Fracture Toughness of Composite Resin Bonded to Itself

Last year, we theorized a fracture study of composite resin bonded to itself might better describe bond quality.  Objective: The fracture toughness of composite resin bonded to itself with several bonding systems was determined using a standard test. Method:  A Teflonä split mold, with a rectangular cavity (3 mm by 6 mm by 30 mm), was half-filled in the long dimension with Vit-l-escenceä composite resin and photo-polymerized for 60 s with the 3M 2500 light.  The cured blank was stored for 24 h, after which, the center end was milled flat.  The new surface was metallographically freshened with 320 grit emery paper, rinsed, blown dry and bonding systems were used to prepare that surface for additional buildup.  All Bond 2 (AB), Tyrian – One Step (TO), i-Bond (IB), Simplicity Adhesive (SA), L-Pop (LP), PQ-1 (PQ), and Tenure Uni-Bond (TU) were used to make the bars.  The half-bars were reinserted into the mold and a contrasting shade of composite resin was packed into the mold and cured as before.  After demolding, a 2 mm notch was cut into the specimen shade junction with a razor blade saw. The bars were stored at 37°C in 100% rh for 24 h.  At a span of 22 mm, the specimens were loaded opposite the notch at 2 mm/min until failure.  Ten specimens comprised a cohort.  Cohort mean fracture toughnesses in MPa/m^½ with standard deviations were calculated and statistical analysis was by ANOVA and Tukey HSD methods at 95% confidence.  Results:  SA, TO, PQ, and AB gave significantly higher fracture toughnesses than did TU, IB, and LP (p < 0.0001).  Conclusion:  Bonding systems, with higher fracture toughness, may yield stronger constructs when joining composite resin.