Effect of bleaching agents on the hardness and morphology of enamel.
OBJECTIVE
The goal of the present laboratory study was to analyze the effect of two home bleaching agents (Opalescence 10%, Ultradent, and Hi-Lite II, Shofu) as well as the separate solutions of 10% carbamide peroxide primary components (3% hydrogen peroxide and 7% urea) on enamel microhardness and surface morphology.


METHODS
Thirty human molars stored in water for no longer than 3 months were selected. Their facial and lingual surfaces were embedded in acrylic resin, and the specimens were polished with up to 600-grit sandpaper. The 30 molar sections were divided into five groups as per treatment modality (n = 6); group 1, 10% carbamide peroxide bleach with carbopol (Opalescence, Ultradent); group 2, oxygen-free gel bleach (Hydroxylite, Hi-Lite II, Shofu); group 3, 3% hydrogen peroxide with carbopol (Dermus Pharmacy, Florianópolis, SC, Brazil); group 4, 7% urea treatment (Dermus Pharmacy); and control, group 5, artificial saliva (Dermus Pharmacy). Prior to treatment, six indentations (Vickers) were made on each of the six surfaces in each group under a load of 100 g for 30 seconds. Bleaching procedure was conducted for 3 hours per day for 2 weeks, the control group excepted. Following each bleaching session, the specimens were washed with deionized water and kept in artificial saliva at 37 degrees C, this solution being changed daily. Pre- and post-treatment microhardness data were analyzed using a two-way analysis of variance. In a similar way, 30 other specimens underwent the same procedures. After the bleaching period, the samples were observed under the scanning electron microscope.


RESULTS
Specimens submitted to bleaching treatment with 3% hydrogen peroxide gel as described in this study showed a significant reduction of surface microhardness (p < .0001). The other treatment modalities had no effect on surface microhardness. No morphologic alterations were observed on enamel submitted to bleaching gel of 10% carbamide peroxide (Opalescence), oxygen-free gel (Hi-Lite II, Shofu), or 7% urea solution compared with the control (artificial saliva). However, the specimens bleached for 3 hours per day for 2 weeks with 3% hydrogen peroxide gel presented areas of mild erosion. The effect, nevertheless, was not uniform, occurring with varying intensity on all samples of enamel bleached with 3% hydrogen peroxide.


CONCLUSIONS
Bleaching treatment conducted with two home bleaching agents (Opalescence 10%, Ultradent, and Hi-Lite II, Shofu) had no adverse effects on enamel microhardness or on surface morphology. Bleaching with 3% hydrogen peroxide can have a negative effect on enamel hardness and surface morphology when performed as described in this study.
Lopes
Guilherme Carpena
GC
Department of Operative Dentistry, Federal University of Santa Catarina, Florianópolis, Brazil. guilherme_lopes@ig.com.br
Bonissoni
Leandro
L
Baratieri
Luiz Narciso
LN
Vieira
Luiz Clóvis C
LC
Monteiro
Sylvio
S
D000180:Acrylic Resins; D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D003743:Dental Enamel / Q000187:drug effects* / Q000648:ultrastructure; D003747:Dental Enamel Solubility / Q000187:drug effects; D004337:Drug Carriers; D004338:Drug Combinations; D006244:Hardness; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008855:Microscopy, Electron, Scanning; D008963:Molar; D016877:Oxidants / Q000494:pharmacology*; D010545:Peroxides / Q000494:pharmacology; D011145:Polyvinyls / Q000494:pharmacology; D012464:Saliva, Artificial; D013223:Statistics as Topic; D013696:Temperature; D013997:Time Factors; D014073:Tooth Bleaching; D014077:Tooth Erosion / Q000139:chemically induced; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology
D000180:Acrylic Resins; D004337:Drug Carriers; D004338:Drug Combinations; D016877:Oxidants; D010545:Peroxides; D011145:Polyvinyls; D012464:Saliva, Artificial; C093177:tooth-bleaching agent, Opalescence; C006912:carboxypolymethylene; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide