The impact of remineralization agents on dental bleaching efficacy and mineral loss in bleached enamel
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Abstract This study evaluated the effect of remineralization agents on bleaching efficiency, enamel mineral changes, and post‐bleaching color stability. A total of 112 enamel‐dentin blocks were prepared from bovine teeth. Following initial color measurements, separate treatment regimens were carried out as follows: negative control (no treatment); positive control (bleaching only); bleaching, then NaF; bleaching + NaF (mix); bleaching, then CPP‐ACPF; bleaching + CPP‐ACPF (mix); bleaching, then nHAP+F; bleaching + nHAP+F (mix). Color measurements were repeated after immersion in distilled water for 7 days, and again after staining with coffee solution for 14 days. The CIELAB‐based whiteness index was used to evaluate bleaching efficiency, and the CIEDE2000 color difference formula for color stability. Chemical investigation was performed using scanning electron microscopy with energy dispersive spectroscopy and X‐ray diffraction analyses. The experimental groups showed significant increases in whiteness compared to the negative control, and the staining after bleaching did not result in statistically significant differences between the groups. Energy dispersive spectroscopic analysis revealed that bleaching protocols had no impact on elemental levels as well as the ratio of Ca/P. The combined use of bleaching agents with remineralization agents did not affect bleaching effectiveness but also did not provide an additional contribution.Keywords:
Distilled water
Color difference
The purpose of this study was to investigate overall degradative changes occurring to enamel matrix proteins in small, freeze-dried pieces of rat incisor enamel homogenized and incubated directly for 0-48 hours in a synthetic enamel fluid solution (165 mM total ionic strength with 0.153 mM calcium chloride) versus other samples homogenized and incubated for the same time intervals in distilled water. The results indicated that many alterations in the apparent molecular weights of enamel matrix proteins took place under both conditions although the rates for many degradative changes over a 48 hour period were often slower in distilled water than in synthetic enamel fluid. Freeze-dried enamel samples homogenized and incubated in 165 mM Tris-HCl buffer at pH 8.0 showed changes comparable to those seen with distilled water. This suggested that differences observed between samples incubated in enamel fluid versus distilled water were unrelated to pH or ionic strength of the solutions and may be the result of a requirement by some enamel proteinases for small amounts of free calcium ions in incubation media. Of interest were findings that some enamel matrix proteins, especially those in strips taken from the first half of the secretory stage of amelogenesis, were degraded much faster in distilled water than in synthetic enamel fluid. The reasons for this effect are unclear although, in this case, calcium ions could be inhibitory to hydrolysis of certain matrix proteins by the enamel proteinases.
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Blue light, especially from LED devices, is a tool very frequently used in dental procedures. However, the investigations of its effects on dental enamel are focused primarily on enamel demineralization and fluoride retention. Despite the fact that this spectral region can inhibit enamel demineralization, the consequences of the irradiation on demineralized enamel are not known. For this reason, we evaluated the effects of blue LED on enamel remineralization. Artificial lesions formed in bovine dental enamel samples by immersion in undersaturated acetate buffer were divided into three groups. In the first group (DE), the lesions were not submitted to any treatment. In the second (RE), the lesions were submitted to remineralization. The lesions from the third group (LED+RE) were irradiated with blue LED (455nm, 1.38W/cm2, 13.75J/cm2 and 10s) before the remineralization. Cross-sectional microhardness was used to assess mineral changes induced by remineralization under pH-cycling. The mineral deposition occurred preferably in the middle portion of the lesions. Specimens from group RE showed higher hardness value than the DE ones. On the other hand, the mean hardness value of the LED+RE samples was not statistically different from the DE samples. Results obtained in the present study show that the blue light is not innocuous for the dental enamel and inhibition of its remineralization can occur.
Tooth Remineralization
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Abstract Objective: The purpose of this study was to evaluate morphological changes in cavities prepared by the Er:YAG laser (2.94 μm) at different parameters of irradiation and by a diamond bur. Experimental design : Cavities were prepared on 27 human molars ( n = 3): G1 , 15 Hz/160 mJ enamel/6 Hz/200 mJ dentin; G2 , 15 Hz/180 mJ enamel/6 Hz/200 mJ dentin; G3 , 15 Hz/160 mJ enamel/6 Hz/250 mJ dentin; G4 , 15 Hz/180 mJ enamel/6 Hz/250 mJ dentin; G5 , 15 Hz/180 mJ enamel/10 Hz/180 mJ dentin; G6 , 15 Hz/160 mJ enamel/10 Hz/180 mJ dentin; G7 , 15 Hz/160 mJ enamel/10 Hz/160 mJ dentin; G8 , 15 Hz/180 mJ enamel/10 Hz/160 mJ dentin; G9 , diamond bur. For SEM analysis, samples were fixed (2.5% glutaraldheyde, 12 h, 4°C), dehydrated (25–100% ethanol), dried, and sputter‐coated with gold. Results : Despite the changes on energy and repetition‐rate settings, all laser‐treated samples showed no evidence of thermal damage or signs of burning and melting. Er:YAG laser ablated dental hard tissues showed exposed enamel prisms, dentin surface without smear layer, and opened dentinal tubules. Conclusion : Different Er:YAG laser parameters were effective for ablation of hard tissues, creating an irregular and microretentive morphological pattern without hard tissue damage. Microsc. Res. Tech., 2007. © 2007 Wiley‐Liss, Inc.
Er:YAG laser
Dentinal Tubule
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A rapid and flexible model system has been developed to study human enamel behaviour under conditions of oscillating pH similar to those experienced in the mouth. The model uses realistic time intervals and operates at in vivo temperatures (35-37 degrees C). Mineral loss or gain is measured quantitatively on a volume basis. Results indicate that for single 1-day periods with three 20-min exposures to acid, 1% v/v of enamel mineral was lost. These results, together with the histological appearance of the tissue, are in close agreement with previous studies of enamel caries.
Cycling
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To study the effect of several fluorides on resistance to erosion of beverage on enamel and remineralization of etched enamel.The enamel slabs were prepared from human retained primary teeth. After treated with 0.1%NaF solution, fluoride Protector and Bifluorid 12 respectively, they were immersed at intervals in beverage. The SMH were measured before and after experiments. Morphological changes of enamel surface were observed by SEM.The SMH of all enamel slabs descended obviously after exposed to beverage. The difference between control group and test groups was significant statistically. The variable degree etch caused by beverage were found by SEM. The SMH of etched enamel increased significantly after treated with fluoride, and the Bifluorid 12 showed the highest significant increase.The treatment of enamel with topical fluoride can enhance the resistance of enamel to acid etch of soft drinks and the remineralization of enamel following exposed to beverage. This study recommends the Bifluorid 12 is an efficacious fluoride in remineralization of etched enamel.
Tooth enamel
Human tooth
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The mechanical properties of enamel and dentin were studied using test specimens having the same shape and dimensions because these properties might vary with the experimental conditions and specimen shapes and dimensions. Healthy human teeth were used as specimens for mechanical tests. The stress (MPa), strain (%), and elastic modulus (E, MPa) of the specimens were obtained from compression tests. The maximum stresses of the enamel, dentin, and enamel-dentin specimens were 62.2 ± 23.8, 193.7 ± 30.6, and 126.1 ± 54.6 MPa, respectively. The maximum strains of the enamel, dentin, and enamel-dentin specimens were 4.5 ± 0.8%, 11.9 ± 0.1%, and 8.7 ± 2.7%, respectively. The elastic moduli of the enamel, dentin, and enamel-dentin specimens were 1338.2 ± 307.9, 1653.7 ± 277.9, and 1628.6 ± 482.7 MPa, respectively. The measured hardness value of enamel specimens (HV = 274.8 ± 18.1) was around 4.2 times higher than that of dentin specimens (HV = 65.6 ± 3.9). Judging from the measured values of the stress and strain of enamel specimens, enamel tended to fracture earlier than dentin; therefore, it was considered more brittle than dentin. However, judging from the measured hardness values, enamel was considered harder than dentin. Therefore, enamel has higher wear resistance, making it suitable for grinding and crushing foods, and dentin has higher force resistance, making it suitable for absorbing bite forces. The different mechanical roles of enamel and dentin may arise from their different compositions and internal structures, as revealed through scanning electron micrographs of enamel and dentin.
Human tooth
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Opalescence
Carbamide peroxide
Tooth Whitening
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Remineralization of human enamel is an important issue in the prevention of caries. Fluoride has an important influence on the remineralization process. A great deal of research has been done into the role played by the method of application and by the concentration and type of fluoride. In the clinical study of this dissertation the process of remineralization of lesions in human enamel was longitudinally followed in vivo during a period of 3 months. Both the remineralization in the surface softened enamel lesion and the subsurface enamel lesion of human enamel were studied. In addition, attention was devoted especially to the influence of fluoride on this remineralization. The results indicated that the use of a 1,500 ppm fluoridated NaF toothpaste was more effective on the remineralization process than the use of a 50 pmm NaF mouthrinse. Important is the fluoride gradient in the enamel lesion, and in particular the fact that fluoride reaches the lesion front. This most likely accounts for the remineralization efficiency.
Tooth Remineralization
Toothpaste
Human tooth
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The aim was to investigate interactions between enamel and dentine at low pH under conditions simulating those at the enamel-dentine junction. Sound enamel blocks were demineralised in acid-gel systems, at pH 4.6, either in isolation, next to one, or in the middle of two, abutting dentine blocks. The gels were initially infinitely undersaturated with respect to enamel. In a second study, enamel blocks containing pre-formed lesions were placed in acid-gel systems, at pH 5.0, either in isolation or next to dentine blocks. The systems were initially either partially or infinitely undersaturated. In the partially saturated systems, calcium and phosphate concentrations were representative of plaque fluid. In the first study, demineralisation of enamel next to one dentine block was reduced in inverse proportion to the distance from the dentine. Demineralisation of enamel between two dentine blocks was retarded markedly across the whole block. In the second study, in the partially saturated systems, enamel lesions next to dentine blocks remineralised, whereas those in isolation demineralised further. We suggest that diffusion of dissolved dentine mineral over the enamel in the infinitely undersaturated system was sufficient to reduce undersaturation, thus retarding demineralisation, and that in the partially saturated systems, dentine dissolution together with the added calcium phosphate caused remineralisation of enamel lesions. Fluoride released from dissolving dentine may have augmented these effects. Different rates of demineralisation in enamel and dentine, or enamel remineralisation with concurrent dentine demineralisation, enabled by differences in their solubilities, could help explain the progression of so-called ‘hidden caries’.
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