Influence of exposure time to saliva and antioxidant treatment on bond strength to enamel after tooth bleaching: an in situ study

Objectives: This study evaluated the influence of different exposure times to saliva in situ in comparison with an antioxidant treatment on composite resin bond strength to human enamel restored after tooth bleaching. Material and Methods: Forty human teeth specimens measuring 5x5 mm were prepared and randomly allocated into 5 groups with 8 specimens each: Gct (control group, restored on unbleached enamel); Gbl (restored immediately after bleaching); Gsa (bleached, treated with 10% sodium ascorbate gel for 60 min and restored); G7d (bleached, exposed to saliva in situ for 7 days and restored); and G14d (bleached, exposed to saliva in situ for 14 days and restored). Restored samples were cut into 0.8 mm2 sticks that were tested in microtensile. Specimens were microscopically analyzed and failure modes were classified as adhesive, cohesive, or mixed. Pretest and cohesive failures were not considered in the statistical analysis, which was performed with one-way ANOVA and Tukey's post-hoc test (α=0.05), with the dental specimen considered as the experimental unit. Results: Mean bond strength results found for Gbl in comparison with Gct indicated that bleaching significantly reduced enamel adhesiveness (P<0.01). However, no statistically significant differences were found between Gct, Gsa and G7d (P>0.05). Bond strength found for G14d was significantly higher than for Gsa (P<0.01). Fractures modes were predominantly of a mixed type. Conclusions: Bonding strength to bleached enamel was immediately restored with the application of sodium ascorbate and exposure to human saliva in situ for at least 7 days. Best results were obtained with exposure to human saliva in situ for 14 days. Treatment with sodium ascorbate gel for 60 min may be recommended in cases patients cannot wait for at least 7 days for adhesive techniques to be performed. .

Chemical cleaning agents and bonding to glass-fiber posts

The influence of chemical cleaning agents on the bond strength between resin cement and glass-fiber posts was investigated. The treatments included 10% hydrofluoric acid, 35% phosphoric acid, 50% hydrogen peroxide, acetone, dichloromethane, ethanol, isopropanol, and tetrahydrofuran. Flat glass-fiber epoxy substrates were exposed to the cleaners for 60 s. Resin cement cylinders were formed on the surfaces and tested in shear. All treatments provided increased bond strength compared to untreated control specimens. All failures were interfacial. Although all agents improved the bond strength, dichloromethane and isopropanol were particularly effective.

Effect of high-concentrated bleaching agents on the bond strength at dentin/resin interface and flexural strength of dentin

This study evaluated the effect of bleaching agents on bond strength at the dentin/resin interface and the flexural strength of dentin. Forty maxillary canines were selected for the study. In the shear strength test, 40 slabs of intracoronary dentin (5 x 5 mm) obtained from buccal surfaces of the crowns were included in acrylic resin. In the flexural strength test, 40 dentin bars (8 x 2 x 2 mm) were obtained from the roots. The 40 hemi-sections of the lingual surface were prepared for scanning electron microscopy (SEM). The specimens were divided into 4 groups according to the bleaching protocol (n=10): Unbleached (control), Sodium perborate + 20 percent hydrogen peroxide (SP + 20 percent HP), 37 percent carbamide peroxide (37 percent CP) and 38 percent hydrogen peroxide (38 percent HP). After 7 days, the bond strength specimens were restored and tested. Dentin bars were bleached and subjected to a three-point bending test. Data (MPa) were analyzed by ANOVA and Tukey's test (α=0.05). In the shear test, the control group was superior (p<0.05) to the bleached groups, which, in turn, were statistically similar (p>0.05). In the flexural strength test, the control group also had the highest values and differed significantly from the other groups (p<0.05). SEM revealed smear layer in all groups, with fissures in the bleached specimens. SP + 20 percent HP and 38 percent HP showed discontinuous interfaces with few tags. In conclusion, bond strength of restorative material to dentin and flexural strength of dentin were reduced after the use of high-concentration bleaching agents.

Este estudo avaliou o efeito de agentes clareadores na resistência de união da interface dentina/resina e resistência à flexão da dentina. Quarenta caninos superiores foram selecionados para o estudo. No teste de cisalhamento, 40 fragmentos de dentina intracoronária (5 x 5 mm) obtidos a partir de superfícies vestibulares das coroas foram incluídos em resina acrílica. No teste de flexão, 40 barras de dentina (8 x 2 x 2 mm) foram obtidas a partir das raízes. As 40 hemi-seções da superfície lingual foram preparadas para microscopia eletrônica de varredura (MEV). Os espécimes foram divididos em 4 grupos de acordo com o protocolo de clareamento (n=10): Não clareados (controle), perborato de sódio + peróxido de hidrogênio 20 por cento (PS + PH 20 por cento), peróxido de carbamida 37 por cento (PC37 por cento) e peróxido de hidrogênio 38 por cento (PH 38 por cento). Após 7 dias, as amostras destinadas à resistência de união foram restauradas e submetidas ao teste. As barras de dentina foram clareadas e submetidas ao teste de flexão de 3 pontos. Os dados (MPa) foram analisados por ANOVA e teste de Tukey (α=0,05). No teste de cisalhamento, o controle foi superior (p<0,05) aos grupos clareados, que foram semelhantes entre si (p>0,05). Na resistência à flexão, o grupo controle também exibiu os maiores valores, diferente dos demais (p<0,05). SEM revelou camada de smear em todos os grupos, com fissuras nos espécimes clareados. PS + 20 por cento PH e PH 38 por cento apresentaram interfaces de descontínuas com poucos tags. A resistência de união do material restaurador à dentina e a resistência à flexão da dentina foram reduzidas após o uso de agentes clareadores de alta concentração.

Clareamento em consultório em sessão única ativado com luz híbrida led/laser / Single visit in office dental bleaching with the use of hybrid light activation

Este caso clínico descreve o clareamento em consultório realizado com gel de peróxido de hidrogênio a 35% e ativado com fonte de luz híbrida (LED + Laser terapêutico). Após anamnese, exame clínico, radiográfico e profilaxia supragengival completa a cor avaliada visualmente com escala VITA e foi realizada a documentação fotográfica digital. Após isolamento dos tecidos moles com barreira gengival, o gel clareador a base de peróxido de hidrogênio a 35% (Lase Peroxide Sensy - DMC) foi manipulado e aplicado na face vestibular dos dentes. Após 1 minuto de aguardo, o gel foi ativado com luz híbrida durante 3 minutos, 1 minuto de aguardo e nova ativação com luz por mais 3 minutos. Foram realizadas 3 aplicações do gel clareador (3x 8 minutos), sendo considerada como satisfatória a cor obtida. Realizou-se o polimento final com pasta para polimento e disco de feltro, seguido da aplicação do dessensibilizante e laserterapia. Esse procedimento clareador em consultório apresentou um bom resultado estético, em apenas uma sessão de atendimento, sem relato de sensibilidade dentária, demonstrando a efetividade do uso da luz híbrida na aceleração do procedimento clareador. Após 3 meses e 1 ano de acompanhamento, pôde-se verificar a efetividade da técnica empregada e a manutenção do clareamento obtido

This clinical case describes in office dental bleaching performed using 35% hydrogen peroxide gel activated with a hybrid light source (LED + therapeutic laser). After anemnesis, clinical exame and supragengival prophilaxy, the color was visually available with VITA scale and digital photograph. After the isolation of the soft tissues using gengival barrier, the 35% hydrogen peroxide gel (Lase Peroxide Sensy - DMC) was prepared and applied to the teeth. After 1 minute, the gel was activated with hybrid light for 3 minutes, 1 minute without light and then applied for 3 more minutes. In total, 3 gel applications were performed (3x8 minutes) and new color evaluation was done and satisfactory color results were obtained. The final polishing was performed with paste and a felt disc, followed by the application of the desensitizing gel and laser therapy. This in office bleaching procedure presented good aesthetic results with only one session, without tooth sensibility and demonstrated the effectiveness of the use of hybrid light on the acceleration of the bleaching procedure. After 3 and 12 month follow-ups, the technique employed proved to be effective and color obtained was maintained