The application of cold atmospheric plasma on human dentin improves its bond strength capacities: an in vitro study

The objective of this study is to evaluate the effect of cold atmospheric plasmas (CAP) in improving dental composite resin bond strength when the plasma jet is applied onto the dentin surface. In vitro, human dentin samples were exposed at 5 mm or 20 mm to a miniaturized mono channel Helium-jet plasma device for times varying from 15 to 180 s. Contact angle measurements were performed on dentin surfaces, before observations under scanning electron microscopy (SEM). Shear bond strength (SBS) tests were carried out on composite resins until the restoration was separated from the tooth. The results showed that CAP exposure reduced the contact angle as early as 30 s of plasma exposure at 20 mm (21.44 ± 3.99°, p < 0.001) or 15 s at 5 mm (21.04 ± 4.36°, p < 0.001). SEM observations revealed widely opened tubules on CAP-exposed surface. SBS tests revealed a significant influence of CAP application on the adhesion of composite resin to the dentin. The control group showed one of the lowest SBS values (14.48 ± 4.7 MPa) whereas the CAP-treated groups at 5 mm exhibited a progressive increase in bond strength, particularly for the 15 s (20.88 ± 5.10 MPa, p < 0.05) and 30 s conditions (24.49 ± 7.26 MPa, p < 0.001), before a new reduction above 60 s of exposition (19.96 ± 4.97 MPa). Finally, this study highlights the benefits of applying plasma jet at atmospheric pressure on human dentin to enhance the adhesion of restorative composite resins. The application of cold atmospheric plasma may act as a secondary etching procedure to provide an optimal cleaning of dentin and then enhance the interconnection between resin, collagen fibers and dentin tubules.