Dental adhesive microtensile bond strength following a biofilm-based in vitro aging model

Abstract Laboratory tests are routinely used to test bonding properties of dental adhesives. Various aging methods that simulate the oral environment are used to complement these tests for assessment of adhesive bond durability. However, most of these methods challenge hydrolytic and mechanical stability of the adhesive- enamel/dentin interface, and not the biostability of dental adhesives. Objective To compare resin-dentin microtensile bond strength (μTBS) after a 15-day Streptococcus mutans (SM) or Streptococcus sobrinus (SS) bacterial exposure to the 6-month water storage (WS) ISO 11405 type 3 test. Methodology A total of 31 molars were flattened and their exposed dentin was restored with Optibond-FL adhesive system and Z-100 dental composite. Each restored molar was sectioned and trimmed into four dumbbell-shaped specimens, and randomly distributed based on the following aging conditions: A) 6 months of WS (n=31), B) 5.5 months of WS + 15 days of a SM-biofilm challenge (n=31), C) 15 days of a SM-biofilm challenge (n=31) and D) 15 days of a SS-biofilm challenge (n=31). μTBS were determined and the failure modes were classified using light microscopy. Results Statistical analyses showed that each type of aging condition affected μTBS (p<0.0001). For Group A (49.7±15.5MPa), the mean μTBS was significantly greater than in Groups B (19.3±6.3MPa), C (19.9±5.9MPa) and D (23.6±7.9MPa). For Group D, the mean μTBS was also significantly greater than for Groups B and C, but no difference was observed between Groups B and C. Conclusion A Streptococcus mutans- or Streptococcus sobrinus-based biofilm challenge for 15 days resulted in a significantly lower μTBS than did the ISO 11405 recommended 6 months of water storage. This type of biofilm-based aging model seems to be a practical method for testing biostability of resin-dentin bonding.

Effect of calcium hydroxide intracanal dressing on the bond strength of a resin-based endodontic sealer

The aim of this in vitro study was to evaluate the bond strength of Epiphany™ resin-based sealer to dentin walls after placement of calcium hydroxide [Ca(OH)2] dressings. Fifteen extracted single-rooted human teeth were instrumented using 2.5 percent NaOCl + EDTA as irrigants. The teeth were randomly assigned to 3 groups (n=5), according to the intracanal dressing: G1= Ca(OH)2 + saline; G2= Ca(OH)2 + 2 percent chlorhexidine gluconate (CHX) gel; and G3= saline (control). After 10 days of storage in 100 percent humidity at 37ºC, the dressings were removed and the root canals were filled with Epiphany™ sealer. After additional 48 h of storage, the specimens were sectioned transversally into 2-mm-thick discs. Push-out tests were performed (1 mm/min, Instron 4411) and the maximum loads at failure were recorded in MPa. One-way ANOVA and Newman-Keuls tests showed a statistically significant decrease in bond strength when a Ca(OH)2 dressing was used before root canal filling with Epiphany™ (G1= 10.18 ± 1.99 and G2= 9.98 ± 2.97) compared to the control group (13.82 ± 3.9) (p< 0.05). It may be concluded that the use of Ca(OH)2 as an intracanal dressing material affected the adhesion of Epiphany™ to the root canal walls, but even though the values were within the acceptable range found in the literature.

O objetivo desse estudo in vitro foi avaliar a resistência de união do cimento resinoso Epiphany™ às paredes dentinárias após aplicação de pastas de hidróxido de cálcio [Ca(OH)2]. Quinze dentes humanos uniradiculares foram igualmente instrumentados sob irrigação com as soluções de NaOCl 2,5 por cento + EDTA. Os dentes foram divididos em três grupos (n=5) e tratados com diferentes pastas de Ca(OH)2: G1= Ca(OH)2 + soro fisiológico; G2= Ca(OH)2 + 2 por cento CHX e G3= tratado apenas com soro fisiológico (grupo controle). Após 10 dias de armazenamento a 37°C e 100 por cento de umidade, as medicações foram removidas e os dentes obturados com o cimento Epiphany. Passadas 48 horas de armazenamento adicional, as amostras foram seccionadas tranversalmente em discos de 2 mm de espessura. Os testes de resistência de união (push-out) foram realizados em máquina de ensaio mecânico (1 mm/min) e os resultados expressos em MPa. Os testes de ANOVA e Newman-Keuls mostraram um significante decréscimo nos valores de resistência de união quando as pastas de Ca(OH)2 foram utilizadas (10,18 ± 1,99 e 9,98 ± 2,97) em comparação ao grupo controle (13,82 ± 3,9) (p<0,05). Pode-se concluir que o uso do Ca(OH)2 como medicação intracanal diminuiu a adesão do cimento Epiphany™ às paredes dos canais radiculares, embora os valores de resistência de união estejam dentro das médias aceitáveis encontradas na literatura.

Efeito do clareamento caseiro sobre o equilíbrio mineral dos tecidos dentais: revisão da literatura / The effect of home bleaching on dental mineral equilibrium: a literature review

O tratamento clareador caseiro consiste na utilização de um gel á base de peróxido de carbamina, o qual permanece em íntimo contato com os tecidos bucais por certo período, diariamente, durante alguns dias ou semanas. Ao longo do clareamento, os processos de des/remineralização podem ocorrer na estrutura dental, alterando o conteúdo mineral do esmalte e da dentina. Neste artigo, revisam-se estudos que descrevem o processo dinâmico do clareamento, outros que discutem os efeitos do clareamento no equilíbrio mineral do dente e os possíveis fatores que levam às alterações no conteúdo mineral. A partir desses artigos, verifica-se que não existem ainda evidências que comprovem o efeito permanente do tratamento clareador sobre o equilíbrio mineral das estruturas dentais. Fortes evidências sugerem que fatores protetores, principalmente os componentes salivares, previnem perda mineral significativa e restabelecem o conteúdo mineral durante e após o tratamento clareador. Para favorecer a remineralização e minimizar a desmineralização durante o clareamento, a escolha do agente clareador parece ser de extrema importância. Nas características esperadas de agentes clareadores caseiros pode-se incluir o pH neutro e a presença de flúor e devem-se evitar altas concentrações de peróxido.

Home bleaching requires that a peroxide-based bleaching gel be in contact with intraoral tissues for a number of hours a day for several days. Throughout bleaching treatment, demineralization and remineralization events likely occur at the dental structure, affecting the tooth mineral content. Studies considering the bleaching dynamic process were reviewed and attention was given to those that discuss the effects of the treatment on the dental mineral equilibrium and the conditions that lead to alteration of the mineral content. There is no definitive conclusion whether home bleaching affects permanently or not dental mineral equilibrium. Strong evidence suggests that protective factors mainly salivary components prevent significant mineral loss and/or restore mineral content during and after bleaching treatment. To favor remineralization and minimize demineralization during bleaching, the choice of bleaching agent is important. Ideal characteristics of home bleaching agents include neutral pH and fluoride content. Furthermore, high concentrations of peroxide should be avoided.