Fracture of Lithia Disilicate Ceramics under Different Environmental Conditions.

The objective of this research was to quantify the effect of surface degradation and abrasion separately and in combination on the flexural strength of lithia disilicate ceramics. Lithia disilicate disks were fabricated using the lost wax technique and pressing in vacuum. The eight groups in this pilot experiment were (i) reference, hydrated in distilled water for 24 h prior to fracture; (ii) reference, non-hydrated group; (iii) 28-day pH cycling group; (iv) 125K chewing cycle group; (v) combined pH cycling + 125K chewing cycle; (vi) constant pH 2 solution for 28 days; (vii) constant pH 7 solution for 28 days; and (viii) constant pH 10 solution for 28 days. pH cycling is a method that alternates between pH 2, 7 and 10 over 28 days. A total of 15 disks were used for each group. All the groups were tested using the biaxial piston and a three-ball flexural strength test to obtain their biaxial flexural strength. pH 2 constant immersion demonstrated the highest fracture strength and was significantly greater than all other groups (p < 0.0001). Chewing and pH cycling + chewing groups exhibited the lowest fracture strengths and were significantly lower than all other groups (p < 0.0001). The damage observed from the chewing simulator does not represent apparent clinical fractures.

Color perceptibility and validity of silicon carbide-based protective coatings for dental ceramics.

STATEMENT OF PROBLEM: A silicon carbide (SiC) protective coating has been developed for dental ceramics, but whether the coated ceramics can match the classical VITA shades is unclear. PURPOSE: The purpose of this observational in vitro study was to evaluate the color adaptability of SiC-coated dental ceramics by testing the hypotheses that SiC-coated disks can be fabricated to match standard tooth shades and have a perceptible color match rate of at least 50% for disks with a color difference (ΔE)<2.0. The effects of ΔE, shade hue, shade value, observer sex, years of experience, profession, and shade guide orientation on color perception were studied. MATERIAL AND METHODS: SiC-coated disks were fabricated to color match (ΔEab<3.3) all 16 VITA classical shades. Uncoated disks of each VITA shade were used as the reference materials to determine whether the SiC-coated disks were color matched to the classical VITA shade guide. Three ΔE formulas (76, 94, and 2000) were applied and compared. Participants (N=120) with an average of 22 years of experience included dental school students, dental faculty members, and dental assistants. Pseudoisochromatic plate and the Farnsworth D-15 Panel test for assessing color deficiency and color blindness were administered. Participants then attempted to match SiC-coated disks to standard shade guides arranged by value or hue. All spectrophotometer readings and color matching were conducted in a light booth with standardized daylight illumination. Statistical analysis used the Fisher's exact test to determine factors associated with improved matching performance (α=.05). RESULTS: A significant difference in color match rate was found between disks with ΔE<2.0 (63.9%) and ΔE≥2.0 (41.7%) (P<.001). Arranging shade by value (72.2%) instead of hue (67.2%) produced better color matching (P<.001). Sex (P=.430), profession (P=.708), and years of experience (P=.902) had no significant influence on color matching. CONCLUSIONS: SiC-coated disks were successfully fabricated to match all VITA classical shades, and clinical visual color matching results confirmed that ΔE was a useful metric in optimizing color matching for the SiC-coated dental ceramics.

In Vitro Corrosion of SiC-Coated Anodized Ti Nano-Tubular Surfaces.

Peri-implantitis leads to implant failure and decreases long-term survival and success rates of implant-supported prostheses. The pathogenesis of this disease is complex but implant corrosion is believed to be one of the many factors which contributes to progression of this disease. A nanostructured titanium dioxide layer was introduced using anodization to improve the functionality of dental implants. In the present study, we evaluated the corrosion performance of silicon carbide (SiC) on anodized titanium dioxide nanotubes (ATO) using plasma-enhanced chemical vapor deposition (PECVD). This was investigated through a potentiodynamic polarization test and bacterial incubation for 30 days. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze surface morphologies of non-coated and SiC-coated nanotubes. Energy dispersive X-ray (EDX) was used to analyze the surface composition. In conclusion, SiC-coated ATO exhibited improved corrosion resistance and holds promise as an implant coating material.

Nanostructured Surfaces to Promote Osteoblast Proliferation and Minimize Bacterial Adhesion on Titanium.

The objective of this study was to investigate the potential of titanium nanotubes to promote the proliferation of human osteoblasts and to reduce monomicrobial biofilm adhesion. A secondary objective was to determine the effect of silicon carbide (SiC) on these nanostructured surfaces. Anodized titanium sheets with 100-150 nm nanotubes were either coated or not coated with SiC. After 24 h of osteoblast cultivation on the samples, cells were observed on all titanium sheets by SEM. In addition, the cytotoxicity was evaluated by CellTiter-BlueCell assay after 1, 3, and 7 days. The samples were also cultivated in culture medium with microorganisms incubated anaerobically with respective predominant periodontal bacteria viz. Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia as monoinfection at 37 °C for 30 days. The biofilm adhesion and coverage were evaluated through surface observation using Scanning Electron Microscopy (SEM). The results demonstrate that Ti nanostructured surfaces induced more cell proliferation after seven days. All groups presented no cytotoxic effects on human osteoblasts. In addition, SEM images illustrate that Ti nanostructured surfaces exhibited lower biofilm coverage compared to the reference samples. These results indicate that Ti nanotubes promoted osteoblasts proliferation and induced cell proliferation on the surface, compared with the controls. Ti nanotubes also reduced biofilm adhesion on titanium implant surfaces.

Qualitative Analysis of Remineralization Capabilities of Bioactive Glass (NovaMin) and Fluoride on Hydroxyapatite (HA) Discs: An In Vitro Study.

Tooth decay is a prevalent disease that initiates when the oral pH becomes acidic. Fluoride and/or bioactive glass (NovaMin) were used to regenerate/repair teeth that had been decalcified. In this present study, we investigated the effect of fluoride and/or bioactive glass (NovaMin) on remineralization of hydroxyapatite (HA) discs, which mimic the enamel surface of natural teeth. HA discs were etched with phosphoric acid and treated with one of the following toothpastes: (1) Sensodyne toothpaste with fluoride; (2) Sensodyne toothpaste with fluoride and bioactive glass (NovaMin); (3) Tom's toothpaste without fluoride or bioactive glass (NovaMin); and (4) Tom's toothpaste with bioactive glass (NovaMin). The toothpastes were applied on the etched discs for two minutes, once a day for 15 days. Scanning electron microscopy (SEM) was used to analyze surface morphologies and X-ray photoelectron spectroscopy (XPS) was used to analyze surface compositions. Tom's toothpaste with only NovaMin demonstrated the most remineralization potential compared with the other groups. In conclusion, incorporating bioactive glass (NovaMin) into toothpastes could benefit the repair and remineralization of teeth.

Fast SARS-CoV-2 virus detection using disposable cartridge strips and a semiconductor-based biosensor platform.

Detection of the SARS-CoV-2 spike protein and inactivated virus was achieved using disposable and biofunctionalized functional strips, which can be connected externally to a reusable printed circuit board for signal amplification with an embedded metal-oxide-semiconductor field-effect transistor (MOSFET). A series of chemical reactions was performed to immobilize both a monoclonal antibody and a polyclonal antibody onto the Au-plated electrode used as the sensing surface. An important step in the biofunctionalization, namely, the formation of Au-plated clusters on the sensor strips, was verified by scanning electron microscopy, as well as electrical measurements, to confirm successful binding of thiol groups on this Au surface. The functionalized sensor was externally connected to the gate electrode of the MOSFET, and synchronous pulses were applied to both the sensing strip and the drain contact of the MOSFET. The resulting changes in the dynamics of drain waveforms were converted into analog voltages and digital readouts, which correlate with the concentration of proteins and virus present in the tested solution. A broad range of protein concentrations from 1 fg/ml to 10 µg/ml and virus concentrations from 100 to 2500 PFU/ml were detectable for the sensor functionalized with both antibodies. The results show the potential of this approach for the development of a portable, low-cost, and disposable cartridge sensor system for point-of-care detection of viral diseases.

Forensic and reliability analyses of fixed dental prostheses.

This article describes the protocol for determining the cause of failure for retrieved failed implant supported fixed dental prostheses (FDPs) in a clinical study of three-unit bridges. The results of loading of flexure bars of different veneer compositions at different stress rates were presented for two veneer materials (leucite reinforced and fluorapatite glass-ceramic veneers) and a Y-TZP core zirconia ceramic used in the clinical study. From these results, the strengths of the fast loading conditions were used to determine the fracture toughness of these materials. Fractal dimension measurements of the flexure bars and selected FDPs of the same materials demonstrated that the values were the same for both the bars and the FDPs. This allowed the use of fracture toughness values from the flexure bars to determine the strengths of the FDPs. The failure analysis of clinically obtained FDP replicates to determine the size of the fracture initiating cracks was then performed. Using the information from the flexure bars and the size of the fracture initiating cracks for the failed FDPs, the strengths of the FDPs were determined. The clinical failures were determined to be most likely the result of repeated crack growth due to initial overload and continuous use after initial cracking.

Novel Coatings to Minimize Corrosion of Titanium in Oral Biofilm.

The aim of this work is to investigate the effects produced by polymicrobial biofilm (Porphyromonas gingivalis, Streptococcus mutans, Streptococcus sanguinis, and Streptococcus salivarius) on the corrosion behavior of titanium dental implants. Pure titanium disks were polished and coated with titanium nitride (TiN) and silicon carbide (SiC) along with their quarternized versions. Next, the disks were cultivated in culture medium (BHI) with P. gingivalis, S. mutans, S. sanguinis, and S. salivarius and incubated anaerobically at 37 °C for 30 days. Titanium corrosion was evaluated through surface observation using Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM). Furthermore, the Ti release in the medium was evaluated by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). SEM images showed that coated Ti disks exhibited lower corrosion compared to non-coated disks, except for the quartenized TiN. This was confirmed by AFM, where the roughness was higher in non-coated Ti disks. ICP showed that Ti levels were low in all coating disks. These results indicate that these SiC and TiN-based coatings could be a useful tool to reduce surface corrosion on titanium implant surfaces.

Hydroxyapatite Formation on Coated Titanium Implants Submerged in Simulated Body Fluid.

Titanium implants are commonly used in the field of dentistry for prosthetics such as crowns, bridges, and dentures. For successful therapy, an implant must bind to the surrounding bone in a process known as osseointegration. The objective for this ongoing study is to determine the potential of different implant surface coatings in providing the formation of hydroxyapatite (HA). The coatings include titanium nitride (TiN), silicon dioxide (SiO2), and quaternized titanium nitride (QTiN). The controls were a sodium hydroxide treated group, which functioned as a positive control, and an uncoated titanium group. Each coated disc was submerged in simulated body fluid (SBF), replenished every 48 h, over a period of 28 days. Each coating successfully developed a layer of HA, which was calculated through mass comparisons and observed using scanning electron microscopy (SEM) and energy dispersive analysis x-rays (EDX). Among these coatings, the quaternized titanium nitride coating seemed to have a better yield of HA. Further studies to expand the data concerning this experiment are underway.

Titanium Corrosion in Peri-Implantitis.

Titanium (Ti) corrodes clinically in the presence of bacteria. We investigated this phenomenon as a function of Ti particles found in biopsied tissues around peri-implantitis sites and surface roughness of failed Ti implants. Tissue biopsies were surgically collected from peri-implantitis sites, processed, and embedded in resin. The resin-embedded samples were hand trimmed to the region of interest and semi-thick (500 nm) sections were collected onto coverslips. One section was toluidine blue post-stained as a reference. The remainder sections were left unstained for energy-dispersive X-ray spectroscopy (EDX) analysis. Processed samples were examined under scanning electron microscopy (SEM) and EDX. Corresponding failed implants were also removed and examined under SEM and EDX. Five out of eight biopsied samples demonstrated the presence of Ti particles in the soft tissue, suggesting the true rate among all failures was between 24.5% and 91.5% (the lower bound of a 95% confidence interval for the true rate of Ti presence). SEM analysis of failed implant bodies also indicated changes in surface morphology and appeared less detailed with decreased weight percent of Ti on the surface of the failed implants. In conclusion, Ti particles were noted in 5/8 biopsied samples. Surface morphologies were smoother in failed implants compared with the reference implant.

The Galvanic Effect of Titanium and Amalgam in the Oral Environment.

The effects of the presence of amalgam on titanium (Ti) dissolution in the oral environment under acidic, neutral, and basic conditions was studied. The presence of amalgam was found to suppress Ti release under acidic conditions due to the redeposition of TiOx/SnOx on the surface of the Ti. The redeposition of SnOx was due to the amalgam releasing its components (Hg, Cu, Sn, Ag) and the thermodynamic preference of Sn to oxidize, which was confirmed using mass measurements, ICP-MS analyses, and X-ray Photoelectron Spectroscopy (XPS). XPS depth profiling was performed to characterize the composition and oxidation states of the redeposited SnOx/TiOx film. Under basic conditions, the amalgam hindered Ti dissolution, but no redeposition of amalgam components was observed for the Ti.

Novel methodology for measuring intraoral wear in enamel and dental restorative materials.

OBJECTIVES: To test the hypotheses that (a) the chairside/handheld dental scanner combined with a metrology software will measure clinical wear in vivo in agreement with measurements from X-ray computed microtomography and; (b) polished monolithic zirconia does not cause accelerated wear of opposing enamel. MATERIALS AND METHODS: Thirty single crowns were randomized to receive a monolithic zirconia or metal-ceramic crown. Two non-restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned using an intraoral dental scanner. Patients were recalled at 6-months and 1-year for re-scanning. Scanned images were compared using a metrology software to determine maximum vertical wear of teeth. The accuracy of the scanning measurements from this new method was compared with X-ray computed microtomography (micro-CT) measurements. Statistical analysis was performed using Mann-Whitney U test to determine significant differences between wear of enamel against zirconia, metal-ceramic or enamel. Linear regression analysis determined agreement between measurements obtained using intraoral scanning and micro-CT. RESULTS: Regression analysis demonstrated that there is a quantitative agreement between depth and volume measurements produced using intraoral scanning and the micro-CT methodologies. There was no significant difference between the wear of enamel against polished monolithic zirconia crowns and enamel against enamel. CONCLUSIONS: Intraoral scanning combined with a matching software can accurately quantify clinical wear to verify that monolithic zirconia exhibited comparable wear of enamel compared with metal-ceramic crowns and control enamel. Agreement between the intraoral scanner and the micro-CT was 99.8%. Clinical Trials.gov NCT02289781.

Effect of pH Cycling Frequency on Glass-Ceramic Corrosion.

The effect of pH changes on the chemical durability of dental glass-ceramic materials was evaluated using weight loss and ion release levels. The hypothesis that increased pH changes will exhibit greater corrosion was investigated. The ion concentration was analyzed using inductively coupled plasma atomic emission spectrometer (ICP). The surface compositions were investigated using X-ray photoelectron spectroscopy (XPS). The surface morphologies were examined using scanning electron microscopy (SEM). Dental glass-ceramics were tested in constant immersion, 3-day cycling, and 1-day cycling with pH 10, pH 2, and pH 7 for 3, 15, and 30 days. The 1-d cycling group demonstrated the highest levels of weight loss compared with 3-d cycling and constant immersion. For the ion release, Si4+ and Ca2+ had the highest rates of release in 1-d cycling, whereas the Al3+ release rate with constant pH 2 was highest. The alteration/passivation layer that was formed on the surface of disks possibly prevented further dissolution of pH 10 corroded disks. XPS analysis demonstrated different surface compositions of corroded disks in pH 10 and pH 2. Si4+, K+, Na+, Al3+, and Ca2+ were detected on the surface of corroded pH 10 disks, whereas a Si4+ and P5+-rich surface formed on corroded pH 2 disks. SEM results demonstrated rougher surfaces for corroded disks in cycling conditions and pH 2 constant immersion. In conclusion, increased pH changes significantly promote the corrosion of dental glass-ceramic materials.

Demonstration of a SiC Protective Coating for Titanium Implants.

To mitigate the corrosion of titanium implants and improve implant longevity, we investigated the capability to coat titanium implants with SiC and determined if the coating could remain intact after simulated implant placement. Titanium disks and titanium implants were coated with SiC using plasma-enhanced chemical vapor deposition (PECVD) and were examined for interface quality, chemical composition, and coating robustness. SiC-coated titanium implants were torqued into a Poly(methyl methacrylate) (PMMA) block to simulate clinical implant placement followed by energy dispersive spectroscopy to determine if the coating remained intact. After torquing, the atomic concentration of the detectable elements (silicon, carbon, oxygen, titanium, and aluminum) remained relatively unchanged, with the variation staying within the detection limits of the Energy Dispersive Spectroscopy (EDS) tool. In conclusion, plasma-enhanced chemical vapor deposited SiC was shown to conformably coat titanium implant surfaces and remain intact after torquing the coated implants into a material with a similar hardness to human bone mass.

Annealing and N2 Plasma Treatment to Minimize Corrosion of SiC-Coated Glass-Ceramics.

To improve the chemical durability of SiC-based coatings on glass-ceramics, the effects of annealing and N2 plasma treatment were investigated. Fluorapatite glass-ceramic disks were coated with SiC via plasma-enhanced chemical vapor deposition (PECVD), treated with N2 plasma followed by an annealing step, characterized, and then immersed in a pH 10 buffer solution for 30 days to study coating delamination. Post-deposition annealing was found to densify the deposited SiC and lessen SiC delamination during the pH 10 immersion. When the SiC was treated with a N2 plasma for 10 min, the bulk properties of the SiC coating were not affected but surface pores were sealed, slightly improving the SiC's chemical durability. By combining N2 plasma-treatment with a post-deposition annealing step, film delamination was reduced from 94% to 2.9% after immersion in a pH 10 solution for 30 days. X-ray Photoelectron spectroscopy (XPS) detected a higher concentration of oxygen on the surface of the plasma treated films, indicating a thin SiO2 layer was formed and could have assisted in pore sealing. In conclusion, post-deposition annealing and N2 plasma treatment where shown to significantly improve the chemical durability of PECVD deposited SiC films used as a coating for glass-ceramics.

Anti-Bacterial Properties and Biocompatibility of Novel SiC Coating for Dental Ceramic.

A 200 nm plasma-enhanced chemical vapor-deposited SiC was used as a coating on dental ceramics to improve anti-bacterial properties for the applications of dental prosthesis. A thin SiO2 (20 nm) in the same system was deposited first, prior to SiC deposition, to improve the adhesion between SiC to dental ceramic. Silane and methane were the precursors for SiC deposition, and the SiO2 deposition employed silane and nitrous oxide as the precursors. SiC antimicrobial activity was evaluated on the proliferation of biofilm, Streptococcus sanguinis, and Streptococcus mutans on SiC-coated and uncoated dental ceramics for 24 h. The ceramic coating with SiC exhibited a biofilm coverage of 16.9%, whereas uncoated samples demonstrated a significantly higher biofilm coverage of 91.8%, measured with fluorescence and scanning electron microscopic images. The cytotoxicity of the SiC coating was evaluated using human periodontal ligament fibroblasts (HPdLF) by CellTiter-BlueCell viability assay. After 24 h of HPdLF cultivation, no obvious cytotoxicity was observed on the SiC coating and control group; both sets of samples exhibited similar cell adhesion and proliferation. SiC coating on a ceramic demonstrated antimicrobial activity without inducing cytotoxic effects.

Novel Coating to Minimize Corrosion of Glass-Ceramics for Dental Applications.

The effect of a novel silicon carbide (SiC) coating on the chemical durability of a fluorapatite glass-ceramic veneer was investigated by examining weight loss and ion release levels. The hypothesis that this novel coating will exhibit significant corrosion resistance was tested. Inductively coupled plasma atomic emission spectrometer (ICP) was used for ion concentration determination and scanning electron microscopy (SEM) for surface morphology analyses. Samples were immersed in pH 10 and pH 2 buffer solutions to represent extreme conditions in the oral cavity. Analyses were done at 15 and 30 days. The SiC coated group demonstrated significant reduction in weight loss across all solutions and time points (p < 0.0001). Ion release analyses demonstrated either a marginally lower or a significantly lower release of ions for the SiC-coated disks. SEM analysis reveals planarization of surfaces by the SiC-coated group. The surfaces of coated samples were not as corroded as the non-coated samples, which is indicative of the protective nature of these coatings. In conclusion, SiC is a novel coating that holds promise for improving the performance of ceramic materials used for dental applications.

Retrospective analysis of survival rates of post-and-cores in a dental school setting.

STATEMENT OF PROBLEM: The clinical survival of different types of post-and-core systems requires assessment. PURPOSE: The purpose of this retrospective clinical study was to evaluate the clinical survival rate (CSR) of custom-fabricated cast metal and prefabricated (both metal- and fiber-reinforced composite resin post) post-and-cores as a function of patient- and restoration-related variables. MATERIAL AND METHODS: A retrospective analysis was conducted on electronic charts indicating that these patients had received some type of post-and-core between January 2003 and January 2018. A total of 754 records were included in the analysis based on the inclusion criteria. Data were analyzed by using the Kaplan-Meier and Cox proportional hazards analysis. RESULTS: Kaplan-Meier analysis demonstrated the mean survival time for each group to be 12.0 years for fiber-reinforced composite resin posts, 11.8 years for cast metal post-and-cores, and 10.2 years for prefabricated metal posts. Although the mean survival time differed by 1.8 years among groups, with prefabricated metal posts having a slightly higher risk of failure, this effect was not statistically significant (P=.067). The effect of post type also failed to reach significance when controlling for patient demographics and post position in a Cox proportional hazards analysis (P=.106). However, the Cox model did show that survival was associated with tooth position (P=.003), cement (P=.021), and type of restoration (P<.001). CONCLUSIONS: Analysis showed no evidence that post-and-core survival was significantly associated with 3 types of post-and-cores (custom-fabricated metal, prefabricated metal, and prefabricated fiber-reinforced composite resin). The percentage of root in the bone, tooth position, cement, and type of restoration, however, were significantly associated with survival.

Comprehensive analysis of laserscanner validity used for measurement of wear.

OBJECTIVES: The aims of this study were to test the hypotheses that (a) a laserscanner used for measuring maximum depth and volume loss will yield the same results as a surface profilometer; (b) the surface roughness will affect the maximum depth and volume loss measured with the laserscanner; (c) analytical results using the laserscanner from multiple operators have no more than 10% inter-rater difference and; (d) replicating samples using either stone or impression material is an accurate method for measuring wear using the laserscanner. MATERIALS AND METHODS: The volume and maximum depth of indentations from fine, medium and rough burs on glass-ceramic disks were measured using two devices, a surface profilometer (Dektak II, Veeco) and a 3D Laserscanner (LAS-20, SD Mechatronik). Replicates of the indentations made from polyvinysiloxane impression material and gypsum were also measured. RESULTS: Comparison of profilometer and laserscanner readings using ceramic disks demonstrated a mean error of 13.61% for depth and 25.32% for volume. Replication errors were minimal (2.6% for impression, 2.5% for stone). Surface profilometer data for volume measurements revealed a difference of 6.1% for impression and 6.5% for stone compared with ceramics. However, when measurements for replicates were compared between laserscanner and surface profilometer, depth had a mean error of 74% for impression and 51% for stone. Volume differences of 78% for impression and 44% for stone were recorded. CONCLUSION: This work demonstrated that the laserscanner was a convenient device for measuring wear but there is a need to validate the accuracy of the measurements.

Effect of carbamide peroxide bleaching on enamel characteristics and susceptibility to further discoloration.

STATEMENT OF PROBLEM: Whether tooth whitening alters the surface topography of enamel causing an increase in surface roughness that could increase susceptibility to restaining is unclear. PURPOSE: The purpose of this in vitro study was to evaluate whether immersing enamel in common solutions produces a color change of ΔE greater than 2; whether the highest concentration carbamide peroxide bleaching agent produces the greatest ΔE; whether bleaching increases the susceptibility to further staining by common solutions; and whether morphologic changes to the enamel surface are observed after staining and bleaching as evidenced by scanning electron microscopy (SEM) analysis and energy-dispersive X-ray spectroscopy (EDS). MATERIAL AND METHODS: Forty-five extracted human teeth were immersed in 5 solutions (wine, coffee, tea, soda, and water) for 15 days at 80°C, and the change in ΔE was assessed with a colorimeter. The teeth were bleached using different concentrations of carbamide peroxide (20%, 35%, and 44%) and ΔE was measured at different time intervals. The teeth were then restained with the same solutions. The ΔE after initial staining was compared with the ΔE after bleaching and restaining of the same teeth. SEM was performed at baseline, after staining, bleaching, and restaining to evaluate the changes in the enamel surface topography. EDS was used to determine the elemental composition of tooth surfaces after restaining. RESULTS: All liquids caused a ΔE greater than 2 after 15 days. The concentration of bleaching agent was not significantly associated with ΔE for any stain types. No significant difference was found in the rate of staining between initial staining and restaining after bleaching. However, a significant effect of time was found for the staining, where the overall ΔE increased by 0.34 for each day in the solution (P<.001). SEM images showed no major changes to enamel topography after bleaching. However, a coating was noted on teeth stained with wine and tea, which had different elemental compositions when compared with the tooth surface. CONCLUSIONS: Based on SEM observation, bleaching teeth with carbamide peroxide does not increase the susceptibility of enamel to staining and does not alter the topography of the enamel. Using higher bleaching concentrations did not increase tooth whitening as a function of time.