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Enamel microhardness and shear bond strength after treatment with an 18% carbamide peroxide bleaching varnish
Robson Tetsuo Sasaki1, Maria Cinthia Barbosa, Flávia Martão Flório
1Department of Restorative Dentistry, São Leopoldo Mandic Research Center, Campinas, São Paulo, Brazil.
Purpose:
To evaluate the microhardness and shear bond strength of human enamel treated with an 18% carbamide peroxide bleaching varnish.
Methods:
40 dental enamel slabs were embedded and ground flat, dividing them into four groups (n=10) which received the varnish application for 14 consecutive days: (G1) one daily varnish application; (G2) two daily varnish applications with an interval of 15 minutes; (G3) two daily varnish applications with an interval of 5 hours. After varnish application, the slabs were immersed in artificial saliva changed daily. The control group (G4) consisted of slabs (n=10) that did not receive any varnish treatment and were maintained in artificial saliva for 14 days. Microhardness tests were performed with Knoop indentation with a load of 25 grams for 5 seconds at the beginning of the treatment (baseline values) and after 7 and 14 days. Cylinders were made with microhybrid resin composite and one-bottle adhesive system for shear bond strength tests. Using a universal testing machine with a speed of 0.5 mm/minute to obtain the values in MPa.
Results:
The Kruskal-Wallis test showed no changes in microhardness values among groups after 7-day varnish application, although there was a decrease in microhardness values when using an 18% carbamide peroxide varnish twice a day with a time-interval of 5 hours between applications (P < 0.05). For enamel shear bond strength, ANOVA test (P > 0.05) did not show significant differences among the groups (G1=15.8; G2=15.2; G3=19.0; G4=15.1).
