Optical properties and flexural strength of translucent zirconia layered with high-translucent zirconia

Optical properties of monolithic zirconia crowns: In vitro and In vivo evaluation

Background/Aim: The aim of this study was to compare the monolithic and layered zirconia crowns by their optical property of translucency, using in vitro and in vivo evaluation methods. Material and Methods: One upper incisor and one canine were prepared to receive 6 monolithic Lava Plus HT and 6 layered Lava crowns using the CAD/CAM technology. The translucency in the vitro evaluation, was determined using a digital photoradiometer to measure the light reflected by the crowns in two different conditions, natural and metal plated abutment tooth. A provisional complete prosthesis of an edentulous patient, with the abutment teeth mounted in their anatomical position, was used for the in vivo evaluation. The crowns were randomly placed and evaluated by two independent operators in the oral cavity conditions. Results: In vitro results showed that monolithic crowns were not significantly less translucent than layered ones in both incisor (p=0.098) and canine (p=0.340): contrast ratio 0.978 vs. 0.956 and 0.941 vs. 0.929, respectively (Student -t test; a=0.05). In vivo evaluation results showed that the difference in the luminance was not statistically significant between Lava Plus HT and layered Lava crowns according to Mann Whitney Test, p=0.089 (a=0.01). Conclusions: The difference in translucency between monolithic and layered zirconia crowns was not statistically significant both in vitro and in vivo evaluation. Monolithic zirconia had a good masking ability of the abutment tooth.

Flexural strength and translucency characterization of aesthetic monolithic zirconia and relevance to clinical indications: A systematic review

OBJECTIVE

Optimizing monolithic zirconia (ZrO2) aesthetically without affecting the unique mechanical properties remains a major ongoing interest. The purpose of this review is to evaluate the improvement of recent monolithic ZrO2 generations to meet aesthetic optimization qualities. Additionally, for how the extent of the former modifications negatively affected their mechanical properties and the impact on their clinical indications.

METHODS

The current literature examines in-vitro studies evaluating both monolithic ZrO2 translucency and mechanical properties. The electronic search was done within these databases: Web of Science, ScienceDirect, Scopus, and PubMed within the period between 2009/10/01 and 2019/10/31. Search results that met eligibility criteria were classified into four groups; one for translucency parameter, two for uniaxial flexural strength and one for biaxial strength.

RESULTS

Articles that remained for comprehensive analysis were fifty-three. They reported a significant impact of composition, microstructure and surface treatment on translucency and flexural strength assessment. Aging was found to be of no concern for zirconia structures with high yttria content. Smooth surface polish was found to significantly enhance strength while coarse grinding and mechanical fatigue was found to do the reverse.

SIGNIFICANCE

Based on analyzing the previous in-vitro studies the following was found: Although significant improvement has occurred with recent monolithic zirconia types with higher yttria content having higher cubic/tetragonal ratio, they are still inferior to glass-ceramics' unique translucency. With improving zirconia aesthetically, some of mechanical performance was sacrificed. Care must be taken when dealing with thin sections of aesthetic zirconia structures especially when used in high bearing stress areas.

Sintering Process Optimization for 3YSZ Ceramic 3D-Printed Objects Manufactured by Stereolithography

A 3YSZ (3 mol% yttria-stabilized zirconia) ceramic green body with 50 vol% of ceramic content was 3D-printed by supportless stereolithography under optimal drying, debinding, and sintering conditions in order to achieve high strength and density. The viscosity and flowability of the ceramic nanocomposite resins were optimized by adjusting the amounts of non-reactive diluents. The ceramic 3D-printed objects have a high polymer content compared to ceramics samples manufactured by conventional manufacturing processes, and the attraction between layers is weak because of the layer-by-layer additive method. This causes problems such as layer separation and cracking due to internal stress generated when materials such as solvents and polymers are separated from the objects during the drying and debinding processes; therefore, the drying and debinding conditions of 3YSZ ceramic 3D-printed objects were optimized based on thermogravimetry–differential thermal analysis. The sintering conditions at various temperatures and times were analyzed using X-ray diffraction, SEM, and flexural strength analysis, and the body of the 3YSZ ceramic 3D-printed object that sintered at 1450 °C for 150 min had a relative density of 99.95% and flexural strength of 1008.5 MPa. This study widens the possibility of manufacturing ceramic 3D-printed objects with complex shapes, remarkable strength, and unique functionality, enabling their application in various industrial fields.

Strength and aging resistance of monolithic zirconia: an update to current knowledge

New zirconia compositions with optimized esthetic properties have emerged due to the fast-growing technology in zirconia manufacturing. However, the large variety of commercial products and synthesis routes, make impossible to include all of them under the general term of “monolithic zirconia ceramics”. Ultra- or high translucent monolithic formulations contain 3–8 mol% yttria, which results in materials with completely different structure, optical and mechanical properties. The purpose of this study was to provide an update to the current knowledge concerning monolithic zirconia and to review factors related to strength and aging resistance. Factors such as composition, coloring procedures, sintering method and temperature, may affect both strength and aging resistance to a more or less extend. A significant reduction of mechanical properties has been correlated to high translucent zirconia formualtions while regarding aging resistance, the findings are contradictory, necessitating more and thorough investigation. Despite the obvious advantages of contemporary monolithic zirconia ceramics, further scientific evidence is required that will eventually lead to the appropriate laboratory and clinical guidelines for their use. Until then, a safe suggestion should be to utilize high-strength partially-stabilized zirconia for posterior or long span restorations and fully-stabilized ultra-translucent zirconia for anterior single crowns and short span fixed partial dentures.

Choice of resin cement shades for a high-translucency zirconia product to mask dark, discolored or metal substrates

PURPOSE

The aim was to study the masking ability of high-translucency monolithic zirconia and provide guidance in selecting resin luting cements in order to mask discolored substrates.

MATERIALS AND METHODS

160 high-translucency zirconia specimens were divided into 32 groups depending on their thickness and shades. Using five shades of try-in paste, the specimens were luted onto the sub strates (Co-Cr, precious-metal, opaque porcelain-sintered Co-Cr, opaque porcelain-sintered precious-metal, and 5M3-shade zirconia). All CIELAB color parameters were measured and statistically analyzed.

RESULTS

Zirconia shade and thickness and try-in paste shade affected CIELAB color parameters (P=.000) in different substrates groups, and there were interactions among these factors (P=.000). All five try-in paste shades can be chosen to achieve ΔE values of zirconia with 1.2 - 1.5 mm for masking dark-tooth-like 5M3-shade and zirconia with 1.5 mm for masking precious-metal groups < 2.6. Only suitable try-in paste shades were used, can ΔE values that less than 2.6 be achieved when applied translucent monolithic zirconia with 0.7-1.0 mm for masking dark-tooth-like 5M3-shade and zirconia with 0.7 - 1.2 mm for masking precious-metal groups.

CONCLUSION

Choosing suitable resin cement shades is necessary for high-translucency monolithic zirconia to achieve ideal masking ability (ΔE < 2.6) on the dark-tooth.

Monolithic Zirconia: An Update to Current Knowledge. Optical Properties, Wear, and Clinical Performance

The purpose of this paper was to update the knowledge concerning the wear, translucency, as well as clinical performance of monolithic zirconia ceramics, aiming at highlighting their advantages and weaknesses through data presented in recent literature. New ultra-translucent and multicolor monolithic zirconia ceramics present considerably improved aesthetics and translucency, which, according to the literature reviewed, is similar to those of the more translucent lithium disilicate ceramics. A profound advantage is their high strength at thin geometries preserving their mechanical integrity. Based on the reviewed articles, monolithic zirconia ceramics cause minimal wear of antagonists, especially if appropriately polished, although no evidence still exists regarding the ultra-translucent compositions. Concerning the survival of monolithic zirconia restorations, the present review demonstrates the findings of the existing short-term studies, which reveal promising results after evaluating their performance for up to 5 or 7 years. Although a significant increase in translucency has been achieved, new translucent monolithic zirconia ceramics have to be further evaluated both in vitro and in vivo for their long-term potential to preserve their outstanding properties. Due to limited studies evaluating the wear properties of ultra-translucent material, no sound conclusions can be made, whereas well-designed clinical studies are urgently needed to enlighten issues of prognosis and long-term survival.