Cytotoxic effect of a 35% hydrogen peroxide bleaching gel on odontoblast-like MDPC-23 cells Ana Paula Dias Ribeiro, MD, a Nancy Tomoko Sacono, MD, b Fernanda Campos Rosetti Lessa, PhD, b Indri Nogueira, MD, b Cármen Regina Coldebella, MD, b Josimeri Hebling, PhD, b and Carlos Alberto de Souza Costa, MS, PhD, c Araraquara, Brazil ARARAQUARA SCHOOL OF DENTISTRY, SÃO PAULO STATE UNIVERSITY Objective. This study evaluated transenamel and transdentinal cytotoxic effects of a bleaching gel on the MDPC-23 cell line. Study design. Discs obtained from bovine incisors were placed in a metallic device to simulate an in vivo pulp chamber. Groups were formed according to the enamel surface treatment: G1: 35% H 2 O 2 bleaching gel; G2: 35% H 2 O 2 bleaching gel + halogen light; G3: halogen light; and G4: control. Cell metabolism was evaluated by the methyltetrazolium assay and cell morphology by scanning electron microscopy. Results. Cell metabolism decreased by 31.7%, 41.6%, and 11.5% in G1, G2, and G3, respectively. Cytotoxic effects observed in G2 were significantly more severe compared with G3 and G4. In G1 and G2, a smaller number of viable cells with major morphologic alterations remained adhered to dentin. Conclusion. The bleaching gel associated with light presented transenamel and transdentinal cytotoxic effects characterised by direct damage to odontoblasts and decrease of their metabolic activity. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:458-464) Vital tooth bleaching therapies include in-office bleach- ing, in which the bleaching gel is applied by the dentist during a clinical session and is either activated or not by a light source, and home bleaching, which is performed by the patient with the use of trays and gels under the dentist’s supervision. 1 In-office bleaching procedures seem to be an appropriate alternative to home-bleach- ing applications, especially in the case of very severe discolorations or if a rapid treatment is desired. In- office bleaching is usually performed using agents with high concentrations (30%-35%) of hydrogen peroxide (H 2 O 2 ). 2 Hydrogen peroxide is a thermally instable chemical agent with a high oxidative power, which may disso- ciate into water, oxygen, and some free radical species, such as hydroxyl radicals (OH - ). These radicals are capable of degrading complex organic molecules that are responsible for tooth coloration, reducing or elim- inating pigments that cause initial tooth darkening. 3-5 Although vital tooth bleaching has become very pop- ular in the last decade, some adverse effects have been associated with this procedure, such as decrease in the microhardness of restorative materials, 6 increase in marginal microleakage at the tooth/restoration interface and gingival irritation, 7 pulp sensitivity, 8 and changes in enamel surface morphology. 4 Other studies have shown that tooth bleaching reduces enamel and dentin microhardness, 9,10 and that the chemical components of bleaching gels may have cytotoxic and carcinogenic effects. 11 A possible occurrence of cervical root resorp- tion after internal bleaching therapies in nonvital teeth has also been reported. 5 However, in vivo studies have demonstrated that the most common adverse effect following vital tooth bleaching therapies is postopera- tive sensitivity, 8 which may result from the transenamel and transdentinal diffusion of H 2 O 2 or other toxic com- ponents released with the degradation of the bleaching gels activated or not by light or heat. 12-14 These by- products released from the bleaching gel act as free radicals and may cause oxidative stress in the pulp cells. 4 It has been reported that oxidative stress refers to the imbalance between the production of reactive oxy- gen species (ROS) and the presence of endogenous and exogenous antioxidants. 15 The increase of ROS levels causes deleterious effects to several cell components, including lipid peroxidation, oxidative alterations of protein, and DNA cell damage. 16,17 Recent studies have evaluated the effects of H 2 O 2 when applied directly on macrophages 18 and rat pulp cells. 19 However, no study has yet investigated the cytotoxicity of components of bleaching gels on odon- toblasts, which are organized in a layer that underlies a Department of Dental Materials and Prosthodontics. b Department of Orthodontics and Pediatric Dentistry. c Department of Physiology and Pathology. Received for publication Mar 25, 2009; returned for revision Apr 29, 2009; accepted for publication May 5, 2009. 1079-2104/$ - see front matter © 2009 Published by Mosby, Inc. doi:10.1016/j.tripleo.2009.05.006 458