Four-year Water Degradation of Total-etch Adhesives Bonded to Dentin
J. De Munck1,
B. Van Meerbeek1,*,
Y. Yoshida2,
S. Inoue3,
M. Vargas4,
K. Suzuki2,
P. Lambrechts1, and
G. Vanherle1
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 Department of Biomaterials, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8525, Japan;
3 Department of Oral Health Science, Hokkaido University Graduate School of Dental Medicine, Kita 13 Nishi 7, Kita-ku, Sapporo 060-8586, Japan; and
4 Department of Operative Dentistry, The University of Iowa, Iowa City, USA;
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Figure 1. Mean µTBS to dentin of the three- and two-step total-etch adhesives investigated for each level of water exposure (mean and 95% confidence interval corrected for the multiple samples gathered from the same tooth).
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Figure 2. Graphed presentation of proportional prevalence of fracture modes for all experimental groups. *All failures cohesive in the bonding layer and resin composite were combined.
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Figure 3. Fractographic failure analysis of Scotchbond MP and Scotchbond 1 (3M Espe). (a) Fe-SEM overview photomicrographs of the fracture surfaces (left = dentin side; right = composite counterpart) of a representative µTBS sample prepared with Scotchbond MP that was stored for 4 yrs with the resin-dentin interface directly exposed to water (4yr-DE). Scratches remaining from smear-layer preparation confirmed that the interface failed adhesively (A) at the level between dentin and the bonding layer for an area of 0.84 mm2 or 84% of the total surface area. A small area of 0.16 mm2 or 16% of the total surface area represents a cohesive (C) failure in the bonding resin. (b) Magnification of the adhesive failure area at the composite side of the same sample as in (a) shows a typical pattern of islands of hybrid layer (H) fragments still attached to the composite (Comp.) and detached from dentin. (c) TEM photomicrograph (non-demineralized, unstained section) of the adhesive failure area sectioned from the same sample as in (a). The thin black line covering the fracture plane (arrows) and underneath the embedding resin (E) represents the gold coating applied for the Fe-SEM examination conducted beforehand. The hybrid layer (H) was pulled from unaffected dentin (U) either at the base (left) or close to the top (right). (d) High-magnification Fe-SEM photomicrograph of the composite site of a fractured four-year-stored Scotchbond 1 sample with direct exposure of the interface to water (4yr-DE). The sample failed within the hybrid layer, part of which remained attached to the composite. A resin tag (T) within a dentinal tubule is surrounded by loosely organized collagen fibrils (Coll.), the typical cross-banding of which can be observed. This suggests either that this hybrid layer collagen was inadequately enveloped by resin or that resin was eluted.
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Figure 4. Fractographic failure analysis of Optibond DC and Optibond Solo (Kerr). (a). Fe-SEM overview photomicrographs of the fracture surfaces (left = dentin side, right = composite counterpart) of a representative µTBS sample prepared with Optibond Dual Cure that was stored for 4 yrs with the resin-dentin interface indirectly exposed to water (4yr-IE). A small area of 0.11 mm2 or 10% of the total surface area represents an adhesive (A, marked with black line) failure, while the major part (1.0 mm2 or 90% of the total surface area) failed cohesively (C) in resin. (b) TEM photomicrograph (non-demineralized, stained section) of a typical failure of Optibond Dual Cure after 4 yrs of water storage (4yr-DE). A thin layer of a few µm of the particle-filled adhesive resin remained attached to the hybrid layer (H), indicating that the adhesive layer failed cohesively. Although this section was stained by heavy metals (UA/LC), collagen seemed not to have picked up much of the staining solution. E = embedding resin; T = resin tag (T) packed with filler; U = unaffected dentin; arrows = gold coating. (c) TEM photomicrograph (non-demineralized, unstained section) of a sample that was prepared with Optibond solo and stored for 4 yrs with the resin-dentin interface directly exposed to water (4yr-DE). The hybrid layer (H) remained attached to unaffected dentin (U). E = embedding resin; T = resin tag (T). (d) TEM photomicrograph (non-demineralized, unstained section) of the same sample as in (c), but now at a site were the sample failed at the base of the hybrid layer. Small hybrid-layer fragments (arrows) remained attached to unaffected dentin (U). The resin tag (T) was fractured at the same level. E = embedding resin.
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