Effect of Finishing and Polishing on the Surface Roughness and Gloss of Feldspathic Ceramic for Chairside CAD/CAM Systems

Effect of repeated firing on the topographical, optical, and mechanical properties of fully crystallized lithium silicate-based ceramics

STATEMENT OF PROBLEM

The influence of different firing protocols on the topographical, optical, and mechanical properties of fully crystallized computer-aided design and computer-aided manufacturing (CAD-CAM) lithium silicate-based glass-ceramics (LSCs) for dental restorations remains unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of different firing regimens on the surface roughness, gloss, Martens hardness, indentation modulus, biaxial flexural strength, and crystalline structure of fully crystallized CAD-CAM LSCs and the effect of their interposition on the irradiance of a light-polymerization unit.

MATERIAL AND METHODS

Three fully crystallized CAD-CAM LSC blocks were evaluated (N=150): lithium disilicate (Initial LiSi Blocks; LS), zirconia-reinforced silicate (Celtra Duo; CD), and lithium aluminum disilicate (CEREC Tessera; CT). Specimens were allocated to 5 subgroups according to their firing protocol. LSC roughness (Sa) was measured with an optical profilometer, and gloss (GU) was detected with a gloss meter. Martens hardness (HM) and indentation modulus (EIT) data were obtained from a hardness testing machine. The irradiance of a light-polymerization unit and transmittance of LSCs were measured with an instrument (Managing Accurate Resin Curing-Light Collector; BlueLight analytics, Inc) subsequent to ceramic interposition. Crystalline phases were analyzed by X-ray diffraction, and biaxial flexural strength (σ) was determined by the ball-on-3-ball method in a universal testing machine followed by Weibull analysis to calculate characteristic strength (σ0) and Weibull modulus (m). Two-way ANOVA and Tukey HSD post hoc tests (α=.05) were used to analyze the data.

RESULTS

Statistically significant differences were found among different treatment groups based on Sa, GU, HM, and EIT values (P<.001). Delivered irradiance was significantly reduced following CT (P<.01) and glazed LSC (P<.005) interposition. CD displayed highest biaxial flexural strength and reliability after 1 firing cycle (σ=568.2 MPa, m=16.8) CONCLUSIONS: The type of material and firing regimens had a significant effect on the topographical, optical, and mechanical properties of fully crystallized CAD-CAM LSCs. Glazing significantly reduced delivered irradiance, Martens hardness, and biaxial flexural strength.

Staining and bleaching susceptibility of zirconia-reinforced lithium silicate glass-ceramics with different thicknesses, translucencies, and fabrication methods

STATEMENT OF PROBLEM

The influence of different thicknesses, translucencies, and fabrication methods on the spectrophotometric and topographical properties of zirconia-reinforced lithium silicate glass-ceramics (ZLSs) for dental restorations remains unclear.

PURPOSE

The purpose of this in vitro study was to investigate the effect of thicknesses, translucencies, and fabrication methods on the color stability, translucency parameter, opalescence parameter, whiteness stability, transmitted irradiance, light transmittance, opacity, gloss, and roughness of ZLSs exposed to coffee staining and bleaching treatments.

MATERIAL AND METHODS

Two pressable ZLSs (VITA AMBRIA, VA and Celtra Press, CP) and 2 machinable ZLSs (VITA Suprinity, VS and Celtra Duo, CD) were examined at high translucency (HT) and low translucency (LT) levels in 2 thicknesses (n=160). The specimens were evaluated at baseline, after coffee staining, and after bleaching. The color stability (ΔE2000), translucency parameter (TP), opalescence parameter (OP), whiteness index (WID), and whiteness stability (ΔWID) were measured with a spectrophotometer. Transmitted irradiance (It), light transmission (T), and opacity (O) were obtained from a light-polymerizing unit and a polymerization light collection device. Roughness stability (ΔSa%) was determined with an optical profilometer, and gloss stability (ΔGU%) was recorded with a gloss meter. Data of ΔCIE2000, ΔWID, ΔSa%, and ΔGU% were analyzed by 4-way ANOVA, and data of the TP, OP, WID, It, T, and O were analyzed by repeated 4-way ANOVA (α=.05).

RESULTS

VS-HT exceeded the ΔCIE2000 acceptability threshold after coffee staining and bleaching protocols. Pressable ZLSs exhibited greater color stability than machinable ZLSs. The 1-mm-thick VA, CP, and CD materials exceeded the ΔWID perceptibility threshold after bleaching. The highest TP and OP was displayed by the 1-mm-thick CP after bleaching. ΔGU increased after water storage and decreased after coffee staining and bleaching. ΔSa% significantly increased after bleaching (P<.05).

CONCLUSIONS

The color stability and other spectrophotometric properties of ZLSs depended on material thickness. The effects of ZLS fabrication methods and translucency levels on their measured properties were inconsistent. Subjecting 1-mm-thick ZLS materials to acidic media adversely impacted their stainability and surface texture.

The Surface Roughness of Contemporary Indirect CAD/CAM Restorative Materials That Are Glazed and Chair-Side-Finished/Polished

The surface roughness (Ra) of indirect computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated dental restorations is crucial for their long-term durability. This study intended to evaluate the Ra of five different types of contemporary indirect CAD/CAM restorative materials with varying compositions that were glazed and finished/polished. A total of 75 specimens, disc-shaped (10 mm × 2 mm), were obtained from five materials (n = 15) (Tetric CAD, IPS e.max CAD, IPS e.max ZirCAD, CELTRA Duo, and Vita Enamic) and fabricated by CAD/CAM. One of the two surfaces for each specimen was subjected to glazing, while the other surface was subjected to finishing/polishing. The Ra of the two surfaces in micrometers (μm) was evaluated using a Profilometer, while the surface topography was examined using a scanning electron microscope. Using SPSS, the Kruskal-Wallis, post hoc Conover, and Mann-Whitney tests were used to statistically evaluate the data. A comparison of the Ra for the finished/polished surfaces of the five test materials showed significant differences (p < 0.0001). Among the finished/polished surfaces, the mean rank values of Vita Enamic were significantly higher than the other four test materials (p < 0.0001). A comparison of the Ra of glazed surfaces among the five study materials revealed significant differences (p < 0.0001). The Ra for the IPS e.max ZirCAD material was significantly higher than the rest of the four materials (p < 0.001). A comparison of the Ra for two types of surface conditioning within each of the five test materials showed a significant difference (p < 0.05). Only for IPS e.max ZirCAD was the Ra of the glazed surface significantly higher than the finished/polished surface (p < 0.0001). Significant variations in the surface roughness (Ra) were exhibited between the finished/polished and glazed surfaces of the five test materials. Hybrid ceramics showed the highest Ra values for the finished/polished surfaces, and zirconia exhibited the highest Ra values among the glazed surfaces among the tested materials. The Ra values of either finished/polished or glazed surfaces of the test materials were within the clinically acceptable range (0.2-0.5 μm), except for the glazed surface of the zirconia ceramics (0.84 μm).

Finishing technique effect on strength of zirconia-reinforced lithium silicate ceramic

The aim of this study was to evaluate the effect of two finishing techniques, glazing or polishing, in comparison with the as-cut condition, on the biaxial-flexural-strength (BFS) of a zirconia-reinforced lithium silicate ceramic (ZLS). Cylinders were milled from CAD/CAM blocks and sliced to obtain disc-shaped specimens (ISO6872:2015). Polished and glazed specimens were processed following the manufacturer's instructions. Thirty-three specimens were obtained for each condition and microstructural and BFS/fractographic characterizations were performed. BFS and roughness data were analyzed using Weibull statistics and ANOVA one-way with Tukey post-hoc test, respectively. While a rougher surface was observed for as-cut specimens, smoother surfaces were observed for polished and glazed ZLS at microscopical evaluation and confirmed through surface-roughness evaluation. X-ray spectra depicted a glass phase for all groups and characteristic metasilicate, lithium disilicate, and lithium phosphate peaks for the as-cut and polished specimens. Glazed specimens showed higher characteristic strength than polished and as-cut specimens, which did not differ significantly. While higher Weibull-modulus was observed for the polished than for the as-cut specimens, no statistically significant differences were noted between glazed and polished, and between glazed and as-cut specimens. ZLS presents higher strength when glazed, and polishing increases the structural reliability of the material relative to the as-cut condition. Both finishing techniques reduced surface roughness similarly.

Ceramic surface conditioning, resin cement viscosity, and aging relationships affect the load-bearing capacity under fatigue of bonded glass-ceramics

This study aimed to evaluate the influence of ceramic surface treatments, resin cement viscosities, and storage regimens on the fatigue performance of bonded glass-ceramics (lithium disilicate, LD; feldspathic, FEL). Ceramic discs (Ø = 10 mm; thickness = 1.5 mm) were allocated into eight groups per ceramic (n = 15), considering three factors: "ceramic surface treatment" in two levels - 5% hydrofluoric acid etching and silane-based coupling agent application (HF), or self-etching ceramic primer (E&P); "resin cement viscosity" in two levels - in high or low viscosity; and "storage regimen" in two levels - baseline, 24 h to 5 days; or aging, 180 days + 25,000 thermal cycles. Adhesive luting was performed onto glass fiber-reinforced epoxy resin discs (Ø = 10 mm; thickness = 2 mm) and the bonded assemblies were subjected to cyclic fatigue tests: initial load = 200 N; step-size = 25 N (FEL) and 50 N (LD); 10,000 cycles/step; 20 Hz. Scanning electron microscopy (SEM) inspections were performed. Regarding the LD ceramic, the fatigue behavior was reduced after aging for HF_HIGH and E&P_LOW conditions, while stable performance was observed for HF_LOW and E&P_HIGH. Regarding the FEL results, aging negatively affected HF_HIGH, E&P_HIGH, and E&P_LOW, being that only the HF_LOW condition presented a stable behavior. The failure initiated from defects on the etched surface of the ceramics, where the cross-sectional analysis commonly revealed unfilled areas. Long-term aging might induce a decrease in mechanical behavior. The 'ceramic microstructure/surface conditioning/resin cement viscosity relationships' modulate the fatigue performance of lithium disilicate and feldspathic glass-ceramics.

Should finishing, polishing or glazing be performed after grinding YSZ ceramics? A systematic review and meta-analysis

The present systematic review and meta-analysis aimed to assess the characteristics and consequences of post-processing methods after grinding procedures in YSZ ceramics on its surface roughness and flexural strength. The protocol of this review was made prospectively and is available online in the PROSPERO database (link). Literature searches on PubMed/MEDLINE, EMBASE, Lilacs, Web of Science and Scopus were conducted on December 2022 to select in vitro studies written in English, without publishing-date restrictions, that considered surface characteristics and mechanical properties of YSZ ceramics submitted to grinding and subsequent post-processing surface treatments as an attempt to revert the effect induced by grinding. Two authors independently selected the studies, extracted the data and assessed the risk of bias. Mean differences (Rev-Man 5.1, random effects model, α= 0.05) were obtained by comparing flexural strength and surface roughness values of ground surfaces with at least one post-processing surface treatment (global analysis). Subgroup analyses were performed considering the most prevalent categories of post-processing methods. A total of 33 (out of 4032) studies were eligible and included in the analysis. In the global analysis, ground surfaces showed higher flexural strength than when post-processing methodologies were employed (p< 0.0001). The subgroup analysis showed that only polishing was able to enhance the flexural strength after grinding (p= 0.001); however, when other protocols were used, the ground surface was always superior in terms of flexural strength (p< 0.0001). Post-processing techniques in both the global and sub-group analyses were able to reduce the surface roughness after grinding in YSZ ceramics (p< 0.00001). High heterogeneity was found in all the meta-analyses. Concerning the risk of bias analysis, the included studies had mixed scores for the considered factors. In conclusion, in terms of improving flexural strength and restoring surface roughness after grinding, polishing protocols can be considered the best indication as post-processing treatment after YSZ ceramics adjustments/grinding.

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.

Analysis of surface characteristics of (Y, Nb)-TZP after finishing and polishing

PURPOSE

This in vitro study aimed to evaluate the surface characteristics of a full veneer crown fabricated chairside (CS) from a (Y, Nb)-TZP zirconia block in response to conventional zirconia grinding and polishing.

MATERIALS AND METHODS

Zirconia crowns (n = 40) were first prepared and divided into two groups of materials: Labside (LS) and CS, after which each specimen went through a five-step grinding and polishing procedure. Following each surface treatment, surface characteristics were analyzed using confocal laser microscopy (CLSM), average surface roughness (Ra) values were processed from the profile data through Gaussian filtering, and X-ray diffraction pattern analysis was performed to evaluate the monoclinic (M) phase content. Then, a representative specimen was selected for field-emission scanning electron microscopy (FE-SEM), followed by a final analysis of the roughness and X-ray diffraction of the specimens using the independent t-test and repeated measures analysis of variance (RM-ANOVA).

RESULTS

In every group, polishing significantly reduced the Ra values (P < .001). There was no significant difference in Ra between the polished state CS and LS. Furthermore, CLSM and FE-SEM investigations revealed that even though grain exposure was visible in CS specimens throughout the as-delivered and ground states, the exposure was reduced after polishing. Moreover, while no phase transformation was visible in the LS, phase transformation was visible in CS after every surface treatment, with the M phase content of the CS group showing a significant reduction after polishing (P < .001).

CONCLUSION

Within the limits of this study, clinically acceptable level of surface finishing of (Y, Nb)-TZP can be achieved after conventional zirconia polishing sequence.

3-D Surface Morphological Characterization of CAD/CAM Milled Dental Zirconia: An In Vitro Study of the Effect of Post-Fabrication Processes

Objective: To investigate the effect on zirconia surface of the post-fabrication surface treatments on the morphological characteristics and mechanical properties of CAD/CAM milled dental zirconia specimens as well as to identify the critical parameters in the measurement of oral retention under in vitro circumstances. Method: The zirconia specimens (N = 20, n = 4) were subjected to CAD/CAM milling and divided into five groups. The specifications were: Group G1—sintered; Group G2—sintered followed by a polishing process; Group G3—sintered followed by polishing and sandblasting with alumina particles Al2O3 (110 µm); Group G4—sintered followed by sandblasting; Group G5—sintered followed by sandblasting with polishing as the end process. All the groups were subjected to Fretting wear tests, 3-D surface roughness measurements, and Vickers’s Micro hardness tests. Investigation of the phase transformation using XRD, and surface feature examination using SEM were also carried out. Additionally, one-way ANOVA, Tukey, and Pearson correlations were statistically analysed. Results: The fabrication processes had a significant effect on the performance of zirconia specimens in all the groups (p > 0.05). Specimens that underwent polishing as the last process exhibited lower surface roughness. The monoclinic phase of zirconia was observed in all the specimens before and after wear except for those in the G2 and G5 groups, where polishing was the end process. In G5, the post-wear surface properties revealed lower surface roughness and hardness. Further, the SEM and 3-D topography show grooves as seen by the dale void volume (Vvv) values; shallow valley depth (Svk); micro craters; and wear track. Conclusion: Specimens in G5 that were subjected to multistep post-fabrication process, namely sandblasting followed by polishing, yielded better results when compared to those in the other groups (G1, G2, G3, and G4). G5 with an interlayer of alumina is recommended for clinical applications due to its enhanced surface properties, mechanical properties, and low wear.

Method for evaluating roughness and valley areas coefficients of surfaces acquired by laser scanner

The quantitative determination of average roughness parameters, from the determination of height variations of the surface points, is frequently used to estimate the adhesion between an adhesive and the surface of a substrate. However, to determine the interaction between an adhesive and a surface of a heterogeneous material, such as a red ceramic, it is essential to define other roughness parameters. This work proposes a method for determining the roughness of red ceramic blocks from a three-dimensional evaluation, with the objective of estimating the contact area that the ceramic substrate can provide for a cementitious matrix. The study determines the average surface roughness from multiple planes and proposes the adoption of 2 more roughness parameters, the valley area index and the average valley area. The results demonstrate that there are advantages in using the proposed multiple plane method for roughness computation and that the valley area parameters are efficient to estimate the extent of adhesion between the materials involved.

Influence different polishing systems on roughness and colour stability of chairside CAD/CAM blocks with laminate veneer thickness

OBJECTIVE

The aim of this study was to evaluate the effect of different polishing systems on the colour stability of different laminate veneer blocks for chair-side CAD-CAM after ultraviolet (UV) ageing.

METHODS

About 240 sample (13 × 13 × 0.7) were prepared from four different CAD-CAM blocks IPS e.max CAD (IP), IPS Empress CAD (IE), Mark II (M) and Lava Ultimate (LU)) with A1 shade. Each group was divided into five subgroups (n = 12) according to the control (C) and four different polishing system: Sof-Lex (S), Edenta (E), Identoflex (I) and Zircon Brite (Z). Surface roughnesses (Ra) were measured by a profilometer before and after polishing. The baseline colour values were recorded according to the CIELab system. The colour coordinates (L*, a* and b*) of the samples were measured before and after UV ageing, and colour differences (ΔE₀₀) were calculated by using the CIEDE2000 colour difference formula. A two-way ANOVA and Tukey test methods were used to analyse the data (α = 0.05).

RESULTS

A significant interaction was observed between CAD-CAM blocks and polishing system (p < 0.001). The higher Ra and colour difference was calculated in LU in the Z group after polished and the lower Ra and colour difference was calculated in the IP in the S group after polished. For the IP group, the glazing procedure showed higher Ra and ΔE values with Z group than polished S system, whereas there is no statistical differences.

CONCLUSION

It is concluded that polishing with the Sof-Lex system improves significantly smoothness and colour stability. However, there is no success in using the Zircon Brite polishing system.

The Effects of a coffee beverage and whitening systems on surface roughness and gloss of CAD/CAM lithium disilicate glass ceramics

OBJECTIVES

To investigate the effects of a coffee beverage and two whitening systems on the surface roughness and gloss of glazed Lithium Disilicate Glass-Ceramics (LDGC) for computer-aided design/computer-aided manufacturing (CAD/CAM) systems.

METHODS

Sixty-eight LDGC disks (12 × 10 × 2 mm) were prepared from blocks of CAD/CAM systems (IPS e.max CAD ceramic). Baseline measurements for surface roughness (Ra) and gloss (GU) were taken using a 3-D optical profilometer and a glossmeter, respectively; then specimens were randomized into four groups (n = 17). All specimens were immersed in a coffee solution (24 h × 12 days) then subjected to two whitening systems. G1-negative control (kept moist × 7 days); G2-positive control (brushed with distilled water, 200 g/load, 2 min twice daily × 7 days); G3-whitening toothpaste (Colgate optic white; relative dentin abrasivity (RDA) = 100, 200 g/load, 2 min twice daily × 7 days); and G4-simulated at-home bleaching protocol (Opalescence,15% carbamide peroxide (CP), 6 h/day × 7 days). The study outcomes were measured at baseline and after the treatments. Data were analyzed using paired T-test and one-way ANOVA (α = 0.05).

RESULTS

The mean surface roughness significantly increased (p ⩽ 0.002) for all groups after the designated treatment protocols. Among groups, the mean surface roughness of G2 and G3 were significantly higher (p ⩽ 0.001) (Ra: 0.51 and 0.57 μm, respectively) compared to the control group (Ra: 0.23 μm), and were not significantly different from G4 (Ra: 0.46 μm). Surface gloss decreased with no significant change within or among groups after treatment.

CONCLUSION

All glazed LDGC had a significant increase in surface roughness after being subjected to simulated 1 year of coffee drinking and whitening systems (15% CP and whitening toothpaste), and the greatest change was associated with brushing (simulating 8 months). However, coffee beverages and whitening systems had no significant effect on the surface gloss.

Comparative Study of the Effectiveness of Laboratory-Formulated Polishing Pastes for Two CAD/CAM Ceramic Restorative Materials

PURPOSE

To evaluate the effect of different polishing pastes with different particle sizes on the surface finish of two different CAD/CAM ceramics.

MATERIALS AND METHODS

A total of 128 specimens were prepared of two CAD/CAM ceramics: lithium disilicate (12.4 × 14.5 × 2 mm) and monolithic zirconia (17.5 × 12.5 × 2.5 mm). They were divided randomly into 8 groups according to surface treatment (n = 8). Group 1 (control) was left as received after crystallization or sintering with no further surface treatment; Group 2 (glazed); Group 3 (positive control), where specimens were polished using standardized surface treatment (medium grit silicon carbide discs, rubber cup and pumice slurry, then rubber cup and toothpaste). For groups 4 to 8, in addition to silicon carbide and pumice slurry polishing, specimens were further polished using a diamond paste (DP), and polishing pastes of microzirconia (MZ), nanosilica (NS), nanodiamond (ND), and nanozirconia (NZ), respectively. Surface roughness (R_a ) was measured using noncontact profilometer. The mean values were compared using ANOVA and Post Hoc Tukey's test (α = 0.05). Specimens' surfaces were studied using a scanning electron microscope (SEM).

RESULTS

Positive control group and MZ exhibited significant R_a of lithium disilicate compared to control (p ˂ 0.001), glazed (p = 0.001), DPs (p = 0.002), NS (p ˂ 0.001), ND (p ˂ 0.001), and NZ (p = 0.002). In the case of zirconia, positive control showed a significantly higher R_a compared to all other groups (p ˂ 0.001). No statistical difference was found between all other polishing techniques (positive control, glazed, DPs, NS, ND, MZ, and NZ) (p > 0.05).

CONCLUSION

Polishing with ND, NZ, and NS lab-formulated pastes produced surfaces with comparable smoothness to control and glazed specimens for lithium disilicate and zirconia ceramic materials.

Surface roughness and gloss of polished nanofilled and nanohybrid resin composites

Background/purpose

There is limited literature on the polishability of new launched nanofilled and nanohybrid. The aim of this study is to evaluate the polishability of nanofilled and nanohybrid composites by measuring surface roughness and gloss values and explore the surface qualities of composite before and after polishing in vitro.

Materials and methods

One nanofilled resin composite, two nanohybrid resin composites and one microhybrid resin composite were selected. All specimens were light cured against celluloid matrix strips. Then surface roughness(Ra) and gloss(GU) values were tested as negative control. Specimens were roughened with a 600-grit silicon carbide paper for 30 s to serve as positive control and then polished with Sof-Lex polishing disk system. Mean Ra and GU values of each step were measured with a profilometer and a small-area glossmeter. The surface qualities were observed by scanning electron microscope.

Results

Ra values of polished surfaces were significantly higher than negative control and lower than positive control(P < 0.05). All materials showed no significant difference on Ra values after polishing(P > 0.05). GU values of polished surfaces were significantly lower than negative control and higher than positive control(P < 0.05). After polishing the microhybrid resin composite showed lower GU values than nanofilled and nanohybrid resin composite groups. The SEM images showed surface textures and irregularities were corresponded to the results of surface roughness and gloss.

Conclusion

No significant differences were noted on surface roughness among nanofilled, nanohybrid, and microhybrid composites after polishing with Sof-Lex disc system. Microhybrid composite presented lower gloss values than nanofilled and nanohybrid resin composites.

Characterization of Reinforced and Unreinforced Glass-Ceramic Veneers

This study aimed to characterize the surface topography, effect of polishing on surface roughness, residual stresses, and hardness in two glass-ceramic veneers. Fifty-two (52) upper incisors were collected, prepared, and scanned for ceramic veneers. Half of the teeth were restored with veneers made up of feldspathic ceramic (FE), and the other half with zirconia-reinforced lithium silicate ceramic (SZ). All the veneers were designed and milled using a CAD/CAM system and later cemented following the manufacturer's guideline. An optical microscope analyzed the topography of the specimens before and after polishing. The surface roughness was measured using the roughness meter (n=12) and the topographical analysis was carried out using an atomic force microscope (n=6). The residual stresses and Vickers' hardness were evaluated by the indentation method in a micro-hardness indenter (n=6). The surface roughness was analyzed using a three-way analysis of variance (ANOVA) followed by a post hoc Tukey test. The Student t-test was used to compare the residual stresses and hardness between the two ceramics. The topographical analysis revealed that both glass-ceramic veneers had similar percentages of specimens with cracks, before (34.6%) and after (42.3%) polishing. The surface roughness decreased after polishing (p<0.001), and the polishing smoothed out the surface of the veneers. The zirconia-reinforced lithium silicate veneer had a lower roughness as compared to the feldspathic one after polishing, while the residual stresses (p=0.722) and hardness (p=0.782) were statistically similar for both ceramic veneers.

A comparative study on the effect of polishing systems on the color and surface texture of different porcelain systems - feldspathic, pressable, and computer-aided design/computer-aided manufacturing

Aim:

To find and compare the qualitative and quantitative change in color and surface texture of feldspathic ceramic, pressable ceramic and ceramic used in computer-aided design/computer-aided manufacturing CAD/CAM after different surface treatments namely glazing, abrading and polishing. To compare the effectiveness of pearl finish polishing paste and Soflex polishing system used in the study.

Setting and Design:

In-vitro, comparative study.

Materials and Methods:

Disc-shaped feldsapathic, pressable, CAD/CAM ceramic specimens were fabricated. Surface roughness and color parameters Δ L*, Δa*, and Δ b* were measured before glazing, after glazing, after abrasion with 02 diamond bur and after polishing with two different polishing systems. Surface roughness was measured qualitatively using scanning electron microscopy and quantitatively using an optical profilometer. The value of color parameters was obtained using a colorimeter. Data were statistically analyzed with ANOVA.

Statistical Analysis Used:

SPSS software 20.0 version (IBM, New York, United states of America).

Results:

Unglazed feldspathic, pressable and CAD/CAM porcelain specimens showed a mean surface roughness value of 2.73 ± 0.38, 3.54 ± 1.42, and 3 ± 1.74 specimens. After glazing and polishing, the surface roughness values decreased. After abrasion, surface roughness values increased. Polishing did not alter the color along the red green axis and yellow blue axis.

Conclusions:

Abraded specimens of feldspathic, pressable and CAD/CAM after polishing using pearl finish polishing paste and Soflex disc became smoother than glazed specimens. When pearl finish polishing paste and Soflex discs were compared for their effectiveness the former appeared to be more superior but not to a significant level. Mechanically altering feldspathic, pressable, and porcelain used in CAD/CAM technology does not cause any change in shade.

Effect of Staining and Aging on Translucency Parameter of CAD-CAM Materials

Objectives

To evaluate different intervals of exposure to staining solutions and artificial aging on translucency parameter (TP₀₀) of CAD-CAM materials.

Material and Methods

One millimeter thick square-shaped specimens (N = 288) were cut from Cerasmart (CS), IPS e.max (IE), Lava Ultimate (LU), Shofu HC (SH), Vita Enamic (VE), and Vita Suprinity (VS) and were divided into laboratory and chairside polishing. Reflection wavelength spectra, CIE D65 standard illuminant, 2 ° standard observer, SCI, UV included, SAV aperture, 6 mm diameter, were recorded at 10 nm sensitivity against white and black calibration tiles using a benchtop spectrophotometer. Subsequently, they were converted into CIEDE 2000 TP₀₀. After baseline measurements (T0), the specimens were divided as follows (n = 8): staining in coffee (C) and wine (W), for 60 (T1) and 120 hours (T2), and accelerated artificial aging (A). Artificial aging (ISO 4892-2 standard) was performed in two cycles of 150 KJ/m², for T1 and T2, respectively. TP measurements were repeated at T1 and T2. Data of TP₀₀ retention were submitted to analysis of variance and Fisher’s PLSD multiple comparison test (α=0.05).

Results

Fisher’s PLSD critical differences among materials, time intervals and staining/aging were 0.16, 0.11 and 0.11, respectively. SH showed the highest TP₀₀ followed by LU > CS > IE = VS > VE. For all time intervals, the lowest TP₀₀ retention was observed with C. W, and A presented similar values.

Conclusions

Translucency Parameter was a time and staining/aging-dependent material. In majority of cases, it decreased upon staining/aging.

Effect of Finishing Systems on Surface Roughness and Gloss of Full-Body Bulk-Fill Resin Composites

Background: In this study, we assess the effect produced on roughness and gloss of full-body bulk-fill materials by different finishing and polishing systems. Methods: Four full-body bulk-fill materials were tested: SonicFill2 (SF), Filtek Bulk Fill Posterior Restorative (FB), Tetric EvoCeram bulk-fill (EC), and Fill-Up! (FU). Sixty discs per material (2 mm in thickness and 7 mm in diameter) were obtained and randomly assigned (n = 15) to four finishing and polishing methods: Sof-Lex Spiral Wheels (SW), HiLusterPLUS (HL), Astropol (AP), and Opti1Step (OS). Surface roughness and gloss were then measured. Results: For roughness, material and surface treatment were significant factors (p < 0.001) with SF = FB = EC < FU and AP < SW < HL = OS. Material and surface treatment had a significant effect also on gloss (p < 0.001), with SF > FB = EC > FU and SW > AP > HL > OS. Conclusions: The tested combinations of bulk-fill and polishing systems provided clinically acceptable results with regard to roughness, while the outcome was poor for gloss. Multistep finishing/polishing systems were able to produce smoother surfaces on full-body bulk-fill materials compared to simplified ones.

Staining and aging-dependent changes in color of CAD-CAM materials

STATEMENT OF PROBLEM

Consumption of some beverages and aging may affect the color of dental materials used in fixed prosthodontics, but their effect on recently introduced materials is not well known.

PURPOSE

The purpose of this in vitro study was to evaluate staining, aging, and the exposure interval on color changes of computer-aided design and computer-aided manufacturing (CAD-CAM) resin nanoceramics (RNC), polymer-infiltrated ceramic-network (PICN) materials, and lithium silicate and lithium disilicate ceramics.

MATERIAL AND METHODS

A total of 288 square-shaped, 1-mm-thick specimens prepared from Cerasmart, IPS e.max, Lava Ultimate, Shofu HC, Vita Enamic, and Vita Suprinity were polished by using laboratory and chairside methods in accordance with the manufacturers' instructions. Color data were recorded with a benchtop spectrophotometer, and CIEDE2000 color differences (ΔE₀₀) were calculated. After the baseline measurements (T0), the specimens were divided into 3 groups (n=8) and exposed to staining in coffee and wine and to accelerated artificial aging. The specimens were stored in staining solutions at 37 °C for 60 (T1) and 120 hours (T2). Accelerated aging was performed by using a xenon lamp weathering test chamber for a total exposure of 150 (T1) and 300 kJ/m² (T2). The results were analyzed by using the t test, ANOVA, and the Tukey honestly significant difference test (α=.05). Color differences of ΔE₀₀ ≤0.8 and ≤1.8 corresponding to the 50:50% perceptibility threshold and 50:50% acceptability threshold were used to interpret the results.

RESULTS

As color differences (ΔE₀₀) between laboratory and chairside polishing were not statistically significant (T=-0.81, P=.418), only the results for chairside polished specimens were presented. Color differences for the T0-T1 comparisons ranged from 0.2 to 4.2, T0-T2 from 0.3 to 6.5, and T1-T2 from 0.1 to 2.3. ANOVA showed significance of factors and for interactions (P<.05). Lithium silicate-based and lithium disilicate-based ceramic materials were more color stable than RCN and PICN materials on exposure to coffee and red wine. Color changes greater than acceptability threshold after immersion in coffee were recorded for 3 (T0-T1), 4 (T0-T2), and 2 (T1-T2) materials. Corresponding findings after immersion in wine were 1, 3, and 0 and after artificial aging 0, 2, and 0. ΔE₀₀ and ΔE_ab values were highly correlated (R²=0.97).

CONCLUSIONS

No difference was found in color stability among laboratory and chairside polished specimens. Coffee caused the greatest color changes for T0-T2 interval. Staining-dependent color differences increased with increased exposure, except for IPS e.max and Vita Suprinity. For artificial aging, color change appeared to be material dependent.

Influence of polishing systems on roughness and color change of two dental ceramics

PURPOSE

To evaluate the polishing effect on roughness and color change of pressed and layering ceramics after immersion in coffee solution.

MATERIALS AND METHODS

88 ceramic discs (1.0 mm × 10.0 mm) were manufactured - 44 nano-fluorapatite layering ceramics (IPS e.max Ceram. Group C) and 44 pressed lithium disilicate ceramic discs (IPS e. max Press - Group P). Each group was divided into 4 subgroups according to surface treatments: (G) Glaze, (S) Shofu polishing system (Shofu Inc.), (E) Edenta AG polishing System, (KG) 30-µm diamond granulation tip. Surface roughness (Ra) and color change (ΔE) measurings after the surface treatments were performed, before and 12 days after the immersion in coffee solution. A samples' qualitative analysis was conducted with a scanning electron microscopy (SEM). Data were statistically-treated with one-way-ANOVA and Duncan's tests, apart from paired t-test and Pearson's correlation test (α=5%).

RESULTS

The decrescent order, both for surface roughness (Ra) and ΔE for both ceramics were: KG > E > S > G (P<.05). With exception for PG and CG subgroups, which did not present statistical difference between them, all other pressed ceramics subgroups presented smaller Ra values and greater ΔE values than the layering ceramics subgroups (P<.05).

CONCLUSION

Although mechanical polishing systems presented intermediate Ra values, their colors were considered clinically acceptable. There is a strong correlation between the surface roughness and the color change of tested ceramics.

Low-fusing porcelain glaze application does not damage the fatigue strength of Y-TZP

This study evaluated and compared the effects of two glaze application methods (brush and spray) on the fatigue strength and surface characteristics (topography and roughness) of a translucent yttrium stabilized partially tetragonal zirconia polycrystal ceramic (Y-TZP) prior to and after grinding. Disc-shaped specimens of translucent Y-TZP (Vita YZ-HT; Vita-Zahnfabrik) were processed (ISO 6872-2015) and randomly allocated into 6 groups, according to the surface treatments performed on the tensile surface: Ctrl - as-sintered (no treatment); Gr - grinding with a diamond bur (181 μm-grit; #3101G); Br - glaze obtained from a powder-liquid mix and applied by brush (Vita Akzent; Vita Zahnfabrik); Sp - glaze application via spray (Vita Akzent Plus; Vita Zahnfabrik); Gr + Br and Gr + Sp - association of grinding + respective glaze method. Analyses of surface roughness (Ra and Rz), fatigue strength (staircase method), surface topography and fractography were carried out. The as-sintered condition had the smoothest surface, while grinding led to the rougher and more heterogeneous topography. Both glaze application methods showed a potential for topography evenness (smoothening effect), while the glaze spray method led to thinner layers of material, showing a limitation in reducing the roughness compared to the brush method. No deleterious effect on fatigue strength of the Y-TZP could be observed, as the glaze-spray application on the as-sintered surface showed the highest values. Fractography depicted two distinct fracture origin regions: from defects in the surface/sub-surface region for the Ctrl and Gr groups; and at the zirconia-glaze layer interface for Br, Sp, Gr + Br and Gr + Sp. The clinical relevance of this work is that the tested glaze application methods did not damage the fatigue strength of the tested Y-TZP.

Effects of Manufacturing and Finishing Techniques of Feldspathic Ceramics on Surface Topography, Biofilm Formation, and Cell Viability for Human Gingival Fibroblasts

Purpose:

Feldspathic ceramic restorations can be obtained by different techniques (stratification or computer-aided design/computer-aided manufacturing [CAD/CAM] blocks) and finishing procedures (polishing or glaze application). This study evaluated the effects of techniques and finishing procedures on surface properties, biofilm formation, and viability of human gingival fibroblasts (FMM-1) in contact with these materials.

Methods and Materials:

Ceramic specimens were obtained through a stratification technique (Vita VM9) and from CAD/CAM blocks (Vita Blocs Mark II; both Vita Zahnfabrik) and their surfaces were finished by polishing (ceramisté diamond rubbers + polishing paste; “p” subgroups) or glaze spray application + sintering (“g” subgroups). Roughness (Ra and RSm parameters) and surface free energy (SFE) were measured. Early biofilm formation of Streptococcus mutans, Streptococcus sanguinis, and Candida albicans was evaluated by counting colony-forming units (CFU). MTT (3-[4.5-dimethyl-thiazol-2-yl-]-2.5-diphenyl tetrazolium bromide) cytotoxicity test evaluated cellular viability for the growth of FMM-1 after 24 hours and seven days of contact. Scanning electron microscopy (SEM) and three-dimensional optical profilometry were performed to qualitatively analyze the surface. Data were analyzed by analysis of variance, Tukey test, and t-test (all α=0.05).

Results:

Polished samples presented lower roughness (Ra, p=0.015; RSm, p=0.049) and higher SFE (p=0.00). Streptococci had higher CFU in all groups, but the CFU of C albicans was lower for polished samples. Biofilm formation was influenced by the interaction of all factors (p=0.018), and the materials showed no cytotoxicity to FMM-1 growth.

Conclusions:

Polishing resulted in the lowest values for surface roughness and higher SFE values. Polished ceramics showed less C albicans adherence while the adherence of Streptococci was greater than C albicans in all conditions.