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Microtensile Testing, Nanoleakage, and Biodegradation of Resin-Dentin Bonds

Department of Restorative Dentistry, Division of Oral Health Science, Hokkaido University Graduate School of Dental Medicine, North 13, West 7, Kita-ku, Sapporo 060-8586 Japan; sano{at}den.hokudai.ac.jp

View larger version (66K): [in a new window]   Figure 1. Microtensile testing and nanoleakage. (A) Original microtensile bond-testing. Resin-bonded specimens were cut perpendicular to the adhesive structure (left). Specimens were trimmed and shaped to a gentle curve along the adhesive interface. They were then attached to the testing device and tested in tension (right). C: cured resin composite. D: dentin. (B) Nanoloeakage expression at the adhesive interface. The hybrid layer showed extensive silver uptake, shown here as a white image because of its high atomic number. Slight silver staining was also observed within the cured adhesive layer.

View larger version (66K): [in a new window]   Figure 2. Water-tree formation and pathway of biodegradation. (A) Different types of nanoleakage expression at the resin-dentin interface. Water-treeing was observed within the adhesive resin (arrow) (courtesy of Dr. F.R. Tay). (B) Pathway of degradation. (1) The first stage of biodegradation involves acid-etching to remove the smear layer and expose the fibrillar matrix. Then resin infiltration into the fibrillar matrix occurs. (2) The second stage involves hydrolysis and extraction of resinous materials within the hybrid layer, exposing collagen fibrils. (3) The third stage involves enzymatic attack by matrix metalloproteinases (MMPs), leading to slowly hydrolyzing collagen fibrils in the hybrid layer. Finally, depletion of collagen fibrils within the hybrid layer takes place, leading to loss of hybrid layer, loss of dentin seal, and loss of retention. (4) There is no evidence of remineralization of the adhesive interface following the use of dentin bonding systems in vivo, although that would be a desirable outcome.