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Introduction: The use of natural products such as essential oils has been suggested due to their promising pharmacological effects and economic viability. This study aimed to determine hydrogenic potential (pH), titratable acidity (TA), and ion concentrations of five solutions containing essential oils (EO), when used as a EO-containing solutions, and evaluate ion concentrations, enamel surface loss, and morphology alterations in enamel. Materials and methods: The pH, TA, calcium (Ca), potassium (K), and sodium (Na) concentrations of five EO-containing solutions were measured. Bovine enamel specimens were submitted to two daily 30-s immersions in artificial saliva, citric acid, distilled water, BaCloTea (Basil, Clove e Tea Tree), GeLaTeaPep (Geranium, Lavender, Tea Tree and Peppermint), EucaLem (Eucalyptus and Lemon), Cinnamon, or Spearmint solutions for 14 days. Ca, K, Na, and phosphorus (P) were quantified through ions chromatography, enamel surface loss was determined by profilometry, and surface morphology was qualitatively analyzed through scanning electron microscopy. Data were submitted to one-way ANOVA and Tukey (p < 0.05). Results: The five EO-containing solutions presented significantly lower pH values than distilled water (p < 0.05). The GeLaTeaPep group presented a significantly higher TA value than BaCloTea (p < 0.05), which in turn showed a significantly higher TA value than the other solutions (p < 0.05). The distilled water presented significantly higher Ca, K, and Na concentrations than all EO-containing solutions (p < 0.05). The enamel exposed to EO-containing solutions showed lower Ca and P concentrations than artificial saliva (control) as well as significantly higher surface loss; however, the surface morphology was similar to the artificial saliva. Conclusion: EO-containing solutions have low pH, TA, and low concentrations of Ca, Na, and K. Moreover, enamel exposed to these solutions showed low Ca and P concentrations and slight surface loss without morphology alteration.

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The objective of this study was to evaluate different delaying times after bleaching and the use of different sodium ascorbate (SA) concentrations (10% and 35%) in the bond strength of adhesive cementation to enamel. This study used 54 sound bovine incisors, which were randomly assigned to the following groups: G1 (unbleached/control+ adhesive cementation (AC)); G2 (bleached + AC after 7 days); G3 (bleached + 10% SA + AC after 24 h); G4 (bleached + 10% SA + AC after 7 days); G5 (bleached + 35% SA + AC after 24 h); and G6 (bleached + 35% SA + AC after 7 days). After bleaching, G3, G4, G5, and G6 received an application of SA before the cylinders build up with RelyX Veneer cement. The samples were subjected to microshear test, and the results were analyzed by two-way ANOVA with Tukey's post hoc test. Group one presented the highest mean bond strength (19.1 MPa) and G3 the lowest (16.96 MPa). There was no statistical difference between the groups tested (p ˃ 0.05). The fracture pattern observed was predominantly mixed. The adhesive cementation may be performed 24 h after bleaching when SA (10% or 35%) is used or after 7 days, without compromising bond strength.

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Aim: The study evaluated the influence of tucupi on enamel surface roughness, microhardness, ultramorphology, and mass variation. Materials and Methods: Ninety healthy bovine incisors were divided into three experimental groups, according to the acidic challenge adopted, being: G1- tucupi, G2- cola-based soft drink, G3-distilled water. The enamel properties (surface roughness, microhardness, ultramorphology and mass variation) of all specimens were evaluated at times T0 (before any intervention), T10 (10 days after the proposed treatments), T20 (20 days after the proposed treatments) and T30 (30 days after the proposed treatments). After confirming the normality of the data (Shapiro-Wilk test), a two-way ANOVA (α = 5%) was performed, followed by Sidak post-test, with results described as mean and standard deviation. Results: The roughness means increased for all tested groups, with no statistical difference only in G3 for all evaluated times. Microhardness of all groups showed a significant decrease over the time, with the lowest average observed in G1 in T30. Considering enamel mass variation, the lowest average was in G2 at time T3, with no statistical difference only in G3 (distilled water) over the time. Regarding ultramorphology (scanning electron microscopy - SEM), only groups G1 and G2, that were exposed to acidic challenges, showed disorganization of the enamel surface layer. Conclusion: It was possible to conclude that tucupi has low pH and high titratable total acidity, being able to gradually decrease enamel microhardness, increasing surface roughness and causing loss of dental enamel.

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This study aimed to evaluate the effects of 22% carbamide peroxide combined with an erosive challenge and simulated brushing on enamel. Bovine incisor teeth were divided into G1, tooth bleaching; G2, tooth bleaching + erosive challenge; and G3, tooth bleaching + erosive challenge + simulated brushing, and evaluated at T0, before any intervention; T1, 14 days after the proposed treatments; and T2, 28 days after the proposed treatments. Tooth bleaching was performed daily for 1 h for 28 days. The microhardness, surface roughness, mass variation, and ultrastructure were analyzed at T0, T1, and T2. Two-way analysis of variance for repeated measures was performed and Tukey's post hoc test (α = 5%) was used. The surface roughness increased in groups G2 and G3 as a function of time, whereas microhardness and mass measurements demonstrated a significant reduction for groups associated with challenges. Ultrastructural evaluation indicated a loss of the aprismatic layer and exposure of the enamel prisms in all groups after 14 days of bleaching, with more pronounced results in G2 and G3 after 28 days. In conclusion, abrasive and erosive challenges potentiated the deleterious effects of tooth whitening on microhardness, ultramorphology, and mass, without affecting the roughness of dental enamel.

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The aim of this in vitro study was to assess the bond strength of self-etching adhesives containing HEMA and 10-MDP monomers. Twenty-four bovine teeth were divided into three groups. Two cylinders of composite resin were made in each tooth (n = 16): G1-Prime and Bond Universal (control); G2-OptiBond All-in-One (HEMA); and G3-Clearfil SE (10-MDP and HEMA). After 24-hour storage in distilled water, the specimens were fixed to a universal testing machine (Kratos Equipamentos Ltda.) for the microshear test at a speed of 0.5 mm/min. A qualitative analysis of the fracture pattern was also performed using scanning electron microscopy (500× magnification). The normality of sample data distribution was determined using the Shapiro-Wilk test. The results were assessed using the Kruskal-Wallis test, and α level of 5% was used for the analysis. The results indicated a statistical difference (p > 0.05) between G3 (15.6080 MPa) and G2 (11.2180 MPa). No statistical difference was observed when G1 (14,6325 MPa) was compared with the other two groups. It was also observed that a mixed fracture pattern was predominant in all groups. The self-etching adhesive containing HEMA and 10-MDP monomers showed to be promising in increasing the bond strength between the dental substrate and the composite resin, whereas the adhesive containing only HEMA exhibited lower bond strength to dentin.

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This in vitro study evaluated the anti-erosive effect of an experimental varnish containing 5% stannous chloride (SnCl2) associated with different concentrations of NaF (NaF-free, 2.5% NaF, or 5.2% NaF) on bovine enamel and root dentin. One hundred samples were pre-eroded (0.3% citric acid, pH 2.6, 10 min) and randomized into five groups (n=10 for each substrate): Negative control - milli-Q water; NaF-free - Experimental varnish SnCl2-free and NaF-free; 2.5 NaF - Experimental varnish 5% SnCl2 associated with 2.5% NaF; 5.2 NaF: Experimental varnish 5% SnCl2 associated with 5.2% NaF and positive control - Commercial varnish containing 5% NaF (Duraphat). After the varnishes were applied, the erosive and abrasive challenges were carried out for five days. Loss of tooth structure (TSL) was determined by optical profilometry, and the loss of calcium (ΔCa2+) using atomic absorption spectroscopy. Dentin analysis was also performed by SEM. A one-way ANOVA/Bonferroni test was performed to analyze the data (α=0.05). The experimental 2.5 NaF and 5.2 NaF groups showed greater effectiveness in preventing TSL when compared to the other groups (p <0.05), regardless of the substrate. In addition, these groups showed lower loss in Ca2+ content when compared to the other groups (p <0.05), for enamel and dentin. Dentin showed greater TSL and ΔCa2+ loss when compared to enamel in all treatments (p <0.05). The 5.2% and 2.5% NaF-containing experimental varnishes showed promising results in both, the prevention of TSL and the loss of Ca2+, regardless of the substrate studied.

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Abstract This in vitro study evaluated the anti-erosive effect of an experimental varnish containing 5% stannous chloride (SnCl₂) associated with different concentrations of NaF (NaF-free, 2.5% NaF, or 5.2% NaF) on bovine enamel and root dentin. One hundred samples were pre-eroded (0.3% citric acid, pH 2.6, 10 min) and randomized into five groups (n=10 for each substrate): Negative control - milli-Q water; NaF-free - Experimental varnish SnCl₂-free and NaF-free; 2.5 NaF - Experimental varnish 5% SnCl₂ associated with 2.5% NaF; 5.2 NaF: Experimental varnish 5% SnCl₂ associated with 5.2% NaF and positive control - Commercial varnish containing 5% NaF (Duraphat). After the varnishes were applied, the erosive and abrasive challenges were carried out for five days. Loss of tooth structure (TSL) was determined by optical profilometry, and the loss of calcium (ΔCa2+) using atomic absorption spectroscopy. Dentin analysis was also performed by SEM. A one-way ANOVA/Bonferroni test was performed to analyze the data (α=0.05). The experimental 2.5 NaF and 5.2 NaF groups showed greater effectiveness in preventing TSL when compared to the other groups (p <0.05), regardless of the substrate. In addition, these groups showed lower loss in Ca2+ content when compared to the other groups (p <0.05), for enamel and dentin. Dentin showed greater TSL and ΔCa2+ loss when compared to enamel in all treatments (p <0.05). The 5.2% and 2.5% NaF-containing experimental varnishes showed promising results in both, the prevention of TSL and the loss of Ca2+, regardless of the substrate studied.

Resumo Este estudo in vitro avaliou o efeito anti-erosivo de um verniz experimental contendo 5% de cloreto estanoso (SnCl₂) associado a diferentes concentrações de NaF (sem NaF, 2,5% NaF ou 5,2% NaF) sobre esmalte e dentina radicular bovinos. Cem amostras foram pré-erodidas (ácido cítrico 0,3%, pH 2,6, 10 min) e randomizadas em cinco grupos (n=10 para cada substrato): Controle negativo - água milli-Q; Sem NaF - Verniz experimental sem SnCl2 e sem NaF; 2,5 NaF - Verniz experimental 5% SnCl2 associado a 2,5% NaF; 5,2 NaF: Verniz experimental 5% SnCl2 associado a 5,2% NaF e controle positivo - Verniz comercial contendo 5% NaF (Duraphat). Após a aplicação dos vernizes, os desafios erosivos e abrasivos foram realizados por cinco dias. A perda de estrutura dentária (PED) foi determinada por perfilometria óptica e a perda de cálcio (ΔCa2+) por espectroscopia de absorção atômica. A análise da dentina também foi realizada por MEV. Um teste ANOVA/Bonferroni de uma via foi realizado para analisar os dados (α=0,05). Os grupos experimentais 2,5 NaF e 5,2 NaF apresentaram maior eficácia na prevenção de PED quando comparados aos demais grupos (p<0,05), independentemente do substrato. Além disso, esses grupos apresentaram menor perda no teor de Ca2+ quando comparados aos demais grupos (p<0,05), para esmalte e dentina. A dentina apresentou maior PED e de ΔCa2+ quando comparada ao esmalte em todos os tratamentos (p<0,05). Os vernizes experimentais contendo NaF 5,2% e 2,5% apresentaram resultados promissores tanto na prevenção de PED quanto na perda de Ca2+, independente do substrato estudado.

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The ultrastructural and mechanical properties of enamel surface were evaluated after prolonged bleaching treatments with 10% carbamide peroxide in the presence or absence of orange juice (erosive challenge) and toothbrushing (abrasive challenge). In total, 145 incisor bovine teeth were used in this study. Twenty-five samples were prepared for the ultrastructural evaluations, and 120 samples were prepared for microhardness and roughness tests. These 120 samples were divided into eight experimental groups (n = 15): G1- artificial saliva; G2- abrasion; G3- erosion; G4- dental bleaching; G5- erosion + abrasion; G6- bleaching + abrasion; G7- bleaching + erosion; and G8- bleaching + erosion + abrasion. All groups were tested at T0 (before treatment), T1 (14 days), T2 (21 days), and T3 (28 days). Two-way analysis of variance for repeated measures and the post hoc Sidak tests (p ≤ 0.05) were used. The roughness evaluation demonstrated an increase in damage for all experimental groups with an increase in the time period. For microhardness, the groups exposed to artificial saliva (AS) and abrasive challenge did not show any differences at any time points, while the other groups showed a decrease in microhardness from T0 to T3. Ultrastructural evaluation showed different surface alterations in response to the treatments. Despite prolonged bleaching periods, the procedure caused lesser enamel surface alterations than exposure to orange juice alone or in combination with brushing.

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OBJECTIVE: Reporting of randomized controlled trials (RCTs) in dentistry remains suboptimal. Considering the positive impact of the Consolidated Standards of Reporting Trials (CONSORT) guidelines on the quality of evidence in RCTs, the main objective of this systematic review was to determine whether RCTs on dental caries prevention conform to these guidelines. The secondary objective was to assess the association between CONSORT adherence and the year and impact factor of the journal in which the study was published. METHODS: A systematic search was conducted in different databases using appropriate terms to retrieve RCTs that assessed the caries-preventive effect of at least 2 of the following materials-fluoride varnish, resin-based fissure sealants, and ionomer-based fissure sealants-on the occlusal surfaces of permanent molars. Since the first CONSORT statement was published in 1996, a time frame from 1997 to 2020 was established for the identification of studies. Selected articles were assessed according to their adherence to the CONSORT statement, risk of bias (Cochrane risk of bias tool, RoB 2.0), and journal impact factor based on the InCites Journal Citation Reports. The year of publication and other relevant data were also recorded. SPSS (SPSS Statistics 25.0, IBM©) was used to perform the linear correlation analyses to determine the relationship between the article CONSORT score (previously determined) and the year of publication and journal impact factor. A significance level of 5% was established for all analyses. RESULTS: Of 3196 references retrieved, 30 articles were selected and evaluated. Using RoB 2.0, 8 studies were classified as having a high risk of bias, 16 as having some concerns about the risk of bias assessment, and 6 as having a low risk of bias. Concerning CONSORT adherence, 77% of the studies adequately reported the intervention domain, since the methodology for the application of fluoride varnish or sealant materials was thoroughly described. However, the participants' setting and location, random sequence generation, randomization, and the flowchart description of the losses/exclusions domains were poorly reported. Meanwhile, the allocation concealment process was not reported in 83% of the articles. Correlation analyses indicated a positive relationship between CONSORT adherence and the year of publication, as well as the journal impact factor. CONCLUSION: When assessing clinical trials on the prevention of occlusal caries, most RCTs examined followed the CONSORT statement. However, some methodological domains remain poorly reported, demonstrating the need to improve CONSORT compliance in these RCTs.

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The objective of this study was to determine the enamel mass variation after a prolonged bleaching treatment using a calcium-containing 4% hydrogen peroxide gel Twenty sound bovine incisors were randomly assigned to two groups (n=10) stored in G1) distilled water and G2) artificial saliva. An electronic analytic scale (.000 grams measurements) was used to determine the enamel mass variation before and after the bleaching procedures at the following evaluation times: T0) before the bleaching procedures; T1) 14 days of treatment, as instructed by the manufacturer; T2) 21 days of treatment, 50 % beyond what is instructed by the manufacturer; and T3) 28 days of treatment, 100 % beyond what is instructed by the manufacturer. The highest mean was observed at T2/G2 (0.3259 g) and the lowest at T2/G1 (0.3265 g). The specimens stored in distilled water (G1) showed 6 % mass reduction when T0 (0.3277 g) was compared to T3 (0.3277 g). On the other hand, the specimens stored in artificial saliva exhibited a significant mass increase of 19 % when T0 (0.3521 g) was compared to T3 (0.3528 g). Prolonged bleaching therapy using 4 % hydrogen peroxide with calcium resulted in a massive reduction when water was used as a storage medium. When the specimens were stored in artificial saliva, an increase in mass was observed, probably due to the mineralizing properties of the artificial saliva.

El objetivo de este estudio fue determinar la variación de la masa del esmalte después de un tratamiento de blanqueamiento prolongado utilizando calcio conteniendo un gel de peróxido de hidrógeno al 4 %. Veinte incisivos bovinos intactos fueron asignados aleatoriamente a dos grupos (n-10) almacenados en G1 - agua destilada y G2- saliva artificial. Se utilizó una escala analítica electrónica (.000 gramos) para determinar la variación de la masa de esmalte antes y después de los procedimientos de blanqueamiento en los siguientes tiempos de evaluación: T0) antes de los procedimientos blanqueadores; T1) 14 días de tratamiento, según las instrucciones del fabricante; T2) 21 días de tratamiento, 50 % más allá del tiempo indicado por el fabricante; y T3) 28 días de tratamiento, 100 % más allá del tiempo indicado por el fabricante. La media más alta se observó en T2/G2 (0,3259 g) y la más baja en T2/G1 (0,3265 g). Los especímenes almacenados en agua destilada (G1) mostraron una reducción de masa del 6 % cuando se comparó T0 (0,3277 g) con T3 (0,3277 g). Por otro lado, los dientes almacenados en saliva artificial mostraron un aumento significativo de masa del 19 % cuando se comparó T0 (0,3521 g) con T3 (0,3528 g). La terapia de blanqueamiemto prolongado con calcio conteniendo un gel de peróxido de hidrógeno al 4 % condujo a una reducción masiva cuando se utilizó agua como medio de almacenamiento, mientras que los dientes almacenados en saliva artificial mostraron un aumento en la masa, probablemente debido a las propiedades remineralizadoras de la saliva artificial.

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Abstract The ultrastructural and mechanical properties of enamel surface were evaluated after prolonged bleaching treatments with 10% carbamide peroxide in the presence or absence of orange juice (erosive challenge) and toothbrushing (abrasive challenge). In total, 145 incisor bovine teeth were used in this study. Twenty-five samples were prepared for the ultrastructural evaluations, and 120 samples were prepared for microhardness and roughness tests. These 120 samples were divided into eight experimental groups (n = 15): G1- artificial saliva; G2- abrasion; G3- erosion; G4- dental bleaching; G5- erosion + abrasion; G6- bleaching + abrasion; G7- bleaching + erosion; and G8- bleaching + erosion + abrasion. All groups were tested at T0 (before treatment), T1 (14 days), T2 (21 days), and T3 (28 days). Two-way analysis of variance for repeated measures and the post hoc Sidak tests (p ≤ 0.05) were used. The roughness evaluation demonstrated an increase in damage for all experimental groups with an increase in the time period. For microhardness, the groups exposed to artificial saliva (AS) and abrasive challenge did not show any differences at any time points, while the other groups showed a decrease in microhardness from T0 to T3. Ultrastructural evaluation showed different surface alterations in response to the treatments. Despite prolonged bleaching periods, the procedure caused lesser enamel surface alterations than exposure to orange juice alone or in combination with brushing.

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This study evaluated the effect of different time intervals between tooth bleaching sessions on the variation of tooth enamel mass, using a 35% hydrogen peroxide (HP35) gel. Twenty bovine incisor teeth were collected and cross-sectioned twice, leaving only the middle coronal portion. The dentin layer was removed, leaving only the buccal dental enamel. The samples were randomly divided into 2 groups (n = 10): G1 (with a 7-day time interval between each bleaching session), and G2 (with a 2-day time interval between each bleaching session). Three bleaching sessions were performed for each group. Each specimen's mass was measured using an electronic analytical scale, first at the beginning of the experiments (T0), and then immediately after each bleaching intervention (T1, T2 and T3, respectively). All samples were stored in artificial saliva and kept in a biological chamber during the time of the study. The data analysis was performed using ANOVA for the related samples (p = 0.05). The results showed a reduction in the enamel mass values in G2 after the 3rd session when comparing to enamel mass values presented at the beginning of the study. On the other hand, G1 presented an increase in the mass values at the end of the third session, and these intragroup differences were statistically significant (p <0.001). It was concluded that bleaching treatment with 7-day intervals between sessions leads to no tooth enamel mass loss, whereas the reduced 2­day time interval between sessions caused a significant tooth enamel mass loss. (AU)

Este estudo avaliou a influência de diferentes intervalos de tempo entre as sessões de clareamento com peróxido de hidrogênio a 35% (PH35) sobre a variação de massa do esmalte dental. Foram utilizados 20 dentes incisivos bovinos hígidos, seccionados em duas porções transversais, com a camada de dentina vestibular toda removida, restando apenas o esmalte dental vestibular. As amostras foram distribuídas em 2 grupos (n=10): G1 - intervalo de tempo de 7 dias entre as sessões de clareamento, e G2 - Intervalo de 2 dias entre as sessões de clareamento. Foram realizadas 3 aplicações de gel clareador em cada grupo. A pesagem dos espécimes foi realizada antes do início do tratamento clareador e ao final de cada intervenção clareadora, em uma balança analítica eletrônica. Os espécimes foram armazenados em saliva artificial, e mantidos em estufa biológica. Os dados foram submetidos à ANOVA para amostras relacionadas (p=0.05). O G2 apresentou uma redução nos valores de massa do esmalte quando comparados os tempos antes do clareamento (T0 - 0.1650g) e após a 3° sessão (T3 - 0.1643g). Entretanto, o G1 apresentou um aumento nos valores de massa ao término da terceira sessão (T0 - 0.1615g e T3 - 0.1624g), sendo essas diferenças intragrupos estatisticamente significantes (p<0.001). Foi possível concluir que no clareamento com intervalo de 7 dias entre as sessões não houve perda de massa do esmalte dental, ao passo que quando reduzido o intervalo entre as sessões para 2 dias, uma perda significativa de massa foi observada. (AU)

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AIM: This study evaluated the effect of sodium ascorbate (SA) on the proteolytic activity of matrix metalloproteinases (MMPs) and investigated the related effects on the bond strength of bleached dentin. MATERIALS AND METHODS: Eighty freshly extracted human third molars were randomly divided according to treatment (bleaching or SA application), type of analysis (microshear or measuring MMP activity), and post-bleaching time to assess bond strength (24 hrs or 30 days). Data from both analyses were subjected to one-way analysis of variance to detect differences among groups, followed by Tukey's multiple comparison test (p≤0.05). RESULTS: Dental bleaching significantly reduced bond strength values when the adhesive strategy was performed after 24 hrs (despite the SA treatment) or 30 days after the bleaching procedure. However, after 30 days, the bond strength values of the groups who received bleaching or SA application were similar to those of the unbleached group. Dental bleaching caused the activation of MMPs, and SA did not influence this activity. CONCLUSION: It was concluded that SA does not affect the activity of MMPs or the bond strength in bleached dentin immediately after the bleaching treatment.

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ABSTRACT: The objective evaluate was the influence of prolonged tooth bleaching with 10 % carbamide peroxide (10CP) on tooth enamel mass variation. Ten healthy bovine incisor teeth were divided (n = 5) into G1 - storage in distilled water and G2 - storage in artificial saliva. The samples were weighed in an electronic analytical balance at the following times: T0 - before application of the bleaching gel, T1 - after 14 days of bleaching (the time recommended by the manufacturer), T2 - after 21 days of bleaching (50 % increase in the time recommended by the manufacturer), and T3 - after 28 days of bleaching (100 % increase in the time recommended by the manufacturer). The data were subjected to ANOVA for related samples (p = 0.05). The highest mean was observed in G2 (0.5982 g) and the lowest mean was observed in G1 (0.3074 g) at T2 and T3, respectively. Significant differences were observed between the groups at all times. Overall, 10CP caused variation in the enamel mass after a 100 % increase in the use time recommended by the manufacturer, with a decrease in mass when distilled water was used as the storage medium and an increase when artificial saliva was used.

RESUMEN: El objetivo fue investigar la influencia del blanqueamiento dental prolongado con peróxido de carbamida al 10 % (10CP) sobre la variación de masa del esmalte dental. Las muestras se dividieron en dos grupos: G1, diez dientes sanos de los incisivos bovinos (n = 5) en agua destilada, y G2, almacenamiento en saliva artificial. Las muestras se midieron en una escala analítica electrónica de precisión en los siguientes tiempos: T0-antes de la aplicación del gel blanqueador, T1-después de 14 días de blanqueo (el tiempo recomendado por el fabricante), T2-después de 21 días de blanqueo (aumento de 50 % en el tiempo recomendado por el fabricante), y T3-después de 28 días de blanqueo (aumento de 100 % en el tiempo recomendado por el fabricante). Los datos se presentaron al ANOVA para las muestras relacionadas (P = 0,5). La media más alta se observó en G2 (0,5982 g) y la media más baja se observó en G1 (0,3074 g) en T2 y T3, respectivamente. Se observaron diferencias significativas entre los grupos en todo momento. En general, la 10 CP causó variación en la masa del esmalte después de un aumento de 100 % en el tiempo de uso recomendado por el fabricante, con una disminución en la masa cuando el agua destilada se utilizó como medio de almacenamiento y aumentó cuando se usó saliva artificial.

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BACKGROUND: Dental bleaching has been increasingly sought out to improve dental aesthetics, but it may cause changes in dental enamel. OBJECTIVE: To assess the influence of different time intervals on bleaching gel applications with regard to the Microhardness (MH) and Surface Roughness (SR) on dental enamel. MATERIAL AND METHODS: Forty bovine incisors were randomly divided into two groups (G1 and G2) and both were bleached with 35% Hydrogen Peroxide (HP35) (n=20; G1: seven-day interval and G2: two-day interval). The MH and SR tests were performed before bleaching (T0) and after the first (T1), second (T2), and third (T3) bleaching gel applications. The specimens were stored in artificial saliva between each application (37°C). The data were analyzed using the student's t-test (p ≤ 0.05) for dependent samples. RESULTS: The reduced time interval (two days) led to a significant reduction in MH, while MH was not affected during the seven-day interval. The SR results increased regardless of the bleaching gel application time interval. CONCLUSION: The decreased time interval of two days between bleaching gel applications caused changes in MH but did not influence the SR of dental enamel.

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INTRODUCTION: The aim of this in vitro study was to evaluate the effects of sodium hypochlorite (NaOCl), ethylenediaminetetraacetic acid (EDTA), chlorhexidine (CHX) and hydroxyethylidene bisphosphonate (HEBP), also known as etidronate, on susceptibility to root fracture resistance (RFR) in human teeth subjected to endodontic preparation. METHODS AND MATERIALS: Seventy extracted single-rooted human teeth were selected, endodontically prepared using the ProTaper Next rotary system (PTN, Dentsply, Maillefer, Ballaigues, Switzerland) and then randomly divided according to the following irrigation regimes (n=10): G1, saline solution (0.9% NaCl); G2, 2.5% NaOCl + 17% EDTA; G3, 2% CHX gel + 17% EDTA; and G4, a mixture of 5% NaOCl + 18% HEBP. After this step, all samples received a final irrigation with distilled water. The samples were subjected to axial forces by mechanical compression testing in a universal testing machine (Dynamometers KRATOS, LTDA, SP, Brazil). Data analyses included the Shapiro-Wilk normality test, analysis of variance (one-way ANOVA) and a subsequent multiple comparison test (Tukey's test). RESULTS: The results indicated that G1 (0.9% NaCl) presented greater resistance to root fracture. No significant differences were observed in G2 (2.5% NaOCl + 17% EDTA) and G3 (2% CHX gel + 17% EDTA). A significant difference was identified in G4 (mixture of 5% NaOCl + 18% HEBP) (P<0.05). CONCLUSION: A mixture of 5% NaOCl + 18% HEBP resulted in a lower fracture resistance when used to irrigate canals during endodontic instrumentation.