Surface roughness and morphology of dental nanocomposites polished by four different procedures evaluated by a multifractal approach

Effect of aging and bleaching on the color stability and surface roughness of a recently introduced single-shade composite resin

OBJECTIVES

To assess the effects of aging and bleaching procedures on the color stability and surface roughness of a new single-shade composite versus multi-shade composite resins.

METHODS

A single-shade composite resin (Charisma Diamond One, CDO) and 3 multi-shade composite resins (Tetric NCeram, Filtek Z350 XT, Clearfil Majesty Posterior) were tested. Thirty specimens of each material were subjected to one of the aging procedures respectively: immersion in distilled water (12 days/37 °C), immersion in coffee (12 days/37 °C), or water thermocycling (10,000 cycles/5-55 °C). All specimens underwent in-office bleaching after aging. Kruskal-Wallis tests and analysis of variance were used for statistical analysis (α=0.05).

RESULTS

All materials exhibited a change of color (ΔE00), translucency (RTP), whiteness (WID) and surface roughness parameters (Sa,Sv) after aging and bleaching procedures. CDO showed the highest ΔE00 among all resins with the highest RTP value, regardless of the aging procedures. Immersion in coffee led to the significantly highest ∆E00 values and lowest RTP values for nearly all resins. Positive ΔWID1 (WID(bleaching)-WID(baseline)) values were found in distilled water immersion and thermocycling groups, while negative ΔWID1 values were found in the coffee immersion group for all materials. Besides, positive ΔWID2 (WID(bleaching)-WID(aging)) values were found in all aging groups for nearly all materials. All materials showed an increasing trend in Sa and Sv after bleaching.

CONCLUSIONS

CDO showed more pronounced discoloration than multi-shade composite resins. Although the whiteness of all resins increased after bleaching, none was completely restored in the coffee immersion group. Bleaching significantly increased the surface roughness of all materials.

CLINICAL SIGNIFICANCE

Charisma Diamond One is more susceptible to discoloration, which may affect its long-term success rate. Bleaching could partially reduce the color change of the composite resins but did not return them completely to their original state. The roughness of the resins increased after bleaching, prompting dentists to repolish them after bleaching.

Effects of in-office bleaching agents on polished and unpolished nanofilled resin composite

BACKGROUND

This study investigates the effects of in-office bleaching agents on the color change and surface roughness of nanofilled resin composite finished by various polishing procedures.

METHODS

The authors made 108 specimens from nanofilled resin composite, and the finishing and polishing procedures were performed with either Sof-Lex (3M ESPE) or OneGloss (Shofu). The specimens were then immersed in tea or coffee solution for 1 week, after which in-office bleaching agents were applied (n = 9). After polishing and bleaching, the surface roughness was measured with a surface profilometer. The specimen color parameters were measured with the Commission Internationale de l'Eclairage L∗a∗b∗ system in 3 stages, namely after polishing, after staining, and at the end of the bleaching procedure. The total color changes (ΔE_ab∗) were calculated, and ΔE_ab∗ not exceeding 2.7 was considered a clinically acceptable threshold.

RESULTS

The highest initial roughness value was observed on surfaces polished with OneGloss. In all groups, the surface roughness increased significantly after bleaching. For the Sof-Lex group specimens stained in both tea and coffee solutions, bleaching agent Opalescence Boost (Ultradent) reduced the color change value to 2.7 or less after bleaching.

CONCLUSIONS

In-office bleaching agents increased surface roughness in all groups, especially on unpolished surfaces. However, surface roughness was at an acceptable threshold for the multistep polished group, Sof-Lex, after bleaching. Nanofilled resin composite staining can be partially reduced by in-office bleaching agents but not completely removed.

PRACTICAL IMPLICATIONS

To reduce the increase in surface roughness of composite restorations due to bleaching, polishing should be applied before and after bleaching.

Mechanical and Tribological Characterization of a Bioactive Composite Resin

Despite developments and advances in dental materials which allow for greater restorative performance, there are still challenges and questions regarding the formulation of new compositions and chemical reactions of materials used in restorative dentistry. The aim of this study was to assess and compare the mechanical and tribological characteristics of a bioactive resin, a composite resin, and a glass ionomer. Twenty specimens of each material were divided into two groups: one control group (n = 10), not subjected to thermocycling, and one test group (n = 10) submitted to thermocycling. The Vickers microhardness test was carried out and surface roughness was evaluated. The tribological sliding indentation test was chosen. The bioactive resin had the lowest hardness, followed by the composite resin, and the glass ionomer. The bioactive resin also showed greater resistance to fracture. For the tribological test, the wear rate was lower for the bioactive resin, followed by the composite resin, and the glass ionomer. The bioactive resin presented a smooth surface without visible cracks, while the other materials presented a brittle peeling of great portions of material. Thus, the bioactive resin performs better in relation to fracture toughness, wear rate and impact absorption than the composite resin and much better than the glass ionomer.

Reduced-step composite polishing systems - a new gold standard?

OBJECTIVES

To compare the surface gloss and surface roughness of three contemporary composites when polished with reduced-step polishing systems or a conventional multiple-step technique.

METHODS

Fifty Discs (8 mm ø x 2 mm) were each fabricated from three composites; Essentia (ES), BRILLIANT EverGlow (EG), and Filtek Universal, (FU). 5 different polishing systems were randomly assigned 10 specimens from each composite group. The 'gold standard' multiple-step system consisted of Sof-Lex XT discs followed by DiaPolisher diamond paste (GC) (P1). The two-step systems were Polishettes (P2) and DIATECH ShapeGuard (P3) and the one-step systems used were; Opti1Step (P4) and OneGloss (P5). Surface gloss was measured using a glossmeter and surface roughness was measured by a profilometer. Statistical analysis was conducted using one-way ANOVA and Pearson correlation tests. Samples were also imaged across different length scales using scanning electron microscopy and macro-lens photography.

RESULTS

The highest gloss was obtained when P2 and P3 were used in all composite groups (p < 0.05). EG composite showed the lowest Sa (0.08 µm) when polished with P3 and highest gloss when polished with P2 (96.7 GU). Polishing with P5 resulted in highest Sa and lowest surface gloss in all composite groups (p < 0.05). A high correlation was found between Sa and gloss, r = 0.73 (p < 0.05). Both SEM and macro-lens photography supported quantitative data.

CONCLUSION

Both two-step composite polishing systems produced superior gloss compared to the traditional multiple-step polishing system. Mean surface roughness (Sa) and surface gloss are highly correlated with each other.

CLINICAL SIGNIFICANCE

Some reduced step composite polishing systems tested in this study produced superior gloss outcomes compared to the traditional gold-standard multi-step polishing system. This may enable significant clinical chair-time reduction and faster polishing protocols.

Characterization of spatial patterns of dental restorative nanocomposites

The aim of this study was to provide important insights into the effects of four different dental polishing protocols (one single-step and one multi-step either followed or not by diamond paste polishing) on the 3D surface morphology of two representative dental resin-based nanocomposites (a nanofilled and a nanohybrid composite) by means of digital image analysis and processing techniques. The 3D surface morphology was investigated by atomic force microscopy. Segmentation, statistics of height distributions (described by statistical parameters, according to ISO 25178-2: 2012) and Minkowski functionals were applied to the images to characterize the spatial patterns of analyzed samples at micrometer scale. The nanofilled composite had significantly lower values of height parameters in comparison with nanohybrid one. Multi-step polishing protocol generated a statistically significant smoother finish for both tested materials, than one-step polishing protocol, even when it was followed by diamond paste polishing. Diamond paste polishing generated a statistically significant smoother surface of tested samples. This suite of surface analysis tools is important in the research and manufacture of these dental resin-based nanocomposites, where material surfaces have a key role in the functionality of objects.

The effect of dental LED light-curing unit photoactivation mode on 3D surface morphology of dental nanocomposites evaluated by two-dimensional multifractal detrended fluctuation analysis

The objective of this study was to evaluate the effect of two photoactivation modes of dental LED light-curing unit (LCUs) (conventional and "Soft Start" mode) on surface texture parameters of two dental resin-based nanocomposites. LED LCUs were considered as standard light-curing devices in contemporary dental practice. Atomic force microscopy (AFM) was applied to investigate surface morphology on 90 × 90 μm² scanning area through 2D multifractal detrended fluctuation analysis with computational algorithms basis. In order to compare 3D surface roughness at nanometer scale, singularity spectrum f[α] was used which characterize local scale properties of multifractal nature of samples. The results confirmed that larger spectrum width Δα (Δα = α_max - α_min ) of f(α) is associated with non-uniform surface morphology. Moreover, materials whose polymerization was photoactivated by the "soft start" polymerization mode, showed better quality of the surface microstructure with lower values of AFM surface texture parameters.

Influence of the artificial saliva storage on 3-D surface texture characteristics of contemporary dental nanocomposites

The aim of this study was to analyse the influence of the artificial saliva on a three-dimensional (3-D) surface texture of contemporary dental composites. The representatives of four composites types were tested: nanofilled (Filtek Ultimate Body, FUB), nanohybrid (Filtek Z550, FZ550), microfilled (Gradia Direct, GD) and microhybrid (Filtek Z250, FZ250). The specimens were polymerised and polished by the multistep protocol (SuperSnap, Shofu). Their surface was examined, before and after 3 weeks' exposure to artificial saliva storage. The surface texture was analysed using the atomic force microscope (AFM). The obtained images were processed to calculate the areal autocorrelation function (AACF), anisotropy ratio S_tr (texture aspect ratio), and structure function (SF). The log-log plots of SF were used to calculate fractal properties, such as fractal dimension D, and pseudo-topothesy K. The analysis showed changes in surface anisotropy ratio S_tr values, which became higher, whereas the S_q roughness (root-mean-square) reduced after the artificial saliva storage. All the samples exhibited bifractal structure before the saliva treatment, but only half of them remained bifractal afterwards (GD, FZ250), whereas the other half turned into a monofractal (FUB, FZ550). The cube-count fractal dimension D_cc was found to be material- and treatment-insensitive.

Micromorphological characterization of zinc/silver particle composite coatings

The aim of this study was to evaluate the three-dimensional (3D) surface micromorphology of zinc/silver particles (Zn/AgPs) composite coatings with antibacterial activity prepared using an electrodeposition technique. These 3D nanostructures were investigated over square areas of 5 μm × 5 μm by atomic force microscopy (AFM), fractal, and wavelet analysis. The fractal analysis of 3D surface roughness revealed that (Zn/AgPs) composite coatings have fractal geometry. Triangulation method, based on the linear interpolation type, applied for AFM data was employed in order to characterise the surfaces topographically (in amplitude, spatial distribution and pattern of surface characteristics). The surface fractal dimension Df , as well as height values distribution have been determined for the 3D nanostructure surfaces.

Morphology of Co-Cr-Mo dental alloy surfaces polished by three different mechanical procedures

The present study aims at characterizing the three-dimensional (3-D) morphology of a Co-Cr-Mo dental alloy surface as a result of three different procedures used for polishing it. The sample surface morphology of the sampled surface was examined employing atomic force microscopy (AFM), statistical surface roughness parameters, and fractal analysis. An extra-hard dental alloy of cobalt-chromium-molybdenum (Co-Cr-Mo) (Wironit(®) , from BEGO, Bremen, Germany) was prepared and moulded. Different polishing treatments were carried out on three groups of six samples each--a total of 18 samples. The first group contained six electropolished (EP) samples. The second group containing six samples went through a mechanical polishing process employing green rubber discs and a high shine polishing paste applied by a rotating black brush (BB). The third group comprising six samples as well went through a mechanical polishing process by means of green rubber discs, high shine polishing paste, and a rotating deer leather brush (DL). Fractal analysis on the basis of a computational algorithm applied to the AFM data was employed for the 3-D quantitative characterization of the morphology of the sampled surfaces. The fractal dimension D (average ± standard deviation) of 3-D surfaces for BB samples (2.19 ± 0.07) is lower than that of the DL samples (2.24 ± 0.08), which is still lower than that of the EP samples (2.27 ± 0.09). The results indicated the BB samples as presenting the lowest values of statistical surface roughness parameters, thus the best surface finish, while the EP samples yielded the highest values.

Surface micromorphology of dental composites [CE-TZP]-[Al2O3] with Ca(+2) modifier

The objective of this study was to characterize the three-dimensional (3D) surface micromorphology of the ceramics produced from nanoparticles of alumina and tetragonal zirconia (t-ZrO2) with addition of Ca(+2) for sintering improvement. The 3D surface roughness of samples was studied by atomic force microscopy (AFM), fractal analysis of the 3D AFM-images, and statistical analysis of surface roughness parameters. Cube counting method, based on the linear interpolation type, applied for AFM data was used for fractal analysis. The morphology of non-modified ceramic sample was characterized by the rather big (1-2 μm) grains of α-Al2O3 phase with a habit close to hexagonal drowned in solid solution of t-ZrO2 with smooth surface. The pattern surfaces of modified composite content a little amount of elongated prismatic grains with composition close to the phase of СаСеAl3О7 as well as hexahedral α-Al2O3-grains. Fractal dimension, D, as well as height values distribution have been determined for the surfaces of the samples with and without modifying. It can be concluded that the smoothest surface is of the modified samples with Ca(+2) modifier but the most regular one is of the non-modified samples. A connection was observed between the surface morphology and the physical properties as assessed in previous works.