Electrobondings effects on dental adhesives applied on dentinal surfaces

The aim of this study was to validate, using electrochemical impedance spectroscopy (EIS) and mechanical tests (such as shear stress strength and resistance to micro-traction forces), the electro-bonding technique (EBT), which involves the use of a low amperage electric current (60 µA), during application of dental adhesives on a dentinal substrate. More in detail, the intention was to investigate the ability of the electro-bonding technique (EBT) to improve mechanical adhesion and sealing of dental adhesives applied on dentinal surfaces [1]. The electro-bonding principle is based on the flow of a current (60 µA) between the dentin substrate and the adhesive applicator, enhancing the adhesive penetration. The benefits of this application technique are correlated with the chemical composition of the adhesives. Better results have been achieved with adhesives whose polymers present a higher degree of polarity. Indeed, the current flow orients the polymeric chains, increasing the penetration on the dental substrate. Recently, some studies have investigated the effects of current flow on the quality of enamel-dentin adhesive bonds, applying the electro-bonding technique on different types of adhesives. Pasquantonio et al. has studied the effectiveness of electrical stimulation on "etch and rise" adhesives [2], whereas Breschi et al. applied the electro-bonding technique on self-etch adhesives [3]. In dentistry, EIS can lead to a valuable method for characterizing surface changes, such as those involved in the application of dental adhesives. Complex adhesion resulting from the penetration on the conductive surface of the dentine of the insulating dental adhesives modifies the capacity and resistance to the surface-electrolyte interface. These electrochemical surface alterations can be measured and evaluated to estimate adhesive penetration on the dental substrate. Other studies have investigated the effects of electro-bonding devices using characterization techniques involving optical methods, such as scanning electron microscopy (SEM), or mechanical tests. Among the latter, shear stress strength has been evaluated by means of a shear bond tester machine, a device that can be used to test and compare different adhesives used in the dental and orthodontic industries. Furthermore, to assess resistance to micro-traction forces, the samples were sectioned with a microtome and stressed under tension until failure with a simplified universal testing machine at a crosshead speed of 1 mm/min (micro-tensile bond test). Therefore, with the aim to investigate the effects of the current flow on the enamel-dentinal adhesives applications, a protocol to compare the standard technique application versus the electro-bonding technique is defined. Finally, the results of this comparative study are shown and final considerations of further implications and future developments are investigated.