Zirconia Bars Research Articles

Effect of chewing simulation in different Ph solutions on flexural strength of monolithic zirconia

Abstract Aim In vitro study is to evaluate the effect of chewing simulation in different ph solutions on flexural strength of monolithic zirconia. Patients and methods Forty zirconia bars (N = 40) were cut off zirconia disc using IsoMet. Each bar was 2 mm thickness, 25 mm length and 5 mm width. Specimens were divided into four groups (n = 10). The first group (control) was ready for universal test of flexural strength. Second, third, and fourth group were ready for chewing simulation but in different PH solutions acidic, neutral, and alkaline respectively. These solutions were collected from the lab (acidic-PH = 4, alkaline PH = 10). Twenty extracted human premolars (divided vertically into two halves by IsoMet) were collected for study as antagonist material for chewing simulation. After chewing simulation of these groups, the flexural strength was measured for them and SEM. Results Group 1 (control) showed the highest flexural strength with the mean value (745.21 ± 69.47) followed by group 3 (neutral) (720.40 ± 92.47), then group 2 (acidic) (507.56 ± 111.99), and finally group 4 (alkaline) (497.26 ± 172.90) with the least flexure of strength. There was significance between group 1 (control) and group 2 (acidic) and highly significant with group 4 (alkaline). There was no significance with group 3 (neutral). SEM showed that no cracks in control group. Group (2) surfaces were very smooth with amorphous structure showing disperessed small pores. Group (3) air voids were found entrapped between zirconia grains. Group (4) the surface was rough showing large compact flacks’ fragmentation and branched cracks. Conclusions This study clearly illustrates the significance of flexural strength in different pH of an aqueous solution in terms of the chewing of zirconia ceramics. Cyclic loading decreases flexural strength of 4% yttrium zirconia in neutral but not significantly. In alkaline and in neutral there were significant decrease in flexural strength with chewing due to degradation of stabilizers and transformation tetragonal phase to monoclinic phase. This degradation was in alkaline group more than in acidic group.

Qualitative SEM analysis of fracture surfaces for dental ceramics and polymers broken by flexural strength testing and crown compression.

To perform qualitative analysis using scanning electron microscopy (SEM) of fracture surfaces for ceramic and polymeric dental materials broken via standardized flexural and crunch-the-crown (CTC) tests. Zirconia, glass-ceramic, and polymeric (Trilor; TRI, Juvora; JUV, Pekkton; PEK) materials were loaded using crowns for CTC tests, discs (zirconia and glass-ceramics) for piston-on-3 ball tests, bars (polymer) for 3-point bend tests, and bars (zirconia, glass-ceramics) for 4-point bend tests. SEM was used to characterize the fracture surfaces and identify fracture surface features (e.g., origin, mist, hackle, and the direction of crack propagation [DCP]). Electron dispersive spectroscopy was used to identify the local chemistry. Fracture surface features were found to be less visually apparent for glass-ceramics than zirconia. For zirconia bars, fractures originated roughly midway between the corner and center for processing defects related to sintering. Fractures originated at the bottom corners of glass-ceramic bars (void or surface flaw) and PEK bars (surface flaw). TRI bar failures exposed glassy fibers. Fracture features were generally less discernable for discs compared to bars for zirconia and glass-ceramics. Ceramic crowns fractured into 2 to 3 pieces, with fractures originating at the occlusal surface and clear evidence for the DCP. Failures of TRI and JUV specimens (bars and crowns) were less catastrophic than for the ceramics, with exposed fibers (TRI) and surface cracks (JUV). PEK crown and bar fractures presented dimple (ductile) features formed due to microvoid coalescence followed by brittle crack propagation. The critical flaws responsible for failure initiation were a function of material composition and test configuration. Fractographic analysis can reveal problems associated with the manufacturing of materials, their handling, grinding and finishing/polishing procedures, the structural design and choice of material, and the quality of the final laboratory-delivered restoration.

15-Methacryloyloxypentadecyl Dihydrogen Phosphate Improves Resin-to-Zirconia Bonding Durability.

To investigate the bond durability of composite cement to zirconia after treatment with a 15-methacryloyloxypentadecyl dihydrogen phosphate (15-MPDP)-containing adhesive and 2 commercially available adhesives. Ninety zirconia bars were fabricated and bonded to prepolymerized resin composite cylinders with a composite cement after surface treatment for 20 s using the following adhesives: Adper Easy One (AEO, negative control), Single Bond Universal (SBU, positive control), and 10 wt% 15-MPDP powder mixed with Adper Easy One (15- MPDP). After storage in distilled water at 37°C for 24 h, the specimens were divided into 3 subgroups according to the aging treatment applied (n = 10): no aging treatment (0/TC), 10,000 thermocycles (1/TC), and 37,500 thermocycles (3/TC). Shear bond strength (SBS) was analyzed using two-way ANOVA (p < 0.05), and the fracture surfaces were examined under a dental microscope. Significant differences in the SBSs among the surface treatments and aging treatments were observed (both p < 0.001). The 15-MPDP and SBU groups showed significantly higher SBSs than the AEO group, whereas similar SBSs were found in the 15-MPDP and SBU groups. Significant reductions in the SBSs were found after 37,500 thermocycles (p < 0.001), although no significant difference between specimens aged with 10,000 thermocycles and non-aged specimens was observed. The 15-MPDP-containing dental adhesive exhibited bond durability comparable to that of a well-established 10-MDP-containing universal adhesive. Aging by 10,000 thermocycles may be insufficient to disrupt the bond of composite cement to zirconia.

Fatigue behavior of zirconia with microgrooved surfaces produced using femtosecond laser.

Femtosecond laser is a promising surface treatment tool for zirconia implant. In this study, the fatigue behavior of zirconia specimens with microgrooved surfaces formed by femtosecond laser is reported. One hundred sixty CAD/CAM zirconia bars (20mm × 4mm × 1.4mm) were evenly divided into four groups with different surface: as sintered; sandblasted with 110μm Al2O3; femtosecond laser produced microgrooves having 50μm width, 30μm depth, and 100μm pitch; microgrooves having 30μm width, 20μm depth, and 60μm pitch. The femtosecond laser formed micro/nanostructured microgrooves with precise size on zirconia surfaces. XRD analysis indicated that microgrooved surface showed no obvious tetragonal-to-monoclinic phase transformation. The fatigue strength of sandblasted specimens (728MPa) was significantly higher than that of as sintered specimens (570MPa). However, the fatigue strength of specimens with microgrooved surface decreased to about 360-380MPa. The results suggest femtosecond laser is an effective technique to regulate the surface microtopography of zirconia, while further investigations are needed to improve its fatigue behavior.

A systematic review and meta-analysis of the clinical performance of implant-supported overdentures retained by CAD-CAM bars.

To evaluate the performance of IODs involving CAD-CAM bars. A comprehensive search of studies published until May 2023 was conducted in many databases, including PubMed/MEDLINE, Web of Science, Cochrane Library, and SciELO, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The population, intervention, comparison, outcome (PICO) question was: "How do IODs retained by bars fabricated by CAD-CAM technology perform in daily clinical practice?" The meta-analysis included clinical studies based on effect size and a two-tailed null test with a 95% confidence interval (CI). Ten studies were included in the meta-analysis. Among them, nine reported a 100% implant survival rate for all CAD-CAM milled bars. Complications were reported in two studies with CAD/CAM-milled titanium bars, and one study reported more fractures in soldered gold bars used in maxillary rehabilitation. However, no fractures were observed in IODs retained by PEEK and zirconia bars. According to six studies, biological complications, including peri-implantitis, were minimal in the BioHPP and PEEK bar groups, while no cases were reported in the titanium or zirconia bar groups. CAD-CAM-milled zirconia bars had higher plaque and bleeding indices compared with titanium bars, as evidenced by findings from five studies. All four studies that evaluated Oral Health Impact Profile (OHIP) scores showed a positive effect of IODs retained by CAD-CAM milled titanium bars on quality of life. Patient satisfaction and acceptance by prosthodontists were significantly high, according to the results of five studies. Overdentures retained with CAD-CAM milled titanium bars show great potential for use in daily clinical practice. Moreover, patient and practitioner satisfaction was very high when this method was used.

Strength and Reliability of Fabricate Zirconia by Additive Manufacturing

Zirconia's distinctive intrinsic qualities have drawn the interest of the dentistry community in medical settings. The technology of additive manufacturing (AM), which produces very little waste, has been utilized to create complex and highly accurate materials. Despite AM has a number of potential benefits for efficiently producing functional, complicated shape zirconia components, there is still a paucity of industrial importance in implementations. Objective: To evaluate the strength and reliability of zirconia manufactured using the AM technology. Methods: A 3D printer was used to create zirconia bars in both horizontal and vertical orientations. The samples' geometrical correctness, density, layer thickness, and ductility were all measured using short bars. In tests for tensile properties, long bars were utilized. Using a caliper, the lengths of three short bars were measured, and the average values were calculated. They were contrasted with the theoretical parameters using a one-sample t-test. Results: It was discovered that varied construction orientations affect dimensional correctness, translucency, and dynamic qualities. Vertical-printed zirconia is denser and translucent than horizontally-printed zirconia. Conclusions: Nonetheless, zirconia that has been printed horizontally has remarkable precision and mechanical qualities. Stress and poor adhesion between the layers of materials should be fixed.

Surface Characteristics and Flexural Strength of Porous-Surface Designed Zirconia Manufactured via Stereolithography.

To design and fabricate zirconia bars with porous surfaces using stereolithography and evaluate their surface characteristics and flexural strengths. Five groups of zirconia bars (20 mm × 4 mm × 2 mm) with interconnected porous surfaces were designed and manufactured: (i) 400-µm pore size and 50% porosity (D400-P50 group), (ii) 400-µm pore size and 30% porosity (D400-P30 group), (iii) 200-µm pore size and 50% porosity (D200-P50 group), (iv) 200-µm pore size and 30% porosity (D200-P30 group), and (v) 100-µm pore size and 30% porosity (D100-P30 group). Zirconia bars without a porous surface (NP) were used as controls. The surface topographies and pore structures were investigated using scanning electron microscopy and three-dimensional laser microscopy. The printed porosity was calculated using the Archimedes method. Fifteen specimens from each group were subjected to a three-point bending test according to the ISO 6872:2015 standard. A Weibull analysis was performed, and the fractured surfaces were examined using scanning electron microscopy. Zirconia bars with porous surfaceswere designed and successfully manufactured. The designed pore size, porosity, and shape of the printed pores were approximately achieved for all the porous surfaces. The flexural strength of the control group was significantly higher than those of the groups with porous surfaces (p < 0.001). For the same porosity, groups with a pore size of 400 µm exhibited a lower flexural strength than the other groups (p<0.001). Additionally, for the same pore-size design, the flexural strengths of group D400-P50 and D400-P30 exhibited no significant differences (p = 0.150), while the flexural strengths of D200-P30 were significantly higher than that of the D200-P50 group (p = 0.043). The control group and D400-P50 group had higher Weibull moduli than the other groups. The fractography of the specimens with porous surfaces indicated more than one crack origin, mainly owing to defects, including pores and cracks. Zirconia bars with porous surfaces were successfully designed and fabricated using the stereolithography technique. Although porous surfaces may be advantageous for osteogenesis, the porous-surface design can reduce the flexural strength of the printed zirconia bars. By reducing the pore size, controlling the porosity, and improving the printing accuracy, a higher strength can be achieved.

Influence of ceramic-coating techniques on composite-zirconia bonding: Strain energy release rate evaluation

ObjectivesTo compare ceramic-coating techniques versus conventional techniques on bonding between composite cements and zirconia by means of strain energy release rate (Gc, J/m2). MethodsTwo sizes of zirconia bars (30 mm × 8 mm × 1.5 mm and 14.8 mm × 8 mm × 1.5 mm) were fabricated. Two smaller bars were treated and cemented to the surface of a large bar using one of the following methods: (i) AlN-nano-structured alumina coating with RelyX Unicem 2; (ii) HOT-DCM hotbond coating with G-Multi Primer and G-Cem Linkforce; (iii) LiDi-lithium disilicate glass-ceramic coating with Monobond N Primer and Multilink Speed; (iv) COJ-tribochemical silica treatment with RelyX Ceramic Primer and RelyX Unicem 2; (v) GCEM-alumina grit blasting with G-Multi Primer and G-Cem LinkForce; (vi) MUL-alumina grit blasting with Multilink Speed; and (vii) PAN-alumina grit blasting with Clearfil Ceramic Primer and Panavia F2.0. A total of 30 bilayered specimens in each group were stored in distilled water at 37 °C for 24 h and assigned to three subgroups (n = 10/test group): short-term test, thermocycling for 5000 cycles, and thermocycling for 10,000 cycles and tested in 4-point bending configuration. Results were analysed using two-way ANOVA, followed by one-way ANOVA and Games-Howell (α = 0.05). Failure mode and surfaces were analysed using optical microscopy and SEM. ResultsThe bonding (J/m2) of COJ and MUL groups was significantly higher than the other groups among all aging conditions. Thermocycling affected the bonding in COJ and GCEM groups. SignificanceSurface pre-treatments and artificial aging affect the bonding between composite cements and zirconia.

The effect of adding nanoparticles to dental porcelain on the fracture resistance and bond strength to zirconia core.

Porcelain combined with zirconia core substructure has low fracture toughness. Nanoparticles are incorporated into the porcelain to boost its mechanical properties. To evaluate the effect of the incorporation of silver oxide and titanium oxide nanoparticles into porcelain powder on the bond strength of porcelain veneer to zirconia core. The flexural strength of nanoparticles-modified porcelain was also evaluated. The flexural strength of feldspathic porcelain was measured (according to ISO specifications number 6872) after the incorporation of silver and titanium oxide nanoparticles. For measuring the bond strength at the porcelain-zirconia interface, 70 bars (4 × 4 × 12 mm) of zirconia were cut and fired in a furnace. The control and nanoparticles-modified porcelain powders were built up on the zirconia bars and fired to create veneers of 3 mm height, 4 mm width and 4 mm thickness. The porcelain veneers were de-attached from the zirconia core by the universal testing machine. The failure load was recorded to calculate the bond strength. The data were analysed with one-way analysis of variance followed by Tukey's test. The addition of 0.5-1.5% silver oxide nanoparticles to feldspathic porcelain increased the flexural strength. The addition of 1.0-4.0% titanium oxide nanoparticles to feldspathic porcelain increased the flexural strength. Either 0.5-1.0% silver oxide or 3.0-4.0% titanium oxide nanoparticles in feldspathic porcelain increased the shear bond strength to zirconia core. The flexural strength of porcelain veneer and the bond strength at porcelain-zirconia interface can be improved by adding either 0.5% silver oxide nanoparticles or 4% titanium oxide nanoparticles to porcelain powder.

The Flexural Strength and Flexural Modulus of Stereolithography Additively Manufactured Zirconia with Different Porosities.

Additive manufacturing (AM) technologies are capable of fabricating complex geometries with different porosities. However, the effect of such porosities on mechanical properties of stereolithography (SLA) AM zirconia with different porosities is unclear. The purpose of this in vitro study was to investigate the mechanical properties namely flexural strength, and flexural modulus of AM zirconia with different porosities. A bar (25 × 4 × 3 mm) for flexural strength test (ISO standard 6872/2015) was designed by CAD software program and standard tessellation language (STL) file was obtained. The STL file was used to fabricate a total of 80 bars in four groups. Three experimental groups each containing 20 samples were manufactured using an SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO2 paste; 3DCeram Co) with different sintering post processing to achieve different porosities including 0%-porosity (AMZ0), 20%-porosity (AMZ20), and 40%-porosity (AMZ40). The same STL file was used for subtractive manufacturing or milling of 20 zirconia bars as control group (CNCZ) with the same dimensions using a commercial zirconia. Three-point bending tests were performed for all groups following ISO standard 6872/2015 specification using a universal testing machine. Outcomes measured included load at fracture, mean flexural strength, and flexural modulus and they were compared across the experimental groups using a one-way ANOVA. Post hoc pair wise comparison between each pair of the groups were performed using Tukey test. There was a significant difference between the four groups, in terms of fracture load, flexural strength and flexural modulus using one-way ANOVA. AM zirconia with 0% porosity (AMZ0) showed the highest value for fracture load (1132.7 ± 220.6 N), flexural strength (755.1 ± 147.1 MPa) and flexural modulus (41,273 ± 2193 MPa) and AM zirconia with 40% porosity (AMZ40) showed the lowest fracture load (72.13 ± 13.42 N), flexural strength (48.09 ± 8.95 MPa) and flexural modulus (7177 ± 506 MPa). Tukey's pairwise comparisons detected a significant difference between all the possible pairs for all variables except flexural modulus between AMZ0 and CNCZ. The Weibull moduli presented the lowest value for AMZ20 (4.4) followed by AMZ40 (6.1), AMZ0 (6.1), and the highest value was for CNCZ (8.1). AM zirconia with 0% porosity showed significantly higher flexural strength and flexural modulus when compared to milled and AM zirconia with 20% and 40% porosities.

Effect of finishing/polishing techniques and aging on topography, C. albicans adherence, and flexural strength of ultra-translucent zirconia: an in situ study.

To investigate the influence of different finishing/polishing techniques and in situ aging on the flexural strength (σ), surface roughness, and Candida albicans adherence of 5mol% yttria-stabilized zirconia (ultratranslucent zirconia). A total of 120 zirconia bars (Prettau Anterior, Zirkonzahn) with dimensions of 8 × 2 × 0.5mm were divided into 8 groups (n = 15) according to two factors: "in situ aging" (non-aged and aged (A)) and "finishing/polishing" (control (C), diamond rubber polishing (R), coarse grit diamond bur abrasion (B), and coarse grit diamond bur abrasion + diamond rubber polishing (BR)). Half of the samples from each group were subjected to a 60-day in situ aging by fixing the bars into cavities prepared in the posterior region of the base of complete or partial dentures of 15 patients. The samples were then subjected to the mini flexural (σ) test (1mm/min). A total of 40 zirconia blocks (5 × 5 × 2mm) were prepared and subjected to roughness (Ra) analyses and fungal adherence and complementary analyses (X-ray diffraction (XRD) and scanning electron microscopy (SEM)). The data of mean σ (MPa) and roughness Ra (μm) were statistically analyzed by two-way and one-way ANOVA, respectively, and Tukey's test. The Weibull analysis was performed for σ data. The fungal adhesion (Log CFU/mL) data were analyzed by Kruskal-Wallis tests. For flexural resistance, the "finishing/polishing" factor was statistically significant (P = 0.0001); however, the "in situ aging" factor (P = 0.4458) was not significant. The non-aged (507.3 ± 115.7MPa) and aged (487.6 ± 118.4MPa) rubber polishing groups exhibited higher mean σ than the other techniques. The non-aged (260.2 ± 43.3MPa) and aged (270.1 ± 48.8MPa) bur abrasion groups presented lower σ. The coarse-grit diamond bur abrasion group (1.82 ± 0.61µm) presented the highest roughness value (P = 0.001). Cell adhesion was not different among groups (P = 0.053). Group B presented the most irregular surface and the highest roughness Ra of 0.61 m. The finishing of ultratranslucent zirconia might be preferably done with a diamond rubber polisher. Moreover, the protocols used did not interfere with Candida albicans adhesion. Coarse-grit diamond burs might be avoided for finishing ultratranslucent monolithic zirconia, which might be preferably performed with a diamond rubber polisher.

Increasing dental zirconia micro-retentive aspect through ultra-short pulsed laser microstructuring: study on flexural strength and crystal phase characterization

ObjectivesAlthough ultra-short pulsed laser (USPL) microstructuring has previously improved zirconia bond-strength, it is yet unclear how different laser-machined surface microstructures and patterns may influence the material’s mechanical properties. Therefore, the aim of this study was to assess the flexural strength of zirconia after different USPL settings creating three different geometrical patterns with structures in micrometer scale.MethodsOne hundred sixty zirconia bars (3Y-TZP, 21 × 4 × 2.1 mm) were prepared and randomly divided into five groups (n = 32): no surface treatment (negative control-NC); sandblasting with Al2O3 (SB); and three laser groups irradiated with USPL (Nd:YVO4/1064 nm/2-34 J/cm2/12 ps): crossed-lines (LC), random-hatching (LR), and parallel-waves (LW). Bars were subjected to a four-point flexural test (1 mm/min) and crystal phase content changes were identified by X-ray diffraction. Surface roughness and topography were analyzed through 3D-laser-profilometry and SEM. Data were analyzed with parametric tests for roughness and Weibull for flexural strength (α = 5%).ResultsLR (Mean[95%CI]: 852.0 MPa, [809.2–894.7]) was the only group that did not show a significantly different flexural strength than NC (819.8 MPa, [796.6–842.9]), (p > 0.05). All laser groups exhibited higher Weibull moduli than NC and SB, indicating higher reliability and homogeneity of the strength data. An increase of monoclinic phase peak was only observed for SB.ConclusionIn conclusion, USPL created predictable, homogeneous, highly reproducible, and accurate surface microstructures on zirconia ceramic. The laser-settings of random-hatching (12 ps pulses) increased 3Y-TZP average surface roughness similarly to SB, while not causing deleterious crystal phase transformation or loss of flexural strength of the material. Furthermore, it has increased the Weibull modulus and consequently material’s reliability.Clinical significancePicosecond laser microstructuring (LR conditions) of 3Y-TZP ceramic does not decrease its flexural strength, while increasing materials realiability and creating highly reproducible and accurate microstructures. These features may be of interest both for improving clinical survival of zirconia restorations as well as enhancing longevity of zirconia implants.

English

BACKGROUND A smooth zirconia surface is necessary to protect the opposing natural dentition, to prevent plaque accumulation and to increase the survival rate of restoration by reducing the chances of failure by crack propagation. Surface roughness can be incorporated by routine dental procedures done in labs and clinics to adjust the restoration. It is unclear which surface treatment is most appropriate to achieve clinically acceptable zirconia surface. The purpose of this study was to evaluate the effect of grinding and subsequent various surface treatments on the surface roughness of full contour monolithic zirconia. METHODS In this invitro study 10 zirconia bars of final dimensions 20 x 4 x 2 mm &amp; 40 zirconia bars of final dimensions 20 x 4 x 2.2 mm were milled and sintered. The zirconia bars with final dimensions 20 x 4 x 2mm were glazed and selected as samples for control group (Group C) (n = 10). Forty zirconia bars with dimensions of 20 x 4 x 2.2 mm were grounded using a standard straight cylindrical diamond point (105 – 125 µm) by placing them in a customized grinding apparatus till the dimensions became similar to that of control group i.e. 20 x 4 x 2 mm. After grinding and confirming the dimensions of each full contour monolithic zirconia bar using digital vernier caliper, zirconia bars were randomly allocated into 4 groups with 10 samples in each group (n = 10), namely (Group G: Grinding only, Group G+R: Grinding &amp; Reheating, Group G+G: Grinding &amp; Glazing, Group G+P: Grinding &amp; Polishing) respectively. Surface roughness values were measured using a profilometer. Differences between groups were examined using one-way analysis of variance (ANOVA) (P ≤ 0.05) and Post hoc Tukey HSD test was done for multiple comparisons of surface roughness in between the groups using Statistical Package for Social Sciences (SPSS) software. RESULTS Group C showed the least surface roughness values. The maximum surface roughness values were seen in Group G. Surface roughness of Group G, Group G + H and Group G + G were statistically significant from Group C and Group G + P. There was no statistically significant difference in surface roughness values between Group C and Group G + P. CONCLUSIONS It can be concluded that polishing after grinding significantly reduced the surface roughness and re-established the surface smoothness of full-contour monolithic zirconia bars. KEY WORDS Surface Roughness, Zirconia, Monolithic, Full Contour, Profilometer

Effects of Veneering Ceramic and Methods on Failure Load of Veneered Zirconia

Background: A variety of veneering options to zirconia frameworks are now available. The purpose of this study is to evaluate the effect of veneer materials, veneering methods, cement materials, and aging on the failure load of bilayered veneer zirconia. Material and methods: Zirconia bars (20 × 4 × 1 mm) were veneered to 2 mm total thickness (n = 10/group). Veneering method groups included: 1. Hand-layered feldsparthic porcelain (VM = Vita VM9, Vident) and fluorapatite glass–ceramic (CR = IPS e.max Ceram, IvoclarVivadent); 2. Pressed feldspathic porcelain (PM = Vita PM9, Vident) and fluorapatite glass–ceramic (ZP = IPS e.max ZirPress, IvoclarVivadent); 3. CAD-/CAM-milled feldspathic ceramic (TF = Vitablocs Triluxe Forte, Vident) and lithium-disilicate glass–ceramic (CAD = IPS e.max CAD, IvoclarVivadent). CAD/CAM veneers were either cemented with resin cements (P = Panavia21, KurarayDental), (R = RelyX Ultimate, 3M ESPE), (M = Multilink Automix, Ivoclar Vivadent) or fused with fusion glass–ceramic (C = CrystalConnect, IvoclarVivadent). A three-point bending test (15 mm span, zirconia on tension side) was performed on Instron universal testing machine (ISO 6872) recording load-to-failure (LTF) of first veneer cracks or catastrophic failure. For group VM, PM, TF-M, TF-C, CAD-M, CAD-C, ten more bars were prepared and aged with cyclic loading (100,000 cycles, 50% LTF) and thermocycling (2000 cycles) before testing. Data were analyzed by ANOVA, Tukey HSD post hoc tests, and t-test (α = 0.05). Zirconia veneered with IPS e.max CAD by fusing had significantly higher failure load compared with zirconia veneered with other veneering materials (p ≤ 0.05). For cemented veneers, the cement type had a significant effect on the failure load of the veneer zirconia specimens. Specimens cemented with Panavia 21 had a lower resistance to loading than other cements. The aging experiment revealed a significant difference in failure load between non-aged and aged bars in groups VM and PM, but not in the groups with CAD-/CAM-milled veneers. In conclusion, veneer materials, veneering methods, and cement materials have a significant effect on the failure load of bilayered veneer zirconia. CAD-/CAM-milled veneer zirconia is not susceptible to aging performed in this study.

Ceramic Printing - Comparative Study of the Flexural Strength of 3D Printed and Milled Zirconia.

To determine and compare the mechanical properties of 3D-printed yttriastabilized zirconia to milled isostatic pressed yttria-stabilized zirconia, with the following hypotheses: (1) The flexural strength of 3D-printed yttria-stabilized zirconia is comparable to milled yttria-stabilized isostatic pressed zirconia; and (2) thermocycling and chewing simulation do not affect the flexural strength of 3D-printed yttria-stabilized zirconia. A total of 30 bars of an experimental 3D-printed 3 mol% yttriastabilized zirconia (LithaCon 3Y 230, Lithoz) and 10 bars of milled isostatic pressed zirconia (Prettau Zirconia, Zirkonzahn) were utilized. The printed zirconia bars were divided into three groups (n = 10 bars per group): (1) untreated (control); (2) thermocycled; and (3) tested after chewing simulation. A flexural strength test was performed on all samples using a three-point bend test in an Instron Universal testing machine. One-way analysis of variance on ranks was used to compare milled to printed zirconia. The effects of thermocycling and load cycling on 3D-printed zirconia were also determined. The flexural strength values for milled and printed zirconia were 936.3 ± 255.0 MPa and 855.4 ± 112.6 MPa, respectively. There was no statistically significant difference in flexural strength between the milled and printed zirconia (P = .178). No statistically significant differences were observed between the control 3D-printed zirconia group and the thermocycled (888.4 ± 59.3 MPa) or load-cycled printed zirconia (789.6 ± 133.8 MPa; P = .119). Printed 3 mol% yttria-stabilized zirconia has comparable flexural strength to milled yttria-stabilized isostatic pressed zirconia. The thermocycling and chewing simulation used in this study did not significantly alter the flexural strength of the printed 3 mol% yttria-stabilized zirconia. These results indicate a promising role for 3D printing in the fabrication of zirconia restorations. Additional studies are needed to explore the full potential of this technology.

Influence of time and hydration (ageing) on flexural strength of Yttrium stabilized Zirconia polycrystals (Y-TZP) fabricated with different CAD-CAM Systems.

Objectives:To evaluate the effect of time and hydration (ageing) on flexural strength of yttrium-stabilized zirconia polycrystals (Y-TZP) zirconia fabricated from three different materials.Methods:This in-vitro study was performed from June to September 2019. Y-TZP bars, measuring 2 x 3 x 20 mm were prepared and sintered from three different materials, Group-1: LAVA™ Zirconia (3M ESPE, US) (control) Group-2: Vita In-Ceram YZ (VITA, Germany) and Group-3: Aadva™ Zirconia (Zr) (GC Advanced technologies Inc.). 30 zirconia bars per group were prepared using sectioning of blocks with isomet saw. Followed by sintering in furnaces for recommended temperature cycles. One side of bars were polished and beveled for flexural testing. Groups of specimens were divided into subgroups of 3 (n=10) based on the ageing (distilled water in the incubator at 37ºC) durations (48 Hrs and two and half years). Ten specimens in each material groups were not aged (controls). Samples were exposed to a static force in a three-point bend test using a universal instron-testing machine until fracture. Scanning electron microscopic assessment was performed for fractured specimens for ageing. Data was analyzed using ANOVA and Tukey post hoc test.Results:The mean flexural strength at baseline for Group-1: LAVA™ Zirconia, group (632.7 ± 136.5 MPa) 2: Vita In-Ceram YZ (1036.3 ± 229.6 MPa), and Group-3: Aadva™ Zirconia (1171.3 ± 266.3 MPa) were significantly different. Group-2 and Group-3 specimens showed higher strength compared to Group-1 specimens, irrespective of the ageing duration (p<0.05). Analysis of pooled data for flexural strength for materials by aging period (baseline, after 48 hours and after 2 and ½ years) showed that there was significant reduction of strength with increasing duration (p<0.05).Conclusions:Y-TZP showed variations in flexural strength depending on the material type. Ageing duration exhibited significant influence on the flexural strength of Y-TZP when comparing no ageing to two and half years. Vita In-Ceram YZ and Aadva Zirconia (Zr) showed higher and clinically acceptable flexural strength outcomes.

Adhesive removable partial denture attachments made from zirconia ceramic: A finite element analysis and in vitro study

Statement of problemWhether adhesive zirconia ceramic removable partial denture attachments are feasible with current technology is unclear. PurposeThe purpose of this finite element analysis and in vitro study was to evaluate the effect of the lever arm, tooth preparation, and aging on the loading of the tooth-zirconia attachment interface. Material and methodsThree different finite element analysis (FEA) models allowing for the loading of an adhesive attachment either directly or through a removable partial denture were used. Two models represented a human tooth with 2 different types of attachments, while the third model also included a removable partial denture. For the evaluation of bond strength, a combination of shear and hydrostatic stress was used. In addition, composite resin teeth were fabricated, and zirconia bars were bonded to them with varying tooth preparations and lever arm lengths. In 1 group the influence of aging was analyzed. Fracture load was determined by using a universal testing machine. Statistical analysis was based on the Shapiro-Wilk normality test, ANOVA, and Games-Howell test (α=.05). ResultsThe maximum stress of 65 MPa occurring in the bonding area was reduced to 37 MPa by adding a retainer to the attachment. Loading of the denture resulted in a maximum stress of 9 MPa. Mean fracture loads ranged from 33.6 N to 209.1 N. Preparing a flat bonding surface showed a nonsignificant increase (P=.197), whereas aging led to a nonsignificant decrease in fracture load (P=.075). A lever arm extended by 2 mm significantly reduced fracture load (P=.002). The addition of an occlusal-distal (OD) cavity led to a nonsignificant increase (P=.186), which became significant when a mesial-occlusal-distal (MOD) preparation was applied (P=.001). ConclusionsAdhesive zirconia attachments should use a MOD cavity and have a cross section of at least 2.5×2.5 mm. The attachment should not extend more than 3 mm.

Flexural strength and Weibull characteristics of stereolithography additive manufactured versus milled zirconia

Statement of problemZirconia restorations can be processed by using stereolithography additive manufacturing (AM) technologies. However, whether additive manufactured zirconia could achieve flexural strength values comparable with those of milled zirconia is unclear. PurposeThe purpose of this in vitro study was to compare the flexural strength and Weibull characteristics of milled and additive manufactured zirconia. Material and methodsA total of 40 zirconia bars (25×4×1.2 mm) were obtained by using 2 manufacturing procedures, subtractive (CNC group) (IPS e.max ZirCAD; Ivoclar Vivadent AG) and additive manufacturing (AM group) (3DMix ZrO2; 3DCeram) technologies and assigned to 2 subgroups according to accelerating artificial aging procedures (mastication simulation): nonaged and aged (n=10). Flexural strength was measured in all specimens by using 3-point bend tests according to ISO/CD 6872.2 with a universal testing machine (Instron Model 8501; Instron Corp). Two-parameter Weibull distribution values, including the Weibull modulus, scale (m), and shape (0) were calculated. Flexural strength values were analyzed by using 2-way ANOVA and Student t statistical tests (α=.05). ResultsThe manufacturing procedure (P<.001), the mastication simulating aging procedure (P<.001), and the interaction between them (P<.001) significantly affected flexural strength values. The CNC group exhibited statistically higher flexural strength values than those in the AM group when the specimens were tested before performing an aging procedure (P<.001) and after mastication simulation (P<.001). Moreover, mastication simulation produced a significant reduction in flexural strength for both the CNC group (P<.039) and the AM group (P<.001). ConclusionsThe manufacturing process reported a significant effect on the flexural strength of the zirconia material tested. Mastication simulation as a means of accelerating artificial aging resulted in the significantly decreased flexural strength values of milled and additively manufactured zirconia material, with the Weibull moduli being significantly higher for the milled groups versus the milled specimens.

Shear bond strength of zirconia ceramic to the primary tooth dentin.

There is no information about the shear bond strengths (SBS) of zirconia ceramic to primary tooth dentin. To investigate the effect of different surface treatments and cements on the shear bond strength (SBS) of zirconia ceramic to primary tooth dentin. Prepared zirconia bars were distributed into four groups according to surface treatment procedure: control, sandblasting, CoJet and hot etching. The zirconia specimens in each group were further divided into subgroups according to cement (n = 13): self-adhesive resin (Rely-X Unicem), resin-modified glass ionomer (Ketac-Cem Plus), and universal bioactive (BioCem). Zirconia specimens were bonded to the primary tooth dentin surface by cement. SBS was measured, and the data were subjected to two-way ANOVA and Tukey's tests. Statistical differences were observed in the surface treatment procedures for Rely-X Unicem (P < 0.05), but no statistically significant differences were found in the sandblasting, CoJet and hot-etching groups for Ketac-Cem Plus (P > 0.05). For BioCem, the SBS value for the hot etching group was significantly lower than those for the CoJet and sandblasting groups (P < 0.05). The SBS values for the Rely-X Unicem subgroups (sandblasting, CoJet and hot etching) were significantly higher than those for the other cements (P < 0.05). The bond strength of zirconia ceramic to primary tooth dentin is affected by surface treatments and cements.

Retention force of zirconia bar retained implant overdenture: Clinical comparative study between PEEK and plastic clips.

Aim: This study aimed to evaluate and compare retention force of two implants retained mandibular overdenture with zirconia bar using two different clip materials.&#x0D; Methodology: 20 completely edentulous patients (8 women and 12 men) with age ranged between 45 and 65 years were selected for this study. All patients received conventional maxillary and mandibular complete dentures. Two implants were inserted bilaterally in the mandibular canine region. CAD-CAM fabricated zirconia bar attachment was used to retain mandibular overdentures. Patients were randomly divided into two equal groups where poly-oxy-methylene (POM) clip was used for Group I and poly-ether-ether-ketone (PEEK) clip for Group II. Retention force was measured at time of overdenture insertion (T0), six months (T6), and twelve months (T12) later.&#x0D; Results: significant difference was recorded between the two groups in initial retention forces (T0) where PEEK clip group recorded higher retention forces in comparison to POM clip group (P=0.029). However, insignificant difference was observed at (T6) and (T12). Within group comparison of mean retention values at different follow-up periods revealed significant difference for both groups.&#x0D; Conclusion:&#x0D; Within parameters of this study, it could be concluded that both POM and PEEK retentive clips can provide comparable retention forces when used with zirconia bar during 12 months period of overdenture use.&#x0D; &#x0D; How to cite this article: Emera RMK, Altonbary GY. Retention force of zirconia bar retained implant overdenture: Clinical comparative study between PEEK and plastic clips. Int Dent Res 2019;9(3):92-8.&#x0D; &#x0D; Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.