Microcomputerised tomography evaluation of 10% carbamide peroxide applied to enamel

An In Vitro Study on the Effects of Hydrogen Peroxide-Based Bleaching Agents on Enamel: Field Emission Scanning Electron Microscopy (FESEM) With Energy Dispersive Spectroscopy (EDS) Evaluation

Aim and objective The aim of the present in vitro study is to evaluate the morphological and elemental alterations in enamel following bleaching with hydrogen peroxide-based bleaching agents of different concentrations and pH values when exposed to different treatment times. Materials and method Twenty extracted maxillary central incisors were selected for the study. Tooth samples were prepared by sectioning the tooth cervico-incisally into two halves. The teeth were divided into different groups based on the bleaching protocol and bleaching agent applied: Group IA, Group IB, Group IIA, and Group IIB. Group IA received a 35% hydrogen peroxide-based bleaching agent of pH 6 for 10 minutes with light application. Group IB received a 35% hydrogen peroxide-based bleaching agent of pH 6 for 30 minutes with light activation. Group IIA received a 40% hydrogen peroxide-based bleaching agent of pH 8.5 for 10 minutes with chemical activation. Group IIB received a 40% hydrogen peroxide-based bleaching agent of pH 8.5 for 30 minutes with chemical activation. The morphology of the enamel before and after the application of the bleaching agent was evaluated using field emission scanning electron microscopy. The elemental analysis of enamel between the control and test samples was done with the help of energy dispersive spectroscopy. Results Paired t-test was used to analyze the data obtained from the study. The test samples showed erosive alterations in enamel surface morphology and also a decrease in the concentration of minerals when compared to the corresponding control groups. Conclusions The present study evidences the erosive potential of hydrogen peroxide-based bleaching agents. It can be concluded that bleaching agents containing high concentrations of hydrogen peroxide with acidic pH can cause mineral loss and surface erosion of enamel which is extremely detrimental to the tooth integrity.

Analysis of Calcium and Phosphate Ion Extraction From Dental Enamel by Bleaching Gels Using Ion Chromatography, Micro-CT, and SEM

OBJECTIVES

To evaluate the volume and depth of enamel loss promoted by 37.5% and 7.5% hydrogen peroxide (HP) gels, and quantify the loss of calcium (Ca) and phosphate (P) ions by using ion chromatography (IC) analysis after bleaching.

METHODS

Sixty bovine enamel specimens were randomly divided into three groups: Control - no bleaching gel; HP37.5%, application of HP 37.5% for 45 minutes for 14 days; and HP7.5%, application of HP 7.5% for 3 applications of 8 minutes. The surface analysis (n=5) was performed using a scanning electron microscope (SEM) and dispersive energy system (EDS) to calcium and phosphorus dosage. The micro-CT was used for the enamel loss analysis (n=5). IC was used to analyze extracted Ca and P (n=10). Data were analyzed by one-way ANOVA and two-way repeated measures ANOVA, followed by Tukey and Dunnett's tests (α=0.05).

RESULTS

Significantly higher volume and depth of enamel loss were found for bleached groups compared with the control group. HP7.5% had significantly higher enamel change than HP37.5%. SEM showed higher enamel porosity for HP37.5% and HP7.5% compared to control. The IC demonstrated a significant increase of Ca incorporated into the gel, however, only HP7.5% had a higher P presence than the control group. The HP7.5% showed higher Ca and P ion exchange than HP37.5% (p<0.001).

CONCLUSION

HP37.5% and HP7.5%, caused enamel mineral changes compared with the control group. The IC method was demonstrated to be an effective methodology for detecting enamel mineral loss by the bleaching gel.

Remineralizing effects of hydroxypropyl methylcellulose film-loaded amorphous calcium phosphate nanoprecursors on enamel artificial caries lesions

OBJECTIVES

This study was to investigate hydroxypropyl methylcellulose (HPMC) film as a carrier for amorphous fluorinated calcium phosphate (AFCP) nanoprecursors to continuously deliver biomimetic remineralization of enamel artificial caries lesions (ACL).

MATERIALS AND METHODS

The AFCP/HPMC films were comprised of 25 wt% AFCP nanoparticles and 75 wt% HPMC. They were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and biocompatibility tests. Forty enamel ACL were prepared and randomly divided into four groups (n = 10): The enamel surfaces were covered with a pure HPMC film, Tooth Mousse Plus (contains 10% CPP-ACP and 0.2% NaF), and AFCP/HPMC film, or without any things (serving as negative control). Subsequently, all samples were alternatively kept in artificial saliva and a modified pH-cycling before they were characterized by Micro-CT, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), attenuated total reflectance (ATR)-FTIR, XRD, and nanoindentation.

RESULTS

After the enamel ACL was challenged by pH cycling, Tooth Mousse Plus and AFCP/HPMC film groups exhibited less lesion depth and mineral loss than the negative control and pure HPMC film groups. Additionally, the AFCP/HPMC film group revealed a highest remineralization rate of 55.34 ± 3.10 % among the all groups (p < 0.001). The SEM findings showed that the enamel ACL were densely deposited with minerals in the AFCP/HPMC film group, and the EDX results suggested a higher content of fluorine in the remineralized tissues. In particular, the AFCP/HPMC film group exhibited the best nanomechanical performance after 2 weeks of pH cycling (p < 0.05), with the hardness (H) restored from 0.29 ± 0.19 to 2.69 ± 0.70 GPa, and elastic modulus (Er) restored from 10.77 ± 5.30 to 68.83 ± 12.72 GPa.

CONCLUSION

The AFCP/HPMC film might be used as a promising strategy for arresting or reversing incipient enamel caries lesions.

Effectiveness and Safety of Over-the-Counter Tooth-Whitening Agents Compared to Hydrogen Peroxide In Vitro

(1) This study investigated the whitening effect, cytotoxicity and enamel surface alterations induced by different over-the-counter (OTC) bleaching agents in comparison to hydrogen peroxide. (2) Human teeth (n = 60) were randomly assigned into 6 groups (n = 10), stained with coffee solution for 7 d, followed by a whitening period of 7 d with either placebo, bromelain, sodium bicarbonate, sodium chlorite, PAP or hydrogen peroxide. Color measurements were performed with a spectrophotometer. Scanning electron micrographs (SEM) were taken to assess the enamel structure. Cytotoxicity of the tested substances was assessed based on the cell viability of primary human fibroblasts. (3) The application of all whitening gels resulted in a greater color difference of the enamel (ΔE) in comparison to the negative control. Hydrogen peroxide caused the greatest color difference. Bromelain and PAP treatment showed no enamel surface changes, in contrast to hydrogen peroxide treatment, which showed very mild interprismatic dissolution. Bromelain was the only non-cytotoxic agent. (4) The maximum effect achieved by all OTC bleaching agents was the removal of stains, whereas hydrogen peroxide was capable of further whitening the teeth. Bromelain treatment was neither cytotoxic, nor resulted in enamel surface alterations, and its whitening effect was less, yet still effective, compared to hydrogen peroxide.

The effect of bleaching on surface roughness and gloss of different CAD/CAM ceramic and hybrid ceramic materials

OBJECTIVE

To assess the effect of bleaching on surface roughness and gloss of different CAD/CAM ceramic materials.

METHODS

The ceramic materials included IPS e.max CAD (lithium disilicate), VITA ENAMIC (polymer infiltrated ceramic), and Celtra Duo CAD (zirconia reinforced lithium silicate). Samples of each material were randomly divided into four groups (n = 10); a control group immersed in distilled water, the second and third groups were treated with 20% carbamide peroxide (20% CP) and 35% carbamide peroxide (35% CP) bleaching agents for 4 h/day and 60 min/day respectively for 7 days. The fourth group was treated with 40% hydrogen peroxide (40% HP) applied twice, each turn for 20 min. After treatment, the surface roughness (using 3D non-contact profilometry) and surface gloss were assessed followed by imaging with a scanning electron microscope. The data were analyzed using multiple linear regression and Kruskal-Wallis one-way ANOVA tests (α = 0.05).

RESULTS

The surface roughness (p = 0.157) and gloss (p = 0.073) of IPS e.max CAD were not significantly affected by the different bleaching treatments. Similarly, no significant effect on surface roughness (p = 0.162) and gloss (p = 0.965) were shown for Celtra Duo CAD. On the other hand, VITA ENAMIC was significantly affected when treated with 20% CP and 35% CP showing increased roughness (p = 0.001) and gloss (p = 0.008).

CONCLUSIONS

Home bleaching treatments (20% CP and 35% CP) significantly affected the surface roughness and gloss of VITA ENAMIC while IPS e.max CAD and Celtra Duo CAD were not affected by the different bleaching treatments.

An Assessment of Mineral Concentration of Dental Enamel Neighbouring Hypothetical Orthodontic Brackets Using X-ray Microtomography

OBJECTIVES

Differences in the mineral concentration (MC) level of dental enamel may represent a precursor of white spot lesions adjacent to fixed orthodontic brackets. The aim of the current in vitro study was to compare the MC level central, occlusal and cervical to orthodontic attachments.

METHODS AND MATERIALS

A total of 16 enamel blocks were obtained from sound human premolar samples extracted for orthodontic reasons. The buccal portion of the dental enamel blocks was divided into central, occlusal, and cervical regions and then imaged and measured to calculate the level of MC using quantitative X-ray microtomography methods (XMT) at each site.

RESULTS

There was a substantial variation in the mineral concentration with the lowest level being detected in the cervical region when compared with other regions. The MC of the gingival zone was significantly lower than that of the middle zone (P<0.05) and was insignificantly lower than that of the occlusal zone.

CONCLUSION

Within the limitations of the current study, it can be concluded that the cervical region of the permanent enamel had the lowest mineral concentration using XMT. The cervical region may therefore be more vulnerable to the development of white spot lesions (WSLs) adjacent to a fixed orthodontic appliance during orthodontic treatment.

CLINICAL SIGNIFICANCE

Using X-ray microtomography lower mineral concentration in the cervical region of the enamel was observed. This may make these areas particularly susceptible to demineralisation during fixed appliance-based orthodontic treatment and may influence the bond strength of fixed orthodontic attachments.

Use of Computerized Microtomography, Energy Dispersive Spectroscopy, Scanning Electron Microscopy, and Atomic Force Microscopy to Monitor Effects of Adding Calcium to Bleaching Gels

OBJECTIVES

The aim of this study was to evaluate the mineral content, expressed by calcium (Ca) and phosphate (P), in dental enamel exposed to bleaching agents using micro-computed tomography (micro-CT), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM).

METHODS

Sixty bovine dental enamel specimens were randomly divided into three groups (n=20): HP35ca (bleached using 35% hydrogen peroxide with Ca); HP35wca (bleached using 35% hydrogen peroxide without Ca); and control (without bleaching). Five specimens from each group were used for SEM and EDS analyses, 10 specimens were used for AFM analysis, and the remaining five specimens were used for micro-CT analysis. The pH of the gels was measured using a pH meter. The EDS and micro- CT data were analyzed using one-way ANOVA and Pearson's correlation test. The AFM data were analyzed using one-way ANOVA (α=0.05).

RESULTS

The weight percentages of Ca and P obtained using EDS were similar between the bleached and control groups. Small, superficial changes were observed by SEM in the HP35wca group. The HP35ca group showed similar patterns to the control group. AFM results showed no significant changes in the enamel roughness in any of the tested groups. No significant difference in the volume or depth of structural enamel loss was found between gels with and without Ca. No mineral loss was observed in the dentin substrate. The EDS and micro-CT analysis data exhibited a high correlation (p<0.001).

CONCLUSION

The addition of Ca to the bleaching gel had no beneficial effect on the bleached tooth enamel in terms of composition, mineral loss, and surface roughness. Micro-CT results exhibited a high correlation with the EDS results.

Vibrational Imaging Techniques for the Characterization of Hard Dental Tissues: From Bench-Top to Chair-Side

Currently, various analytical techniques, including scanning electron microscopy, X-Ray diffraction, microcomputed tomography, and energy dispersive X-ray spectroscopy, are available to study the structural or elemental features of hard dental tissues. In contrast to these approaches, Raman Microspectroscopy (RMS) has the great advantage of simultaneously providing, at the same time and on the same sample, a morpho-chemical correlation between the microscopic information from the visual analysis of the sample and its chemical and macromolecular composition. Hence, RMS represents an innovative and non-invasive technique to study both inorganic and organic teeth components in vitro. The aim of this narrative review is to shed new light on the applicative potential of Raman Microspectroscopy in the dental field. Specific Raman markers representative of sound and pathological hard dental tissues will be discussed, and the future diagnostic application of this technique will be outlined. The objective and detailed information provided by this technique in terms of the structure and chemical/macromolecular components of sound and pathological hard dental tissues could be useful for improving knowledge of several dental pathologies. Scientific articles regarding RMS studies of human hard dental tissues were retrieved from the principal databases by following specific inclusion and exclusion criteria.

A Hydroxypropyl Methylcellulose Film Loaded with AFCP Nanoparticles for Inhibiting Formation of Enamel White Spot Lesions

Objective

This study investigated the effects of mineralizing film consisting of hydroxypropyl methylcellulose (HPMC) and amorphous fluorinated calcium phosphate (AFCP) nanoparticles on enamel white spot lesions (WSLs).

Material and Methods

The AFCP nanoparticles and mineralizing film were prepared via nanoprecipitation and solvent evaporation, respectively. They were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma atomic emission spectrometry (ICP-AES), and fluoride ion selective electrode. Thirty-two human enamel slices (4 mm × 4 mm × 1.5 mm) were highly polished and randomly assigned to four groups: negative control (no treatment); pure HPMC film; mineralizing film; GC Tooth Mousse Plus^® (contains 10% CPP-ACP and 0.2% NaF). Subsequently, samples were challenged by a modified pH-cycling and characterized by color measurement, Micro-CT, SEM/EDX, and nanoindentation.

Results

The mineralizing film could sustain release of Ca, P and F ions over 24 h and maintain AFCP nanoparticles in metastable state over 8~12 h. During 4 weeks of pH cycling, the mineralizing film group exhibited least color change (∆E), mineral loss and lesion depth (120 ± 10 µm) among four groups (p < 0.05). SEM findings revealed that the porosities among enamel crystals increased in negative control and pure HPMC film groups after pH cycling, whereas in mineralizing film group, the original microstructure of enamel was well conserved and mineral deposits were detected between enamel prisms. Mineralizing film group demonstrated a least reduction of nanomechanical properties such as elastic modulus of 77.02 ± 6.84 GPa and hardness of 3.62 ± 0.57 GPa (p < 0.05).

Conclusion

The mineralizing film might be a promising strategy for prevention and management of WSLs via inhibiting enamel demineralization and promoting enamel remineralization.

Effects of Different Bleaching Agents on the Surface Topography and the Microhardness of Artificial Carious Lesions

Objectives The aim of this study was to evaluate the effects of in-office and at-home bleaching agent applications on the surface topography and microhardness of artificially demineralized enamel.

Materials and Methods A total of 224 enamel specimens were prepared using bovine sound central incisors. 4 mm × 4 mm enamel windows were exposed on the buccal surfaces covering the remaining surface with nail varnish. Samples were immersed in a demineralizing solution for 16 hours to produce artificial caries lesions, then divided into four groups according to the bleaching agent’s type and concentration. Group I; in-office bleaching 35% hydrogen peroxide (HP) (Whiteness HP Maxx; FGM, Brazil), Group II and Group III at-home bleaching 16 and 22% carbamide peroxide CP, respectively (Whiteness Perfect). Group IV; control (not bleached). The microhardness Vickers hardness number (VHN) was measured at the baseline, after demineralization, and after bleaching consequently. The micro-surface changes of the enamel surface after demineralization and bleaching were evaluated by scanning electron microscope (SEM).

Statistical Analysis Data were evaluated by the one-way analysis of variance (ANOVA) test followed by Post Hoc Tukey’s and Fisher’s least significant difference. Tow- sided p -values were considered statistically significant at p ≤ 0.05.

Results A significant reduction was noticed in the enamel microhardness after demineralization p < 0.05. However, there is no statistically significant difference between the mean VHN of the demineralized and bleached enamel ( p > 0.001). SEM images showed significant changes on the surface of the demineralized enamel after bleaching (pattern type III).

Conclusions The low and high concentrations of HP and CP bleaching agents increased the demineralization severity of artificial caries lesions without significantly altering their microhardness values.

Analysis of enamel structure and mineral density after different bleaching protocols using micro-computed tomography

OBJECTIVE

This study aims to investigate the effect of three different bleaching applications on structural integrity, mineral volume (MV) and density of the enamel by using micro-computed tomography (Micro-CT) and evaluate the colour effectiveness using CIEDE2000.

MATERIALS AND METHODS

Twenty-four maxillary premolar teeth were divided into three groups (n = 8) (group 1: 40% HP gel with erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser activation; group 2: 40% HP gel with diode laser activation; group 3: 16% CP gel). Bleaching protocols were applied and colour alteration was obtained. Data were calculated with CIEDE2000 before and after bleaching. A Micro-CT was used to scan the specimens before and after the bleaching application. Statistical analysis was performed by ANOVA.

RESULTS

No significant difference was observed between the groups for colour changes (p > .05). Micro-CT analysis showed significant differences in structural thickness, structural separation, mineral density and MV for the different ROIs before and after bleaching for all groups (p<.05).

CONCLUSIONS

All of the bleaching methods represented similar efficiency. However, bleaching with Er,Cr:YSGG laser was less harmful to enamel in comparison with other bleaching methods. The present results may be useful for establishing a numerical standard for the change in bleaching with laser systems in dental hard tissues.

In Vitro Re-Hardening of Bleached Enamel Using Mineralizing Pastes: Toward Preventing Bacterial Colonization

The search for materials able to remineralize human hard tissues is a modern medical challenge. In this study, the protective effect on the enamel microhardness by a paste based on hydroxyapatite and sodium fluoride (Remin Pro) was evaluated after two different enamel bleaching procedures. Forty sound human incisors were randomly assigned to different treatments: bleaching with an in-office agent (Perfect Bleach Office+); bleaching with an at-home agent (Perfect Bleach); bleaching with the in-office agent followed by the prophylaxis paste; bleaching with the at-home agent followed by the prophylaxis paste; no treatment (control). Bleaching was performed at 0, 8, 24 and 32 h, followed by a 3-min re-mineralizing treatment in the subgroups designed to receive it. Specimens underwent a micro-hardness tester and a mean Vickers Hardness number was considered for each specimen. ANOVA exhibited significant differences among groups. Post-hoc Tukey testing showed significant micro-hardness decrease after the application of both the two bleaching agents. The treatment with prophylaxis paste significantly increased the micro-hardness values of bleached enamel.

Whitening Efficacy of Chewing Gum Containing Sodium Metaphosphate on Coffee Stain: Placebo-controlled, Double-blind In Situ Examination

This study aimed to evaluate the ability of chewing gum containing sodium metaphosphate (SMP) to remove coffee stains from enamel in situ. This was a double-blind (subjects, evaluators), parallel-group, crossover, randomized clinical trial with 30 healthy adult volunteers. Each participant held an appliance with a hydroxyapatite (HA) pellet on the lower lingual side of his or her mouth for two hours to allow pellicle formation. The appliances were subsequently immersed in coffee solution at 37°C for 48 hours. The color of the HA pellet before and after coffee immersion was measured using a spectrophotometer. The participant set the appliance and chewed two pieces of test gum, which contained 7.5 mg of SMP per piece, or control gum without SMP. Each cycle included five minutes of exposure to chewing gum, after which the appliances were placed in 100% relative humidity at room temperature for a 30-minute incubation. This cycle was repeated five times for each gum type. The color of the HA pellet was measured after each chewing cycle using the spectrophotometer. In addition, ΔE* values, which indicate the change in pellet color after each chewing cycle compared with after coffee immersion, were calculated. Data were analyzed using the paired t-test with Bonferroni adjustment to compare ΔE* values of control and test gum after each chewing cycle. The ΔE* values of test gum were significantly higher than those of control gum after all chewing cycles, excluding the first cycle (p<0.05). This finding indicates that test gum containing SMP was more effective at removing coffee stains from the HA pellet than control gum. We conclude that chewing gum containing SMP can effectively remove coffee stains from HA pellets. Thus, SMP is a promising agent to be further explored in tooth-cleaning studies.

Whitening toothpastes effect on nanoparticle resin composite roughness after a brushing challenge: An in vitro study

Background

Nowadays, the use of whitening toothpastes is a common habit, especially among young adults, due to aesthetic appeal. On the other hand, little is known regarding the effects of brushing with those newly dentifrices on wear properties of resin composites.

Material and Methods

Thirty specimens of nanoparticle composite resin were fabricated and stored in distilled water for 24 h at 370C. After this, the roughness analysis was performed and submitted to the simulated brushing technique using three types of toothpastes: conventional (GI), and two with whitening effect (GII and GIII) for a period of 15 days, with 2 brushing sessions per day for 2 minutes each. The final surface roughness was analyzed after completing all the brushing cycles and stereoscopic images were taken for each group. The data was analyzed by one-way ANOVA and Tukey-test post hoc for intergroup comparison and the T-test for dependent samples as well (α = 0.05).

Results

However showing an increase of roughness for all groups after the brushing cycles (p = 0.01), no statistically significant differences among the groups after simulated brushing was verified (p = 0.17). Yet, just some cracks of the stereoscopic images were shown, demonstrating no distinct visual effects among the studied groups.

Conclusions

After simulated brushing with the whitening toothpastes, similar degree of roughness was verified on the composite resin tested. Key words:Composite resin, toothpastes, whitening.

Effect of Toothpaste Use Against Mineral Loss Promoted by Dental Bleaching

AIM

To investigate the effect of different toothpaste formulations used prior to dental bleaching with 35% hydrogen peroxide (HP) on the mineral content and surface morphology of enamel.

METHODS

Seventy bovine enamel blocks (4×4×2 mm) were submitted to in vitro treatment protocols using a toothbrushing machine prior to dental bleaching or a placebo procedure (n=10) as proposed in the following groups: unbleached control (PLA), bleached control (HP), and brushing with differing toothpastes prior to HP bleaching, including: potassium nitrate toothpaste containing sodium fluoride (PN), sodium monofluorophosphate/MFP toothpaste (FT), arginine-carbonate (8% arginine) (PA) or arginine-carbonate (1.5% arginine) toothpaste (SAN), and toothpaste containing bioactive glass (NM). Phosphorus concentration in gel ([P]) was evaluated (μg of P/mg of gel), and the elemental levels (wt%) of Ca, P, and Na as well as the proportion between Ca and P and spectra graphics were determined using an energy-dispersive X-ray spectrometer (EDS). The surface morphology was assessed using scanning electron microscopy (SEM). The data were subjected to analysis of variance and the Tukey test (α=0.05).

RESULTS

HP demonstrated the greatest [P] values in gel, being statistically different from PLA. The [P] of NM was statistically similar to PLA. HP showed a significant decrease in the Ca% and Ca/P values when compared to PLA in EDS analysis. PA showed Ca/P values statistically different from HP. In accordance with SEM analysis, the PA, SAN, and NM groups presented a smooth and uniform enamel surface, while HP and FT demonstrated some alterations in morphology.

CONCLUSION

The toothpastes containing bioactive glass or arginine carbonate used prior to dental bleaching were effective in protecting enamel against mineral loss promoted by the whitening procedure.

Crystallographic texture and mineral concentration quantification of developing and mature human incisal enamel

For human dental enamel, what is the precise mineralization progression spatially and the precise timing of mineralization? This is an important question in the fundamental understanding of matrix-mediated biomineralization events, but in particular because we can use our understanding of this natural tissue growth in humans to develop biomimetic approaches to repair and replace lost enamel tissue. It is important to understand human tissues in particular since different species have quite distinct spatial and temporal progression of mineralization. In this study, five human central incisors at different stages of enamel maturation/mineralization were spatially mapped using synchrotron X-ray diffraction and X-ray microtomography techniques. From the earliest developmental stage, two crystallite-orientation populations coexist with angular separations between the crystallite populations of approximately 40° varying as a function of position within the tooth crown. In general, one population had significantly lower texture magnitude and contributed a higher percentage to the overall crystalline structure, compared to the other population which contributed only 20-30% but had significantly higher texture magnitude. This quantitative analysis allows us to understand the complex and co-operative structure-function relationship between two populations of crystallites within human enamel. There was an increase in the mineral concentration from the enamel-dentin junction peripherally and from the incisal tip cervically as a function of maturation time. Quantitative backscattered-electron analyses showed that mineralization of prism cores precedes that of prism boundaries. These results provide new insights into the precise understanding of the natural growth of human enamel.

The Tooth: Its Structure and Properties

This article provides a brief review of recent investigations concerning the structure and properties of the tooth. The last decade has brought a greater emphasis on the durability of the tooth, an improved understanding of the fatigue and fracture behavior of the principal tissues, and their importance to tooth failures. The primary contributions to tooth durability are discussed, including the process of placing a restoration, the impact of aging, and challenges posed by the oral environment. The significance of these findings to the dental community and their importance to the pursuit of lifelong oral health are highlighted.

Effect of Mouth Rinse Treatments on Bleached Enamel Properties, Surface Morphology, and Tooth Color

OBJECTIVE:

To evaluate, in vitro, the effect of mouth rinse exposure on bleached enamel.

METHODS:

Enamel/dentin bovine blocks (4×4×2 mm) were bleached with 35% hydrogen peroxide (HP) and were submitted to immersion twice daily for 14 days with different rinses (n=10), including those involving: distilled water (C [control]), 225-ppm NaF (FM, Colgate Plax Classic), essential oil (EM, Listerine Tartar Control), 1.5% hydrogen peroxide (HPM, Colgate Plax Whitening), and 2% hydrogen peroxide, pyrophosphates, and 225-ppm NaF (HPM+P, Colgate® Luminous White). The specimens were stored in a remineralizing solution during all experiments. Analyses of color (ΔE, L*, a*, b*) and roughness (Ra) were performed at the baseline, after HP, and after exposure to the rinse. The cross-sectional microhardness (CSMH) and images by scanning electron microscopy (SEM) were assessed at the end. The data were subjected to analysis of variance (ANOVA) (ΔE), repeated measures ANOVA (Ra), and split-plot ANOVA (CSMH), followed by the Tukey test. The L*, a*, and b* values were analyzed by generalized linear models (α=0.05).

RESULTS:

Color changes were not statistically different in the groups. Ra increased in all groups after bleaching; however, it was reestablished in C, FM, and HPM+F and increased in EM after 14 days of the rinse. EM and HPM reduced the CSMH values differing from C and promoted alterations on the enamel surface visualized by SEM.

CONCLUSION:

The mouth rinses did not affect the whitening efficacy or promote benefits on bleached enamel properties. Moreover, the 1.5% hydrogen peroxide- or essential oil-based mouth rinses affected the bleached enamel properties, promoting an alteration in morphologic surface and mineral loss in depth.

The potential of statistical shape modelling for geometric morphometric analysis of human teeth in archaeological research

This paper introduces statistical shape modelling (SSM) for use in osteoarchaeology research. SSM is a full field, multi-material analytical technique, and is presented as a supplementary geometric morphometric (GM) tool. Lower mandibular canines from two archaeological populations and one modern population were sampled, digitised using micro-CT, aligned, registered to a baseline and statistically modelled using principal component analysis (PCA). Sample material properties were incorporated as a binary enamel/dentin parameter. Results were assessed qualitatively and quantitatively using anatomical landmarks. Finally, the technique’s application was demonstrated for inter-sample comparison through analysis of the principal component (PC) weights. It was found that SSM could provide high detail qualitative and quantitative insight with respect to archaeological inter- and intra-sample variability. This technique has value for archaeological, biomechanical and forensic applications including identification, finite element analysis (FEA) and reconstruction from partial datasets.

Micro-CT and FE-SEM enamel analyses of calcium-based agent application after bleaching

OBJECTIVES

The objective of the present study is to evaluate the effects of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on bleached enamel.

MATERIALS AND METHODS

A bleaching agent (35% hydrogen peroxide) was applied, 4 × 8 min on premolar teeth (n = 8). A CPP-ACP paste was applied for 7 days. Prior and post-treatment, microtomography images were obtained and 3D regions of interest (ROIs) were selected, from outer enamel, extending to 110.2-μm depth. CT parameters of structure: thickness (St.Th), separation (St.Sp), and fragmentation index (Fr.I.) were calculated for each (ROI). Data was submitted to paired t tests at a 95% confidence level. The samples were evaluated at 3000 to 100,000 magnification. Quantitative analysis of enamel mineral content was also determined by SEM EDX.

RESULTS

There was a significant increase in structure thickness and calcium content. The phosphorus content increased after bleaching. There was also a decreased separation and fragmentation index on the outer enamel to a depth of 56.2 μm (p < 0.05). There were no changes at 110.2-μm depth for the bleaching CPP-ACP association. A covering layer and decreased spaces between the hydroxyapatite crystals appeared around the enamel prisms, 7 days after the CPP-ACP application.

CONCLUSIONS

The application of a CPP-ACP provides a compact structure on the enamel's outer surface, for 7 days, due to calcium deposition. CT parameters seem to be a useful tool for mineralizing and remineralizing future studies.

CLINICAL RELEVANCE

CPP-ACP neutralizes any adverse effects on enamel surface when applied during a week after bleaching and minimizes any side effects of the bleaching treatment due to a more compact structure.

Correlation between micro-hardness and mineral content in healthy human enamel

BACKGROUND

Enamel is the hardest and the stiffest tissue in the human body. The enamel undergoes multidirectional stresses, withstands multimillion chewing cycles, all while protecting the internal dentin and pulp from damage due to mechanical overload and exposure to the harsh chemical environment of the mouth. Raman spectroscopy allows to study enamel mineral content in a non-destructive and site-specific way. While Raman spectroscopy has been applied in other studies to assess tooth mineralization, there are no studies that examine the relationship between micro-hardness and mineral content of the untreated enamel. An understanding of this relationship is extremely important in a clinical context. The effect of various agents on enamel hardness was investigated, though the relationship between healthy enamel mineral content and micro-hardness remains obscure.

MATERIAL AND METHODS

Twenty human incisor teeth were obtained in compliance with the NIH guidelines and imaged site-specifically with a Raman microscope and evaluated with a Brinell hardness measurement device. The front portion of each tooth was divided into apical, medium and cervical regions and subsequently imaged with a Raman microscope in these three locations.

RESULTS AND CONCLUSIONS

The results demonstrated that enamel mineral content varies significantly between individuals and is correlated with the hardness of the enamel. Non-invasive, sample preparation free Raman spectroscopy was successfully employed to measure the mineral content of healthy enamel and it correlated the mineralization score to the hardness measurements of the selected cervical location. The overall level of enamel mineral content may serve as a robust predictor of patients' susceptibility to developing caries, and overall enamels wear resistance, thus allowing for the prevention of caries via clinically available methods of remineralization, fluoride treatment and frequent cleaning. Key words:Enamel, raman spectroscopy, micro-hardness, extracted teeth.

Pattern of Hydroxyapatite Crystal Growth on Bleached Enamel Following the Application of Two Antioxidants: An Atomic Force Microscope Study

OBJECTIVES

This study observed the topographical pattern of hydroxyapatite deposition and growth (D&G) on bleached enamel following application of two antioxidants (sodium ascorbate and catalase) using atomic force microscope.

STUDY DESIGN

Twenty enamel specimens (4×3×2mm), prepared from extracted impacted third molars, were mounted in self-cure acrylic and randomly grouped as: Group I-untreated; Group II- 35%H₂O₂; Group III- 35%H₂O₂ + artificial saliva; Group IV- 35%H₂O₂ + catalase+ artificial saliva; Group V- 35%H₂O₂ + sodium ascorbate+ artificial saliva. Groups I and II were observed immediately after treatment. Groups III-V were observed after 72 hrs. Roughness average was also calculated and analyzed with non-parametric Kruskall-Wallis ANOVA and Mann-Whitney tests.

RESULTS

H₂O₂ dissolved matrix, exposed hydroxyapatite crystals (HACs), causing dissolution on the sides of and within HACs and opening up of nano-spaces. Artificial saliva showed growth of dissoluted crystals. Antioxidants+saliva showed potentiated remineralization by D&G on dissoluted HACs of bleached enamel. Catalase potentiated blockshaped, while sodium ascorbate the needle-shaped crystals with stair-pattern of crystallization. Evidence of oxygen bubbles was a new finding with catalase. Maximum roughness average was in group V followed by group II > group IV > group III > group I.

CONCLUSION

Post-bleaching application of catalase and sodium ascorbate potentiated remineralization by saliva, but in different patterns. None of the tested antioxidant could return the original topography of enamel.

A portable fiber-optic raman spectrometer concept for evaluation of mineral content within enamel tissue

Background

Measurement of tooth enamel mineralization using a clinically viable method is essential since variation of mineralization may be used to monitor caries risk or in assessing the effectiveness of remineralization therapy. Fiber optic Raman systems are becoming more affordable and popular in context of biomedical applications. However, the applicability of fiber optic Raman systems for measurement of mineral content within enamel tissue has not been elucidated significantly in the prior literature.

Material and Methods

Human teeth with varying degrees of enamel mineralization were selected. In addition alligator, boar and buffalo teeth which have increasing amount of mineral content, respectively, were also included as another set of samples. Reference Raman measurements of mineralization were performed using a high-fidelity confocal Raman microscope.

Results

Analysis of human teeth by research grade Raman system indicated a 2-fold difference in the Raman intensities of v1 symmetric-stretch bands of mineral-related phosphate bonds and 7-fold increase in mineral related Raman intensities of animal teeth. However, fiber optic system failed to resolve the differences in the mineralization of human teeth.

Conclusions

These results indicate that the sampling volume of fiber optic systems extends to the underlying dentin and that confocal aperture modification is essential to limit the sampling volume to within the enamel. Further research efforts will focus on putting together portable Raman systems integrated with confocal fiber probe.

Key words:Enamel, mineral content, raman spectroscopy.

Evaluation of mineral content in healthy permanent human enamel by Raman spectroscopy

Background

An understanding of tooth enamel mineral content using a clinically viable method is essential since variations in mineralization may serve as an early precursor of a dental health issues, and may predict progression and architecture of decay in addition to assessing the success and effectiveness of the remineralization strategies.

Material and Methods

Twenty two human incisor teeth were obtained in compliance with the NIH guidelines and site specifically imaged with Raman microscope. The front portion of the teeth was divided into apical, medium and cervical regions and subsequently imaged with Raman microscope in these three locations.

Results

Measured mineralization levels have varied substantially depending on the regions. It was also observed that, the cervical enamel is the least mineralization as a populational average.

Conclusions

Enamel mineralization is affected by a many factors such as are poor oral hygiene, alcohol consumption and high intake of dietary carbohydrates, however the net effect manifests as overall mineral content of the enamel. Thus an early identification of the individual with overall low mineral content of the enamel may be a valuable screening tool in determining a group with much higher than average caries risk, allowing intervention before development of caries. Clinically applicable non-invasive techniques that can quantify mineral content, such as Raman analysis, would help answer whether or not mineralization is associated with caries risk.

Key words:Enamel, Raman spectroscopy, mineral content, dental caries.

Ultrastructural evaluation of enamel surface morphology after tooth bleaching followed by the application of protective pastes

The aim of the present in vitro study was to evaluate the morphology of bleached enamel surface followed by the application of different protective pastes. Specimens were prepared from 50 human incisors free of caries and defects. The bleaching procedure was performed with 35% hydrogen peroxide (Perfect Bleach Office+). For the remineralization treatment, different protective pastes (Tooth Mousse, MI Paste Plus, Remin Pro, and Profluorid Varnish) were evaluated. Specimens were randomly assigned to 10 groups of 5 specimens each. The specimens were analyzed under scanning electron microscopy. The superficial morphology of enamel was examined and scored as follows: 0, enamel with smooth surface morphology; 1, enamel with slight irregularities; 2, enamel with moderate irregularities; 3, enamel with accentuated irregularities. The photomicrographs were evaluated in a double-blind manner by three examiners, previously calibrated. Results were analyzed by a Kruskal-Wallis nonparametric test, at the significance level of 0.05. Dunn method posttest was applied for multiple comparisons. A different superficial morphology was observed among control group specimens and specimens treated with bleaching agent and protective pastes (p < 0.05). Enamel bleached showed pronounced surface changes and irregularities, significantly different from other groups except for groups 8 (enamel + Perfect Bleach Office+ + Remin Pro) and 10 (enamel + Perfect Bleach Office+ + Profluorid Varnish) (p > 0.05). The application of the tested pastes after bleaching is effective on repairing enamel surface morphology, demonstrating a higher efficacy for the CPP-ACP products compared to fluoridated ones. SCANNING 38:221-226, 2016. © 2015 Wiley Periodicals, Inc.

On the importance of aging to the crack growth resistance of human enamel

With improvements in oral health and an overall increase in quality of life, the percentage of fully or largely dentate seniors is increasing. Understanding the effects of aging on the mechanical properties of teeth is essential to the maintenance of lifelong oral health. In this investigation the effects of aging on the fracture toughness of human enamel were evaluated from incremental crack growth experiments performed on tissue of donor teeth representing "young" (17 ⩽ age ⩽ 25) and "old" (age ⩾ 55) age groups. Results showed that the old enamel exhibited significantly lower resistance to fracture than that of the young tissue in two orthogonal directions of crack growth. For crack growth transverse to the enamel rods, the fracture toughness of the old enamel (0.37 ± 0.15 MPa m(0.5)) was nearly 70% lower than that of tissue from the young teeth (1.23 ± 0.20 MPa m(0.5)). Based on results from a mechanistic analysis of crack growth, the reduction in fracture resistance is attributed to a decrease in the degree of extrinsic toughening. The practice of restorative dentistry should account for these changes in tooth tissues in the treatment of senior patients.

STATEMENT OF SIGNIFICANCE

The mechanical behavior of enamel has been studied for over 3 decades. Due to the limited volume of tissue available for evaluation, past work has been largely based on indentation methods. In this investigation we have evaluated the resistance to fracture of human enamel using a conventional fracture mechanics approach and incremental crack growth. We compared the fracture resistance of cuspal enamel obtained from the teeth of representative "young" and "old" donor groups. Our results show that there is a substantial reduction in the resistance to fracture with age, that it is anisotropic, and that the degradation is more severe than that which occurs to dentin. As such, we feel this work is a significant contribution to the field.

The role of organic proteins on the crack growth resistance of human enamel

With only 1% protein by weight, tooth enamel is the most highly mineralized tissue in mammals. The focus of this study was to evaluate contributions of the proteins on the fracture resistance of this unique structural material. Sections of enamel were obtained from the cusps of human molars and the crack growth resistance was quantified using a conventional fracture mechanics approach with complementary finite element analysis. In selected specimens the proteins were extracted using a potassium hydroxide treatment. Removal of the proteins resulted in approximately 40% decrease in the fracture toughness with respect to the fully proteinized control. The loss of organic content was most detrimental to the extrinsic toughening mechanisms, causing over 80% reduction in their contribution to the total energy to fracture. This degradation occurred by embrittlement of the unbroken bridging ligaments and consequent reduction in the crack closure stress. Although the organic content of tooth enamel is very small, it is essential to crack growth toughening by facilitating the formation of unbroken ligaments and in fortifying their potency. Replicating functions of the organic content will be critical to the successful development of bio-inspired materials that are designed for fracture resistance.

Demineralization and hydrogen peroxide penetration in teeth with incipient lesions

The aim of this study was to evaluate the demineralization and hydrogen peroxide (HP) penetration in teeth with incipient lesions submitted to bleaching treatment. For analysis of HP penetration, sound and demineralized enamel/dentin discs were placed in artificial pulp chambers containing acetate buffer solution. After bleaching treatment, this solution was subjected for analysis of optical density by spectrophotometry and the disc surfaces were analyzed with scanning electron microscopy (SEM) and polarized light microscopy (PLM). The remaining discs were subjected for cross-sectional hardness analysis at different depths. Data were analyzed by repeated measures ANOVA and PLSD Fisher test (a=0.05). It was observed that previously demineralized teeth showed greater HP penetration (p<0.05). The bleaching treatment caused changes to a depth of 20 µm in sound enamel and up to 90 µm in demineralized enamel. SEM and PLM images revealed that the bleaching treatment caused superficial changes that were considerably more accentuated in previously demineralized teeth. It may be concluded that the enamel mineralization level influences HP penetration and the bleaching agent contributed to increase the demineralization depth.

Effect of low-concentration bleaching products on enamel bond strength at different elapsed times after bleaching treatment

This study evaluated the effects of several low-concentration bleaching products on microtensile bond strength (µTBS) to enamel at different elapsed times after the bleaching treatment. One hundred and fifty bovine incisors were divided into five groups: No treatment, 10% carbamide peroxide (Opalescence), 10% hydrogen peroxide (Opalescence Treswhite Supreme), 3% carbamide peroxide plus lactoperoxidase (WhiteKin), or 3% carbamide peroxide plus 2.7% carbamide peroxide (Clysiden Kit Express). All treatments lasted 4 weeks. After bleaching treatment or non-treatment, teeth were restored immediately, at 1, 3, 7, or 14 days after bleaching and submitted to µTBS test. Data were analyzed by ANOVA and Tukey's test (p<0.05). For WhiteKin and Clysiden, µTBS to enamel was significantly reduced immediately, at 1, 3 and 7 days after bleaching. At 14 days after bleaching, similar µTBS values were obtained regardless of bleaching product. Therefore, while over-the-counter (OTC) products might affect bond strength to enamel, this effect was no longer observed after 14 days.

Spectrophotometric and computerized evaluation of tooth bleaching employing 10 different home-bleaching procedures: In-vitro study

Objective:

The aim of this in-vitro study was to evaluate the efficacy of bleaching products, determine the applicability and validation of the measurement methods.

Materials and Methods:

Freshly extracted 110 human incisor teeth were stained with whole blood and hemolysate solution prior to the application of 10 different home-bleaching products. Spectrophotometric measurements of the tooth shades were performed for each specimen before and after bleaching at the 1^st, 3^rd, 7^th, and 14 days. Differences in lightness (Δl), chroma (Δc), hue (Δh) values and shade changes were measured to evaluate process. Computerized digital imaging analyses to determine the color changes were performed with Photoshop CS4 software (Adobe, San Jose, CA, USA). Statistical analyses were performed with analysis of variance, Scheffe and Tukey tests.

Results:

In all of the test groups regardless of the material used, a significant increase in lightness and hue, and decrease of chroma were observed, as compared to the control group. After recommended bleaching applications, Δl and Δh values respectively increased in group Zaris White and Brite (ZWB) and group Pola Night and Δc values showed significant decrease in groups ZWB and Rembrandt REM3 (P < 0.05). At the end of the procedure both spectrophotometric and digital imaging analysis showed ZWB was the most effective product among the others while Yotuel and Happy Smile were the least (P < 0.05).

Conclusions:

Home-bleaching systems showed slower but almost permanent bleaching effect likewise office-based methods. Both software and spectrophotometric analyses have advantages such as evaluating the results objectively and numerically, also treatment outcomes could be preserved.

Effects of applying antioxidants on bond strength of bleached bovine dentin

Objectives

Some antioxidants are believed to restore dentin bond strength after dental bleaching. This study was done to evaluate the influence of antioxidants on the bond strength of bleached bovine dentin.

Materials and Methods

Thirty incisors were randomly assigned to 10 groups (two unbleached control and eight bleached groups: immediate bonding IB, 4 wk delayed bonding DB, 10% sodium ascorbate treated SA, 10% α-tocopherol treated TP groups). Teeth in half of groups were subjected to thermal stress, whereas the remaining groups were not. Resin-dentin rods with a cross-sectional area of 2.25 mm² were obtained and microtensile bond strength was determined at a crosshead speed of 1 mm/min. Fifteen specimens were prepared for SEM to compare the surface characteristics of each group. The change in dentin bond strength from thermal stress and antioxidant treatment was evaluated using two-way analysis of variance (ANOVA) and Sheffe's post hoc test at a significance level of 95%.

Results

The control group exhibited the highest bond strength values, whereas IB group showed the lowest value before and after thermocycling. The DB group recovered its bond strength similar to that of the control group. The SA and TP groups exhibited similar bond strength values with those of the control and DB groups before thermocycling. However, The TP group did not maintain bond strength with thermal stress, whereas the SA group did.

Conclusions

Applying a 10% sodium ascorbate solution rather than 10% α-tocopherol solution for 60 sec is recommended to maintain dentin bond strength when restoring non-vitally bleached teeth.

In vitro demineralization of tooth enamel subjected to two whitening regimens

BACKGROUND

The resistance of bleached enamel to demineralization has not been elucidated fully. In this study, the authors aimed to examine the level of in vitro demineralization of human tooth enamel after bleaching by using two common bleaching regimens: home bleaching (HB) and office bleaching (OB) with photoirradiation.

METHODS

The authors bleached teeth to equivalent levels by means of the two bleaching regimens. They used fluorescence spectroscopy to measure the reduction in enamel density and the release of calcium into solution after storing the treated teeth in a demineralizing solution for two weeks. They also visualized and quantified mineral distribution in demineralized bleached enamel over time by using a desktop microcomputed-tomographic analyzer.

RESULTS

Enamel subjected to HB or to photoirradiation without bleaching showed increased demineralization. In contrast, enamel treated with OB was more resistant to demineralization. This resistance to demineralization in teeth treated with OB presumably is due to peroxide's permeating to deeper layers of enamel before being activated by photoirradiation, which enhances mineralization.

CONCLUSIONS

The mineral distribution pattern of enamel after treatment plays a critical role in providing resistance to demineralization in whitened teeth.

PRACTICAL IMPLICATIONS

OB confers to enamel significant resistance to in vitro demineralization. Dentists should supervise the nightguard HB process.

High-resolution micro-CT scanning as an innovative tool for evaluating dental hard tissue development

Microcomputerized tomography (micro‐CT) allows discriminating very small changes in dental hard tissue volumes. The aim of the present study was to create a new method for obtaining high‐resolution, three‐dimensional images of dental hard tissue development using micro‐CT, and to observe the changes in dental hard tissue development and composition in growing rat pups. Tooth germs from rats at the end of the 20‐day embryonic period (E20) and during the neonatal period (D1‐14) were subjected to micro‐CT. Three‐dimensional reconstructions were analyzed to compare dental hard tissue formation and mineralization during the different development periods. Scanning electron microscopy and energy dispersive spectroscopy were used to confirm mineral density (MD). Dental hard tissue began to form during the E20, but the process was slow and resulted in minimal deposition. Hard tissue volume increased by approximately 0.040 mm³/day from E20 to D3, and by 0.12‐0.42 mm³/day after D3, peaking at 0.42 mm³/day at D12. This increase in hard tissue volume resulted in continuous increases in hard tissue thickness, from 90.0 ± 20.7 μm at E20 to 545.2 ± 14.1 μm by D14. MD was 298 ± 3.1 mg HA/cm at E20 and increased to 678.2 ± 6.1 mg HA/cm by D14. The degree of calcification also progressively increased during the first 14 days of development. Dental MD was strongly associated with calcification. This study indicates that micro‐CT is a nondestructive, high‐resolution, reliable, and innovative tool for the evaluation of volume and MD of dental hard tissues during development. Micro‐CT minimizes artifacts caused by sample preparation.

PACS number: 87

Tooth-bleaching procedures and their controversial effects: A literature review

AIM

This review article will help clinicians improve their understanding of the history of bleaching procedures, bleaching types, components, mechanisms, and their effects on soft tissue, tooth structures, resin composite, and bonding.

METHODS

The controversial issues about bleaching procedures and their effects are reviewed. Additionally, the consequences of pre- and post-bleaching on the bonding potential of composite resin restorations to tooth structure are discussed.

CONCLUSION

The overall goal of the paper is to help reduce risks for patients.

Effects of Tooth Coating Material and Finishing Agent on Bleached Enamel Surfaces by KTP Laser

OBJECTIVE

The purpose of this study was to evaluate the effect of tooth coating material and finishing agent on bleached enamel surfaces after using KTP laser with 27% hydrogen peroxide.

BACKGROUND DATA

There have been few reports on the effects of tooth coating materials and finishing agents after bleaching.

METHODS

After 40 crowns of human extracted maxillary incisors were bleached by KTP laser, bleached enamels were finished with fluoride only or both of fluoride and nano-hydroxyapatite as a finishing agent. After application(s) of fluoride and/or finishing agent, the enamel surfaces were divided into 2 groups, which were covered with the coating material or without coating material. After application of coating materials, all specimens were kept for 2 weeks at 37°C of 100% humidity. After removing the coating material, color changing was measured and enamel surfaces were examined by scanning electron microscopy (SEM).

RESULTS

SEM observation of enamel surfaces treated the fluoride gel, finishing agent and coating material showed the most flattered surface compared to other groups. By measuring the color changing, few color changing was observed on the enamel surfaces treated the fluoride gel, finishing agents and coating material.

CONCLUSION

These results suggested that applications of fluoride gel, finishing agent and coating material made the enamel-surfaces flattered and kept effects of bleaching, could prevent the re-coloration. After applications of fluoride gel and finishing agent, covering the bleached-enamel surfaces with the coating material enhanced the keeping whiteness. It would give the patients satisfaction of whiteness.

Antioxidant agents and their effects on shear bond strength of bleached enamel

AIM

The goal of this study was to fnd a method to eliminate bond strength reduction after vital bleaching.

MATERIALS AND METHODS

Sixty fat surfaces of enamel central human incisors were prepared by diamond disks. In the frst group, the samples immediately bonded to the tooth after bleaching. For the second group, the bleached samples were treated by sodium ascorbate for 1 hours. In the third and fourth groups the treatment was down using a new antioxidant agent for 1 hour and 15 minutes respectively. For the ffth group no bleaching was done. Cylindrical composite resin (Z 100) with a Single Bond adhesive system was bonded to the enamel with a special metal mold. After thermocycling, the samples were loaded at a crosshead speed of 0.5 mm/min. The mode of failures was inspected by the Dino Lite microscope and the microstructure of the debonding surfaces was observed by SEM. Considering normal data, statistical analysis was conducted by ANOVA and Tukey tests (p = 0.05).

RESULTS

The fourth group had maximum (21.82), while the frst group had the least (9.0971) shear bond strength. The ANOVA test showed a signifcant difference among the fve groups (p = 0.0002). There was not any signifcant statistical difference between the three types of debonding (p = 0.165).

CONCLUSION

The usage of sodium ascorbate or sodium ascorbate with detergent after vital bleaching are effective methods for reducing the damaging effects of bleaching agents on the shear bond strength of composite resin restoration to enamel. CLINICAL SIGNIFCANCE: Using antioxidants is necessary post bleaching and before resin bonding.

An Innovative Approach to Treat Incisors Hypomineralization (MIH): A Combined Use of Casein Phosphopeptide-Amorphous Calcium Phosphate and Hydrogen Peroxide-A Case Report

Molar Incisor Hypomineralization (MIH) is characterized by a developmentally derived deficiency in mineral enamel. Affected teeth present demarcated enamel opacities, ranging from white to brown; also hypoplasia can be associated. Patient frequently claims aesthetic discomfort if anterior teeth are involved. This problem leads patients to request a bleaching treatment to improve aestheticconditions.Nevertheless, hydrogen peroxide can produce serious side-effects, resulting from further mineral loss. Microabrasion and/or a composite restoration are the treatments of choice in teeth with mild/moderate MIH, but they also need enamel loss. Recently, a new remineralizing agent based on Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) has been proposed to be effective in hypomineralized enamel, improving also aesthetic conditions. The present paper presents a case report of a young man with white opacities on incisors treated with a combined use of CPP-ACP mousse and hydrogen peroxide gel to correct the aesthetic defect. The patient was instructed to use CPP-ACP for two hours per day for three months in order to obtain enamel remineralization followed by a combined use of CPP-ACP and bleaching agent for further two months. At the end of this five-month treatment, a noticeable aesthetic improvement of the opacities was observed.

Potential Mechanism for the Laser-Fluoride Effect on Enamel Demineralization

Laser-induced prevention of dental caries has been studied extensively. However, the cariostatic mechanisms of a combined fluoride-laser treatment are not well-understood. Using micro- computed tomography (micro-CT), we quantified the effect of fluoride and/or Er:YAG laser treatment on enamel demineralization. The mean mineral loss (%/V) for each group was 4,870 ± 1,434 (fluoride followed by laser treatment), 6,341 ± 2,204 (laser treatment), 7,669 ± 2,255 (fluoride treatment), and 10,779 ± 2,936 (control). The preventive effect of the laser ( p < 0.001) and fluoride ( p = 0.010) treatment was statistically significant. Characterized by micro-x-ray diffraction (XRD) analysis, the significant contraction in the a-axis after both laser and combined laser/fluoride treatment was revealed (both p < 0.05). In conclusion, subablative low-energy Er:YAG laser irradiation following fluoride treatment may instantaneously transform enamel hydroxyapatite into fluoridated hydroxyapatite to reduce enamel solubility as a preventive treatment for enamel demineralization.

Effect of delaying toothbrushing during bleaching on enamel surface roughness: an in vitro study

This study aimed to evaluate the effect of toothbrushing on enamel surface roughness at three different intervals after daily bleaching treatment. Eighty enamel slabs were initially evaluated for surface roughness and then randomly divided into four groups. The bleaching procedure was carried out for 21 days, six hours daily. In the control group (group 1), the specimens were not brushed after bleaching, but in groups 2-4, they were brushed with toothpaste immediately, one hour, or two hours after bleaching, respectively. Then the specimens were stored in artificial saliva. Enamel surface roughness was reevaluated at the end of the period. Kruskal-Wallis and Mann-Whitney U tests showed statistically significant differences in the means of surface roughness values between the immediately brushed group and the three other groups (p<0.001). Daily toothbrushing immediately after bleaching increased enamel surface roughness; however, postponing the procedure for one or two hours after daily bleaching and exposing the specimens to artificial saliva during the study period resulted in enamel surface roughness comparable to that of the control group.

Enamel properties after tooth bleaching with hydrogen/carbamide peroxides in association with a CPP-ACP paste

BACKGROUND

This study evaluated the impact of bleaching teeth using blends of a CPP-ACP paste (MI Paste; MI) and carbamide/hydrogen peroxides in different proportions on surface properties of bleached enamel.

METHODS

Ninety bovine incisors were bleached with 7.5% hydrogen peroxide (HP), 16% carbamide peroxide (CP), MI and blends of HP or CP:MI at three proportions (1:1, 2:1, 1:2). Hardness and roughness were measured at baseline and after bleaching. Enamel morphology was evaluated by Scanning Electron Microscopy (SEM). The data were analyzed by two-way ANOVA for repeated measurements and Tukey's test.

RESULTS

Most of the samples bleached with MI in combination with peroxides presented increased hardness and roughness which were associated to mineral deposition, as observed by SEM images. Blends with higher fractions of MI did not offer superior benefits.

CONCLUSIONS

The use of a CPP-ACP paste mixed to carbamide/hydrogen peroxides can decrease adverse side-effects from tooth bleaching on an enamel surface.

Effect of bleaching on sound enamel and with early artificial caries lesions using confocal laser microscopy

The aim of this study was to evaluate effect of bleaching agents on sound enamel (SE) and enamel with early artificial caries lesions (CL) using confocal laser scanning microscopy (CLSM). Eighty blocks (4 x 5 x 5 mm) of bovine enamel were used and half of them were submitted to a pH cycling model to induce CL. Eight experimental groups were obtained from the treatments and mineralization level of the enamel (SE or CL) (n=10). SE groups: G1 - unbleached (control); G2 - 4% hydrogen peroxide (4 HP); G3 - 4 HP containing 0.05% Ca (Ca); G4 - 7.5% hydrogen peroxide (7.5 HP) containing amorphous calcium phosphate (ACP). CL groups: G5 - unbleached; G6 - 4 HP; G7 - 4 HP containing Ca; G8 - 7.5 HP ACP. G2, G3, G6, G7 were treated with the bleaching agents for 8 h/day during 14 days, while G4 and G8 were exposed to the bleaching agents for 30 min twice a day during 14 days. The enamel blocks were stained with 0.1 mM rhodamine B solution and the demineralization was quantified using fluorescence intensity detected by CLSM. Data were analyzed using ANOVA and Fisher’s tests (α=0.05). For the SE groups, the bleaching treatments increased significantly the demineralization area when compared with the unbleached group. In the CL groups, no statistically significant difference was observed (p>0.05).The addition of ACP or Ca in the composition of the whitening products did not overcome the effects caused by bleaching treatments on SE and neither was able to promote remineralization of CL.

Effects of pH Values of Hydrogen Peroxide Bleaching Agents on Enamel Surface Properties

This study investigated the influence of pH values of bleaching agents on the properties of the enamel surface. Sixty freshly extracted premolars were embedded in epoxy resin and mesiodistally sectioned through the buccal aspect into two parts. The sectioned slabs were distributed among six groups (n=10) and treated using different solutions. Group HCl was treated with HCl solution (pH=3.0) and served as a positive control. Group DW, stored in distilled water (pH=7.0), served as a negative control. Four treatment groups were treated using 30% hydrogen peroxide solutions with different pH values: group HP3 (pH=3.0), group HP5 (pH=5.0), group HP7 (pH=7.0), and group HP8 (pH=8.0). The buccal slabs were subjected to spectrophotometric evaluations. Scanning electron microscopy investigation and Micro-Raman spectroscopy were used to evaluate enamel surface morphological and chemical composition alterations. pH value has a significant influence on the color changes after bleaching (p&lt;0.001). Tukey's multiple comparisons revealed that the order of color changes was HP8, HP7&gt;HP5, HP3&gt;HCl&gt;DW. No obvious morphological alterations were detected on the enamel surface in groups DW, HP7, and HP8. The enamel surface of groups HCl and HP3 showed significant alterations with an erosion appearance. No obvious chemical composition changes were detected with respect to Micro-Raman analysis. Within the limitations of this study, it was concluded that no obvious morphological or chemical composition alterations of enamel surface were detected in the neutral or alkaline bleaching solutions. Bleaching solutions with lower pH values could result in more significant erosion of enamel, which represented a slight whitening effect.

Efficacy of a Novel At-home Bleaching Technique With Carbamide Peroxides Modified by CPP-ACP and Its Effect on the Microhardness of Bleached Enamel

This study was designed to evaluate in vitro the efficacy of a novel at-home bleaching technique using 10% or 16% carbamide peroxide modified by casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and its influence on the microhardness of bleached enamel. A total of 40 bovine incisors were divided into four groups (n=10) according to the bleaching agent used: 10% carbamide peroxide only; a blend of 10% carbamide peroxide and a CPP-ACP paste; 16% carbamide peroxide only; and a blend of 16% carbamide peroxide and a CPP-ACP paste. During the 14-day bleaching regimen, the samples were stored in artificial saliva. The Vickers microhardness and color of the teeth were assessed at baseline (T0) and immediately after the bleaching regimen (T14) using a microhardness tester and a spectrophotometer, respectively. The degree of color change was determined by the Commission Internationale de l'Eclariage (CIE) L*a*b* system (ΔE, ΔL*, Δa*, and Δb*) and Vita shade guide parameters. The data were analyzed by analysis of variance and the Tukey test (p&lt;0.05). The teeth that were bleached with a blend of peroxide (10% or 16%) and the CPP-ACP paste presented increased microhardness values at T14 compared with T0, whereas the samples that were bleached with peroxide only did not show any differences in their microhardness values. All of the bleaching agents were effective at whitening the teeth and did not show a statistically significant difference using the CIEL*a*b* system (ΔE, ΔL*, Δa*, and Δb*) or the Vita shade guide parameters. The use of a CPP-ACP paste with carbamide peroxide bleaching agents increased the bleached enamel's microhardness and did not have an influence on whitening efficacy.