Monolithic Zirconia Specimens Research Articles

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

To investigate the esthetic outcomes based on the color differences in zirconia (Zr) of varying thickness, resin cement color, and types of titanium (Ti) implant surface treatments. Overall, 28 high-translucency monolithic zirconia (HTMZ) specimens were arranged into four groups based on Zr thickness: 1.0, 1.5, 2.0, and 2.5 mm (n &#61; 7 per thickness). Each group was tested using two resin cement colors (clear and opaque) in combination with six surface-treated Ti groups (n &#61; 7), including untreated titanium (UT), anodization (AN), 50-μm alumina airborne-particle abrasion followed by AN (SBAN), AN followed by 50-μm alumina airborne-particle abrasion (ANSB), 9.5% hydrofluoric acid followed by AN (HFAN), and AN followed by 9.5% hydrofluoric acid (ANHF). This created a total of 48 experimental groups, including the use of composite resin (n &#61; 7, shade A2D) for four control groups. All specimens were measured using a spectrophotometer and subsequently compared with composite resin (control) with the corresponding Zr thickness to establish color differences. A color difference of < 2.7 was considered clinically acceptable. The data obtained were statistically analyzed using ANOVA and post hoc test (P &#61; .05). Zr thickness, resin cement color, and type of Ti implant surface treatment significantly affected the observed color differences (P < .05). When using 2.5-mm HTMZ with clear resin cement on AN, UT, SBAN, HFAN, and ANSB, the mean color differences were below the clinically acceptable values, and the 95% CIs of color differences were below the clinically acceptable values for AN, UT, and SBAN groups. HTMZ with a minimum thickness of 2.5 mm and clear resin cement on AN, UT, and SBAN groups potentially result in acceptable color matching with 95% CIs.

Evaluation of the effects of different composite materials and surface roughening techniques in bonding attachments of clear aligner on monolithic zirconia.

The aim of this study is to evaluate the bond strengths of two different composite types used in the production of clear aligner attachments on monolithic zirconia with three different surface roughening processes. Packable composite Filtek Z250 was used in one group (PC-G) and flowable composite Filtek Supreme Ultra Flowable was used in the other group (FC-G). PC-G and FC-G groups were also divided into three subgroups as diamond bur+silane (Group 1), 50μm aluminium oxide (Al2 O3 ) sandblasting+silane (Group 2) and 110μm Al2 O3 sandblasting+silane (Group 3). Scanning electron microscopy (SEM) analysis was performed. Clear aligner attachments were bonded to the monolithic zirconia specimens. Shear bond strength (SBS) values were measured. Statistical analysis was performed using two-way ANOVA and post-hoc Tukey's tests (P < .05). The highest SBS value was found in PC-G sandblasted with 110 μm Al2 O3 (P ≤ .001). The etching method with 110 μm sandblasting showed high SBS values in both composite types. The lowest SBS value gave FC-G in diamond bur roughening (P ≤ .001). For the bonding of clear aligner attachments on monolithic zirconia, roughening with 110 μm particle size sandblasting and the choice of packable composite could be recommended in terms of retention.

Effect of abutment types and resin cements on the esthetics of implant-supported restorations.

The aim of the study was to evaluate the optical properties of new generation (3Y-TZP) monolithic zirconia (MZ) with different abutment types and resin cement shades. A1/LT MZ specimens were prepared (10 × 12 × 1 mm, N = 30) and divided into 3 groups according to cement shades as transparent (Tr), yellow (Y) and opaque (O). Abutment specimens were obtained from 4 different materials including zirconia (Group Z), hybrid (Group H), titanium (Group T) and anodized yellow titanium (Group AT). MZ and abutment specimens were then cemented. L*, a*, and b* parameters were obtained from MZ, MZ + abutment, and MZ + abutment + cement. ΔE001* (between MZ and MZ + abutment), ΔE002* (between MZ and MZ + abutment + cement) and ΔE003* (between MZ + abutment and MZ + abutment + cement) values were calculated. Statistical analyses included 2-way ANOVA, Bonferroni, and Paired Sample t-Tests (P < .05). Abutment types and resin cements had significant effect on L*, a*, b*, ΔE001*, ΔE002*, and ΔE003* values (P < .001). Without cementation, whereas zirconia abutment resulted in the least discoloration (ΔE001* = 0.68), titanium abutment caused the most discoloration (ΔE001* = 4.99). The least ΔE002* = 0.68 value was seen using zirconia abutment after cementation with yellow shaded cement. Opaque shaded cement caused the most color change (ΔE003* = 5.24). Cement application increased the L* values in all groups. The least color change with/without cement was observed in crown configurations created with zirconia abutments. Zirconia and hybrid abutments produced significantly lower ΔE002* and ΔE003* values in combination with yellow shaded cement. The usage of opaque shaded cement in titanium/anodized titanium groups may enable the clinically unacceptable ΔE00* value to reach the acceptable level.

The effect of aging on the fracture resistance of different types of screw-cement-retained implant-supported zirconia-based restorations.

Structural durability of screw-cement-retained implant-supported zirconia-based restorations is an important factor in choosing the best type of restoration for clinical use. This study aimed to evaluate the effects of thermocycling on the fracture resistance of different types of screw-cement-retained implant-supported zirconia-based restoration. Two experimental groups (monolithic zirconia and porcelain-veneered zirconia) and a control group of porcelain-fused-to-metal restorations were fabricated via CAD-CAM (n = 14 per group). Half of the specimens of each group (n = 7) were subjected to 10000 thermal cycles. The compressive force was applied and the force leading to fracture was measured by using a Universal Testing Machine. The fractured modes were classified under a scanning electron microscope. The data were analyzed through two-way ANOVA, one-way ANOVA, and independent samples t-test (α = 0.05). Among the non-thermocycled subgroups, the monolithic zirconia specimens were significantly more fracture-resistant than the porcelain-veneered zirconia and porcelain-fused-to-metal groups (P<0.05); but it was not the same with aging (P>0.05). Thermocycling decreased the fracture resistance of all groups; however, the difference was not statistically significant (P<0.05). The monolithic zirconia presented higher fracture resistance than the bilayered restorations for screw-cement retained implant-supported restorations. Thermocycling decreased the fracture resistance of all types of restorations insignificantly which can be clinically important.

The effect of adjustment and finishing procedure on roughness, strength, and phase transformation of monolithic zirconia.

To evaluate the effect of adjustment and finishing procedures and thermal aging of monolithic zirconia on the surface roughness, phase transformation, and flexural strength. One hundred disk-shaped monolithic zirconia specimens were randomly divided into 5 groups: control, received only glazing; group Gr, was grinded; group GrP, was grinded and polished; group GrG, was grinded and re-glazed; group GrPG, was re-glazed after grinding and polishing. Half of the each group were stored in distilled water for 24h and the remaining were thermocycled for 5000 cycles. Topographic evaluations were done with profilometer and scanning electron microscope. Phase changes were assessed through X-ray diffractometer. The biaxial flexural strength test was calculated by universal test machine. Statistical analysis was performed by using two-way ANOVA and Tukey multiple comparison test (p < 0.05). Group Gr showed statistically higher surface roughness and flexural strength values than the other groups (p < 0.001). However, no significant differences were observed between finishing groups (p >0.05). Phase transformation was occurred in all groups but the differences were not statically significant (p >0.05). Artificial aging had no effect on surface roughness, flexural strength, and phase transformation (p >0.05). Surface roughness significantly increased after grinding, but finishing procedure approximated it to the control group. Glazing after grinding decreased the flexural strength, but polishing did not. Zirconia polishing system may be an alternative to re-glazing for monolithic zirconia. Polishing is one of the most effective finishing procedures that can improve the physical properties of the material without damaging its mechanical properties.

A Comparative Study on Simulated Chairside Grinding and Polishing of Monolithic Zirconia.

This study evaluated the effects of different simulated chairside grinding and polishing protocols on the physical and mechanical properties of surface roughness, hardness, and flexural strength of monolithic zirconia. Sintered monolithic zirconia specimens (15 mm × 3 mm × 3 mm) were abraded using three different burs: diamond bur, modified diamond bur (zirconia specified), and tungsten carbide bur, along with a group of unprepared specimens that served as a control group. The study was divided into two phases, Phase 1 and Phase 2. Surface roughness, surface hardness, and flexural strength were assessed before and after the grinding procedure to determine the ‘best test group’ in Phase 1. The best abrasive agent was selected for Phase 2 of the study. The specimens in Phase 2 underwent grinding with the best abrasive agent selected. Following the grinding, the specimens were then polished using commercially available diamond polishing paste, a porcelain polishing kit, and an indigenously developed low-temperature sintered zirconia slurry. The physical and mechanical properties were again assessed. Results were analyzed using one-way ANOVA test. Specimens were observed under scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their microstructure and crystalline phases, respectively. Grinding with diamond burs did not weaken zirconia (p > 0.05) but produced rougher surfaces than the control group (p < 0.05). Tungsten carbide burs did not significantly roughen the zirconia surface. However, specimens ground by tungsten carbide burs had a significantly reduced mean flexural strength (p < 0.05) and SEM revealed fine surface cracks. Phase transformation was not detected by XRD. Polishing with commercially available polishing agents, however, restored the surface roughness levels to the control group. Dental monolithic zirconia ground with tungsten carbide burs had a significantly reduced flexural strength and a smooth but defective surface. However, grinding with diamond burs roughened the zirconia surface. These defects may be reduced by polishing with commercially available polishing agents. The use of tungsten carbide burs for grinding dental zirconia should not be advocated. Grinding with diamond abrasives does not weaken zirconia but requires further polishing with commercially available polishing agents.

Push-Out Force and Microleakage of Screw Access Hole Filling Materials in Monolithic Zirconia Implant Crowns.

To test the push-out force and marginal leakage of different screw hole-sealing methods in monolithic zirconia implant crowns. Ninety monolithic zirconia (Prettau, Zirkonzahn) specimens were milled with two different screw access hole designs: conventional smooth hole or threaded screw hole (for group PMMA-SC), and divided into five groups (n = 18) according to filling method: unbonded composite (UBC); bonded composite (BC); airborne-particle abrasion of screw hole and unbonded composite (ABR-UBC); airborne-particle abrasion of screw hole and bonded composite (ABR-BC); and PMMA screw plugs (PMMA-SC). Twelve specimens per group were subjected to static push-out force with a universal testing machine. Before testing, 6 specimens per group were stored in dry conditions, and 6 were kept in water storage (+37°C) for 7 days. For the remaining specimens (n = 6), cotton pellets were placed under the screw access hole fillings, and the specimens were immersed in 0.5% basic fuchsin solution for 2 weeks. Dye in cotton pellets was dissolved in 2 mL of water, and absorbances of the solutions were measured with a spectrophotometer at 465 nm. Data are reported as mean and SD. Statistical analysis was made using a generalized linear model with logarithmic transformation. PMMA-SC specimens showed the highest push-out forces (P < .0001) and lowest fuchsin penetration (P = .009). Airborne-particle abrasion increased the push-out force and decreased the microleakage in composite groups. The storage conditions affected the results of both unbonded groups. The design and sealing method of the screw access hole affect push-out force and microleakage.

Effects of Grinding and Polishing on Surface Characteristics of Monolithic Zirconia Fabricated by Different Manufacturing Processes: Wet Deposition and Dry Milling.

To evaluate the effects of grinding and polishing on surface characteristics of monolithic zirconia fabricated by two different manufacturing processes. Two types of monolithic zirconia specimens, self-glazed zirconia (SZ) and conventional zirconia (CZ), were fabricated by wet deposition and dry milling, respectively. The specimens were randomly assigned into 4 groups (n = 10): as-sintered, ground, polished with a special zirconia polishing kit, and polished with a general-purpose ceramic polishing kit. Surface morphology and roughness (Ra ) were characterized, followed by one-way ANOVA analysis (α = 0.05). The as-sintered SZ exhibited a smooth surface with obvious different morphologies compared with the as-sintered CZ (Ra : 0.26 ± 0.05 μm versus 0.33 ± 0.10 μm). Ra of the ground SZ was significantly higher than that of the as-sintered SZ (p < 0.001) and the ground CZ (p = 0.011). For both SZ and CZ, Ra decreased significantly after polishing (p < 0.001), and there was no significant difference between the two groups with different polishing kits (SZ- p = 0.144; CZ- p = 0.322). Surface morphologies of SZ and CZ became similar after grinding and polishing. Monolithic zirconia SZ fabricated by wet deposition exhibited a smooth surface with specific patterns compared to the dry milled CZ. Grinding significantly changed the surface morphology of SZ and increased surface roughness of both zirconia specimens, which can be improved by polishing without being influenced by polishing kit selection.

Effects of sintering protocol and dipping time on the optical properties of monolithic zirconia

Statement of problemThe use of monolithic zirconia for restorations has become popular. However, the effects of the coloring process and sintering procedure on the optical properties of monolithic zirconia remain unclear. PurposeThe purpose of this in vitro study was to evaluate the effects of the different sintering protocols and dipping times on the CIELab color parameters, color difference (ΔE00), translucency parameter (TP00), opalescence parameter (OP), and contrast ratio (CR) of monolithic zirconia. Material and methodsOne hundred and fifty monolithic zirconia specimens were prepared and divided into 5 groups according to different dipping times in A2 shade coloring liquid: no immersion (D0), 3 minutes (D3), 5 minutes (D5), 7 minutes (D7), and 9 minutes (D9). The specimens were further divided into 3 subgroups according to different sintering protocols (n=10): classic (C); speed (S); and super-speed sintering (SS). The CIE L∗a∗b∗ values, ΔE00, TP00, OP, and CR values were determined with a spectrophotometer. The data were analyzed with 2-way ANOVA and Bonferroni post hoc tests (α=.05). ResultsThe effects of the sintering protocol, dipping time, and interaction of the sintering protocol and dipping time were significant for the L∗, a∗, b∗, ΔE00, TP00, OP, and CR parameters (P<.001). The ΔE00 values of the SS groups were significantly higher than those of the C and S groups for all the dipping times assessed. However, only the CD3 and CD5 groups had ΔE00 values below the acceptability threshold (<1.8). Coloring significantly reduced TP00 values and significantly increased OP and CR values in the colored groups compared with those in the D0 groups. The C and S protocols for different dipping times showed similar optical properties in TP00, OP, CR, and ΔE00 (excluding the D0 and D9 groups) compared with the SS protocol. ConclusionsDifferent sintering protocols combined with various dipping times significantly affected the optical properties of monolithic zirconia. However, C and S sintering with a 3-minute and 5-minute coloring process yielded more favorable optical results than SS sintering and prolonged dipping times.

Bracket Bonding to All-Ceramic Materials with Universal Adhesives.

The need for bracket bonding to ceramic restorations is increasing. The aim of this study was to evaluate the effect of universal adhesives on bracket adhesion to polished or glazed lithium disilicate (LDS) and monolithic zirconia (MZ) surfaces. One hundred and twenty brackets (N = 10) were bonded to either polished or glazed LDS (e.max CAD B32, Ivoclar Vivadent, Schaan, Liechtenstein) and MZ (In-Ceram® YZ, VITA, Bad Sackingen, Germany) blocks using three different adhesives combined with Transbond™ XT Paste (3M Unitek, Monrovia, CA, USA). Tested universal adhesives were Scotchbond™ Universal Adhesive (SU, 3M St. Paul, MN, USA) and Assure Plus (AP, Reliance, Itasca, IL, USA). Transbond™ XT Primer (XTP, 3M Unitek, Monrovia, CA, USA) served as a control adhesive. Bracket bond strength was measured in shear mode (SBS). Failure type was determined by the Modified Adhesive Remnant Index (ARI). Data were statistically analyzed. On polished LDS, SU yielded bracket SBS significantly superior to those of AP and XTP. On polished MZ, the use of SU and AP significantly enhanced bracket retention as compared with XTP. Low SBS values, below the threshold of clinical acceptability, were reached by all tested adhesives on glazed LDS and MZ specimens. SBS measurements corresponded with failure type observations. Universal adhesives SU and AP could be considered for use on polished LDS and MZ surfaces.

Influence of zirconia/glass veneer thickness and implant abutment material on the final shade of implant restorations.

The aim of this study was to investigate the combined effect of ceramic material, ceramic thickness, and implant abutment background to the final color of restorations. This was a comparative in vitro study. Three different types of monolithic and porcelain-veneered zirconia disc-shaped specimens (Prettau Anterior, VITA YZ ST, and VITA YZ HT) were prepared in A3 shade with two different thicknesses (1 mm and 1.5 mm) (n = 10). Each zirconia material was made of 4-mm thickness as a control specimen of each monolithic zirconia type, and 4-mm thick veneering ceramic (VITA VM9 Base Dentine) was made as a control for veneered zirconia groups. Three simulated implant abutments were fabricated from titanium, white-shaded and yellow-shaded zirconia. The zirconia specimens were placed on different abutment backgrounds, and the color difference (ΔE) between experimental and control specimens was measured. The three-way ANOVA and the Scheffé test were used for data analysis (α = 0.05). The mean ΔE values between two thicknesses were significantly different in every background for all zirconia materials. The ΔE values of zirconia specimens on yellow zirconia were lower than those of other abutments. The clinically acceptable ΔE value (ΔE <3) was found in some monolithic zirconia specimens on white-shaded and yellow-shaded abutments, while the ΔE value is approximately 3 or less in all 1.5-mm thick porcelain-veneered zirconia groups. Different zirconia materials on implant abutments affected the final color of restorations. To achieve satisfactory color, the minimum thickness of zirconia restorations should be at least 1.5 mm on yellow zirconia abutment.

A comparative evaluation of different saliva cleaning regimens on the shear bond strength of two different ceramics with resin cement

Contamination of all-ceramic restorations with oral fluids during clinical try-in can have a detrimental effect on their clinical performance. Objective: The aim of this study was to compare the efficiency of four different saliva cleaning regimens on the shear bond strength (SBS) of lithium disilicate and zirconia with resin cement. Materials and Methods: Ten cubic samples of lithium disilicate pressable ceramic (Group A) and monolithic zirconia (Group B) were fabricated. Four surfaces from each sample were coated with saliva, washed with water, and dried. These surfaces were subsequently treated with four different cleaning protocols (water [A1, B1], isopropyl alcohol [A2, B2], sodium hypochlorite [A3, B3], and Ivoclean™ [A4, B4]) and bonded to composite cylinders using dual-cure resin cement. The specimens were then tested for SBS. Results: Group A, subgroup A4 had a significantly higher mean SBS compared to other groups, and for Group B, subgroup B4 had a significantly higher mean SBS compared to other groups. The mean difference in the SBS for subgroup A1 and B1 was −3.862 at P = 0.01; for subgroup A2 and B2, it was −4.164 at P = 0.03; for A3 and B3, it was −4.845 at P &lt; 0.001; and for subgroup A4 and B4, it was −24.990 at P &lt; 0.001. Conclusion: Monolithic zirconia specimens showed significantly more SBS compared to lithium disilicate specimens in all subgroups. The mean SBS was highest for surfaces cleaned using Ivoclean in both groups.

Bending strength of ceramic compounds bonded with silicate-based glass solder

AbstractIn the field of dental technology, the length of ceramic pontics is limited to avoid mechanical failure. To reduce thermal-induced residual stress within the ceramic, using smaller subcomponents and subsequent bonding with silicate-based glass solder may be a favorable approach. Thus, the bending strength of zirconia compounds bonded with different silicate-based glass solders was investigated. For this purpose, rectangular specimens made of zirconia were bonded by glass solder. Parameters such as the scarf angle (45° and 90°), two different glass solders, as well as the soldering process (pressure and surface treatment) were varied. All specimens were subjected to quasi-static four-point bending tests according to DIN EN ISO 843-1. Additionally, the quality of the glass solder connection was evaluated usingμCT and fractography. In the present study, zirconia compounds were sucessful bonded of zirconia compounds using silicate-based glass solder was. No significant differences in terms of bending strength were observed with respect to the different bonding parameters analyzed. The highest bending strength of 130.6 ± 50.5 MPa was achieved with a 90° scarf angle combined with ethanol treatment of the specimens before soldering and an additional application of a pressure of 2 bars in a dental pressure pot before subsequent soldering. Nevertheless, the bending strengths were highly decreased when compared to monolithic zirconia specimens (993.4 ± 125.5 MPa).

On the production of novel zirconia-reinforced bioactive glass porous structures for bone repair

The objective of this study was to develop a replica method for producing zirconia-reinforced bioactive glass (ZRBG) porous structures for bone repair. Four different types of porous structures were produced: zirconia (G1), 58S BG-coated zirconia (G2), zirconia-reinforced BG (G3) and 58S BG-coated zirconia-reinforced BG (G4). A complete characterization of the specimens was performed via SEM-EDS, Archimedes method, 3D X-ray micro-tomography, micro-indentation, compressive strength tests and SBF immersion tests. G3 and G4 specimens presented a BG matrix (~ 33% glassy phase) with dispersed zirconia particles. The porosity of the specimens ranged from 86% up to 93%. BG58S-zirconia groups G3 and G4) exhibited lower YM (38.76 ± 11.20 GPa and 43.49 ± 2.16 GPa) than that of G1 monolithic zirconia specimens (94.39 ± 12.62 GPa), which were more compatible to that of the bone. No significant difference in compressive strength between BG58S-zirconia (G3: 0.41 ± 0.20 MPa; G4: 0.45 ± 0.11 MPa) and zirconia (G1: 0.32 ± 0.11 MPa) was detected observed (p > 0.05). In vitro SBF tests showed a potential bioactivity for ZRBG porous structures.

Effect of different cleaning methods on resin bond strength of contaminated monolithic zirconia

The present study evaluated the effects of cleaning methods on resin bond strength to contaminated monolithic zirconia. A total of 180 bar-shaped monolithic zirconia specimens (12 mm × 4 mm × 1.2 mm) were abraded with aluminum oxide and divided into nine groups (n = 10). The control group (Cnt) comprised non-contaminated or cleaned monolithic zirconia specimens. Half of the remaining samples were contaminated with saliva (S) and the other half with a silicone disclosing agent (F; Fit checker). The bonding surfaces of the specimens were cleaned with water (Sw and Fw), 0.5% sodium hypochlorite (NaOCl) solution (Sh and Fh), 37% phosphoric acid gel (Sa and Fa), or plasma treatment (Sp and Fp). The bars were luted end-to-end on the bonding surfaces using a self-adhesive resin cement with a custom-made stainless-steel mold. After 72 h of water storage, the bond strength was measured using a four-point bending test. Data were analyzed using two-way ANOVA and Tukey’s test. The Cnt group showed the highest four-point bending strength (p < .05). There were no significant differences among the groups subjected to the cleaning methods, except the NaOCl groups (p > .05). These findings indicate that the cleaning protocol for saliva- or fit checker-contaminated monolithic zirconia ceramics must be taken into account to ensure zirconia–resin cement bond strength resistance. The plasma treatment that an alternative cleaning method for decontamination did not affect the bond strength between monolithic zirconia and resin cement.

Effect of in vitro aging and acidic storage on color, translucency, and contrast ratio of monolithic zirconia and lithium disilicate ceramics

Statement of problemHow the translucency and color of ceramic restorations are affected by surface changes from the corrosive environment in the oral cavity and aging of materials is unclear. PurposeThe purpose of this in vitro study was to compare the impact of acidic exposure and aging on the color and translucency of monolithic zirconia and lithium disilicate ceramics. Material and methodsTwenty computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic zirconia specimens and 20 pressed lithium disilicate specimens were fabricated. Half of the specimens of each group were aged in an autoclave (7.5 hours, 134 °C, 0.2 MPa), and the rest were immersed in hydrochloric acid to simulate the acidic conditions in the oral cavity from gastric reflux. The color coordinates L∗, a∗, and b∗ were measured with an ultraviolet spectrophotometer before and after aging or acidic storage. The translucency parameters and contrast ratios were calculated, and the CIEDE2000 color difference formula was used to determine color differences before and after each treatment. ANOVA and ANCOVA test models were used for data analysis (α=.05), while differences of color parameters in respect to acceptability and perceptibility thresholds were evaluated with the 1-sample t test (α=.05). ResultsLithium disilicate presented a significantly higher translucency parameter and lower contrast ratio at baseline compared with monolithic zirconia specimens (P<.001). Acidic storage significantly impacted all parameters compared with aging, especially for the lithium disilicate group. Color differences were above the acceptability ΔΕ00 threshold for lithium disilicate after acidic storage (P=.001) and below for monolithic zirconia after acidic storage (P=.003). ConclusionsThe performance of lithium disilicate was slightly inferior compared with that of monolithic zirconia specimens, as they presented significant and clinically observable differences for the translucency parameter and ΔΕ00 after acidic storage and aging.

Microhardness of resin cements after light activation through various translucencies of monolithic zirconia.

PURPOSEThis study aimed to investigate the Vickers Hardness Number (VHN) of light- and dual cured resin cements cured through monolithic zirconia specimens (VITA YZ) of various translucencies: translucent (T); high translucent (HT); super translucent (ST); and extra translucent (XT) at 0, 24, and 48 h after curing.MATERIALS AND METHODSFour zirconia specimens from each translucency were prepared. Two light-cured resin cements (Variolink N LC; VL and RelyX Veneer; RL) and two dual-cured resin cements (Variolink N DC; VD and RelyX U200; RD) were used. The cement was mixed and loaded in a mold and cured for 20 s through the zirconia specimen. The upper surface of cements was tested for VHN using a microhardness tester at 0, 24, and 48 h after curing. The VHN were analyzed using two-way repeated, Brown-Forsythe ANOVA with Games Howell post-hoc analysis and independent t-tests (P < .05).RESULTSAll cements showed significantly higher VHN from 0 h to 24 h (P < .001). At 48 h, the VHN of light-cured cements were significantly lower when cured under the T groups than under XT groups (P = .001 in VL, P = .014 in RL). At each post curing time of each translucency, VD showed higher VHN than VL (P < .05), and RD also showed higher VHN than RL (P < .05).CONCLUSIONThe translucency of zirconia has an effect on the VHN for light-cured resin cements, but has no effect on dual-cured resin cements. Dual-cured resin cement exhibited higher VHN than the light-cured resin cement from the same manufacturer. All resin cements showed significantly higher VHN from 0 h to 24 h.

A comparative study of the wear of dental alloys against monolithic zirconia

Statement of problemMaterials used for dental restorations should cause wear similar to that of natural teeth. Studies on the wear of dental alloys against monolithic zirconia are lacking. PurposeThe purpose of this in vitro study was to compare the wear of Co-Cr, gold, and Ni-Cr alloys against monolithic zirconia of different surface roughness. Material and methodsCylindrical monolithic zirconia specimens were prepared by a sintering process. Sintered zirconia was then polished to prepare 30 zirconia substrate specimens with a smooth surface (Ra<0.1 μm) and 30 with a rough surface (3.5 μm<Ra<4.5 μm). As antagonist specimens, 3 types of metal alloys (Co-Cr, gold, and Ni-Cr alloys) were used. Twenty cast crowns were prepared from each metal alloy in the shape of a maxillary premolar. For each alloy, 10 cast crowns were randomly selected to oppose the smooth-surface zirconia specimens and 10 to oppose the rough-surface zirconia specimens. A total of 6 wear test groups were formed. Wear tests were performed by using a mastication simulator at 240 000 mastication cycles. Wear on the antagonist specimens was measured by using a laser 3D scanner. After wear testing, antagonist and substrate specimens were inspected by using a scanning electron microscope (SEM). For statistical analysis of the data, the 2-way ANOVA and the Scheffé multiple comparison tests were used (α=.05). ResultsOf the 6 test groups, the gold alloy specimens opposed to rough-surface zirconia exhibited the most wear, while the Co-Cr alloy specimens opposed to smooth-surface zirconia exhibited the least wear (P<.05). Rough-surface monolithic zirconia caused significantly more wear of the metal alloy specimens than did smooth-surface monolithic zirconia (P<.01). ConclusionsIncreased surface roughness of monolithic zirconia was associated with increased wear of the opposing dental alloy. When monolithic zirconia surface roughness was increased, wear of dental alloys increased most for gold alloys, followed by Ni-Cr, and then Co-Cr alloys.

Optical and Surface Properties of Monolithic Zirconia after Simulated Toothbrushing.

This in vitro study investigated the impact of various dentifrices on the shade, translucency, gloss, and surface characteristics of polishing- or glazing-finished monolithic zirconia surfaces after simulated toothbrushing. Eighty square-shaped monolithic zirconia specimens were divided into two major groups based on the finishing methods—polished (P) and glazed (G). Next, specimens from the two major groups were categorized into four subgroups: stored in distilled water (DW, control); brushed with a fluoride-free conventional dentifrice (C); brushed with a fluoride dentifrice (F); and brushed with a whitening dentifrice (W). Overall, eight groups were created—PDW, PC, PF, PW, GDW, GC, GF, and GW (n = 10 each). Shade, translucency, surface gloss, surface roughness, crystalline phase, and superficial topography data were obtained. Repeated-measures ANOVA and two-way ANOVA were used for intergroup comparison (all α = 0.05). The color differences (ΔE00) between pre- and posttreatment were 0.3158 (PDW), 0.7164 (PC), 0.7498 (PF), 0.8106 (PW), 0.1953 (GDW), 0.301 (GC), 0.3051 (GF), and 0.4846 (GW). A statistically significant difference was observed among the ΔE00, surface gloss, and surface roughness of monolithic zirconia. Thus, brushing with several dentifrices markedly affects the optical properties and surface characteristics of monolithic zirconia finished with polishing or glazing methods.

Influence of heating rate on the flexural strength of monolithic zirconia.

PURPOSEFabrication of zirconia restorations with ideal mechanical properties in a short period is a great challenge for clinicians. The purpose of the study was to investigate the effect of heating rate on the mechanical and microstructural properties of monolithic zirconia.MATERIALS AND METHODSForty monolithic zirconia specimens were prepared from presintered monolithic zirconia blanks. All specimens were then assigned to 4 groups according to heating rate as Control, Group 15℃, Group 20℃, and Group 40℃. All groups were sintered according to heating rates with the sintering temperature of 1500℃, a holding time of 90 minutes and natural cooling. The phase composition was examined by XRD analysis, three-point bending test was conducted to examine the flexural strength, and Weibull analysis was conducted to determine weibull modulus and characteristic strength. Average grain sizes were determined by SEM analysis. One-way ANOVA test was performed at a significance level of 0.05.RESULTSOnly tetragonal phase characteristic peaks were determined on the surface of analyzed specimens. Differences among the average grain sizes of the groups were not statistically significant. The results of the three-point bending test revealed no significant differences among the flexural strength of the groups (P>.05). Weibull modulus of groups was ranging from 3.50 to 4.74. The highest and the lowest characteristic strength values were obtained in Group 20℃ and Control Group, respectively.CONCLUSIONHeating rate has no significant effect on the flexural strength of monolithic zirconia. Monolithic zirconia restorations can be produced in shorter sintering periods without affecting the flexural strength by modifying the heating rate.