Dental Enamel Surfaces Research Articles

Effect of hydrogen peroxide activated by ultraviolet light and carbamide peroxide in teeth bleaching

Summary:Objective: to evaluate dental enamel surface alterations after bleaching treatments with Hydrogenperoxide and Fluoride. Methods: Extracted pre-molars were analys under SEM after bleachingtreatment; the samples were storaged in saline solution. Two phases were made, without and withfluoride application after bleaching treatment using Nitewhite® and Zoom2® as bleaching agents, theshade was taken at baseline and after the bleaching procedure. Results: 36.6% of samples showedmoderate alterations and 32.9% showed severe enamel alterations. Post/treatment with fluoride showedvariable outcomes, but mild alterations in the fluoride/treated samples were found to be morefrequent, A statistically significant result was found among fluoride/treated and non/treated groupsafter bleaching (P<0.005) chisquare test. In contrast, within fluoride/treated groups it was notfound significant differences. Conclusions: The use of high concentrated in/office carbamideperoxide may require limited application sessions as recommended by the manufacturer. The use ofpost/treatment fluoride may bring great benefit to patient’s dental hypersensitivity. Key words:Carbamide Peroxide. Hydrogen Peroxide. Enamel roughness. Fluoride. Remineralization.

Effect of 10% Strontium Chloride and 5% Potassium Nitrate with Fluoride on Bleached Bovine Enamel.

Background:Dental whitening has been increasingly sought out to improve dental aesthetics, but may cause chemical and morphological changes in dental enamel surfaces.Objective:This study evaluated in vitro the effect of 10% strontium chloride and 5% potassium nitrate with fluoride on bovine enamel, through tristimulus colorimetry, Knoop microhardness (KHN), and roughness after bleaching with 35% hydrogen peroxide (HP).Methods:The specimens were divided into three groups (n=15): GControl received bleaching treatment with 35% HP; GNitrate received bleaching with 35% HP followed by the application of 5% potassium nitrate with 2% sodium fluoride; and GStrontium received bleaching with 35% HP followed by the application of 10% strontium chloride on the enamel. Next, five specimens of each experimental group were subjected to KHN and tristimulus colorimetry tests, and 10 specimens were subjected to surface roughness (SR) tests. The values obtained for the different groups were compared through analysis of variance (ANOVA) followed by a post-hoc Tukey-Kramer test in addition to Student’s T-test for paired data.Results:In the intergroup comparison, KHN final differed statistically (p<0.05). The mean SR final of the experimental groups differed statistically from the GControl group (p<0.05). In addition, the groups did not differ in color variation (p>0.05).Conclusion:10% strontium chloride and 5% potassium nitrate combined with 2% fluoride downplayed morphological changes to the enamel, without interfering with the effectiveness of the bleaching process.

The Effect of ortho-Phosphoric Acid Etching Application on Enamel Surface ATR-FTIR and SEM studies

The acid etching procedure represents a procedure that increases the bond strength between the etched enamel and the composite resin. The aim of this study was to evaluate the effect of ortho-phosphoric acid 37% on the morphology and composition of the enamel surface. The surfaces of four extracted teeth (two incisors and two premolars) were etched with 37% ortho-phosphoric acid solution for 15 seconds. The teeth were examined by ATR-FTIR spectroscopy and SEM microscopy in order to determine the degree of the enamel demineralization. A major change on teeth composition and morphology has been found. The results are discussed and compared with those of the effects of different concentrations of bleaching agent (carbamide peroxide) on the enamel surface. Etching with 37% ortho-phosphoric acid caused structural and morphological changes to the dental enamel surfaces.

Influence of subinhibitory concentrations of extracts from Psidium cattleianum (Sabine) and Myracrodruon urundeuva (Allemao) on mutans streptococci adhesion to glass and enamel surfaces.

This study evaluated the influence of subinhibitory concentrations of extracts from Myracrodruon urundeuva and Psidium cattleianum on the adhesion of cariogenic cocci to the surface of glass and bovine enamel. The aqueous extracts were prepared from leaves by heating in deionized water and sterilized by filtration (22μm). The minimum inhibitory concentration (MIC) of the extracts on S. mutans ATCC 1910 and ATCC 35688 was determined by the broth dilution method. In the tests of adhesion to glass surfaces, glass tubes were treated with saliva and sucrose and the bacterial strains were cultivated in concentrations equivalent to 25% of MIC, which were also maintained in the adhesion assay. After the contact between the cells and the glass, the unbound cocci were removed and, finally, it was performed the removal of the cells adhered to the glass by sonication. The percentage of adhesion was determined by comparing the number of bacteria adhered to the total inoculated bacteria, in the presence and absence of the subinhibitory concentrations of the extracts. For enamel adhesion tests, bovine enamel samples were standardized, polished, treated with saliva and, in the test group, received the bacterial inoculum and 25% of the MIC of the extracts. The enamel blocks were removed and the total of adhered cocci was determined by cultivation on BHI agar supplemented with horse blood in anaerobic conditions for 48h at 37oC. The results were evaluated through analysis of variance (ANOVA). The extracts were effective in inhibiting bacterial adhesion to glass and dental enamel surfaces, although inhibition varied according to bacterial strain and extract, producing from 40 to 60% of inhibition. The results reinforce the possibility of the use of extracts of plants of the Brazilian savanna in the control of cariogenic biofilms.Descriptors: Bacteria; Prevention &amp; Control; Plant Extracts; Dental Caries.

Chemical Composition and Microhardness of Human Enamel Treated with Fluoridated Whintening Agents. A Study in Situ.

Background:Dental whitening has been increasingly sought out to improve dental aesthetics, but may cause chemical and morphological changes in dental enamel surfaces.Objective:Assess in situ the effects of high-concentration hydrogen peroxide with and without fluoride on human dental enamel using the ion chromatography test (IC) and the Knoop hardness test (KHN).Material and Methods:Nineteen enamel specimens were prepared using third human molars. These specimens were fixed on molars of volunteers and were divided into groups: OP38-Opalescence Boost PF38%, PO37-Pola Office 37.5% and CO-Control group. For chemical analysis (n= 3), the dentin layer was removed, keeping only the enamel, which was subjected to acidic digestion by microwave radiation. It was necessary to perform sample dilutions for the elements fluorine (F), calcium (Ca) and phosphorus (P) for quantification using the IC test. The KHN (n= 5) was performed before and after the treatments. Five indentations were made, separated by 100 µm, for each specimen using a load of 25 gf for 5 seconds in the microdurometer. The data were analyzed using ANOVA with a 5% significance level.Results:The OP38 group had the largest concentrations of F, Ca and P ions. The PO37 group showed the lowest concentrations of F and Ca ions. The average KHN was not significantly different between the OP38 and PO37 groups.Conclusion:Enamel whitened with hydrogen peroxide containing fluoride had greater concentrations of F, Ca and P ions. The presence of fluoride in the whitening agent did not influence the enamel microhardness.

Intraoral electric potential via oral bacterial power generation -A novel mechanism of biofilm formation.

In the early stages of biofilm accumulation, the electric charge of the dental enamel and pellicle surfaces is known to be involved. We therefore investigated the relationship between oral hygiene and intraoral electric potential (IoP) in 45 male participants using a double-blind study. IoP, but not body surface electric potential, was loosely correlated with oral hygiene condition (Oral Hygiene Index; OHI). IoP was also loosely correlated with smartphone use; however, there was no significant correlation between smartphone use and OHI. IoP elevation might be caused by OHI elevation resulting from biofilm formation as an internal factor, with smartphone use as an external factor. This in vitro study revealed the generating capacity of Streptococcus mutans accompanied by biofilm accumulation using a microbial fuel cell. These results suggest that IoP elevation is caused by biofilm accumulation induced by power generation of oral bacteria, resulting in elevation of OHI.

Effects of Bleaching Agents, Neutral Fluoride Gels, and Surface Sealants on Enamel Surface Roughness

ABSTRACT Aim The aim of this in vitro study was to evaluate the surface roughness of enamel after the application of different bleaching agents and to determine the effect of fluoride and bonding agent application on the roughness of bleached enamel. Materials and methods Forty-two dental slice polished enamel surfaces were randomly assigned to six groups. The surfaces of the slices were treated with 30% carbamide peroxide (CP) (groups I to III), or 38% hydrogen peroxide (HP) (groups IV to VI). Groups I and IV were only bleached. Topical fluoride was applied to the bleached surface of groups II and V. Groups III and VI were covered with a bonding agent. The surface roughness was analyzed with a profilometer. Data were subjected to analysis of one-way analysis of variance, Kruskal-Wallis, and Mann-Whitney U tests (p &gt; 0.05). Results There were no statistically significant differences between the surface roughness of the untreated control specimens and the specimens treated with the bleaching materials, fluoride gel, and dental bonding agent (p &gt; 0.05). Conclusion Bleaching treatment with 38% HP and 30% CP does not alter enamel surface roughness. Clinical significance The application of topical neutral sodium fluoride agents and dental bonding agents does not have any influence on enamel surface roughness. How to cite this article Gümüştaş B, Gürbüz Ö, Efes BG. Effects of Bleaching Agents, Neutral Fluoride Gels, and Surface Sealants on Enamel Surface Roughness. J Oper Dent Endod 2017;2(2):74-78.

Frequency of Application of AmF/NaF/SnCl2 Solution and Its Potential in Inhibiting the Progression of Erosion in Human Dental Enamel - An In Vitro Study.

To evaluate whether increasing the frequency of its use can enhance the protective effect of AmF/NaF/SnCl2 solution against dental erosion. Sixty human enamel samples were obtained from sound human third molars, and after the formation of incipient erosive lesions (1% citric acid, pH 4.0, for 3 min), they were divided into five treatment groups (n = 12): G1 - deionised water (negative control); G2 - NaF solution (positive control) once a day; G3 - NaF solution (positive control) twice a day; G4 - AmF/NaF/SnCl2 solution once a day; G5 - AmF/NaF/SnCl2 solution twice a day. The samples were then subjected to 5 days of erosive cycling through 6 daily immersions (2 min each) in citric acid solution (0.05 M, pH 2.6). At the end of erosive cycling, surface wear was determined by means of optical profilometry. One-way ANOVA showed that the surface wear was affected by surface treatments (p < 0.001). Tukey's test showed no difference between the groups in which NaF was applied once or twice, but they showed limited reduction in wear compared to the deionised water group (G1). In the groups treated with the AmF/NaF/SnCl2 solution, there was a statistically significant difference between one and two application times (p < 0.001). Although both demonstrated statistically significantly reduced tissue loss, increasing the frequency increased its anti-erosive potential. The AmF/NaF/SnCl2 solution proved to be effective in reducing dental enamel surface loss and its use twice a day potentiated its anti-erosive effect.

Explorations in LEXT image and profile capture for dental enamel surface morphology

Bioarchaeology as a field of study can contribute important insights to our understanding of how stress-related phenomena experienced in childhood influence later life conditions. One area that is especially effective is looking at the dental enamel surface microstructures reflecting patterns of growth and growth disruption. Since dental enamel grows incrementally, and because it does not remodel once formed, a record of growth disruption (formed during childhood) is preserved for the rest of an individuals' life. Enamel surface defects are commonly observed macroscopically as enamel hypoplasia. However, this method does not capture the smaller defects reflecting a disruption in only a few of the growth lines visible on the tooth surface. Previous approaches to the assessment of these structures have included scanning electron microscopes and polarized light microscopes with photomontaging and z-stacking capacity. This paper presents the application of the Olympus LEXT 3D Laser Measuring Microscope OLS4000 and Olympus LEXT analytical software to capture and examine dental enamel surface microstructures. The use of the LEXT for these purposes is critically assessed, and the strengths and challenges discussed. Recommendations are made for future application of this instrument to bioarchaeological research.

Effects of CO2 laser irradiation on matrix-rich biofilm development formation-an in vitro study.

BackgroundA carbon dioxide (CO2) laser has been used to morphologically and chemically modify the dental enamel surface as well as to make it more resistant to demineralization. Despite a variety of experiments demonstrating the inhibitory effect of a CO2 laser in reduce enamel demineralization, little is known about the effect of surface irradiated on bacterial growth. Thus, this in vitro study was preformed to evaluate the biofilm formation on enamel previously irradiated with a CO2 laser (λ = 10.6 µM).MethodsFor this in vitro study, 96 specimens of bovine enamel were employed, which were divided into two groups (n = 48): 1) Control-non-irradiated surface and 2) Irradiated enamel surface. Biofilms were grown on the enamel specimens by one, three and five days under intermittent cariogenic condition in the irradiated and non-irradiated surface. In each assessment time, the biofilm were evaluated by dry weigh, counting the number of viable colonies and, in fifth day, were evaluated by polysaccharides analysis, quantitative real time Polymerase Chain Reaction (PCR) as well as by contact angle. In addition, the morphology of biofilms was characterized by fluorescence microscopy and field emission scanning electron microscopy (FESEM). Initially, the assumptions of equal variances and normal distribution of errors were conferred and the results are analyzed statistically by t-test and Mann Whitney test.ResultsThe mean of log CFU/mL obtained for the one-day biofilm evaluation showed that there is statistical difference between the experimental groups. When biofilms were exposed to the CO2 laser, CFU/mL and CFU/dry weight in three day was reduced significantly compared with control group. The difference in the genes expression (Glucosyltransferases (gtfB) and Glucan-binding protein (gbpB)) and polysaccharides was not statically significant. Contact angle was increased relative to control when the surface was irradiated with the CO2 laser. Similar morphology was also visible with both treatments; however, the irradiated group revealed evidence of melting and fusion in the specimens.ConclusionIn conclusion, CO2 laser irradiation modifies the energy surface and disrupts the initial biofilm formation.

In vivo confocal microscopy analysis of enamel defects after orthodontic treatment: A preliminary study

ABSTRACTAfter orthodontic treatment with fixed appliances, bonded brackets and residual adhesive must be removed. This procedure should lead to restitutio ad integrum of the enamel or, at least, restore the enamel surface as closely as possible to its pre-treatment conditions. The purpose of this study is the in vivo assessment at a microscopic resolution of enamel surfaces after bracket debonding while avoiding the tooth extraction. Nine orthodontic patients who had brackets removed at the conclusion of orthodontic treatment were enrolled. In vivo reflectance confocal microscopy imaging of dental enamel surface after debonding was performed for each patient. Eighteen upper incisors were analyzed, 10 in which the enamel demineralization appeared after the treatment and 8 in which the demineralization was present before the treatment. RCM analyses showed some speckled or roundish dark areas within the enamel. Moreover enamel alterations were detected at different levels of depth. The present in vivo microscopic study allowed for highlighting structural features in dental enamel, after debonding, at a microscopic resolution in real-time and in a non-invasive way, without the need for extraction or processing of the samples.

Identification of ssDNA aptamers specific to clinical isolates of Streptococcus mutans strains with different cariogenicity.

Streptococcus mutans, a Gram-positive facultative anaerobic bacterium, is considered to be a major etiological factor for dental caries. In this study, plaques from dental enamel surfaces of caries-active and caries-free individuals were obtained and cultivated for S. mutans isolation. Morphology examination, biochemical characterization, and polymerase chain reaction were performed to identify S. mutans The cariogenicity of S. mutans strains isolated from clinical specimens was evaluated by testing the acidogenicity, aciduricity, extracellular polysaccharide production, and adhesion ability of the bacteria. Finally, subtractive SELEX (systematic evolution of ligands by exponential enrichment) technology targeting whole intact cells was used to screen for ssDNA aptamers specific to the strains with high cariogenicity. After nine rounds of subtractive SELEX, sufficient pool enrichment was achieved as shown by radioactive isotope analysis. The enriched pool was cloned and sequenced randomly, followed by MEME online and RNA structure software analysis of the sequences. Results from the flow cytometry indicated that aptamers H1, H16, H4, L1, L10, and H19 could discriminate highly cariogenic S. mutans strains from poorly cariogenic strains. Among these, Aptamer H19 had the strongest binding capacity with cariogenic S. mutans strains with a dissociation constant of 69.45±38.53 nM. In conclusion, ssDNA aptamers specific to highly cariogenic clinical S. mutans strains were successfully obtained. These ssDNA aptamers might be used for the early diagnosis and treatment of dental caries.

Analysis of Dental Enamel Surface Submitted to Fruit Juice Plus Soymilk by Micro X-Ray Fluorescence: In Vitro Study.

Objective. This paper aimed to analyze the in vitro industrialized fruit juices effect plus soy to establish the erosive potential of these solutions. Materials and Methods. Seventy bovine incisors were selected after being evaluated under stereomicroscope. Their crowns were prepared and randomly divided into 7 groups, using microhardness with allocation criteria. The crowns were submitted to the fruit juice plus soy during 15 days, twice a day. The pH values, acid titration, and Knoop microhardness were recorded and the specimens were evaluated using X-ray microfluorescence (µXRF). Results. The pH average for all juices and after 3 days was significantly below the critical value for dental erosion. In average, the pH value decreases 14% comparing initial time and pH after 3 days. Comparing before and after, there was a 49% microhardness decrease measured in groups (p < 0.05). Groups G1, G2, G5, and G6 are above this average. The analysis by μXRF showed a decrease of approximately 7% Ca and 4% P on bovine crowns surface. Florida (FL) statistical analysis showed a statistically significant 1 difference between groups. Thus, a tooth chance to suffer demineralization due to industrialized fruit juices plus soy is real.

Dental Enamel Quality and Black Tooth Stain: A New Approach and Explanation by using Raman and AFM Techniques

This contribution takes in account investigation of dental enamel regarding “quality” of hydroxyapatite material involved in the mineralization process. Areas damaged by black stain were investigated in order to evaluate changes in chemical composition as compared to those of healthy dental enamel.Different sectors on tooth surfaces were analyzed using micro-Raman spectroscopy. The integral areas of ν1 (960 cm−1) phosphate peak as well as of B-type carbonate peak ν2 (1070 cm−1) were obtained to investigate structural differences between the specimens (healthy/unhealthy enamel tooth and different sectors on unhealthy surface tooth). A complete list of chemical specimens involved in chemical processes on dental enamel surface was obtained by Energy Dispersive x-rays (EDX) investigation.It was noticed that mineralized carbonate peak at 1070 cm−1 decreased significantly for unhealthy tooth enamel or spots areas (as fluorite groups), suggesting that carbonate ions are easily dissolved in the presence of fluoride.The present study is confirming an organic origin for the dental “black stain.” The “black stain” is the result of a complex generation process from the damaged enamel, thus explaining their reappearance after the mechanical removing. A possible model for the “black stain” generation process is advanced.

Brief Communication: An enigmatic enamel alteration on the anterior maxillary teeth in a prehistoric North Italian population.

In this paper we describe a hitherto undocumented modification of the dental enamel surface observed in an Early Bronze Age population from northern Italy. The defect, which can be described as a curvilinear groove, is located on the lingual surface of incisors and canines in the upper jaw. This groove, documented both in the permanent and deciduous dentition, is located at approximately 1 mm from the cervix and extends from the mesiolingual to the distolingual surface. The occurrence of the groove is not related to the sex of the affected individuals, but its degree of expression is related to age at death. Because of its morphology, the groove cannot be considered as a result of disruptions in the process of enamel deposition. At the present stage of research we suggest that the groove might have been the result of some kind of dental erosion caused by as yet unidentified chemical factors.

Development of a composite resin disclosing agent based on the understanding of tooth staining mechanisms

ObjectivesTo characterize the surface composition of dental enamel and composite resin, assess the ability of dyes with different affinities to stain these surfaces, and use this information to develop a disclosing agent that stains composite resin more than dental enamel. MethodsOne hundred and ten sound extracted teeth were collected and 60 discs of composite resin, 9mm diameter and 3mm thick, were prepared. X-ray photoelectron spectroscopy (XPS) was employed to determine the elemental composition on the different surfaces. A tooth shade spectrophotometer was used to assess the change in shade after staining the surfaces with different dyes. ResultsXPS analysis revealed that surfaces of both outer dental enamel and composite resin contained relatively high amounts of carbon, specifically hydrocarbons. Both dental enamel and composite surfaces were stainable with the hydrophobic dye (p<0.05); however, the composite resin was stained more than the dental enamel (p<0.05). ConclusionsThe hydrophobic surface of dental enamel and composite resin might explain their high affinity to be stained by food and beverages containing hydrophobic molecules. The composite resin is more stainable by hydrophobic dyes than dental enamel. We used this information to develop an agent for disclosing composite resins that could be used to visualize composite resins that need to be removed. Clinical significanceRemoval of composite resin can be problematic, time consuming and stressful to the dental practitioner. A composite disclosing agent would help the dental practitioner identify the composite resin and facilitate its removal without damaging the adjacent healthy tooth tissues.

Abrasive Effect of Mastic-essential-oil Compound Dentifrice on Dental Enamel Surface

Abrasive Effect of Mastic-essential-oil Compound Dentifrice on Dental Enamel Surface

Adherence inhibition of Streptococcus mutans on dental enamel surface using silver nanoparticles

The aim of this ex vivo study was to evaluate the adherence capacity of Streptococcus mutans after being exposed to three different sizes of silver nanoparticles on healthy human dental enamel. Three different sizes of silver nanoparticles (9.3, 21.3 and 98nm) were prepared, characterized and an adherence testing was performed to evaluate their anti-adherence activity on a reference strain of S. mutans on healthy dental enamel surfaces. Colony-Forming Unit count was made for adherence test and light microscopy, atomic force microscopy and scanning electron microscopy were used to compare qualitative characteristics of S. mutans. 9.3nm and 21.3nm groups did not show differences between them but statistical differences were found when 9.3nm and 21.3nm groups were compared with 98nm and negative control groups (p<0.05). Microscopy analysis shows a better inhibition of S. mutans adherence in 9.3nm and 21.3nm groups than the 98nm group when compared with control group. Silver nanoparticles showed an adherence inhibition on S. mutans and the anti-adherence capacity was better when silver nanoparticles were smaller.

Morphology and structure of polymer layers protecting dental enamel against erosion

ObjectivesHuman dental erosion caused by acids is a major factor for tooth decay. Adding polymers to acidic soft drinks is one important approach to reduce human dental erosion caused by acids. The aim of this study was to investigate the thickness and the structure of polymer layers adsorbed in vitro on human dental enamel from polymer modified citric acid solutions. MethodsThe polymers propylene glycol alginate (PGA), highly esterified pectin (HP) and gum arabic (GA) were used to prepare polymer modified citric acids solutions (PMCAS, pH 3.3). With these PMCAS, enamel samples were treated for 30, 60 and 120s respectively to deposit polymer layers on the enamel surface. Profilometer scratches on the enamel surface were used to estimate the thickness of the polymer layers via atomic force microscopy (AFM). The composition of the deposited polymer layers was investigated with X-ray photoelectron spectroscopy (XPS). In addition the polymer–enamel interaction was investigated with zeta-potential measurements and scanning electron microscopy (SEM). ResultsIt has been shown that the profilometer scratch depth on the enamel with deposited polymers was in the range of 10nm (30s treatment time) up to 25nm (120s treatment time). Compared to this, the unmodified CAS-treated surface showed a greater scratch depth: from nearly 30nm (30s treatment time) up to 60nm (120s treatment time). Based on XPS measurements, scanning electron microscopy (SEM) and zeta-potential measurements, a model was hypothesized which describes the layer deposited on the enamel surface as consisting of two opposing gradients of polymer molecules and hydroxyapatite (HA) particles. SignificanceIn this study, the structure and composition of polymer layers deposited on in vitro dental enamel during treatment with polymer modified citric acid solutions were investigated. Observations are consistent with a layer consisting of two opposing gradients of hydroxyapatite particles and polymer molecules. This leads to reduced erosive effects of citric acid solutions on dental enamel surfaces.

Effect of the simulated body fluid containing bleaching agent on the hypersensitivity and surface microhardness of the tooth

In this study, the whitening effect of simulated body fluid (SBF) and side effects of a hydrogen peroxide (H 2O 2) as the bleaching treatment of tooth enamel surfaces was investigated. H 2O 2 solution of 25% and 30% was prepared by diluting the commercially available 35% H 2O 2 solution with either distilled water (DW) or SBF of 1×, 3×, and 5× concentrations. These diluted H 2O 2 solutions were applied to the dental enamel surface of eighty human premolars for 15 min, followed by rinsing with DW. The procedure was repeated 4 times. The changes in color and surface microhardness before and after the bleaching procedure were recorded. The enamel surfaces of bleached teeth were examined with SEM. The results indicated that the brightness and microhardness of the tooth surface increased after bleaching with the SBF diluted agent compared to teeth treated with the DW diluted agent. These results might be due to the deposition of bone-like apatite that was observed with SEM. This bone-like apatite fills the area of roughness and holes in the enamel surfaces that were caused by bleaching, and created smoother and harder enamel surfaces. The result of this study suggested that a bleaching agent comprised of hydrogen peroxide and SBF would prevent the destructive side effects of bleaching and increase surface microhardness as well as having a whitening effect.