Effects of non-thermal atmospheric plasma treatment on dentin wetting and surface free energy for application of universal adhesives

Objectives: The study aims to evaluate the effects of non-thermal atmospheric plasma (NTAP) treatments on dentin wetting and surface free energy (SFE) and compare the effects of NTAP treatment, etch-and-rinse, and self-etch protocols for application of universal adhesives. Materials and methods: Mid-coronal dentin of intact third molars was used to measure contact angles of distilled water, ethyleneglycol, and diiodomethane and calculate SFE following different NTAP preset treatments (feeding gas consisting of pure He, He+ 1% O2, He + 1.5% O2), power input (1 or 3 W), and tip-to-surface distance (2, 4, or 8 mm). Contact angles of reference liquids and SFE of dentin following He + 1.5% O2 at 3-W and 4-mm treatment was compared to phosphoric acid etching. Contact angles of Single Bond Universal (SBU; 3M ESPE) and Clearfil Universal Bond (CUB; Kuraray Noritake) were measured following NTAP, etch-and-rinse, and self-etch protocols. Results: NTAP significantly reduced contact angles of reference liquids and increased dentin SFE compared to untreated dentin (p < 0.05). O2 intensified the effect of He NTAP (p < 0.05). NTAP and phosphoric acid increased dentin polarity and Lewis base surface characteristics. Phosphoric acid increased contact angles of adhesives compared to the self-etch protocol (p < 0.05). NTAP resulted in lower adhesive contact angles than phosphoric acid, the difference being statistically significant for CUB (p < 0.05). Compared to the self-etch protocol, NTAP slightly reduced CUB contact angle but not that of SBU (p > 0.05). Conclusions: He NTAP with and without O2 increased dentin wetting and SFE, surpassing the effect of phosphoric acid and lowering adhesive contact angles. NTAP produced no apparent micro-morphological changes on dentin surface comparable to acid etching. Clinical significance: NTAP treatment of dentin prior to adhesive application increases dentin wetting and surface free energy facilitating better adhesive distribution on dentin surface compared to phosphoric acid etching and similar to the Bself-etch^ application protocol.