The present study aims to evaluate in vitro the effect of desensitizing toothpastes, regular and whitening versions, on the dentine surface loss using an erosion-abrasion cycling model. Seventy human third molars will be used. Dentin slabs of 4mm x 4mm x 2mm from the radicular portion will be cut and embedded in acrylic resin. The resulting specimens will be ground flat and polished with sandpapers in a decreasing sequence of grits, using a polishing machine, under water-cooling. Specimens without any cracks or other structure defects, and with maximum curvature of 0,3 ¼m (measured with an optic profilometer), will be immersed in a 17% of EDTA solution for 2min. This will open dentine tubules and simulate a sensitive dentine. The specimens will be randomly divided into 7 experimental groups (n=10), according with the toothpaste to be used: 1. Sensodyne Repair and Protect regular, 2. Sensodyne Repair and Protect whitening, 3. Colgate Pro-Alívio regular, 4. Colgate Pro-Alívio whitening, 5. Colgate Sensitive Pró-Alívio regular, 6. Colgate Sensitive Pró-Alívio whitening, 7. Deionized water (negative control). They will undergo an abrasive-erosive cycling for 5 days, which consists of 2min immersion in 0.3% citric acid (pH 2.6), followed by 60min immersion in artificial saliva, 4x/day. Thirty min after the first and last acid exposures, the specimens will be brushed with an electric toothbrush for 15s, with standardized and constant force. The total exposure time to the dentifrice suspensions will be of 2min. At the end of the cycling, surface loss (¼m) will be measured in an optic profilometer. The resulting data will be statistically analyzed, considering a significance level of 5%.
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