Effect of various veneering techniques on mechanical strength of computer-controlled zirconia framework designs

Evaluation of shear bond strength based on substructure materials and ceramic veneering techniques

PURPOSE

Bilayered restorations have both the strength of the substructure material and the esthetics of the veneer material; however, they should have appropriate bonding between the two materials. This study aimed to evaluate the shear bond strength (SBS) according to the substructure material and veneering technique used in bilayered restorations.

MATERIALS AND METHODS

The experimental group was divided into four groups (n = 15 per group) based on the substructure materials (cobalt-chromium [Co-Cr] alloy and 3 mol% yttrium-stabilized tetragonal zirconia polycrystal [3Y-TZP]) and veneering techniques (pressing and layering). Veneering was performed with disk shape (diameter: 5 mm, height: 2 mm) on a substructure using each veneering technique. Shear stress was applied to the interface of the substructure and the veneering ceramic using a universal testing machine. The shear bond strength, according to the substructure and veneering technique, was analyzed using a two-way analysis of variance with a post-hoc Tukey's honestly significant difference test. The failure mode was observed, and the surface was analyzed using a scanning electron microscope and energy-dispersive spectroscopy.

RESULTS

The shSBS of the Co-Cr alloy and 3Y-TZP substructure was not different (p > 0.05); however, the pressing technique showed a higher SBS than the layering technique (p < 0.05). The SBS did not differ depending on the veneering technique in the Co-Cr alloys (p > 0.05), whereas the SBS in the pressing technique was higher than that in the layering technique for 3Y-TZP (p < 0.05). In the layering technique, the Co-Cr alloy showed a higher SBS than 3Y-TZP (p < 0.05). In the failure mode, mixed failure occurred most frequently in all groups. Extensive elemental interdiffusion was observed through the opaque layer in the Co-Cr alloy, regardless of the veneering technique. In 3Y-TZP, a wider range of elemental interdiffusion was observed in the pressing technique than in the layering technique.

CONCLUSIONS

In bilayered restorations with a 3Y-TZP substructure, the pressing technique yielded higher bonding strength than layering. Using the layering technique, 3Y-TZP showed a lower SBS than the Co-Cr alloy. In bilayered restorations using 3Y-TZP as a substructure, the veneering technique and thermal compatibility of the materials must be considered.

Color match of ultra-translucency multilayer zirconia restorations with different designs and backgrounds

PURPOSE

The purpose of this in vitro study was to assess the color match of ultra-translucency multilayer zirconia restorations with different designs and backgrounds.

MATERIALS AND METHODS

Thirty ultra-translucency multilayer zirconia crown specimens were made in VITA classical shade B2 for a prepared maxillary central incisor. The specimens were divided into three groups based on the restoration design: veneered zirconia with a trestle design (VZT), veneered zirconia with a dentin core design (VZD), and full-contour zirconia (FCZ). In the groups VZT and VZD, the zirconia specimens were layered with a feldspathic veneering ceramic. The specimens were seated on five different backgrounds: shade B2 composite resin, shade B2 zirconia, copper-colored metal alloy, silver-colored metal alloy, and the prepared central incisor. CIELab values of the labial middle sections of the crown specimens were measured with a spectrophotometer. Color differences between the specimens and a shade B2 VITA classical tab (as a control) were calculated from the ΔE* ab formula and compared with an acceptability threshold (ΔE* ab = 3.7) to be clinically explicated.

RESULTS

Mean ΔE* ab values ranged between 1.17 and 8.48. The restoration design, the background type, and their interaction affected the ΔE* ab (p < 0.001). The mean ΔE* ab values for VZT with all backgrounds and for VZD with the silver-colored metal background were greater than the threshold (p < 0.001), whereas the mean ΔE* ab values for VZD with the other backgrounds and FCZ with all backgrounds were less than the threshold (p = 1).

CONCLUSIONS

Restoration design and background type affected the color match of ultra-translucency multilayer zirconia restorations. VZT restorations on all backgrounds and VZD restorations on a silver-colored metal background showed color mismatches. However, VZD restorations on the other backgrounds and FCZ restorations on all backgrounds demonstrated color matches.

FEA Comparison of the Mechanical Behavior of Three Dental Crown Materials: Enamel, Ceramic, and Zirconia

The restoration of endodontically treated teeth is one of the main challenges of restorative dentistry. The structure of the tooth is a complex assembly in which the materials that make it up, enamel and dentin, have very different mechanical behaviors. Therefore, finding alternative replacement materials for dental crowns in the area of restorative care isa highly significant challenge, since materials such as ceramic and zirconia have very different stress load resistance values. The aim of this study is to assess which material, either ceramic or zirconia, optimizes the behavior of a restored tooth under various typical clinical conditions and the masticatory load. A finite element analysis (FEA) framework is developed for this purpose. The 3D model of the restored tooth is input into the FEA software (Ansys Workbench R23)and meshed into tetrahedral elements. The presence of masticatory forces is considered: in particular, vertical, 45° inclined, and horizontal resultant forces of 280 N are applied on five contact points of the occlusal surface. The numerical results show that the maximum stress developed in the restored tooth including a ceramic crown and subject to axial load is about 39.381 MPa, which is rather close to the 62.32 MPa stress computed for the natural tooth; stresses of about 18 MPa are localized at the roots of both crown materials. In the case of the zirconia crown, the stresses are much higher than those in the ceramic crown, except for the 45° load direction, while, for the horizontal loads, the stress peak in the zirconia crown is almost three times as large as its counterpart in the ceramic crown (i.e., 163.24 MPa vs. 56.114 MPa, respectively). Therefore, the zirconia crown exhibits higher stresses than enamel and ceramic that could increase in the case of parafunctions, such as bruxism. The clinician's choice between the two materials should be evaluated based on the patient's medical condition.

Initial damage and failure load of zirconia-ceramic and metal-ceramic posterior cantilever fixed partial dentures

OBJECTIVES

The aim of this study was to compare failure load and initial damage in monolithic, partially veneered, and completely veneered (translucent) zirconia cantilevered fixed partial dentures (CFPDs), as well as completely veneered metal-ceramic CFPDs under different support and loading configurations.

MATERIALS AND METHODS

Eight test groups with anatomically congruent CFPDs (n = 8/group) were fabricated, differing in CFPD material/support structure/loading direction (load applied via steel ball (Ø 6 mm) 3 mm from the distal end of the pontic for axial loading with a 2-point contact on the inner cusp ridges of the buccal and oral cusps and 1.3 mm below the oral cusp tip for 30° oblique loading): (1) monolithic zirconia/CoCr abutment teeth/axial, (2) monolithic zirconia/CoCr abutment teeth/oblique, (3) partially veneered zirconia/CoCr abutment teeth/axial, (4) partially veneered zirconia/CoCr abutment teeth/oblique, (5) completely veneered zirconia/CoCr abutment teeth/axial, (6) completely veneered CoCr/CoCr abutment teeth/axial (control group), (7) partially veneered zirconia/implants/axial, and (8) partially veneered zirconia/natural teeth/axial. Restorations were artificially aged before failure testing. Statistical analysis was conducted using one-way ANOVA and Tukey post hoc tests.

RESULTS

Mean failure loads ranged from 392 N (group 8) to 1181 N (group 1). Axially loaded monolithic zirconia CFPDs (group 1) and controls (group 6) showed significantly higher failure loads. Oblique loading significantly reduced failure loads for monolithic zirconia CFPDs (group 2). Initial damage was observed in all groups except monolithic zirconia groups, and fractography revealed design flaws (sharp edges at the occlusal boundary of the veneering window) in partially veneered zirconia CFPDs.

CONCLUSIONS

Monolithic zirconia CFPDs might be a viable alternative to completely veneered CoCr CFPDs in terms of fracture load. However, oblique loading of monolithic zirconia CFPDs should be avoided in clinical scenarios. Design improvements are required for partially veneered zirconia CFPDs to enhance their load-bearing capacity.

CLINICAL RELEVANCE

Monolithic zirconia may represent a viable all-ceramic alternative to the established metal-ceramic option for CFPD fabrication. However, in daily clinical practice, careful occlusal adjustment and regular monitoring should ensure that oblique loading of the cantilever is avoided.

The influence of core-build up materials on biaxial flexural strength of monolithic strength-gradient zirconia; an in-vitro study

BACKGROUND

Since their introduction, there has been limited research regarding the mechanical properties of novel strength-gradient monolithic zirconia. In addition to that, studies evaluating the effect of different core-build materials on the strength of indirect restorations are scarce. Therefore, the aim of this study was to investigate the effect of using different core build-up materials on biaxial flexural strength of a new monolithic multilayered zirconia material.

METHODS

Forty zirconia discs were fabricated from IPS e.max ZirCAD Prime (Ivoclar Vivadent AG, Schaan, Liechtenstein) and divided into 2 groups (n = 20). Forty composite discs were prepared from Tetric N-Ceram (Ivoclar Vivadent AG, Schaan, Liechtenstein) and MultiCore Flow (Ivoclar Vivadent AG, Schaan, Liechtenstein). The zirconia discs were adhesively cemented to the 2 types of composite forming 2 groups (Zirconia-Tetric N-Ceram and Zirconia-MultiCore Flow). Biaxial flexural strength was determined using a piston-on-3-ball test. The data were statistically analyzed with an independent t-test for significant differences (p = 0.05).

RESULTS

Tetric N-Ceram had significantly higher strength than MultiCore Flow (p < 0.001) but no statistically significant differences were found in strength values between Zirconia-Tetric N-Ceram and Zirconia-MultiCore Flow bilayered samples (p = 0.27).

CONCLUSIONS

It was concluded that although the tested composite core materials significantly differ in their biaxial flexural strength values, they had no influence on the biaxial flexural strength of the overlying zirconia.

Shear bond strength characteristics on surface treatment modalities of CAD-CAM resin polymers

PURPOSE

The purpose of this in vitro study was to analyze the shear bond strength of composite resin to a commercially available high-performance polymer material for fixed, screw-retained full arch restorations.

MATERIAL AND METHODS

A total of 135 computer-aided design and computer-aided manufacturing, high-performance polymer (HPP) blocks were cut and obtained from discs (Trilor 95, Harvest Dental, Brea, CA). The samples were 10 mm × 10 mm × 10 mm. The specimen surfaces were grouped as untreated (Group A), 50 μm Al2O3 (Group B), 110 μm Al2O3 (Group C), Rocatec (3 M, St. Paul, MN) activated with silica-modified alumina oxide treatment (Group D); and trimmed coarsely with a carbide bur (Group E). Group A samples were used as controls. After surface treatments, the specimens were gently cleansed with oil-free steam and alcohol wipes. Surface conditioning was performed on all physically treated samples.  The manufacturer's recommendations were followed for bonding composite resin to the samples with light-cured Visio.link (Bredent, Chesterfield, UK). Cylinders were veneered with composite resins (diameter 5 mm, height 4 mm) and polymerized on the specimen surfaces through plastic tubes. Twenty-seven specimens were used for each testing group and aging tests were performed. The experimental samples were thermocycled.  Shear bond strength and scanning electron microscopic tests were performed. Means and standard deviations were calculated.  Statistical analysis was performed with post-hoc Tukey tests.

RESULTS

Statistical analysis revealed that there was a significant difference between the groups (p<0.001). The highest shear bond strengths were achieved for the specimens bonded with Visio.link without physical surface treatments (270.47 MPa). The lowest bond strengths were found for specimen surfaces abraded with 110 μm Al2O3 (117.03 Mpa) CONCLUSIONS: The results of this laboratory study indicated that the specimens used with Visio.link as provided by the manufacturer had the highest shear bond strengths between the composite resin and high-performance polymer test specimens. Modifications of the high-performance polymer surfaces with carbide burs did not change bonding strengths with the composite materials.

Digital versus conventional veneering of zirconia and cobalt chromium crowns: Fracture load before and after thermomechanical aging

STATEMENT OF PROBLEM

To complement the digital workflow for manufacturing fixed dental prostheses, both high-strength frameworks and esthetic veneers should be designed and fabricated digitally. However, how the fracture load of digitally veneered restorations compares with conventionally fabricated restorations is unclear.

PURPOSE

The purpose of this in vitro study was to examine the fracture load of digitally and conventionally veneered zirconia and cobalt chromium crowns initially and after thermomechanical aging.

MATERIAL AND METHODS

Milled zirconia and cobalt chromium copings for a maxillary canine were fabricated (N=96). Digital veneers were milled and connected to the copings with a sintered ceramic slurry. The conventional veneers were fabricated by using a master mold, and the crowns were bonded to the cobalt chromium abutments. Half the specimens were subjected to 6000 thermal (5 °C to 55 °C, 60 seconds) and 1 200 000 mechanical (50 N, 1.5 Hz, 0.7 mm lateral movement) cycles opposed by steatite antagonists, and the fracture load was determined. Fracture types were categorized, and scanning electron microscopy performed. The data were analyzed with a 3-way global univariate analysis of variance, t test, the Pearson chi-squared test, and the Weibull modulus (α=.05).

RESULTS

Unlike the framework material (P=.316) and artificial aging (P=.064), the veneering protocol affected the fracture load (P=.007). Digital veneers (range: 2242 to 2929 N) led to lower values than conventional veneers (range: 2825 to 3166 N), which was significant for aged cobalt chromium copings (P=.024; 2242 versus 3107 N). Conventionally veneered crowns showed lower Weibull moduli after thermomechanical aging (range: 3.2 to 3.5) than initially (range: 7.8 to 11.4). The copings of all the zirconia specimens fractured, while chipping occurred with the cobalt chromium specimens.

CONCLUSIONS

The high fracture load values of the veneered crowns, even after simulated 5-year aging, indicated sufficient mechanical properties (nearly 4-fold the average occlusal force of 600 N) for the successful clinical application of digitally veneered zirconia and cobalt chromium copings.

Effect of CAD-CAM Framework Design Fabricated from Sintered Cobalt-Chromium Alloy on Fracture Resistance of Metal-Ceramic Restorations

Introduction

Porcelain fracture is a common problem of metal-ceramic restorations (MCRs). One suggested strategy to prevent it is to modify the metal framework design; however, the available information regarding the effect of framework design on porcelain fracture is scarce.

Objective

This study aimed to assess the effect of computer-aided design and computer-aided manufacturing (CAD-CAM) framework design fabricated from sintered cobalt-chromium (Co-Cr) alloy on fracture resistance of MCRs.

Materials and Methods

Twenty premolar metal dies were fabricated for this in vitro study. Ten standard frameworks were designed with 0.5 mm thickness, and 10 customized frameworks were designed with 1 mm thickness at the lingual margin and 0.5 mm thickness in all other areas. All specimens were fabricated from sintered Co-Cr alloy (Ceramill Sintron) using soft metal milling technology. After porcelain application, the specimens underwent thermocycling and cyclic loading for 3,000 cycles between 5 and 55°C. The fracture resistance was measured by a universal testing machine. The failure mode was also determined. Data were statistically analyzed by independent t-test (α = 0.05).

Results

The mean fracture resistance of porcelain was 2,379 ± 531 N in the standard and 2,557 ± 448 N in the customized group. No significant difference was found in fracture resistance of the two groups (P > 0.05). All specimens in both groups showed mixed failure.

Conclusion

The fracture resistance of porcelain and the failure mode were not affected by the framework design of MCRs fabricated from sintered Co-Cr alloy (Ceramill Sintron).

Four-point flexural strength and microtensile bond strength of digitally and conventionally veneered zirconia

This study intended to evaluate the effect of digital veneering on four-point flexural strength (FS) and microtensile bond strength (μTBS) of veneered zirconia. Two different zirconia blocks, a lithium disilicate and a feldspathic ceramic block, and two different layering ceramics were used. IPS e.max Zir CAD (ZC) and Vita In-Ceram YZ (YZ) with yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) were used as substructures. IPS e.max CAD (LD), Vita Mark II (VMII), IPS e.max Ceram (EC) and Vita VM9 (VM9) were used for veneering. Resin cement and fusion ceramic were placed between veneer and zirconia substructure for digital veneering. A total of one hundred and fifty specimens in five groups (n = 30) were prepared for FS and tested in universal machine at 1.0 mm/min. One hundred specimens in five groups (n = 20) were obtained for the μTBS and tested at 1.0 mm/min. Statistical analysis was made by one way ANOVA and Tukey HSD. Conventional veneering showed statistically significant FS. ZC veneered with EC had the highest mean FS and the lowest was obtained in groups veneered through resin cement. YZ layered with VM9 had the highest mean μTBS. ZC veneered through fusion ceramic and YZ veneered through resin cement showed significantly lower and similar μTBS.

Effect of Nanosilica Incorporation on Flexural Strength, Shear Bond Strength, and Color of Veneering Porcelain after Thermocycling

AIM: The focus of this research was to see how silica nanoparticles changed veneering porcelain over a zirconia core affected flexure strength, shear bond strength, and color. METHODS: A total number of 30 zirconia core veneer samples were constructed and classified according to silica nanoparticles modification of veneering porcelain into two groups: Group 1 (control group) veneering porcelain without any modification (n = 15) and Group 2 (modified group) veneering porcelain modified by silica nanoparticles (n = 15). Silica nanoparticles were added to the veneering porcelain powder at a rate of 5% by weight. Silica nanoparticles powder and veneering porcelain powder were manually crushed for about 10 min using a pestle and mortar then the mixed powder was combined with the porcelain moldings liquid to make a paste. After thermal cycling, each group was examined for flexural strength, shear bond strength, and color measurement (n = 5). Universal testing equipment was used to determine flexural and shear bond strength. The color shift was measured using a spectrophotometer. RESULTS: Flexural strength levels in the modified group (280.9 ± 29.85 Mpa) were substantially higher than in the control group (431.78 ± 22.73 Mpa). Shear bond strength values in the modified group (34.31 ± 5.6) were significantly higher than in the control group (26.97 ± 4.03). Color change was within the clinical acceptable range (1.71 ± 0.32). CONCLUSIONS: The addition of silica nanoparticles to veneering porcelain improved the flexural and shear bond strength, as well as, color change was within the clinical acceptable limits.

Fracture Resistance of Sintered Monolithic Zirconia Dioxide in Different Thermal Units

The purpose of this study was to compare the fracture strength of monolithic zirconium dioxide subjected to a sintering process in two different furnaces: InFire HTC Speed and CEREC SpeedFire. Methods: Forty restorations were designed and machined using a computer aided design / computer aidded machine (CAD/CAM) system. The restorations were randomly assigned to two groups of 20 samples each, Group 1 for the SpeedFire furnace (fast sintering) and Group 2 for the InFire furnace (slow sintering). Each of the crowns was subjected to a maximum compression load recorded in Newtons (N) and a displacement control with a speed of 1 mm/min. Results: Group 1 presented an average of 1222.8 N and a standard deviation of 136.91 N. Group 2 obtained a mean of 1068.5 N and a standard deviation of 316.39 N. Conclusions: There were no significant differences between the two groups, and the mechanical strength of the material was not affected, which would imply a saving of clinical and laboratory time when performing rapid sintering on monolithic translucent zirconium dioxide restorations. However, rapidly sintered restorations have limited reliability.

Prospective 5-year clinical evaluation of posterior zirconia fixed dental prostheses veneered with milled lithium disilicate (CADon)

OBJECTIVE

Bi-layer zirconia-based posterior fixed dental prostheses (FDPs) have reportedly a high incidence of veneering ceramic fractures. The CADon technique employs zirconia frameworks veneered with milled lithium disilicate glass-ceramic to overcome these shortcomings but long-term clinical studies are missing. This study evaluated the clinical efficacy of posterior 3-unit CADOn FDPs over a 5-year period.

MATERIALS AND METHODS

A total of 25 patients, 16 male and 9 female with a mean age of 55.6 years, received a total of 25 posterior three-unit CADOn FDPs. Patients were recalled for baseline and for follow-up visits at 6, 12, 24, and 60 months. Parameters evaluated were fracture, marginal adaptation, marginal discoloration, wear, polish, color match, surface staining, and retention of these restorations as well as secondary caries of the abutment teeth.

RESULTS

A total of 21 FDPs evaluated at 60-months revealed a 100% survival rate. All evaluated clinical parameters were satisfactory (alpha or bravo) and there was no statistically significant difference at different time points, except for surface staining, which was also worse at 60 months compared to baseline (p  ≤  0.001).

CONCLUSIONS

CADOn three-unit posterior FDPs demonstrate excellent fracture resistance after 5 years of clinical function. All evaluated clinical parameters were satisfactory, except for surface stain, which also increased over time.

CLINICAL SIGNIFICANCE

Conventionally veneered bi-layer zirconia-based posterior FDPs have limited clinical success. Based on this study, alternative methods such as zirconia frameworks veneered with milled lithium disilicate glass-ceramic provide a viable alternative with excellent long-term clinical outcomes.

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

Purpose

To evaluate the fracture resistance and fracture mode of high-translucency monolithic zirconia (HTZ) crowns and porcelain-veneered zirconia (PVZ) crowns.

Material and methods

A 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.

Results

The 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.

Conclusion

The 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.

Effect of processing methods on the chipping resistance of veneered zirconia

OBJECTIVES

To evaluate the edge chipping resistance (R_eA) and the fracture toughness (K_C) of 3Y-TZP bilayers produced with the following materials/processing combinations: fluorapatite glass-ceramic applied on zirconia using the traditional layering and hot-pressing (press-on) techniques; feldspathic porcelain using rapid layer technology (RLT); and lithium disilicate glass-ceramic using CAD-on method. The influence of the cooling rate (slow and fast) was analyzed for layering and hot-pressing.

METHODS

Bilayer bars (25x4x2 mm) were made following manufacturers' instructions. The edge chipping test was performed in an universal testing machine, using a coupled Vickers indenter. R_eA was calculated dividing the critical load at fracture by the edge distance. Fracture toughness was calculated by a regression fit with a fixed slope of 1.5 correlating the critical chipping load regarding edge distance and also with indentation fracture (IF) method. Data were statistically analyzed using ANOVA and Tukey's test (α = 5%).

RESULTS

R_eA and K_C was significantly higher for the CAD-on bilayers. RLT showed intermediate R_eA means, and layering and hot-pressing techniques showed the lowest R_eA values. For both processing methods there was no effect of the cooling protocol on the R_eA and fracture toughness.

CONCLUSIONS

There is a significant effect of the material/processing association on the edge chipping resistance and fracture toughness of the bilayers. There was no effect of the cooling protocol on the edge chipping resistance and fracture toughness for the specimens processed by both the layering and hot-pressing techniques.

On the behaviour of zirconia-based dental materials: A review

Zirconia-based dental materials are extensively used in clinical practice due to their tooth-like appearance, biofunctionality, biocompatibility, and affordability. However, premature clinical failures of veneering porcelains raise a concern about their integrity. Extensive studies have been performed over a decade to resolve this issue, but it is challenging to reference all information effectively. A single source identifying the significance of potential parameters on material performance has not previously been available. An evidence-based meta-narrative review technique was used to review the characteristic parameters that can affect the overall behaviour of zirconia-based materials. Keywords were chosen to assess manuscripts based on scientific coherence with this paper's research objective. Online keyword searches were carried out on ScienceDirect, PubMed, and SAGE databases for relevant published manuscripts from year 1985-2020.261 out of 3170 identified manuscripts were included. A total of 10 parameters were identified and classified into the material, manufacturing, and geometric aspects. The effect of every parameter was reviewed on the performance of the material. A discrepancy in findings was observed and is attributed to the fact that there is no standard methodology. This review acts as a single source that summarizes various parameters' contribution to zirconia-based dental materials' performance. This review facilitates manufacturing improvements by accounting for every parameter's effect on overall performance.

Clinical wear and quality assessment of monolithic and lithium disilicate layered zirconia restorations

BACKGROUND

Wear and quality assessments of translucent monolithic zirconia and CAD-on^® restorations were performed.

METHODS

Forty 3-unit posterior fixed partial denture (FPD) in 18 patients (age:18-50 years) were made from translucent monolithic zirconia (tm) (Zenostar T) and zirconia-frameworked, lithium disilicate layered (c) (CAD-on), materials in a split-mouth design. Restorations were digitally fabricated and their internal and marginal adaptations were measured before cementation followed by luting (Multilink Speed). Clinical evaluations were made by modified United States Public Health Service criteria at baseline, 6, 12, and 24-months. Wear of the restorations and the antagonists were digitally evaluated after optical scanning of stone casts at 1st week and 24 m through a software (Cerec 4.4). Statistical analysis was made (analysis of variance, Shapiro-Wilk, Friedman and Wilcoxon tests (SPSS 20)) at α = 0.05 significance level.

RESULTS

At 24 m, all restorations were clinically acceptable. Insignificant differences were found between tm and c restorations (P > 0.05). Mean internal and marginal adaptation of c restorations were significantly better (145 µm (premolar)-174 µm (molar)) than tm (190 µm (premolar)-207 µm (molar)) (P < 0.05). C restorations significantly caused more wear (0.3 ± 0.1 mm) than tm (0.1 ± 0.07 mm) on the antagonistic dentition (P < 0.05).

CONCLUSIONS

Translucent monolithic zirconia restorations caused less wear and antagonist wear than CAD-on restorations. CAD-on restorations exhibited higher internal and marginal adaptation.

Fracture Load of CAD/CAM Fabricated Cantilever Implant-Supported Zirconia Framework: An In Vitro Study

The fracture resistance of computer-aided designing and computer-aided manufacturing CAD/CAM fabricated implant-supported cantilever zirconia frameworks (ISCZFs) is affected by the size/dimension and the micro cracks produced from diamond burs during the milling process. The present in vitro study investigated the fracture load for different cross-sectional dimensions of connector sites of implant-supported cantilever zirconia frameworks (ISCZFs) with different cantilever lengths (load point). A total of 48 ISCZFs (Cercon, Degudent; Dentsply, Deutschland, Germany) were fabricated by CAD/CAM and divided into four groups based on cantilever length and reinforcement of distal-abutment: Group A: 9 mm cantilever; Group B: 9 mm cantilever with reinforced distal-abutment; Group C: 12 mm cantilever; Group D: 12 mm cantilever with reinforced distal-abutment (n = 12). The ISCZFs were loaded using a universal testing machine for recording the fracture load. Descriptive statistics, ANOVA, and Tukey's test were used for the statistical analysis (p < 0.05). Significant variations were found between the fracture loads of the four ISCZFs (p = 0.000); Group-C and B were found with the weakest and the strongest distal cantilever frameworks with fracture load of 670.39 ± 130.96 N and 1137.86 ± 127.85 N, respectively. The mean difference of the fracture load between groups A (810.49 + 137.579 N) and B (1137.86 ± 127.85 N) and between C (670.39 ± 130.96 N) and D (914.58 + 149.635 N) was statistically significant (p = 0.000). Significant variations in the fracture load between the ISCZFs with different cantilever lengths and thicknesses of the distal abutments were found. Increasing the thickness of the distal abutment only by 0.5 mm reinforces the distal abutments by significantly increasing the fracture load of the ISCZFs. Therefore, an increase in the thickness of the distal abutments is recommended in patients seeking implant-supported distal cantilever fixed prostheses.

Effects of porcelain veneering methods on conformity of the marginal and internal fit of three-unit zirconia framework

The purpose of this study is to investigate the effects of porcelain veneering methods on the marginal and internal fit of a three-unit zirconia framework. A zirconia master model, in which the lower-left second premolar and the second left molar were used as the abutment, was obtained using an intraoral scanner. Based on the data, three-unit zirconia frameworks for fabricating all-ceramic bridges were designed and milled (FW group). Two types of all-ceramic bridge were fabricated by veneering porcelain onto these frameworks using the press-over technique (P group) and the layering technique (L group). The replica technique was used to measure the gap size between the abutments and the bridges. Measurements were taken in the marginal opening area (MO), chamfer area (CH), axial area (AX), and occlusal area (OC). Statistical analysis was performed using the Mann-Whitney U-test. There was no significant difference in MO and CH between the P and L groups. However, in AX, the L group had a significantly larger gap size than that of the P group (p = 0.003). In addition, compared with the FW group, the P group showed a significantly larger gap size in MO (p < 0.000), CH (p = 0.008), and OC (p < 0.000). These results indicate that the gap size increased after porcelain veneering using the press-over and layering techniques. In addition, the all-ceramic bridges fabricated using the press-over and layering techniques had approximately equal gap sizes in MO.

Effects of sintering time on translucency and color of translucent zirconia ceramics

OBJECTIVE

To investigate the effect of sintering time on translucency and color of translucent zirconia ceramics.

MATERIALS AND METHODS

Sixty translucent zirconia (5Y-TZP) specimens (12 × 1.6 mm, Katana (KAT) and NexxZr (NEX)) were divided into six groups (n = 10) according to sintering time; 1, 2 (specified by manufacturer-control), and 3 hs. Color differences (ΔEab) within same material when sintered using different times and between materials when same sintering time was used were calculated, as well as translucency parameters (TP) after the use of each sintering time. Data for ΔEab and TP were analyzed with two-way ANOVAs, pairwise comparisons, and Fisher's LSD Test (Post-hoc).

RESULTS

When 1 or 3 h were used, color difference from the color of specimens when manufacturer-specified time (2 h) was used was similar for both KAT and NEX. ΔEab values of NEX were significantly higher than KAT when sintered for 1 or 3 h (P < 0.001). TP increased for KAT when sintered for 1 h, and was higher than NEX. TP for NEX increased when sintered for 3 h (P < 0.001), but was not significantly different than that of KAT.

CONCLUSIONS

Effect of 1 or 3-h sintering on color was similar for both zirconias. For NEX, this effect resulted in greater differences from the color of specimens when manufacturer-specified time was used. Sintering for 1 h increased the translucency of KAT.

CLINICAL SIGNIFICANCE

When high translucency is desired, clinicians may prefer 1-h sintering for KAT zirconia. When lower translucency is desired, 3-h sintering for NEX can be used. However, for NEX, the color after 1- or 3-h sintering was different than the color obtained with manufacturer-specified time, and this difference may affect the final color of restoration compared to the final color when manufacturer-specified time is used.

Impact of Coping Veneering Techniques on the Survival of Implant-Supported Zirconia-Based-Crowns Cemented to Hybrid-Abutments: An-In-Vitro Study

The objective of this study is to investigate the influence of veneering technique (hand-layering vs. milling) on the fracture resistance of bi-layer implant-supported zirconia-based hybrid-abutment crowns. Mandibular molar copings were anatomically designed and milled. Copings were then veneered by hand-layering (HL) (n = 20) and milling using the Cad-On technique (LD) (n = 20). Crowns were cemented to zirconia hybrid-abutments. Ten samples of each group acted as a control while the remaining ten samples were subjected to fatigue in a chewing simulator. Crowns were loaded between 50 and 100 N for 1.2 million cycles under simultaneous temperature fluctuation between 5 and 55 °C. Crowns were then subjected to static load a to fracture test. Data were statistically analysed using the one-way ANOVA. Randomly selected crowns from each group were observed under scanning electron microscopy to view fractured surfaces. Study results indicate that during fatigue, LD crowns had a 100% survival rate; while HL crowns had a 50% failure rate. Fracture resistance of LD crowns was statistically significantly higher than that of HL crowns at the baseline and after fatigue (p ≤ 0.05). However, fatigue did not cause a statistically significant reduction in fracture resistance in both LD and HL groups (p > 0.05). Copings fractured in the LD crowns only and the fracture path was different in both LD and HL groups. According to the results, it was concluded that milled veneer implant-supported hybrid-abutment crowns exhibit significantly higher fracture resistance, and better withstand clinical masticatory loads in the posterior region compared to the hand-layered technique. Also, fatigue application and artificial aging caused no significant strength reduction in both techniques. Clinical significance: Different veneering techniques and materials (hand-layering or milling) act differently to clinical forces and environment and may be prone to early chipping during service. Therefore, practitioners are urged to consider the appropriate veneering protocol for posterior implant-supported hybrid-abutment restorations.

Does veneering technique affect the bond strength of bilayer Y-TZP? A systematic review and meta-analysis

STATEMENT OF PROBLEM

Reasons for failures of bilayer yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations include the core-veneer interface bond strength. The influence of the veneering method on the bond strength of veneered Y-TZP is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the effect of the veneering method on the bond strength of bilayer Y-TZP.

MATERIAL AND METHODS

This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Searches were performed on PubMed/MEDLINE, Web of Science (Core Collection), and Scopus for in vitro studies evaluating the effect of the veneering technique on the bond strength of bilayer Y-TZP. Statistical analyses were performed with random-effect models (α=.05).

RESULTS

From 619 identified studies, 140 were selected for full-text analysis and 16 were included. Manual searching yielded no additional articles. The meta-analyses comprised 15 studies, and 1 study was included only in the descriptive analysis. Meta-analyses compared the hand-layered method (control) with pressed, fused, and cemented veneering methods. The fused and cemented techniques were analyzed by using subgroups assessing the veneering ceramic type (predominantly glass-ceramics and particle-filled glass-ceramics). Similar bond strength results (P=.540) were found for pressed and hand-layered veneered Y-TZP specimens. Fused veneers achieved higher bond strength values (P<.001) than the hand-layered veneers on Y-TZP frameworks, irrespective of the veneering ceramic type (predominantly glass-ceramics: P=.002; particle-filled glass-ceramics: P<.001). Global and subgroup analyses indicated that lower core-veneer bond strength values (P<.001) were found for cemented in relation to hand-layered veneers.

CONCLUSIONS

Core-veneer interfacial adhesion was equivalent for pressed and hand-layered veneering techniques. Improved bond strength, regardless of the veneer ceramic material type, was achieved by the fused veneering method, which seems to be a promising choice for the veneering of Y-TZP. In contrast, the cemented method may be unsuitable for veneering Y-TZP structures because of its lower bond strength than the hand-layered veneering technique.

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.

In vitro lifetime of zirconium dioxide-based crowns veneered using Rapid Layer Technology

Rapid Layer Technology (RLT) uses computer-aided design/computer-aided manufacturing (CAD/CAM) to manufacture a veneer layer that is adhesively bonded to the zirconia framework, avoiding firing steps during the fabrication process and thus preventing build-up of residual stresses. This work studied, using sliding contact fatigue, the in vitro lifetime of restorations produced using RLT compared with restorations produced using conventional veneering techniques. Zirconia copings were veneered with a conventional hand-layering method (VM9) using a fast (n = 16) or a slow (n = 16) cooling protocol, or with RLT. For the latter, the veneers were CAD/CAM fabricated using a feldspathic reinforced-glass (Vitablocs Mark II; n = 16) or a polymer-infiltrated reinforced-glass network (Enamic; n = 16) and adhesively bonded to the zirconia frameworks. Crowns thus obtained were submitted to sliding contact fatigue against a steatite indenter in a chewing simulator until failure. A Kaplan-Meier survival analysis was conducted. None of the hand-layered restorations survived after a 2 × 10⁶ -cycle interval, whereas no fractures in the RLT groups were observed. Vitablocs Mark II veneers survived for a longer testing period (3.5 × 10⁶ cycles) than their Enamic counterparts (2.5 × 10⁶ cycles) owing to their superior wear behavior. The RLT represents an efficient method to veneer zirconia frameworks by reducing processing steps and, more importantly, increasing the lifetime of the restorations.

Fatigue failure load and finite element analysis of multilayer ceramic restorations

OBJECTIVE

To evaluate the fatigue failure load via staircase approach and stress distribution via FEA of different ceramic configurations arranged in multilayers composed of ceramic materials with different elastic moduli and compare them to monolayer models.

METHODS

CAD-CAM ceramic blocks were used to shape 0.3mm and 1.5mm thick discs, corresponding to: feldspathic (F), 64GPa; lithium disilicate (L), 95GPa; and Yttrium-partially stabilized tetragonal zirconia (Y-TZP) (Y), 209.3GPa. The 0.3mm discs were arranged in 4 layers cemented with resin cement (Multilink N), and the 1.5mm discs were not treated, in such a way that the final thickness of all specimens was 1.5mm (±0.15mm). The following 6 groups were tested: F (F: monolithic); L (L: monolithic); LLFF (L+L+F+F); FFLL (F+F+L+L); YLFF (Y+L+F+F); YLLF (Y+L+L+F). The loads-to-fracture were obtained using the biaxial flexural strength test until failure and the data were run using one-way ANOVA and Tukey's multiple comparisons (α=0.05) tests. The biaxial bending test was also simulated through finite element analysis (FEA) to identify the tensile stress generated at each layer of the groups. Mean fatigue failure load (100,000 cycles; 20Hz) was determined using the staircase approach. The fracture analysis was performed by stereomicroscope and scanning electron microscopy.

RESULTS

The load to fracture (N) were obtained as follows: L (592.9±73.8)^D>FFLL (319.78±43.59)^C>YLLF (246.75±24.89)^B>F (167.13±9.84)^A>YLFF (166.51±15.24)^A>LLFF (165.46±22.75)^A; and the fatigue failure load (N): L (310.92±26.73)^F>FFLL (190.17±8.32)^E>F (106.21±2.81)^D>YLLF (96.48±5.73)^C>YLFF (89.56±2.38)^B>LLFF (77.23±6.33)^A. The origin of all of the tested specimens was located at the tensile region of the discs, as encountered in FEA.

SIGNIFICANCE

The material under tensile stress is determinant for the restoration's strength and the adhesive interface negatively influenced the mechanical behavior of the multilayer structures.

Recent advances in understanding the fatigue and wear behavior of dental composites and ceramics

Dental composite and ceramic restorative materials are designed to closely mimic the aesthetics and function of natural tooth tissue, and their longevity in the oral environment depends to a large degree on their fatigue and wear properties. The purpose of this review is to highlight some recent advances in our understanding of fatigue and wear mechanisms, and how they contribute to restoration failures in the complex oral environment. Overall, fatigue and wear processes are found to be closely related, with wear of dental ceramic occlusal surfaces providing initiation sites for fatigue failures, and subsurface fatigue crack propagation driving key wear mechanisms for composites, ceramics, and enamel. Furthermore, both fatigue and wear of composite restorations may be important in enabling secondary caries formation, which is the leading cause of composite restoration failures. Overall, developing a mechanistic description of fatigue, wear, and secondary caries formation, along with understanding the interconnectivity of all three processes, are together seen as essential keys to successfully using in vitro studies to predict in vivo outcomes and develop improved dental restorative materials.

Effects of New Generation All-Ceramic and Provisional Materials on Fibroblast Cells

PURPOSE

The purpose of this in vitro study was to evaluate the cytotoxic and apoptotic effects of seven new-generation all-ceramic materials for CAD/CAM (Lava Ultimate [LU], VITA Mark II [VM], InCoris TZI [IC], IPS e.max CAD [EM], VITA Suprinity [VS], Cerasmart [CS], IPS Empress CAD [EC]) and six provisional materials (Protemp 4 [PT], Telio CAD [TC], CAD-Temp [CT], Telio Lab [TL], Temdent Classic [TD], Telio CS C&B [TS]) on L929 mouse fibroblast cells.

MATERIALS AND METHODS

24 disc-shaped specimens (∅ = 5 mm, h = 2 mm) were prepared from each test material. Medium extracts were collected at the 1st, 3rd, and 7th days for each group and tested using the L929 cell line. Cytotoxicity was evaluated using XTT assay, and apoptosis was determined by Annexin-V/PI staining. Data were analyzed using one-way ANOVA, Tukey's multiple comparison tests at a significance level of p < 0.05.

RESULTS

The cell viability results among all-ceramic material groups after the 1st and 7th days of incubation periods showed statistically significant differences (p < 0.05). There were significant differences within the ceramic groups in different incubation periods regarding apoptosis rate (p < 0.05). Throughout the entire test period, LU and VM from the CAD/CAM all-ceramic materials and PT and TC from the provisional restoration materials showed cell viability higher than 90%. EC and TD showed the lowest cell viability and highest apoptosis rates in their own groups. For the provisional materials, there were significant differences in cell viability and apoptosis rate in all the incubation periods for each material (p < 0.05).

CONCLUSIONS

Although some new-generation CAD/CAM and provisional restoration materials display slight cytotoxicity values, the results are still within the reliable range, and they can safely be used in clinical conditions.

Does veneering technique affect the flexural strength or load-to-failure of bilayer Y-TZP? A systematic review and meta-analysis

STATEMENT OF PROBLEM

Causes of failures of bilayer yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations include the processing technique and the properties of the veneer ceramic. The effect of the veneering method on the mechanical behavior of veneered Y-TZP remains unclear.

PURPOSE

The purpose of this systematic review was to assess the effect of the veneering method on the flexural strength and failure load of bilayer Y-TZP.

MATERIAL AND METHODS

This study followed the Preferred Reporting Items for the Systematic Reviews and Meta-Analyses (PRISMA) statement. Searches were performed through August 2017 in PubMed/MEDLINE, Web of Science (Core Collection), Scopus, and Embase, with no year or language limit, targeting in vitro studies evaluating the effect of the veneering technique on the flexural strength and load-to-failure of bilayer Y-TZP immediately or after aging. Statistical analyses were conducted using an appropriate software. Comparisons were drawn with random effect models (α=.05).

RESULTS

From 3242 identified studies, 241 were selected for full-text analysis; from these, 33 studies were included. Manual searching yielded no additional papers. The meta-analysis consisted of 32 studies. Meta-analysis was performed separately for flexural strength and failure load data to compare the hand-layered method (control) with pressed, fused, and cemented veneering techniques. The cemented and fused methods were analyzed using subgroups depending on the veneering material being examined (predominantly glass-ceramics and particle-filled glass-ceramics), and the results were compared with those of the hand-layered method. The pressed group presented flexural strength (7 studies) (P=.150) and failure load (19 studies) (P=.140) values that were similar to those of the hand-layered group. Subgroup analysis revealed that the fused group with particle-filled glass-ceramics (7 studies) produced higher load-to-failure (P=.006) values than the hand-layered group. Subgroup analyses showed a statistical difference that favored the hand-layered over the cemented method, with predominantly glass-ceramic materials (5 studies) (P=.002).

CONCLUSIONS

The fused technique with particle-filled glass-ceramics seems more appropriate for the veneering of Y-TZP, with improved failure load, than the hand-layered method with predominantly glass-ceramic materials. The use of predominantly glass-ceramics for the cemented method is not recommended as failure load was lower than for the hand-layered group. Pressed veneers showed failure load and flexural strength values similar to those of the the hand-layered technique.

Fracture Resistance of Monolithic Glass-Ceramics Versus Bilayered Zirconia-Based Restorations

PURPOSE

To compare the fracture resistance of monolithic reinforced glass-ceramic restorations with bilayer zirconia-based restorations.

MATERIALS AND METHODS

Fifteen ceramic crowns were fabricated on epoxy dies duplicated from a stainless steel master die. They were divided into 3 equal groups (n = 5) according to the type of ceramic material used: group I, monolithic lithium disilicate (IPS e.max CAD), group V, monolithic zirconia-reinforced lithium silicate (Vita Suprinity), and group B (bilayered zirconia substructure with veneering ceramic). All specimens were cemented on epoxy dies with a self-adhesive resin cement (Rely X Unicem), subjected to a chewing simulator, and then loaded until fracture in a universal testing machine. The results were tabulated and statistically analyzed using one-way ANOVA to compare among the 3 materials. The Bonferroni post hoc test was used for pairwise comparisons when the ANOVA test was significant.

RESULTS

Zirconia-reinforced lithium silicate (Vita Suprinity) crowns showed the highest statistically significant (p < 0.05) mean fracture resistance values (1742.9 ± 102.7 N), followed by lithium disilicate (IPS e.max CAD) (1565.2 ± 89.7 N). Bilayered zirconia-based crowns showed the lowest statistically significantly mean fracture resistance values (1267.8 ± 86.1 N).

CONCLUSIONS

Monolithic reinforced glass-ceramics (lithium disilicate and zirconia-reinforced lithium silicate) have better fracture resistance than bilayered zirconia-based ceramics.

CLINICAL IMPLICATIONS

The use of monolithic reinforced ceramic restorations (lithium disilicate and zirconia-reinforced lithium silicate) is preferred to bilayered zirconia-based restorations to avoid chipping of the ceramic veneer.

Shear bond strength of indirect composite material to monolithic zirconia

PURPOSE

This study aimed to evaluate the effect of surface treatments on bond strength of indirect composite material (Tescera Indirect Composite System) to monolithic zirconia (inCoris TZI).

MATERIALS AND METHODS

Partially stabilized monolithic zirconia blocks were cut into with 2.0 mm thickness. Sintered zirconia specimens were divided into different surface treatment groups: no treatment (control), sandblasting, glaze layer & hydrofluoric acid application, and sandblasting + glaze layer & hydrofluoric acid application. The indirect composite material was applied to the surface of the monolithic zirconia specimens. Shear bond strength value of each specimen was evaluated after thermocycling. The fractured surface of each specimen was examined with a stereomicroscope and a scanning electron microscope to assess the failure types. The data were analyzed using one-way analysis of variance (ANOVA) and Tukey LSD tests (α=.05).

RESULTS

Bond strength was significantly lower in untreated specimens than in sandblasted specimens (P<.05). No difference between the glaze layer and hydrofluoric acid application treated groups were observed. However, bond strength for these groups were significantly higher as compared with the other two groups (P<.05).

CONCLUSION

Combined use of glaze layer & hydrofluoric acid application and silanization are reliable for strong and durable bonding between indirect composite material and monolithic zirconia.

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.

Effect of Different Surface Treatments on the Bond Strength of Lithium Disilicate Ceramic to the Zirconia Core

OBJECTIVE

The aim of this study was to evaluate the effect of different surface treatments [sandblasting, Erbium:Yttrium-Aluminium-Garnet (Er:YAG), and femtosecond lasers] on the shear bond strength (SBS) of the CAD-on technique.

BACKGROUND DATA

Although demand for all-ceramic restorations has increased, chipping remains one of the major problems for zirconia-based restorations.

MATERIALS AND METHODS

Forty yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) zirconia plates (IPS e.max ZirCAD, Ivoclar Vivadent) were cut, sintered (12.4 × 11.4 × 3 mm) and divided into four groups according to the surface treatments (n = 10): a control group with no surface treatment (Group C), sandblasting with 50 μm Al2O3 (Group S), Er:YAG laser irradiation (Group E), and femtosecond laser irradiation (Group F). Also, 40 cylindrical (5 mm diameter, 2 mm height) lithium disilicate (IPS e.max CAD) veneer ceramics were cut and fused to all zirconia cores by a glass-fusion ceramic and crystallized according to the CAD-on technique. Specimens were subjected to shear force using a universal testing machine. The load was applied at a crosshead speed of 0.5 mm/min until failure. Mean SBS (MPa) were analyzed with one way ANOVA (p < 0.05). The failed specimens were examined under a stereomicroscope at ×20 to classify the mode of failure.

RESULTS

The highest SBS was observed in Group F (36 ± 3.31 MPa), followed by Group S (33.03 ± 5.05 MPa), and Group C (32.52 ± 10.15 MPa). The lowest SBS was observed in Group E (31.02 ± 4.96 MPa), but no significant differences were found between the control and surface treated groups (p = 0.377). All the specimens showed a mixed type of failure.

CONCLUSIONS

Femtosecond laser application increased the bond strength between zirconia-veneer specimens. However, the novel CAD-on technique with no surface treatment also showed high bonding strength. Thus, this technique could prevent ceramic chipping without additional surface treatments.

Influence of core design, production technique, and material selection on fracture behavior of yttria-stabilized tetragonal zirconia polycrystal fixed dental prostheses produced using different multilayer techniques: split-file, over-pressing, and manually built-up veneers

AIM

To investigate and compare the fracture strength and fracture mode in eleven groups of currently, the most commonly used multilayer three-unit all-ceramic yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) fixed dental prostheses (FDPs) with respect to the choice of core material, veneering material area, manufacturing technique, design of connectors, and radii of curvature of FDP cores.

MATERIALS AND METHODS

A total of 110 three-unit Y-TZP FDP cores with one intermediate pontic were made. The FDP cores in groups 1-7 were made with a split-file design, veneered with manually built-up porcelain, computer-aided design-on veneers, and over-pressed veneers. Groups 8-11 consisted of FDPs with a state-of-the-art design, veneered with manually built-up porcelain. All the FDP cores were subjected to simulated aging and finally loaded to fracture.

RESULTS

There was a significant difference (P<0.05) between the core designs, but not between the different types of Y-TZP materials. The split-file designs with VITABLOCS(®) (1,806±165 N) and e.max(®) ZirPress (1,854±115 N) and the state-of-the-art design with VITA VM(®) 9 (1,849±150 N) demonstrated the highest mean fracture values.

CONCLUSION

The shape of a split-file designed all-ceramic reconstruction calls for a different dimension protocol, compared to traditionally shaped ones, as the split-file design leads to sharp approximal indentations acting as fractural impressions, thus decreasing the overall strength. The design of a framework is a crucial factor for the load bearing capacity of an all-ceramic FDP. The state-of-the-art design is preferable since the split-file designed cores call for a cross-sectional connector area at least 42% larger, to have the same load bearing capacity as the state-of-the-art designed cores. All veneering materials and techniques tested in the study, split-file, over-press, built-up porcelains, and glass-ceramics are, with a great safety margin, sufficient for clinical use both anteriorly and posteriorly. Analysis of the fracture pattern shows differences between the milled veneers and over-pressed or built-up veneers, where the milled ones show numerically more veneer cracks and the other groups only show complete connector fractures.

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.

The effect of various veneering techniques on the marginal fit of zirconia copings

PURPOSE

This study aimed to evaluate the fit of zirconia ceramics before and after veneering, using 3 different veneering processes (layering, press-over, and CAD-on techniques).

MATERIALS AND METHODS

Thirty standardized zirconia CAD/CAM frameworks were constructed and divided into three groups of 10 each. The first group was veneered using the traditional layering technique. Press-over and CAD-on techniques were used to veneer second and third groups. The marginal gap of specimens was measured before and after veneering process at 18 sites on the master die using a digital microscope. Paired t-test was used to evaluate mean marginal gap changes. One-way ANOVA and post hoc tests were also employed for comparison among 3 groups (α=.05).

RESULTS

Marginal gap of 3 groups was increased after porcelain veneering. The mean marginal gap values after veneering in the layering group (63.06 µm) was higher than press-over (50.64 µm) and CAD-on (51.50 µm) veneered groups (P<.001).

CONCLUSION

Three veneering methods altered the marginal fit of zirconia copings. Conventional layering technique increased the marginal gap of zirconia framework more than pressing and CAD-on techniques. All ceramic crowns made through three different veneering methods revealed clinically acceptable marginal fit.

Clinical Advantages and Limitations of Monolithic Zirconia Restorations Full Arch Implant Supported Reconstruction: Case Series

Purpose. The purpose of this retrospective case series is to evaluate the clinical advantages and limitations of monolithic zirconia restorations for full arch implant supported restorations and report the rate of complications up to 2 years after insertion. Materials and Methods. Fourteen patients received implant placement for monolithic zirconia full arch reconstructions. Four implants were placed in seven arches, eleven arches received six implants, two arches received seven implants, two arches received eight implants, and one arch received nine implants. Results. No implant failures or complications were reported for an implant survival rate of 100% with follow-up ranging from 3 to 24 months. Conclusions. Monolithic zirconia CAD-/CAM-milled framework restorations are a treatment option for full arch restorations over implants, showing a 96% success rate in the present study. Some of the benefits are accuracy, reduced veneering porcelain, and minimal occlusal adjustments. The outcome of the present study showed high success in function, aesthetics, phonetics, and high patient satisfaction.

Fracture load of ceramic restorations after fatigue loading

STATEMENT OF PROBLEM

A clinician must decide what ceramic coping and veneer material to prescribe based on the amount of tooth reduction possible and the desired esthetic outcome of the restoration.

PURPOSE

The purpose of this in vitro study was to compare the fracture strength of monolithic and bilayered lithium disilicate (IPS e.max) and zirconia (LAVA) crowns at clinically relevant thicknesses after load cycling.

MATERIAL AND METHODS

Crowns (n=8) were fabricated from 6 groups: 1.2-mm monolithic lithium disilicate, 1.5-mm monolithic lithium disilicate, 1.5-mm bilayered lithium disilicate with hand-layered veneer, 0.6 mm monolithic zirconia, 1.2-mm bilayered zirconia with hand-layered veneer, and 1.2-mm bilayered zirconia with milled veneer (dimension represents thickness at the occlusal pit). Crowns were cemented to identical milled resin dies with resin-modified glass ionomer cement. Cemented crowns were stored at 37°C for 24 hours and load cycled for 200,000 cycles at 25 N at a rate of 40 cycles/minute. The ultimate fracture load for each specimen was measured in a universal testing machine. Data were analyzed with a 1-way ANOVA and Tukey honest significant difference post hoc analysis (α=.05).

RESULTS

Mean ±SD fracture load values were 1465 ±330 N for monolithic lithium disilicate (1.2-mm thickness) and 2027 ±365 N (1.5-mm thickness) and 1732 ±315 N for bilayered hand-veneered lithium disilicate (1.5-mm thickness). Fracture loads were 1669 ±311 N for monolithic zirconia crowns (0.6mm thickness), 2625 ±300 N for zirconia milled-veneered (1.2-mm thickness), and 2655 ±590N for zirconia hand-veneered crowns (1.2mm thickness). One-way ANOVA showed a statistically significant difference among the groups (P<.01). Veneered zirconia crowns showed the highest fracture strength, 1.2-mm hand veneered zirconia was similar to that of 1.5-mm monolithic zirconia, and all other groups were not statistically different.

CONCLUSIONS

Crowns of 1.2-mm bilayered zirconia had higher fracture loads than 0.6-mm zirconia or 1.2-mm lithium disilicate monolithic crowns.