Differential nanofiller cluster formations in dental adhesive systems

Abstract

Nanofillers are added to dental adhesives to improve mechanical properties of the hybrid layer. Ethanol or water added to the demineralized dentin to improve adhesive infiltration may produce filler aggregation. To assess the effect of 5 vol% water or ethanol addition on nanoparticles distribution in dental adhesives. Six available commercial adhesives systems were selected: Clearfil SE Bond (CSE), Clearfil Protect Bond (CPB), FL-Bond (FLB), Clearfil S3 (CS3), Bond Force (BF), One Up Bond F plus (OUB), and an experimental adhesive system without filler (EXP). Polymer films were obtained by adding 0 (control) or 5 vol% water or ethanol into the bonding resins. Preparations were light-cured (40 s). Three specimens were analyzed for each mixture. Three phases and 3D images were taken from each specimen by means of an atomic force microscope in taping mode (TM/AFM). Cluster sizes and surface nanoroughness were assessed. Control specimens from CSE, FLB, OUB, and BF presented clusters. The addition of solvents lead to particles aggregation in tested bonding resins. Ethanol addition produced more aggregates, particularly in adhesives containing fluoraluminosilicate as fillers. Nanofillers aggregation occurred in all adhesive systems in presence of additional solvents. In general, aggregate sizes were higher after the addition of ethanol. Formed clusters size values are always above the dimensions of the spaces existing between the demineralized collagen fibers.