Objective: To investigate the influence of non-thermal plasma treatment on the penetration
of a model dental adhesive into the demineralized dentine.
Methods: Prepared dentine surfaces were conditioned with Scotchbond Universal etchant for
15 s and sectioned equally perpendicular to the etched surfaces. The separated halves were
randomly selected for treatment with an argon plasma brush (input current 6 mA, treatment
time 30 s) or gentle argon air blowing (treatment time 30 s, as control). The plasma-treated
specimens and control specimens were applied withamodel adhesive containing 2,2-bis[4-(2-
hydroxy-3-methacryloxypropoxy) phenyl]-propane (BisGMA) and 2-hydroxyethyl methacrylate
(HEMA) (mass ratio of 30/70), gently air-dried for 5 s, and light-cured for 20 s. Crosssectional
specimens were characterized using micro-Raman spectral mapping across the
dentine, adhesive/dentine interface, and adhesive layer at 1-mm spatial resolution. SEM was
also employed to examine the adhesive/dentine interfacial morphology.
Results: The micro-Raman result disclosed that plasma treatment significantly improved
the penetration of the adhesive, evidenced by the apparently higher content of the adhesive
at the adhesive/dentine interface as compared to the control. Specifically, the improvement
of the adhesive penetration using plasma technique was achieved by dramatically enhancing
the penetration of hydrophilic monomer (HEMA), while maintaining the penetration of
hydrophobic monomer (BisGMA). Morphological observation at the adhesive/dentine interface
using SEM also confirmed the improved adhesive penetration. The results further
suggested that plasma treatment could benefit polymerization of the adhesive, especially in
the interface region.
Conclusion: The significant role of the non-thermal plasma brush in improving the adhesive
penetration into demineralized dentine has been demonstrated. The results obtained may
offer a better prospect of using plasma in dental restoration to optimize adhesion between
tooth substrate and restorative materials.
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