Classification and Properties of Dental Zirconia as Implant Fixtures and Superstructures

Enhanced Osteoconductivity of Zirconia Implants with One-Step Femtosecond Laser Treatment Through Morphological and Chemical Modifications

Improving surface bioactivity is crucial to acquiring zirconia implants with ideal osteoconductivity. In this work, we enhanced the surface properties of zirconia implants, specifically roughness, hydrophilicity, and osteoconductivity, using a "one-step" femtosecond laser (FSL) treatment in air, deionized water, and sodium hydroxide solution. Zirconia specimens were treated in these media, and their surface morphology, chemical composition, and osteoconductivity were evaluated through various assays. The results showed that FSL treatment successfully created micro/nanoporous structures and increased roughness across all specimens. The liquid media treatment facilitated the grafting of hydroxyl (-OH) groups, significantly improving hydrophilicity. The L-NaOH group exhibited a higher hydroxyl content (28%) compared to the L-Air group (10%), reducing the contact angle significantly. Enhanced osteoblast differentiation and mineralization, along with improved gene expression, were observed in the L-Water and L-NaOH groups. In conclusion, the one-step FSL treatment developed a dual-function bioactive zirconia surface, offering an effective method for the biomedical functionalization of zirconia implants.

The impact of various substrates, ceramic shades, and brands on the ultimate color and masking capacity of highly translucent monolithic zirconia: an in vitro study

This study aimed to examine the impact of substrates, ceramic shades, and brands on the color and masking ability of highly translucent monolithic zirconia (HTMZ) using CIELab and CIEΔE2000 metrics. A total of 156 1-mm thick HTMZ disks in shades A1, A2, and A3 were produced using Dental Direkt and Kerox zirconia brands. Four 3-mm thick substrates (nickel-chromium alloy, non-precious gold alloy (NPG), zirconia shade A2, and resin composite shade A2) were prepared. HTMZ disks were overlaid on these substrates, and color measurements were taken with a spectrophotometer. Color differences (ΔE) were analyzed using CIELab and CIEΔE2000 formulas. The influence of brand, shade, substrate, and their interactions on ΔE values was assessed with a General Linear Model (GLM) and LSD pairwise comparison test. Spearman's correlation test examined the relationship between CIELab and CIEΔE2000 values. Results indicated that ΔEab was significantly influenced by substrate type and shade, while ΔE2000 was also affected by the ceramic brand. Mean color differences across ceramic-substrate groups were within clinically acceptable and perceptible ranges (clinically perceptible: ∆Eab ≥ 1.3 and ∆E2000 ≥ 0.8; clinically acceptable: 0.8 < ∆E2000 ≤ 1.8 and 1.3 < ∆Eab ≤ 2.7), except for NPG, which had ΔE values exceeding the perceptible range (ΔE2000: 1.1 ± 0.11 to 1.8 ± 0.31; ΔEab: 1.61 ± 0.15 to 2.16 ± 0.36). A significant correlation (r = 0.974, P < 0.001) was found between ΔEab and ΔE2000. Various ceramic brands and shades led to notable ΔE variations, yet average color differences within all ceramic-substrate groups remained clinically acceptable. Both ΔEab and ΔE2000 were reliable methods with a strong correlation for measuring color differences.

Comparison of Mechanical and Optical Properties of Multilayer Zirconia After High-Speed and Repeated Sintering

This study aims to investigate the mechanical and optical properties of two different multilayer monolithic zirconia materials after the high-speed and repeated sintering process recommended by the manufacturers. In this study, specimens with a diameter of 12 mm and a thickness of 1 mm were fabricated using KATANA Zirconia YML (Kuraray Noritake) and IPS e.max ZirCAD Prime (Ivoclar Vivadent) multilayer zirconia. These specimens were processed with two different protocols to be used in the sintering process: high-speed and conventional sintering. Both protocols were repeated three times, after which the changes in the mechanical, microstructural and optical properties of the specimens were compared and analyzed. According to the biaxial flexural strength result, KATANA Zirconia YML (840.84 MPa) showed higher biaxial flexural strength compared to IPS e.max ZirCAD Prime (627.64 MPa) after repeated high-speed sintering. When the optical properties were analyzed, the translucency parameters of the IPS e.max ZirCAD Prime block were reliable in certain protocols. A comparison of mechanical and optical properties after repeated and high-speed sintering reveals that both materials offer advantages for different application requirements. The high biaxial flexural strength of KATANA Zirconia YML is more suitable for applications requiring strength. The homogeneous translucency of IPS e.max ZirCAD Prime is esthetically and optically safer for high-speed and repeated sintering processes.

Light-curing of restorative composite through milled and 3D-printed full-contour zirconia for adhesive luting

OBJECTIVES

To evaluate the effect of different zirconia compositions and manufacturing processes on the light irradiance (LI), to measure the degree of conversion (DC) of solely light-curing restorative composite underneath these zirconia grades and to evaluate the respective zirconia microstructures.

METHODS

Six dental zirconia grades (GC HT, GC UHT [GC]; Katana HT, Katana UTML [Kuraray Noritake]; Lava Esthetic, Lava Plus [3 M Oral Care]) were cut and sintered per manufacturer instructions. One 3D-printed zirconia grade (XJet [XJET]) was prepared according to previous research. Zirconia plates were ground to four thicknesses (0.5, 1.0, 1.5, 3.0 mm). The LI through these zirconias was measured using light spectrometry using two light-curing units (Demi Plus [Kerr], Bluephase G4 [Ivoclar]). Restorative composite (Clearfil AP-X [Kuraray Noritake]) was light-cured through the zirconia plates and the DC was determined by micro-Raman spectrometry 5 min, 24 h and 1 w after light-curing. Statistical analysis of LI and DC data involved linear mixed-effects modelling and multi-way ANOVA. Microstructural analysis of zirconia was performed by scanning electron microscopy.

RESULTS

Zirconia type and thickness, and LCU had a significant effect on LI (p < .0001). DC significantly increased over time (p < .0001) and was not influenced by curing-light attenuation if LI reached at least 40 mW/cm². Increased yttria content resulted in an increased zirconia grain size.

SIGNIFICANCE

Despite significant light attenuation, DC of composite light-cured through zirconia at almost all thicknesses, approached DC measured without zirconia interposition for five out of seven zirconia grades. Additionally, the manufacturing process did not seem to influence LI or DC.

Implant-Supported Cantilever Fixed Dental Prosthesis in the Anterior Region: Effect of Implant Type and Aging In Vitro

OBJECTIVES

To investigate if the fracture load of implant-supported cantilever fixed dental prostheses (ICFDPs) in the anterior region is affected by the implant type and the aging protocol.

MATERIALS AND METHODS

Sixty ICFDPs were prepared using multilayer monolithic zirconia for restoring bone-level (BL) and tissue-level (TL) titanium-zirconium implants. Fracture load was measured at baseline (no aging) or after aging in a chewing simulator loading the implant crown or the cantilever in a 30° angle (n = 10 per group). A two-way ANOVA was applied (α = 0.05) for the effects of implant type and aging protocol.

RESULTS

Implant type (p < 0.001) and aging (p < 0.001) had a significant effect on fracture load values. Baseline specimens of both BL (665 ± 62 N) and TL (554 ± 23 N) had significantly higher mean fracture load values than those of aged specimens(BL implant crown 545 ± 46 N, BL cantilever 563 ± 45 N, TL implant crown 455 ± 32 N, TL cantilever 476 ± 24 N) (p < 0.001). The loading position during aging did not affect fracture load values for BL (p = 0.980) nor TL (p = 0.749). BL implants failed by cement fracture and abutment deformation, while for TL the transmucosal part of the implant deformed.

CONCLUSIONS

The fracture load values of anterior ICFDPs decrease with aging in a chewing simulator. BL implants are preferable over TL implants for anterior ICFDPs as higher fracture load values were achieved, and no implant deformation occurred.

Evaluating the Impact of Pontic Geometry on Load to Failure and Displacement in Implant-Supported Monolithic Zirconia Prostheses: An In Vitro Analysis

The pontic design may influence the load-to-failure performance of fixed implant-supported screw-retained monolithic zirconia prostheses. This study aimed to evaluate the effect of pontic geometry on the fracture resistance of such restorations. Forty restorations were designed using dental CAD software and divided into four groups (n = 10 each): (A) Flat + Wide-pontics with a flat contour, 10 mm in width and 8 mm in height; (B) Concave + Wide-pontics with a concave contour, 10 mm in width and 5.5 mm in height; (C) Flat + Narrow-pontics with a flat contour, 6 mm in width and 8 mm in height; and (D) Concave + Narrow-pontics with a concave contour, 6 mm in width and 5.5 mm in height. All specimens underwent thermal and mechanical cycling, followed by a fracture load test using a three-point bending setup. Maximum fracture loads and displacements were analyzed using one-way ANOVA. Statistically significant differences were observed among the groups for both load to failure (p = 0.001) and displacement (p = 0.002). These findings indicate that pontic geometry significantly influences the fracture resistance and deformation behavior of monolithic zirconia prostheses.

Factors Affecting the Color Change of Monolithic Zirconia Ceramics: A Narrative Review

Zirconia restorations are widely used in dentistry due to their high esthetic expectations and physical durability. However, zirconia's opaque white color can compromise esthetics. Therefore, zirconia is often veneered with porcelain, but fractures may occur in the veneer layer. Monolithic zirconia restorations, which do not require porcelain veneering and offer higher translucency, have been developed to address this issue. Zirconia exists in three main crystal phases: monoclinic, tetragonal, and cubic. Metal oxides such as yttrium are added to stabilize the tetragonal phase at room temperature. 3Y-TZP contains 3 mol% yttrium and provides high mechanical strength but has poor optical properties. Recently, 4Y-PSZ and 5Y-PSZ ceramics, which offer better optical properties but lower mechanical strength, have been introduced. This review examines the factors affecting the color change in monolithic zirconia ceramics. These factors are categorized into six main groups: cement type and color, restoration thickness, substrate color, sintering, aging, and zirconia type. Cement type and color are crucial in determining the final shade, especially in thin restorations. Increased restoration thickness reduces the influence of the substrate color while the sintering temperature and process improve optical properties. These findings emphasize the importance of material selection and application processes in ensuring esthetic harmony in zirconia restorations. This review aims to bridge gaps in the literature by providing valuable insights that guide clinicians in selecting and applying zirconia materials to meet both esthetic and functional requirements in restorative dentistry.

Mechanisms of Strength Degradation of Dental Zirconia Due to Glazing: Dependence on Glaze Thickness

Glazing is a common method for smoothing the surface of zirconia and imitating the appearance of natural teeth. Several authors have previously reported that glazing reduces the strength of zirconia. However, the dependence of strength on glaze thickness and the mechanism of strength reduction remains unclear. Clarifying these factors is particularly important for improving the reliability of zirconia prostheses. In this study, three types of zirconia were glazed with various thicknesses, and their strength was evaluated. The results showed that the strength of the materials decreased with increasing glaze thickness. The decrease in the fracture load of the glazed test specimen stopped at a load where the stress necessary to fracture the glaze material was applied to the surface of the glaze layer. Furthermore, the strength reduction mechanism was investigated using FEM analysis, fractography, and Raman spectroscopy. The results suggested that the strength reduction due to glazing was a consequence of the crack-tip stress concentration developed upon the preliminary fracture of the glaze layer.

Fracture resistance, 3-dimensional finite element analysis, and safety factors for five post-and-core restorations with crowns placed in the noncircular-shaped canals of premolars

STATEMENT OF PROBLEM

Restoring endodontically treated premolars with noncircular canals presents a significant challenge.

PURPOSE

The purpose of this study was to compare the in vitro fracture resistance and the finite element computational calculation-based stress and safety factor of noncircular-shaped, endodontically treated premolars restored with 5 different prefabricated and custom computer-aided design and computer-aided manufactured post-and-core systems.

MATERIAL AND METHODS

Fifty single-rooted oval-shaped canal maxillary premolars were endodontically treated and post spaces were prepared. The specimens were divided into 5 categories on the basis of the post-and-core system used: Group CN composite resin core without a post, Group CF prefabricated fiber-reinforced composite resin post and composite resin core, Group IC interpenetrating phase composite post-and-core, Group LS lithium disilicate post-and-core, and Group ZR zirconia post-and-core. Lithium disilicate crowns were fabricated and cemented on the 5 different post-and-core systems and subjected to a fracture resistance test using a spherical indenter with static loading. Differences in fracture resistance were evaluated using a 1-way analysis of variance (ANOVA) (α=.05). The 3-dimensional finite element method was used to determine the von Mises stress and safety factors, defined as the ratio of the material's strength to the von Mises stress experienced, within different compartments of the restored tooth model.

RESULTS

In the in vitro fracture resistance test, the mean ±standard deviation fracture loads of the 5 groups were 2144 ±515 N, 1801 ±600 N, 1690 ±312 N, 1612 ±545 N, and 1487 ±600 N, respectively and were statistically similar (P=.078). All specimens within the ZR group exhibited restorable fractures. In contrast, only 30% of the CN group specimens showed restorable fractures. The incidence of restorable fractures in the CF, IC, and LS groups was 70%, 80%, and 70%, respectively. Although all groups showed similar maximum von Mises stress and stress distribution, safety factors in the models varied significantly. The ceramic crown was the weakest component in the LS and ZR groups, with much lower safety factors than dentin and post-and-core regions. Additionally, the CN group's wider dentin area had a demonstrably lower safety factor.

CONCLUSIONS

Endodontically treated noncircular-shaped canal premolars showed minimal effect on fracture resistance regardless of post type. However, for teeth with sufficient ferrule, using any post-and-core system significantly reduced the incidence of nonrestorable fractures compared with just a coronal foundation restoration, with custom zirconia offering the potential of achieving a restorable outcome after fracture.

Optical and Mechanical Properties of the Multi-Transition Zones of a Translucent Zirconia

OBJECTIVE

To characterize the composition, flexure resistance, and optical properties of a multilayer translucent zirconia in relation to its multi-transition zones.

MATERIALS AND METHODS

A multilayer zirconia (5Y/4Y) and a conventional 3 mol% yttria partially stabilized zirconia (3Y) were investigated. Bar-shaped specimens were obtained from the enamel and dentin layers, and the vertical cross-section of 5Y/4Y (N = 10). A four-point flexural (σf) test was performed using a universal testing machine (1.0 mm/min). Plate-shaped specimens (N = 6) were also produced from the enamel, transition 1, transition 2, and dentin layers. Translucency parameters (TPab and TP00) were determined using a dental spectrophotometer (N = 6). X-ray fluorescence and X-ray diffraction techniques were used to analyze elemental (N = 2) and phase compositions (N = 2), respectively. Data were analyzed using analysis of variance (ANOVA) and Tukey's test (α = 0.05).

RESULTS

The yttrium content and σf varied between layers of 5Y/4Y. 3Y had the highest σf, followed by dentin. Enamel and cross-section showed lower and statically similar σf. 3Y and dentin groups had similar but statistically lower TPab and TP00 than the enamel.

CONCLUSIONS

Different layers of multilayered zirconia have distinct compositions, which affect their mechanical and optical properties. The weak enamel layer compromises the mechanical properties of cross-sectional specimens.

CLINICAL SIGNIFICANCE

The development of novel cubic-containing multilayer zirconia ceramics to produce monolithic restorations brings new challenges to dental clinicians and laboratory technicians. The CAD/CAM design of multilayered 5Y/4Y restorations should consider the esthetic and mechanical requirements of each clinical case, as different properties are found in the different layers of these materials.

Two-step sintering suppresses grain growth and improves flexural strength of dental zirconia

OBJECTIVES

This study aimed to elucidate the effect of various two-step sintering (TSS) protocols on the physical, mechanical, and optical properties of partially stabilized zirconia with different yttria dopant concentrations (Y-PSZ).

METHODS

Disc-shaped specimens were obtained from most widely used commercial dental zirconia powders of various Y contents (Tosoh Corp.) by uniaxial pressing followed by cold-isostatic pressing. Densification was carried out using TSS protocols with varying temperatures for both sintering steps. Relative density (ρRel), microstructure, and phase content were analyzed. Biaxial flexural strength (σ) and translucency parameter (TP) were evaluated.

RESULTS

The TSS results were compared with optimized conventional sintering (CS) results from a previous study for the same Y-PSZ compositions. TSS 3Y-PSZ and 4Y-PSZ reached similar ρRel to those of their CS counterparts, whereas 5Y-PSZ failed to achieve that regardless of TSS protocol. TSS yielded less cubic phase compared to CS, especially for 3Y-PSZ and for higher temperatures. TSS suppressed the grain growth throughout the temperature range investigated, promoting smaller grains than CS (p < 0.05). The TP values for TSS Y-PSZ were lower than those of CS (p ≤ 0.0001), except for 3Y-PSZ. The σ values for TSS Y-PSZ were significantly higher than those of CS (p ≤ 0.0002).

SIGNIFICANCE

TSS increased strength without significantly jeopardizing the optical properties of various Y-PSZ compositions relative to their CS counterparts. This alternative sintering method appears to be a promising technique for controlling grain growth while eliminating porosities in dental Y-PSZ ceramics, thus potentially enhancing the clinical longevity of zirconia restorations.

Effect of occlusal adjustment and subsequent repolishing on the surface roughness and volumetric wear of different types of glazed monolithic zirconia after chewing simulation

The objective was to evaluate the effect of material (four monolithic zirconia) and surface condition [glazed (G) versus polished after simulation of occlusal adjustment (GAP)] on roughness and volumetric wear (VW) of dental zirconia after chewing simulation (CS). Zirconia specimens (ZS) were fabricated with an approximate diameter of 12.0 mm and a thickness of 1.0 mm. The four types of monolithic zirconia utilized were Prettau 4 Anterior (PA), Lava Plus (LP), Cercon hT (hT), and Cercon xT (xT). All specimens were coated with a thin and uniform layer of Prettau Plus glaze. Additionally, half of the ZS underwent a simulation of occlusal adjustment followed by clinical polishing. The sliding wear test was performed using a chewing simulator set at 30 N, 2 Hz, and 500,000 cycles, employing steatite specimens (SS) to simulate opposing dentition. ZS and SS underwent topographic analysis through optical profilometry to assess volumetric wear (VW) and surface roughness. The average roughness values (μm) of the zirconia ranged from 0.38h (PA-G before CS) to 2.55a (PA-GAP after CS), while for the antagonist the values ranged from 1.3b (LP-G before CS) to 2.6a (PA-GAP after CS). The VW values (mm3) of the ZS ranged from 0.7b (LP-G) to 2.5a (LP-GAP), while for the antagonist the values ranged from 0.17a (xT-GAP) to 0.33a (LP-G). The CS increased the roughness of all materials tested, regardless of the surface condition. The glazed condition showed lower roughness than the glazed/occlusal adjustment/polishing condition before the CS for three zirconia (PA, LP and xT) and after the CS for all materials. The surface condition did not significantly influence volumetric wear (VW) for three materials (PA, hT, and xT); however, for the Lava Plus (LP) group, the glazed condition resulted in reduced VW. The VW of the SS was unaffected by the material type or surface condition. In summary, zirconia specimens that underwent occlusal adjustment followed by repolishing demonstrated increased surface roughness compared to the glazed ones, while their wear behavior varied depending on the type of zirconia used.

Effect of different surface treatments on shear bond strength of zirconia with various yttria contents

BACKGROUND

Achieving a stable bond with zirconia requires mechanical and chemical bonding methods. Information regarding the optimal treatment method for zirconia with varying yttrium content is scarce. This study evaluated the effect of different surface treatments on the shear bond strength of zirconia with various yttria contents.

MATERIALS AND METHODS

A total of 168 disc-shaped zirconia specimens were classified into 12 groups based on the surface treatment method, including airborne-particle abrasion (APA), selective infiltration etching (SIE), hot etching (HE), and control group with no treatment; and yttria contents including Zolid Zi (4.5-5.6 wt% yttrium), Zolid HT White (6.7-7.2 wt% yttrium), and Ceramill Zolid FX (9.15-9.55 wt% yttrium). The surface roughness (Ra and Rz) of the specimens and the shear bond strength was measured (α = 0.05).

RESULTS

The results indicated that the mean bond strength of all specimens was higher after different surface treatments compared to the control group, of which the APA method resulted in higher bonding strength in all kinds of zirconia than other methods (P < 0.05). In all types of zirconia, a significant difference was observed in surface roughness (Ra and Rz) resulting from various surface treatment methods (P < 0.001). Interaction of surface treatment methods and zirconia type significantly affected shear bond strength and surface roughness (P < 0.05).

CONCLUSION

APA significantly enhanced shear bond strength and surface roughness across all zirconia types and yttria contents. The SIE and HE methods also showed promising results. Zolid Zi showed superior bond strength, whereas Zolid FX demonstrated reduced bond strength.

Effect of metal elements in coloring liquids used in the infiltration method on the physical properties of zirconia

OBJECTIVES

This study aimed to clarify the effect of metal elements in the coloring liquids used in the infiltration method on the physical properties of zirconia.

METHODS

Two types of zirconia discs 5Y-PSZ (SHOFU Disc ZR Lucent FA, SHOFU, Kyoto, Japan) were used: with monolayer shades from W2 to W3 (Pearl White) and 5Y-PSZ with multilayer shades from A3 to A4 (L). Five kinds of coloring liquid were used to infiltrate into semi-sintered Pearl White (T-glass [CT], A4 [CA], White-Opaque [CW], Gingiva 1 [CG], and Blue X [CB]). In addition, uncolored Pearl White set to as the control (C). These specimens were analyzed using a three-point bending test (3PBT), and the fracture surface after the test was analyzed by scanning electron microscopy, elemental analysis, and crystal structure analysis. In addition, from the polished surface part of the after the 3PBT specimens, the elemental composition was analyzed using X-ray fluorescence spectroscopy (XRF).

RESULTS

The flexural strength of CB and CG were lower than that of C (p < 0.05). XRF results showed that the Erbium (Er) content of CG was significantly greater than that of C (p < 0.05). CB exhibited a significantly higher Yttrium (Y) content compared with C (p < 0.05), and numerous pores were observed in the micrographs of the fracture surface of CG and CB.

SIGNIFICANCE

In zirconia, where the content of Y and Er was significantly increased by infiltration with a coloring liquid, pores were observed between the zirconia crystals, and the mechanical strength decreased.

Fatigue strength of bilayer yttria-stabilized zirconia after low-temperature degradation

This study examined the impact of interfacial interactions on bilayer yttria-stabilized zirconia (YSZ) used in dental restorations. In-house bilayer structures of 3YSZ and 5YSZ composition underwent hydrothermal degradation to compare the properties of control and low-temperature degradation (LTD) treated groups. Biaxial flexural strength via piston-on-three-balls, staircase fatigue strength over 106 cycles at 15 Hz, phase characterization and quantification through XRD and Rietveld refinement, and fractography were conducted. Weibull analysis was employed to determine the Weibull modulus and characteristic strength. Results demonstrated an enhancement in the mechanical performance of 3YSZ composition after LTD treatment, whereas the mechanical properties of 5YSZ remained largely unaffected post-degradation. Fractographic analysis revealed that failure originated at the surface tensile location across all specimen groups. These findings offer insights into the mechanical behavior of bilayer zirconia structures and reinforce the significance of hydrothermal treatment in enhancing their performance, particularly in the case of 3Y compositions.

Tribological aspects of enamel wear caused by zirconia and lithium disilicate: A meta-narrative review

The contact between enamel and an antagonist surface is the primary factor in tooth wear. Loss of tooth structure can cause changes in occlusion, chewing functionality, dental sensitivity, and appearance. However, enamel wear caused by opposing restorations is multifactorial and there is a lack of consensus regarding its behavior. This meta-narrative review assesses the multiple factors that affect enamel wear when using two common indirect restorative materials, lithium disilicate and zirconia. PubMed, Google Scholar, MEDLINE, and CINAHL databases were searched using keywords "zirconia," "lithium disilicate," "antagonistic tooth wear," and "enamel wear" to identify studies related to enamel wear caused by zirconia and lithium disilicate restorations. The Realist and Meta-narrative Evidence Syntheses: Evolving Standards (RAMESES) publication standard was used to report this meta-narrative literature review. Four broad categories of influencing factors were identified and reviewed: (1) mechanical and physical properties, (2) wear behavior and microstructural characteristics, (3) surface state, and (4) environmental factors. We conclude that well-polished zirconia is a more favorable indirect restorative material than lithium disilicate in terms of tribology because of its microstructure and surface integrity during wear. This review will enable clinicians to better comprehend the intricate nature of tooth wear caused by dental restorations.

Amelogenesis imperfecta: Analysis of the genetic basis and treatment with a digital workflow: A clinical report

A 20-year-old woman with type I hypoplastic amelogenesis imperfecta (AI) experiencing esthetic concerns and hypersensitivity is presented. The treatment was aimed at both functional and esthetic aspects, focusing on complete mouth rehabilitation using a fully digital workflow. In an interdisciplinary approach, a multigene panel analysis was performed. Digital intraoral scans and a face scan facilitated precise virtual planning, guiding minimally invasive preparations. Long-term interim restorations milled from high-performance polycarbonate preceded definitive restorations in translucent zirconia. This approach resulted in a time- and cost-efficient treatment, helped the patient to understand her disease by highlighting the pivotal role of genetics, and demonstrated the success of collaborative dental interventions. A strict recall program will be most important for the long-term success of this patient with AI and a pathogenic frameshift variant in the AMELX gene.

Impact of Substrate Material, Esthetic Material Thickness, and Cement on Color Reproduction in Implant-Supported Fixed Restorations

Purpose  This study aimed to evaluate the impact of substrate material, esthetic material type and thickness, and cement shade on the final color reproduction of implant-supported fixed restorations. The goal was to identify optimal combinations for achieving clinically acceptable esthetic outcomes. Material and methods  An in vitro study was conducted using four substrate materials, hybrid polyetherketoneketone (PEEK)-based ceramic-reinforced polymer (BioHPP), chromium-cobalt alloy (CrCo), grade 5 titanium (Ti), and white zirconium oxide ceramic (WZirCAD), and three esthetic materials, lithium disilicate ceramic (e.max CAD), polymethyl methacrylate (PMMA), and zirconia oxide ceramic (e.max ZirCAD), at five different thicknesses (0.5, 1, 1.5, 2, and 2.5 mm). Color differences (ΔE*) were measured using a spectrophotometer, both with and without cement application. Statistical analysis was performed using the Kruskal-Wallis test and Bonferroni correction to assess the effects of material combinations on color reproduction. Results  The study found that a 1 mm thickness of e.max CAD on BioHPP and CrCo substrates provided the best color matching, with ΔE* values closest to clinical acceptability. PMMA showed higher ΔE* values, indicating lower color stability compared to e.max CAD and e.max ZirCAD. Cement shade had a near-significant influence on final color perception, particularly with e.max ZirCAD on CrCo substrates. Conclusions  The study suggests that using e.max CAD at 1 mm thickness on BioHPP or CrCo substrates provides superior esthetic results, underscoring the need for careful material selection in clinical practice. Further in vivo research is recommended to validate these findings and explore long-term outcomes.

Effect of hydrothermal aging on color stability and translucency of two zirconia generations compared to lithium disilicate ceramics

Background

An esthetically acceptable ceramic restoration should have optical properties like the teeth and reflect, transmit, and absorb light. The present investigation compared how hydrothermal aging affected the properties of two types of zirconia and lithium disilicate.

Methods

Thirty rectangular samples (12×14×1 mm) were prepared and sectioned from three different ceramic blocks/blanks (n=10), then assigned into three groups according to the ceramic type: group Z: IPS e.max ZirCAD prime, gradient zirconia (3Y/5Y-TZP); group K: Katana UTML (5Y-TZP); and group E: IPS e.max CAD (lithium disilicate). Color analysis of samples was performed before and after hydrothermal aging (1, 3, and 5 hours) using a spectrophotometer. Color difference (∆E00), translucency parameter (TP00), and contrast ratio (CR) were evaluated. The microstructural analysis was performed using x-ray diffraction (XRD). Data were statistically analyzed at a significance level of P<0.05.

Results

A statistically significant variation was observed across means of ∆E00, TP00, and CR at different times. Group Z displayed the highest statistically significant mean ∆E00. Group E demonstrated the greatest statistically significant mean TP00. Group K exhibited the most statistically significant mean CR.

Conclusion

Hydrothermal aging significantly affected the optical characteristics of lithium disilicate and zirconia ceramics. The translucency of samples increased with aging.

Critical evaluations on the crystallographic properties of translucent dental zirconia ceramics stabilized with 3-6 mol% yttria

OBJECTIVES

This study aimed to determine the crystalline phase composition of 3-6 mol% yttria-stabilized zirconia (3-6YSZ), specifically investigating the presence of tetragonal (t), cubic (c), and/or additional yttria-rich tetragonal (t') phase.

METHODS

Laboratory-fabricated specimens comprising 3-5YSZ, resembling translucent dental zirconia ceramics (TZ specimens), and a blend of 3YSZ and 8YSZ, representing a c-phase reference, were prepared. Additionally, 25 dental zirconia products stabilized with 3-6 mol% yttria were analyzed. Whole X-ray diffraction (XRD) patterns were obtained for Rietveld analysis, complemented by fine scanning in the 2θ region from 72º to 76º for qualitative phase analysis. Moreover, yttria concentrations in each specimen were determined using X-ray fluorescence (XRF) spectroscopy.

RESULTS

In the 2θ region from 72º to 76º, TZ and dental zirconia product specimens displayed four peaks attributed to t- and t'-phases, but the c-phase peak was absent. Rietveld analysis of the whole XRD patterns, utilizing a t-t' model, demonstrated the t-phase fraction ranging from 86 mass% in 3YSZ to 11 mass% in 6YSZ. Rietveld analysis appeared reliable, as the yttria contents calculated based on lattice parameters aligned well with those measured by XRF. This study established that dental 3-6YSZ consisted of yttria-lean t- and yttria-rich t'-phases.

SIGNIFICANCE

The present study enhances understanding of the crystalline structure of dental zirconia ceramics. Future crystallographic analyses of these ceramics should consider the presence of t- and t'-phases.

Effect of toothbrushing on surface roughness, gloss, and topography of polished and glazed ultra-translucent zirconia

PURPOSE

This study evaluated the effect of toothbrushing cycles on surface roughness (Ra), gloss (GU), and morphology of two zirconia finishing and polishing protocols.

MATERIALS AND METHODS

An ultra-translucent zirconia disc was sectioned into rectangular plates (12 mm × 7 mm × 3 mm) and divided into two groups according to the polishing and finishing system used (diamond rubber abrasive/DRA or glazing/GLA). Bovine enamel (BEN) plates with the same dimensions were used as a Control. Specimens of zirconia and enamel were analyzed for Ra and GU (n = 11) and surface morphology by scanning electron microscopy (n = 3) before toothbrushing (baseline) and after 15,000 and 30,000 toothbrushing cycles. Ra and GU data were analyzed by ANOVA two-way and post-hoc Tukey's test (α = 0.05), while the surface morphology was analyzed qualitatively.

RESULTS

The Ra decreased significantly after 30,000 toothbrushing cycles for DRA and GLA zirconia ceramics. DRA showed a higher GU at the baseline, after 15,000 and 30,000 toothbrushing cycles than GLA and BEN. Toothbrushing polished the zirconia, creating a smooth surface, while no changes were observed for BEN.

CONCLUSIONS

The increase in toothbrushing cycles (30,000) changed the surface roughness of DRA and GLA zirconia ceramics. DRA zirconia presented the highest GU, which did not change with toothbrushing.

Advances in zirconia-based dental materials: Properties, classification, applications, and future prospects

OBJECTIVES

Zirconia (ZrO2) ceramics are widely used in dental restorations due to their superior mechanical properties, durability, and ever-improving translucency. This review aims to explore the properties, classification, applications, and recent advancements of zirconia-based dental materials, highlighting their potential to revolutionize dental restoration techniques.

STUDY SELECTION, DATA AND SOURCES

The most recent literature available in scientific databases (PubMed and Web of Science) reporting advances of zirconia-based materials within the dental field is thoroughly examined and summarized, covering the major keywords "dental zirconia, classification, aesthetic, LTD, applications, manufacturing, surface treatments".

CONCLUSIONS

An exhaustive overview of the properties, classifications, and applications of dental zirconia was presented, alongside an exploration of future prospects and potential advances. This review highlighted the importance of addressing challenges such as low-temperature degradation resistance and optimizing the balance between mechanical strength and translucency. Also, innovative approaches to improve the performances of zirconia as dental material was discussed.

CLINICAL SIGNIFICANCE

This review provides a better understanding of zirconia-based dental biomaterials for dentists, helping them to make better choice when choosing a specific material to fabricate the restorations or to place the implant. Moreover, new generations of zirconia are still expected to make progress on key issues such as the long-term applications in dental materials while maintaining both damage resistance and aesthetic appeal, defining the directions for future research.

A 3D printed ultra-short dental implant based on lattice structures and ZIRCONIA/Ca2SiO4 combination

Additive Manufacturing (AM) enables the generation of complex geometries and controlled internal cavities that are so interesting for the biomedical industry due to the benefits they provide in terms of osseointegration and bone growth. These technologies enable the manufacturing of the so-called lattice structures that are cells with different geometries and internal pores joint together for the formation of scaffold-type structures. In this context, the present paper analyses the feasibility of using diamond-type lattice structures and topology optimisation for the re-design of a dental implant. Concretely, a new ultra-short implant design is proposed in this work. For the manufacturing of the implant, digital light processing additive manufacturing technique technology is considered. The implant was made out of Nano-zirconia and Nano-Calcium Silicate as an alternative material to the more common Ti6Al4V. This material combination was selected due to the properties of the calcium-silicate that enhance bone ingrowth. The influence of different material combination ratios and lattice pore sizes were analysed by means of FEM simulation. For those simulations, a bio-material bone-nanozirconia model was considered that represents the final status after the bone is integrated in the implant. Results shows that the mechanical properties of the biocompatible composite employed were suitable for dental implant applications in dentistry. Based on the obtained results it was seen that those designs with 400 μm and 500 μm pore sizes showed best performance and led to the required factor of safety.

Color stability of precolored and extrinsically colored monolithic multilayered polychromatic zirconia: Effects of surface finishing and aging

PURPOSE

To explore the impact of zirconia types, coloring methods, and surface finishing on the color stability of monolithic multilayered polychromatic zirconia after artificial aging, including thermocycling and simulated toothbrushing.

MATERIALS AND METHODS

Eighty square-shaped zirconia samples were divided into 2 types (M3Y-TZP and M6Y-PSZ), further categorized based on coloring methods (precolored and extrinsically colored) and surface finishing techniques (mechanical polishing or glazing). The color stability was assessed using the CIEDE2000 formula. Artificial aging was simulated via thermocycling and toothbrushing. All samples were analyzed with a spectrophotometer to determine the post-aging color changes (ΔE00). The ΔE00 were interpreted and classified using the 50:50% perceptibility threshold (PT) and the 50:50% acceptability threshold (AT). Comparisons between groups for ΔE00 differences were performed using three-way ANOVA, with pairwise comparisons facilitated by Fisher's protected least significant difference test, α = 0.05.

RESULTS

The study results indicated significant impacts of zirconia type, coloring method, and surface finishing on color stability. The M6Y groups experienced significantly greater color changes (6.61 ± 1.63) compared to the M3Y groups (3.40 ± 2.24), p < 0.0001. For both types of zirconia, extrinsically colored samples exhibited significantly higher ΔE00 when mechanically polished (p = 0.004). However, surface finishing had no significant effect on ΔE00 in precolored samples of either zirconia material (p = 1.000). The evaluation and categorization of ΔE00 variations indicated that nearly all color changes in the M6Y groups, regardless of being precolored, extrinsically colored, polished, or glazed, were deemed extremely unacceptable (Grade 1). In contrast, the M3Y groups showed more acceptable results, with the majority of color changes classified as moderately unacceptable (Grade 3).

CONCLUSIONS

The color stability of multilayered polychromatic zirconia is influenced by the type of material, extrinsic coloring, and the chosen surface treatment post-artificial aging. The translucent 6Y-PSZ exhibited lower color stability, especially with only mechanical polishing. For the fabrication of M3Y-TZP and 6Y-PSZ monolithic multilayered polychromatic zirconia restorations, extrinsic coloring should be paired with glazing to maintain color stability. Conversely, in the absence of extrinsic coloring, both glazing and mechanical polishing are effective in preserving color stability.

Nanoscale osseointegration of zirconia evaluated from the interfacial structure between ceria-stabilized tetragonal zirconia and cell-induced hydroxyapatite

BACKGROUND

The osseointegration of zirconia implants has been evaluated based on their implant fixture bonding with the alveolar bone at the optical microscopic level. Achieving nano-level bonding between zirconia and bone apatite is crucial for superior osseointegration; however, only a few studies have investigated nanoscale bonding. This review outlines zirconia osseointegration, including surface modification, and presents an evaluation of nanoscale zirconia-apatite bonding and its structure.

HIGHLIGHT

Assuming osseointegration, the cells produced calcium salts on a ceria-stabilized zirconia substrate. We analyzed the interface between calcium salts and zirconia substrates using transmission electron microscopy and found that 1) the cell-induced calcium salts were bone-like apatite and 2) direct nanoscale bonding was observed between the bone-like apatite and zirconia crystals without any special modifications of the zirconia surface.

CONCLUSION

Structural affinity exists between bone apatite and zirconia crystals. Apatite formation can be induced by the zirconia surface. Zirconia bonds directly with apatite, indicating superior osseointegration in vivo.

Recent advances in dental zirconia: 15 years of material and processing evolution

OBJECTIVES

The objective was to discuss the research on zirconia published in the past 15 years to help the dental materials community understand the key properties of the types of zirconia and their clinical applications.

METHODS

A literature search was performed in May/2023 using Web of Science Core Collection with the term "dental zirconia". The search returned 5102 articles, which were categorized into 31 groups according to the research topic.

RESULTS

The current approach to improving the translucency of zirconia is to decrease the alumina content while increasing the yttria content. The resulting materials (4Y-, 5Y-, and above 5 mol% PSZs) may contain more than 50% of cubic phase, with a decrease in mechanical properties. The market trend for zirconia is the production of CAD/CAM disks containing more fracture resistant 3Y-TZP at the bottom layers and more translucent 5Y-PSZ at the top. Although flaws located between layers in multilayered blocks might represent a problem, newer generations of zirconia layered blocks appear to have solved this problem with novel powder compaction technology. Significant advancements in zirconia processing technologies have been made, but there is still plenty of room for improvement, especially in the fields of high-speed sintering and additive manufacturing.

SIGNIFICANCE

The wide range of zirconia materials currently available in the market may cause confusion in materials selection. It is therefore imperative for dental clinicians and laboratory technicians to get the needed knowledge on zirconia material science, to follow manufacturers' instructions, and to optimize the design of the prosthetic restoration with a good understanding where to reinforce the structure with a tough and strong zirconia.

Translucency of recent zirconia materials and material-related variables affecting their translucency: a systematic review and meta-analysis

BACKGROUND

Recent forms of translucent zirconia material have been developed, offering a wide range of options and varieties for enhancing aesthetics, making it a preferred choice in the field of prosthetic dentistry. However, there is insufficient understanding regarding the recent types of zirconia materials and their optical behavior. Understanding the variables that influence the translucency of zirconia and identifying strategies to enhance its esthetics are crucial.

PURPOSE

The current systemic review highlights a comprehensive understanding of different zirconia generations in relation to their optical characteristics and evaluates material-related variables affecting their translucency.

METHODS

The present review studied in-vitro studies that evaluated the optical characteristics of different yttria content of yttria stabilized materials. The topics explored were: (1) the different zirconia material generations and their optical behavior; (2) material-related factors that affect their translucency. The research was restricted to online publication in the English language from July 1, 2010, to July 31, 2023, using PubMed, Scopus, and Science Direct resources. The search key terms and their combinations were "zirconia," "translucent zirconia," "cubic zirconia," "highly translucent zirconia," "yttria partially stabilized zirconia," "monolithic zirconia," "translucency," "optical properties," and "light transmission."

RESULTS

The data obtained from fifty-three studies addressed the optical characteristics of various zirconia generations. They reported that changing yttria content had a significant impact on translucency. Different kinds of zirconia ceramics of the same generation have varying translucencies. Achieving optimum aesthetics with monolithic zirconia is challenging due to factors related to material aspects such as the presence of additives, point defects, microstructure, thickness, phase distribution, and sintering conditions.

CONCLUSIONS

Newly developed monolithic dental zirconia ceramics have improved aesthetics and translucency. However, additional research is necessary to evaluate their performance and long-term durability.

TRIAL REGISTRATION

This systematic review was registered in PROSPERO, under number CRD42023474482.

Microstructure, physical and mechanical properties of dental polychromic multilayer zirconia of uniform composition

The present study aimed to compare the microstructure, physical, and mechanical properties of three commercially available dental polychromatic multilayer zirconia materials of uniform composition: Dima Mill Zirconia ML, VITA YZ/ST Multicolor, and VITA YZ/XT Multicolor (with 3, 4, and 5 mol% Y2 O3 , respectively); thus, the influence of Y2 O3 content on the above properties of the produced materials was experimentally studied. Homogeneous zirconia ceramics with a dense micro- and nanostructure, without pores or defects, were produced after milling the blocks and sintering, which resulted in yttrium-stabilized tetragonal and cubic zirconia. Statistical analysis of the results of measurable magnitudes was performed by the one-way ANOVA test. The increase of Y2 O3 content (from 3 to 5 mol%) favored larger grain and crystallite sizes and a decrease of the values of the mechanical properties; yet, the differences were statistically insignificant. Clinically, these differences are expected to have no impact on their function in the oral cavity, both in terms of their fracture propensity and the damage that can be caused to the opposing teeth. Accordingly, the experimental results qualify the polychromic multilayer zirconia ceramics of uniform composition fabricated by milling technology for use in dental restorations.

Zirconia Ceramics

Zirconia ceramics have become popular among other dental ceramics thanks to their biological, mechanical, optical, and aesthetic properties. CAD/CAM (computer-aided design/ computer-aided manufacturing) technology improvement has played a vital role in the increased popularity of zirconia ceramics; easy computer manipulation significantly expanded the possibility of using different types of restorations. Zirconia ceramics have a broad spectrum of indications in prosthetic dentistry, from simple restorations to complex structures supported by dental implants. A good orientation in the classification, features, and manipulation of zirconia ceramics is the main key to success.

Fracture Resistance of a Two-Piece Zirconia Implant System after Artificial Loading and/or Hydrothermal Aging-An In Vitro Investigation

The purpose of the present study was to assess the fracture resistance of a two-piece alumina-toughened zirconia implant system with a carbon-reinforced PEEK abutment screw.

METHODS

Thirty-two implants with screw-retained zirconia abutments were divided into four groups of eight samples each. Group 0 (control group) was neither loaded nor aged in a chewing simulator; group H was hydrothermally aged; group L was loaded with 98 N; and group HL was subjected to both hydrothermal aging and loading in a chewing simulator. One sample of each group was evaluated for t-m phase transformation, and the others were loaded until fracture. A one-way ANOVA was applied to evaluate differences between the groups.

RESULTS

No implant fracture occurred during the artificial chewing simulation. Furthermore, there were no statistically significant differences (p > 0.05) between the groups in terms of fracture resistance (group 0: 783 ± 43 N; group H: 742 ± 43 N; group L: 757 ± 86 N; group HL: 740 ± 43 N) and bending moment (group 0: 433 ± 26 Ncm; group H: 413 ± 23 Ncm; group L: 422 ± 49 Ncm; group HL: 408 ± 27 Ncm).

CONCLUSIONS

Within the limitations of the present investigation, it can be concluded that artificial loading and hydrothermal aging do not reduce the fracture resistance of the investigated implant system.

Translucent Zirconia in Fixed Prosthodontics-An Integrative Overview

Over the past two decades, dental ceramics have experienced rapid advances in science and technology, becoming the fastest-growing field of dental materials. This review emphasizes the significant impact of translucent zirconia in fixed prosthodontics, merging aesthetics with strength, and highlights its versatility from single crowns to complex bridgework facilitated by digital manufacturing advancements. The unique light-conducting properties of translucent zirconia offer a natural dental appearance, though with considerations regarding strength trade-offs compared to its traditional, opaque counterpart. The analysis extends to the mechanical attributes of the material, noting its commendable fracture resistance and durability, even under simulated physiological conditions. Various zirconia types (3Y-TZP, 4Y-TZP, 5Y-TZP) display a range of strengths influenced by factors like yttria content and manufacturing processes. The study also explores adhesive strategies, underlining the importance of surface treatments and modern adhesives in achieving long-lasting bonds. In the realm of implant-supported restorations, translucent zirconia stands out for its precision, reliability, and aesthetic adaptability, proving suitable for comprehensive dental restorations. Despite its established benefits, the review calls for ongoing research to further refine the material's properties and adhesive protocols and to solidify its applicability through long-term clinical evaluations, ensuring its sustainable future in dental restorative applications.

Comparison of the Surface Roughness of CAD/CAM Metal-Free Materials Used for Complete-Arch Implant-Supported Prostheses: An In Vitro Study

The roughness of the intra-oral surfaces significantly influences the initial adhesion and the retention of microorganisms. The aim of this study was to analyze the surface texture of four different CAD-CAM materials (two high-performance polymers and two fifth-generation zirconia) used for complete-arch implant-supported prostheses (CAISPs), and to investigate the effect of artificial aging on their roughness. A total of 40 milled prostheses were divided into 4 groups (n = 10) according to their framework material, bio.HPP (B), bio.HPP Plus (BP), zirconia Luxor Z Frame (ZF), and Luxor Z True Nature (ZM). The areal surface roughness "Sa" and the maximum height "Sz" of each specimen was measured on the same site after laboratory fabrication (lab as-received specimen) and after thermocycling (5-55 °C, 10,000 cycles) by using a noncontact optical profilometer. Data were analyzed using SPSS version 28.0.1. One-way ANOVA with multiple comparison tests (p = 0.05) and repeated measures ANOVA were used. After thermocycling, all materials maintained "Sa" values at the laboratory as-received specimen level (p = 0.24). "Sz" increased only for the zirconia groups (p = 0.01). B-BP exhibited results equal/slightly better than ZM-ZF. This study provides more realistic surface texture values of new metal-free materials used in real anatomical CAISPs after the manufacturing and aging processes and establishes a detailed and reproducible measurement workflow.

Biomaterials and Clinical Application of Dental Implants in Relation to Bone Density-A Narrative Review

Titanium has been the material of choice for dental implant fixtures due to its exceptional qualities, such as its excellent balance of rigidity and stiffness. Since zirconia is a soft-tissue-friendly material and caters to esthetic demands, it is an alternative to titanium for use in implants. Nevertheless, bone density plays a vital role in determining the material and design of implants. Compromised bone density leads to both early and late implant failures due to a lack of implant stability. Therefore, this narrative review aims to investigate the influence of implant material/design and surgical technique on bone density from both biomechanical and biological standpoints. Relevant articles were included for analysis. Dental implant materials can be fabricated from titanium, zirconia, and PEEK. In terms of mechanical and biological aspects, titanium is still the gold standard for dental implant materials. Additionally, the macro- and microgeometry of dental implants play a role in determining and planning the appropriate treatment because it can enhance the mechanical stress transmitted to the bone tissue. Under low-density conditions, a conical titanium implant design, longer length, large diameter, reverse buttress with self-tapping, small thread pitch, and deep thread depth are recommended. Implant material, implant design, surgical techniques, and bone density are pivotal factors affecting the success rates of dental implant placement in low-density bone. Further study is required to find the optimal implant material for a clinical setting's bone state.

Residual stress associated with crystalline phase transformation of 3-6 mol% yttria-stabilized zirconia ceramics induced by mechanical surface treatments

Monolithic dental prostheses made of 3-6 mol% yttria-stabilized zirconia (3-6YSZ) have gained popularity owing to their improved material properties and semi-automated fabrication processes. In this study, we aimed to evaluate the influence of mechanical surface treatments, such as polishing, grinding, and sandblasting, on the residual stress of 3-6YSZ used for monolithic prostheses in association with crystalline phase transformation. Plate specimens were prepared from five dental zirconia blocks: Aadva Zirconia ST (3YSZ), Aadva Zirconia NT (6YSZ), Katana HT (4YSZ), Katana STML (5YSZ), and Katana UTML (6YSZ). The specimens were either polished using 1, 3, or 9 μm diamond suspensions, ground using 15, 35, or 55 μm diamond discs, or sandblasted at 0.2, 0.3, or 0.4 MPa. The residual stress, crystalline phase, and hardness were analyzed using the cosα method, X-ray diffraction (XRD), and Vickers hardness test, respectively. Additionally, we analyzed the residual stress on the surfaces of monolithic zirconia crowns (MZCs) made of 4YSZ, 5YSZ, and 6YSZ, which were processed using clinically relevant procedures, including manual grinding, followed by polishing using a dental electric motor on the external surface, and sandblasting on the internal surface. Residual stress analysis demonstrated that grinding and sandblasting, particularly the latter, resulted in the generation of compressive residual stress on the surfaces of the plate specimens. XRD revealed that the ground and sandblasted specimens contained a larger amount of the rhombohedral phase than that of the polished specimens, which may be a cause of the residual stress. Sandblasting significantly increased the Vickers hardness compared to polishing, which may possibly be due to the generation of compressive residual stress. In the case of MZCs, compressive residual stress was detected not only on the sandblasted surface, but also on the polished surface. The difference in the residual stress between the plate and crown specimens may be related to the force applied during the automated and manual grinding and polishing procedures. Further studies are required to elucidate the effects of the compressive residual stress on the clinical performance of MZCs.

Microstructural features, physicο-mechanical properties, and wear behavior of dental translucent polychromic multilayer zirconia of hybrid composition prepared by milling technology

OBJECTIVE

The present study determined the mechanical properties and the wear behavior, as results of the micro(nano)structure, of the enamel, transition, and dentine layers, which comprise the polychromic multilayer zirconia materials of hybrid composition fabricated by milling technology.

MATERIALS AND METHODS

Prismatic blocks were fabricated from two commercial pre-sintered dental polychromic multilayer zirconia materials of hybrid composition, IPS e.max ZirCAD Prime (medium and high translucency, from the dentine to the incisal layer) and 3D Pro ML (translucency gradient, from the dentine to the incisal layer) by milling technique, and then, cut into 3 distinct parts to separate the enamel, transition, and dentine layers. The samples were sintered, thermally treated (similarly to the glazing procedure), and polished for characterization. Their microstructure, mechanical properties (determined by nanoindentation and microhardness), and wear behavior (evaluated by scratch test), were examined.

RESULTS

The produced materials had a homogeneous and dense nanostructure, where the grain size decreased from the enamel to dentine layer. The mechanical properties decreased from the dentine to enamel layer. However, the three layers manifested similar dynamic friction coefficient.

CONCLUSION

The differences in the above properties in the three layers negligibly influenced the wear behavior of the entire multilayer zirconia material.

CLINICAL SIGNIFICANCE

The properties of dental restorations produced from polychromic multilayer zirconia of hybrid composition by milling technology (i.e., strong, non-fragile, and esthetic materials), anticipate good performance in oral cavity.

Influences of luting cement shade on the color of various translucent monolithic zirconia and lithium disilicate ceramics for veneer restorations

PURPOSE

The purpose of this study was to assess the effect of resin cement shade on the color of different novel ultratranslucent monolithic zirconia and lithium disilicate veneer materials.

MATERIALS AND METHODS

For a total of 40 specimens, flat cylindrical discs with a 9-mm diameter and 0.5-mm thickness were created using CAD/CAM technology. The specimens were divided into five groups according to their material (n = 8) (e.max, Prettau, Aidite, Shofu and Dima) using A1 shade. Resin discs with the same diameter and shade as the specimens served as tooth-colored substructures. Three shades (neutral, light and warm) of resin cement try-in pastes (Variolink Esthetic LC) were used as the luting cement material. The color of each material group was measured before and after cementation using the three cement shades, and the CIE L*a*b* coordinates were obtained with a spectrophotometer. Values for the translucency parameter (TP) and color change delta E (E) before (baseline) and after cementation of each specimen were determined. To compare differences among the material groups within each shade of cement and among various shades of cement within each material, the data were analyzed using one-way ANOVA and post hoc testing.

RESULTS

Color coordinates L*, a* and b* significantly changed after the application of try-in pastes relative to baseline values, with a noticeable decrease in lightness (L*) (P < .05). A significant color change (ΔE) was observed in all tested materials after cementation, with ΔE values exceeding 3.3 (P < .05). Although TP changed after cementation for most materials tested, these changes were not statistically significant (P > .05). Shofu and Dima ceramics showed the lowest TP values, while Aidite and Prettau showed the highest TP values. For e.max, translucency decreased after cementation with neutral and warm shades, and it significantly increased after cementation with a light shade.

CONCLUSION

The shade of cement significantly altered the final color of the ceramic veneer material to a level above the threshold at which the clinical perception of color change occurred (> 3.3). The TP was not influenced by the cement shade. The translucency levels of the novel ultratranslucent multilayer monolithic zirconia ceramics Aidite and Prettau were higher than that of the lithium disilicate e.max material.

Thermal Effects of 445-nm Diode Laser Irradiation on Titanium and Ceramic Implants

This study aimed to evaluate temperature changes in titanium and ceramic implants after using a 445-nm diode laser under different in vitro conditions. Titanium (Ti) and ceramic (Zr) dental implants were placed into a bone analog, and an intrabony defect was created at each implant. A 445-nm diode laser was used to irradiate the defects for 30 seconds, noncontact, at 2 W in continuous wave (c.w.) and pulsed mode. The experiment was done at room temperature (21.0 ± 1°C) and in a water bath (37.0 ± 1°C). Two thermocouple probes were used to record real-time temperature changes (°C) at the coronal part of the implant (Tc) and the apex (Ta). The temperature was recorded at time 0 (To) and after 30 seconds of irradiation (Tf). The average temperature change was calculated, and a descriptive analysis was conducted (P < .05). The Ti implant resulted in the highest ΔT values coronally (29.6°C) and apically (6.7°C) using continuous wave at 21°C. The Zr implant increased to 26.4°C coronally and 5.2°C apically. In the water bath, the coronal portion of the Ti and Zr implants rose to 14.2°C and 14.01°C, respectively, using continuous waves. The ΔT values for Ti were 11.9°C coronally and 1.7°C apically when placed in a water bath using pulsed mode. The lowest ΔT occurred on the Zr implant with ΔTc and ΔTa of 4.8°C and 0.78°C, respectively. Under in vitro conditions, the 445-nm diode laser in pulsed mode seems to be safe for use on ceramic implants and should be used with caution on titanium implants.

Current classification of zirconia in dentistry: an updated review

Zirconia, a crystalline oxide of zirconium, holds good mechanical, optical, and biological properties. The metal-free restorations, mostly consisting of all-ceramic/zirconia restorations, are becoming popular restorative materials in restorative and prosthetic dentistry choices for aesthetic and biological reasons. Dental zirconia has increased over the past years producing wide varieties of zirconia for prosthetic restorations in dentistry. At present, literature is lacking on the recent zirconia biomaterials in dentistry. Currently, no article has the latest information on the various zirconia biomaterials in dentistry. Hence, the aim of this article is to present an overview of recent dental zirconia biomaterials and tends to classify the recent zirconia biomaterials in dentistry. This article is useful for dentists, dental technicians, prosthodontists, academicians, and researchers in the field of dental zirconia.

In Vitro Study of Zirconia Surface Modification for Dental Implants by Atomic Layer Deposition

Zirconia is a promising material for dental implants; however, an appropriate surface modification procedure has not yet been identified. Atomic layer deposition (ALD) is a nanotechnology that deposits thin films of metal oxides or metals on materials. The aim of this study was to deposit thin films of titanium dioxide (TiO₂), aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), and zinc oxide (ZnO) on zirconia disks (ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn, respectively) using ALD and evaluate the cell proliferation abilities of mouse fibroblasts (L929) and mouse osteoblastic cells (MC3T3-E1) on each sample. Zirconia disks (ZR; diameter 10 mm) were fabricated using a computer-aided design/computer-aided manufacturing system. Following the ALD of TiO₂, Al₂O₃, SiO₂, or ZnO thin film, the thin-film thickness, elemental distribution, contact angle, adhesion strength, and elemental elution were determined. The L929 and MC3T3-E1 cell proliferation and morphologies on each sample were observed on days 1, 3, and 5 (L929) and days 1, 4, and 7 (MC3T3-E1). The ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn thin-film thicknesses were 41.97, 42.36, 62.50, and 61.11 nm, respectively, and their average adhesion strengths were 163.5, 140.9, 157.3, and 161.6 mN, respectively. The contact angle on ZR-Si was significantly lower than that on all the other specimens. The eluted Zr, Ti, and Al amounts were below the detection limits, whereas the total Si and Zn elution amounts over two weeks were 0.019 and 0.695 ppm, respectively. For both L929 and MC3T3-E1, the cell numbers increased over time on ZR, ZR-Ti, ZR-Al, and ZR-Si. Particularly, cell proliferation in ZR-Ti exceeded that in the other samples. These results suggest that ALD application to zirconia, particularly for TiO₂ deposition, could be a new surface modification procedure for zirconia dental implants.

Evaluation of the Effect of Electronic Cigarette Devices/Vape on the Color of Dental Ceramics: An In Vitro Investigation

The use of vaping or electronic cigarette devices (ECDs) has recently increased as an alternative to conventional tobacco smoking products. By recording the CIELAB coordinates (L*a*b*) and computing the total color difference (ΔE) values using a spectrophotometer, the effect of ECDs on contemporary aesthetic dental ceramics was investigated in this in-vitro study. A total of seventy-five (N = 75) specimens from five different (n = 15) dental ceramic materials (Pressable ceramics (PEmax); Pressed and layered ceramics (LEmax); Layered zirconia (LZr); Monolithic zirconia (MZr) and Porcelain fused to metal (PFM)) were prepared and exposed to aerosols produced by the ECDs. The color assessment was performed using a spectrophotometer at six time intervals (0 = baseline; 250-puff exposures; 500-puff exposures; 750-puff exposures; 1000-puff exposures; 1250-puff exposures; and 1500-puff exposures). By recording L*a*b* and computing total color difference (ΔE) values, the data were processed. A one-way ANOVA and Tukey procedure for pairwise comparisons were used to assess color differences between tested ceramics (p < 0.05). All test materials demonstrated significant color differences (ΔE) after exposure to vaping (p < 0.05). The LZr group displayed noticeably high ΔE values at all the distinct puff exposure intervals, with the highest ΔE value of (13.67) after 1500 puffs. The lowest (ΔE) values were observed in the PFM group after 250 and 500 puffs (0.85 and 0.97, respectively). With the exception of the group PEmax (p = 0.999), all groups produced readings of "ΔE" that indicated significant differences (p < 0.05) at various degrees of puff exposures. ECDs can noticeably alter the color of the dental ceramics affecting the esthetics of the patients. All the materials tested demonstrated significant color changes (ΔE > 3.33) above the clinically acceptable threshold, except for the PFM and PEmax group (ΔE < 3.33) which showed color stability after exposure to the ECDs.

Layer characteristics in strength-gradient multilayered yttria-stabilized zirconia

OBJECTIVES

To investigate crystallography, translucency, phase content, microstructure and flexural strength of two commercial strength-gradient multilayered dental zirconia grades.

METHODS

Two zirconia grades, i.e., KATANA Zirconia YML (Kuraray Noritake; referred to as "YML"; composed of four layers: enamel, body 1-3) and IPS e.max ZirCAD Prime (Ivoclar Vivadent; referred to as "Prime"; composed of three layers: enamel, transition, body) were investigated. Fully sintered square-shaped zirconia specimens from each layer were prepared. Microstructure, chemical composition, translucency parameter and zirconia-phase composition of each layer were characterized. Four-point and biaxial flexural strength of each layer was measured using fully sintered bar- and square-shaped specimens. Square-shaped samples were used to measure strength across the layers.

RESULTS

For both multilayer zirconia grades, the 'enamel' layer contains a higher amount of c-ZrO₂, which resulted in higher translucency but lower flexural strength than the 'body' layers. The characteristic 4-point flexural strength of the YML 'body 2' (923 MPa) and 'body 3' (911 MPa) layers, and of the Prime 'body' (989 MPa) layer were comparable and higher than for the YML 'enamel' (634 MPa), Prime 'transition' (693 MPa) and 'enamel' (535 MPa) layers. The biaxial strength of specimens sectioned across the layers was in-between that of the 'enamel' and 'body' layers for both YML and Prime, implying the interfaces did not form a weak link.

SIGNIFICANCE

The difference in yttria content affects the phase composition and mechanical properties of each layer of the multi-layer zirconia. The strength-gradient approach allowed to integrate monoliths with irreconcilable properties.

Development and characterization of ultra-high translucent zirconia using new manufacturing technology

This review describes the development of ultra-high translucent zirconia (referred to as UHTZ) using new manufacturing technology and its characterization results. The development of UHTZ was primarily due to the adoption of two basic manufacturing technologies, "Cyclic CIP" and "Plus Y Technology". This manufacturing technology could provide stable processing characteristics, which improves chipping resistance during milling. Furthermore, the enlargement factor (processing coefficient) for UHTZ is smaller than those for conventional products. In general, the higher the light transmittance, the lower the flexural strength. Despite its extremely high translucency, the most significant feature of UTHZ is that its flexural strength is comparable to that of 5Y. Furthermore, UHTZ has higher chemical durability and uniform microstructure, which results in less wear on the opposing teeth and superior discoloration resistance. Therefore, UHTZ is a new option for inlay, onlay, and laminate veneer applications, where lithium disilicate glass ceramics has been widely used.

Zirconia Nanoparticles as Reinforcing Agents for Contemporary Dental Luting Cements: Physicochemical Properties and Shear Bond Strength to Monolithic Zirconia

Nanofillers in resin materials can improve their mechanical and physicochemical properties. The present work investigated the effects of zirconia nanoparticles (NPs) as fillers in commercial dental luting cements. Two dual-cured self-adhesive composites and one resin modified glass ionomer (RMGI) luting cement were employed. Film thickness (FT), flexural strength (FS), water sorption (W_sp), and shear bond strength (SBS) to monolithic zirconia were evaluated according to ISO 16506:2017 and ISO 9917-2:2017, whereas polymerization progress was evaluated with FTIR. Photopolymerization resulted in double the values of DC%. The addition of 1% wt NPs does not significantly influence polymerization, however, greater amounts do not promote crosslinking. The sorption behavior and the mechanical performance of the composites were not affected, while the film thickness increased in all luting agents, within the acceptable limits. Thermocycling (TC) resulted in a deteriorating effect on all composites. The addition of NPs significantly improved the mechanical properties of the RMGI cement only, without negatively affecting the other cements. Adhesive primer increased the initial SBS significantly, however after TC, its application was only beneficial for RMGI. The MDP containing luting cement showed higher SBS compared to the RMGI and 4-META luting agents. Future commercial adhesives containing zirconia nanoparticles could provide cements with improved mechanical properties.

Effect of Ga2O3 Dopant on High Speed Sintered 5 mol% Y2O3 Stabilized Dental Zirconia

The high-speed sintering of zirconia has become essential for ceramic dental prosthesis treatment in a single visit. Previous studies have shown that 5 mol% yttria-stabilized zirconia (5Y zirconia), with the exception of some types, loses strength and translucency with high-speed sintering. In this study, 0.15-0.92 wt% Ga₂O₃, which is expected to promote the sintering of zirconia, was added to improve the properties of 5Y zirconia high-speed sintered bodies, and the effect of its addition was evaluated. The specimens were characterized by density and translucency measurements, a three-point bending test, X-ray diffraction (XRD), scanning electron microscopy (SEM), and shrinkage measurement. The addition of Ga₂O₃ improved both translucency and flexural strength of 5Y zirconia high-speed sintered bodies. XRD and SEM observations revealed that this improvement in properties was due to the change in the crystal phase composition and the decrease in the amount and size of pores due to the addition of Ga₂O₃. Shrinkage measurements also revealed that the addition of Ga₂O₃ changed the sintering behavior of 5Y zirconia, suggesting that this change led to a reduction in porosity. From the above results, it was concluded that Ga₂O₃ addition is effective in improving the properties of 5Y zirconia high-speed sintered bodies.

Translucent and Highly Toughened Zirconia Suitable for Dental Restorations

Background: There is a limit to improving the characteristics of zirconia with only one kind of stabilizing element such as yttrium. The purpose of this study is to systematically evaluate the effects of various co-doped elements on mechanical and optical properties and to develop a novel composition of zirconia with enough properties to apply to dental restorations. Methods: Forty-four kinds of zirconia were prepared by combining trivalent cations yttrium (Y) and ytterbium (Yb), and pentavalent cations niobium (Nb) and tantalum (Ta) oxide as stabilizers. The combined contents ranged from 0 to 5.6 mol% for Y2O3, 0 to 4.2 mol% for Yb2O3, 0 to 1.5 mol% for Nb2O5, and 0 and 1.2 mol% for Ta2O5. These specimens were determined for fracture toughness and opacity. X-ray diffraction studies were undertaken to evaluate the microstructural change. Results: The present study revealed that adding of the trivalent cations Y and Yb reduced fracture toughness and opacity, whereas the addition of pentavalent cations Nb and Ta to zirconia stabilized with trivalent cations increased both properties. There was no clear difference in the effects of Y and Yb, Nb, and Ta. Conclusions: Considering many factors, the following composition is optimal: 3–4.2 mol% Y2O3 and/or Yb2O3 stabilized zirconia with up to 1.5 mol% Nb2O5 has sufficiently high fracture toughness values and sufficiently high translucency suitable for dental restorations.

Durability of cantilever inlay-retained fixed dental prosthesis fabricated from multilayered zirconia ceramics with different designs

PURPOSE

The purpose of this in-vitro study was to investigate the effect of framework design on fracture resistance and failure modes of cantilever inlay-retained fixed partial dentures (IRFDPs) fabricated from two multilayered monolithic zirconia materials.

MATERIALS AND METHODS

Seventy-two natural premolar teeth were prepared as abutments for cantilever IRFDPs using three designs: mesial-occlusal (MO) inlay with short buccal and palatal wings (D1), MO inlay with long palatal wing (D2), MO inlay with long palatal wing and occlusal extension (D3). Full-contoured IRFDPs were fabricated from two monolithic zirconia materials; IPS e.max ZirCAD Prime and Zolid Gen-X. Adhesive surfaces were air-abraded and bonded with MDP-containing resin cement. Specimens were subjected to thermocycling (5-55 °C, 5000 cycles); then, mechanical loading (1.2 × 10⁶ cycles, 49 N). Surviving specimens were loaded until failure in the universal testing machine. All specimens were examined under stereomicroscope, and two samples from each group were evaluated using Scanning Electron Microscope.

RESULTS

Mean failure loads were not significantly different between different framework designs or between two materials. However, IPS e.max ZirCAD Prime showed significantly higher failure rate than Zolid Gen-X during dynamic fatigue (p = 0.009). Samples with D1 design showed higher debonding rate, D2 failed mainly by fracture of the palatal wing and debonding, and D3 failed mainly by fracture of the abutment tooth. Debonded restorations showed mainly mixed failures.

CONCLUSION

Cantilever IRFDPs with framework designs that maximize adhesion to enamel exhibited promising results. IPS e.max ZirCAD Prime was more susceptible to fractures with the long palatal wing design.

Clinical and radiographic prospective study of customized one-piece titanium and one-piece fusion-sputtered zirconia implants: five-year mean follow-up

BACKGROUND

To evaluate the clinical and radiographic assessment of customized fusion-sputtered one-piece zirconia implants.

METHODS

Twenty-eight patients received either fusion sputtered one-piece zirconia implants (n = 14) or one-piece titanium implants (n = 14). All implants were one-piece designs. After 4 months of immediate loading, all implants were restored with a monolithic zirconia crown. All implants were evaluated at baseline, 6 months, 1 year, 2 years, and 5 years. Implant mobility, plaque index, and gingival index evaluations were performed. The measurements of marginal bone level were calculated radiographically.

RESULTS

All implants were well maintained through the evaluation period with a 100% survival rate without any clinical complications. Regarding gingival index, there was no statistically significant difference (P = .364) between zirconia (3.3 ± 0.7 mm) and titanium (3.5 ± 0.6 mm) implants, after 5 years. There was no statistically significant difference (P = .470) between zirconia (1.77 ± 0.039 mm) and titanium (1.80 ± 0.28 mm) implants regarding marginal bone loss, after 5 years.

CONCLUSIONS

One-piece fusion-sputtered zirconia implant represents a reliable treatment modality in replacing a missing tooth in the esthetic zone.

Preparation and Characterization of a Polyetherketoneketone/Hydroxyapatite Hybrid for Dental Applications

Here, we developed a new synthetic method for the production of a new class of polymeric inorganic hybrid biomaterial that has potential for dental implant applications and, in general, other orthopedic applications owing to its excellent mechanical properties and biomechanical compatibility. The new hybrid biomaterial is a composite consisting of polyetherketoneketone (PEKK) and hydroxyapatite (HA). This hybrid material boasts several unique features, including its high HA loading (up to 50 wt%), which is close to that of natural human bone; the homogeneous HA distribution in the PEKK matrix without phase separation; and the fact that the addition of HA has no effect on the molecular weight of PEKK. Nanoindentation analysis was used to investigate the mechanical properties of the composite, and its nano/microstructure variations were investigated through a structural model developed here. Through nanoindentation technology, the newly developed PEKK/HA hybrid biomaterial has an indentation modulus of 12.1 ± 2.5 GPa and a hardness of 0.42 ± 0.09 GPa, which are comparable with those of human bone. Overall, the new PEKK/HA biomaterial exhibits excellent biomechanical compatibility and shows great promise for application to dental and orthopedic devices.

Evaluation of the Effect of High-Speed Sintering and Specimen Thickness on the Properties of 5 mol% Yttria-Stabilized Dental Zirconia Sintered Bodies

High-speed sintering of zirconia has become essential to single-visit dental prosthetic treatments. This important prosthetic dentistry technique demands a translucent material tougher than porcelain. Previous studies on high-speed sintered zirconia did not take heat and material thickness into consideration. We evaluated pre-sintered specimen thickness and the effect of high-speed sintering on the properties of 5 mol% Y₂O₃-stabilized zirconia (5Y zirconia). High-speed sintered bodies of 5Y zirconia were evaluated by density measurements, translucency measurements, three-point flexural and fracture toughness tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). High-speed sintering reduced the translucency and mechanical properties of 5Y zirconia. XRD and SEM observation results clarified that these reductions were due to the change in crystal phase composition and to the increase in residual pores, respectively, both resulting from high-speed sintering. Moreover, in high-speed sintering, as the thickness of the specimen increased, the number and size of internal pores increased, and the translucency and strength decreased. The threshold value for avoiding a reduction in translucency and mechanical properties was found to lie at ~4.4 mm. From the above results, it was concluded that 5Y zirconia is not suitable for high-speed sintering applications.

Biocompatibility of ZrO2 vs. Y-TZP Alloys: Influence of Their Composition and Surface Topography

The osseointegration of implants is defined as the direct anatomical and functional connection between neoformed living bone and the surface of a supporting implant. The biological compatibility of implants depends on various parameters, such as the nature of the material, chemical composition, surface topography, chemistry and loading, surface treatment, and physical and mechanical properties. In this context, the objective of this study is to evaluate the biocompatibility of rough (Ra = 1 µm) and smooth (Ra = 0 µm) surface conditions of yttria–zirconia (Y-TZP) discs compared to pure zirconia (ZrO₂) discs by combining a classical toxicological test, morphological observations by SEM, and a transcriptomic analysis on an in vitro model of human Saos-2 bone cells. Similar cell proliferation rates were observed between ZrO₂ and Y-TZP discs and control cells, regardless of the surface topography, at up to 96 h of exposure. Dense cell matting was similarly observed on the surfaces of both materials. Interestingly, only 110 transcripts were differentially expressed across the human transcriptome, consistent with the excellent biocompatibility of Y-TZP reported in the literature. These deregulated transcripts are mainly involved in two pathways, the first being related to “mineral uptake” and the second being the “immune response”. These observations suggest that Y-TZP is an interesting candidate for application in implantology.