Monomer-Solvent Phase Separation in One-step Self-etch Adhesives
K.L. Van Landuyt1,
J. De Munck1,
J. Snauwaert2,
E. Coutinho1,
A. Poitevin1,
Y. Yoshida3,
S. Inoue4,
M. Peumans1,
K. Suzuki3,
P. Lambrechts1, and
B. Van Meerbeek1,*
1 Leuven BIOMAT Research Cluster, Department of Conservative Dentistry, School of Dentistry, Oral Pathology and Maxillo-Facial Surgery, Catholic University of Leuven, Kapucijnenvoer 7, B-3000 Leuven, Belgium;
2 Laboratory of Solid-State Physics and Magnetism, Department of Physics, Catholic University of Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium;
3 Department of Biomaterials, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8525, Japan; and
4 Division for General Dentistry, Hokkaido University Dental Hospital, Kita 13 Nishi 7, Kita-ku, Sapporo 060-8586, Japan;
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Figure 1. Microscopic examination of the experimental adhesives Exp-Eth and Exp-Ac. (a) Non-demineralized, non-stained TEM of Exp-Ac revealing a multitude of entrapped droplets, particularly at the bottom of the adhesive layer (Ar). The droplets are round or oval, with various sizes. A distinctive oxygen-inhibition layer (O2-I) was present in the top of the adhesive layer. C = flowable composite; Hy = hybrid layer; Ud = unaffected dentin. (b) Demineralized stained TEM of the submicron hybrid layer formed by Exp-Eth. (c) Feg-SEM of a µTBS failure pattern of Exp-Ac that exhibited mixed adhesive failure (dentin side). Note the high distribution of droplets at the bottom of the adhesive layer, while no droplets are seen near the top. (d) LM image of a drop of uncured adhesive solution of Exp-Ac dispensed on a glass plate. This drop contains many droplets centrally, and is bordered by a droplet-free halo, which becomes wider with time. The time indication indicates the time elapsed after the adhesive was applied.
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Figure 2. Microscopic examination of Exp-Eth/SA, Exp-Eth/UB, Clearfil SE Bond, and iBond. (a) Non-demineralized, non-stained TEM of Exp-Ac/SA. Strong air-blowing before light-curing reduced the number of droplets considerably. Ar = adhesive resin; Hy = hybrid layer; Ud = unaffected dentin. (b) Non-demineralized, non-stained TEM of Exp-Eth/UB. Following a two-step self-etch approach with the HEMA-containing UB bonding agent, the adhesive layer was free of droplets. The hybrid layer resembled that of Exp-Eth. (c) LM of uncured Clearfil SE Bond (Kuraray) primer dispensed on a glass plate. Note the transparency of the drop, some curves representing convection streams caused by solvent evaporation, and the absence of droplets. Original magnification 5x. (d) LM of uncured iBond (Hereaus Kulzer) applied on a glass plate, showing an extensive phase-separation reaction (time after dispensing of adhesive is indicated in sec). Original magnification 5x. (e) Non-demineralized, non-stained TEM of the resin-dentin bond produced by iBond. A partially demineralized hybrid layer and hybridized smear plug (HySp) were formed. Note the presence of small droplets entrapped in the adhesive resin adjacent to the hybrid layer. (f) Feg-SEM of a µTBS failure pattern of iBond (composite side). The bond failed between the adhesive and composite (C) and near the bottom of the adhesive layer, which appeared to be very porous due to the droplets entrapped after the sample was light-cured.
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Figure 3. Box-whisker plot (min-[lower quartile-median-upper quartile]-max) of the µTBS to dentin (mean ± standard deviation; n = total number of specimens; ptf = pre-testing failure). The diamond represents the mean µTBS. Means with unlike superscript letters are statistically significantly different.
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