimens were then randomly divided into 3 groups of 25 each: Group A (control) was restored with a composite resin , Group B was restored with the composite resin reinforced with nano-scale electrospun glass fibres and Group C was restored with the composite resin reinforced with the fibre substructure. All specimens were thermocyled 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. Maximum force before failure (F max in N) was recorded for each group. Specimens were subsequently stained using India ink to highlight fracture patterns and studied at 10x magnification. Fractures were classified as favourable (restorable) or unfavourable (unrestorable). Sub-classification included adhesive and cohesive failures. Results: (A) Maximum force before failure. Group A: F max 313±64.3N ; Group B: F max 393±92.3N; Group C: F max 461.6±62N. (B) Repairable restorations. Group A: 11 restorations; Group B: 3 restorations; Group C: 21 restorations. Conclusions: Statistical analysis of the results indicate a significantly higher flexural strength for the fibre reinforced (fibre substructure) composite restorations, and statistically significantly more of the fibre reinforced (fibre substructure) restorations were classed as repairable.