Dentists should wait seven days after completing in-office bleaching with 35% hydrogen peroxide before placing adhesive restorations, according to a new study in the Journal of the American Dental Association (March 2010, Vol. 141:3, pp. 300-306).
Researchers from the University of Passo Fundo and São Leopoldo Mandic Research Center in Brazil conducted an in situ study of the influence of various time intervals after tooth bleaching with 35% hydrogen peroxide on the bond strength of resin-based composite restorations.
"It is important to evaluate the time that needs to elapse after bleaching before replacing restorations so that they are not damaged by possible chemical alterations resulting from the presence of bleaching agents in the enamel and dentin structure," the authors wrote.
They evaluated the bond strength of bleached enamel and dentin at different times after bleaching, basing the study on previous research in which investigators recommended that clinicians wait from one to 21 days after bleaching before replacing restorations.
The researchers randomly fixed enamel and dentin blocks onto the buccal surfaces of posterior maxillary teeth in 20 participants one week before performing tooth bleaching with 35% hydrogen peroxide. After treatment, they removed one block of dentin or enamel and prepared it for the bond strength tests according to these time intervals: no bleaching treatment (controls), immediately after bleaching, seven days after bleaching, 14 days after bleaching, and 21 days after bleaching.
"Thirty-five percent hydrogen peroxide reduces the bond strength to enamel and dentin, and it is necessary to wait seven days before performing adhesive restorative procedures," the authors concluded.
However, the results also showed that one week after the completion of bleaching, the bond strength to enamel and dentin increased to values similar to those found in the control group, they noted.
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