Single-step, self-etch adhesives behave as permeable membranes after polymerization. Part I. Bond strength and morphologic evidence.
OBJECTIVE
To test the hypotheses that microtensile bond strengths of single-step, self-etch adhesives to hydrated dentin are adversely affected by delayed-activation of a light-cured composite, as well as the use of a chemical-cured composite.


METHODS
Seven commercially available and one experimental single-step, self-etch adhesives were bonded to hydrated human dentin. A dual-cured composite was used and activated using: [1] the light-cured mode (base paste only-control), [2] the chemical-cured mode (base and catalyst pastes, in the dark); and [3] delayed light-activation (base syringe only, left on top of cured adhesives in the dark for 20 minutes before activation). After microtensile bond strength evaluation, fractured samples were examined using SEM. Intact, unstressed interfaces of [1] and [3] were examined with TEM. Microtensile bond strengths were also evaluated for selected adhesives bonded to dehydrated dentin and coupled with the composite activated by [2] or [3].


RESULTS
For all adhesives, bond strengths decreased significantly to bonded hydrated dentin when the composites were activated with [2] or [3] (P< 0.001). Whereas the hybrid layer-adhesive interface was intact, water-blisters that developed along the adhesive-composite interface in these two modes were responsible for the decline in bond strength. When bonded to dehydrated dentin, delayed light-activation of the light-cured composite did not result in compromised bond strength. The results of chemical-cured composites improved but were more variable and system-dependent.
Tay
Franklin R
FR
Department of Pediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong SAR, China. kfctay@hknet.com
Pashley
David H
DH
Suh
Byong
B
Carvalho
Ricardo
R
Miller
Michael
M
D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D003804:Dentin / Q000648:ultrastructure; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D019234:Dentinal Fluid / Q000502:physiology; D003890:Desiccation; D006801:Humans; D008027:Light; D008422:Materials Testing; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D010539:Permeability; D011108:Polymers / Q000737:chemistry; D013499:Surface Properties; D013718:Tensile Strength; D014867:Water / Q000737:chemistry
D003188:Composite Resins; D017220:Dentin-Bonding Agents; D011108:Polymers; D014867:Water