Potential of fluoridated carbamide peroxide gels to support post-bleaching enamel re-hardening

OBJECTIVE: Aim of the in vitro study was to evaluate the time period needed to re-establish enamel surface microhardness after bleaching with fluoridated (0.5% F(-) as NaF) and unfluoridated carbamide peroxide (CP) bleaching gels under a daily de- and remineralization protocol. MATERIALS AND METHODS: Ninety enamel specimens were prepared from bovine incisors and prepared for Knoop microhardness determination. The samples were divided into five groups and bleached for 7 days (8h per day) with experimentally designed neutral and acidic 10% CP gels: A (0.5% F(-), pH 7.0), B (0.5% F(-), pH 5.5), C (no F(-), pH 7.0) and D (no F(-), pH 5.5). Group E served as control and was not bleached. After each 8-h bleaching period the samples were subjected to a de- and remineralization protocol. In the following 5 days, the specimens were not bleached, but stored in artificial saliva for 8h instead; the daily de- and remineralization cycles were maintained during this period. Knoop microhardness determinations were conducted at baseline, after each bleaching interval and after completion of each daily de- and remineralization cycle. A repeated measures two-way ANOVA statistical analysis and a comparison of confidence intervals was conducted to check for hardness recovery during the post-bleaching period. RESULTS: After completion of bleaching therapy on day 7 a statistically significant hardness loss was observed for all bleaching groups in the range of about 7-15% hardness reduction as compared to baseline. The fluoridated gels proved significantly less hardness loss than the unfluoridated gels. In the following period, from days 8 to 12 recovery of hardness to baseline data was observed in the fluoridated groups (A and B) after the first de-/remineralization cycle on day 8 (group A) and after the second 8-h remineralization period on day 9 (group B), respectively. Hardness of the specimens treated with the unfluoridated bleaching gel C returned to baseline values after day 10. The samples of group D did not show recover of hardness data during the 5-day post-bleaching period. CONCLUSION: Fluoridated 10% carbamide peroxide bleaching gels support re-hardening of bleached enamel with a shorter period needed for hardness recover as compared to unfluoridated gels.     

Effect of fluoride on ion exchange, remineralization and acid resistance of surface enamel

Abstract. In a system of constant ion activities the rates of F⁻ exchange in enamel, under conditions of exchange alone and remineralization, depended on the concentration of F⁻ in solutions. Acid resistance of surface minerals resulted from exchange of F⁻ for OH⁻ in the enamel at pH 7.0 and 4.5 The leve lof 0.5 mM NaF, compared to 0.05 and 5.0 mM, caused maximum rates of isotopic exchange of ⁴⁵Ca and maximum acid resistance of enamel. Similarly low levels of F⁻ may be feasible for use in caries prevention in the absence and presence of remineralization.     

Effects of phosphoric acid on bovine enamel bleached with carbamide peroxide

The aim of this study was to measure the demineralization capacity of 37% phosphoric acid on bovine enamel at different time-points after bleaching with 30% carbamide peroxide. Five, 4 × 4-mm sections were obtained from the enamel of 10 bovine incisors. After applying 30% carbamide peroxide (Vivastyle) for 90 min, specimens were stored in artificial saliva for 0, 24, 72 h, or 7 d and then immersed in 37% phosphoric solution. At 15, 30, 60, 90, and 120 s, 5-ml aliquots were extracted. A control group of specimens was not bleached. Ca²⁺ concentrations were measured by atomic absorption spectrophotometry. A larger amount of Ca²⁺ was extracted from enamel by phosphoric acid after the application of 30% carbamide peroxide. Twenty-four hours after bleaching, significantly more Ca²⁺ was extracted from bleached than from control specimens at all time-points, and this greater susceptibility to the action of the acid persisted for at least 1 wk after bleaching.     

Fluoride uptake and development of artificial erosions in bleached and fluoridated enamel in vitro

The aim of the present in vitro study was to evaluate the effect of carbamide peroxide (CP) bleaching on fluoride uptake in enamel. Additionally, the susceptibility for erosion in bleached and fluoridated enamel was tested. Each four enamel specimens were prepared from 44 bovine incisors. The four samples gained from each tooth were distributed among four groups (A-D) of 44 specimens each: A: (unbleached/unfluoridated) served for determination of baseline fluoride concentration; B: (unbleached/fluoridated) four times in 2000 ppm NaF solution (2 min); C: (bleached/unfluoridated) four times in 10% CP (8 h); D: (bleached/fluoridated) four times in 10% CP and fluoridation. In 22 specimens of each group both KOH-soluble and structurally bound fluoride were determined in the outermost 30 micro m of the enamel. In the remaining specimens erosions were induced by immersing the samples in 5 mL of 1% citric acid (20 min) and microhardness was evaluated before and after demineralization. Statistical analysis showed that KOH-soluble fluoride uptake was similar for group B and D specimens. Structurally bound fluoride uptake after fluoride application in unbleached samples was significantly higher than in bleached ones. Bleaching only resulted in a highly significant fluoride loss. In all samples erosion caused a significant microhardness loss. The study showed that pre-treatment of enamel with CP followed by fluoridation does not improve erosive resistance. Moreover the study reveals that CP treatment decreases concentration of structurally bound fluoride in enamel which could not be outweighed by fluoridation with 2000 ppm NaF. It is concluded that it is not feasible to improve fluoride uptake in enamel with a pre-treatment with 10% CP.     

Effects of new formulas of bleaching gel and fluoride application on enamel microhardness: an in vitro study

This in vitro study evaluated the new formulas of bleaching products and the effect of subsequent applications of fluoride on the hardness of enamel during and after tooth bleaching. The crowns of 60 extracted intact human molars were sectioned longitudinally; the buccal part was embedded in acrylic resin, the occlusal part was ground flat, exposing enamel and dentin, and then polished. Baseline Knoop microhardness (KHN) of enamel was determined. The specimens were then randomly divided into six groups of 10 specimens, and each group was assigned to a specific 10% carbamide peroxide (CP) bleaching agent. A: Opalescence, B: Opalescence PF (3% potassium nitrate and 0.11% fluoride), C: Nite White Excel 3 (ACP), D: Opalescence + F (acidulated phosphate fluoride 1.23%), E: Opalescence PF + F, F: Nite White Excel 3 + F. The teeth were bleached for eight hours; after each procedure, the specimens were stored in artificial saliva at 37 degrees C. Immediately after day 21 of bleaching, the specimens in groups D, E and F received fluoride 1.23% for five minutes. KHN tests w ere performedbefore (baseline = control), during (14, 21) and two weeks (35 days) after the bleaching procedure and were statistically compared using ANOVA/Tukey's t-test (alpha < 0.05). The statistical analysis revealed no significant difference among the bleaching materials (p = 0.123). A significant enamel KHN reduction (p < 0.001) was observed for all bleaching materials, with no difference among them. Two weeks after bleaching, all the groups that received fluoride showed a significant increase in microhardness. For the new bleaching formulas, the enamel was restored to a value similar to baseline.     

Tin-containing fluoride solutions as anti-erosive agents in enamel: an in vitro tin-uptake, tissue-loss, and scanning electron micrograph study

Tin-containing fluoride solutions can reduce erosive tissue loss, but the effects of the reaction between tin and enamel are still not clear. During a 10-d period, enamel specimens were cyclically demineralized (0.05 M citric acid, pH 2.3, 6 × 5 min d⁻¹) and remineralized (between the demineralization cycles and overnight). In the negative-control group, no further treatment was performed. Three groups were treated (2 × 2 min d⁻¹) with tin-containing fluoride solutions (400, 1,400 or 2,100 ppm Sn²⁺, all 1,500 ppm F⁻, pH 4.5). Three additional groups were treated with test solutions twice daily, but without demineralization. Tissue loss was determined profilometrically. Energy-dispersive X-ray spectroscopy was used to measure the tin content on and within three layers (10 μm each) beneath the surface. In addition, scanning electron microscopy was conducted. All test preparations significantly reduced tissue loss. Deposition of tin on surfaces was higher without erosion than with erosion, but no incorporation of tin into enamel was found without demineralization. Under erosive conditions, both highly concentrated solutions led to the incorporation of tin up to a depth of 20 μm; the less-concentrated solution led to small amounts of tin in the outer 10 μm. The efficacy of tin-containing solutions seems to depend mainly on the incorporation of tin into enamel.     

Enamel microhardness and fluoride uptake underneath fermenting and non-fermenting artificial plaque

abstract – Washed cells of Streptococcus sanguis were used to form artificial plaque on the surface of bovine enamel and incubated underneath buffer solutions, initial pH 6, for 36 h at 37°C. The decrease in the microhardness of the enamel surface under fermenting "plaque" could be prevented with fluoride. Enamel under a fermenting "plaque" took up significantly more (P < 0.01) fluoride than enamel under a non-fermenting "plaque" (initial F⁻ in buffer: 10 parts/10⁶). The) artificial plaque did not accumulate fluoride. Within fermenting "plaques", the pH decreased significantly more without fluoride ( P <0.01) than with fluoride. Fluoride combined with sucrose more than negated the softening of the enamel caused by sucrose fermentation, i.e. it increased the hardness above the original values. The diffusion of fluoride through the fermenting artificial plaque was more rapid than through a non-fermenting plaque. These findings suggest that caries-conducive circumstances may promote fluoride uptake by enamel compared with non-caries-conducive circumstances.     

The effect of different fluoridation methods on the red wine staining potential on intensively bleached enamel in vitro

PURPOSE: To study the effect in vitro of different fluoridation methods after intensive bleaching on the color of enamel slabs during a severe staining challenge with red wine. METHODS: 75 specimens were equally divided among five groups. Group 1 (no bleaching, no wine) served as control. Groups 2, 3 and 4 underwent bleaching with 35 % H2O2 for 10 minutes followed by home-bleaching for 8 hours/day with 10% carbamide peroxide on 14 consecutive days. Groups 2 and 3 were fluoridated for 1 hour with either Elmex gelée or Duraphat, respectively whereas Group 4 remained without fluoridation. Group 5 (no bleaching, no fluoride, wine) served as control for the influence of red wine on the color of untreated enamel. Color determination was accomplished using the CIE-Lab System. RESULTS: Nine successive cycles of wine saliva treatment (10 minutes wine, 23 hours 50 minutes saliva) for Groups 2-5 revealed the highest changes of a-values (deltaa= 4.17) (towards red) for the Duraphat-treated group (bleaching, Duraphat, wine) with significantly higher deltaa-values compared with Group 4 (bleaching, no fluoride, wine) (deltaa= 2.97). After final cleaning no differences were found between the three bleached groups (Groups 2, 3 and 4) for deltaL, deltaa, deltab and deltaE, respectively. Exposure to red wine led to an increase in a-values (deltaa= 0.44) of the intrinsic tooth color in Group 5 (no bleaching, no fluoride, wine) that was significantly different from baseline.     

Susceptibility of enamel surfaces to demineralization after application of fluoridated carbamide peroxide gels

The aim of the present study was to evaluate the effect of experimental, fluoridated carbamide peroxide gels on formation of erosively induced demineralization of enamel. Seventy-five bovine enamel specimens were polished for microhardness determination and evenly distributed among 5 groups (A-E). The specimens were treated with 10% carbamide peroxide gel (8 h) and subjected twice to remineralization for 2 h in artificial saliva and demineralisation for 90 s in 1% citric acid, pH 2.2. The cycles of treatment with carbamide peroxide and twofold re- and demineralization were repeated three times. The carbamide peroxide gels were different in pH and fluoride content. Gel A (pH 7.0) and gel B (pH 5.7) were fluoridated (0.5% F), gel C (pH 7.0) and gel D (pH 5.7) were not fluoridated. In control group E the samples were not treated with a gel, but stored in 100% humidity for 8 h instead. Knoop microhardness of the specimens was assessed directly after polishing, and after each carbamide peroxide treatment and demineralization. All specimens showed a loss of microhardness at the end of the experiment. After 3 days, the controls revealed a significantly lower hardness loss compared to the specimens treated with the carbamide peroxide gels. Surface softening was significantly lower for the specimens of group A compared to the remaining groups (B-D), which were not significantly different among each other. It is concluded that treatment with either fluoridated or unfluoridated carbamide peroxide gels, at either neutral and acidic pH, renders enamel more susceptible to demineralization. Use of a fluoridated neutral gel decreases the degree of surface softening compared to the other gels investigated.     

Effect of different peroxide bleaching regimens and subsequent fluoridation on the hardness of human enamel and dentin

STATEMENT OF PROBLEM: Bleaching of teeth by "in-office" or "home" bleaching techniques are popular methods of whitening teeth. However, bleaching may reduce the surface hardness of enamel and dentin. PURPOSE: The purpose of this study was to evaluate (1) the effect of different concentrations of 2 "in-office bleaching" and 2 "home bleaching" agents applied for different time periods on the hardness of enamel and dentin and (2) the effect of subsequent immersion in a low-concentration fluoride solution on the hardness of bleached enamel and dentin. MATERIAL AND METHODS: The enamel and dentin of 12 extracted intact human molar teeth were sectioned lengthwise, ground, polished, embedded in acrylic resin and divided into 4 groups each (n=12). An area of approximately 5 x 5 mm of enamel and dentin tested for Knoop hardness number (KHN; kg/mm 2 ) at a load of 100 g for 20 seconds (baseline). The specimens were stored in distilled water for 1 hour and the microhardness testing repeated as a control group. The groups were bleached as follows: Group OX and Group OQ were bleached "in office" with Opalescence Xtra (35% hydrogen peroxide) and Opalescence Quick (35% carbamide peroxide), respectively, for 5, 15, or 35 minutes and retested for KHN at the end of each time period. "Home bleaching" products Opalescence F (15% carbamide peroxide) and Opalescence (10% carbamide peroxide) were applied in 14-hour applications at 24-hour intervals to Groups OF and O, respectively, which were then tested for KHN. Specimens were immersed in 0.05% fluoride solution (Meridol) for 5 minutes and retested for KHN. The hardness values were analyzed by 2-way ANOVA and Scheffe post hoc test (alpha=.05). Comparisons of KHN between each time and the baseline measurement for each group were of interest. RESULTS: Significant decreases in KHN of enamel and dentin were found after bleaching for all test groups, dependent on the accumulated bleaching time. Group OX showed a 25% KHN reduction for enamel and 22% for dentin after 35 minutes bleaching (P < .0001). Group OQ showed a 13% KHN reduction (P < .0001) for enamel and 10% for dentin after 35 minutes (P < .005). Group OF showed a KHN reduction of 14% for enamel (P < .05) and 9% for dentin (P < .0001) after 14 hours bleaching, and Group O showed an 18% reduction in enamel (P < .0001) and 13% in dentin (P < .0001) for the same period. Fluoridation completely restored the softened dental tissues. CONCLUSION: The "in-office" bleaching technique reduced the hardness significantly more than the "home" bleaching technique. Low-concentration fluoride mouth rinse (Meridol) restored the softened dental tissues.     

不同再矿化处理对漂白后釉质表面形貌及钙磷比的影响

目的 探究不同再矿化处理对漂白后釉质表面形貌及钙磷比的影响。方法 制备牛牙釉质样本,漂白处理后,随机分为5组：去离子水(DW)组;2%氟化钠(NaF)组;10%原花青素(PC)组;酪蛋白磷酸肽-无定形磷酸钙(CPP-ACP)组;PC+CPP-ACP组。用色差仪、扫描电镜、能谱仪和原子力显微镜分别检测样本漂白前、漂白后即刻及再矿化1周的颜色、表面形貌、元素和粗糙度变化。结果 各组间色差值无统计学意义(P>0.05)。扫描电镜显示,再矿化后各组均可见程度不一的矿物质沉积,PC+CPP-ACP组沉积物更明显。能谱仪显示,漂白后釉质表面钙磷比降低,再矿化后均有升高,NaF及PC+CPP-ACP组更高(P<0.05)。原子力显微镜显示,再矿化后各组均可见沉积物且粗糙度降低(P<0.05),PC+CPP-ACP组沉积物更明显、粗糙度更小(P<0.05)。结论 PC和CPP-ACP均能促进漂白后釉质再矿化,联合作用效果更佳。PC和CPP-ACP没有影响漂白效果。     

Effect of fluoride containing bleaching agents on enamel surface properties

OBJECTIVES: To evaluate the effects of fluoridated bleaching agents and post-bleaching fluoridation treatment on the whitening efficiency and microhardness of bovine enamel. METHODS: Twenty five freshly extracted bovine incisors were cut into halves, embedded and then divided into the following five groups: Group 1, untreated controls; Group 2, treatment with 10% carbamide peroxide (CP) bleaching agent; Group 3, treatment with 10% CP followed by a 0.9% sodium fluoride gel application, Group 4, treatment with 10% CP containing 0.11% fluoride; Group 5, treatment with an experimental bleaching agent consisting of 10% CP and 0.37% fluoride. Groups 2-5 were treated 8h per day for 14 days then immersed in saliva for 2 weeks. Enamel morphology changes were evaluated under SEM on Day 14. Changes in enamel color and microhardness were evaluated on Days 7 and 14, and compared with the baseline data. Additionally, microhardness was determined on post-bleaching Days 21 and 28. RESULTS: After 2 weeks, an erosion pattern was noted on the specimens in Groups 2 and 3. Groups 4 and 5 showed a milder demineralized pattern. All the bleached enamel specimens revealed increased whiteness and overall color value. Groups 2 and 3 showed significantly decreased enamel microhardness compared to their baseline data. The specimens treated with fluoridated bleaching agents showed relatively less reduction in enamel microhardness than those treated with nonfluoridated agents during the bleaching treatment. CONCLUSIONS: The fluoridated bleaching agents produced less demineralization of surface morphology and microhardness. The addition of fluoride did not impede the whitening effect.     

Effect of a combined chlorhexidine and NaF mouthrinse: an in vivo human caries model study

Chlorhexidine (CHX) is probably the most widely used and the most potent chemical plaque inhibitory agent, whereas fluoride (F⁻) is the only truly accepted anticaries agent available at present. As they have discrete mechanisms of action, a combination effect of these agents on human dental caries may exist. The inhibitory effect of CHX on the formation of, and acid production in, plaque may reduce a relatively extreme cariogenic challenge sufficiently for it to be overcome by the local F⁻ concentrations achieved by brushing or rinses. The aim of this study was to evaluate the possible caries inhibitory effect of combining 2.2 mM CHX mouthrinses used twice daily with daily 11.9 mM NaF rinses in an in vivo human caries model using plaque-retaining bands on premolars scheduled for extraction. Nine subjects (a total of 28 teeth) were fitted with the bands for 4 wk. Saliva and plaque samples were collected before and after the study period for bacterial cultures, and the tooth surfaces were analyzed by microradiography after careful tooth extractions. The combination of CHX and F⁻ rinses resulted in enamel mineral loss only slightly higher than that observed in "sound" enamel and clearly less than with F⁻ rinses alone. Both total plaque bacteria and Streptococcus mutans were reduced by CHX rinses, confirming the discrete mechanisms of action.     

含氟牙膏对离体脱矿恒牙再矿化作用的实验研究

目的评价含氟牙膏促进离体脱矿恒牙再矿化的作用。方法选取和制作牙体硬度170KHN左右的16颗离体年轻脱矿恒牙标本,随机分成A、B两组(P>0.05)。A组用无氟Crest牙膏作再矿化处理,B组用含氟的Crest牙膏作再矿化处理,同时将A、B组标本浸泡于人唾液中。用微硬度测量仪测定并记录每个牙标本的硬度。结果A组脱矿牙的硬度平均值为151.9±38.3,而再矿化后牙齿的硬度平均值为143.4±18.8,两组比较P>0.05。B组脱矿牙的硬度平均值为160.1±16.5,而再矿化后牙齿的硬度平均值为200.5±21.3,两组比较P<0.05。再矿化后AB两组的硬度值比较P<0.001。结论含氟牙膏对离体脱矿恒牙有较明显的再矿化作用。     

Defluoridation of drinking water with pottery: effect of firing temperature

Excessive fluoride (F) in drinking water should be removed, but simple, inexpensive methods of fluoride removal are not readily available. This study examines the F⁻-binding capacity of clay and clayware, especially the effect of the firing temperature on the F⁻-binding process. A series of pots were made from ordinary potter's clay and fired at 500–1000°C. Likewise, small clay bricks were fired and then crushed and sieved. NaF solutions containing 10 mg/l F⁻ (10 ppm F⁻) were prepared. Suitable aliquots of the solutions were poured into clay pots or exposed to powdered clayware. Samples were taken at storage periods of 30 min to 20 days and analyzed for F⁻ by ion-selective electrodes. The rate and capacity of F⁻-binding in the clayware varied with the firing temperature. Clay fired at approximately 600°C was most effective. Temperatures over 700°C caused a decline in F⁻-binding, and pottery fired at 900°C and above seemed unable to remove F⁻ from water. Pots fired at 500°C or less cracked in water. The findings indicate that clayware, fired at an optimal temperature, may be of practical value for partial defluoridation of drinking water.     

Effect of mucin alone and in combination with various dentifrices on in vitro Remineralization

The aim of this in vitro study was to evaluate the effect of combining various fluoridated dentifrices with mucin on remineralization of bovine enamel. Enamel specimens were embedded in epoxy resin, partly covered with nail varnish, and demineralized in a lactic acid solution (pH 5.0, 14 days). Parts of the demineralized areas of the specimens were then covered with nail varnish. Half of the samples were exposed to a mucin-containing (2.7 g/l) remineralizing solution, the other half to a mucin-free remineralizing solution for 30 days. In each group, the specimens were divided into four subgroups, which were brushed twice a day with a toothpaste containing sodium, stannous/amine, or amine fluoride. The specimens of the fourth subgroup were not brushed, but stored in one of the two solutions. Mineral loss and lesion depth were evaluated from microradiographs. After the remineralization period, specimens that were brushed with one of the dentifrices and stored in the mucin-containing remineralizing solution reacquired more mineral than those brushed and stored in the mucin-free solution (p < 0.05; Bonferroni post hoc test). The results indicate that mucin in combination with various fluorides seems to affect enamel remineralization significantly. Thus, mucin could be considered as an additive to saliva substitutes or mouthwashes in patients with hyposalivation.     

Effects of dental bleaching on micro- and nano-morphological alterations of the enamel surface

PURPOSE: To investigate the effects of dental bleaching on the enamel surface micromorphology using SEM and TEM. METHODS: Fine-polished enamel slabs were randomly divided into eight groups (n = 3). Unbleached specimens served as control (1). The enamel slabs were bleached either with home Illuminé 15% for 8 hours per day, over 7 days (2), 14 days (3), 28 days (4), and 42 days (5) or with Whitestrips for 30 minutes each time, for 14 times (6), 28 times (7) and 42 times (8). The micromorphological surface pattern of the specimens was analyzed by SEM. In addition, two specimens per group (1, 2 and 6) were embedded and analyzed by TEM. RESULTS: SEM and TEM findings revealed that dental bleaching with carbamide peroxide or H2O2 over short periods of time (Groups 2, 6) caused nanomorphological alterations of the enamel surface, whereas prolonged exposure to the bleaching agents resulted in micromorphological changes of the enamel surface. Due to the bleaching process, the thickness of the enamel smear layer was significantly reduced.     

氟保护漆对冷光漂白后釉质表面粗糙度和细菌粘附影响的实验研究

目的:观察氟保护漆对冷光漂白后牙釉质表面粗糙度和细菌粘附状况的影响。方法:将25个新鲜牛牙建立着色模型,共切割成75个唇颊面釉质块,随机分为漂白组、漂白+氟保护漆组和对照组,每组25块。漂白组行常规冷光漂白,漂白+氟保护漆组在常规冷光漂白后于釉质表面涂布1 g/L氟保护漆,对照组不做任何处理。用T100粗糙度轮廓仪检测3组釉质表面粗糙度;通过细菌体外粘附实验分析6、24、48、72 h时釉质表面粘附的细菌量;并用扫描电镜观察各组釉质表面形貌和细菌粘附情况。结果:漂白组的釉质表面粗糙度和菌落形成计数明显大于对照组和漂白+氟保护漆组(P<0.05);氟保护漆组和对照组无显著差异(P>0.05)。扫描电镜观察见漂白组釉质表面局部脱矿,釉质呈蜂窝状,有大量变异链球菌粘附;漂白+氟保护漆组釉质表面光滑,有少量变异链球菌粘附和矿物质沉积。结论:漂白后釉质表面粗糙度增加,细菌粘附量增加;漂白后氟保护漆处理可降低釉质表面粗糙度,使细菌粘附量减少。     

Effect of fluoridated carbamide peroxide gels on enamel microtensile bond strength

The aim of this study was to examine the resin bond strength on enamel treated with different fluoridated bleaching agents. Forty-eight bovine incisors were divided into four groups to receive bleaching treatments, over a 14-d period, as follows: no treatment; 10% carbamide peroxide (CP) bleaching; 10% CP containing 0.11% fluoride; and 10% CP containing 0.37% fluoride. Immediately, and 7 and 14 d after bleaching, the enamel surfaces were respectively bonded with composite and sectioned to create resin–enamel beams. These beams were subjected to the microtensile bond strength (μTBS) test, then assessed for failure mode under scanning electron microscopy. The results showed that the 0.37% fluoridated group demonstrated a μTBS equivalent to that of the unbleached group at all stages. Non-fluoridated and 0.11% fluoridated groups showed a weaker μTBS after bleaching but regained the bond strength after 14 or 7 d of storage, respectively. In the non-fluoridated group, adhesive failure was the predominant fracture pattern that comprised the enamel prism demineralization change and widely dispersed voids on the resin–enamel interfaces. No evident enamel erosion and fewer microporosities were found in the 0.37% fluoridated group. Accordingly, treatment with 0.37% fluoridated CP maintained the μTBS as effectively as the unbleached enamel. Additional fluoride in the bleaching agents may facilitate subsequent restorative treatment by inhibiting enamel demineralization.     

In situ mineral loss inhibition by CO2 laser and fluoride

Laser and fluoride treatments have been shown to inhibit enamel demineralization in the laboratory. However, the intra-oral effects of this association have not been tested. This study assessed in situ the effect of a Transversely Excited Atmospheric CO2 laser (lambda = 9.6 mum) and the use of pressure fluoridated dentifrice on enamel demineralization. During two 14-day phases, 17 volunteers wore palatal appliances containing human enamel slabs assigned to treatment groups, as follows: (1) non-fluoride dentifrice, (2) CO2 laser irradiation plus non-fluoride dentifrice, (3) fluoride dentifrice, and (4) CO2 laser irradiation plus fluoride dentifrice. A 20% sucrose solution was dripped onto the slabs 8 times per day. The specimens treated with laser and/or fluoridated dentifrice presented a significantly lower mineral loss when compared with those from the non-fluoride dentifrice group. The results suggested that CO2 laser treatment of enamel inhibits demineralization in the human mouth, being more effective when associated with fluoride.