title: Monomer-solvent phase separation in one-step self-etch adhesives.
abstract: One-step adhesives bond less effectively to enamel/dentin than do their multi-step versions. To investigate whether this might be due to phase separation between adhesive ingredients, we characterized the interaction of 5 experimental and 3 commercial self-etch adhesives with dentin using transmission electron microscopy. All adhesives were examined for homogeneity by light microscopy. Bonding effectiveness to dentin was determined with the use of a micro-tensile bond-strength protocol. The lower bond strength of the one-step adhesives was associated with light-microscopic observation of multiple droplets that disappeared slowly. Interfacial analysis confirmed the entrapment of droplets within the adhesive layer. The prompt disappearance of droplets upon application of a small amount of HEMA (2-hydroxyethyl methacrylate) or a HEMA-containing bonding agent, as well as the absence of droplets at the interface of all HEMA-containing adhesives, strongly suggests that the adhesive monomers separate from water upon evaporation of ethanol/acetone. Upon polymerization, the droplets become entrapped within the adhesive, potentially jeopardizing bond durability. This can be avoided by strong air-drying of the adhesive, thereby removing interfacial water and thus improving bonding effectiveness.
authors.affiliation: 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.
authors.forename: K L
authors.initials: KL
authors.lastname: Van Landuyt
authors.forename: J
authors.initials: J
authors.lastname: De Munck
authors.forename: J
authors.initials: J
authors.lastname: Snauwaert
authors.forename: E
authors.initials: E
authors.lastname: Coutinho
authors.forename: A
authors.initials: A
authors.lastname: Poitevin
authors.forename: Y
authors.initials: Y
authors.lastname: Yoshida
authors.forename: S
authors.initials: S
authors.lastname: Inoue
authors.forename: M
authors.initials: M
authors.lastname: Peumans
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.forename: P
authors.initials: P
authors.lastname: Lambrechts
authors.forename: B
authors.initials: B
authors.lastname: Van Meerbeek
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D045424:Complex Mixtures / Q000737:chemistry; D001840:Dental Bonding / Q000379:methods*; D003738:Dental Cements / Q000737:chemistry*; D003799:Dental Stress Analysis; D003804:Dentin / Q000737:chemistry* / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D008964:Molar, Third; D012997:Solvents / Q000737:chemistry
chemical_list: D045424:Complex Mixtures; D003738:Dental Cements; D017220:Dentin-Bonding Agents; D012997:Solvents