Correlative analysis of cement-dentin interfaces using an interfacial fracture toughness and micro-tensile bond strength approach.

OBJECTIVES: To determine the interfacial fracture toughness (iFT) and micro-tensile strength (muTBS) of composite cements bonded to dentin. METHODS: Fifty feldspar ceramic blocks (Vita Mark II, Vita Zahnfabrik) were luted onto dentin using two self-adhesive (G-CEM LinkAce, GC; SpeedCEM, Ivoclar Vivadent), two self-etch (Multilink Primer & Multilink Automix, Ivoclar Vivadent; Scotchbond Universal & RelyX Ultimate, 3 M ESPE), and one etch-and-rinse (Excite F DSC & Variolink II, Ivoclar Vivadent) composite cement (n=10). After 48h in 100% relative humidity at 37 degrees C, one half of each tooth was sectioned in sticks with a chevron notch at the cement-dentin interface and tested in a 4-point bending test setup (iFT). The remaining half of the tooth was sectioned in micro-specimens and stressed in tension until failure (muTBS). The mode of failure was determined with a stereomicroscope at 50x magnification. Data were submitted to Weibull analysis and Pearson's correlation (alpha=0.05). RESULTS: At 10% probability of failure, no significant differences could be found using iFT, while the etch-and-rinse composite cement Variolink II presented a significantly higher muTBS at this level. At 63.2% probability of failure, the self-adhesive composite cement G-CEM LinkAce revealed a significantly lower muTBS and iFT, and the self-etch cement Multilink Automix also revealed a significantly lower muTBS than all other cements. The correlation found between iFT and muTBS was moderate and not significant (r(2)=0.618, p=0.11). SIGNIFICANCE: Overall, the etch-and-rinse and 'universal' self-etch composite cements performed best. The micro-tensile bond strength and interfacial fracture toughness tests did not correlate well.