Improving bond strength of ground and intact enamel to mild self-etch adhesive by plasma treatment

Abstract

Effects of non-thermal plasma treatment on ground and intact enamel surfaces to improve their bond strength to a mild self-etch adhesive were investigated in this study. Thirty-two bovine incisors were randomly divided into four groups (n=8). Their enamels were subjected to the following preparations: (1) ground and unetched (GU), (2) ground and etched (GE), (3) intact and unetched (IU), and (4) intact and etched (IE). After teeth preparation, each tooth was divided in two portions. One half was treated with a non-thermal plasma brush; the other half was shielded with a blade and used as untreated control. A mild, self-etch adhesive and a dental composite resin were subsequently applied on both surfaces following the manufacturers' instructions. The bond strength of the enamel with the adhesive was evaluated using the micro-tensile bond strength test (μTBS). μTBS results indicate that after plasma treatment, the bond strengths of GU, GE, IU, and IE enamel surfaces to the adhesive significantly increased by 33%, 15%, 35%, and 38% respectively, compared with untreated same tooth control. The mean bond strength of plasma-treated GU and IU enamel substrates to the adhesive were similar to that of untreated GE and IE enamel surfaces (p>0.05). A scanning electron microscope (SEM) was used to examine the fractured surfaces, which shows that more adhesive and composite left on plasma-treated enamel surfaces compared with untreated control. Water and adhesive contact angles measurements indicate that the plasma treatment increased surface energy, which enabled the adhesive to more effectively spread out and cover treated substrates. The Weibull analysis demonstrates that plasma treatment reduced defects in the interfaces and improved GU and IU enamel bond strengths with the adhesive to 41.7MPa and 26.0MPa respectively, which equals the GE and IE enamel bond strengths. This study provides the prospect of replacing the traditional selective etching step using a simple non-thermal plasma treatment technique.