Novel Zirconia Materials in Dentistry

Innovation Glass-Ceramic Spray Deposition Technology Improving the Adhesive Performance for Zirconium-Based Dental Restorations

Glass-ceramic spray deposition (GCSD) is a novel technique for coating lithium disilicate (LD) glass-ceramics onto zirconia through simple tempering steps. GCSD has been proven to improve the bonding of zirconia to resin cement, but the effect of etching time on GCSD and the long-term durability of the bond achieved remain unknown. The effects of air abrasion with aluminum particles (ABB) and air abrasion (GAB) or etching with 5.0% hydrogen fluoride (HF) for 20, 60, 90, and 120 s (G20, G60, G90, and G120) on the resin cement−zirconia bond were studied. LD was included as a control (LDG). The microstructure, sub-micron roughness, wettability, and phase changes of samples were analyzed. After resin cement was bonded to zirconia, half of the samples were subjected to thermocycling (5000 cycles at 5−55 °C). The bond strengths of the samples were determined in shear bond strength (SBS) tests (n = 10 per group). An LD structure can be formed on zirconia after GCSD and proper etching processes, which result in high roughness and a hydrophilic nature. GCSD and HF etching significantly improved SBS, with G90 and G120 samples with pre- or post-thermocycling exhibiting SBS values comparable to those of LDG (p > 0.760). The surface characteristics of the LD layer are influenced by the etching time and affect the SBS of the bond of zirconia to resin cement. HF etching for 90−120 s after GCSD results in zirconia with SBS and bond durability comparable to LD.

Wear Properties of Conventional and High-Translucent Zirconia-Based Materials

This study investigated the two-body wear resistance of a first generation 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), a second generation 3Y-TZP, a third generation 4 mol% yttria partially stabilized zirconia (4Y-PSZ), a 5 mol% yttria partially stabilized zirconia (5Y-PSZ), and a type III gold alloy (Aurocast 8), performed using opposing antagonistic cusps made out of the same material. Eight cylindrical specimens were prepared for each material (n = 8) for a total of forty specimens (N = 40). Conical cusps were fabricated for each material. Each cylinder−cusp pair was arranged inside a two-axis chewing simulator over up to 360,000 loading cycles. The wear resistance was analyzed by measuring the vertical substance loss (mm) and the volume loss (mm3). The antagonist wear (mm) was recorded before and after the wear test to evaluate the linear difference. Statistical analysis was performed using one-way analysis of variance (ANOVA); multiple comparisons were performed according to Tukey’s method. No statistically significant differences (p > 0.05) among the first generation 3Y-TZP, second generation 3Y-TZP, and 4Y-PSZ wear were found. 5Y-PSZ showed statistically significant higher wear compared to other the zirconias. Aurocast 8 displayed the highest values in terms of vertical wear, antagonist cusp wear, and volumetric loss. Although still not statistically comparable, the wear behavior of the latest 5Y-PSZ was the closest to the widely recognized gold standard represented by the type III gold alloy.

Physical and biological implications of accelerated aging on stereolithographic additive-manufactured zirconia for dental implant abutment

PURPOSE

This study aimed to comparatively investigate the effects of accelerated aging on the physical and biological features of zirconia manufactured by digital light processing (DLP) and conventional subtractive manufacturing (SM) with similar composition.

METHODS

Both the DLP- and SM-fabricated zirconia samples (7 mm × 7.5 mm × 1.5 mm) were grouped according to aging (134 °C, 0.2 MPa, 100% humidity) times, including 0 h, 5 h, and 10 h. Phase assemblage and surface topography of zirconia manufactured by different technologies were evaluated before and after aging. The biological effects of zirconia on human gingival fibroblast (HGF) cell events, including cell viability, proliferation, morphology and adhesion, were also evaluated by live/dead viability assay, cck-8 assay, scanning electron microscopy and confocal laser scanning microscopy respectively.

RESULTS

The DLP-fabricated zirconia showed a higher initial cubic phase content and rate of phase transformation than the SM-fabricated zirconia. Among the different aging time-based groups, the 5 h-aged group exhibited significantly lower sub-micron scale surface roughness compared with the other groups. Aging did not significantly alter cellular behavior in any zirconia type, except for minor changes in adhesive cell numbers recorded in an aging time/culturing time-dependent manner. In addition to small differences in cell alignment patterns and overall cell morphology, the two zirconia types presented comparable biological performance before and after aging.

CONCLUSION

Although the microstructure and surface characteristics of DLP-fabricated zirconia can be affected by autoclave aging, this newly manufactured zirconia is likely to maintain desirable long-term biocompatibility as an implant abutment material.

The Effect of Multiple Applications of Phosphate-Containing Primer on Shear Bond Strength between Zirconia and Resin Composite

Occasional chipping can still occur with zirconia material despite its high strength. Emergency repairs can be accomplished using zirconia primer, adhesive agent, and resin composite when the fracture of zirconia exposes the zirconia framework. Phosphate-containing primers play an important role in zirconia surface treatment. The objective of this investigation was to evaluate the effect of multiple applications of phosphate-containing primer on shear bond strength between zirconia and resin composite. In this case, 78 zirconia discs were sandblasted by alumina particles; the zirconia was then randomized into six groups for single application and multiple applications of phosphate-containing primer according follows; group 1: no application, group 2: one application, group 3: two applications, group 4: three applications, group 5: four applications, and group 6: five applications. Adhesive was applied on the zirconia surface and the resin composite was bonded. Shear bond strength was assessed using a universal testing machine. The de-bonded surface was examined using a stereomicroscope. The shear bond strengths were statistically analyzed with one-way ANOVA and Bonferroni. Group 1 had the lowest shear bond strength with a significant difference compared to groups 2–6, whereas group 4 had the highest shear bond strength, with no significant difference compared to groups 5–6. The failure mode revealed 100% adhesive failure in all groups. In conclusion, to maximize shear bond strength at zirconia and resin composite interfaces, sandblasted zirconia surfaces should be treated with three applications of phosphate-containing primer prior to the adhesive agent.

Advances in Ceramics for Dental Applications

The purpose of this study is to present current dental ceramic materials and processing methods. The clinical indication was emphasized on basis of the material's microstructure and composition. Studies of ceramic characterization were also discussed, as they impact the clinical indication and serve as a parameter for the development of new materials. The novel strategies were mostly found aiming to mimic the natural dental structures, provide mechanical reliability, and develop predictable restorations in terms of adaptation and design.

Translucency and mechanical behavior of partially stabilized monolithic zirconia after staining, finishing procedures and artificial aging

Partially stabilized zirconia (5Y-PSZ) has been widely used to manufacture indirect monolithic restorations, and the effect of finishing procedures on the optical and mechanical properties of these materials are still unclear. The purpose of this study was to evaluate the effect of staining, polishing and glazing on surface roughness, crystalline phase content, microhardness, fracture toughness, dynamic elastic modulus, three-point flexural strength, strain distribution, color (∆E₀₀/∆L/∆a/∆b), and translucency before and after artificial accelerated aging (water spray and ultraviolet) of 5Y-PSZ. Bar-shaped and rectangle-shaped specimens of the 5Y-PSZ were prepared and divided into six groups, according to finishing procedure: GC (control), GS (staining), GG (glazing), GSG (staining and glazing), GP (polishing), GSP (staining and polishing). There was a significant difference between groups for surface roughness (p < 0.05), dynamic elastic modulus (p = 0.007), microhardness (p =  < 0.05), ∆E₀₀ (p = 0.010), and ∆a (p = 0.008). GC presented higher cubic phase content, and the stained groups (GS, GSG and GSP) presented higher monoclinic content. The different finishing procedures affected roughness, dynamic elastic modulus, microhardness, and color of 5Y-PSZ; polishing being the finish that provides minors changes to the 5Y- PSZ. Accelerated artificial aging caused color change, regardless of finishing procedure used.

Fracture Resistance of CAD/CAM Implant-Supported 3Y-TZP-Zirconia Cantilevers: An In Vitro Study

(1) Introduction: Implant-supported fixed complete dentures are mostly composed of cantilevers. The purpose of this work was to evaluate the fracture resistance of zirconia (Prettau®, second generation, or Ice Zirkon Translucent, first generation) with cantilever lengths of 6 and 10 mm, and zirconia’s fracture resistance in relation to an average bite force of 250 N. (2) Materials and methods: Forty structures were created in CAD/CAM and divided into four groups: group A (6 mm cantilever in IZT), group B (10 mm cantilever in IZT), group C (6 mm cantilever in Pz), and group D (10 mm cantilever in pz). The study consisted of a traditional “load-to-failure” test. (3) Results: A statistically significant result was found for the effect of cantilever length, t(38) = 16.23 (p < 0.001), with this having a large effect size, d = 4.68. The 6 mm cantilever length (M = 442.30, sd = 47.49) was associated with a higher mean force at break than the 10 mm length (M = 215.18, sd = 40.74). No significant effect was found for the type of zirconia: t(38) = 0.31 (p = 0.757), and d = 0.10. (4) Conclusions: All the components with cantilever lengths of 6 mm broke under forces higher than 250 N. Cantilevers larger than 10 mm should be avoided.

Clinical assessment of different implant-supported esthetic crown systems fabricated with semi-digital workflow: Two-year prospective study

OBJECTIVE

To assess the clinical outcome of three esthetic implant-supported crown systems fabricated with semi-digital workflow and their influence on the clinical outcome of dental implants.

MATERIAL AND METHODS

A total of 30 participants had received dental implants restoring missing maxillary first/second premolars. After 6 weeks, customized zirconia abutments were early loaded. Two months later, the definitive crowns were fabricated using semi-digital workflow and cemented. According to the crown material, 3 groups were randomly allocated; group (Z): ultrahigh-translucent monolithic zirconia, group (C): resin-matrix ceramic and group (P): polyetherketoneketone veneered with light-cured composite resin. Clinical outcomes including the survival and success rates were evaluated at baseline, 6, 12, 18, and 24 months.

RESULTS

The survival rate for all studied groups was 100%, while their success rate was 100% for group (Z) and 90% for group (C) and group (P). Based on the functional implant prosthodontic score, a statistically significant difference was detected between group (Z) and group (P) (p < 0.001) as well as between group (C) and group (P) (p = 0.01).

CONCLUSIONS

The zirconia group had the most favorable clinical behavior, while the polyetherketoneketone had the least. All crown systems had comparable success rates with similar values of the peri-implant marginal bone loss.

CLINICAL SIGNIFICANCE

Using semi-digital workflow, ultrahigh-translucent monolithic zirconia, resin-matrix ceramic and polyetherketoneketone veneered with light-cured composite resin can be considered as favorable implant-supported crowns. The implant-supported crown system based on polyetherketoneketone veneered with light-cured composite resin is counted as a promising esthetic and restorative option.

Zirconia fixed dental prostheses fabricated by 3D gel deposition show higher fracture strength than conventionally milled counterparts

Zirconia restorations, which are fabricated by additive 3D gel deposition and do not require glazing like conventional restorations, were introduced as "self-glazed" zirconia restorations into dentistry. This in vitro investigation characterized the surface layer, microstructure and the fracture and aging behavior of "self-glazed" zirconia (Y-TZP_SG) three-unit fixed dental prostheses (FDP) and compared them to conventionally CAD/CAM milled and glazed controls (Y-TZP_C-FDPs). For this purpose, the FDPs were analyzed by (focused ion beam) scanning electron microscopy, laserscanning microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and a dynamic and static loading test. For the latter, half of the samples of each material group (n = 16) was subjected to 5 million cycles of thermocyclic loading (98N) in an aqueous environment in a chewing simulator. Afterwards, all FDPs were loaded to fracture. Y-TZP_SG-FDPs demonstrated a comparable elemental composition but higher surface microstructural homogeneity and fracture strength compared to Y-TZP_C-FDPs. Microstructural flaws within the FDPs' surfaces were identified as fracture origins. The high fracture strength of the Y-TZP_SG-FDPs was attributed to a finer-grained microstructure with fewer surface flaws compared to the Y-TZP_C-FDPs which showed numerous flaws in the glaze overlayer. A decrease in fracture strength after dynamic loading from 5165N to 4507N was observed for the Y-TZP_SG-FDPs, however, fracture strength remained statistically significantly above the one measured for Y-TZP_C-FDPs (before chewing simulation: 1923N; after: 2041N). Within the limits of this investigation, it can therefore be concluded that Y-TZP_SG appears to be stable for clinical application suggesting further investigations to prove clinical applicability.

Mechanical characterization of a multi-layered zirconia: Flexural strength, hardness, and fracture toughness of the different layers

This study compared the flexural strength under monotonic (static - sσ) and cyclic load application (fatigue - fσ), hardness (H) and fracture toughness (K_IC) of different layers of a multi-layered zirconia (IPS e.max ZirCAD MT Multi, Ivoclar). Each layer was sectioned, classified into three groups according to yttria content (4-YSZ, 4/5-YSZ and 5-YSZ), and shaped on samples for flexural strength and fracture toughness tests (bars: 1.0 × 1.0 × 11 mm); and Vickers hardness test (plates: 1.5 × 4.0 × 5.0 mm). Flexural strength under monotonic load application (sσ; n = 10) was obtained through two different devices (three-point-bending and ball-in-hole device) and fatigue flexural strength (fσ; n = 15; initial load: 10 N; step-size: 5 N; 10,000 cycles/step) was assessed using a ball-in-hole device under cyclic load application. Vickers hardness test (n = 5), fracture toughness test (n = 10), and additional analyzes (Finite Element Analysis - FEA, Energy-dispersive X-ray spectroscopy - EDS and Scanning Electron Microscopy - SEM) were also performed. No differences were found between the different devices in the monotonic flexural strength test, and FEA showed similar tensile stress distribution for the two devices. 4-YSZ showed higher values of flexural strength under monotonic and cyclic load application modes (sσ = 1114.73 MPa; fσ = 798.84 MPa), and fracture toughness (K_IC = 3.90 MPa√m). 4/5-YSZ had an intermediate sσ; however, fσ was similar to 5-YSZ (404.00-429.36 MPa) and K_IC similar to 4-YSZ (K_IC = 3.66 MPa√m). No statistical differences were found for hardness and Weibull modulus for fatigue flexural strength data. The amount of yttria in the layer compositions increased from 4-YSZ to 5-YSZ, and larger zirconia crystals were observed in the topographic images of 5-YSZ. Failures in the flexural strength and toughness tests started from the face subjected to tensile stress. Different layers of the multi-layered zirconia blank presented distinct mechanical properties. 4-YSZ (cervical layer) presented the highest flexural strength under monotonic and cyclic loads (fatigue), and higher fracture toughness even similar to the transition layer (4/5-YSZ). Hardness was similar between the layers. The ball-in-hole device performed similarly to the three-point bending device and can be used as an alternative to the traditional method.

Thickness and yttria percentage influences the fracture resistance of laminate veneer zirconia restorations

OBJECTIVES

Mechanical properties are cardinal for the long-term clinical success of laminate veneer restorations but the selection of new restorative materials should ideally be based on clinical evidence, therefore, in vitro testing of dental materials is a good alternative to evaluate their properties and understand their behavior so this study aimed to compare and evaluate the effect of two different thicknesses and yttria percentage on the fracture resistance of laminate veneer zirconia restorations.

MATERIALS AND METHODS

Forty laminate veneer restoration prepared from partial sintering zirconia of 3Y (yttria), 5Y (yttria), combined 3Y&5Y (yttria), and lithium disilicate. Specimens were assigned into four main groups according to their percentage of yttria content (n = 10) and subgrouped into two thicknesses (0.5 mm thickness and 0.3 mm thickness) (n = 5) as follows: Group I, II, III, and IV (Group I for lithium disilicate (control), Group II for 3Y zirconia, Group III for 5Y zirconia, and Group IV for combined 3Y&5Y zirconia), each of them subdivided according to their thickness into two subgroups (n = 5 for each one) and resistance to fracture for each restoration was evaluated using a universal testing machine. Data were analyzed using a one-way analysis of variance and Duncan's tests at a 5% level of significance.

RESULTS

The thickness of laminate veneer restoration significantly affects the fracture resistance value of all type of laminate veneers restorations (fracture resistance mean value was highest for 0.5 mm thickness and lower for 0.3 mm thickness restorations) and yttria percentage significantly affect fracture resistance value of zirconia laminate veneer restorations (fracture resistance mean value was highest for 0.5 mm thickness of 3Y zirconia [865 N] and combined 3Y&5Y zirconia [846 N]).

CONCLUSIONS

Reducing the thickness of laminate zirconia veneer restorations to 0.3 mm reduces its fracture resistance and increasing yttria percentage had an adverse effect on fracture resistance of zirconia laminate veneer restorations.

Finite Element Analysis of Zirconia Dental Implant

Titanium dental implants have had new competitors in recent years, such as fixtures made of zirconia, which promise better aesthetics. The purpose of this study is to evaluate their mechanical performance in silico (Finite Element Analysis). The investigation was performed on a single tooth Patent™ Dental Implant (Zircon Medical®, Altendorf, Switzerland) in two configurations: without offset (Test I) and with offset (Test II, 1.5 mm within the cortical bone). The Patent Implant system consists of two components: the implant with integrated abutment and the fibreglass post. The components of the dental implants were tested using a compression load of 400 N along the implant axis. The results showed that the chewing load generates stress distribution on the bone, therefore, the offset configuration should be avoided.

Fractographic analysis of 35 clinically fractured bi-layered and monolithic zirconia crowns

OBJECTIVES

The aim of this retrieval study was to analyze the fracture features and identify the fracture origin of zirconia-based single crowns that failed during clinical use.

METHODS

Thirty-five fractured single crowns were retrieved from dental practices (bi-layered, n=15; monolithic, n=20). These were analyzed according to fractographic procedures by optical and scanning electron microscopy to identify fracture patterns and fracture origins. The fracture origins were closely examined. The crown margin thickness and axial wall height were measured.

RESULTS

Three types of failure modes were observed: total fractures, marginal semilunar fractures, and incisal chippings. Most of the crowns (23) had fracture origins at the crown margin and seven of them had defects in the fracture origin area. The exact fracture origin was not possible to identify due to missing parts in four crowns. The crown wall thickness was 20% thinner and wall height 30% shorter in the fracture origin area compared to the opposite side.

CONCLUSIONS

The findings in this study show that fractography can reveal fracture origins and fracture modes of both monolithic and bi-layered dental zirconia. The findings indicate that the crown margin on the shortest axial wall is the most common fracture origin site.

CLINICAL SIGNIFICANCE

Crown design factors such as material thickness at the margin, axial wall height and preparation type affects the risk of fracture. It is important to ensure that the crown margins are even and flawless.

Fracture Load and Fracture Patterns of Monolithic Three-Unit Anterior Fixed Dental Prostheses after In Vitro Artificial Aging-A Comparison between Color-Gradient and Strength-Gradient Multilayer Zirconia Materials with Varying Yttria Content

(1) Background: Due to advantages such as avoidance of chipping, pulp-friendly tooth preparation and cost reduction, zirconia is increasingly being used monolithically without veneering. Nevertheless, to enable good aesthetics, various multilayer systems have been developed. The aim of this study was to investigate the impact of different zirconia multilayer strategies and yttria levels on fracture load, fracture pattern, stress distribution and surface roughness. (2) Methods: Monolithic three-unit anterior FDPs were made from three different color-gradient zirconia multilayer materials with different yttria levels corresponding to varying strength and degrees of translucency grades (Katana HTML, STML, UTML, Kuraray) and one strength-gradient zirconia multilayer material (Katana YML, Kuraray) and artificially aged in a chewing simulator (1.2 × 106 load cycles, 50 N, 2 × 3000 thermocycles, 5−55 °C). Analyses of fracture load, fracture pattern, fracture surfaces, stress distribution and roughness were performed after the fracture load test. Shapiro−Wilk, Kruskal−Wallis, Mann−Whitney U-tests and one-way ANOVA were used (p < 0.05). (3) Results: Fracture loads of the high strength color-gradient material HTML and the strength-gradient material YML were comparable after 5 years of aging (p = 0.645). Increasing yttria levels resulted in a decrease in fracture resistance of 42−57% (p < 0.05). Surface roughness of different zirconia generations is comparable after polishing and aging. (4) Conclusions: Color-gradient multilayer zirconia materials and new strength-gradient zirconia materials with similar yttria levels in the basal layers show comparable mechanical properties and are suitable for anterior FDPs.

In-lab simulation of CAD/CAM grinding and intaglio surface treatments of 4YSZ monolithic restorations: Effect on its load-bearing capacity under fatigue

OBJECTIVES

To evaluate the effect of in-lab simulation of CAD/CAM grinding and intaglio surface treatments on the surface characteristics (topography and roughness) and fatigue behavior of adhesively luted 4YSZ simplified restorations.

METHODS

Ceramic discs (Ø = 10 mm, thickness = 1 mm) were randomly allocated into 6 groups considering: "In-lab simulation of CAD/CAM grinding" (ground or polished) and "intaglio surface treatments": Ctrl (without surface treatment), AlOx (aluminum oxide air abrasion) or GLZ (glaze spray application). The surface roughness of all samples was measured, the treated discs received a ceramic primer, were luted with resin cement onto a dentin analogue material (woven glass-reinforced epoxy resin) and tested under a cyclic fatigue test (step-stress approach, n = 15; 1.4 Hz, 10,000 cycles/step, step-size of 100N starting at 200N until failure). A complementary analysis was performed to corroborate the findings in the fatigue test that the glaze fill defects increase the mechanical properties of the ceramic. To do so, bars (n= 10; 1.0 × 1.0 × 12 mm; considering the groups: N-ID: non-indented; ID: indented; ID-GLZ: indented plus glaze spray application) were indented in a vickers hardness tester to produce a crack pattern, treated with glaze or not, and then submitted to flexural strength tests (FS). Fractographic and topographic analysis were performed.

RESULTS

In-lab simulation of CAD/CAM grinding decreased the fatigue failure load of the 4YSZ ceramic when comparing polished and ground groups, regardless of surface treatment. GLZ induced better fatigue performance compared to the air abrasion, regardless of the grinding condition (ground or polished surface). The results of the flexural strength test corroborated the findings in the fatigue test, as the ID-GLZ group presented superior FS than the ID group, however both had inferior FS than N-ID. There is an inverse association between roughness and fatigue failure load, as the higher the surface roughness, the lower the fatigue failure load. Failures in the fatigue and flexural strength tests started from the face subjected to tensile stresses.

CONCLUSION

In-lab simulation of CAD/CAM grinding had a detrimental effect on the fatigue behavior of 4YSZ and glaze spray induced better 4YSZ performance compared to the air abrasion. The intaglio surface treatments differently influenced the 4YSZ fatigue performance, however, only glaze spray can reverse the damage caused by the grinding.

Pre-sintering pigmentation techniques do not affect the fatigue behavior of adhesively luted 4YSZ restorations

This study aims to characterize the effect of shading techniques on the fatigue behavior of a 4YSZ ceramic (4 mol% yttrium stabilized zirconia) adhesively bonded to a dentin analogue (fiber-reinforced epoxy resin). 4YSZ ceramic discs (IPS e.max ZirCAD, Ø = 10 mm and 1 mm of thickness) were allocated according to the factor 'shading technique' into 4 groups: Brush- unshaded ceramic disc (IPS e.max ZirCAD BL) pigmented at the pre-sintered stage with pigment solution applied manually using a round liner brush; Immersion- unshaded ceramic disc pigmented through immersion in the solution for 1 s on only one side of the ceramic disc; Manufacturer- specimens already shaded by the manufacturer (IPS e.max ZirCAD MT A2 - Manufacturer group); Control- a control condition with absence of pigment (i.e. non-pigmented specimens). The specimens were sintered and a spectrophotometer (SP60, EX- Rite) was used to ensure that the same perceived color (i.e. pigment saturation) was achieved in the different shading strategies (Manufacturer, Brush or Immersion groups). To do so, the color differences (ΔE00) were calculated using the CIEDE 2000 equation; and an ΔE00 of up to 1.77 was considered as an acceptability threshold. Dentin analogue discs were obtained (Ø = 10 mm and 2.5 mm of thickness) and randomly allocated into pairs with the 4YSZ ceramic discs. Next, the pairs were adhesively bonded using a resin cement (Multilink N). The bonded assemblies (n = 15) were tested for fatigue using the step-stress test method (frequency of 20 Hz; 10,000 cycles per step, initial load 200 N; step-size of 100 N, up to 700 N; and after, step-size of 50 N, until specimen failure/fracture or radial cracks). Fatigue failure load (FFL) and number of cycles for failure (CFF) were recorded for statistical analysis. Fractographic features were accessed, and complementary roughness, topography, grain size and phase content analyses were performed. No statistical differences were observed in the fatigue behavior among the non-shaded condition (Control group - 880 N) and the shaded specimens (Manufacturer - 887 N, Brush - 820 N, and Immersion - 850 N groups; p > 0.05). However, the use of a brush shading technique induced slightly inferior fatigue mechanical behavior of the restorative set compared to the specimens already shaded by the manufacturer (p = 0.027). No differences in Weibull modulus were observed among the tested groups. The specimens pigmented by the brush technique demonstrated a rougher surface, with statistically higher Rz values, in addition to a larger grain size in comparison to all other conditions (p< 0.05). No m-phase content was identified (only t and c phases were detected). Thus, the shading techniques used to provide a Vita classic A2 shade does not negatively affect the mechanical fatigue properties of a bonded 4YSZ ceramic. However, the brush technique has detrimental effect on the fatigue behavior compared to when the ceramic was already provided in a shaded format by its manufacturer.

Treatment of Tooth Wear Using Direct or Indirect Restorations: A Systematic Review of Clinical Studies

Tooth wear is considered a well-developed issue in daily clinical practice; however, there is no standard protocol for treatment. The aim of this manuscript was to systematically review the literature to evaluate the clinical outcomes of direct or indirect restorations for treating tooth wear. A literature search was conducted through the PubMed MedLine, Scopus, ISI Web of Science, Scielo, and EMBASE databases up to 29 April 2022. Clinical studies evaluating the clinical performance of direct or indirect restorations for treating tooth wear for a minimum follow-up of 6 months were included in the review. A total of 2776 records were obtained from the search databases. After full-text reading, 16 studies were included in the qualitative analysis. Considering the high heterogenicity of the studies included, a meta-analysis could not be performed. All studies included the rehabilitation of anterior and posterior teeth with extensive wear, using both indirect and direct restorations for a maximum follow-up of 10 years. Restoration materials included ceramo-metal crowns, full gold crowns, lithium disilicate ceramic, zirconia, polymer infiltrated ceramic networks, and resin composites. Most of the reports assessed the survival rate of the restorations and the clinical features using the United States Public Health Service (USPHS) Evaluation System criteria. Contradictory discoveries were perceived concerning the type of restoration with better clinical performance. Considering the current literature available, there is no evidence in the superiority of any restoration technique to ensure the highest clinical performance for treating tooth wear.

Influence of the Surface Chemical Composition Differences between Zirconia and Titanium with the Similar Surface Structure and Roughness on Bone Formation

The osseointegration of zirconia (ZrO2) implants is still controversial. In this study, we aimed to make clear the influence of surface chemical composition, Ti or ZrO2, to osseointegration. First, a roughened Ti surface was prepared with a combination of large-grit sandblasting and acid treatment. Then, we applied molecular precursor solution containing Zr complex onto roughened Ti surface and can deposit thin ZrO2 film onto roughened Ti surface. We can change surface chemical composition from Ti to ZrO2 without changing the surface structure and roughness of roughened Ti. The tetragonal Zr was uniformly present on the ZrO2-coated Ti surface, and the surface of the ZrO2-coated Ti showed a higher apparent zeta potential than Ti. Ti and ZrO2-coated Ti rectangular plate implant was placed into the femur bone defect. After 2 and 4 weeks of implantation, histomorphometric observation revealed that the bone-to-implant contact ratio and the bone mass values for ZrO2-coated Ti implants inserted into the femur bone defects of the rats at 2 weeks were significantly higher than those for Ti implants (p < 0.05). It revealed that ZrO2 with a similar surface structure and roughness as that of roughened Ti promoted osteogenesis equivalent to or better than that of Ti in the early bone formation stage.

Shear Bond Strength of Two Repair Systems to Zirconia Ceramic by Different Surface Treatments

Introduction: Intraoral repair has been suggested as a treatment option to repair the chipping or fracture of veneered zirconia; the success of the procedure is mainly determined by the bonding between zirconia and composite resin. The present study aimed to investigate and compare the shear bond strength (SBS) of two intraoral repair systems to zirconia ceramic treated with a laser or air-abrasion surface modification. Methods: Ninety tube-shaped samples (diameter of 10 mm and height of 4 mm) were divided into three main groups: Group I (zirconia 100%, n=30); Group II (veneer ceramic 100% n=30); Group III (zirconia with a veneer ceramic n=30). Each main group was subdivided into two subgroups (n=15): Subgroup A: samples repaired with Ceramic Repair N; Subgroup B: samples repaired with the Cimara Repair System. The subgroup samples were further subdivided based on the treated surface (n=5 samples): Control (no surface modification), Er,Cr:YSGG laser surface modification, and air-abrasion surface modification. The SBS was employed using a universal testing machine. The mode of failure was observed using a stereomicroscope. Results: Significant differences were observed in the mean SBS values between the different surface modifications (P˂0.05). Tukey's post hoc test showed that the air-abrasion surface modification of the veneer ceramic repaired with the Ceramic repair N system had the highest mean value (13.74 MPa) among the different groups, while no surface modification of zirconia repaired with the Cimara repair system had the lowest mean value (2.84 MPa). The control group (no surface modification) had the lowest mean value among all the treated groups. Conclusion: The SBS is surface modification-dependent, and higher SBS is obtained by air-abrasion than Er, Cr:YSGG laser surface modifications with the selected parameters. The Ceramic repair N system had significantly higher SBS for all surface-treated substrates than the Cimara repair system.

Overview of Several Typical Ceramic Materials for Restorative Dentistry

With the development of ceramic technology, prosthodontic ceramics are becoming a useful option for improving esthetic outcomes in dentistry. In this paper, various ceramic materials were reviewed and evaluated, and their advantages and disadvantages and indications in oral prosthodontics were analyzed objectively. The properties of resin-based ceramics, polycrystalline ceramics, and silicate ceramics were compared and analyzed. Resin-based ceramics may replace other ceramic materials in the CAD/CAM field.

Wear behavior and abrasiveness of monolithic CAD/CAM ceramics after simulated mastication

Objectives

To evaluate the wear resistance and abrasiveness of monolithic CAD/CAM ceramics.

Materials and methods

Rectangular-shaped specimens (12 mm × 6.5 mm × 1.5 mm) were sectioned from the following CAD/CAM blocks (n = 10); partially crystallized lithium disilicate (PLD), experimental fully crystallized lithium disilicate (FLD), zirconia-reinforced lithium silicate (ZLS), super-translucent monolithic zirconia (SMZ), and ultra-translucent monolithic zirconia (UMZ). Silicon carbide papers were used to mechanically flatten and polish the surfaces. PLD specimens were subjected to a combined crystallization/glazing firing cycle. Ceramic specimens were mounted to the wear device and tested for 200,000 cycles against human premolars at 20 N force and 2 mm sliding distance. Artificial saliva was used as a lubricant. The teeth were scanned using micro-CT before and after the wear test and the generated models were overlapped to determine the volumetric tooth loss. Before and after the test, specimens’ weights and surface roughness (R_a) values were measured, and the differences were calculated. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were utilized for microstructural and chemical analysis. Statistical analysis was performed using one-way ANOVA or an equivalent test for non-parametric results. Significance level was set at P ≤ 0.05.

Results

The type of ceramic material affected the ceramic and antagonist wear rates (P < 0.001). PLD and ZLS had the highest ceramic and antagonist wear, whereas UMZ and SMZ demonstrated the lowest wear values. The FLD group showed comparable antagonist wear and significantly less ceramic wear than PLD and ZLS.

Conclusions

Monolithic zirconia demonstrated the best wear resistance and least abrasiveness to the antagonist. The experimental lithium disilicate was more wear-resistant than other glass–ceramic groups.

Clinical relevance

Monolithic zirconia is wear-resistant and gentle on the antagonist. In contrast, glass–ceramics are more abrasive to enamel.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-022-04611-w.

Color changes of dental zirconia immersed in food and beverage containing water-soluble/lipid-soluble pigments

The present study examined color changes in the tooth-colored restorative materials, zirconia (3Y-TZP), resin composite, and porcelain. The colors (CIELab) of these materials were measured using a spectrophotometer. Specimens were immersed in black tea or curry for 1 and 7 days, after which colors were re-assessed. Color differences (∆E^*ab) before and after immersion were calculated. Specimens after the 7-day immersion were ultrasonically cleaned, and colors were measured again to assess the color recovery rate. The surface free energy, roughness, and water sorption/solubility of each material were also evaluated. Specimens were observed under a scanning electron microscope. The ∆E^*ab of 3Y-TZP was the smallest with both immersions. Resin composite had the smallest recovery rate. The surface free energy and roughness of 3Y-TZP were smaller than those of porcelain. 3Y-TZP and porcelain showed almost no sorption during the 7-day period. The present results revealed that 3Y-TZP exhibited the strongest resistance to discoloration.

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.

[Optical and mechanical properties of translucent zirconium as an optimal restorative material in fixed prosthesis: A review of the literature]

Introduction

The main consequence of not treating tooth decay in time is the total or partial loss of the tooth. One of the alternatives to replace the lost tooth and return the functions is through fixed prostheses. Today there are 3 generations of yttrium-stabilized zirconium polycrystals (Y-TZP). Seeing that in the third Generation the yttrium content was increased to approximately 5% in moles (5Y), stabilizing the materials approximately 50% of cubic phase and 50% of tetragonal phase, thus giving a translucent zirconium (5Y) with a high aesthetics and greater naturalness to the dental crown.

Objective

To identify the different optical and mechanical properties of translucent zirconium compared to other restorative materials used in fixed prostheses.

Materials and methods

This narrative review evaluated 115 scientific articles from the Medline information sources (via PubMed), Science Direct, Scopus, SciELO and LILACS from the last 5 years, published in Spanish, Portuguese and English. We included 51 articles that met the selection criteria which were randomized clinical trials and observational studies, in vitro studies and in vivo studies that evaluated the optical and mechanical properties of translucent zirconium as an optimal restorative material in fixed prostheses. We excluded systematic reviews, case reports and editorials.

Results

It was observed that zirconium being a relatively new material and in constant evolution has studies mostly in vitro, among which stand out those that speak both of the mechanical and optical properties that vary depending on the generation to which the material belongs, as well as the adhesiveness of the material which is for now not viable, therefore, it is essential that more studies be carried out on this material.

Conclusions

We can mention that zirconium has evolved over time, providing better optical properties, but as a consequence it has been reducing flexural strength and fracture toughness. However, this material provides good biocompatibility with oral structures. On the other hand, translucent zirconium according to studies is a non-recordable material, so new methods are sought to improve its adhesion.

Effect of air abrasion, acid etching, and aging on the shear bond strength with resin cement to 3Y-TZP zirconia

This study investigates the effect of acid etching treatment on the surface microstructure, surface roughness, and surface contact angle of zirconia and compares the effects of air abrasion, different etching times, and aging on the shear bond strength (SBS) of resin cement on the zirconia surface. 480 specimens (9 × 10 × 10 mm) were divided into as-sintered and air-abraded groups, and each group was further subdivided into six groups based on etching time (0, 3, 5, 10, 20, and 30 min). The etching solution comprised hydrofluoric acid 25%, sulfuric acid 16%, hydrogen peroxide, methyl alcohol, and purified water. The shear bond strength (SBS), scanning electron microscopy, surface roughness, contact angle, and failure mode were measured. The results indicated that the mean SBS values increased and decreased significantly when the etching times increased to 20 min and 30 min, respectively, in both groups. Further, SBS after aging was lower than that before aging in all groups. Sandblasting, etching time, and aging all showed significant effects (p < 0.001) in the three-way analysis of variance. In addition, the surface roughness increased and the contact angle decreased significantly with an increase in etching time. Thus, the acid-etching treatment induced significant changes on the zirconia surface and increased the SBS of the resin cement. The results of this in vitro study suggest that acid etching is a promising alternative for zirconia surface treatment.

Rhombohedral Phase Formation in Yttria-Stabilized Zirconia Induced by Dental Technical Tools and Its Impact on Dental Applications

In the study the influence of different dental technical tools on the surface temperature and phase composition of fixed dental prostheses (FDPs) made of yttria-partially stabilized zirconia polycrystals (3Y-/4Y-/5Y-PSZ) was investigated. FDPs were fabricated by using computer-aided manufacturing (CAM). The FDPs were treated with a contra-angle handpiece equipped with different burs and polishers. The resulting surface temperatures were measured with a thermographic camera, and the resulting phase transformations were investigated by X-ray diffraction and quantified by Rietveld refinement. Processing with burs resulted in no phase transformation, but a preferred orientation shift. Using coarse polisher induced a phase transformation to the rhombohedral phase, while fine polishers produced no relevant phase transformations and no preferred orientation shift. Compared to the monoclinic phase (ca. 9% theoretical volume increase), which is associated with low-temperature degradation (LTD), the rhombohedral phase is much more voluminous (ca. 15% theoretical volume increase) and distorted and, therefore, has a greater degradation potential.

Influence of Adhesion Promoter Primers on Polymerization Kinetics and Long-term Bond Strength of Composite Cements to Zirconia

PURPOSE

To investigate the influence of primers on polymerization kinetics of resin-based luting and its effect on the microhardness and bond strength to zirconia. Materials and Methods: Panavia V5 (PV; Kuraray Noritake) with Tooth Primer (TPprimer; Kuraray Noritake) or Clearfil Ceramic Primer (CPprimer; Kuraray Noritake), and RelyX Ultimate (RU; 3M Oral Care) with Scotchbond Universal (SUadhesive; 3M Oral Care) were evaluated. Polymerization kinetics of luting materials with or without primers (TPprimer or SUadhesive) were evaluated using Fourier transform near-infrared (FT-NIR) spectroscopy in self- and dual-curing modes (n = 5). Microhardness of luting materials was evaluated after 1, 12, and 24 h (n = 5). Shear bond strengths to zirconia ceramics (Katana Zirconia, Kuraray Noritake; and Lava Esthetic, 3M Oral Care) after 24 h and 1 year (n = 8) were assessed to determine the effect of the following surface treatments: no treatment, non-thermal atmospheric plasma, primer (CPprimer or SUadhesive), and the combination of plasma + primers. Statistical analyses were performed at a 5% significance level.

RESULTS

PV achieved a significantly higher degree of conversion (DC) when TPprimer was used, while there was no increase in conversion for RU combined with SUadhesive. Light activation significantly improved polymerization, which also produced greater microhardness. CPprimer and SUadhesive significantly improved immediate bond strength to zirconia ceramics. However, after 1 year, only SUadhesive with RU was able to maintain the bond strength. Plasma surface treatment did not improve bonding to zirconia.

CONCLUSION

The use of primers improved the DC for PV only. Light curing produced higher conversion and microhardness for both resin-based luting materials. Bond strength to zirconia was improved when primers were used. However, only RU demonstrated reliable long-term adhesion to zirconia.

Bone Tissue Engineering through 3D Bioprinting of Bioceramic Scaffolds: A Review and Update

Trauma and bone loss from infections, tumors, and congenital diseases make bone repair and regeneration the greatest challenges in orthopedic, craniofacial, and plastic surgeries. The shortage of donors, intrinsic limitations, and complications in transplantation have led to more focus and interest in regenerative medicine. Structures that closely mimic bone tissue can be produced by this unique technology. The steady development of three-dimensional (3D)-printed bone tissue engineering scaffold therapy has played an important role in achieving the desired goal. Bioceramic scaffolds are widely studied and appear to be the most promising solution. In addition, 3D printing technology can simulate mechanical and biological surface properties and print with high precision complex internal and external structures to match their functional properties. Inkjet, extrusion, and light-based 3D printing are among the rapidly advancing bone bioprinting technologies. Furthermore, stem cell therapy has recently shown an important role in this field, although large tissue defects are difficult to fill by injection alone. The combination of 3D-printed bone tissue engineering scaffolds with stem cells has shown very promising results. Therefore, biocompatible artificial tissue engineering with living cells is the key element required for clinical applications where there is a high demand for bone defect repair. Furthermore, the emergence of various advanced manufacturing technologies has made the form of biomaterials and their functions, composition, and structure more diversified, and manifold. The importance of this article lies in that it aims to briefly review the main principles and characteristics of the currently available methods in orthopedic bioprinting technology to prepare bioceramic scaffolds, and finally discuss the challenges and prospects for applications in this promising and vital field.

Composition, processing, and properties of biphasic zirconia bioceramics: relationship to competing strength and optical properties

A study is made of relationships between composition, processing, structure and properties of biphasic zirconia bioceramics. The focus is on zirconia compositions with different yttria dopant contents used in modern dental restorations, namely 3 - 5 mol% yttria stabilized zirconia (3YSZ, 4YSZ, and 5YSZ). Crystallographies and densities are surveyed, sintering conditions examined, and microstructures characterized. Strength and optical tests are conducted on each YSZ, and dependencies on sintering temperature, cubic content and grain size analyzed. Strength correlates with the amount of tetragonal zirconia (t-ZrO2) crystals with large lattice distortions (tetragonality). YSZ translucency correlates with content of cubic zirconia (c-ZrO2) and t-ZrO2 with low levels of tetragonality. Consistent with literature reporting, the materials rank in decreasing order 3YSZ, 4YSZ to 5YSZ for strength but increasing order for translucency. However, for a given composition, the data suggest that the strengths of densely sintered 3YSZ and 4YSZ actually increase with translucency, although that of 5YSZ remains undiminished. These trends are in apparent contradiction to prevailing experience, and offer potential future processing routes to optimization of clinical materials.

Evaluating the Effect of Different Polymer and Composite Abutments on the Color Accuracy of Multilayer Pre-Colored Zirconia Polycrystal Dental Prosthesis

With increasing aesthetic awareness and emphasis on time costs in today’s society, monolithic multilayer precolored zirconia ceramics (M-Zr) facilitate aesthetic restorations in a convenient and straightforward manner without the need for veneering porcelain to modify the color. However, the effect of abutment materials on the final color of M-Zr remains unclear. Herein, we placed Vita A1 Shade M-Zr on six different abutment materials, zirconia (Y-TZP), 3D printed composite resin (CR), dental model resin (MR), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and cobalt−chromium alloy (Co−Cr), to evaluate their effect on the color accuracy of M-Zr. The color attributes (L*, a*, and b*) were measured using a dental spectrophotometer. The translucency parameter (TP), contrast ratio, color difference (ΔE) between each background substrate and the Vita A1 Shade Guide, and chroma values (C) were calculated to evaluate the color accuracy of M-Zr. A statistical analysis was performed using one-way analysis of variance and post hoc Tukey’s HSD tests (α = 0.05). The experimental results indicate that the TP values and contrast ratio of the M-Zr samples were 14.85 and 0.83, respectively. Co−Cr had the highest ΔE (6.08) and lowest C value (7.52); PEKK had the lowest ΔE (2.60), and PEEK had the highest C value (12.23) (p < 0.05). Notably, the ΔE values of CR (3.13), PEEK (2.86), and PEKK were within clinical indicators (ΔE < 3.7). Based on these results, it can be concluded that the abutment material has a significant effect on the final color of the M-Zr, and PEEK or PEKK resulted in good color accuracy. When choosing the dental MR, traditional zirconia, or metals as abutment materials, colored or opaque cement might be required to eliminate color distortion and achieve desirable optical properties.

Do tooth-supported zirconia restorations present more technical failures related to fracture or loss of retention? Systematic review and meta-analysis

OBJECTIVES

This systematic review was performed to determine the main cause of technical failure of tooth-supported zirconia crowns and fixed partial dentures (FPDs), categorizing them as fracture/chipping or loss of retention/decementation.

MATERIALS AND METHODS

Electronic and manual searches were performed for randomized clinical trials, prospective clinical trials, and prospective cohort studies that reported the technical failure rates of zirconia restorations. The Cochrane Collaboration risk-of-bias tool and Newcastle-Ottawa scale were used to assess the quality of the studies.

RESULTS

Fifty-two studies were included and most of them had unclear risk of bias. Considering all reported fractures/chipping, for veneered crowns with 1 to 3 years of follow-up, the relative risk (RR) of fracture in relation to loss or retention was 3.95 (95% CI 1.18-13.23; p = 0.03). For 4 to 6 years of follow-up, the RR was 5.44 (95% CI 1.41-20.92; p = 0.01). For veneered FPDs with 1 to 3 years of follow-up, the RR was 5.98 (95% CI 2.31-15.01; p = 0.0002). For 4 to 6 years of follow-up, the RR was 3.70 (95% CI 1.63-8.41; p = 0.002). For 7 years or more of follow-up, the RR was 3.45 (95% CI 1.84-6.46; p = 0.0001). When only framework fractures were considered, there were no significant differences for the RR in all follow-up periods (p > 0.05).

CONCLUSIONS

Higher RR for fracture/chipping in relation to decementation for veneered zirconia crowns and FPDs at all follow-up times. For framework fractures, no difference was observed between the risk of failure of the restoration due to fracture or decementation.

CLINICAL RELEVANCE

Zirconia crowns and FPDs showed relatively high success and survival rates. However, considering the technical failures, there is approximately four times higher chance of fracture/chipping than loss of retention for both single and multi-unit tooth-supported veneered zirconia restorations.

Effect of artificial aging on the translucency of monolithic zirconia materials sintered at different temperatures

STATEMENT OF PROBLEM

Translucent zirconia materials were developed as an alternative to lithium disilicate materials. However, the effect of sintering temperature and artificial aging on the translucency of zirconia materials is unclear.

PURPOSE

The purpose of this in vitro study was to investigate the translucency of recently developed zirconia materials after different sintering temperatures and the effect of artificial aging.

MATERIAL AND METHODS

Disk-shaped specimens (Ø15×1 mm) of 3 different monolithic zirconias (Katana UTML, Prettau Anterior, VITA YZ XT) and a control lithium disilicate reinforced glass ceramic (IPS e.max CAD LT) were evaluated. The zirconia specimens were divided into 2 subgroups with different sintering temperatures (1450 °C, 1550 °C) (n=5, N=35). The specimens were artificially aged in a thermocycle tester and a mastication simulator. The translucency parameter (TP) was calculated by measuring with a spectrophotometer. Kruskal-Wallis and Wilcoxon signed-rank tests were used to analyze the data (α=.05).

RESULTS

While the overall TP of monolithic zirconia increased after artificial aging, the lithium disilicate specimens did not show a statistically significant difference (P=.35). The Prettau Anterior and VITA YZ XT specimens had a statistically significant higher TP than Katana UTML (P=.009). Sintering temperature did not have a statistically significant effect on the TP value of monolithic zirconia materials (P>.05).

CONCLUSIONS

Artificial aging increased the TP, and the sintering temperature did not affect the TP of monolithic zirconia. The use of fully stabilized zirconia may be an alternative to lithium disilicate in esthetic restorations in clinical practice.

Comparative analysis on intaglio surface trueness, wear volume loss of antagonist, and fracture resistance of full-contour monolithic zirconia crown for single-visit dentistry under simulated mastication

PURPOSE

This analysis aimed to evaluate the intaglio surface trueness, antagonist’s wear volume loss, and fracture resistance of full-contour crowns of (Y, Nb)-stabilized fully-sintered zirconia (FSZ), 4 mol% or 5 mol% yttria-stabilized partially sintered zirconia (4YZ or 5YZ) with high-speed sintering.

MATERIALS AND METHODS

A total of 42 zirconia crowns were separated into three groups: FSZ, 4YZ, and 5YZ (n = 14). The intaglio surface trueness of the crowns was evaluated at the inner surface, occlusal, margin, and axial areas and reported as root-mean-square, positive and negative average deviation. Half of the specimens were aged for 120,000 cycles in the chewing simulator, and the wear volume loss of antagonist was measured. Before and after chewing, the fracture load was measured for each group. The trueness values were analyzed with Welch's ANOVA, and the wear volume loss with the Kruskal-Wallis tests. Effect of the zirconia type and aging on fracture resistance of crowns was tested using two-way ANOVA.

RESULTS

The intaglio surface trueness measured at four different areas of the crown was less than 50 µm, regardless of the type of zirconia. No significant P in wear volume loss of antagonists were detected among the groups (P > .05). Both the type of zirconia and aging showed statistically significant effects on fracture resistance (P < .05).

CONCLUSION

The full-contour crowns of FSZ as well as 4YZ or 5YZ with high-speed sintering were clinically acceptable, in terms of intaglio surface trueness, antagonist’s wear volume loss, and fracture resistance after simulated mastication.

In Vitro Evaluation of the Shading Effect of Various Zirconia Surface Stains on Porcelain Crowns

Human teeth display various colors under natural light. Dental restorations, such as zirconia crowns, are generally used to rehabilitate the oral function of patients with tooth loss due to trauma or natural tooth falls. However, significant improvements in the color and translucency of zirconia are required to meet the clinical needs for dental restoration. In the past, a large amount of ceramic powder has been used to improve the appearance of zirconia. However, the interface between the ceramic powder and zirconia makes them prone to falling off. Therefore, the aesthetics of zirconia crowns remains a major challenge. Recently, substantial advances have been made in the field of dental materials, as special staining agents for zirconia have been introduced as alternatives to ceramic powders. Therefore, this study tested zirconia-specific staining agents that were used to produce zirconia samples with A1 and A3 colors. A dental colorimetric plate was used as the control group to assess the staining effects of the different brands of staining agents. Meanwhile, two hypotheses were proposed: that the staining effects of these special staining agents for zirconia met the criteria for clinical application and that there was no significant difference between the different staining agents for zirconia. The results showed that the coatings of different brands of staining agents were ultrathin, with a thickness of approximately 27–78 µm. In addition, the coloring effects of the zirconia staining agents were not significantly different from those of the colorimetric plates. After staining, the zirconia samples had decreased surface roughness and contact angle values, which improved surface smoothness and cleanliness. In summary, the results support the hypothesis of this study that zirconia stains can be used as an alternative to the current fabrication methods for clinical dental restorations. We sought to identify the clinical techniques that are easier to perform and to overcome the current problem of dental technicians requiring considerable dentin space for staining. It is expected that the results of this study will be useful in clinical dental restorations.

How home bleaching agents affect the color and translucency of CAD/CAM monolithic zirconia materials

To assess the effect of 10% carbamide peroxide (CP) and 6% hydrogen peroxide (HP) home bleaching agents on the translucency and color of monolithic zirconia. Ninety disc specimens were fabricated (diameter, 10 mm) from multi-layered (ML), ultra translucent multi-layered (UTML), and super translucent multi-layered (STML) zirconia blocks at three thicknesses (0.4,1,1.5 mm) (n=5). The samples were divided into two subgroups, which were treated with 6% HP (45 min per day) or 10% CP (8 h per day) for 14 days. The color of specimens was measured before bleaching (T0) and after bleaching on the third (T3), seventh (T7), and 14th (T14) day. Color (∆E) and translucency (TP) changes were calculated. The thickness varieties used in the samples and the bleaching agent types used created statistically significant differences only in TP and ∆E₀₀, respectively (p<0.05). Bleaching agents can affect TP and ∆E. Patients who have zirconia restorations should be careful when using home bleaching agents.

Stability of Cantilever Fixed Dental Prostheses on Zirconia Implants

Background: The objective was to determine the optimal connector size and position within zirconia disks for implant-supported cantilever fixed dental prostheses (ICFDP). Methods: Two-unit ICFDPs (n = 60) were designed for the premolar region with connector sizes of either 9 or 12 mm² and positioned in the enamel or dentin layer of two different types of zirconia disks. The restorations were milled and cemented onto zirconia implants. After simulated chewing for 1.2 Mio cycles, the fracture load was measured and fractures were analyzed. Results: No fractures of ICFDPs or along the implants were detected after simulated aging. The mean fracture load values were significantly higher for a connector size of 9 mm² (951 N) compared with 12 mm² (638 N). For the zirconia material with a higher biaxial flexural strength, the fracture load values were increased from 751 to 838 N, but more implant fractures occurred. The position within the zirconia disk did not influence the fracture load. Conclusions: A connector size of 9 mm² and a zirconia material with a lower strength should be considered when designing ICFDPS on zirconia implants to reduce the risk of fractures along the intraosseous implant portion.

Surface Characteristics of High Translucent Multilayered Dental Zirconia Related to Aging

(1) Background: The purpose of this study was to evaluate the differences in terms of surface characteristics (roughness, topography, microhardness) among layers for multi-layered high translucent and super-high translucent zirconia and the influence of finishing and aging on surface characteristics and microstructure. (2) Methods: Three types of translucent multilayer zirconia were evaluated: STML (4Y-TZP); IPS e.maxZirCAD CEREC/in Lab MT Multi (4Y-TZP + 5Y-TZP); CeramillZolidfx ML (5Y-TZP). Ninety-six plate-shaped samples (32 for a material), 16 mm × 14 mm × 1 mm size, were cut with a precision disc, polished on both sides with sand papers and sintered respecting the manufacturer’s protocol. Half of the specimens (16) were finished by polishing and the other half by glazing and then equally divided into one control group and one group subject to aging by autoclaving (1 h, 134 °C, 0.2 MPa), resulting in four groups of eight samples, for each zirconia. The specimens were evaluated in three areas: cervical, medium, incisal-of each glazed or polished surface, before and after aging. Tests were performed to determine the surface roughness using a profilometer; the surface topography by an atomic force microscope (AFM) and a scanning electron microscope (SEM). Microhardness was recorded using a microhardness tester. Statistical analyses were performed using two-way ANOVA test, unpaired sample t-Test, paired sample t-Test (α = 0.05) and Pearson’s correlation. (3) Results: Before and after autoclaving, for glazed samples significance (p < 0.05) higher surface roughness, respectively lower microhardness in comparison with the polished group was assessed. No significant differences (p > 0.05) were reported between the three areas, on glazed or polished surfaces of a material. Although, after aging an increase in surface roughness was observed both on glazed and polished samples, statistical differences were found for STML (p < 0.05). No significant differences (p> 0.05) concerning microhardness among the same areas, on glazed and polished surfaces, recorded before and after aging, except CeramillZolidfx ML glazed samples. (4) Conclusions: For tested zirconia materials no significant differences among layers were registered regarding surface characteristics. Surface treatment (glazing or polishing) has a significant impact on surface roughness and microhardness. Both before and after aging, the surface roughness values for the glazed samples were higher than for those polished. The super translucent 4Y-TZP material was more affected by aging compared to the super-high translucent 5Y-TZP material. The combined material revealed similarities for each layer corresponding to the microstructure.

A Review on Biomaterials for Orthopaedic Surgery and Traumatology: From Past to Present

The principal features essential for the success of an orthopaedic implant are its shape, dimensional accuracy, and adequate mechanical properties. Unlike other manufactured products, chemical stability and toxicity are of increased importance due to the need for biocompatibility over an implants life which could span several years. Thus, the combination of mechanical and biological properties determines the clinical usefulness of biomaterials in orthopaedic and musculoskeletal trauma surgery. Materials commonly used for these applications include stainless steel, cobalt-chromium and titanium alloys, ceramics, polyethylene, and poly(methyl methacrylate) (PMMA) bone cement. This study reviews the properties of commonly used materials and the advantages and disadvantages of each, with special emphasis on the sensitivity, toxicity, irritancy, and possible mutagenic and teratogenic capabilities. In addition, the production and final finishing processes of implants are discussed. Finally, potential directions for future implant development are discussed, with an emphasis on developing advanced personalised implants, according to a patient’s stature and physical requirements.

Effects of Different Polishing Systems on Surface Roughness and Crystal Structure of Zirconia

Objective

Intraoral polishing systems have become an alternative method for reglazing, which is important to prevent or minimize rapid wear of the opposing teeth. To assess the influence of different polishing systems and duration on surface roughness and crystal structure of zirconia was compared, contributing to the preparation and effect improvement of clinical zirconia restorations.

Methods

Forty-eight zirconia specimens with equal size were fabricated by cutting and sintering zirconia discs. Then X-ray diffractometer (XRD) was adopted for examination of the specimens. Six specimens were selected as the grinding-polishing group (GL) after polishing, grinding, and glazing. Then six specimens were randomly selected from the remaining specimens as the grinding-unpolished group (GR) after surface conditioning by dental diamond burs. Subsequently, based on different polishing systems and duration, the rest of specimens were divided into following groups (n = 6): Youdent-20s group (Y20), Youdent-40s group (Y40), Youdent-60s group (Y60), Toboom-20s group (T20), Toboom-40s group (T40), and Toboom-60s group (T60). Additionally, a contour graph was applied for assessing the surface roughness of zirconia, scanning electron microscope (SEM) for observing surface topography, and X-ray diffraction analysis (XRD) for determining crystal structure of zirconia.

Results

The GR group had the highest roughness, and the roughness of the specimens polished for 20 s with different polishing systems was significantly higher than those polished for 40 s and 60 s with the same polishing systems. There were no significant difference between the Y20 and T20 groups, while the roughness of the specimens in both Y40 and Y60 groups was significantly higher than that of the T40 and T60 groups. And with the increasing polishing duration, the surface morphology of the specimen was gradually smooth and the morphology was gradually regular. Besides, the surface scratches of the T group were shallower than that of the Y group at the same polishing duration. The peak value of XRD profile of the specimen after grinding and polishing process was consistent with the baseline pattern of that the original specimen.

Conclusion

Glazing can reduce the surface roughness of the specimens. Besides, the polishing effect of Toboom (TOB) system (polishing duration = 60 s) is the best. And different polishing durations of TOB system have no significant effect on the crystal surface structure of the specimen.

Mechanical properties-translucency-microstructure relationships in commercial monolayer and multilayer monolithic zirconia ceramics

OBJECTIVES

To evaluate the phase composition, microstructure, optical properties and mechanical properties of eight commercially available multilayer and monolayer monolithic dental zirconias.

METHODS

Five commercial 3Y-TZP (GC ST, GC HT [GC, Tokyo Japan]; Katana ML, Katana HT [Kuraray Noritake] and Lava Plus [3M Oral Care]) and three Y-PSZ (Katana STML, Katana UTML [Kuraray Noritake]; GC UHT [GC, Tokyo Japan]) zirconia ceramic grades were cut in plate-shaped specimens, sintered according to the manufacturer's instructions and mirror polished. The zirconia chemical composition was determined using X-ray fluorescence (XRF), phase composition was characterized using X-ray diffraction (XRD), while the grain size was measured using scanning electron microscopy (SEM). The translucency Parameter (TP) and Contrast Ratio (CR) were measured with a spectrophotometer (n = 10/group). The indentation fracture toughness (n = 10), Vickers hardness (n = 10) and biaxial strength (n = 20) of the sintered ceramics were assessed. The stress distribution during biaxial testing was assessed by Finite element analysis (FEA). Statistical analysis involved one-way ANOVA and post-hoc Tukey's HSD test and Pearson correlation test (α = 0.05).

RESULTS

FEA showed that the stress distribution in plate shape specimens was the same as for disks, rationalizing the use of plates for biaxial strength testing. As expected, higher quantities of Y₂O₃ were related to a higher cubic ZrO₂ phase content and lower tetragonality t-ZrO₂, which improved translucency but diminished flexural strength and toughness. While there was no significant correlation between grain size and other material properties, addition of pigments to the zirconia grade statistically negatively affected hardness.

CONCLUSION

Even though an improvement in strength and translucency could be recorded for the last Y-TZP generation, future research still needs to strive for combined improvement of optical properties and mechanical reliability of zirconia ceramics.

Digital Tools for Translucence Evaluation of Prosthodontic Materials: Application of Kubelka-Munk Theory

Translucency is one of the most important parameters to be considered by digital systems when predicting the matching appearance and hence the quality of prosthodontic restoration work. Our objective has been to improve the effectiveness of the algorithmic decision systems employed by these devices by (a) determining whether Kubelka-Munk theory can be used as an algorithm for predicting restoration suitability, and (b) evaluating the correlation between the visual evaluation of prosthodontic materials and the predicted translucency based on the use of the ΔE*, OP, CR, and K/S algorithms. In this regard, three zirconia systems and one lithium disilicate have been spectrophotometrically and visually characterized. Based on the results of this study, it has been proven that zirconia systems and lithium disilicate systems exhibit different optical behaviors. The psychophysical experience suggests that none of the existing mathematical methods can adequately estimate translucency, spectrophotometric, and colorimetric techniques, and that which is perceived by an experienced observer. However, translucency evaluation through the K/S algorithmic decision system should not be disregarded. New methods to measure translucency should be developed to improve digital systems for prosthodontic applications.

Bonding CAD/CAM materials with current adhesive systems: An overview

Objective

Data sources

Results

Conclusion

Fracture Resistance of Sintered Monolithic Zirconia Dioxide in Different Thermal Units

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

Wear of Polymer-Infiltrated Ceramic Network Materials against Enamel

Polymer-infiltrated ceramic network materials (PICNs) have high mechanical compatibility with human enamel. However, the wear properties of PICN against natural human enamel have not yet been clarified. We investigated the in vitro two-body wear behaviors of PICNs and an enamel antagonist. Two PICNs were used: Experimental PICN (EXP) prepared via the infiltration of methacrylate-based resin into the porous silica ceramic network and commercial Vita Enamic (ENA). Two commercial dental ceramics, lithium disilicate glass (LDS) and zirconia (ZIR), were also characterized, and their wear performance was compared to PICNs. The samples were subjected to Vickers hardness tests and two-body wear tests that involve the samples being cyclically impacted by enamel antagonists underwater at 37 °C. The results reveal that the Vickers hardness of EXP (301 ± 36) was closest to that of enamel (317 ± 17). The volumetric wear losses of EXP and ENA were similar to those of LDS but higher than that of zirconia. The volumetric wear loss of the enamel antagonist impacted against EXP was moderate among the examined samples. These results suggest that EXP has wear behavior similar to that of enamel. Therefore, PICNs are mechanically comparable to enamel in terms of hardness and wear and are excellent tooth-restoration materials.