Abstract
The objective of this in vitro study was to assess the influence of prolonged bleaching pre- and postrestoration on the bond strength (microshear) to enamel using 4% hydrogen peroxide (PH4). In the postrestorative bleached specimens evaluation, the composite cylinders were assembled after bleaching, while in the prebleached specimens, the cylinders were assembled before. Therefore, in the postbleached specimens, 60 bovine teeth were randomly assigned as follows: G1: control; G2: 14 days bleaching before bond strength (BS) testing; G3: 21 days; and G4: 28 days. In prebleached specimens, 180 bovine teeth were randomly assigned as follows: G1: control; G5: 14 days bleaching, storage in artificial saliva (AS) for 24 h before BS testing; G6: 14 days beaching, AS storage for 7 days before BS testing; G7: 21 days bleaching, AS storage for 24 h before BS testing; G8: 21 days bleaching, AS storage for 7 days before BS testing; G9: 28 days bleaching, AS storage for 24 hours before BS testing; and G10 : 28 days bleaching, AS storage for 7 days before BS testing. The results were submitted to ANOVA one-way (postrestoration bleaching) and two-way (prerestoration bleaching) and Tukey's post hoc test (p ≤ 0.05). In the postrestoration bleaching, no statistical difference between times was found. However, when bleached groups were compared to the control (G1), an expressive difference was detected (p ≤ 0.0001). For prerestoration bleaching, all experimental groups were statistically different from G1 (p ≤ 0.05), except G6 (p ≥ 0.01), and for G5 and G6, statistical differences were found (p ≤ 0.01). There were no significant differences between G7 and G8 and between G9 and G10, regardless of the AS storage times (p ≥ 0.05). It was concluded that prolonged bleaching with PH4 decreased adhesion resistance regardless of the moment of the bleaching (post- and prerestoration bleaching).
Highlights
International Journal of Dentistry metallic ions, and decrease bond strength to dental structures [5,6,7,8]. e surrounding enamel may be affected during bleaching, compromising the integrity of the interface adhesion [9, 10]
Depending on the concentration of the bleaching agent, the bond strength to enamel decreases by approximately 60% when compared to unbleached teeth. is reduction seems to be related to trapped residual oxygen, which interferes with the infiltration of the bonding monomers, the subsequent reduction in length and number of resin tags, and the inhibition of polymerization reaction. erefore, a delay of one to three weeks is recommended before the adhesive restoration procedures take place [11,12,13,14]
Searching for more expressive results, some patients extend the use of dental bleaching, especially in athome treatment. is prolonged use may overcome the socalled “saturation point.” is is the point at which the dental bleaching gels no longer act only in the chromogens, but they will negatively affect the mineral composition, resulting in chemical and mechanical property alterations of enamel [19, 20]. us, the aim of this study was to verify the influence of prolonged dental bleaching protocols in the bond strength to dental enamel, in two different moments: post- and prerestoration bleaching using 4% hydrogen peroxide with calcium
Summary
Dental bleaching treatments provide fast and expressive results without wearing dental structure away. ese facts, associated with the desire for a brighter and more attractive smile, made this treatment quite popular, increasing its demand in the last decades. [1, 2] When hydrogen peroxide dental bleaching gels are activated, they release oxidizing agents, which can penetrate the enamel and dentin ultrastructures, producing a chemical reaction. e hydrogen peroxide, under alkaline conditions, undergoes ionic dissociation, giving rise to hydroxyl anions (OH-), a highly unstable free radical [3]. e double bonds involving carbon atoms and the chemical elements nitrogen and oxygen (present in the pigments of the dental structure) are very susceptible to electron donators and represent the main target of the action of the peroxide. e double bonds are present in the organic molecules and are responsible for the color darkening. E literature has shown that the addition of fluorides and calcium to bleaching agents reduces enamel susceptibility to erosion and caries [15,16,17], preserves its mechanical strength, and reduces the mineral loss during the treatment without influencing the effectiveness of the dental bleaching process [9, 18]. Is prolonged use may overcome the socalled “saturation point.” is is the point at which the dental bleaching gels no longer act only in the chromogens, but they will negatively affect the mineral composition, resulting in chemical and mechanical property alterations of enamel [19, 20]. Us, the aim of this study was to verify the influence of prolonged dental bleaching protocols in the bond strength to dental enamel, in two different moments: post- and prerestoration bleaching using 4% hydrogen peroxide with calcium Searching for more expressive results, some patients extend the use of dental bleaching, especially in athome treatment. is prolonged use may overcome the socalled “saturation point.” is is the point at which the dental bleaching gels no longer act only in the chromogens, but they will negatively affect the mineral composition, resulting in chemical and mechanical property alterations of enamel [19, 20]. us, the aim of this study was to verify the influence of prolonged dental bleaching protocols in the bond strength to dental enamel, in two different moments: post- and prerestoration bleaching using 4% hydrogen peroxide with calcium
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