Journal of Dental Research, Vol 77, 1881-1888, Copyright © 1998 by International & American Associations for Dental Research Online Journals
Effects of N-methacryloyl amino acid applications on hybrid layer formation at the interface of intertubular dentin
K. Suzuki, N. Nishiyama, K. Nemoto, Y. Torii and K. Inoue
Department of Biomaterials, Okayama University Dental School, Japan.
To understand the role of NMAA in the bonding of composite resin to a
dentin surface, we investigated the effects of N-methacryloyl amino acid
(NMAA) application on the expansion of aggregated collagen fibers,
formation of a hybrid layer, and the tensile bond strength between
composite resin and dentin. Four NMAA
derivatives--N-methacryloyl-alpha-glycine (NMGly),
N-methacryloyl-gamma-amino n-butyric acid (NMBu),
N-methacryloyl-alpha-hydroxyproline (NMHPro), and
N-methacryloyl-alpha-glutamic acid (NMGlu)--were prepared and applied to
dentin surfaces which had been etched with 40% by mass H3PO4 and air-blown.
The shrunken collagenous layer expanded by approximately 50% to 70% by
volume of the original collagenous layer thickness after application of the
NMAA primers. Application of the bonding agent and composite resin after
NMAA treatment resulted in the formation of a hybrid layer. The thickness
of the hybrid layer was somewhat smaller than the collagenous layer formed
by the NMAA treatment only, regardless of the type of NMAA used. The
thickness of the hybrid layer was approximately ten times larger than that
formed without NMAA treatment. Although all NMAA primers formed hybrid
layers of similar thickness, higher tensile bond strengths, from 13 to 15
MPa, were obtained when etched and air-blown dentin was treated with NMBu,
NMGly, or NMGlu. NMHPro gave only 6.6 MPa, a value similar to that obtained
when no NMAA was used. We concluded, therefore, that formation of the
hybrid layer is a necessary but insufficient condition for high bond
strength.
