grazing incidence angle was fixed at 0.5°, whereas the scanning angle 2θ was varied between 20 and 75°, with a step size of 0.02°.
On the other hand, before and 72 hrs afterbleaching treatment, mechanical properties such as hardness and elastic modulus were evaluated by means of nanoindentation, employing a Nano Indenter G200 coupled with a DCM II head. The equipment was calibrated by using a standard fused silica sample. Tests parameters were the following; the constants of area function were C 0 =24.05, C 1 = -178.33, C 2 = 6724.30, C 3 = -24407.23, and C 5 = 18701.80. Berkovich diamond indenter with a tip radius of 20 ±5 nm, maximum load of 35 mN, strain rate of 0.05 s −1 , and harmonic displacement and frequency of 1 nm and 75 Hz, passion’s coefficient of ν=0.25 respectively. 90 indentations tests were evaluated in each sample. Residual indentation of samples was recorded by the AFM Nano Vision system attached to the nanoindenter system. During indentation, a curve describing the relationship between load (P) and displacement (h) is continuously monitored and recorded as illustrated in Fig. (5). On the other hand, with propose to measurement the nano-mechanical properties of the enamel before and afterbleaching treatment was used the Oliver and Pharr method with controlled cycles . The basic analysis of nanoindentation load-displacement curve (P-h) was established based on the elastic contact theory given by Sneddon  and Doerner . The Sneddon equation’s following was used to determinate the elastic modulus.
enamel, the specimens from the bleaching group exhibited similar μSBS values to those from the control group, regard- less of thermocycling. Although the bond strength of bleached enamel without surface reduction was not tested in the present study, a reduction in the enamel bond strength afterbleaching has been well documented by previous stud- ies [14–16]. Evidence has also shown a reduction in resin tags as well as a lower degree of adhesive penetration into the bleached enamel substrate [13, 36]. The abovemen- tioned phenomena have been attributed to the residual free radicals being released from the bleaching agents and to bleaching-induced structural changes in the enamel [14, 15, 25]. Although no information is available regarding the amount of residual free radicals or structural changes found at different depths of dental hard tissues, it is conceivable that changes due to bleaching occur primarily on the en- amel surface. The residual oxygen and structural changes caused by bleaching would therefore be eliminated, at least to some extent, by the enamel reduction process. This hy- pothesis is supported by previous studies that found that
In terms of dentistry, extrinsic discoloration raises aesthetic problems, which consequently encourages patients to seek improvement. One
treatment to overcome extrinsic discoloration is extracoronal bleaching. 2,3 Extracoronal bleaching is performed with the principle of oxidation reaction of bleaching material to the tooth structure. One of the most commonly used bleaching materials is hydrogen peroxide (H 2 O 2 ). However, the bleaching material application of extracorporeal bleaching procedures is not free from side effects as it may lead to sensitive teeth and changes in enamel structure. Sensitive teeth were felt by 15-78% of post-bleaching patients. 4 Research conducted by Heshmat et al. 5 unveiled changes in microstructure that might take place after extracorporeal bleaching such as demineralization, degradation, increasing enamel microporosity, decreasing micro hardness, and increasing surface roughness of enamel.
Another finding in this study was that the profilome- trically analyzed samples showed a greater depth in the periphery of the etched area than in the central area. It was assumed that the hydrochloric acid was locked into the applied area for soak times of 2 min or more, but due to the convex surface of the tooth, the acid flowed into the periphery of the square delineated by the nail varnish. The size of the lesion may limit the ability to condition the surface, increasing the clinical difficulty of treatment. When lesions are located near adjacent teeth, preparatory precautions are mandatory to protect nearby tooth structures.
In our study, it is possible to observe that in SEM image from dentin control group [Figure 3] there was not signifi cant change, the dentinal tubules were obliterated, grinding grooves were evident and part of smear layer was still persisted. In addition, particles can be observed on dentin surface for the group treated with Dessensiblize NanoP ® paste; however, images from samples bleached with 16% CP and treated with Bioglass and Biosilicate suggested incorporation of the particles on dentin surfaces. Also, the dentinal tubules seemed to be completely obliterated when treated with Biosilicate ® for samples bleached with 35% HP.
Regarding to the “whitening agent” factor, materials may vary according to their hydro- gen peroxide concentration, time of application, and pH of the gel; considering that only pH would more importantly influence SBS, the present study also evaluated the mor- phology of enamelafterbleaching. According to the SEM imagens shown in Fig. 2, the gel exposed the prism rods of enamel in a similar way that phosphoric acid does. More- over, a clear rougher surface could be observed when compared to the non-bleached specimen.
Final color (T2) assessment:
Aftersurface treatment and pH cycling, the color of the specimens was reevaluated by the same method and the same formula as described above. The color assigned at T1 and T2 for each specimen was converted to the previously established numeric values. The color difference was determined by calculating the difference between T1 and T2 values. For CIELAB data, the colors were compared using ∆L*, ∆a*, and ∆b* parameters as well as the total color difference (∆E) according to the following formula:
The machine consists of two jigs. The upper jig was attached to the moving element of the machine cross head element. The immovable part was attached to the lower jig.
The crosshead elements were connected to the plotter and the monitor. The teeth mounted vertically on the acrylic block, were carefully oriented in the jig in order to maintain distance and parallel orientation of the labial surface of the tooth and the shearing die. The shear force at a crosshead speed of 1 mm/minute was transmitted to the bracket by a chisel edge blade. The blade was custom made approximately the same size as the bracket edge. The force required to shear the bracket causing bonding failure was recorded in Newtons and the bond strengths were calculated in MegaPascals.
Micromorphological changes in enamelsurface are asso- ciated with the increase in roughness, porosity, and erosion areas. After pH cycling, a significant increase in surface roughness of enamel was observed. Furthermore, bleaching promoted the increased surface roughness for sound 6,10,11 and slightly demineralized enamels, 10 which related to subprod- ucts of peroxide oxidation reaction. Urea is able to penetrate into interprismatic regions of enamel, increasing its perme- ability and causing structural changes due to the dissociation of hydrogen bonds between the NH and CO groups and due to the protein-denaturing ability. 2 However, urea raises the pH of bleaching gel, promoting a reduction in the adverse effects. 33 Some studies 34,35 that assessed unbleached and bleached enamels observed no difference in surface roughness; this discrepancy may be related to different methodologies used, such as bleaching agent, saliva presence, exposure time to whitening product, and others.
But these readings were comparable to baseline scores and no statistically significant difference was found. Although artificial saliva was used in our study, it was not able to reestablish baseline enamel microhardness values without application of CPP-ACP or Reminpro. Also in this in vitro study, teeth were not brushed with toothpaste. In vivo, if the patient brushes with fluoridated toothpaste, it might help with remineralization process. The oral environment provides conditions for enamel remineralization because of some important factors, such as salivary flow, buffering capacity of saliva, oral hygiene and the use of topical fluorides that may increase the remineralization of bleached enamel (Basting, 2003). However, these results illustrate the need for at home whitening agents to be used with professional supervision, to ensure proper application of the bleaching agents. Also our study highlights the beneficial effects of using remineralizing products afterbleaching for both at home and in office bleaching protocols.
SUMMARY: The aim of this study was to evaluate the effects of external bleaching agents on morphology of human enamelafter excessive homemade dental bleaching. 20 intact human third molars were submitted to mesio-distal crosscut and embedded in polystyrene resin. The specimens were submitted to finish and a half of enamelsurface of each specimen was covered with cosmetic varnish, meaning control group (G0). The specimens were randomly divided into four groups (n=10): G1 – 1 bleaching session by 16% carbamide peroxide; G2 – 3 bleaching sessions by 16% carbamide peroxide; G3 – 1 bleaching session by 22% carbamide peroxide; G4 – 3 bleaching sessions by 22% carbamide peroxide. Each session lasted 8 hours a day, during two weeks, with 45 days of interval between sessions. In this period, the specimens were kept in artificial saliva at 37° C. The specimens were observed by scanning electron microscopy and the results showed depression areas, irregularities, erosion, and enamel prisms exposition, which was more evident in G4. It can be concluded that the excess of bleaching produced many alterations on enamelsurface, mainly when was used carbamide peroxide in higher concentration.
Dovepress Dental structures undergoing at-homebleaching
In general, ﬁndings of damage to the enamelsurfaceafterbleaching treatment come from studies carried out in vitro, with the methodological limitations inherent in this type of study. Such ﬁndings may not be representative of the in vivo condition, in which the oral cavity is continually bathed with saliva containing various minerals, including fluoride, calcium, and phosphate, lipids, carbohydrates, proteins, and other substances. 44 Evaluation of specimens was usually performed soon after the bleaching protocols, without any period of storage in artiﬁcial saliva and consequently with no remineralizing effect. 44,46–48 Storage in artiﬁcial saliva was performed only between clinical sessions or from the ﬁrst to the last session. 24,40–49 The relevant studies identiﬁed in the MedLine database are summarized in Table 1, with information regarding the type of study, measurement used, tissue evaluated, product concentration, pH values, changes observed, and possible reversibility after remineralization.
Etch (CERKAMED, Poland), rinsed with distilled water and dried with compressed air. The adhesive system Ortho Solo (ORMCO, USA) was applied to the etchedsurface. A bracket was attached with the use of clamping tweezers for tooth enamel so that its centre was 3.5 mm below the edge of the occlusal surface, in the middle of the mesial-distal axis of the tooth. The test teeth were stored in water at 37˚C for 24 hours. Adhesive material residue was removed from enamel in two ways: by the use of a carbide cutter and by means of cup-shaped elastics OneGloss 0181 (Shofu Dental Corp., USA).
carbamide peroxide (Opalescence, Ultradent Products Inc.) was applied on the ena- mel surfaces for 5 hours according to the manufacturer’s recommendations.
Afterwards the specimens were rinsed thoroughly with distilled water for 60 seconds and dried with compressed air. Immediately afterbleaching, bonding regimes similar to groups A, B, and C were carried out in groups D, E, and F, respectively. Then, cylinders of hybrid composite were bonded to the facial enamelsurface of all speci- mens, using 3 dental bonding agents. After 24 hours, the specimens were thermo- cycled (5–55°C, 1000cycles), and then subjected to shear bond testing by a universal machine Zwick (Zo20, Germany). The data were analyzed by one- and two-way ANOVA and post hoc tests. All statistical tests were performed with SPSS version 11.
Dental bleaching is a frequently requested procedure in clinical dental practice. The literature is contradictory regarding the effects of bleaching agents on both morphology and demineralization of enamelafterbleaching. The aim of this study was to analyze by SEM the effect of 35% neutral hydrogen peroxide cured by green LED. Buccal surfaces of 15 pre-molars were sectioned and marked with a central groove to allow experimental and control groups on the same specimen. For SEM, 75 electron micrographs were evaluated by tree observers at 43X, 220X and 1000X. Quantitative analysis for the determination of the surface elemental composition of the samples through X-ray microanalysis by SEM was also performed. The protocol tested neither showed significant changes in mineral composition of the samples nor to dental enamel structure when compared to controls. SEM analysis allowed inferring that there were marked morphological differences between the enamel samples highlighting the need for the use of the same tooth in comparative morphological studies. The tested protocol did not cause morphological damage the enamelsurface when compared to their respective controls.
Direct bracket bonding offers many benefits in contemporary orthodontics; however, the enamelsurface preparation method and type of adhesive can significantly affect the bracket bonding. As explained by Martinez-Insua et al  in 2000, conventional acid-etching has several disadvantages including removal of the superficial protective enamel layer and demineralization, which make the teeth more vulnerable to long-standing acid attacks. This is especially important when the acid-etchedsurface is not entirely covered by resin and is exposed to saliva. Considering the shortcomings of acid-etching, Ozer et al in 2008 , and Lee et al in 2003 , introduced laser- etching as a suitable alternative to acid-etching of the enamelsurface. In the current study, the frequency and length of enamel cracks in the buccal surface and the ARI scores were compared between the two groups of teeth subjected to acid-etching and laser- etching. The results revealed no significant difference in terms of the length or number of cracks between the two groups after orthodontic bracket debonding. The fragility of enamel depends on the age of the patient since the organic and mineral contents of the enamelsurface change with aging;
Keeping in view the relative bond strength of different species formed at the surface, given above, Arita et al.
 have analyzed that Si-Si bond is weak as compared to Si-O bonds at higher temperatures, 300 ˚C to 635˚C.
Si-Si bond easily changes into Si-O bond with the increase in temperature i.e. oxidation. Oxidation reaction on the surface in regions I, II, III, and IV follow different paths that also indicates the formation of a layer due dif- ferent Hydrogen, oxygen and Fluorine related chemical species. In our opinion both layer of chemical species and quantum dots/wires can produce luminescence but wave length of the luminescence will be different which solely depends upon the energy states (due to quantum confinement) induced in the band-gap of the materials.
Background. Several bleaching systems have been introduced in response to the patients’ demands in range of the improvement of the colour teeth placed to aesthetic dentistry. The active agents commonly used for the bleaching in−office and at home are hydrogen peroxide or carbamide peroxide. Although positive results have been reported as for the teeth whitening ability of these chemical compounds, concerns still remain as to their impact on dental tissues.
The evaluation of enamel samples falling under Group III by both the SEM analysis and surface microhardness test revealed that demineralization had occurred around the orthodontic bracket in spite of varnish application. These findings were in accordance with the findings of Basdra EK et al., who used SEM to study the effect of fluoride releasing agents and found that maximum fluoride release was seen in the first 24 hours of application with a steady decline thereafter. They found fluoride release to be negligible after 90 days . Our findings for fluoride varnish were also in accordance with the study conducted by Vivaldi Rodrigues G et al., where they evaluated the effect of varnish in limiting demineralization.