Interpretation of bond failure through conversion and residual solvent measurements and Weibull analyses of flexural and microtensile bond strengths of bonding agents

Objectives: An inverse correlation between initial acetone content of bonding agents and microtensile bond strength (MTBS) has previously been reported. Here it was investigated whether the inferior MTBS of acetone-rich bonding agents was caused by flaws and low adhesive layer strength, insufficient to resist polymerization shrinkage stresses of the overlying composite. Methods: Bonding solutions with (27-67) mass fraction% acetone were dried for 10s or 30 min. Specimens for infrared (IR) spectroscopy and flexural strength (FS) were cured for 10 s (cure mode 1) to represent the adhesive layer properties when polymerizing the composite resin or for 10s plus an additional 60s through composite resin (cure mode 2) to represent adhesive layer properties when testing the bond strength. Degree of conversion (DC) and residual acetone content were evaluated for films by mid-IR and bulk specimens by near-IR spectroscopy. FS and MTBS data using these bonding solutions were interpreted by Weibull statistics and ANOVA (alpha=0.05). Results: In bulk specimens, initial and residual acetone content were positively correlated (P=0.003). FS in cure mode 1 was significantly tower than in cure mode 2 and decreased with increasing initial acetone content, white DC remained consistent, suggesting pores from acetone evaporation as flaw initiating sites affecting the mechanical adhesive properties. Significance: From DC and Weibull analyses of MTBS and FS, early low strength of the adhesive layer and shrinkage stresses acting on pre-existing flaws are suggested as critical factors affecting the dentin/adhesive bond strength. (c) 2004 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.