Influence of surface roughness on the color of dental-resin composites

Effects of Different Concentrations of Carbamide Peroxide on Color, Surface Roughness, and Hardness of CAD/CAM Dental Ceramics

OBJECTIVES

This study assessed the effects of 15% and 20% carbamide peroxide (CP) on color, surface roughness, and hardness of computer-aided design/computer-aided manufacturing (CAD/CAM) dental ceramics.

MATERIALS AND METHODS

This in vitro study was conducted on 120 Vita Mark II, Celtra Duo, and Suprinity CAD/CAM ceramic specimens. The ceramic specimens in each group (n = 40) were randomly assigned to two subgroups (n = 20) for polishing and glazing, and their baseline color, surface roughness (Ra), and hardness were assessed. In each subgroup, half of the specimens were exposed to 15% CP, while the other half were exposed to 20% CP. Their color change (ΔE), surface roughness, and hardness were then measured again. Surface roughness, hardness, and color were analyzed sequentially by profilometer, Vickers hardness tester, and spectrophotometer, respectively. Data were analyzed by repeated measures ANOVA, one-way ANOVA, and post hoc Bonferroni test (α = 0.05).

RESULTS

The surface roughness of all groups significantly increased after bleaching treatment (p < 0.05). Surface hardness of all groups decreased after bleaching treatment, but this reduction was only significant in Vita Mark II subgroups (glazed, polished, 15%, and 20% CP). The ΔE was not clinically and visually perceivable in any group.

CONCLUSION

The present results revealed that concentration of CP and type of surface treatment affected the surface properties of CAD/CAM ceramics. Type of surface treatment only affected the surface hardness of Vita Mark II ceramics (p < 0.05). Concentration of CP had a significant effect only on polished Vita Mark II.

Comparison of different illumination intensities of mobile units for tooth color differentiation: An in vitro study

STATEMENT OF PROBLEM

Visual color determination in clinics or dental offices should take place under reproducible environmental conditions. To reduce false tooth color measurements, daylight and illumination lamps (5000-7500 K) have been recommended. Those can be used either as stationary or mobile handheld illumination units. However, depending on the manufacturer, the handheld lights use different illuminance brightness, and whether the choice of unit affects shade selection is unclear.

PURPOSE

The purpose of this in vitro study was to determine whether the mobile handheld light-emitting diode (LED) lighting unit shows a significantly better result in visual color determination than the conventional reference lighting unit.

MATERIAL AND METHODS

Trained preclinical dental students (N=23) with a mean ±standard deviation age of 24 ±5 years participated in the study. Two color differentiation lamps (Smile lite 1620lx and Dialite Color 4450lx) (SL and DC) were each placed at a 15-cm distance to determine the color of the shade tabs (templates, N=10) with the VITA Linear Guide 3D Master in a double-blinded study. According to the manufacturer's recommendation, polarization filters were used with the Smile lite lamp.

RESULTS

Of N=220 shade determinations each, 31.8% (SL) and 33.2% (DC) were correct; the median (ΔE00) and interquartile range were 0.96 (±3.32) for SL and 1.35 (±3.28) for DC. The differences between the groups were not statistically significant (P=.67).

CONCLUSIONS

The results show that the use of the mobile LED illumination unit did not improve color determination compared with the reference illumination. The different illumination intensities of 980 lux (SL) with a polarizing filter or 1500 lux (DC) did not have a positive effect.

Clinical Performance of Glass Ionomer Cement in Load-Bearing Restorations: A Systematic Review

Glass ionomer cement (GIC) is a self-adhesive dental restorative material composed of a polyacrylic acid liquid and fluoro-aluminosilicate glass powder. It is commonly used for cementation during dental restoration. This study aimed to systematically review the existing literature regarding the clinical performance of GIC in load-bearing dental restorations. A comprehensive literature search was conducted in EBSCO, PubMed, Embrace, and Cochrane databases. Only randomized controlled trials (RCTs) were included in the search, and a broad search technique was used, where inclusion and exclusion criteria were applied. After a thorough evaluation, 12 RCTs were extensively reviewed, and whether GIC is suitable for load-bearing restorations was determined. Significant variations in staining surface or margin, color match, translucency, esthetic anatomical form, retention, material fracture, marginal adaptation, surface luster, occlusal contour, wear, and approximal anatomical form indicated the unsuitability of GIC. By contrast, significance differences in patient view and periodontal response indicated that GIC is suitable. No significant differences in postoperative sensitivity, recurrence of caries, or tooth integrity were observed. Nevertheless, the results of the review demonstrated that the clinical performance of GIC is comparable to that of traditional restorative materials with regard to the parameters analyzed. GIC is a suitable restorative material for load-bearing restorations regarding surface margin, esthetic anatomical form, material retention and fracture, marginal adaptation, occlusal contour, wear, and approximal anatomical form. It reduces other parameters, such as postoperative sensitivity, recurrence of caries, and tooth integrity.

Changes in Gloss Alteration, Surface Roughness, and Color of Direct Dental Restorative Materials after Professional Dental Prophylaxis

In the context of optimizing dental care for patients who are elderly, the purpose of this in vitro study was to evaluate the surface gloss (with a micro-area gloss meter) of, surface roughness (with a compact surface roughness measuring instrument) of, and color change (with a dental colorimeter) in two commercially available injectable resin-based composites (Estelite Universal Flow (EUF) and Beautifil Flow Plus F00 (BFP)) as well as two glass-ionomer cements (GC Fuji II LC CAPSULE (FLC) and GC Fuji IX GP EXTRA CAPSULE (FGP)), before and after dental prophylaxis. After 24 h, the surfaces of each specimen were polished at 2500 rpm with a prophy brush (Mersage Brush, Shofu) and one-step prophylaxis paste (Prophy Paste Pro, Directa): under 100 or 300 gf load, and for 10 or 30 s, 4× cycles of cleaning. After mechanical cleaning, conditions were found for a significant reduction in the gloss level (EUF, BFP, or FLC; p < 0.05) and a significant increase in surface roughness (BFP; 300 gf load, 10 s × four cycles of cleaning). Overall, the longer time or higher prophylaxis load tended to decrease the surface gloss. However, the observed change in surface roughness varied between the restorative materials. There was no color change post-prophylaxis.

Color stability and degree of conversion of gingiva-colored resin-based composites

OBJECTIVES

To evaluate gingiva-colored resin-based composites' (GCRBC) color stability and degree of conversion (DC%).

METHODS

Eight discs (8 × 1 mm) of 20 shades of GCRBC were prepared. Color coordinates were measured against a gray background with a calibrated spectroradiometer, CIE D65 illuminant and the CIE 45°/0° geometry at baseline and after 30 days of storage in distilled water, coffee, and red wine. Color differences ( ∆ E 00 ) between final and baseline conditions were calculated. An ATR-FTIR spectrometer with a diamond tip was used to calculate DC%. The results were analyzed statistically using ANOVA and Tukey post-hoc test. The level of significance was p < 0.05.

RESULTS

DC% and color stability correlated with each other and with the GCRBC brand. DC% ranged between 43% and 96%, highest values correspond to flowable composites. All composites have experienced color changes after immersion in water, wine and coffee. However, the magnitude of the color change has varied widely depending on the immersion medium and the GCRBC. Color changes generated by the wine were, globally, greater than those induced by coffee (p < 0.001) and above the acceptability thresholds.

CONCLUSIONS

The DC% of GCRBCs is sufficient to achieve adequate biocompatibility and physicomechanical properties, but the high susceptibility to staining could compromise aesthetic long-term results.

CLINICAL SIGNIFICANCE

The degree of conversion and the color stability of gingiva-colored resin-based composites correlated with each other. All composites have experienced color changes after immersion in water, wine and coffee. Color changes generated by wine were, globally, greater than those induced by coffee and above the acceptability thresholds that could compromise aesthetic long-term results.

Effects of in vitro erosion on surface texture, microhardness, and color stability of resin composite with S-PRG fillers

OBJECTIVES

To evaluate the effect of acid erosion on different physical properties of resin composite with S-PRG (surface pre-reacted glass) fillers, by conducting simulations of intrinsic and extrinsic sources.

MATERIALS AND METHODS

Cylindrical samples (Ø6 vs. 2 mm) of a conventional nanohybrid resin composite (Forma, Ultradent) and of a nanohybrid resin composite with S-PRG filler (Beautifil II, Shofu) were exposed to erosive cycling (5 days), based on (n=12) remineralizing solution (control); 0.3% citric acid (pH=2.6); or 0.01 M hydrochloric acid (pH=2). Roughness (Ra), microhardness (KHN), and color (CIEL*a*b*, CIEDE2000, and Vita scale (SGU)) factors were analyzed at the initial and final time points, and the general color changes (ΔE_ab, ΔE₀₀, ΔSGU) were calculated. Final images were obtained using scanning electron microscopy (SEM). The data were evaluated by generalized models, Mann-Whitney, Wilcoxon, Kruskal-Wallis, and Dunn tests (α=0.05).

RESULTS

Regarding KHN, there was no difference between the groups or the time periods (p = 0.74). As for Ra, there was a significant increase in the Ra of both composites after cycling with hydrochloric acid, but only the resin composite with S-PRG filler showed a change in Ra after cycling with citric acid (p = 0.003). After cycling with citric and hydrochloric acid, the highest Ra values were found for the resin composite with S-PRG filler (p < 0.0001), corroborating the result of images (SEM) indicating loss of filler and porosities in this material. The resin composite with S-PRG filler showed higher ΔE_ab and ΔE₀₀, in addition to more negative ΔSGU values and lower L* values after exposure to both acids, compared to the control (p < 0.05).

CONCLUSION

The acidic conditions altered the roughness and color stability of the materials tested, pointing out that the resin composite containing S-PRG filler showed greater degradation of its physical properties than the conventional resin composite.

CLINICAL RELEVANCE

Bioactive materials are relevant, considering that their properties interact with dental hard tissues; however, the S-PRG-based resin composite showed greater degradation under acidic conditions than the conventional resin composite.

Comparative Evaluation of Colour Stability and Surface Roughness of Nanohybrid Composite Resins in Mouth Rinse and Colouring Beverages

Objectives An ideal restorative material should be capable of supplanting the biological, functional, and aesthetic qualities of a healthy tooth structure. There has always been a search for optimal and aesthetically pleasing restorative materials. This study aims to evaluate the surface roughness and colour stability of three nanohybrid composite resins post-exposure to mouth rinse and colouring beverages. Methods One hundred and twenty specimens of dimension 10 mm x 8 mm x 1 mm were randomly allocated into three equal-sized groups and fabricated using three different nanohybrid composites (Group A: Filtek Z250 XT, Group B: Tetric N-Ceram, and Group C: Solare Sculpt). Sixty samples, comprising 20 from each group, were examined for colour stability and 60 for surface roughness after exposure to chlorhexidine and coffee. Baseline and post-exposure readings of the surface roughness and colour absorbance of the specimens were obtained by atomic force microscopy and spectrophotometer, respectively. A one-way analysis of variance (ANOVA) test followed by a post hoc Tukey's test and an independent t-test were used for data analysis, considering a p-value<0.05 as significant. Results Irrespective of the composite, the surface roughness and colour change were substantially higher in the samples exposed to coffee (p-value<0.01). Filtek Z 250XT showed significantly minor changes in colour and surface roughness, followed by Solare Sculpt and Tetric N-Ceram (p-value<0.05). Conclusion Coffee caused more surface roughness and colour changes compared to chlorhexidine. Filtek 250 XT showed minor changes in colour and surface roughness on exposure to both solutions.

The Effect of Home and In-Office Bleaching on Microhardness and Color of Different CAD/CAM Ceramic Materials

The aim of this study is to assess the effect of different bleaching agents on microhardness and color of CAD/CAM ceramics including IPS e.max CAD (lithium disilicate), VITA ENAMIC (polymer-infiltrated ceramic), and Celtra Duo CAD (zirconia-reinforced lithium silicate). Materials' samples were divided into three groups (n = 10) and each received a different bleaching treatment; 20% carbamide peroxide, 35% carbamide peroxide, and 40% hydrogen peroxide. A fourth group was stored in water acting as a control. Vickers microhardness and spectrophotometric color measurements were taken at baseline and after bleaching. IPS e.max CAD showed a significant reduction (about 14%), while VITA ENAMIC showed a significant increase (about 78%) in microhardness after bleaching (p ˂ 0.001). Celtra Duo CAD did not demonstrate a significant change in microhardness (p ≥ 0.609). The color difference (ΔE_ab) after bleaching was 0.29 (±0.08), 2.84 (±0.64), and 1.99 (±0.37) for IPS e.max CAD, VITA ENAMIC, and Celtra Duo CAD, respectively. It could be concluded that the effect of bleaching on color and microhardness was mainly material-dependent. Bleaching significantly affected the microhardness of IPS e.max CAD and VITA ENAMIC. The color difference was within the clinically imperceptible range for IPS e.max CAD, while VITA ENAMIC and Celtra Duo CAD demonstrated perceptible color change.

Comparison of surface roughness and color stability of different denture characterizing composite resins: the effect of different surface treatments

PURPOSE

This study aimed to investigate the effect of surface treatment and type of composite resin material on the color stability and surface roughness of different denture characterizing composites.

MATERIALS AND METHODS

Two nanohybrids [Gradia Plus Gum, (GP) and SR Nexco Paste Gingiva, (SR)] and one microhybrid gingiva-colored composite resin (Amaris Gingiva, (AG)] were investigated. A total of 120 disk-shaped samples were prepared, 40 of each material. Samples were divided into two groups (n = 20) for each material according to the surface treatment applied: conventional polishing (control) and coated with a sealant in addition to the surface polishing. All groups were thermocycled. The surface roughness (Ra) was measured using a profilometer after thermal cycling. The samples were then divided into 2 subgroups (n = 10) and stored for 7 days in distilled water or coffee solution. Color differences (ΔE₀₀ ) were calculated with a spectrophotometer. Results were evaluated with Kruskal-Wallis and Mann-Whitney U statistical analysis.

RESULTS

The type of denture characterizing composite material and surface treatment method revealed statistically significant differences for the ΔE₀₀ (after immersion both in coffee and distilled water) and the Ra values of denture characterizing composite (p < 0.001 for both). All sealed groups showed significantly higher Ra than the all polished groups. Both in the polished groups and the sealant applied groups, the GP had the highest mean Ra values (0.29 ±0.05 μm and 0.47 ±0.09 μm, respectively). It was followed by SR (0.23 ±0.06 μm and 0.41 ±0.10 μm, respectively), and AG groups (0.20 ±0.06 μm and 0.39 ±0.09 μm, respectively). According to the mean ΔE₀₀ results, all composite groups showed significantly higher ΔE₀₀ values immersed in coffee solutions compared to distilled water. In coffee solutions, the highest ΔE₀₀ was observed in the polished GP (1.90 ±0.40), and the lowest ΔE₀₀ was observed in the polished SR (0.97 ±0.36). The sealed groups showed higher ΔE₀₀ than the polished groups, except for GP.

CONCLUSIONS

The surface roughness value of sealant applied groups were significantly higher than those of their polished groups. The surface sealant application significantly increased the staining of all composite groups compared to conventional polishing, except for GP. This article is protected by copyright. All rights reserved.

Effects of tooth bleaching protocols assisted by Er,Cr:YSGG and diode (980 nm) lasers on color change of resin-based restoratives

OBJECTIVE

To evaluate color change of three resin-based restorative materials after two laser-assisted in-office tooth bleaching protocols using Er,Cr:YSGG and diode (980 nm) lasers.

MATERIALS AND METHODS

A nanohybrid composite resin (EP), a Bis-GMA free composite resin (EPBio) and a resin-matrix CAD-CAM ceramic (HC) were tested. Ninety specimens were prepared and stored in artificial saliva. Group 1 received an in-office bleaching treatment using 40% H₂ O_2. The same bleaching procedure was assisted by Er,Cr:YSGG laser in Group 2 and by a diode laser (980 nm) in Group 3. Color measurements were performed using a double-beam UV-Vis spectrophotometer at four time intervals (before, 24 h, 15 and 30 days), converted to L*, a*, and b* units of the CIELAB color space and assessed on the basis of 50:50% acceptability (ΔΕ_ab * = 2.7 and ΔΕ₀₀  = 1.77) and 50:50% perceptibility (ΔΕ_ab * = 1.2 and ΔΕ₀₀  = 0.81) thresholds. Three-way ANOVA with repeated measurements was used for statistical analysis of the data.

RESULTS

Color and whiteness changes did not exceed the established 50:50% acceptability thresholds. EP presented the highest color change after the bleaching followed by EPBio and HC (p ≤ 0.05). Three-way ANOVA revealed that type of material and time interval significantly affected color change (p ≤ 0.001).

CONCLUSIONS

The tested bleaching treatments assisted by Er,Cr:YSGG and diode (980 nm) lasers did not induce unacceptable color and whiteness changes in the resin-based restorative materials.

CLINICAL SIGNIFICANCE

The tested Er,Cr:YSGG and diode (980 nm) laser-assisted tooth bleaching protocols which may be recommended to accelerate the clinical procedures cannot affect the color of the existing resin-based restorations in case they are accidentally exposed on the bleaching gel and laser irradiation.

Color adjustment potential of single-shade resin composite to various-shade human teeth: Effect of structural color phenomenon

This study evaluated the effect of the structural color phenomenon in resin composites (RCs) on the color adjustment of restorations by investgating their color reproduction performance in human incisors of various shade. Cervical cavities were filled with a single-shade RC with 260 nm spherical fillers (Omnichroma (OMN)), conventional A2-shade RCs (Estelite Σ Quick or Clearfil AP-X), or experimental RCs with 5-50 nm fumed silica fillers (R1) and 100 nm spherical fillers (R2). Color parameters (L*C*h*) were measured using a CIE XYZ camera along the centerline of the restorations, and the color difference (∆E₀₀) between corresponding areas of intact and restored teeth was calculated. Additionally, the reflectance spectra of OMN, R1, and R2 were investigated. OMN exhibited significantly lower ∆E₀₀ than other tested RCs (p<0.05) and its reflection spectrum ranged from blue to red, while a blue peak was observed with R1 and R2, indicating a higher color adjustment potential of OMN.

Influence of Bleaching and Aging Procedures on Color and Whiteness of Dental Composites

Bleaching can cause perceptible color changes on resin-based composite (RBC) restorations that may not be stable with aging. The objective of this study was to evaluate color stability and whiteness variations of RBCs after bleaching and aging procedures. Discs (10 mm in diameter and 1 mm thick) of shades A2 and A3 were fabricated from two RBCs (Filtek Z250 and Filtek Z350 XT) and divided into three subgroups (for each composite and shade) (n=5) as follows: control (no bleaching), at-home bleaching, and in-office bleaching. All specimens underwent an accelerated artificial aging up to 450 KJ/m2 and 900 KJ/m2 in an aging chamber (Suntest XXL+). A spectroradiometer (SpectraScan PR-670) was used to obtain CIE L*a*b* coordinates. CIEDE2000 color difference (ΔE00) and whiteness index for dentistry (WID) were used to evaluate color stability. Color and whiteness differences data were analyzed considering the 50:50% visual color difference thresholds (perceptibility [PT] and acceptability [AT]) and 50:50% whiteness thresholds (whiteness perceptibility [WPT] and whiteness acceptability [WAT]). Analysis of variance and Tukey tests (α=0.05) were used to statistically analyze the data. After bleaching, all specimens showed ΔE00 and ΔWID values below their corresponding acceptability thresholds (AT and WAT, respectively). After aging, L* and WID values decreased while b* values increased (p≤0.05), resulting in ΔE00 and ΔWID values above AT and WAT, respectively. Color changes after bleaching RBCs were clinically acceptable, while aging provoked clinically perceptible color changes.

Polydimethylsiloxane materials with supraphysiological elasticity enable differentiation of myogenic cells

Myogenic differentiation during muscle regeneration is guided by various physical and biochemical factors. Recently, substratum elasticity has gained attention as a physical signal that influences both cell differentiation and tissue regeneration. In this work, we investigated the influence of substratum elasticity on proliferation and differentiation of myogenic cells, mouse myoblasts of the C2C12 cell line and mouse primary myoblasts derived from satellite cells-muscle stem cells playing key role in muscle regeneration. Materials with different elastic moduli within the MPa scale based on polydimethylsiloxane (PDMS) were used as cell substratum and characterized for surface roughness, wettability, and micromechanical characteristics. We found that surface properties of PDMS substrates are alter nonlinearly with the increase of the material's elastic modulus. Using this system we provide an evidence that materials with elastic modulus higher than that of physiological skeletal muscle tissue do not perturb myogenic differentiation of both types of myoblasts; thus, can be used as biomaterials for muscle tissue engineering. PDMS materials with elasticity within the range of 2.5-4 MPa may transiently limit the proliferation of myoblasts, but not the efficiency of their differentiation. Direct correlation between substratum elasticity and myogenic differentiation efficiency was not observed but the other surface properties of the PDMS materials such as nanoroughness and wettability were also diverse.

Effect of protective coating on microhardness of a new glass ionomer cement: Nanofilled coating versus unfilled resin

Background and Objectives:

EQUIA^TM is a new gastrointestinal (GI) system with high compressive strength, surface microhardness (MH), and fluoride release potential. This in vitro study aimed to assess the effect of aging and type of protective coating on the MH of EQUIA^TM GI cement.

Materials and Methods:

A total of 30 disc-shaped specimens measuring 9 mm in diameter and 2 mm in thickness were fabricated of EQUIA^TM GI and divided into three groups of G-Coat nanofilled coating (a), no coating (b) and margin bond (c). The Vickers MH value of specimens was measured before (baseline) and at 3 and 6 months after water storage. Data were analyzed using repeated measures ANOVA.

Results:

Group B had significantly higher MH than the other two groups at baseline. Both G-Coat and margin bond increased the surface MH of GI at 3 and 6 months. The MH values of G-Coat and margin bond groups did not significantly increase or decrease between 3 and 6 months.

Conclusion:

The increase in MH was greater in the G-Coat compared to the margin bond group in the long-term. Clinically, margin bond may be a suitable alternative when G-Coat is not available.

The effect of three polishing systems on surface roughness of flowable, microhybrid, and packable resin composites

Objectives:

The aim of this study was to evaluate the effects of three different polishing systems on the surface roughness of three types of resin composite materials.

Materials and Methods:

Three types of resin composites (Heliomolar flow, TPH spectrum, and Tetric Ceram HB) and three polishing systems (Astropol, Enhance, and Soflex) were used. A total number of 40 samples were prepared from each one of the restorative materials and divided randomly into four groups (n = 10) according to the polishing procedure. The first group underwent no treatment and was used as a control group. Each one of the remaining groups was polished with one of the tested polishing systems. After completion of sample preparation, the mean surface roughness (Ra) value was measured using a surface profilometer. Data were analyzed using one-way analysis of variance (ANOVA).

Results:

The control group of each material recorded the lowest Ra value. Among the tested polishing systems, the groups finished with Soflex system exhibited the lowest Ra value. Among the resin composites, Heliomolar flow exhibited the lowest Ra value, regardless of the polishing system used.

Conclusions:

The smoothest surface of all types of resin composite was achieved under Mylar strip.

Color Stability and Surface Roughness of Composite submitted to Different Types and Periods of Finishing/Polishing: Physical Properties of Composites

AIM

The aim of this study was to evaluate the influence of accelerated artificial aging (AAA) on color stability (AE) and surface roughness of composite submitted to different systems and periods of finishing/polishing.

MATERIALS AND METHODS

A Teflon matrix was used to fabricate 60 specimens that were separated into four groups, according to the finishing/polishing system: G1: no polishing; G2: abrasive papers; G3: rubber polishing disks; and G4: G2 + G3. Polishing was performed at three different time intervals (n = 6): immediately (Im), 24 hours (24 hours) and 7 days (7 day) after specimen fabrication. Initial color and surface roughness readouts were taken. Afterwards, specimens were submitted to AAA (480 hours) and new readouts were taken.

RESULTS

Results demonstrated that G2 (7 day) presented lower AE, statistically different from G1 and G4 (7 days) (two-way analysis of variance (ANOVA), Bonferroni, p < 0.05).

CONCLUSION

Regarding roughness, there was no difference among groups and periods. Polishing performed with abrasive papers, 7 days after performing the restoration, promoted less color alteration.

CLINICAL SIGNIFICANCE

Most of composite restorations are replaced within a period shorter than 5 years due to esthetic failure, and correct finishing and polishing procedures are fundamental to avoid these problems.

Effect of 15% carbamide peroxide bleaching gel on color stability of giomer and microfilled composite resin: an in vitro comparison

Objectives: The effect of 15% carbamide peroxide bleaching gel on color stability and surface topography of a giomer and a microfilled composite resin was evaluated in the present in vitro study. Study design: Forty discs measuring 10 mm in diameter and 1 mm in thickness were prepared from a giomer and a microfilled composite resin. Each material yielded 20 discs with completely smooth surfaces. Then a spectrophotometer was used to measure L* (lightness), a* (redness, greenness) and b* (blueness, yellowness) color coordinates of all the discs. Subsequently, the specimens were subjected to 15% carbamide peroxide bleaching gel. After measuring the color coordinates once again, color changes (ΔE*) were calculated by the CIELAB system. Six specimens from each material (three specimens before bleaching agent application and three specimens thereafter) were viewed under an atomic force microscope (AFM) for surface topography evaluation. Data were analyzed by Mann-Whitney U and Kruskal-Wallis tests at α=0.05. Results: There were no statistically significant differences in color changes (ΔE*) between the two materials (P>0.05). In addition, no significant differences were detected in surface roughness between composite resin and giomer discs before and after bleaching (P>0.05 for both). However, in both materials the differences in surface roughness were significant before and after bleaching procedures (P<0.001). Conclusions: Based on the results of the present study it was concluded that 15% carbamide peroxide does not induce clinically detectable color changes in composite resin and giomer despite an increase in surface roughness.

Key words:Bleaching, color stability, giomer, microfilled composite.