Monomer-solvent phase separation in one-step self-etch adhesives.
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.
Van Landuyt
K L
KL
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.
De Munck
J
J
Snauwaert
J
J
Coutinho
E
E
Poitevin
A
A
Yoshida
Y
Y
Inoue
S
S
Peumans
M
M
Suzuki
K
K
Lambrechts
P
P
Van Meerbeek
B
B
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
D045424:Complex Mixtures; D003738:Dental Cements; D017220:Dentin-Bonding Agents; D012997:Solvents