ORIGINAL ARTICLE Influence of different thickeners in at-home tooth bleaching: a randomized clinical trial study Juliana do Carmo Públio 1 & Marília Zeczkowski 1 & Jonny Burga-Sánchez 2 & Gláucia Maria Bovi Ambrosano 3 & Franscico Carlos Groppo 2 & Flávio Henrique Baggio Aguiar 1 & Débora Alves Nunes Leite Lima 1 Received: 26 June 2017 /Accepted: 4 September 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Objectives To evaluate the effects of 10% carbamide peroxide (CP) with two different thickeners, carbopol (CPc) and natrosol (CPn), on color variation (CV), tooth sensitivity (TS), and cytotoxicity (CC). Methods Seventy subjects were distributed into the CPc or CPn groups (n = 35), in a parallel group, randomized, controlled, single-blind clinical trial. Bleaching gels were used by volunteers for 4 h daily for 2 weeks. Color evaluation was performed using a reflectance spectrophotometer, before bleaching treatment (BT), immediately after the first and second weeks of BT, and 1 week and 1 month after BT ended. TS was evaluated using two pain scales, before, during, and after BT. CC was evaluated using MTT after exposure of MDPC-23 cells to the bleaching gels for 4 h. Epoxy replicas of the subjects teeth were made before and after BT and analyzed using a scanning electronic microscope. The data was analyzed using statistical methods. Results CV and TS showed similar variation between both bleaching gels (p ≤ 0.05). None of the protocols affected cellular metabolism or the surface morphology of enamel. Conclusions Bleaching gels with carbopol and natrosol as thickening agents produced similarly effective tooth bleaching and TS, but did not cause cytotoxicity. Clinical relevance Natrosol could be an alternative as a thickener used in bleaching gels due to its similar bleaching effect and TS when compared with Carbopol. Keywords Carbamide peroxide . Tooth sensitivity . Tooth bleaching . Carboxypolymethylene . Hydroxyethylcellulose . Toxicity tests Introduction Bleaching with 10% carbamide peroxide is one of the most accepted bleaching treatments due to its effectiveness, bio- safety, because it does not cause cellular changes [1–4]. In fact, this product has the ADA (American Dental Association) [5] Seal of Acceptance, which is considered the gold standard in certifying dental products. A major concern with bleaching treatment is the adverse effects that bleaching gels can cause on tooth tissues, especial- ly regarding tooth sensitivity. Sensitivity to the bleaching pro- cedure seems to be the result from the facilitated passage of either hydrogen peroxide or related free radicals through the enamel and dentin and into the pulp tissue [4, 6, 7]. In vitro studies have been performed using MDPC-23 odontoblast cell cultures to evaluate the cytotoxicity of these bleaching agents [8, 9]. Additionally, other studies have been performed using Scanning Electron Microscopy to determine the possible morphological changes of the enamel surface after tooth bleaching treatment, both in vitro [10, 11] and in vivo, using the replica technique [12, 13]. Carbamide peroxide bleaching gel typically contains the thickener, carbopol (carboxypolymethylene polymer), in its formulation, which is responsible for bleaching gel viscosity * Débora Alves Nunes Leite Lima dalima@unicamp.br 1 Department of Restorative Dentistry, Piracicaba Dental School, University of Campinas, Av. Limeira, 901, P.O. BOX 52, Piracicaba, SP 13414-903, Brazil 2 Department of Physiological Sciences, Piracicaba Dental School, University of Campinas, Av. Limeira, 901, Piracicaba, SP 13414-903, Brazil 3 Department of Social Dentistry, Piracicaba Dental School, University of Campinas, Av. Limeira, 901, Piracicaba, SP 13414-903, Brazil Clinical Oral Investigations https://doi.org/10.1007/s00784-018-2613-9