Effect of bleaching agents containing fluoride or calcium on enamel microhardness, roughness and permeability

Abstract

Aim: To evaluate the effect of different in-office bleaching agents on the permeability, roughness and surface microhardness of human enamel. Methods: For evaluation of roughness and microhardness, 40 hemi-faces of 20 premolars were subjected to initial roughness (Ra parameter) and microhardness (VHN) measurements. Thirty-two premolar's crowns were used for permeability test. Then, all specimens were randomly divided into four groups: C -without bleaching (control), HP35 -bleaching with 35% hydrogen peroxide (HP), HPF38 -38% HP+fluoride, HPC35 -35% HP+calcium. Final roughness (FR) and microhardness (FM) measurements were evaluated. For permeability, the 32 crowns were immersed in 1% sodium hypochlorite (20 min) and silver nitrate solutions (2 h) and subjected to developing solution under fluorescent light (16 h). Three sections from the crowns were analyzed in light microscope (100x) to evaluate the scores of permeability: Score 0 -no tracer agent penetration; Score 1 -less than half the thickness of enamel penetration; Score 2 -tracer agent reaching half the enamel thickness; Score 3 -entire enamel depth penetration, without reaching dentin and Score 4 -tracer agent reaching dentin. For roughness and microhardness evaluation were used one-way ANOVA and Dunnet post-test for independent samples, and t test for paired samples. For permeability, the data were analyzed by Kruskal Wallis and Dunn tests. Results: A significantly higher permeability and surface roughness were observed in groups HP35, HPF38 and HPC35 compared to the C group, as well as decreased microhardness (p<0.05). Conclusions: All bleaching agents increased permeability and surface roughness, and decreased microhardness of human enamel; thus, the addition of fluoride or calcium was not beneficial.

Effect of in-office bleaching gels with calcium or fluoride on color, roughness, and enamel microhardness

“…Therefore, when considering the final values of Ra, the groups exposed to the commercial bleaching gel containing F behaved as the intact unbleached enamel, whereas the roughness variation was not detected in the 40% HP with F group. Previous studies (14,15) indicated that the addition of Ca and F to the bleaching gels did not provide additional protection for the enamel. These findings partially contrast with the results obtained in the present study, where the 35% HP with Ca group showed microhardness values similar to the unbleached control group.…”

“…Regardless of the technique and bleaching agent employed, adverse effects have been reported, to include: tooth sensitivity (8); changes in surface morphology; and changes to the physical-chemical properties of the dental hard tissues such as an increase in enamel roughness, a decrease in surface microhardness, and an alteration in mineral content (9)(10)(11)(12)(13). Some remineralizing compounds, such as fluoride, calcium, bioactive glass, arginine/calcium carbonate, and nanohydroxyapatite; have been investigated to minimize these adverse effects (10,12,(14)(15)(16). These compounds could be used before or after treatment, or incorporated into gels to prevent demineralization or enhance remineralization during the bleaching therapy.…”

Effect of carbamide peroxide bleaching with and without topical desensitizing gels on enamel roughness, microhardness, and bond strength to orthodontic brackets

“…This reduction in enamel microhardness may be explained by mineral loss from enamel after bleaching procedures, Preliminary studies reported that the application of peroxides could reduce the calcium and phosphate enamel content, as well as its fluoride concentration. 12,14,16,20 It is widely accepted that, surface hardness is used as a characteristic property to determine mineral loss, because it is an established technique for evaluating the mineralization rate of enamel. 17 Beside this, carbopol, which is the thickening agent in most bleaching agents, can decrease the enamel microhardness during bleaching, as carbopol's high calcium-binding capacity and inhibits hydroxyapatite crystal growth.…”

“…[9][10][11] Decreasing in enamel surface microhardness and increasing in both permeability and surface roughness are the most common adverse effects of bleaching agents whether hydrogen or carbamide peroxide. 12 It is well established that, superficial characteristics of the enamel such as roughness, porosity, and depression could contribute to pigment precipitation 13 . So, after bleaching, coloring pigments may adhere more rapidly to such rough enamel surface and cause discoloration more easily than the original tooth.…”

“…14,15 Fluoride becomes widely accepted as an important contributing factor in repairing microstructural defects of enamel through the adsorption and precipitation of calcium and phosphate present in saliva. 12,14 Patients who need orthodontic treatment and choose esthetic brackets give much importance to the smile. Some of them have stained teeth and request that bleaching treatment be performed prior to orthodontic treatment.…”