Effect of whitening dentifrices on color, surface roughness and microhardness of dental enamel in vitro

PURPOSE

To evaluate the color, surface roughness and microhardness of human dental enamel subjected to brushing with whitening dentifrices.

METHODS

The enamel samples (4 x 4 x 2 mm) were darkened using 0.2% chlorhexidine and black tea, and were randomly divided into seven groups (n= 15) for brushing cycles with only water; control; conventional dentifrice (Colgate Maximum Anticaries Protection); dentifrice containing 2% hydrogen peroxide (Colgate Luminous White Advanced); dentifrice containing sodium tripolyphosphate (Sensodyne True White); dentifrice containing activated charcoal (Black is White); and dentifrice containing blue covarine (Close Up White Now). The samples were submitted to 1,000 and 30,000 brushing cycles. The color values (CIE L*a*b*), surface roughness (Ra) and microhardness (Knoop) were recorded at four time points: baseline, after staining, after 1,000 and after 30,000 brushing cycles. The data were submitted to statistical analyses using paired t-test, ANOVA and Tukey.

RESULTS

The color analysis, roughness and microhardness results showed interaction between the effect of the dentifrices and the time point (P< 0.001). The bleaching dentifrices brought about color changes (ΔE) significantly greater than those obtained with conventional dentifrices and the control; however, there were no significant color changes among the bleaching dentifrices. When the color coordinates were evaluated individually, the L* values increased and the a* and b* values decreased throughout the experiment. The conventional toothpaste and the toothpastes containing blue covarine, activated charcoal or hydrogen peroxide promoted a statistically significant increase in the surface roughness of the samples after the last brushing cycle. The sodium tripolyphosphate dentifrice caused a progressive reduction in roughness. The microhardness increased statistically after 30,000 cycles for the conventional toothpaste, blue covarine and hydrogen peroxide. It was concluded that the whitening dentifrices lightened the samples, which evidenced greater luminosity and reduction in reddish and yellow tones. Moreover, they did not have deleterious effects on microhardness, and caused acceptable changes in surface roughness.

CLINICAL SIGNIFICANCE

Dentifrices with different whitening strategies changed the color of the samples, resulting in samples with greater luminosity and reduced reddish and yellowish tones. They also caused changes in surface roughness within the acceptable clinical limit and did not have a deleterious effect on the microhardness of dental enamel.