A statistical evaluation of microtensile bond strength methodology for dental adhesives

The purpose of this study was to determine the correlation between beams from the same tooth in a microtensile bond strength study and to examine their effect on the interpretation of results.

A flat occlusal dentin surface was exposed using wet 180, 240, and 320-grit SiC paper on caries-free human molar teeth. Adhesive was applied followed by 6mm of composite (CoreRestore2) applied in 2mm increments. Four adhesives were used: Optibond FL, light-cure, dual-cure, and self-cure Optibond Solo Plus. Nine beams (1 mm2) were obtained from fifteen teeth for each group, labeled to indicate the orientation of the beams to each other and stored in artificial saliva at 37 degrees C for 1 week or 3 months. Microtensile dentin bond strengths were determined using a non-trimming technique. Statistical comparisons between adhesive-storage combinations were performed using ANOVA. Analyses were performed assuming statistical independence between all beams and then repeated using a random tooth effect to account for correlations between beams from the same tooth.

Significant correlations were found between beams. No pattern was observed in the correlations related to the orientations of the beams to each other. Conclusions regarding statistical significance of comparisons (at alpha=0.05) were sometimes affected by the incorrect assumption of independent beams. The degree of correlation was large enough to severely affect power and sample size calculations.

Analyses of microtensile dentin bond strength studies need to account for correlations between beams to avoid over-stating statistical significance of study results.