Zirconia Core Material Research Articles

Translucency and color differences of polycrystalline ceramic materials before and after layering

Objective: To evaluate the transmittance (%T) and color difference (ΔE*) of six zirconia core materials compared to alumina, over eight colored substrates before and after ceramic application. Methods: Experimental groups (n=5) of standardized disk-shaped cores of alumina, white zirconia, medium-colored zirconia, Ice Translucent, and Prettau (white and D3 colored) were veneered to a uniform thickness to convenient color by layering. Their %T and ΔE* over eight different substrates were determined before and after glazing. Data were analyzed with Kruskal-Wallis and Mann-Whitney tests (α<0.05). Results: %T and ΔE* values were significantly different (p<0.001) before and after ceramic application for all materials. Regarding %T, Prettau white zirconia was the most affected, overpassing alumina. Colored zirconia cores decreased %T equally. In terms of ΔE*, zirconia materials initially performed high above the clinically acceptable threshold but were under it after ceramics application. White zirconia was the only material to perform below the clinical perceptibility threshold. Alumina initially performed under the clinically acceptable threshold for two substrates, but after ceramic application, only performed under the clinical perceptibility threshold over four. Substrates influenced ΔE* values of all core materials but were only evident on three of them. Conclusions: Core materials influenced %T and ΔE* values. Colored zirconia cores showed less %T than white cores and both less than alumina before and after ceramic application. After ceramic application, all materials performed under the clinically acceptable threshold over all the substrates. Substrates have more influence on ΔE* values before ceramic application.

Investigation of the effect of different experimental acid solutions applied on the zirconia surface on the bond strength between zirconia and resin cement: A pilot study

Aim: The purpose of this study is to examine the effects of two different experimental acid solutions and sandblasting on the bond strength between zirconia ceramic core material and resin cement. Methodology: Forty zirconia core materials were prepared and separated into four groups based on the surface treatment to be applied (n = 10) as follows: 1) Control Group: no surface treatment was performed; 2) Sandblasting Group: the specimen surfaces were sandblasted with 50 µm aluminum oxide particles from a distance of 10 mm at 3 bar pressure for 15 seconds; 3) Sol-1 Group: H2O:HF:H2O2 solution was applied for 60 seconds, washed, and then dried; and 4) Sol-2 Group: H2O:HF:HNO3 solution was applied to the surfaces of the specimens for 60 seconds, washed, and then dried. All specimens were coated with a dual-cure resin cement with a 2.8-mm diameter. After 24 hours, the specimens were tested for shear bond strength (SBS) at 1 mm/min using a universal testing device. Statistical analysis was conducted using one-way analysis of variance (ANOVA) and Tukey HSD tests with a confidence interval of 95%. Results: The difference among the groups was statistically significant (p = 0.002) based on the one-way ANOVA results. The Control Group had the lowest SBS (8.06 ± 4.52), whereas the Sol-1 Group had the highest SBS (17.10 ± 5.67). The Sol-1 and Sol-2 Groups demonstrated comparable bonding strength values (p = 0.17). The Sandblasting and Sol-1 Groups exhibited considerably stronger bond strength than the Control Group (p = 0.05). Conclusion: The experimental acid solutions enhanced the bond strength between the resin cement and the zirconia ceramic at the sandblasting treatment level. How to cite this article: Yılmaz Savaş T, Savaş A, Akın C, Tunçdemir AR. Investigation of the effect of different experimental acid solutions applied on the zirconia surface on the bond strength between zirconia and resin cement: A pilot study. Int Dent Res 2022;12(Suppl.1):69-73. https://doi.org/10.5577/intdentres.458 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Effect of surface treatment on bond strength between zirconia and composite resin core material

Effect of surface treatment on bond strength between zirconia and composite resin core material

Investigation of Fracture Resistance of Zirconia Restorations After Different Surface Treatments

Objective: The purpose of this study was to investigate the effects of the different surface treatments on fracture strength of the zirconia-based ceramic restorations. Methods: Each of 120 dental implant abutments and analogs were used in the present study. Zirconia core materials were manufactured on dental implants by using CAD/CAM device and they were randomly divided into 6 groups (n=20) according to surface pretreatments; control group (Group C), airborne-particle abrasion (Group AA), silica-coating (Group SC), Nd:YAG laser (Group N), bur-cut from cervical region (Group BC), and bur-cut on the functional tubercule (Group BT). Cementation was succeeded with two different types of cements including a dual-cure resin-cement and a glass ionomer cement. The obtained data were evaluated statistically using one-way ANOVA and Tukey tests (p=0.05). Results: No statistically significant difference was found between the groups (p>0.05). Similarly, no statistically significant difference was found between the resin cement and glass ionomer groups with respect to fracture strength values (p>0.05). Conclusion: Within the limitations of the present study, surface treatments and cement have no effect on the flexural strength of zirconia ceramic crowns.

Shear Bond Strength of Zirconia Ceramic to Four Different Core Materials, An in vitro Study.

Statement of the Problem: Different materials can be used to reconstruct the core foundation in all-ceramic restorations. Bond strength of the core material to zirconia is an important factor in long-term restoration success. Purpose: The aim of this study was to assess shear bond strength (SBS) of zirconia to four different core materials.Materials and Method: In this experimental in vitro study, 40 zirconia ceramic disks (10×3 mm) were prepared and divided to four groups based on core material. Cylinder shaped core specimens (3×4 mm) of non-precious gold alloy (NPG), zirconia ceramic, natural dentin, and composite resin were prepared and bonded perpendicularly to the zirconia disks using Gillmore Needle Apparatus and dual cure resin cement. All samples were thermocycled for 2000 cycles. To evaluate SBS, the specimens were tested by universal testing machine. Data were analyzed using Kruskal-Wallis test followed by Dunn's test with Bonferroni correction. Statistical significance was set at p< 0.05.Results: The highest values for SBS were achieved in composite resin group (11.58±1.74 MPa) followed by NPG (10.32±0.94 MPa), zirconia (7.3±1.11 MPa) and dentin group (6.53±0.56 MPa). SBS in composite resin and NPG core materials were significantly higher than other core materials (p< 0.05).Conclusion: Composite resin and NPG cores showed significant higher bond strength to zirconia in comparison to dentine and zirconia core materials.

Comparative In Vitro Evaluation Between Zirconia and Veneer Ceramic Materials Using Different Techniques

Zirconia surface treatment using different techniques could be employed to overcome the delamination issue reported between veneering ceramic materials and the corresponding zirconia core. The study subjected yttria partially stabilized zirconia core material to grinding and sandblasting as a first surface treatment. An airbrush gun spraying technique was used to coat a uniform thin layer of veneering ceramic (IPS e.max Ceram and Noritake Cerabien ZR) on the core materials followed by performing laser scanning as a second surface treatment. The specimens were investigated for surface topography, interface analysis, elemental compositions, phase transformation, and fracture mode patterns using profilometer, SEM, EDS, XRD, and stereomicroscope. The impact of laser scanning on the shear bond strength before and after storage of specimens in artificial saliva was also studied. Transformable tetragonal phase to monoclinic was predominant in sandblasted specimens followed by laser scanning with observation of micro-cracks at interface. The grinding followed by laser scanning yielded satisfactory outcomes in terms of the presence of coating property. The phase transformation was not detected through the latter technique. The technique greatly enhanced the roughness property and bond strength values which might be considered as a reliable application to improve the longevity of fixed dental crowns in load bearing areas.

Effect of sintering parameters on the mechanical properties of monolithic zirconia.

Background. Zirconia restorations with high mechanical properties are the current treatment options for fixed restorations with advantages of high biocompatibility and low pulp irritation. Although the effect of sintering time and temperature on the optical and mechanical properties of zirconia core material were investigated, the effect of these parameters on the translucent monolithic zirconia is still uncertain. This study aimed to evaluate the effect of the changes in sintering temperature and holding time on the mechanical and structural properties of monolithic zirconia. Methods. Totally, 340 self-colored (A2) zirconia specimens from two different monolithic zirconia groups (n=170) were prepared, measuring 15.5×12.5×1.2 mm. Then, 17 subgroups (n=10), including the control groups, were sintered according to sintering parameters. XRD analysis was used to determine phase transformations. The surface roughness of the specimens was evaluated using profilometry, and the flexural strength of the specimens was evaluated by the three-point bending test. The data were analyzed using three-way ANOVA and post hoc multiple comparison test with Bonferroni correction (a=0.05) at a significance level of 0.05. Independent-samples t-test was used to compare the subgroups between the control groups (P˂0.05). Results. No tetragonal-to-monoclinic phase transformation was observed in the groups. Changes in the sintering parameters did not significantly affect the surface roughness and flexural strength of monolithic zirconia. Surface roughness values for all the subgroups were above the clinically critical limit. Conclusion. According to the results of this study, changes in the sintering parameters did not affect the surface phase transformation, surface roughness, and flexural strength of monolithic zirconia.

Effect of color shading procedures and cyclic loading on the biaxial flexural strength of zirconia.

Zirconia is the most preferred ceramic restoration in posterior areas because of its flexural strength. The aim of the study is the evaluation of biaxial flexural strength of different colored zirconium oxide core materials after cyclic loading. Zirconia discs (12 mm diameter and 1.2 mm thickness) were divided into 6 groups of 12 discs each. Groups were colored according to the Vita Classic shade guide: A3 and D4. One group was not colored and left as control. Each group was randomly divided into subgroups and subjected to mechanical cycling prior to biaxial flexural strength test. Cyclic loading was applied as 50 N loads for 20,000 times for the loaded groups. Samples were subjected to biaxial flexural strength test in a universal testing machine with a crosshead speed of 1 mm/min. Two-way analysis of variance (ANOVA) and Tukey's HSD tests were used for comparisons of the groups. Biaxial flexural strength values did not vary significantly depending on coloring procedure or loading process tested (p>.05). XRD analysis displayed that the monoclinic volume fraction of zirconia was highest in cyclic loaded D4 and was lowest in non-loaded control group. The SEM image revealed that A3 color solution created metallic coloring pigments at grain boundaries. Coloring procedures and cyclic loading did not affect the biaxial flexural strength of zirconia core material; however, microstructural analysis displays changes, which may weaken the zirconia structure on the long term.

Effect of different surface processes on the bond strength between zirconia framework and veneering ceramic

To compare the effect of different surface processes on bond strength and microscopic structure using a scanning electron microscope (SEM) and an energy distribution spectrum (EDS) at the bonding interface between zirconia framework and veneering ceramic. WIELAND zirconia core material was cut into 33 rectangular specimens and fired on into rectangular specimens (10 mm×5 mm×5 mm). The specimens were randomly divided into three groups (n= 11). The sandblasting group was sandblasted before firing. The sandblasting and liner coverage group was sandblasted before firing and then sintered with liner coverage after firing. The control group was not processed. All the veneering ceramics (5 mm× 5 mm×5 mm) were fired on into the zirconia substructure by slip-casting technique. One bilayered specimen in each group was prepared for SEM and EDS to examine the bonding conditions. The other specimens were measured for shear force using an electronic universal dynamometer. The data obtained were analyzed by using the statistical software SPSS 17.0. The values of the shear bond strength test were (13.80±1.54) MPa for the control group, (18.06±0.59) MPa for the sandblasting group, and (21.04±1.23) MPa for the sandblasting and liner coverage group. Significant differences existed among the three groups (P<0.01). Abrasion before firing significantly increases the shear bond strength of zirconia to veneering porcelain. The use of porcelain combined with liner increases the shear bond strength.

Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia

Statement of problemRecent monolithic zirconia materials used for indirect restorations are predominantly fully stabilized zirconia with claims of enhanced optical properties. These restorations may behave differently from the conventional partially stabilized zirconia restorations, which may negatively affect some of the core properties required for restoration success. PurposeThe purpose of this in vitro study was to evaluate and compare the effects of staining, airborne-particle abrasion, and artificial aging on the flexural strength of fully and partially stabilized zirconia material. Material and methodsEach partially stabilized monolithic zirconia (PSZ) and fully stabilized zirconia (FSZ) material and a zirconia core material (control) were prepared as bar-shaped specimens (2×2×25 mm) and divided into 6 groups (n=8/subgroup): regular sintering, vacuum sintering, stained, airborne-particle abrasion, artificially aged regular sintering, and artificially aged vacuum sintering. Critical load to fracture was determined for all groups by using monotonic uniaxial loading in accordance with International Organization for Standardization standard 6872. Data were analyzed using univariate analysis of variance, followed by the Tukey honest significant difference post hoc test (α=.05). ResultsThe control and PSZ (1034 and 1008 MPa) displayed a significantly higher (P<.05) flexural strength than FSZ (582 MPa). Airborne-particle abrasion significantly (P<.05) enhanced the strength of the control and PSZ (1413 and 1227 MPa) but significantly (P<.05) reduced the flexural strength of the FSZ (442 MPa). Staining, artificial aging, and vacuum sintering had no significant effects on any of the groups. ConclusionsFully stabilized zirconia may behave differently from conventional PSZ, especially with regard to airborne-particle abrasion, which may weaken the FSZ. The strength of PSZ is approximately double the strength of FSZ. Both of the zirconia materials showed resistance to artificial aging.

The effect of coloring liquid dipping time on the fracture load and color of zirconia ceramics.

PURPOSEThe aims of the study were to evaluate the fracture load of zirconia core material after dipping in coloring liquid at different time intervals and to compare the color of dipped blocks with that of prefabricated shaded blocks.MATERIALS AND METHODS3-unit bridge frameworks were designed digitally. Sixty frameworks were fabricated using uncolored zirconia blocks by CAD/CAM and divided into 4 groups randomly (n = 15). Group 2 (G2) was subjected to coloring liquids for 2 minutes, Group 4 (G4) for 4 minutes, and Group 6 (G6) for 6 minutes. CFS group was not subjected to any coloring procedure. After coloring, color differences between the test groups and a prefabricated shaded zirconia group (CPZ, n = 15) were evaluated by using a spectrophotometer. Fracture test was conducted immediately after shade evaluation with a Testometric test device at a cross-head speed of 1 mm/sec. Statistical analysis for evaluating color and fracture load was performed by using one way ANOVA followed by Tukey HSD test (P ≤ .05). Weibull analysis was conducted for distribution of fracture load.RESULTSThere was no difference in terms of fracture load and color between CFS (1176.681 N) and G2 (985.638 N) group and between CPZ (81.340) and G2 (81.140) group, respectively. Fracture load values of G4 (779.340 N) and G6 (935.491 N) groups were statistically significantly lower than that of CFS group (P ≤ .005). The color values of G4 (79.340) and G6 (79.673) groups were statistically different than that of CPZ group (P ≤ .005).CONCLUSIONProlonged immersion of zirconia in coloring liquid not only negatively affected the fracture load of the zirconia being tested in the current study but also deteriorated the desired shade of the restoration.

Microtensile Bond Strength of Three Restorative Core Materials with IPS e.max Press Ceramic by Two Resin Cements

Objectives: The aim of this study was to compare the microtensile bond strengths (µ TBS) of three core materials with one lithium disilicate reinforced ceramic using two resin cements.Methods: Three core materials (Nulite F® (Biodental Technologies), Filtek Z250® (3M-ESPE), Prettau-Anterior® (Zirkonzhan, Germany)) were prepared as blocks (10×10×4 mm3) according to the manufacturer’s instructions. Lithium disilicate ceramic blocks were also constructed and bonded to core specimens with two dual curing luting resin cements (Duo-Link® (Schaumburg, IL), Bifix QM® (VOCO, Cuxhaven, Germany)). Micro-bar specimens were prepared and loaded in tension to determine the µ TBS Failure modes were classified by scanning electron microscope (SEM). Data were analysed using two-way ANOVA and Tukey HSD test.Results: The µ TBS varied significantly depending on the core materials and resin cements used (P 0.05). The highest bond strength was obtained between zirconia core and Bifix QM (45.3 ± 6.7 MPa).Conclusion: In vitro µ TBS of glass ceramic blocks bonded to zirconia core material showed higher bond strength values than resin-based core material, regardless of the resin cement type used.

Shear Bond Strengths between Three Different Yttria-Stabilized Zirconia Dental Materials and Veneering Ceramic and Their Susceptibility to Autoclave Induced Low-Temperature Degradation.

A study was undertaken to evaluate the effect of artificial aging through steam and thermal treatment as influencing the shear bond strength between three different commercially available zirconia core materials, namely, Upcera, Ziecon, and Cercon, layered with VITA VM9 veneering ceramic using Universal Testing Machine. The mode of failure between zirconia and ceramic was further analyzed as adhesive, cohesive, or mixed using stereomicroscope. X-ray diffraction and SEM (scanning electron microscope) analysis were done to estimate the phase transformation (m-phase fraction) and surface grain size of zirconia particles, respectively. The purpose of this study was to simulate the clinical environment by artificial aging through steam and thermal treatment so as the clinical function and nature of the bond between zirconia and veneering material as in a clinical trial of 15 years could be evaluated.

Bond Strength of Zirconia to Different Core Materials

ABSTRACT Background Since bonding to zirconia is still questionable, the aim of this study was to evaluate the bond strength of yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) to different materials used to manufacture dental cores, employing a universal self-etching adhesive system. Materials and methods Cylinders obtained from blocks of Y-TZP Zirconia were sintered in a high-temperature oven. The surfaces to be bonded were blasted with aluminum oxide, then silica-coated aluminum oxide, and finally cleaned in ultrasonic bath. The specimens were divided into six groups according to the core material tested: Silver alloy (Ag/Sn/Cu, Tecnofix), copper alloy (Cu/Ni/Zn, Goldent LA), core buildup resin (Rebilda DC — VOCO), Y-TZP zirconia (IPS e.max ZirCAD, Ivoclar Vivandent), enamel, and dentin. The zirconia cylinders were bonded to the core substrates using the Futurabond U adhesive system (VOCO) and resinous cement (Bifix QM — VOCO). The specimens were shear tested in a universal testing machine at 1 mm/ min. Data was analyzed using ANOVA and Tukey's test. Results Bond strength in MPa (±SD) for the different materials tested were dentin: (12.80 ± 3.18)a; enamel: (15.13 ± 3.09) ab; resin: (17.20 ± 4.67)ab; copper alloy: (18.93 ± 4.66)bc; silver alloy: (22.86 ± 5.47)c; and zirconia: (23.65 ± 3.64)c. Groups followed by the same letters are not significantly different at p &lt; 0.05. Conclusion The metallic alloys and zirconia core materials showed significantly higher bond strength than those obtained directly on dentin. The core buildup resin bond strength to zirconia is similar to that obtained with enamel and dentin. How to cite this article Frattes FC, de Oliveira JBS, Pucci CR, Borges AB, Torres CRG. Bond Strength of Zirconia to Different Core Materials. World J Dent 2016;7(4):169-174.

Optical properties and light irradiance of monolithic zirconia at variable thicknesses

ObjectivesThe aims of this study were to: (1) estimate the effect of polishing on the surface gloss of monolithic zirconia, (2) measure and compare the translucency of monolithic zirconia at variable thicknesses, and (3) determine the effect of zirconia thickness on irradiance and total irradiant energy. MethodsFour monolithic partially stabilized zirconia (PSZ) brands; Prettau® (PRT, Zirkonzahn), Bruxzir® (BRX, Glidewell), Zenostar® (ZEN, Wieland), Katana® (KAT, Noritake), and one fully stabilized zirconia (FSZ); Prettau Anterior® (PRTA, Zirkonzahn) were used to fabricate specimens (n=5/subgroup) with different thicknesses (0.5, 0.7, 1.0, 1.2, 1.5, and 2.0mm). Zirconia core material ICE® Zircon (ICE, Zirkonzahn) was used as a control. Surface gloss and translucency were evaluated using a reflection spectrophotometer. Irradiance and total irradiant energy transmitted through each specimen was quantified using MARC® Resin Calibrator. All specimens were then subjected to a standardized polishing method and the surface gloss, translucency, irradiance, and total irradiant energy measurements were repeated. Statistical analysis was performed using two-way ANOVA and post-hoc Tukey's tests (p<0.05). ResultsSurface gloss was significantly affected by polishing (p<0.05), regardless of brand and thickness. Translucency values ranged from 5.65 to 20.40 before polishing and 5.10 to 19.95 after polishing. The ranking from least to highest translucent (after polish) was: BRX=ICE=PRT<ZEN<KAT<PRTA (p<0.05). The ranking from least to highest total irradiant energy was: BRX<PRT<ICE=ZEN<KAT=PRTA (p<0.05). There was an inverse relationship between translucency, irradiant energy, and thickness of zirconia and the amount was brand dependent (p<0.05). SignificanceBrand selection, thickness, and polishing of monolithic zirconia can affect the ultimate clinical outcome of the optical properties of zirconia restorations. FSZ is relatively more polishable and translucent than PSZ.

A comparative study of biaxial flexural strength and Vickers microhardness of different zirconia materials: Effect of glazing and thermal cycling

Objective:This study evaluated the effect of glazing and thermal cycling on biaxial flexural strength and Vickers hardness of different zirconia core materials. Material and Methods: Disc shaped zirconia specimens (15 mm x 1.15 mm) were fabricated out of three systems (ZirkonZahn, Cercon, Ceramill) according to each manufacturer`s instructions. The specimens of each system were randomly divided into initially 2 groups. While half of the specimens were glazed, the other half was left unglazed. Each group was further divided into 4 subgroups to be subjected to thermal cycling (0-control, 1000, 3000, 5000 cycles, 5-55 ºC). Biaxial flexural strength was tested in a universal testing machine (1 mm/min). Another set of unglazed zirconia specimens were made and tested for Vickers microhardness with and without thermocycling (0-control, 1000, 3000, 5000 cycles, 5-55 ºC). Data were statistically analyzed using one-way ANOVA, two-way ANOVA and Tukey’s test (p &lt; 0.05). Results: In non-aged conditions (11034-1388 MPa), glazing significantly decreased the biaxial flexural strength of all zirconia ceramics (845.65-897.35 MPa) (p = 0.000). While in the non-glazed groups, all thermal cycling regimens significantly decreased the biaxial flexural strength (864-1156 MPa) (p=0.000), in glazed groups thermal cycling did not affect the results (829.4-854.9 MPa) (p = 0.405). Compared to the non-aged group (1414.1 VHN), thermal cycling decreased the Vickers hardness significantly only for Cercon (1365.9 VHN) (p = 0.005). Conclusion: Glazing decreased the biaxial flexural strength of the zirconia ceramics tested. Unglazed zirconia ceramics were weaker against thermal cycling compared to glazed ones. For monolithic zirconia restorations, this information may have clinical importance.Keywords:Biaxial flexural strength; Glazing; Thermal cycling; Vickers microhardness; Zirconia.

Effect of surface treatments on the biaxial flexural strength, phase transformation, and surface roughness of bilayered porcelain/zirconia dental ceramics

Statement of problemVeneered zirconia restorations are widely used in prosthetic applications. However, these restorations often fail because of chipping of the veneer porcelain. Surface treatments of zirconia core materials may affect the connection between the 2 layers. PurposeThe purpose of this study was to evaluate the effect of surface treatments on the biaxial flexural strength, phase transformation, and mean surface roughness of different bilayered porcelain/zirconia ceramics. Material and methodsForty disk-shaped specimens were obtained for each material (Kavo and Noritake) and divided into 4 (n=10) groups (control, airborne-particle abraded, ground, and ground and airborne-particle abraded). Airborne-particle abrasion was performed with 110-μm Al2O3 particles for 15 seconds and at 400 kPa. Diamond rotary instruments with 100-μm grain size were used for grinding. The monoclinic phase transformation and surface roughness of the specimens were measured. Then, the specimens were veneered and subjected to a biaxial flexural strength test to calculate the Weibull moduli (m values) and the stresses occurring at the layers, outer surfaces of the bilayer, and interfaces of the layers. ResultsThe Kavo airborne-particle abraded group showed higher strength values in both layers (P<.05) than those of all experimental groups. The Kavo airborne-particle abraded group showed the lowest m values at the core and veneer layers. According to the phase analysis, significantly higher Xm values were found in the ground and airborne-particle abraded groups for both materials (P<.05). In both materials, except in the airborne-particle abraded groups, the relative monoclinic phases showed no difference (P<.05). ConclusionSurface treatments affected the phase transformation, surface roughness, and biaxial flexural strength of Kavo and Noritake zirconia ceramics differently. Surface treatments increased the relative monoclinic phase content and average surface roughness.

Influence of cyclic loading on the fracture toughness and load bearing capacities of all-ceramic crowns

The purpose of this study was to investigate how cyclic loading influenced the fracture toughness of hot-press lithium disilicate and zirconia core materials and whether there was an increase in the propensity for crown failure. Two types of all-ceramic crowns including the IPS e.max Press system (n=24) and the Lava zirconia system (n=24), were selected. Sectioned specimens were subjected to cyclic loading with the maximum magnitude of 200 N (R=0.1) until two million cycles. The material properties including Young's modulus (E) and hardness (H) and the fracture toughness (KIC) of the core materials were evaluated using indentation methods (n=12 each). The load-bearing capacities of the specimens were examined by means of monotonic load to fracture (n=12 each). It was found that the material properties, including E, H and KIC, of the two types of dental ceramics, were reduced. Statistical analysis indicated that there were no significant influences of fatigue loading on material properties E and H for both types of dental ceramics or KIC for zirconia, while for the IPS e.max Press core, KIC, which was parallel to the direction of the lithium disilicate crystals, was significantly reduced (P=0.001). A conclusion was drawn that zirconia possesses high mechanical reliability and sustainable capacity to resist fatigue loading, while fatigue loading remarkably degraded the anisotropic mechanical behaviour of hot-press lithium disilicate ceramics.

Influence of dentin and core porcelain thickness on the color of fully sintered zirconia ceramic restorations

The influence of the thickness of dentin and core porcelain, and the glazing procedure on the color of computer-aided design and computer-aided manufacturing ceramic restorations has not been investigated. This study evaluated the influence of the thickness of dentin and core porcelain and glazing on the color of fully sintered zirconia ceramic restorations. Fully sintered zirconia core material was cut into 90 specimens of 0.3 mm (n=30, group ZC1), 0.4 mm (n=30, group ZC2), and 0.5-mm thickness (n=30, group ZC3). On a dentin disk obtained from an extracted molar, the L*, a*, b* values of the specimens were measured at different steps in the laboratory procedures (Zirconia core, Effect Bonder, Effect Liner, dentin porcelain, glazing) with a spectrophotometer. One millimeter dentin porcelain was applied on half of the specimens of each group and 1.5-mm dentin porcelain on the rest. To assess the ability of porcelain substructures to mask the underlying dark colored tooth structure, color difference (ΔE) values between the steps were calculated. Results were statistically analyzed with ANOVA. Glazing caused a decrease in the L* values and an increase in the a* and b* values (P<.05). Increasing the thickness of dentin porcelain decreased the L*, a*, and b* values (P<.05). Increasing the zirconia core thickness resulted in an increase inthe L* values and a decrease in the a* and b* values (P<.05). Increasing the dentin porcelain thickness from 1 mm to 1.5 mm resulted in a color change below the perceptibility threshold (ΔE<2.6). In the ZC1 group, glazing resulted in a color change perceptible to 50% of observers, whereas, in the ZC2 and ZC3 groups with 1-mm dentin porcelain, the ΔE value was higher than 5.5. However, the color change was perceptible to 50% of the observers in all of the groups with 1.5-mm dentin porcelain. Although the thicknesses of the dentin and core porcelain did not influence the final shade of the restoration, glazing resulted in a perceptible color difference.

Effect of colouring green stage zirconia on the adhesion of veneering ceramics with different thermal expansion coefficients

This study evaluated the adhesion of zirconia core ceramics with their corresponding veneering ceramics, having different thermal expansion coefficients (TECs), when zirconia ceramics were coloured at green stage. Zirconia blocks (N=240; 6 mm×7 mm×7 mm) were manufactured from two materials namely, ICE Zirconia (Group 1) and Prettau Zirconia (Group 2). In their green stage, they were randomly divided into two groups. Half of the specimens were coloured with colouring liquid (shade A2). Three different veneering ceramics with different TEC (ICE Ceramic, GC Initial Zr and IPS e.max Ceram) were fired on both coloured and non-coloured zirconia cores. Specimens of high noble alloys (Esteticor Plus) veneered with ceramic (VM 13) (n=16) acted as the control group. Core–veneer interface of the specimens were subjected to shear force in the Universal Testing Machine (0.5 mm⋅min−1). Neither the zirconia core material (P=0.318) nor colouring (P=0.188) significantly affected the results (three-way analysis of variance, Tukey's test). But the results were significantly affected by the veneering ceramic (P=0.000). Control group exhibited significantly higher mean bond strength values (45.7±8) MPa than all other tested groups ((27.1±4.1)−(39.7±4.7) and (27.4±5.6)−(35.9±4.7) MPa with and without colouring, respectively) (P<0.001). While in zirconia–veneer test groups, predominantly mixed type of failures were observed with the veneering ceramic covering <1/3 of the substrate surface, in the metal–ceramic group, veneering ceramic was left adhered >1/3 of the metal surface. Colouring zirconia did not impair adhesion of veneering ceramic, but veneering ceramic had a significant influence on the core–veneer adhesion. Metal–ceramic adhesion was more reliable than all zirconia–veneer ceramics tested.