High-translucency Monolithic Zirconia Research Articles

Effect of Zirconia Thickness, Cement Color, and Titanium Implant Abutment Surface Treatment Type on the Esthetic Outcomes of High Translucency Monolithic Zirconia.

To investigate the esthetic outcomes based on the color differences in zirconia of varying thickness, resin cement color, and types of titanium implant surface treatments. Twenty-eight HTMZ specimens were arranged into four groups based on zirconia thickness: 1.0, 1.5, 2.0, and 2.5 mm (n=7). Each group was tested using two resin cement colors (n=7) (clear and opaque) in combination with six surface-treated titanium groups (n=7): untreated titanium (UT), anodization (AN), 50-μm alumina airborne-particle abrasion followed by AN (SBAN), AN followed by 50-μm alumina airborne-particle abrasion (ANSB), 95% hydrofluoric acid followed by AN (HFAN), and AN followed by 95% hydrofluoric acid (ANHF) for the 48 experimental groups, and using composite resin (n=7) (A2D) for the four control groups. All the specimens were measured using a spectrophotometer and subsequently compared with composite resin (control) with the corresponding zirconia thickness to establish the color differences. A color difference of <2.7 was considered clinically acceptable. The data obtained were statistically analyzed using the analysis of variance and post hoc test (p=0.05). Zirconia thickness, resin cement color, and type of titanium implant surface treatment significantly affected the observed color differences (p<0.05). When using 2.5-mm HTMZ with clear resin cement on AN, UT, SBAN, HFAN, and ANSB, the mean color differences obtained were below the clinically acceptable values. However, when using 2.5-mm HTMZ with clear resin cement on AN, UT, and SBAN, the 95% confidence intervals of color differences obtained were below the clinically acceptable values. HTMZ with a minimum thickness of 2.5 mm and clear resin cement on AN, UT, and SBAN groups potentially result in acceptable color matching with 95% confidence intervals.

How could mouthwashes affect the color stability and translucency of various types of monolithic zirconia? An in-vitro study.

This study aimed to evaluate the color stability and translucency of various types of monolithic zirconia after immersion in chlorhexidine and Listerine mouthwashes. This experimental study was performed on 36 disk-shaped specimens fabricated from low-translucent, high-translucent, and multilayered monolithic zirconia (n = 12 per group). Each group was equally divided and immersed in either 2% chlorhexidine (CHX) or Listerine mouthwash for 2 min daily over 7 days. Changes in color (ΔE) and the translucency parameter (ΔTP) were evaluated and compared. The data were analyzed with one-way ANOVA followed by Tukey's post-hoc tests (α = 0.05). Chlorhexidine caused a significantly lower ΔE and a significantly higher ΔTP in multilayered zirconia compared to the low-translucency (ΔE: P = 0.0027, ΔTP: P<0.001) and the high-translucency zirconia group (ΔE: P<0.001, ΔTP: P = 0.022). Listerine caused a significantly higher ΔE in the high-translucency zirconia group compared to the multilayered zirconia group (P = 0.0165). It also resulted in a significantly higher mean ΔTP in the multilayered zirconia group compared to the low-translucency (P = 0.0003) and high-translucency zirconia groups (P = 0.019). In both mouthwashes, multilayered monolithic zirconia exhibited the highest color stability among the tested materials; albeit with the most pronounced changes in translucency. Meanwhile, high-translucency monolithic zirconia was more prone to discoloration when exposed to both mouthwashes.

Fit of High-Translucency Zirconia Fixed Dental Prostheses Using Two Different Intraoral Scanners.

To assess the marginal and internal fit of monolithic zirconia fixed dental prostheses (FDPs) comparing two different intraoral scanners (IOSs) and assessment methods. A maxillary typodont with three prepared teeth allowed fabrication of five-unit high-translucency monolithic zirconia FDPs. The typodont was scanned with two IOSs: Cerec Omnicam and 3Shape TRIOS 3. In total, 30 FDPs were milled from presintered high-translucency zirconia blocks. Dual-scan and silicone replica assessments were used to determine marginal and internal gaps. A statistical significance was observed for marginal gaps (3Shape [74.27 ± 10.4 μm] and Cerec [86.45 ± 14.3 μm]) and for internal gaps (3Shape [126.12 ± 12.7 μm] and Cerec [112.38 ± 17.2 μm]). The outcomes of this study showed that the 3Shape TRIOS 3 produced a better overall marginal fit, while the Cerec Omnicam created a better internal fit. Additionally, a greater overall marginal and internal gap was noted with the silicone replica method over the dual-scan method.

Is Ammonium Hydrogen Difluoride a Solution for Zirconia Surface Conditioning?

This research investigated the topographical features and phase transformation of high-translucent monolithic zirconia after different surface conditioning methods. Zirconia slabs were divided into six groups according to surface treatment method. Group I: etched with hydrofluoric acid (HF); Group II: etched with an experimental acid solution (EAS); Group III: melt-etched with ammonium hydrogen difluoride (AHD); Group IV: air abrasion (AB); Group V: etched with EAS after air abrasion (AB+EAS); Group VI: melt-etched with AHD after air abrasion (AB+AHD). Surface topographies of specimens were documented by scanning electron microscopy (SEM). Tetragonal-to-monoclinic phase transformation was detected by X-ray diffraction and surface evaluation of zirconia specimens; surface roughness and contact angle measurements were performed. The data were statistically analyzed by the Kruskal- Wallis test and post hoc tests (P⟨0.05). The acid-etched zirconia groups (Group I, II, and III) showed the lowest contact angle and surface roughness values (P⟨0.05), while the air abrasion groups (Group IV, V, VI) showed the highest. The SEM images also supported these results. Within the limitations of this in vitro study, treating the monolithic zirconia surfaces with EAS or AHD after air abrasion may be recommended to alter the zirconia surfaces.

An Evaluation of the Colour Stability and Surface Roughness of High Translucency Zirconia Dental Ceramic after Immersion in Different Acidic Media: An In-vitro Study

Introduction: Demand for increasingly appealing metal-free ceramic restorations drives research. With its exceptional mechanical and biological properties, zirconia crown outperforms other traditional ceramic materials. With outstanding mechanical and biological qualities, zirconia has several therapeutic applications. Temperature, environment, diet, and smoking habits all affect colour and surface roughness of dental restorations. Aim: To investigate the colour stability and surface roughness of high translucency monolithic zirconia following immersion in various acidic solutions. Materials and Methods: This in-vitro study was conducted at Yenepoya Dental College, Mangalore, Karnataka, India. Duration of the study was 6 months, from December 2019 to June 2020. Thirty rectangular samples from a CAD (computer-aided Design)/ Computer Aided Manufacturing (CAM) machined Zirconia blank with 10x8x1 mm dimensions was sintered at 1350°C, tested for colour stability (E) and surface roughness prior to immersion (R). Classified into Groups CO (coffee), TO (tobacco) and CA (citric acid medium). Colour stability and surface roughness were re-evaluated post immersion on all samples using spectrophotometers and profilometer respectively. A significant difference in surface roughness and colour stability between the test groups was assessed using the paired-t test. The data was analysed using Statistical Package for Social Sciences (SPSS) version 24.0. Results: Colour stability and surface roughness variations between the baseline value and three groups were found to be unaltered by different acidic media. The intergroup comparison of spectrophotometric analysis between the three groups had a standard deviation of 0.422 for citric acid medium, 0.316 for Coffee medium and 0.422 for Tobacco medium with an overall p-value of 0.804. The intergroup comparison of profilometric analysis had a standard deviation of 0.316 for Citric acid medium, 0.00 for Coffee medium and 0.00 for Tobacco medium with an overall p-value of 0.381. The paired-t-test study showed that immersion in different acidic media had little effect on surface roughness of samples with a p-value of 0.343 but it was under clinically acceptable range. Conclusion: According to the present study, high translucency monolithic zirconia had greater colour stability when treated with citric acid, followed by tobacco and then with coffee media, whereas, zirconia in coffee media had greater surface roughness, followed by tobacco, and then with citric acid media. However, both the results were clinically acceptable, indicating a 10 year lifespan when properly glazed.

Effect of surface treatment and surface region on the color stainability of a cemented high-translucency monolithic zirconia ceramic after coffee thermocycling

Statement of problemRestorations should show low color stainability after clinical and laboratory procedures; however, the impacts of surface treatment and surface region on the color stainability of zirconia restorations are unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of surface treatment and surface region on the color stainability of a cemented high-translucency monolithic zirconia ceramic after coffee thermocycling. Material and methodsThirty high-translucency Ø10×0.5-mm monolithic zirconia disk specimens were divided into 3 groups based on the surface treatment applied: adjusting (A), polishing (P), and glazing (G). Specimens were cemented to composite resin backings and given 10 000 thermocycles in a coffee solution. CIELab values were measured with a spectrophotometer before and after thermocycling in central and marginal surface regions. ΔE00 values were calculated and compared with perceptibility (ΔE00=0.8) and acceptability (ΔE00=1.8) thresholds to interpret the color changes due to coffee thermocycling. Repeated measures ANOVA and Bonferroni tests were used for data analysis (α=.05). ResultsMean ΔE00 values ranged between 0.72 and 1.26. The surface treatment significantly affected the ΔE00 (P=.005); however, the surface region (P=.499) and the interaction of surface treatment and surface region (P=.998) did not affect the ΔE00. The mean ΔE00 values were less than 0.8 for group G, but greater than 0.8 and less than 1.8 for groups A and P. ConclusionsGlazing provides the lowest color stainability for cemented high-translucency monolithic zirconia, inducing imperceptible color changes after coffee thermocycling.

Biaxial Flexural Strength of Different Monolithic Zirconia upon Post-Sintering Processes.

Objective Different post-sintering processes are expected to be a reason for alteration in the strength of zirconia. This study evaluated the effect of post-sintering processes on the flexural strength of different types of monolithic zirconia. Materials and Methods A total of 120 classical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness and 14 mm in Ø) were prepared, sintered, and randomly divided into four groups to be surface-treated with (1) as-glazed (AG); (2) finished and polished (FP); (3) finished, polished, and overglazed (FPOG); and (4) finished, polished, and heat-treated (FPHT) technique ( n = 15). Biaxial flexural strength (σ) was determined on a piston-on-three ball in a universal testing machine at a speed of 0.5 mm/min. Statistical Analysis Analysis of variance, and post hoc Bonferroni multiple comparisons were determined for significant differences ( α = 0.05 ). Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic strength (σ 0 ). The microstructures were examined with a scanning electron microscope and X-ray diffraction. Results The mean ± standard deviation value of σ (MPa), m, and σ 0 were 1,626.43 ± 184.38, 9.51, and 1,709.79 for CzAG; 1,734.98 ± 136.15, 12.83, and 1,799.17 for CzFP; 1,636.92 ± 130.11, 14.66, and 1,697.63 for CzFPOG; and 1,590.78 ± 161.74, 10.13, and 1,663.82 for CzFPHT; 643.30 ± 118.59, 5.59, and 695.55 for HzAG; 671.52 ± 96.77, 3.28, and 782.61 for HzFP; 556.33 ± 122.85, 4.76, and 607.01 for HzFPOG; and 598.36 ± 57.96, 11.22, and 624.89 for HzFPHT. The σ was significantly affected by the post-sintering process and type of zirconia ( p < 0.05), but not by their interactions ( p > 0.05). The Cz indicated a significantly higher σ than Hz. The FP process significantly enhanced σ more than other treatment procedures. Conclusion Post-sintering processes enabled an alteration in σ of zirconia. FP enhanced σ, while FPOG and FPHT resulted in a reduction of σ. Glazing tends to induce defects at the glazing interface, while heat treatment induces a phase change to tetragonal, both resulted in reducing σ. Finishing and polishing for both Cz and Hz monolithic zirconia is recommended, while overglazed or heat-treated is not suggested.

Dynamic wear characteristics and fracture strength of high-translucent monolithic zirconia crowns

The dental ceramic restorations inevitably undergo a wear damage. The dynamic wear behavior and fracture strength after wear fatigue of the high-translucent zirconia crowns have rarely been studied. In the present study, the zirconia crowns were fabricated using a high-translucent zirconia material and subsequently cemented to the PMMA abutments with a resin cement. The specimens were fixed in a chewing simulator and dynamically loaded for 3.6 million fatigue cycles (a maximal load of 350 N, 1.7 Hz). The wear volume and wear rate at the designated checkpoints between 0–36 × 105 cycles with an interval of 3 × 105 cycles were measured. The fracture strength of the zirconia specimens before wear fatigue as well as after 9, 24 and 36 × 105 cycles was analyzed. The morphology of the wear surface was observed by SEM. The results showed that the wear volume increased with the wear cycles. In the initial stage (0–9 × 105 cycles), the wear rate remained at a significantly high level (about 0.289–0.349 mm3/105 cycles). Subsequently, it decreased rapidly and stabilized at a relatively low level (about 0.052–0.081 mm3/105 cycles). As the number of fatigue cycles was increased, the fractured strength decreased significantly, except after 9 × 105cycles. The worn surface after wear were flattened, and only a small number of scattered cracks and small punctate defects were observed. The high-translucent zirconia crowns exhibited dynamic wear characteristics, and the fracture strength decreased significantly.

Fracture Resistance of Monolithic High-Translucency Crowns Versus Porcelain-Veneered Zirconia Crowns After Artificial Aging: An In Vitro Study.

PurposeTo evaluate the fracture resistance and fracture mode of high-translucency monolithic zirconia (HTZ) crowns and porcelain-veneered zirconia (PVZ) crowns.Material and methodsA master die was scanned to design and fabricate the HTZ group (n = 10) and PVZ group (n = 10). Both groups were artificially aged before loaded to fracture. The means of fracture loads of the two groups were compared using an independent t-test at a significance level of 0.05. The mode of fracture was determined using a digital magnifier.ResultsThe mean fracture strength for the HTZ group (4,425 ± 177 newtons (N)) was significantly higher than in the PVZ group (1,798 ± 30.9 N) (p-value < 0.001). All crowns in the HTZ group presented core fracture mode. However, crowns in the PVZ group showed both a core and adhesive fracture mode of 60% and 40%, respectively.ConclusionThe fracture strength of HTZ crowns is superior to PVZ crowns. The fracture strength of both types surpassed the maximum bite force in the posterior region, which may be deemed clinically adequate.

The Effect of Different Foundation Materials on the Color of Monolithic Zirconia at Different Thicknesses

Statement of the Problem: Monolithic zirconia restoration has been introduced to overcome the porcelain chipping. Different factors can affect the color of monolithic zirconia, so achieving the desired color in the restorations is considered as a challenge.Purpose: The purpose of this in vitro study was to determine the effect of different foundation materials on the color of monolithic zirconia at different thicknesses.Materials and Method: In this experimental study, thirty ceramic disks in three thicknesses (i.e. 0.6mm, 1.1mm and 1.5mm) were fabricated from high translucency shade A2 monolithic zirconia block. Disk shaped foundation materials were fabricated from nickel chromium alloy (Ni-Cr), non-precious gold alloy (NPG), zirconia, and shade A2 composite resin. The color was measured by a spectrophotometer. The color differences (∆E) in the control and the test groups were calculated. The data were analyzed using two way ANOVA and compared with the posthoc Tukey test (a=0.05).Results: Ceramic thickness and foundation materials had a significant effect on the mean values of ∆E of monolithic zirconia ceramics (p= 0.001). The highest amount of ∆E value was observed in NPG, while Ni-Cr resulted in the lowest ∆E. Unacceptable results (∆E>2.25) were observed for monolithic zirconia ceramics on NPG foundation material with a thicknesses of 0.6 and 1.1mm. The mean L* values of all foundation materials were higher than those of the control group except for Ni-Cr. The highest a* was seen in NPG and the mean b* values of all tested foundation materials were higher than those of the control group except for Ni-Cr.Conclusion: Increasing the thickness of monolithic zirconia decreased the color mismatch. High translucent monolithic zirconia could mask the color of Ni-Cr and zirconia in all three thicknesses (∆E<2.25), while it could not mask the color of NPG under thickness of 1.5mm.

The effect of thermocyclic aging on color stability of high translucency monolithic lithium disilicate and zirconia ceramics luted with different resin cements: an in vitro study

BackgroundHigh-translucency monolithic zirconia were developed to combine the esthetics of all ceramic restorations with the strength properties of zirconia. The purpose of this study was to compare the color stability of high-translucency monolithic zirconia ceramics with lithium disilicate luted using light-cure versus dual-cure resin cements following thermocyclic aging.MethodsForty specimens, each composed of 10 × 10 × 1 mm ceramic slice luted to dentin surface of an extracted tooth, were prepared and assigned into four groups (n = 10) as follows; LiDi/LC: lithium disilicate luted by light-cure resin cement; LiDi/DC: lithium disilicate luted by dual-cure resin cement; Zr/LC: zirconia luted by light-cure resin cement; and Zr/DC: zirconia luted by dual-cure resin cement. Color analysis of the specimens was performed before and after 3000 thermal cycles by means of spectrophotometry. The CIE L*a*b* values of the specimens were measured, and data were analyzed statistically at a significance value of p < 0.05.ResultsThermocycling resulted in a significant change in color coordinates of specimens with an overall ΔE = 3.59 ± 1.60, but there was no statistically significant difference in the color change value among all tested groups (P = 0.756).ConclusionsAt 1 mm restoration thickness, the color stability of high-translucency monolithic lithium disilicate and zirconia ceramics were not significantly different irrespective of the cement type used.Clinical implication Understanding the difference in color stability of dental ceramics may help in determining long-term esthetic result.

Effect of Two Brands of Glaze Material on the Flexural Strength and Probability of Failure of High Translucent Monolithic Zirconia.

(1) Background: The effect of glazing on the mechanical properties of monolithic high translucent zirconia is not well reported. Therefore, the purpose of this study was to evaluate the effect of glazing on the flexural strength of high translucent zirconia; (2) Methods: Ninety specimens were prepared from second-generation 3Y-TZP high translucent blocks and divided into three groups. Glaze materials were applied on one surface of the specimen and subjected to a four-point bending test and flexural stress and flexural displacement values were derived. Descriptive fractographic analysis of surfaces was conducted to observe the point of failure and fracture pattern.; (3) Results: Control-nonglazed (647.17, 1σ = 74.71 MPa) presented higher flexural strength values compared to glaze I (541.20, 1σ = 82.91 MPa) and glaze II (581.10, 1σ = 59.41 MPa). Characteristic strength (σƟ) from Weibull analysis also observed higher (660.67 MPa) values for the control specimens. Confocal microscopy revealed that glazed surfaces were much rougher than control surfaces. Descriptive fractographic analysis revealed that there was no correlation between the point of failure initiation and flexural strength; (4) Conclusions: The test results demonstrated that glazing significantly decreased the flexural strength and flexural displacement of the zirconia specimens.

Novel Femto Laser Patterning of High Translucent Zirconia as an Alternative to Conventional Particle Abrasion.

Background: currently applied surface treatments for zirconia bonding may create undesired microcracks and surface flaws. The aim of the present study was to evaluate the efficacy of alternative surface treatments on the shear bond strength of high translucency zirconia to 10-Methacryloyloxydecyl dihydrogen phosphate (MDP)-containing resin-based cement. Methods: fifty disk-shaped specimens (10 mm × 5 mm) were fabricated from a commercial yttria-stabilized zirconia with 5 mole% yttrium oxide tetragonal zirconia polycrystal (5Y-TZP), and underwent air-abrasion with alumina particles (50 μm-AL50 and 90 μm-AL90), glass beads (GB 10–60 μm), and ablation with femtosecond laser (FEMTO). Shear bond strength was evaluated with a universal testing machine under a crosshead speed of 0.5 mm/min until fracture. Fracture type was evaluated with an optical stereomicroscope. Differences among groups were evaluated by one-way ANOVA and Bonferroni pairwise comparison tests (p < 0.05). Results: the highest shear bond strength values were presented by the laser treated group (23.97 ± 3.7 MPa). No statistically significant differences were found among the Cl, Al50, Al90 and FEMTO groups. The lowest mean value was presented by the glass-beads treated group (11.93 ± 2.88 MPa) which was significantly lower compared to all other groups (p < 0.001). Conclusions: under the limitations of this in vitro study, femtosecond laser treatment of High-translucent monolithic zirconia (HTZ) ceramics is a promising alternative method for the mechanical retention of resin cements.

Fracture toughness of different monolithic zirconia upon post-sintering processes.

BackgroundSurface treatments are expected to be a reason for alteration in fracture resistance of zirconia. This study evaluated the effect of post-sintering processes on the fracture toughness of different types of monolithic zirconia. Material and MethodsClassical- (Cz) and high-translucent (Hz) monolithic zirconia discs (1.2 mm thickness, 14 mm in Ø) were prepared, and randomly divided for surface treatments with 1) as-glazed (AG); 2) finished and polished (FP); 3) finished, polished, and overglazed (FPOG); and 4) finished, polished, and heat-treated (FPHT) technique (n=15/group). Fracture toughness (KIC) was determined with indentation fracture toughness method at load 1 kg for AG, FPOG and 10 kg for FP, FPHT with 15 sec dwelling time. Weibull analysis was applied for survival probability, Weibull modulus (m), and characteristic toughness (K0). Microstructures were examined with SEM and XRD. ANOVA and multiple comparisons were determined for significant differences (α=0.05). ResultsThe mean±sd value of KIC (MPa.m1/2), m, and K0 were 1.60±0.19, 7.27, 1.71 for CzAG; 9.57±0.89, 9.97, 10.96 for CzFP; 1.61±0.15, 10.56, 1.68 for CzFPOG; 6.45±0.31, 20.31, 6.60 for CzFPHT; 1.45±0.13, 10.91, 1.51 for HzAG; 6.58±0.24, 27.00, 6.70 for HzFP; 1.24±0.05, 23.90, 1.27 for HzFPOG; and 5.07±0.16, 30.51, 5.15 for HzFPHT. The KIC was significantly affected by the post-sintering process, type of zirconia (p<0.05). The Cz indicated a significantly higher KIC than Hz. The FP significantly enhanced KIC, while OG was unable to raise KIC. HT reduced KIC due to reverse phase transformation. ConclusionsPost-sintering processes caused alteration in fracture resistance of zirconia. Fracture toughness was enhanced with FP, but not with either OG or HT process for both Cz and Hz. Surface treatment of zirconia through a finished-polished process is recommended, while glazing and heat-treated are not suggested. Key words:Fracture toughness, glazing, heat treatment, polishing, post-sintering process, zirconia.

Masking of High-Translucency Zirconia for Various Cores.

Various core materials with different shades affect the final color of high-translucency monolithic zirconia restorations. The blue core shows the greatest color difference in final zirconia restorations followed by metal, A3 dentin-shade resin core, and white core. The purpose of this study was to evaluate the masking ability of high-translucency monolithic zirconia for various core materials. A computer-aided design-computer-aided manufacturing system was used to design a zirconia disc with a diameter of 10 mm and a thickness of 1.0 mm. Four groups of cores (n=15 each) were fabricated with blue-colored dual-cure resin, white-colored dual-cure resin, A3 dentin-shade composite resin, and titanium block with 10-mm diameter and 5-mm thickness.Dual-cure, self-adhesive resin cement discs with a thickness of 25.0 ± 0.02 μm were fabricated. The color was measured using a handheld spectrophotometer. Color measurements of all specimens were performed on a white background. To assess the masking ability of zirconia, the difference between the values measured with zirconia on a white background and the values measured with zirconia on each of the four types of core material as a background with the cement specimens interposed (zirconia + cement + core) was determined. To enhance the optical connection between the specimens, distilled water was applied between each layer during each measurement.The results showed that the value of ΔE was highest for the blue core followed by metal, A3 dentin-shade resin core, and white-resin core. No significant differences were observed between the metal core and the A3 dentin-shade resin core or between the A3 dentin-shade resin core and the white core. The blue core had the significantly highest ΔE value based on Tukey's honest significant difference test.Different core materials affect the final color of high-translucency monolithic zirconia restorations. Thus, our study showed that the final color of high-translucency monolithic zirconia restorations could be affected by the type of core material used.

Influence of Margin Designs on Crack Initiation of High Translucency Monolithic Zirconia Crowns.

Zirconia crowns often crack at the margin. This study determined the loads and the times at which cracks are initiated in high-translucency monolithic zirconia crowns with different margin designs. A total of 90 crowns were fabricated from Zirconia blanks. The fabricated crowns had different margin thicknesses (light-chamfer, CL and heavy-chamfer, CH ) and collar heights (no-collar, NC ; low-collar, LC ; high-collar, HC ). They were grouped as CL NC , CL LC , CL HC , CH NC , CH LC , and CH HC (15 crowns/group). The crowns were seated on a metal model and loaded vertically through round end punch (Φ = 10 mm) at 0.2 mm/min crosshead speed until cracks began to be seen. Videos of the crack initiation were recorded at the rate of 50 frames/second. Load-initiated cracks and durability time were compared for significant differences using analysis of variance. The mean ± standard deviation values of load (N) and time (s) taken to initiate cracks were 3190 ±775, 212 ±47 for CL NC ; 2754 ±1109, 180 ±42 for CL LC ; 2887±832, 191±27 for CL HC ; 4082 ±896, 241 ±36 for CH NC ; 4180 ±1029, 220 ±28 for CH LC ; 4119 ±1124, 222 ±39 for CH HC . This indicates that the thickness of the margin has a significant influence on load-withstanding crack initiation capacity and durability time (p < 0.05). No significant impact of collar height was observed on either load-withstanding capacity or durability time (p > 0.05). No interaction was observed among these factors. Heavy chamfer margin provided a stronger zirconia crown than the light chamfer margin, but both of them were capable of withstanding crack-initiated load higher than the theoretical maximum masticatory force. The presence or absence of a collar did not have any impact on the crack initiation. Fabrication of zirconia crowns with either a heavy or light chamfer margin and with or without the presence of a collar should be generated by considering the relevant emergence profile.

Effect of Thickness Variation on the Translucency of Two Recent High Translucent Monolithic Zirconia Ceramics

Objective of the study. The objective of this study was to evaluate the effect of thickness change on the translucency of two recent monolithic zirconia dental ceramics used at different thicknesses. Materials and methods. A total of 60 disk-shaped specimens were prepared from two high-translucent tetragonal zirconia (Zolid ht+) and ultra-translucent cubic zirconia (Zolid fx), and divided equally into two groups according to material, each group with further subdivided into 3 subgroups according to thickness 0.5, 1, and 1.5 mm (n=10). A spectrophotometer was used to assess the CIE L*, a*, and b* for each thickness of the two zirconia ceramics. The Translucency Parameter (TP) was calculated. 1-way ANOVA and 2-way ANOVA statistical analysis of variance were performed (α=.05). Results. A statistically significant higher mean TP value was recorded with the ultra-translucent cubic zirconia group compared to that of high-translucent tetragonal zirconia regardless of thickness (P=0.008*< 0.05). Thickness had a significant effect on the translucency parameter of the two zirconia ceramics. Within group comparisons showed that for each of the two materials, the 0.5mm thickness recorded the statistically significant highest mean TP value, followed by the 1mm subgroup, whereas the statistically significant lowest mean TP value was recorded for the 1.5mm subgroup. Conclusions. Within the limitations of this study, it was found that material type and thickness had a significant effect on the translucency of high translucent monolithic zirconia.

Effect of Thickness Variation on the Translucency of Two Recent High Translucent Monolithic Zirconia Ceramics

Effect of Thickness Variation on the Translucency of Two Recent High Translucent Monolithic Zirconia Ceramics

Effect of Marginal Designs on Fracture Strength of High Translucency Monolithic Zirconia Crowns.

Introduction Monolithic zirconia is able to achieve certain aesthetic, but its durability in resisting fracture has been questioned, as fractures often originate from margins of restoration. This study determined fracture resistance of highly translucent monolithic zirconia crowns with different margin designs in terms of marginal thickness and collar height. Materials and Methods Zirconia blanks (Ceramill® Zolid HT+) were selected for the fabrication of zirconia crowns according to different designs, including varying margin thicknesses (light chamfer, CL; heavy chamfer, CH) and collar heights (no collar, NC; low collar, LC; high collar, HC), which resulted in CLNC, CLLC, CLHC, CHNC, CHLC, and CHHC groups (15 crowns each). The crowns were seated on a metal die and loaded vertically through round end punch (θ = 10 mm), contacting with inclined planes of cusp in a testing machine with crosshead speed of 0.2 mm/min until fracture. Videos with a rate of 50 frames/second were used to record fracture. Fracture load (N) and durable period (s) were compared for significant differences using ANOVA and Bonferroni test (α = 0.05). Results The mean ± sd of fracture load (N) and durable time (s) were 3211 ± 778 and 212 ± 47 for CLNC; 3041 ± 1370 and 188 ± 53 for CLLC; 2913 ± 828 and 192 ± 27 for CLHC; 4226 ± 905 and 245 ± 35 for CHNC; 4486 ± 807 and 228 ± 29 for CHLC; and 4376 ± 1043 and 227 ± 37 for CHHC. This indicated that marginal thickness had a significant influence on load-bearing capacity and durable time (p < 0.05). No significant impact of collar height was shown, either on load-bearing capacity or durable time (p > 0.05). No interaction between two factors was presented (p > 0.05). Conclusions Heavy chamfer margin provided stronger zirconia crown than light chamfer, but both were capable of withstanding fracture load higher than maximum masticatory force. Neither presence nor absence of collar indicated any impact on strength. Fabrication of zirconia crowns with either heavy or light chamfer margin and either presence or absence of collar, with the consideration of emergence profile, should be considered.

Color match of high translucency monolithic zirconia restorations with different thicknesses and backgrounds.

To assess the effects of ceramic thickness and background type on the color match of high translucency monolithic zirconia restorations. Fifty A2 shade high translucency zirconia disk specimens with five different thicknesses (0.7, 0.9, 1.1, 1.4, 1.6 mm) were placed on 12 backgrounds: A1, A2, A3, A3.5, B1, and B2 shade composite resin, A3 shade zirconia, nonprecious gold-colored alloy, nickel-chromium alloy, amalgam, and A2 and A3 shade tooth. Color measurements were performed to determine the specimens' CIELab values. CIEDE2000 formula was used to determine ΔE00 color differences between specimens and A2 VITA classical shade (target). The ΔE00 values were compared with perceptibility (0.8) and acceptability (1.8) thresholds to assess color matches. Data were analyzed using repeated measures ANOVA, Bonferroni, and 1-sample t tests (P < .05). Mean ΔE00 values ranged between 1.3 and 5.7. Ceramic thickness, background type, and their interaction significantly affected the ΔE00 (P < .001). Ceramic thicknesses of ≥1.1 mm with the A2 or A3 shade tooth background showed 0.8 < ΔE00 ≤ 1.8 producing acceptable color matches. High translucency monolithic zirconia restorations with a minimum thickness of 1.1 mm on tooth backgrounds could create acceptable color matches; however, with other backgrounds tested, they could not. Ceramic thickness and background type affect the color of high translucency monolithic zirconia restorations. A minimum zirconia thickness of 1.1 mm and normal color tooth structures, as a background, are essential for achieving the acceptable color match of these restorations.