Inflammatory response of human dental pulp to at-home and in-office tooth bleaching

ABSTRACT Tooth bleaching is a technique of choice to obtain a harmonious smile, but bleaching agents may damage the dental pulp. Objective: This study evaluated the inflammatory responses of human dental pulp after the use of two bleaching techniques. Material and Methods: Pulp samples were collected from human third molars extracted for orthodontic reasons and divided into three groups: control - no tooth bleaching (CG) (n=7); at-home bleaching with 15% carbamide peroxide (AH) (n = 10), and in-office bleaching with 38% hydrogen peroxide (IO) (n=12). Pulps were removed and stained with hematoxylin-eosin for microscopic analysis of inflammation intensity, collagen degradation, and pulp tissue organization. Immunohistochemistry was used to detect mast cells (tryptase+), blood vessels (CD31+), and macrophages (CD68+). Chi-square, Kruskal-Wallis, and Mann Whitney tests were used for statistical analysis. The level of significance was set at p<.05. Results: The inflammation intensity and the number of macrophages were significantly greater in IO than in AH and CG (p<0.05). The results of CD31+ (blood vessels per mm2) were similar in CG (61.39±20.03), AH (52.29±27.62), and IO (57.43±8.69) groups (p>0.05). No mast cells were found in the pulp samples analyzed. Conclusion: In-office bleaching with 38% hydrogen peroxide resulted in more intense inflammation, higher macrophages migration, and greater pulp damage then at-home bleaching with 15% carbamide peroxide, however, these bleaching techniques did not induce migration of mast cells and increased the number of blood vessels.


INTRODUCTION
Tooth bleaching has been widely used to correct tooth discolorations and to produce a harmonious smile 13 . Techniques to improve tooth color include the use of whitening toothpastes, professional cleaning by scaling and polishing to remove stain and tartar, tooth bleaching, microabrasion of enamel with abrasives and acid, and placement of crowns and veneers. Tooth bleaching, in particular, is an effective and conservative technique to treat discolored teeth [11][12][13] .
Several techniques and approaches available for vital tooth bleaching [11][12][13] vary in type of bleaching agent, its concentration, time of application, product presentation, application mode, and light activation [11][12][13] . Main differences between techniques consist in bleaching agent concentration and application time 11,12 . Three bleaching approaches have been used: at-home of both techniques 2,11,13 . For at-home bleaching, studies recommend the use of a low concentration of bleaching agent (10-16% carbamide peroxide) applied for at least 16 days 2,11,13 . In power bleaching, or in-office bleaching, hydrogen peroxide (25-38%) is applied for shorter time periods 2 .
As oxygen diffuses through enamel and dentin, it may affect the pulp 11,12,18,21,28 and result in tooth sensibility, an adverse effect of toxic components 2,3,12,15,27 . The low molecular weight of hydrogen peroxide promotes tooth bleaching, but the pulp, which may damage pulp cells 3,12,26,27 . The rate of hydrogen peroxide penetration differs between bleaching agents and depends on their concentration and time of application as well as on the presence or absence of restorations 3,17,21 . aggressors involves non-specific events that include vascular-exudative phenomena and cells and macrophages 1 . These cells play an important role in pulp defense, but they also participate in the degradation of the extracellular matrix, neovascularization, cell recruitment and repair 20,23,29 . Nevertheless, mast cells are responsible for the secretion of histamine, a vasodilator that participates in the early 1,7,16 . Several researchers evaluated the bleaching agents damage in dental pulps of animal models and in vitro studies 3,8,17,22 . However, few studies aimed to evaluate the effect of bleaching agents on human pulps 9,13,22,24 response should be better understood before a bleaching technique is clinically used. This study used immunochemistry to evaluate some tooth bleaching. The null hypothesis was that there would be no pulp changes after at-home

Sample selection
Twenty-nine human pulps were collected from caries-free third molars extracted for orthodontic reasons at the Dentistry Clinic of the School of Dentistry, Federal University of Goiás, Brazil. Patient's mean age was 23.5 years (ranging from 17 to 30 years). The clinical histories of all patients were reviewed to ensure that the experimental group included only healthy patients. All teeth extracted were fully erupted and healthy (no cracks, fractures, caries, or Hygenic Corp; Akron, OH, USA). This study was Ethics Committee of the institution where it was conducted, and all participants signed an informed consent form.

Study design
Pulp samples were randomly divided into three groups according to the bleaching technique used. Molars were extracted seven days after tooth bleaching. No tooth bleaching was used in the control group (CG) (n=7). In the second group, at-home bleaching with 15% carbamide peroxide (AH, n=10) (Opalescence PF 15-Ultradent Products; South Jordan, UT, USA) was applied for 16 days, 2 hours a day. In the third group, group (IO, n=12) (Opalescence Xtra Boost-Ultradent Products, South Jordan, UT, USA) was applied for 45 minutes in each of three visits. All tooth bleaching systems were used following manufacturer's instructions. Immediately

Semiquantitative, quantitative, and statistical analysis
For microscopic analysis, histological features and pulp tissue organization) were scored as described below.
The gradation of the inflammation was performed as described previously by Bruno, et al. 20 (2010). It was determined in 10 representative using an integration graticule (Carl Zeiss; Jena, Turingia, Germany). The specimens were scored The evaluation criteria for pulp tissue organization were adapted from Soares, et al. 14 (2014). Pulp tissue organization was scored as follows: 0, normal tissue, with preserved odontoblastic layer and central pulp; 1, disorganized odontoblastic layer, but normal central pulp; 2, total disorganization of pulp tissue morphology, but no areas of necrosis; 3, pulp necrosis. Collagen In immunohistochemistry, the number of cells or vessels/mm 2 of mast cells tryptase + , blood vessels CD31 + , and macrophage CD68 + were determined using an integration graticule (12.5x, 4740680000000-Carl Zeiss; Jena, Turingia, Germany). Only blood vessels with visible vascular lumens were counted. Cells and integration graticule had an area of 0.0961 mm 2 . Descriptive analyses were expressed as mean ± standard deviation (SD) of n observations, per mm 2 .
Data were analyzed using a chi-square test followed by the Mann-Whitney test for immunohistochemistry findings. Statistical analyses were performed using the SPSS 21.0 set at p<.05.

RESULTS
The microscopic analysis of the dental pulp samples in the CG showed that collagen was preserved (score 0) in 86%, pulp tissue was well were small-caliber blood vessels in the pulp tissue ( Figure 1A and 2A). In AH, collagen was preserved (score 0) and no inflammatory infiltrate was found (score 0) in 80% of the samples, whereas pulp tissue was disorganized (scores 1 and 2) in 60% of cases. There were a large number of congested small-caliber blood vessels ( Figure 1B and 2B). In contrast, in the pulp samples in IO, intense (score 2) in 75% of the cases, collagen was degraded (score 1) in 58%, and pulp tissue was disorganized (scores 1 and 2) in 83%. There were congested blood vessels of a larger caliber in the pulp samples ( Figures 1C and 2C). greater in IO than in AH and in the CG (p=0.038 and p=0.005, respectively). There were also differences in collagen degradation and pulp tissue organization between the samples in IO, since collagen was degraded and pulp tissue was disorganized, but this difference was not microscopic features of the samples.
The immunohistochemical analysis showed that CD68 + cells had a brown staining pattern in membranes and cytoplasm (Figure 4). In addition, CD31 was found in endothelial cells of blood vessels (Figure 3). No mast cells (tryptase + ) were found in the pulp samples analyzed.  Table 2). There was no relation between the number of macrophages and of blood vessel in IO, AH, and control groups (p>0.05).

DISCUSSION
Bleaching with 15% carbamide peroxide (athome bleaching) or 38% hydrogen peroxide (in-characterized by an increase in vascular dilation, intensity response. However, this response seemed

Histopathologic features
Group Scores  used. Thus, the null hypothesis was rejected. Dental materials, including bleaching agents 11,12,18,21,24,[26][27][28] , may cause cell damage in human dental pulp tissues 4,19,25 . The results of studies that examine the effects of bleaching agents on the pulp-dentin complex may be adopted, bleaching agent and its concentration, group of teeth that undergo bleaching, and duration and number of applications. Bowles and Thompson 5 (1986) studied the effects of heat and hydrogen peroxide on pulp enzymes and found that both agents tested had a destructive effect, since they inactivated those enzymes and consequently disrupted normal cell activities. Bowles and Ugwuneri 6 (1987) found that the use of high temperature increases the penetration of hydrogen peroxide into the dental pulp. Cintra, et al. 11     In our study, concentration and bleaching with increased macrophage migration was more intense in pulps in the AH group that in those in the (Table 1) showed that the IO group had the highest number of pulp samples with moderate or severe from the CG to the IO group is shown in Figure 1. Several factors may contribute to pulp agent concentration, application time, and tooth group. In a study on bleaching agent concentration and application time, Soares, et al. 26 (2014) bleaching techniques in pulp cells. They tested different agent concentrations (17.5% or 35%) and application times (1x5 min; 1x15 min; 3x15 min) using enamel and dentin discs placed on odontoblast-like cells (MDPC-23). The reduction in bleaching time to 5 minutes when hydrogen peroxide was used at 35% or a reduction of 17.5% in concentration for any period of time produced gradual changes in tooth color and reduced toxicity to pulp cells. Camargo, et al. 8 (2007) compared the presence of hydrogen peroxide in the pulp chamber of human and bovine teeth. In their analysis according to tooth thickness, thinner human teeth had higher amounts of hydrogen peroxide in the pulp chamber. Costa, et al. 12 (2010) found irreversible pulp changes and areas of necrosis in human incisors, but not in premolars that 24 (1980) and Kina, et al. 22 (2010) found no pulp changes in human premolars treated with should consider that human molars were used.
presence of mast cells (tryptase + ), macrophages (CD68 + ), and blood vessels (CD31 + ) in human dental pulp after the use of two bleaching techniques. The evaluation of the mast cell density, macrophages, and endothelial cells at the site of immunohistochemistry, allows investigating cells involved in diverse events of the innate immune response, such as vasodilation, angiogenesis, and extracellular matrix degradation, usually present in tissue aggression caused by chemical agents.
The present study demonstrated that there were no mast cells in human dental pulp in experimental and control groups. Mast cells are present in all connective tissues of the body, including those in the oral cavity, but there is still controversy about whether they are found 7,14,16 . Freitas, et al. 16 (2007) used immunohistochemistry to evaluate the presence of mast cells in 40 samples of human dental pulps of permanent teeth in different clinical circumstances: unerupted teeth, partially erupted teeth without dental caries, erupted teeth without dental caries, erupted teeth with shallow carious dentin, and teeth with hyperplastic pulpitis (pulp polyp). Mast cells were found only in the samples of hyperplastic pulpitis. Dockrill 14 (1961) also found mast cells only in pulp polyps. Similarly, + cells) mediators not secreted by mast cells, such as substance P (SP) 9 , may be responsible for the both in the center, next to blood vessels, and in the periphery 10 . Neuropeptides are key in the and occlusal trauma as well as after cavity preparation, application of dentin bonding agents, and tooth bleaching 6 . This study found a higher density of bleaching with 38% hydrogen peroxide (applied for 45 minutes in each of three visits), which suggests that this bleaching protocol may cause more aggressive damage in dental pulp than athome bleaching with 15% carbamide peroxide (applied for 16 days, 2 hours a day) ( Table 1  This study found no differences in pulp tissue organization between groups. The mechanical method of dental pulp removal used in this study might have disorganized the odontoblastic layer of all pulps and, therefore, affect the evaluation of this criterion. This is a limitation of this study, and future studies using mostly the same method but replacing mechanical removal with demineralization should contribute to the The use of third molars in this study might be a limitation, but it may contribute to the in this group of teeth, in which the structure of the enamel-dentin-pulp complex is different from that found in other groups. However, the thickness of the enamel-dentin of these teeth may be associated with the type of pulp response found for the bleaching protocols under evaluation. In teeth with a thinner enamel-dentin complex, as well as in samples with cracks, cervical lesions intense. For the tooth group evaluated here, practice may lead to damages.
Teeth were extracted seven days after bleaching have been different if teeth had been extracted after a longer time. Repair might have happened earlier, and a different response pattern might be found. Further clinical trials should include the extraction of teeth at different periods after the completion of tooth bleaching.
The clinical relevance of this study lies in techniques should be carefully selected and that this treatment should be selectively indicated, since mild to moderate short-term changes were bleaching.
38% hydrogen peroxide (applied for 45 minutes in each of three visits) caused higher macrophages pulp damage than at-home bleaching with 15% carbamide peroxide (applied for 16 days, 2 hours a day). The number of blood vessels was similar in all groups, regardless of the tooth bleaching technique employed. Mast cells were not found in pulp tissue and were probably not associated chemical aggression.

ACKNOWLEDGMENTS
related to this study. This study was supported in part by grants from CAPES -Coordination for the Improvement of Higher Education Personnel