comparison of the effects of two whitening toothpastes on microhardness of the enamel and a microhybride composite resin: an in vitro study

introduction: whitening toothpastes which have been accepted in populations may affect properties of enamel and restorative materials. the aim of this study was to compare the microhardness of human enamel and z250 microhybrid composite resin after brushing with two whitening toothpastes. materials and methods: in this experimental study of enamel specimens, forty five freshly extracted human incisors were prepared and divided into three groups of control enamel (cle), crest enamel (cte) and aquafresh enamel (afe). for composite resin specimens, forty five cylindrical-shaped specimens of light-cured z250 composite were prepared and divided into three groups of control composite (clc), crest composite (ctc) and aquafresh composite (afc). the control groups were brushed without toothpaste. crest and aquafresh group specimens were brushed with crest and aquafresh whitening toothpastes, respectively. vickers microhardness test wasperformed for all groups. data were analyzed by one-way anova and tukey tests. results: microhardness values of cle, cte, afe, clc, ctc and afc groups were332.99 ± 26.59, 313.99 ± 20.56, 323.57 ± 27.96, 137.1 ± 3.16, 122.95 ± 3.27 and 130.36 ± 4.8, respectively. one-way anova showed no significant differences among three enamel groups but there was significant difference among composite groups (p<0.01). conclusion: crest and aquafresh whitening toothpastes did not affect enamel hardness but reduced the microhardness value of z-250 composite resin. however, crest whitening toothpaste decreased the microhardness more than aquafresh.