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Effect of a 10% carbamide peroxide on wear resistance of enamel and dentine: In situ study

Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
Journal of dentistry (Impact Factor: 2.84). 02/2009; 37(4):273-8. DOI: 10.1016/j.jdent.2008.12.001
Source: PubMed

ABSTRACT This triple-blind, 2x2 crossover in situ study, was undertaken to verify whether the wear resistance of enamel and root dentine would be affected by bleaching with a 10% carbamide peroxide agent and a placebo agent.
Thirty slabs of each substrate (2mm x 3mm x 2mm) were selected for each phase, after flattening and polishing procedures and microhardness test. After a 7-day lead-in period, one specimen of each substrate was randomly bonded on the facial surface of each one of 30 subject's upper second premolars. The volunteers received instructions on how to perform toothbrushing and application of gel in the tray. Fifteen volunteers bleached their maxillary arch with a 10% carbamide peroxide bleaching agent for a 2-week period, while the remainders used a placebo agent. After a 1-week washout period, a new set of enamel and root dentine slabs were bonded to the premolars and volunteers were crossed over to the alternate agent for 14 days. The resistance of enamel and root dentine to wear following bleaching, toothbrushing and intraoral exposure was measured with a profilometer, using reference areas.
For enamel, ANOVA did not demonstrate significant difference between wear provided by placebo and bleaching agent (p=0.3713), but higher wear depth was observed for bleached root dentine (p=0.0346).
While overnight bleaching caused no alteration in wear resistance of enamel, root dentine showed increased tissue loss.

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    • "Erosive challenge provided by the use of this product in relation to control (DW) results in the softening dentin, which, in combination with abrasion, results in pathological wear of this tissue. The detrimental effects of bleaching and abrasion have been previously investigated (Engle et al., 2010; Faraoni-Romano et al., 2009; Sulieman et al., 2004). Considering the high demand for bleaching procedures and increased use of OTC whitening products, it is possible that the association of these factors would advance the dentin loss. "
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    ABSTRACT: The aim of this study was to determine the erosive potential of hydrogen peroxide (HP) containing mouthwash on dentin assessed by Focus variation three-dimensional (3D) microscopy. Twenty dentin slabs were selected and randomly allocated into two groups (n = 10): DW-Distilled water (pH = 7.27) and HP-1.5% (pH = 3.78). Each specimen was cyclically demineralized (4 × 60 s/day, 10 days) with HP or DW and brushed 3×/day (200 g, 150 strokes-toothpaste with 1,450 ppmF as NaF). Between the challenges, the specimens were exposed to artificial saliva. Afterward, dentin loss was analyzed using focus variation 3D microscopy, and the data were submitted to unpaired t-test (α = 0.05). Statistically significant difference was found between the mean wear rate (μm, ±SD) of HP (1.98 ± 0.51) and DW (1.45 ± 0.39). The results suggest that the use of HP-containing mouthwash associated to brushing may increase the risk of tissue loss and focus variation 3D microscopy may be used as a technique for quantifying dental wear. Microsc. Res. Tech., 2013. © 2013 Wiley Periodicals, Inc.
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    ABSTRACT: The aim of this study was to evaluate the influence of sterilization methods (ethylene oxide, steam autoclave and 10% formalin) on microhardness of extracted human teeth (enamel and root dentin) submitted to pH cycling, and to determine the influence of these methods on shear bond strength (enamel, coronary and root dentin). For microhardness test, 40 root dentin and 40 enamel blocks were prepared from freshly-extracted third molars. Specimens were randomly assigned to 4 groups according to sterilization method: control group no sterilized, ethylene oxide (7h- EtO gas cycles and 48 degassing period), steam autoclave (30´ at 121oC) and 10% formalin (7 days). After sterilizing, specimens were rinsed, moisten and submitted to pH cycling. Microhardness test in different depths (30, 60, 90, 120 and 300µm) was realized on sound and demineralized areas. For shear bond strength test, 60 enamel, coronary and root dentin fragments were randomly divided into 4 groups according to sterilization method: control group, ethylene oxide, steam autoclave and 10% formalin. The bonding site was delimited and a resin composite cylinder was built. After 24h, the specimens were tested to failure. Data were analyzed using ANOVA and Fishers test (α=0.05). Sound enamel microhardness showed the highest values for control group, followed by ethylene oxide and steam autoclave, while the 10% formalin provided the lowest values. For depths, ANOVA showed no statistical difference among them. For demineralized enamel, control group was similar to steam autoclave group and higher than formalin and ethylene oxide (control ≈ steam autoclave >formalin ≈ ethylene oxide). Comparing depths, it was observed that 30µm <60µm ≈ 90µm ≈ 120µm <300µm. For sound root dentin, control group was similar to formalin and ethylene oxide and higher than steam autoclave, being formalin similar to ethylene oxide and different from steam autoclave. It was not verified statistical difference for depths in this substrate. For desmineralized root dentin, ANOVA showed no statistical difference among the methods. For depths, 30µm was similar to 90µm and different from 300 and 120µm. 300µm provided the highest values. For bond strength in root dentin, it was observed statistically significant difference among sterilization methods, presenting formalin the highest values. However, when enamel and dentin were evaluated, ANOVA showed no statistical difference among sterilization methods. It can be concluded that, the sterilization methods employed in this study affect the microhardness of sound and demineralized enamel and sound dentin. On the other hand, the sterilization methods did not affect the microhardness of demineralized root dentin. Shear bond strength was affected by the sterilization methods only in root dentin. O objetivo do presente estudo foi avaliar a influência de métodos de esterilização do substrato dental sobre a microdureza de dentes extraídos (esmalte e dentina radicular) submetidos a ciclos de pH, e ainda verificar a influência destes métodos sobre a resistência adesiva do esmalte, dentina coronária e radicular. Para os testes de microdureza, dez terceiros molares extraídos foram seccionados em 40 fragmentos de esmalte e 40 de dentina radicular, sendo divididos aleatoriamente em 4 grupos (para ambos os substratos): Controle - não esterilizado, Óxido de Etileno 7h ciclo de OE/48h aeração, Autoclave 30 à 121oC e Formalina 10% - por 7 dias. Após a esterilização, as amostras foram lavadas, reumidificadas e submetidas a ciclos de pH. Os testes de microdureza em profundidade (30, 60, 90, 120 e 300µm) foram realizados no substrato hígido e desmineralizado. Para os teste de resistência adesiva, 30 terceiros molares extraídos foram seccionados em 60 fragmentos de esmalte, 60 fragmentos de dentina coronária e 60 fragmentos de dentina radicular, sendo divididos aleatoriamente em 4 grupos (para todos os substratos): Controle, Óxido de Etileno, Autoclave e Formalina 10%. Em seguida, os sítios de adesão foram demarcados e cilindros de resina composta foram confeccionados em 3 incrementos. Após 24 horas, os espécimes foram submetidos a testes de cisalhamento. Os dados obtidos para ambas as avaliações foram submetidos à ANOVA e teste de Fisher (α =0,05). Para microdureza em esmalte hígido pode-se verificar que o controle apresentou maior valor de dureza e estatisticamente diferente dos outros grupos, sendo que os métodos promoveram alteração da dureza, diminuindo-a (controle>óxido de etileno>autoclave>formalina). Contudo, para as profundidades não houve diferença estatística. Para o esmalte desmineralizado, o grupo controle apresentou maiores valores de dureza diferente estatisticamente da formalina e óxido de etileno e semelhante a autoclave (controle ≈ autoclave >Formalina ≈ óxido de etileno). Para as profundidades, observou-se que 30µm <60µm ≈ 90µm ≈ 120µm <300µm. Para dentina radicular hígida pode-se observar que grupo controle apresentou maior valor de dureza, semelhante ao óxido de etileno e a formalina e diferente da autoclave, sendo a formalina similar ao óxido de etileno e diferente da autoclave. Entretanto, para as profundidades testadas não houve diferença estatística neste substrato. Para a dentina desmineralizada pode-se observar que o método não apresentou diferença significante, contudo para as profundidades ocorreu diferença, 30µm foi similar a 90µm e diferente de 300µm e 120µm. 300µm apresentou as maiores médias de microdureza. Com relação aos testes de resistência adesiva em esmalte os métodos foram semelhantes entre si, assim como em dentina coronária, contudo em dentina radicular a formalina proporcionou maiores valores de adesão. Pode-se concluir que os métodos de esterilização influenciaram na microdureza do esmalte hígido e desmineralizado, bem como, na dentina hígida não promovendo alteração na dentina desmineralizada. Entretanto, os métodos não influenciaram nos resultados dos testes de resistência adesiva em esmalte e dentina coronária, alterando apenas a adesão em dentina radicular.
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