Effect of thickener agents on dental enamel microhardness submitted to at-home bleaching

Abstract

Dental bleaching occurs due to an oxidation reaction between the bleaching agents and the macromolecules of pigments in the teeth. This reaction is unspecific and the peroxides can also affect the dental matrix causing mineral loss. On the other hand, recent studies have suggested that the thickener agent carbopol can also cause mineral loss. Thus, the objective of this study was to evaluate in vitro the effect of at-home dental bleaching on dental enamel microhardness after the use of bleaching agents with and without carbopol as a thickener agent. Bovine dental slabs with 3 x 3 x 3 mm were obtained, sequentially polished, and randomly divided into 4 groups according to the experimental treatment: G1: 2% carbopol; G2: 10% carbamide peroxide with carbopol; G3: carbowax; G4: 10% carbamide peroxide with poloxamer. Bleaching was performed daily for 4 weeks, immersed in artificial saliva. Enamel microhardness values were obtained before the treatment (T0) and 7 (T1), 14 (T2), 21 (T3), 28 (T4), and 42 (T5) days after the beginning of the treatment. ANOVA and Tukey's test revealed statistically significant differences only for the factor Time (F = 5.48; p < 0.01). All bleaching and thickener agents caused no alterations on the enamel microhardness.

Effects of different concentrations of carbamide peroxide and bleaching periods on the roughness of dental ceramics

“…6,8,9,13 Although an increase in roughness has been observed in composite resins or glass ionomers after bleaching treatment, [18][19][20][21][22][23][24]27 no alteration in ceramic surfaces was observed after bleaching in the current study, 23 so the impact of bleaching agents on surface roughness may be considered material-dependent, as also demonstrated by previous studies. 16,[20][21][22][23] In these studies, the chemical stability of ceramics against bleaching agents was observed after treatment with 15% carbamide peroxide for 56 h, 23 16% carbamide peroxide for 126 h, 17 10% or 15% carbamide peroxide 27 and 38% hydrogen peroxide for 30 minutes 23 or 45 minutes, respectively.…”

“…The respective treatment agent was applied for six hours a day over 21 days, corresponding to 126 hours of treatment. Specimens to be bleached were covered with 0.03 ml of the respective bleaching agent, were placed in vacuum-formed custom trays with a drop of artificial saliva, 8,13 and were stored in a plastic container at 37 °C. [6][7][8] Specimens from control groups were stored only with artificial saliva drops in the vacuum-formed custom tray to mimic oral conditions.…”

“…Specimens to be bleached were covered with 0.03 ml of the respective bleaching agent, were placed in vacuum-formed custom trays with a drop of artificial saliva, 8,13 and were stored in a plastic container at 37 °C. [6][7][8] Specimens from control groups were stored only with artificial saliva drops in the vacuum-formed custom tray to mimic oral conditions. After bleaching exposure, specimens were washed with distilled water to remove residual carbamide peroxide gel and were stored in a plastic container for the remaining day period in relative humidity at 37 °C.…”

“…1,[3][4][5] Several microscopic changes on the enamel surface morphology are also observed, due to enamel mineral loss and surface roughening. [6][7][8][9][10][11][12][13][14][15] Extremely unstable and reactive H + free radicals, released by bleaching agents, and low pH are described as the main cause of the side effects of prolonged use of these products. [6][7][8][9][10][11][12][13][14][16][17] Similarly, bleaching agents may cause structural changes on restorative materials that may compromise their physical properties and lead to premature failure.…”

“…[6][7][8][9][10][11][12][13][14][15] Extremely unstable and reactive H + free radicals, released by bleaching agents, and low pH are described as the main cause of the side effects of prolonged use of these products. [6][7][8][9][10][11][12][13][14][16][17] Similarly, bleaching agents may cause structural changes on restorative materials that may compromise their physical properties and lead to premature failure. [18][19][20][21][22][23][24] Although conventional dental ceramics are considered the most inert among all dental restorative materials, their surfaces can exhibit surface deterioration in contact with acidulated fluoride gels or other solutions.…”