Shear bond strength of veneering porcelain to zirconia and metal cores

Evaluation of the Bonding Shear Strength between Enamel and Dentin Feldspathic Porcelain and Two Different Monolithic Zirconia with Low and High Translucency

Introduction

The utilization of ceramics in the field of dentistry has seen a significant rise owing to their esthetic appeal and excellent functional properties. The use of ceramics in the field of dentistry has witnessed a notable surge, driven by their appealing esthetics and exceptional functional attributes. Zirconia, distinguished by its exceptional mechanical strength, plays a pivotal role in the fabrication of posterior crowns and bridges. Among zirconia variants, monolithic zirconia stands out, where the entire restoration is crafted from zirconia material. In parallel, feldspathic porcelain, chosen for its remarkable resemblance to natural tooth enamel, represents another significant ceramic type. This study aims to evaluate the shear bond strength (SBS) between two types of monolithic zirconia with two types of feldspathic porcelain.

Methods and Materials

Forty-four monolithic zirconia veneered discs with feldspathic porcelain were subjected to SBS testing. The dimensions of the discs were 7 mm in diameter and 5 mm in height (3 mm of zirconia and 2 mm of porcelain). Subsequently, the specimens were subjected to a universal testing machine at a speed of 0.5 mm/min until failure occurred. The type of failure was examined using scanning electron microscopy. One-way analysis of variance (ANOVA), two-way ANOVA, Fisher's test, and multiple Tukey comparisons were used as statistical analyses.

Results

The highest SBS was achieved by the high-translucency monolithic zirconia with enamel porcelain group (18.81 ± 3.18 MPa) and the high-translucency monolithic zirconia with dentin porcelain group (17.89 ± 2.75 MPa), followed by the low-translucency monolithic zirconia with dentin porcelain group (15.04 ± 2.24 MPa) and the low-translucency monolithic zirconia with enamel porcelain group (14.33 ± 2.00 MPa), respectively. Additionally, the most common type of failure pattern observed was mixed, followed by adhesive failure.

Conclusion

The translucency of the porcelain did not significantly affect SBS, while the type of monolithic zirconia used had a significant impact. Furthermore, there was no discernible relationship between the four groups in terms of the distribution of failure patterns.

In vitro effect of zirconia type on shear bond strength to feldspathic porcelain and wear of the opposing teeth

Background

Multilayer zirconia has more optical and aesthetic features than regular zirconia. Therefore, its mechanical properties should be compared with monochromatic zirconia. Among the mechanical characteristics that can be checked are the wear of the opposite tooth and the bond to the porcelain. This study assessed the effect of zirconia type (multilayer versus monochromatic) on the shear bond strength (SBS) to feldspathic porcelain and the wear of the opposing teeth.

Methods

The present in vitro study was conducted in two phases. In the first phase, 15 multilayer and 15 monochromatic zirconia blocks measuring 10×5×5 mm were designed, milled, sintered, veneered with porcelain, and underwent thermocycling. Their SBS was then measured in a universal testing machine. In the second phase, 15 multilayer and 15 monochromatic zirconia blocks were placed in a chewing simulator, and 30 sound premolars served as antagonistic teeth. The magnitude of wear of the buccal cusp of premolars was quantified from a 4-mm reference point after 100000 cycles. Data were analyzed by independent t test (α=0.05).

Results

The mean SBS of monochromatic zirconia to porcelain (24.49±3.58 MP) was slightly higher than that of multilayer zirconia (22.98±2.98 MP), but the difference was not significant (P>0.05). The mean wear of the opposing teeth was also slightly higher in the monochromatic group (284.1±66.53 µm) than in the multilayer group (263.2±58.69 µm), but this difference was not significant either (P>0.05).

Conclusion

Monochromatic and multilayer zirconia showed comparable SBS to feldspathic porcelain and caused comparable wear of the opposing teeth in vitro. Thus, multilayer zirconia may serve as an alternative to monochromatic zirconia.

Composite Resin Bond Strength to Zirconia and Base Metal Alloys Using Two Types of Intraoral Porcelain Repair Systems

Objectives: This study aimed to evaluate the shear bond strength (SBS) of two repair composites (Crea.lign vs. PermaFlo) to a base metal alloy and zirconia ceramic. Materials and Methods: Sixty-four discs (12mm diameter, 1mm thickness) were fabricated using Wirobond base metal alloy and zirconia. They were then bonded with their respective composite resins (N=16) in each of the two porcelain chipping repair kit subgroups consisting of PermaFlo and Crea.lign. All specimens were stored in 37°C distilled water for 24 hours. Half of them were subjected to 10,000 thermal cycles (5-55°C, 30s). All specimens were tested for SBS with a universal testing machine. Failure types were analyzed using a digital camera. Analysis of the data was done by two-way ANOVA and Bonferroni post-hoc tests. Results: SBS was significantly affected by the type of composite resin. PermaFlo had a significantly higher SBS than Crea.lign to base metal alloy (P<0.001) and zirconia ceramic (P<0.001). Thermocycling decreased the SBS of both composites to base metal alloy (P<0.001) and zirconia (P<0.001). Conclusion: A universal adhesive could provide higher shear bond strength of zirconia and base metal alloy to composite resin than Crea.lign composite and the MKZ primer supplied by its manufacturer.

Comparison of porcelain veneer fracture in implant-supported fixed full-arch prostheses with a framework of either titanium, cobalt-chromium, or zirconia: An in vitro study

Objectives

The aim of this study was to compare porcelain veneer strength on screw‐retained implant‐supported fixed full‐arch prostheses with a framework of either milled titanium (Ti), cobalt–chromium (CoCr), and yttria‐stabilized zirconia (Y‐TZP) in an in vitro loading model.

Materials and Methods

Fifteen screw‐retained maxillary implant‐supported full‐arch prostheses (FDP), five each of Ti, CoCr, and Y‐TZP frameworks with porcelain veneers were included. All FDPs were subjected to thermocycling before loading until fracture of the veneer. The load was applied at the distal fossa of the occlusal area of the pontic replacing 24. Fracture loads were analyzed, and the fracture quality was assessed. Statistical analysis on the fracture load was performed using Kruskal–Wallis test. The statistical significance was set at p < .05.

Results

There was no statistical significance found between the groups regarding fracture load. The highest and lowest load was seen within the CoCr FDP, varying between 340 and 1484 N. Different types of fracture appearances were seen. The Y‐TZP FDPs had a higher number of fractures locally in the loaded area while CoCr and Ti more often showed cracks in the anterior region, at a distance from the loaded area.

Conclusions

Within the limitations of this study, the conclusion was that framework material may affect the fracture behavior of maxillary full‐arch bridges; however, there were no differences in veneer fracture strength when frameworks of Ti, CoCr, or Y‐TZP were compared.

An Intraoral Repair Method for Chipping Fracture of a Multi-unit Fixed Zirconia Reconstruction: A Direct Dental Technique

Fracture or chipping of veneering ceramic is one of the most frequent clinical failures in dentistry in fixed dental and implant-borne prostheses. Due to the friable nature of the ceramic material, chippings may result in an aesthetic and functional problem for the patient requiring a rapid solution. Direct repairs have been indicated for the restoration of function, aesthetics and comfort, especially in cases where the fractured prosthesis presents good adaptation and satisfactory aesthetics. This case report aims to present and discuss the techniques of the direct reveneering method, their advantages and disadvantages, as well as the importance of adhesive procedures in the success of these restorative approaches. Success in repairing the fractured area, regardless of the technique used, is fundamental to establish a strong and stable adhesion between the repaired and the fractured areas, since the longevity of the repair will depend on the quality of the interface generated.

Zirconia-ceramic versus metal-ceramic posterior multiunit tooth-supported fixed dental prostheses: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

The authors aimed to compare the survival and complication rates of zirconia-ceramic (ZC) versus metal-ceramic (MC) restorative material in multiunit tooth-supported posterior fixed dental prostheses (FDP).

TYPES OF STUDIES REVIEWED

The authors conducted a systematic search of randomized controlled trials (RCTs), with no time or language restrictions, up to May 2019 using the MEDLINE (PubMed), Scopus, Web of Science, and Cochrane Central Register of Controlled Trials databases, followed by a manual search.

RESULTS

The authors included 7 RCTs in the review and 5 RCTs in the meta-analysis. All studies had a low risk of bias. The authors included 330 participants (177 ZC and 173 MC tooth-supported FDP) in the meta-analysis, which revealed a medium-term survival rate of 95.4% (95% confidence interval [CI], 90.5% to 99.1%) for ZC FDP compared with 96.9% (95% CI, 94.3% to 99.4%) for MC FDP, with no significant differences (P = .364). The biological or technical complications did not show statistically significant differences, except in the global ceramic veneering chipping analysis (P = .023; risk difference [RD], 22.3%; 95% CI, 3.0% to 41.6%) and their subanalysis: minor chipping or chipping that can be solved with polishing (P = .044; RD, 19.5%; 95% CI, 0.5% to 38.4%), and major chipping or chipping that needs repair in the laboratory (P = .023; RD, 6.0%; 95% CI, 0.8% to 11.3%).

CONCLUSIONS AND PRACTICAL IMPLICATIONS

Posterior multiunit ZC restorations are considered a predictable treatment in the medium term, although they are slightly more susceptible to chipping of the veneering ceramic than MC restorations.

Shear Bond Strength of Ceramic Bonded to Different Core Materials and Their Pattern of Failure: An In Vitro Study

Introduction

In metal-ceramic restoration, most of the bond failures between the ceramic layer and the metal coping is the chipping of the ceramic layer, thus exposing the metal surface, which compromises the aesthetics. Hence, this leads to the introduction of zirconia-based restorations in dentistry. However, even zirconium coping has the common complication of delamination or porcelain chipping from the zirconium core. Hence, the shear bond strength between the commonly used core materials and ceramic requires investigation to facilitate the materials in clinical use for longevity. Therefore, this study was conducted to compare the shear bond strength between different core materials and ceramic layering to find out the best core material for ceramic bonding.

Materials and methods

A total number of 45 samples were made as per ISO standardization (base 5 mm diameter and 1 mm thickness, step with 4 mm diameter and 4 mm in length). These samples were divided into three groups, Group A: Nickel-chromium, Group B: Cobalt-chromium, and Group C: Zirconium. Ceramic layering was layered on the top surface of each sample until an ideal height of 4 mm was obtained, and it was subjected to shear bond strength using a universal testing machine with a 50-KN load cell. This was followed by analyzing the nature of the fracture pattern using scanning electron microscopy (SEM).

Results

 There were no significant differences found for the shear bond strength among group A and group B. The zirconium (group C), however, had significantly lower values than both group A and group B. The microscopic examination also revealed that the failure between the coping and the ceramic layer primarily occurred near the interface with the residual veneering porcelain remaining on the core.

Conclusions

It was found that the shear bond strength of the metal-ceramic group is better than the zirconium ceramic group, however, the fracture between the copings and the ceramic layering is found to be similar for both adhesive and cohesive failure.

A comparative evaluation of the effect of liners on the shear bond strength of veneered zirconia block: An in vitro study

Aim:

This study aims to evaluate the effect of lithium disilicate glass–ceramic liner, silicon dioxide based liner, and glass–ceramic interlayer on the shear bond strength (SBS) of a commercially available veneered zirconia block and to study fractographic behavior of the samples using universal testing machine, scanning electron microscope (SEM).

Setting and Design:

In vivo – comparative study.

Materials and Methods:

60 samples were fabricated from VITA (vita zahnfabrik. Bad sackingen, Germany) zirconia discs. Samples were divided into 4 groups with 15 samples each. First is the control group, second is lithium disilicate glass–ceramic liner group, third is silicon dioxide based liner, and fourth is glass–ceramic interlayer group. SBS of samples was recorded using universal testing machine. Samples were further analyzed for fractographic behavior using SEM.

Statistical Analysis Used:

One Way ANOVA test, and Chi-Square test.

Results:

The intergroup comparison of mean SBS (Mpa) was done using the post hoc Bonferroni test. The mean SBS (Mpa) was significantly more among lithium disilicate and glass–ceramic interlayer groups in comparison to silicon dioxide-based liner group. Fractographic analysis was done using the Chi-square test.

Conclusion:

It was concluded that maximum SBS was obtained for lithium disilicate liner. Maximum adhesive failures were found with lithium disilicate liner, and silicon dioxide-based liner group showed cohesive failures.

Comparing two intraoral porcelain repair systems for shear bond strength in repaired cohesive and adhesive fractures, for porcelain-fused-to-metal restorations: An in vitro study

Aim

The objective of research was to evaluate the shear bond strength of two commercially available intraoral porcelain repair systems, Clearfil repair system (Kuraray) and P and R repair system (Shofu) for repairing cohesive and adhesive fracture in metal-ceramic restorations.

Settings and Design

In vivo - comparative study.

Materials and Methods

Ninety samples of Nickel-Chromium metal discs were fabricated. Each disc was veneered with 2 mm thickness of ceramic material using custom made metal jig. Samples were divided into control (Group I n = 10) and two test groups (Group II n = 40 and Group III n = 40). Adhesive and cohesive fractures were created in test group samples, Group II (Ceramic substrate or cohesive defect) and Group III (metal substrate or adhesive defect). The samples of ceramic substrate (Group II) and metal substrate (Group III) were further subdivided into A and B containing 20 samples each according to the repair material used (A; Clearfil porcelain repair system and B; P and R porcelain repair system). All specimens were subjected to a standard shear load in the UTM until fracture occurred. Data were analyzed using one-way analysis of variance and post hoc Bonferroni test.

Statistical Analysis used

One-way analysis of variance (ANOVA) and post hoc Bonferroni test.

Results

Clearfil repair system showed significantly higher shear bond strength value (29.16 Mpa) as compared to P and R repair system (27.23 Mpa) for cohesive fractures. Whereas if compared for repairing adhesive fractures P and R repair system had significantly higher shear bond strength values (26.59 Mpa) than Clearfil repair system (25.74 Mpa).

Conclusions

From the present study, it was be concluded that for cohesive fracture Clearfil repair system is a better material and for adhesive fractures P and R repair material gives better results.

Influence of Radius of Curvature at Gingival Embrasure in Connector Area on Stress Distribution of Three-Unit Posterior Full-Contour Monolithic Zirconia Fixed Partial Denture on Various Amounts of Load Application: A Finite Element Study

Objectives

To test the hypothesis that radius of curvature at gingival embrasure in connector area significantly affects the fracture resistance of full-contour monolithic zirconia three-unit posterior Fixed partial denture (FPD) on various amounts of load application.

Materials and Methods

In this study, two types of three-dimensional finite element models of a three-unit posterior full-contour monolithic zirconia FPD with two gingival embrasure radii (r_GE I, 0.45 mm and r_GE II, 0.25 mm) were constructed. The components modeled through finite element modeling were subjected to 400, 600, and 800 N vertical loads at the central fossa of the pontic, and further analysis was carried out.

Results

All the results were displayed by post-processor finite element analysis software (ANSYS). The study revealed that with increase in the amount of load application as well as decrease in the gingival embrasure radii, stress concentration values were increasing gradually for both the full-contour monolithic zirconia FPD.

Conclusion

The fracture resistance of the zirconia posterior FPD was significantly affected by the gingival embrasure radii and the mode of load application. When there is a clinical situation of heavier occlusal forces, the fracture resistance can be increased by designing greater gingival embrasure radii in the connector region.

Effect of slow-cooling protocol on biaxial flexural strengths of bilayered porcelain-ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks

OBJECTIVE

The present study investigated the biaxial flexural strengths of bilayered ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks with various layering porcelains veneered using a slow-cooling protocol.

METHODS

Five porcelain materials (VITA VM9, Cercon Ceram Kiss, and Vintage ZR with experimental coefficient of thermal expansions; CTEs of 8.45, 9.04, and 9.61ppm/°C) were veneered on Ce-TZP/A disks and slow-cooled after firing to fabricate bilayered specimens (core-to-porcelain thickness: 0.8mm/1.5mm). Biaxial flexural strengths of the specimens with the porcelain layer in tension were tested based on the piston-on-three-ball method (ISO 6872:2008). The data were statistically analyzed using Weibull distribution and Fisher's exact test.

RESULTS

Tensile stresses were observed in the entire porcelain layer while compressive stress at the surface of the Ce-TZP/A layer shifted to tensile stress at the interface between the materials. The cases of small CTE mismatches between the materials showed high Weibull characteristic strengths at the internal and external surfaces of the specimens, except the VM9 group (CTE: 9.0-9.2ppm/°C). The maximum tensile stress was observed on the surface of the porcelain layer, where cracks originated and continuously propagated into the Ce-TZP layer. The Ce-TZP/A fractured into two pieces for large CTE mismatches between the materials, resulting in significantly lower flexural strengths than those fracturing into three pieces for small CTE mismatches.

SIGNIFICANCE

Flexural strengths and fracture behaviors of bilayered porcelain-Ce-TZP/A disks were influenced by the CTE mismatches, and a small CTE mismatch between the materials was preferred when using a slow-cooling protocol.

Evaluation of mold-enclosed shear bond strength between zirconia core and porcelain veneer

This study aimed to evaluate the mold-enclosed shear bond strength (ME-SBS) of zirconia to veneering porcelain with different surface treatments. Colored or uncolored zirconia coupons were either highly polished or airborne-particle abraded. The specimens were divided into groups with/without application of liner. Veneering porcelain was fired into an alumina ring mold on the zirconia coupons. The assembled specimens were subjected to the ME-SBS test. The mean ME-SBS for groups ranged from 7-10 MPa with no significant difference (p>0.05). A three-way ANOVA showed that coloring and surface roughening of the zirconia specimen had no significant influence on the ME-SBS value, but liner application exhibited a significant effect with a minor decrease in the MESBS (p=0.049). Surface treatments (coloring, airborne-particle abrasion, and liner application) were found to not cause a significant increase to the zirconia-porcelain bond strength. The application of zirconia liner had a slight negative influence on the ME-SBS results.

Effect of ceramic cooling protocols and zirconia coloring on fracture load of zirconia-based restorations

Background:

Residual thermal stresses in dental porcelains can cause clinical failure. Porcelain cooling protocols may affect the amount of residual stresses within porcelain and also porcelain–zirconia bond strength. The objective of this study was to assess the effect of cooling protocols on the fracture load of porcelain veneered zirconia restorations.

Materials and Methods:

Forty zirconia bars (31 mm × 6.5 mm × 1.35 mm ± 0.1 mm) were fabricated by computer-aided design and computer-aided manufacturing technology. Half of the specimens were immersed in the coloring agent for 2 min before sintering (yellow group). Thus, the specimens were divided into two groups of white (W) and yellow (Y) samples (n = 20). Heat-pressed ceramic was applied to all bars. After pressing, half of the samples in each group were immediately removed from the oven (fast cooling) while the other specimens remained in the partially open door (30%) oven until the temperature reached to 500°C. Samples were thermocycled for 5000 cycles and subjected to modified four-point flexural strength test by a universal testing machine at a crosshead speed of 0.5 mm/min. Two-way ANOVA, One-way ANOVA followed by post hoc Tukey honest significant difference tests were used for data analysis (α = 0.05).

Results:

Fractures were cohesive in all samples (within the porcelain adjacent to the interface). Two-way ANOVA showed that the effect of cooling protocol on the fracture load of samples was statistically significant (P < 0.001). In addition, the fracture load of W and Y groups was significantly different (P < 0.001). The white slow group showed the highest fracture load (179.88 ± 23.43 N).

Conclusion:

Slow cooling protocol should be preferably applied for zirconia restorations. Coloring agent used in this study had a significant negative effect on fracture load.

Pre-sintered Y-TZP sandblasting: effect on surface roughness, phase transformation, and Y-TZP/veneer bond strength

Sandblasting is a common method to try to improve the Y-TZP/veneer bond strength of dental prostheses, however, it may put stress on zirconia surfaces and could accelerate the t→m phase transformation. Y-TZP sandblasting before sintering could be an alternative to improve surface roughness and bonding strength of veneering ceramic.

Effect of Firing Temperature at the Porcelain-Metal Alloy Interface in Porcelain-Fused-to-Metal Restorations. A SEM/EDS Study

PURPOSE

To probe in greater detail the changes at the ceramometal interface induced by heat energy absorption, using energy diffraction X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) and correlate these changes with the shear bond strength of porcelain to nickel chromium alloy.

MATERIALS AND METHODS

Seventy-five strips of nickel-chromium alloy (20 mm long, 5 mm wide, 3 mm thick) were prepared and layered with porcelain, conforming to ANSI/ADA specification no. 38 (for Metal-Ceramic Dental Restorative Systems: 2010). These test specimens were divided equally into three groups. Specimens of each group (25) were fired to a specific temperature range, that is 700°C, 900°C, and 960°C. SEM and EDS were performed on all specimens, at the metal alloy/ceramic interface. Bonding of the ceramic layer to the metal alloy was evaluated by a shear bond strength test as per ANSI/ADA specification no. 38. The data were recorded and analyzed using one-way ANOVA and post hoc Tukey HSD test.

RESULTS

SEM images of the porcelain/metal alloy interface revealed roughness of the metal alloy surface adjacent to the ceramic layer. EDS study revealed that an oxygen depletion zone was formed at the interface region, facilitating the formation of intermetallic compounds. The mean shear bond strength showed an upward trend until 900°C and decreased thereafter.

CONCLUSION

Formation of intermetallic compounds at the interface, in the presence of an oxygen depletion zone, was the prime factor in bonding of porcelain to metal alloy. This provides a new concept of ceramometal bonding.

To Evaluate Effect of Airborne Particle Abrasion using Different Abrasives Particles and Compare Two Commercial Available Zirconia on Flexural Strength on Heat Treatment

BACKGROUND AND OBJECTIVE

The popularity of ceramic restorations can be attributed to its life-like appearance, durability and biocompatibility and therefore ceramic restorations have been widely used for anterior and posterior teeth. Ceramic restorations have esthetic and biocompatible advantages but low fracture resistance. Since it has high flexural strength and fracture resistance, yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) is the dental material most commonly used for the core of ceramic crowns and fixed dental prosthesis. In spite of improved mechanical properties, acceptable marginal adaptation and biocompatibility the whitish opacity of zirconia is an obvious esthetic disadvantage. The zirconia framework is often veneered with conventional feldspathic porcelain to achieve a natural appearance. However it is difficult to achieve sufficient bond strength between zirconia and the veneering material. Achieving sufficient bond strength between the veneering ceramic and the zirconia core is a major challenge in the long term clinical success of veneered zirconia restorations. The main objective of this study is to evaluate the effect of different surface treatments on the fracture strength of the two commercially available Zirconia namely Ceramill and ZR-White (AMANNGIRRBACH and UPCERA) respectively.

METHOD

Two commercially available pre-sinteredyttrium stabilized Zirconia blanks (ZR-White and Ceramill) from AMANNGIRRBACH and UPCERA respectively are used to produce the disc shaped specimens of size (15.2 ± 0.03 mm in diameter and 1.2 ± 0.03 mm thick) from each Zirconia blank. All disc shaped specimens are heated at 1200°C in a furnace for 2 hours to form homogenous tetragonal ZrO₂. The dimensions of the specimens are measured with a digital caliper (aerospace). The thickness and diameter of each specimen are calculated as the means of 3 measurements made at random sites. 80 discs from each Zirconia blank are divided into ten groups of 8 specimens each. Heat treatment after airborne-particle abrasion using 50 µm Al₂O₃ particles and 50 µm silica coated Al₂O₃ are applied to the upper and lower surfaces of the specimens. Each specimen is held under a pressure of 30 psi for 15 seconds at a direction perpendicular to the surface and at a distance of 30mm with an airborne particle abrasion device for the specimens in the airborne particle abraded groups. Heat treatments were performed at a starting temperature of 500°C, heating rate of 100°c/ min, ending at a temperature of 1000°C and 15 minutes holding time without vacuum for the specimens in the group 4, 5, 9 and 10. Airborne-particle abrasion mimicking the preparation for cementation was applied to the lower surfaces with 50 µm alumina and silica coated alumina particles for the specimens in the groups 6, 7, 8, 9 and 10. The specimens were cleaned for 15 minutes in an ultrasonic bath containing distilled water. To determine the fracture strength, a disc of 10 mm diameter was used to place 3 hardened steel balls of 3 mm diameter separated each other by 120 degrees (described in the ISO standard 6872 for dental ceramics). Each specimen was centrally placed on this disc. The lower surface mimicking the internal surface of zirconia was the tension side, facing the supporting device testing, while the upper surface mimicking the external surface of the zirconia core was loaded with a flat punch (1 mm in diameter). A universal testing machine was used to perform the test at a cross head speed of 1mm/min. The failure stress was calculated with the equation listed in ISO 6872. The results were then statistically analyzed. A post hoc test was used for pair wise comparisons.

RESULT

The mean fracture strength of commercially available Zirconia Ceramill (AMANNGIRBACH) showed a significant higher value compared to the ZR-White (UPCERA) Zirconia (P<0.001), Airborne abrasion treatment to the specimens showed a significant difference between the abraded groups and the control group (P<0.001); further AMANNGIRRBACH specimens gave a higher value compare to the UPCERA specimens. The study also revealed that the heat treatment of the specimens gave significant value (P<0.001) compared to the control group, but heat treatment following the air abrasion reduces the fracture strength of the sample than the air abraded group.

CONCLUSION

Within the limitation of this study, it is concluded that, the in vitro fracture strength of Zirconia specimens treated with an airborne abrasion both on the veneering surface (50 µm silica coated Al2O3) and the cementing surface (50 µm Al₂O₃) was significantly higher than the heat treated and the control group. Airborne particle abrasion followed by the heat treatment reduces the fracture strength of the specimen than that ofthe group treated only by the air abrasives. The fracture strength of a commercially available Ceramill (AMANNGIRRBACH) is greater than that of a Zirconia from ZR-White (UPCERA) variety.

Shear bond strength of veneering ceramic to coping materials with different pre-surface treatments

PURPOSE

Pre-surface treatments of coping materials have been recommended to enhance the bonding to the veneering ceramic. Little is known on the effect on shear bond strength, particularly with new coping material. The aim of this study was to investigate the shear bond strength of veneering ceramic to three coping materials: i) metal alloy (MA), ii) zirconia oxide (ZO), and iii) lithium disilicate (LD) after various pre-surface treatments.

MATERIALS AND METHODS

Thirty-two (n = 32) discs were prepared for each coping material. Four pre-surface treatments were prepared for each sub-group (n = 8); a) no treatment or control (C), b) sandblast (SB), c) acid etch (AE), and d) sandblast and acid etch (SBAE). Veneering ceramics were applied to all discs. Shear bond strength was measured with a universal testing machine. Data were analyzed with two-way ANOVA and Tukey's multiple comparisons tests.

RESULTS

Mean shear bond strengths were obtained for MA (19.00 ± 6.39 MPa), ZO (24.45 ± 5.14 MPa) and LD (13.62 ± 5.12 MPa). There were statistically significant differences in types of coping material and various pre-surface treatments (P<.05). There was a significant correlation between coping materials and pre-surface treatment to the shear bond strength (P<.05).

CONCLUSION

Shear bond strength of veneering ceramic to zirconia oxide was higher than metal alloy and lithium disilicate. The highest shear bond strengths were obtained in sandblast and acid etch treatment for zirconia oxide and lithium disilicate groups, and in acid etch treatment for metal alloy group.

Veneered Zirconia-Based Restorations Fracture Resistance Analysis

PURPOSE

To examine the effects of the veneering technique on the fracture resistance of zirconia-based crowns.

MATERIALS AND METHODS

An artificial tooth was prepared with a 1.2 mm heavy chamfer finish line and 8° taper. The prepared tooth was scanned using CAD/CAM technology to fabricate 45 cobalt chromium (CoCr) testing dies. One CoCr die was scanned, and 45 zirconia copings were milled and divided according to the veneering technique into three groups of 15 specimens each: layering veneering (LV) using Vita Vm9, overpressing veneering (OV) using Vita Pm9, and digital veneering (DV) using Vita Triluxe forte. The crowns were cemented onto the testing dies using glass ionomer cement. The specimens were thermocycled (3000 cycles, 5° to 55°) then statically loaded (3.7 mm ball, 0.5 mm/min crosshead speed) until failure. Failed crowns were inspected using a magnifier, and failure patterns were identified. One-way ANOVA and multiple comparison Bonferroni tests were applied for statistical analysis of the results.

RESULTS

Means and standard deviations of failure loads were 1200 ± 306 N for the LV group, 857 ± 188 N for the OV group, and 638 ± 194 N for the DV group. The differences in failure loads were statistically significant between all groups (p < 0.05). Failure mode was predominantly cohesive for LV and OV groups, whereas it was predominantly adhesive for the DV group.

CONCLUSIONS

The LV group was superior to other groups in terms of fracture resistance, while the DV group was inferior to the other groups in the same aspect.

The effect of silane applied to glass ceramics on surface structure and bonding strength at different temperatures

PURPOSE

To evaluate the effect of various surface treatments on the surface structure and shear bond strength (SBS) of different ceramics.

MATERIALS AND METHODS

288 specimens (lithium-disilicate, leucite-reinforced, and glass infiltrated zirconia) were first divided into two groups according to the resin cement used, and were later divided into four groups according to the given surface treatments: G1 (hydrofluoric acid (HF)+silane), G2 (silane alone-no heat-treatment), G3 (silane alone-then dried with 60℃ heat-treatment), and G4 (silane alone-then dried with 100℃ heat-treatment). Two different adhesive luting systems were applied onto the ceramic discs in all groups. SBS (in MPa) was calculated from the failure load per bonded area (in N/mm²). Subsequently, one specimen from each group was prepared for SEM evaluation of the separated-resin–ceramic interface.

RESULTS

SBS values of G1 were significantly higher than those of the other groups in the lithium disilicate ceramic and leucite reinforced ceramic, and the SBS values of G4 and G1 were significantly higher than those of G2 and G3 in glass infiltrated zirconia. The three-way ANOVA revealed that the SBS values were significantly affected by the type of resin cement (P<.001). FIN ceramics had the highest rate of cohesive failure on the ceramic surfaces than other ceramic groups. AFM images showed that the surface treatment groups exhibited similar topographies, except the group treated with HF.

CONCLUSION

The heat treatment was not sufficient to achieve high SBS values as compared with HF acid etching. The surface topography of ceramics was affected by surface treatments.

Comparative evaluation of shear bond strengths of veneering porcelain to base metal alloy and zirconia substructures before and after aging - An in vitro study

OBJECTIVE

The aim of this study was to evaluate and compare the shear bond strength of veneering porcelain to base metal alloy and zirconia substructures before and after aging. Scanning electron microscopy (SEM) was used to determine the failure pattern.

MATERIALS AND METHODS

Twenty rectangular blocks (9 mm length × 4 mm height × 4 mm width) of base metal alloy (Bellabond plus, Bego, Germany) and zirconia (Will ceramZ zirconia K block) were fabricated for shear bond strength test. Surface of the base metal alloy block (4 mm × 4 mm area) was veneered with corresponding veneering porcelain (Ivoclar, IPS classic, vivadent). Similarly, surface of the zirconia rectangular block (4 mm × 4 mm) was veneered with corresponding veneering ceramic (Cercon ceram kiss, Degudent). Out of forty rectangular porcelain veneered core specimen, ten porcelain veneered base metal alloy specimen and ten porcelain veneered zirconia specimen were immersed in water at 37°C for one month to simulate the oral environment.

RESULTS

On comparison, the highest shear bond strength value was obtained in porcelain veneered base metal alloy before aging group followed by porcelain veneered base metal alloy after aging group, Porcelain veneered zirconia before aging group, porcelain veneered zirconia after aging group. SEM analysis revealed predominantly cohesive failure of veneering ceramic in all groups.

CONCLUSION

Porcelain veneered base metal alloy samples showed highest shear bond strength than porcelain veneered zirconia samples. Study concluded that aging had an influence on shear bond strength. Shear bond strength was found to be decreasing after aging. SEM analysis revealed cohesive failure of veneering ceramic in all groups suggestive of higher bond strength of the interface than cohesive strength of ceramic. Hence, it was concluded that veneering ceramic was the weakest link.

Influence of Veneering Fabrication Techniques and Gas-Phase Fluorination on Bond Strength between Zirconia and Veneering Ceramics

PURPOSE

Porcelain chipping has been one of the main problems of porcelain-fused-to-zirconia restorations. This study evaluates the bond strengths of layered, pressed, and adhesively bonded porcelain to yttria-stabilized zirconia substrates that have undergone traditional preparation or gas-phase fluorination.

MATERIALS AND METHODS

A three-point bending test was used to evaluate the bond strength of the porcelain and zirconia interface. Sixty-six specimens were prepared (n = 11) following ISO 9693 and loaded until failure using an Instron testing machine. One-half of the zirconia substrates received gas phase fluorination treatment before veneering application. Three porcelain veneering methods were evaluated: layered, pressed, and adhesively bonded porcelain. Bond strength results were interpreted using a two-way ANOVA and a Bonferroni multiple comparisons test. Statistical significance was set at α = 0.05.

RESULTS

ANOVA revealed a statistically significant effect of the veneering fabrication methods. No main effect was observed regarding the surface treatment to the zirconia. There was a significant effect related to the veneering method used to apply porcelain to zirconia. For untreated zirconia, layered porcelain had a significantly higher flexural strength compared to pressed or bonded, while pressed and bonded porcelains were not significantly different from one another. For zirconia specimens receiving fluorination treatment, both layered and pressed porcelains had significantly higher bond strengths than adhesively bonded porcelain. In addition, fluorinated pressed porcelain was not statistically different from the control layered or fluorinated layered porcelain.

CONCLUSION

The choice of veneering fabrication technique was critical when evaluating the zirconia to porcelain interfacial bond strength. Bonded porcelain to zirconia had a lower flexural strength than layered or pressed porcelain, regardless of zirconia surface treatment. In addition, fluorination had an effect on the bond strength of pressed porcelain.

Evaluation of shear bond strength of veneering ceramics and zirconia fabricated by the digital veneering method

PURPOSE

The purpose of this study was to evaluate the shear bond strength (SBS) of veneering ceramic and zirconia fabricated by the digital veneering method.

METHODS

A total of 50 specimens were fabricated, i.e., 10 specimens each for the metal-ceramic (control) group and the four zirconia groups. The zirconia groups comprised specimens fabricated by the digital veneering method, the heat pressing method, and hand layering method for two groups, respectively. Furthermore, the shear bond strength was measured with a universal testing machine (Model 3345, Instron, Canton, MA, USA) and statistically analyzed using one-way ANOVA set at a significance level of P<0.05. The corresponding mode of failure was determined from Scanning Electron Microscope (FESEM JSM 6701F, Jeol Ltd., Japan) observations.

RESULTS

One-way analysis of variance (ANOVA) revealed that the metal-ceramic group had the highest SBS (43.62MPa), followed by the digital veneering method (28.29MPa), the heat pressing method (18.89MPa), and the layering method (18.65, 17.21MPa). The samples fabricated by digital veneering had a significantly higher SBS than the other zirconia samples (P<0.05). All of the samples exhibited mixed failure.

CONCLUSIONS

Veneering ceramic with a zirconia core that was fabricated via the digital veneering method is believed to be effective in clinical use since, its shear bond strength is significantly higher than that resulting from the conventional method.

Effect of various intermediate ceramic layers on the interfacial stability of zirconia core and veneering ceramics

OBJECTIVES

The purposes of this study were to evaluate the effects of intermediate ceramics on the adhesion between the zirconia core and veneer ceramics.

MATERIALS AND METHODS

The polished surfaces of fully sintered Y-TZP blocks received three different treatments: (1) connector (C), (2) liner (L) or (3) wash layer (W). All the treated zirconia blocks were veneered with either (a) fluorapatite glass-ceramic (E) or (b) feldspathic porcelain (V) and divided into four groups (CE, CV, LE and WV). For the control group, the testing surfaces of metal blocks were veneered with feldspathic porcelain (VM). A half of the samples in each group (n = 21) were exposed to thermocycling, while the other half of the specimens were stored at room temperature under dry conditions. All specimens were subjected to the shear test and the failed surfaces were microscopically examined. The elemental distribution at the zirconia core/veneer interface was analyzed.

RESULTS

The specimens in Groups CE and CV exhibited significantly greater mean bond strength values than those in Groups LE and WV, respectively (p < 0.05). However, the mean bond strengths significantly decreased in the connector groups (CE and CV) after thermal cycling (p < 0.05). The elemental analysis suggested diffusion of ceramic substances into the zirconia surface.

CONCLUSIONS

A glass-ceramic based connector is significantly more favorable to core/veneer adhesion than the other intermediate ceramics evaluated in the study. However, thermal cycling affected the bond strength at the core/veneer interface differently according to the intermediate ceramics.

Effects of coloring procedures on zirconia/veneer ceramics bond strength

PURPOSE

The most common failure seen in restorations with a zirconia core is total or layered delamination of the ceramic veneer. In the present study, the shear bond strengths between veneering ceramics and colored zirconia oxide core materials were evaluated.

MATERIALS AND METHODS

Zirconia discs (15 × 12 × 1.6 mm) were divided into 11 groups of 12 discs each. Groups were colored according to the Vita Classic scale: A3, B1, C4, D2, and D4. Each group was treated with the recommended shading time for 3 s, or with prolonged shading for 60 s, except for the control group. Samples were veneered with 3 mm thick and 3.5 mm in diameter translucent ceramic and subjected to shear test in a universal testing machine with a crosshead speed of 1 mm/min. One-way analysis of variance (ANOVA) and Tukey's HSD tests were used for comparisons of the groups having the same shading times. A paired t-test was used for groups of the same color (3 s/60 s).

RESULTS

Among the 11 groups investigated C4 (3 s) had the highest bond strength with a value of 36.40 MPa, while A3 (3 s) showed the lowest bond strength with a value of 29.47 MPa.

CONCLUSION

Coloring procedures can affect zirconia/ceramic bond strength. However, the results also showed that bond strengths of all the investigated groups were clinically acceptable.

Bond strength and Raman analysis of the zirconia-feldspathic porcelain interface

STATEMENT OF PROBLEM

Zirconia has the best mechanical properties of the available ceramic systems. However, the stability of the zirconia-feldspathic porcelain interface may be jeopardized by the presence of the chipping and debonding of the feldspathic porcelain.

PURPOSE

The purpose of this study is to evaluate the shear bond strength of 3 cold isostatic pressed zirconia materials and a feldspathic veneer by analyzing their interface with micro-Raman spectroscopy.

MATERIAL AND METHODS

The test groups were experimental zirconia, Zirkonzahn zirconia, and Schuetz zirconia. Blocks of partially sintered zirconia were cut into disks (n=20) and then veneered with a feldspathic porcelain. Half of the specimens from each group (n=10) were incubated in 37°C water for 24 hours, and the other half were thermocycled. All the specimens were then subjected to shear testing. The fractured areas were analyzed with optical stereomicroscopy and classified as adhesive, cohesive, or an adhesive-cohesive failure. Spectral patterns were examined to detect bands related to the zirconia and feldspathic porcelain phases. The shear strength data were submitted to 2-way ANOVA.

RESULTS

No significant differences in shear bond strength were observed among the 3 groups, regardless of whether or not the specimens were thermocycled. Adhesive failures were the most prevalent types of failure (70%). Raman spectra were clearly distinguished for all the materials, which showed the presence of tetragonal and monoclinic phases.

CONCLUSIONS

The controlled production of the experimental zirconia did not influence the results of the bond strength. Raman analysis suggested a process of interdiffusion by the presence of peaks associated with the zirconia and feldspathic ceramics.

Zirconia in fixed prosthesis. A literature review

Statement of problem: Evidence is limited on the efficacy of zirconia-based fixed dental prostheses. Objective: To carry out a literature review of the behavior of zirconium oxide dental restorations. Material and Methods: This literature review searched the Pubmed, Scopus, Medline and Cochrane Library databases using key search words “zirconium oxide,” “zirconia,” “non-metal restorations,” “ceramic oxides,” “veneering ceramic,” “zirconia-based fixed dental prostheses”. Both in vivo and in vitro studies into zirconia-based prosthodontic restoration behavior were included. Results: Clinical studies have revealed a high rate of fracture for porcelain-veneered zirconia-based restorations that varies between 6% and 15% over a 3- to 5-year period, while for ceramo-metallic restorations the fracture rate ranges between 4 and 10% over ten years. These results provoke uncertainty as to the long-term prognosis for this material in the oral medium. The cause of veneering porcelain fractures is unknown but hypothetically they could be associated with bond failure between the veneer material and the zirconia sub-structure.

Key words:Veneering ceramic, zirconia-based ceramic restoration, crown, zirconia, tooth-supported fixed prosthesis.

Fracture and shear bond strength analyses of different dental veneering ceramics to zirconia

The purpose of this work was to evaluate the interaction of different layering porcelains with zirconia via shear bond strength test and microscopy. Four different groups of dental veneering porcelains (VM9, Zirkonzanh, Ceramco, IPS) were fused onto forty zirconia-based cylindrical substrates (8mm in diameter and 12 mm in height) (n=10), according to the manufacturer's recommendations. Additionally, layered dental porcelain (D-sign, Ivoclar) was fired on ten Ni-Cr cylindrical substrates Shear bond strength tests of the veneering porcelain to zirconia or Ni-Cr were carried out at a crosshead speed of 0.5mm/min. After the shear bond tests, the interfaces were analyzed by scanning electron microscopy (SEM). The fracture type exhibited by the different systems was also assessed. The results were statistically analyzed by ANOVA at a significant level of p<.05. The shear bond strength values of the porcelain-to-NiCr interfaces (25.3±7.1 MPa) were significantly higher than those recorded for the following porcelain-to-zirconia systems: Zirkonzanh (18.8±1 MPa), Ceramco (18.2±4.7 MPa), and IPS (16±4.5 MPa). However, no significant differences were found in the shear bond strength values between the porcelain-to-NiCr and porcelain (VM9)-to-zirconia (23.2±5.1 MPa) groups (p>.05). All-ceramic interfaces revealed mixed failure type, cohesive in the porcelain and adhesive at the interface. This study demonstrated that all-ceramic systems do not attain yet the same bond strength standards equivalent to metal-ceramic systems. Therefore, despite the esthetic appeal of all-ceramic restorations, the adhesion between the porcelain and zirconia framework is still an issue considering the long term success of the restoration.

A Comparison between Shear Bond Strength of VMK Master Porcelain with Three Base-metal Alloys (Ni-cr-T3, VeraBond, Super Cast) and One Noble Alloy (X-33) in Metal-ceramic Restorations

STATEMENT OF PROBLEM

The increase in the use of metal-ceramic restorations and a high prevalence of porcelain chipping entails introducing an alloy which is more compatible with porcelain and causes a stronger bond between the two. This study is to compare shear bond strength of three base-metal alloys and one noble alloy with the commonly used VMK Master Porcelain.

MATERIALS AND METHOD

Three different groups of base-metal alloys (Ni-cr-T3, Super Cast, and VeraBond) and one group of noble alloy (X-33) were selected. Each group consisted of 15 alloy samples. All groups went through the casting process and change from wax pattern into metal disks. The VMK Master Porcelain was then fired on each group. All the specimens were put in the UTM; a shear force was loaded until a fracture occurred and the fracture force was consequently recorded. The data were analyzed by SPSS Version 16 and One-Way ANOVA was run to compare the shear strength between the groups. Furthermore, the groups were compared two-by-two by adopting Tukey test.

RESULTS

The findings of this study revealed shear bond strength of Ni-Cr-T3 alloy was higher than the three other alloys (94 MPa or 330 N). Super Cast alloy had the second greatest shear bond strength (80. 87Mpa or 283.87 N). Both VeraBond (69.66 MPa or 245 N) and x-33 alloys (66.53 MPa or 234 N) took the third place.

CONCLUSION

Ni-Cr-T3 with VMK Master Porcelain has the greatest shear bond strength. Therefore, employment of this low-cost alloy is recommended in metal-ceramic restorations.

Effect of various intraoral repair systems on the shear bond strength of composite resin to zirconia

PURPOSE

This study compared the effect of three intraoral repair systems on the bond strength between composite resin and zirconia core.

MATERIALS AND METHODS

Thirty zirconia specimens were divided into three groups according to the repair method: Group I- CoJet™ Repair System (3M ESPE) [chairside silica coating with 30 µm SiO₂ + silanization + adhesive]; Group II- Ceramic Repair System (Ivoclar Vivadent) [etching with 37% phosphoric acid + Zirconia primer + adhesive]; Group III- Signum Zirconia Bond (Heraus) [Signum Zirconia Bond I + Signum Zirconia Bond II]. Composite resin was polymerized on each conditioned specimen. The shear bond strength was tested using a universal testing machine, and fracture sites were examined with FE-SEM. Surface morphology and wettability after surface treatments were examined additionally. The data of bond strengths were statistically analyzed with one-way ANOVA and Tamhane post hoc test (α=.05).

RESULTS

Increased surface roughness and the highest wettability value were observed in the CoJet sand treated specimens. The specimens treated with 37% phosphoric acid and Signum Zirconia Bond I did not show any improvement of surface irregularity, and the lowest wettability value were found in 37% phosphoric acid treated specimens. There was no significant difference in the bond strengths between Group I (7.80 ± 0.76 MPa) and III (8.98 ± 1.39 MPa). Group II (3.21 ± 0.78 MPa) showed a significant difference from other groups (P<.05).

CONCLUSION

The use of Intraoral silica coating system and the application of Signum Zirconia Bond are effective for increasing the bond strength of composite resin to zirconia.

Comparison of shear bond strength of two veneering ceramics to zirconia

BACKGROUND

Chip-off fracture of veneering porcelain has been described as the most frequent reason for the failure of zirconia-based fixed partial dentures. The purpose of this study was to evaluate the shear bond strength (SBS) of two commercial zirconia core ceramics to their corresponding veneering ceramics.

MATERIALS AND METHODS

Zirconia disks with 7-mm diameter and 3-mm height were prepared (Cercon and Biodenta systems) and veneered with recommended layering ceramics (Cercon ceram and 2 in 1 ceramic, respectively) (n = 10). The disks were polished with diamond paste and airborne-particle abraded before layering. The specimens were mounted in a T-shaped metal holder using autopolymerized acrylic resin and stored in 37°C distilled water for one week, after which they were subjected to thermal cycling. SBS of zirconia core to veneering ceramic was measured using a universal testing machine and failure modes were determined microscopically. Data were analyzed using t test (α < 0.05).

RESULTS

Mean (±SD) SBS values were 27.19(±3.43) and 28.22(±4.08) MPa for Cercon and Biodenta systems, respectively, with no significant difference. Biodenta system showed more adhesive failure compared to more combined (adhesive and cohesive) failures in Cercon system.

CONCLUSION

Within the limitations of this study it can be concluded that SBS of Biodenta and Cercon specimens were nearly the same, but the fracture mode of these two systems were different. Since Biodenta fracture pattern was predominantly adhesive, it seems that maybe Biodenta porcelain was stronger than Cercon porcelain where as its adhesive bond was weaker.

Confocal Raman microscopy and SEM/EDS investigations of the interface between the zirconia core and veneering ceramic: the influence of a liner and regeneration firing

The aim of this study was to evaluate the changes in the transition layer at the interface between yttria partial stabilized tetragonal zirconia polycrystalline (Y-TZP) core and veneering feldspathic ceramic (VITA VM(®)9), under different manufacturing methods. Confocal Raman microscopy and energy dispersive X-ray spectroscopy (EDS) analyses were carried out on tapered veneered cross sections of the interface. For some samples, an additional firing of the core was used, as the application of an optional liner material between the core and veneer. Single Raman spectra were distinguishable between Y-TZP and the veneering materials. VM(®)9 and liner spectra were broadly superimposable. No substantial differences appeared in their chemical elemental composition. 2D Raman images and EDS analysis emphasized changes in the interdiffusion thickness; the additional firing of the core decreased the interdiffusion zone, and the highest firing temperature of the liner increased the interdiffusion zone. These results, which will help us understand the changes in this transition layer, are discussed.

Influence of surface modification techniques on shear bond strength between different zirconia cores and veneering ceramics

PURPOSE

Veneering porcelain might be delaminated from underlying zirconia-based ceramics. The aim of this study was the evaluation of the effect of different surface treatments and type of zirconia (white or colored) on shear bond strength (SBS) of zirconia core and its veneering porcelain.

MATERIALS AND METHODS

Eighty zirconia disks (40 white and 40 colored; 10 mm in diameter and 4 mm thick) were treated with three different mechanical surface conditioning methods (Sandblasting with 110 µm Al₂O₃ particle, grinding, sandblasting and liner application). One group had received no treatment. These disks were veneered with 3 mm thick and 5 mm diameter Cercon Ceram Kiss porcelain and SBS test was conducted (cross-head speed = 1 mm/min). Two and one way ANOVA, Tukey's HSD Past hoc, and T-test were selected to analyzed the data (α=0.05).

RESULTS

In this study, the factor of different types of zirconia ceramics (P=.462) had no significant effect on SBS, but the factors of different surface modification techniques (P=.005) and interaction effect (P=.018) had a significant effect on SBS. Within colored zirconia group, there were no significant differences in mean SBS among the four surface treatment subgroups (P=0.183). Within white zirconia group, "Ground group" exhibited a significantly lower SBS value than "as milled" or control (P=0.001) and liner (P=.05) groups.

CONCLUSION

Type of zirconia did not have any effect on bond strength between zirconia core and veneer ceramic. Surface treatment had different effects on the SBS of the different zirconia types and grinding dramatically decreased the SBS of white zirconia-porcelain.