Effect of bleaching on µ-TBS to enamel at different times

Objectives: To asses the effect of 10% carbamide peroxide, 10% hidrogen peroxide and two over-the-counter (OTC) whitening products on µ-TBS to enamel at different times after the treatment.

Methods: One hundred incisors were randomly divided into five groups to receive bleaching treatments: No treatment (control), 10% carbamide peroxide (Opalescence, Ultradent Products), 10% hydrogen peroxide (Opalescence Treswhite Supreme, Ultradent Products), 3% carbamide peroxide plus lactoperoxidase (Whitekin, Kin) or 3% carbamide peroxide plus 2.7% carbamide peroxide (Clysiden Kit Express, Ern) for four weeks. Teeth were always stored in artificial saliva at 37ºC and were cleaned with 1450 ppm NaF tooth paste twice a day. Teeth were restored 1, 3, 7 and 14 days after bleaching using Adper Scotchbond 1 XT  adhesive (3M ESPE) and Filtek Z250 resin composite (3M ESPE). After 24 hours of storage, samples were subsequently prepared for µ-TBS testing. Beams of approximately 1 mm² were tested in tension at 1 mm/min in a universal tester (Instron 3345). Data were analyzed one-way ANOVA and S-N-K test (p<0.05).

 Results: Mean µ-TBS values in MPa (sd) are shown in the table. As mean values were similar for the control group at different times, they were all grouped. Different letters indicate statistically different µ-TBS values among treatments. Bleaching treatment with Whitekin and Clysiden significantly reduced µ-TBS mean values at 1, 3 and 7 days after the treatment. No differences were detected on µ-TBS mean for the bleaching products tested 14 days after bleaching.

 Conclusion: Whitekin and Clysiden products reduced the µ-TBS to enamel. However, all bleaching treatments showed µ-TBS similar 14 days after treatment. This period after treatment would be necessary to re-establish the µ-TBS to enamel when Whitekin and Clysiden products are used.