Nancy Tomoko Sacono

Human pulp responses to in-office tooth bleaching

OBJECTIVE To evaluate and compare the responses of human incisor and premolar pulps after bleaching. STUDY DESIGN A bleaching agent with 38% hydrogen peroxide (H(2)O(2)) was applied on the buccal surface of 10 sound lower teeth (G1: 6 premolars; G2: 4 incisors) for 45 minutes. Three premolars and 3 incisors that received only rubber/pumice prophylaxis were used as control groups G3 and G4, respectively. Two days after the bleaching procedure, the teeth were extracted and processed for histologic evaluation. RESULTS Only in G2 (4 incisors) were any changes in the pulp detected. In the coronal pulp there was a large zone of coagulation necrosis. The radicular pulp showed mild inflammatory changes manifested as an accumulation of mononuclear cells around congested and dilated blood vessels. No pulpal damage was seen in either of the control groups (G3 and G4) or in group G1. CONCLUSION Bleaching with 38% H(2)O(2) for 45 minutes causes irreversible pulp damage in lower incisors but not in premolars.

Trans-enamel and trans-dentinal cytotoxic effects of a 35% H2O2 bleaching gel on cultured odontoblast cell lines after consecutive applications.

AIM To evaluate the trans-enamel and trans-dentinal cytotoxic effects of a 35% H(2)O(2) bleaching gel on an odontoblast-like cell lines (MDPC-23) after consecutive applications. METHODOLOGY Fifteen enamel/dentine discs were obtained from bovine central incisor teeth and placed individually in artificial pulp chambers. Three groups (n = 5 discs) were formed according to the following enamel treatments: G1: 35% H(2)O(2) bleaching gel (15 min); G2: 35% H(2)O(2) bleaching gel (15 min) + halogen light (20 s); G3: control (no treatment). After repeating the treatments three consecutive times, the extracts (culture medium + gel components that had diffused through enamel/dentine discs) in contact with the dentine were collected and applied to previously cultured MDPC-23 cells (50 000 cells cm(-2)) for 24 h. Cell metabolism was evaluated by the MTT assay and data were analysed statistically (alpha = 5%; Kruskal-Wallis and Mann-Whitney U-test). Cell morphology was analysed by scanning electron microscopy. RESULTS Cell metabolism decreased by 92.03% and 82.47% in G1 and G2 respectively. G1 and G2 differed significantly (P < 0.05) from G3. Regardless of halogen light activation, the application of the bleaching gel on the cultured odontoblast-like cells caused significantly more severe cytotoxic effects than those observed in the nontreated control group. In addition, significant morphological cell alterations were observed in G1 and G2. CONCLUSION After three consecutive applications of a 35% H(2)O(2) bleaching agent, the diffusion of the gel components through enamel and dentine caused severe toxic effects to cultured pulp cells.

Cytotoxic effect of a 35% hydrogen peroxide bleaching gel on odontoblast-like MDPC-23 cells

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.

Response of human pulps after professionally applied vital tooth bleaching

AIM To evaluate in vivo the microscopic pulpal response in sound human premolar teeth subjected to vital tooth bleaching with a 38% hydrogen peroxide (H(2)O(2)) bleaching gel (Opalescence X-tra Boost) catalysed or not by a halogen light source. METHODOLOGY Twelve pairs of sound maxillary and/or mandibular premolar teeth from 12 to 18-year-old patients were selected and randomly assigned to the following experimental (n = 10) and control (n = 4) groups: group 1: bleaching gel + halogen light; group 2: bleaching gel; group 3: no treatment (control). The teeth were extracted 2-15 days after bleaching and were subjected to routine laboratory processing for histological analysis of the pulpal response under light microscopy. RESULTS In almost all specimens of the experimental groups, the pulp tissue exhibited histological characteristics of normality. Only one specimen in each group exhibited some dilated and congested blood vessels among a discrete number of mononuclear inflammatory cells in the peripheral pulp region related to the buccal surface of the tooth. These specimens had a slight disruption to the odontoblastic layer, which characterized discrete tissue disorganization. Some deposition of reactionary dentine occurred in only one specimen of group 2. CONCLUSIONS Professionally applied vital tooth bleaching with a 38% H(2)O(2) gel with or without activation by a halogen light source did not cause damage to the pulp tissue of sound human premolar teeth.

Indirect cytotoxicity of a 35% hydrogen peroxide bleaching gel on cultured odontoblast-like cells

The aim of this study was to evaluate the trans-enamel and trans-dentinal effects of a 35% hydrogen peroxide (H2O2) bleaching gel on odontoblast-like cells. Enamel/dentin discs obtained from bovine incisors were mounted in artificial pulp chambers (APCs). Three groups were formed: G1- 35% H2O2; G2- 35% H2O2 + halogen light application; G3- control. The treatments were repeated 5 times and the APCs were incubated for 12 h. Then, the extract was collected and applied for 24 h on the cells. Cell metabolism, total protein dosage and cell morphology were evaluated. Cell metabolism decreased by 62.09% and 61.83% in G1 and G2, respectively. The depression of cell metabolism was statistically significant when G1 and G2 were compared to G3. Total protein dosage decreased by 93.13% and 91.80% in G1 and G2, respectively. The cells in G1 and G2 exhibited significant morphological alterations after contact with the extracts. Regardless of halogen light application, the extracts caused significantly more intense cytopathic effects compared to the control group. After 5 consecutive applications of a 35% H2O2 bleaching agent, either catalyzed or not by halogen light, products of gel degradation were capable to diffuse through enamel and dentin causing toxic effects to the cells.

Transenamel and transdentinal cytotoxicity of carbamide peroxide bleaching gels on odontoblast-like MDPC-23 cells

AIM To evaluate the transenamel and transdentinal cytotoxicity of bleaching gels based on carbamide peroxide (CP) on odontoblast-like cells after different contact times of the products with enamel. METHODOLOGY Enamel/dentine discs were obtained from bovine incisors and placed in artificial pulp chambers. Bleaching gels containing 10% or 16% CP were applied for 8 h day(-1) on the enamel side of the discs during periods of 1, 7 or 14 days. Deionized water and artificial saliva served as controls. The extracts (culture medium plus bleaching gel products that diffused through the discs) were collected and applied on previously cultured MDPC-23 cells for 1 h. Cell metabolism was evaluated by the MTT assay, and the data were analysed statistically by one-way anova and Tukeys test (α=0.05). Cell morphology was analysed by SEM. RESULTS There was no significant difference (P>0.05) between the controls and the groups bleached with 10% CP gel. In the groups bleached with 16% CP gel, however, cell metabolism decreased significantly (P<0.05) by 40.32%, 30.16% and 26.61% at 1, 7 and 14 days, respectively. There was no significant difference (P>0.05) between 1, 7 or 14 applications of the gels for either of the CP concentrations. CONCLUSION Regardless of the number of applications on an enamel surface, the 10% CP bleaching gel did not cause transenamel and transdentinal cytotoxicity to the MDPC-23 cell cultures. However, diffusion of products from the 16% CP gel through enamel and dentine and cytopathic effects to the pulp cells occurred even after a single application of this product on enamel.

Effect of Fluoride-Treated Enamel on Indirect Cytotoxicity of a 16% Carbamide Peroxide Bleaching Gel to Pulp Cells

The aim of this study was to evaluate the possibility of fluoride solutions applied to enamel to protect pulp cells against the trans-enamel and transdentinal cytotoxicity of a 16% carbamide peroxide (CP) bleaching gel. The CP gel was applied to enamel/dentin discs adapted to aicial pulp chambers (8 h/day) during 1, 7 or 14 days, followed by fluoride (0.05% or 0.2%) application for 1 min. The extracts (culture medium in contact with dentin) were applied to MDPC-23 cells for 1 h, and cell metabolism (MTT assay), alkaline phosphatase (ALP) activity and cell membrane damage (flow cytometry) were analyzed. Knoop microhardness of enamel was also evaluated. Data were analyzed statistically by ANOVA and Kruskal-Wallis tests (α=0.05). For the MTT assay and ALP activity, significant reductions between the control and the bleached groups were observed (p<0.05). No statistically significant difference occurred among bleached groups (p>0.05), regardless of fluoride application or treatment days. Flow cytometry analysis demonstrated 30% of cell membrane damage in all bleached groups. After 14 days of treatment, the fluoride-treated enamel presented significantly higher microhardness values than the bleached-only group (p<0.05). It was concluded that, regardless of the increase in enamel hardness due to the application of fluoride solutions, the treated enamel surface did not prevent the toxic effects caused by the 16% CP gel to odontoblast-like cells.

Mechanical and biological characterization of resin-modified glass-ionomer cement containing doxycycline hyclate

OBJECTIVES To characterize the mechanical and biological properties of a resin-modified glass ionomer cement (RMGIC) containing doxycycline hyclate. METHODS The antibacterial effect of RMGIC containing 1.5, 3.0 and 4.5% doxycycline hyclate was assessed using two experiments - agar diffusion test for 24h and biofilm assay for 24h and 7 days - against some cariogenic bacteria. Briefly, base layers of BHI agar and 300μL of each inoculum were prepared in Petri dishes with 6 wells that were completely filled with materials. After 24h incubation, zones of bacterial growth inhibition were measured using a digital caliper. Biofilm assays were conducted using RMGIC specimens immersed in 24-well plates containing the inoculum in BHI broth. After 24h and 7 days, each specimen were removed, vortexed and the suspension diluted and inoculated in BHI plates for subsequent bacterial counting. Cytotoxicity tests used 50 specimens made in sterilized metal molds, including Vitrebond as positive control. Extracts from every specimen were applied on the MDPC-23 odontoblast-like cells for 24h. The MTT assay and SEM evaluation determined cell metabolism and morphology, respectively. 80 cylindrical specimens were made from the previously cited groups, and were submitted to testing with a universal testing machine (Instron 4411) using a crosshead speed of 1.0mm/min for compressive strength and 0.5mm/min for diametral tensile strength, respectively. Data from antibacterial and cytotoxic effects, and mechanical properties were submitted to appropriated statistical tests. RESULTS All tested groups showed growth inhibition of all tested strains (p<0.05) in 24h for both microbiological tests, but only 4.5% doxycycline have antibacterial effect after 7 days. None of doxycycline concentrations caused toxic effect to the MDPC-23 cells or presenting alterations to mechanical properties. CONCLUSION The incorporation of up to 4.5% doxycycline hyclate into RMGIC inhibits important oral microorganisms, without modifying biological and mechanical characteristics of the dental material, suggesting a new alternative for the treatment of dental caries.

Mineral Loss and Morphological Changes in Dental Enamel Induced by a 16% Carbamide Peroxide Bleaching Gel

The aim of this study was to compare the effect of a 16% carbamide peroxide (CP) gel and a 10% CP gel on mineralized enamel content and morphology. Enamel blocks from bovine incisors were subjected to a 14-day treatment (8 h/day) with 10% or 16% CP gels. Knoop microhardness was evaluated before bleaching and at 1, 7 or 14 days after this treatment (50 g/15 s). Mineral content (energy-dispersive x-ray spectroscopy), surface roughness and topography (atomic force microscopy) were evaluated at the 14-day period. Data were analyzed statistically by two-way ANOVA and Tukeys test (α=0.05). Significant microhardness reduction was observed at the 7 th and 14 th days for 10% CP gel, and for all bleaching times for 16% CP gel (p<0.05). At the 14-day period, a significant decrease in Ca and P content, increase on surface roughness (p<0.05) as well as on picks and valleys distance were observed when both bleaching gels were used. These enamel alterations were more intense for 16% CP gel. It was concluded that both CP-based gels promoted loss of mineral structure from enamel, resulting in a rough and porous surface. However, 16% CP gel caused the most intense adverse effects on enamel.

Toxic effects of daily applications of 10% carbamide peroxide on odontoblast-like MDPC-23 cells

Abstract Background. Tooth bleaching has been widely studied, mainly due to the possible undesirable effects that can be caused by this esthetic procedure. The cytotoxicity of the bleaching agents and its components to pulp cells has been demonstrated in several researches. The aim of this study was to evaluate the toxic effects of successive applications of 10% carbamide peroxide (CP) gel on odontoblast-like cells. Materials and methods. Enamel-dentin discs obtained from bovine incisors were adapted to artificial pulp chambers (APCs). The groups were formed as follows: G1: Without treatment (control group); G2: 10% carbamide peroxide, CP (five applications/one per day); G3: 10% CP (one unique application); and G4: 35% hydrogen peroxide, HP (three applications of 15 min each). After treatment, cell metabolism (MTT), alkaline phosphatase (ALP) activity and plasma membrane damage (flow cytometry) were analyzed. Results. Reductions in cell metabolism and alkaline phosphatase activity along with severe damage of the cytoplasmic membrane were noted in G2. In G3, no damage was observed, compared to the control group. Intermediary values of toxicity were obtained after 35% HP application. Conclusion. It can be concluded that one application of 10% CP did not cause toxic effects in odontoblast-like cells, but the successive application of this product promoted severe cytotoxic effects. The daily application of the bleaching agents, such as used in the at-home bleaching technique, can increase the damages caused by this treatment to the dental pulp cells.