Agradecimentos: This study was funded by the Coordination of Higher Education and Graduate Training, Brazil (CAPES) (Finance Code 001), and the São Paulo Research Foundation (FAPESP) (grant 2018/24446-1). We thank the Dental Clinic and Oral Medicine Clinic (Orocentro) of the Piracicaba Dental School, University of Campinas, Brazil, for all support given for this study. We also thank the Drogal Drugstore for providing the materials used in this study Ver menos

Abstract: Bleaching gel thickeners induce important changes in tooth enamel and these changes are reversed by saliva. This in situ study aimed to evaluate the effect of bleaching gels with different thickeners on tooth enamel under normal and hyposalivation conditions. Of 28 participants, 14 had normal salivary flow and 14 had low salivary flow. For each salivary flow, four types of treatment were performed with different thickeners: no bleaching (negative control), bleaching with a commercial 10% carbamide peroxide (CP) gel with carbopol (positive control) and bleaching with experimental 10% CP gels with natrosol and aristoflex. Participants used a palatal appliance containing bovine enamel/dentin specimens for 15 days. From day 2 to day 15, specimens were bleached extraorally. The bleaching gel was applied according to the groups for four hours. When the bleaching gel was removed, the palatal appliance was inserted again in the participants' mouth until the next day for another bleaching application. This procedure was repeated for 14 days and on day 15, surface microhardness (SMH), color ('delta'E*ab and 'delta'E00), surface roughness (Ra), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometry (EDS) analyses were performed and data were subjected to statistical analysis. Neither salivary flow nor thickeners influenced 'delta'E*ab and 'delta'E00 results. Carbopol had the lowest SMH, the highest Ra, and the lowest Ca% among all groups. For normal flow, natrosol and aristoflex had higher SMH. For low flow, aristoflex had higher SMH and natrosol and aristoflex had lower Ra. Aristoflex had higher Ca% and Ca/P and differed from carbopol for normal flow. For normal flow, 10% CP gels with natrosol and aristoflex caused fewer surface changes, and for low flow, only the 10% CP gel with aristoflex Ver menos