Nanoleakage, ultramorphological characteristics, and microtensile bond strengths of a new low-shrinkage composite to dentin after artificial aging

Abstract 

Objectives

To study the microtensile bond strengths and nanoleakage of low-shrinkage composite to dentin. The null hypotheses tested were (1) aging does not affect the bonding of low-shrinkage composite; (2) there is no difference in microtensile bond strengths and nanoleakage using different bonding strategies.

Methods

32 extracted molars were assigned to one of four groups: LS System Adhesive (LS, 3M ESPE); dentin etched for 15s with phosphoric acid+LS System Adhesive (LSpa); Adper Single Bond Plus (SB, 3M ESPE); SB+LS Bond (SBLS). Occlusal dentin was exposed and restored with Filtek LS (3M ESPE). The samples were tested after 24h or after 20,000 thermocycles and 6 months of aging. Teeth were sectioned with a cross-section of 0.8±0.2mm² and fractured at a crosshead speed of 1mm/min. The data were submitted to ANOVA/Duncan's post hoc test, at p<0.05. Five slabs from each group were selected and immersed in 50wt% ammoniacal silver nitrate. Then, specimens were processed for SEM, the silver penetration was measured and data analyzed with Kruskal–Wallis at p<0.05.

Results

No statistically significant difference was found among the experimental groups for the factor dentin treatment (p=0.165) and aging (p=0.091). All experimental groups exhibit some degree of nanoleakage. There was no adhesion of Filtek LS applied directly over dentin surfaces treated with SB.

Significance

The new low-shrinkage resin composite showed compatibility only with its dedicated adhesive. Pre-etching did not improve the bond strengths to low-shrinkage resin composite. Some degree of nanoleakage was evident in all groups.

Keywords: Microtensile bond strengths, Nanoleakage, Dentin adhesion, Hybrid layer thickness, Aging, Silorane, Scanning electron microscopy