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I have some concerns about "The Effects of Seven Carbamide Peroxide Bleaching Agents on Enamel Microhardness Over Time," by Dr. Roberta Tarkany Basting and colleagues (October JADA). The article needs to be critically evaluated.

I would like to know why there was a decrease in Knoop microhardness after eight hours and no additional decrease, even though the tooth samples remained in the bleaching agents for an additional 44 days. The decrease in microhardness, therefore, cannot be attributed only to the carbamide peroxide in agents.

Perhaps the baseline values were taken some time before the study started and the specimens placed in distilled water, which has been reported to decrease microhardness.¹ Perhaps distilled water caused the decrease in microhardness, as the placebo continued to decrease in microhardness for an additional two weeks.

I also find it confusing that a majority of the tooth samples began increasing in microhardness before they were removed from the bleaching agent. It would seem reasonable that the pattern of microhardening would only begin after removal.

Another article from the same three authors² reported a mean Knoop microhardness of unerupted third molars using placebo for three weeks of 244 and 275, whereas, in this study, after three weeks the mean value of the placebo was 45.7. The aforementioned study is an in situ study; however, this study kept the teeth in distilled water. This points again to distilled water, not carbamide peroxide, as being the agent in some studies to decrease microhardness.

Knoop microhardness values in an in situ study by Araujo and colleagues¹ showed no significant decrease in hardness after 21 days of bleaching with 10 percent carbamide peroxide. Now we have a dilemma—which study do we accept?

	REFERENCES

TOP REFERENCES

1. Araujo EM, Baratieri LN, Vieira LC, Ritter AV. In situ effect of 10% carbamide peroxide on microhardness of human enamel: function of time. J Esthet Restor Dent 2003;15(3):166–73.[Medline]
   
   
2. Basting RT, Rodrigues Junior AL, Serra MC. The effect of 10% carbamide peroxide bleaching material on microhardness of sound and demineralized enamel and dentin in situ. Oper Dent 2001;26(6):531–9.[Medline]
   
   

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Matis, B. A. Search for Related Content PubMed Articles by Matis, B. A.