title: A Mechanistic study of Plasma Treatment Effects on Demineralized Dentin Surfaces for Improved Adhesive/Dentin Interface Bonding.
abstract: Our previous work has shown that non-thermal plasma treatment of demineralized dentin significantly (p<0.05) improved adhesive/dentin bonding strength for dental composite restoration as compared with the untreated controls. This study is to achieve mechanistic understanding of the plasma treatment effects on dentin surface through investigating the plasma treated dentin surfaces and their interaction with adhesive monomer, 2-Hydroxyethyl methacrylate (HEMA). The plasma treated dentin surfaces from human third molars were evaluated by water contact angle measurements and scanning electron microscopy (SEM). It was found that plasma-treated dentin surface with subsequent HEMA immersion (Plasma/HEMA Treated) had much lower water contact angle compared with only plasma-treated (Plasma Treated)or only HEMA immersed(HEMA Treated)dentin surfaces. With prolong water droplet deposition time, water droplets spread out completely on thePlasma/HEMA Treateddentin surfaces. SEM images ofPlasma/HEMA Treateddentin surfaces verified that dentin tubules were opened-up and filled with HEMA monomers. Extracted type I collagen fibrils, which was used as simulation of the exposed dentinal collagen fibrils after acid etching step, were plasma treated and analyzed with Fourier transform infrared spectroscopy (FT-IR) and circular dichroism (CD) spectra. FT-IR spectra of thePlasma/HEMA Treatedcollage fibrils showed broadened amide I peak at 1660 cm-1and amide II at 1550 cm-1, which indicate secondary structure changes of the collagen fibrils. CD spectra indicated that 67.4% collagen helix structures were denatured after plasma treatment. These experimental results demonstrate that non-thermal argon plasma treatment was very effective in loosing collagen structure and enhancing adhesive monomer penetration, which are beneficial to thicker hybrid layer and longer resin tag formation, and consequently enhance adhesive/dentin interface bonding.
authors.affiliation: Center for Surface Science and Plasma Technology, Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Dong
authors.affiliation: Nanova, Inc., Columbia, MO 65203, USA.
authors.forename: Meng
authors.initials: M
authors.lastname: Chen
authors.affiliation: Center for Research on Interfacial Structure & Properties, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO 64108, USA.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Center for Surface Science and Plasma Technology, Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA.
authors.forename: Qingsong
authors.initials: Q
authors.lastname: Yu
keywords: Plasma treatment; adhesive penetration; adhesive/dentin bonding: denatured collagen; demineralized dentin surface