Cross-link density evaluation through softening tests: Effect of ethanol concentration

Objectives The aim of this study was to investigate whether the ethanol concentration used would influence the outcomes obtained through softening tests when comparing light-activation modes. Methods Disc specimens (n=20) of Filtek Z250 and Filtek Z100 (3M ESPE) were light activated by standard (S) and pulse-delay (PD) modes. Initial Knoop hardness (KHN) measurements were performed 24h after dry storage at 37 degrees C. Half of the specimens (n=10) of each resin-composite were stored in absolute ethanol (100%) and the other half in 75% ethanol solution, for 24h at room temperature, and KHN was determined anew. Initial hardness data were submitted to Student's t-test (p=0.05). Percentages of hardness decrease were analyzed by two-way ANOVA followed by pairwise Tukey's test (p=0.05). The statistical analyses were performed separately for each resin-composite. Results No statistically significant differences were observed between standard and pulse-delay modes for initial Knoop hardness values. After storage in 75% ethanol solution, KHN was decreased in all cases but no significant differences were detected between light-activation modes (Filtek Z250: PD=12.6%, S=13.5%; Filtek Z100: PD=13.5%, S=11.8%) regardless of the resin-composite tested. After absolute ethanol storage, higher decrease in KHN were observed. Samples light-activated by the PD mode (Filtek Z250=20.4% and Filtek Z100=16.9%) exhibited significantly higher percentage decrease of KHN than specimens light-activated by the standard mode (Filtek Z250=14.1% and Filtek Z100=8.8%), regardless of the resin-composite tested. Conclusion The ethanol concentration affected the outcomes of the softening test.