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Bonding BisGMA to Dentin—a Proof of Concept for Hydrophobic Dentin Bonding

¹ Department of Oral Biology & Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA;
² School of Dentistry, Medical College of Georgia, Augusta, GA, USA;
³ Department of Restorative Dentistry, Piracicaba School of Dentistry, University of Campinas, Piracicaba, SP, Brazil; and
⁴ University of Toronto, Ontario, Canada

View larger version (21K): [in this window] [in a new window]   Figure 1. The principle behind bonding of BisGMA to acid-etched dentin may be illustrated by a plot of the Hoy’s solubility parameter for polar forces (p) against the corresponding Hoy’s solubility parameter for hydrogen bonding forces (h) for water-saturated collagen, ethanol-saturated collagen, BisGMA solvated in 50 wt% ethanol, and neat BisGMA. This two-dimensional plot represents a simplified version of the original Hansen’s 3-D solubility sphere, which uses only 2 of the 3 solubility parameter components, most commonly p and h. The white and gray circles with radii of 5 (MPa)1/2 represent the respective miscibility range of water- and ethanol-saturated collagen. Both neat BisGMA and BisGMA solvated in 50 wt% ethanol are outside the miscibility range of water-saturated collagen, and hence are immiscible with the latter. When water is replaced with ethanol, the dentin collagen matrix is rendered more hydrophobic (black arrow), enabling it to be infiltrated by a relatively hydrophobic resin monomer. Dissolving BisGMA in 50 wt% ethanol results in a less viscous, more hydrophilic (black dotted arrow) primer solution that falls within the miscibility range of the ethanol-saturated collagen.

View larger version (155K): [in this window] [in a new window]   Figure 2. Representative resin-dentin interfaces created by the experimental hydrophobic BisGMA adhesives (A,C,E) and the hydrophilic OptiBond FL adhesive (B,D,F). In both cases, the acid-etched dentin was treated with 2.8% half-neutralized oxalic acid for 1 min, to occlude the dentinal tubules with calcium oxalate crystals prior to bonding under 20 cm of water pressure. (A,B) SEM micrographs of polished, acid-treated, and sodium-hypochlorite-deproteinized resin-dentin interfaces depicting hybrid layers (H) resistant to the acid/base challenge, and resin tags containing trapped calcium oxalate crystals (open arrowheads). D, deep coronal dentin; FA, filled adhesive. The experimental three-step BisGMA adhesive is shown in (A), with the filled adhesive layer consisting of a low-viscosity flowable composite. (C,D) TEM micrographs of unstained, undemineralized silver-infiltrated interfaces showing the extent of nanoleakage in the form of silver deposits (pointers) within the hybrid layers (H). The experimental two-step BisGMA adhesive is shown in (C). D, mineralized dentin; A, unfilled BisGMA adhesive; FA, filled OptiBond FL adhesive; open arrowheads, spaces that were previously occupied by partially dislodged, subsurface calcium oxalate crystals. (E,F) High-magnification TEM views of stained sections showing the dimensions of the collagen fibrils and interfibrillar spaces within the hybrid layers. Wider interfibrillar spaces and more extensive shrinkage of the collagen fibrils were evident when water in the dentin matrix was replaced with ethanol before bonding.

Journal of Dental Research, Vol. 86, No. 11, 1034-1039 (2007)
DOI: 10.1177/154405910708601103


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