Norziha Yahaya

Comparison between Slip Casting and Cold Isostatic Pressing for the Fabrication of Nanostructured Zirconia

Consolidation of ceramic parts may be achieved by several techniques, including the slip casting and cold isostatic pressing (CIP) methods. In the present work, the performances of the two methods are compared in the fabrication of nanostructured zirconia compacts for dental crown applications. First, a zirconia suspension suitable for slip casting was prepared. The rheological properties of the zirconia suspension were optimized by adding a dispersant agent and controlling the pH. Zirconia slurries were then slip-cast into a pellet. Second, another group of zirconia pellets were fabricated using uniaxial pressing and were then cold-isostatically pressed. Both slip-cast and CIP samples were sintered at 1300 °C with a soaking time of 2 hrs. The mechanical properties of both samples were compared. The samples prepared by slip casting were denser compared with those prepared via CIP. Slip casting technique produced samples with 98.8% of the theoretical density, which resulted in the high Vickers hardness (11.4 GPa) of the slip-cast samples. Morphological studies revealed that the microstructures of the slip cast-sample were more homogeneous and contain no porosity. The formation of such a structure is due to the enhancement of the particle packing efficiency by slip casting as well as to the removal of larger agglomerates by colloidal processing prior to casting. As a consolidation stage, slip casting appears to be more suitable than the CIP technique in preparing reliable nanostructural ceramic parts.

Types of Failures in Porcelain-Fused-to-Metal Dental Restoration

Porcelain-fused-to-metal (PFM) restoration is a type of dental prosthesis introduced since the early 1960s. This prosthesis is strong, aesthetically satisfactory, and affordable. This study aims to classify the types of failures observed in PFM prostheses that were constructed in a dental laboratory in Misrata, Libya. Data from six months of laboratory fabrication and clinical observation were collected. Approximately 12% of the PFM prostheses demonstrated the following defects: bubbles (31%), fractures and cracks in the porcelain (25%), chipping (13%), porosity (13%), shade defects (13%), and fractures in the metal framework (6%). These defects can impair PFM restorations. Hence, future studies must determine the cause of these defects and improve the materials used for dental restorations.

Decomposition of Hydroxyapatite in Hydroxyapatite/Zirconia Composites for Dental Applications

Hydroxyapatite (HA) has been widely used as a biomaterial because HA has excellent biocompatibility, but the mechanical properties of HA are not sufficiently strong for dental applications. To enhance these mechanical properties, zirconia (ZrO2) has been introduced as a second phase material. However, doping of ZrO2 favors HA decomposition at low temperatures. In this paper, the effect of adding ZrO2 on HA decomposition is discussed. Experimental results in previous studies are compared with theoretical results of chemical equations. The ideal percentage of doped ZrO2 should be <10 wt.% to prevent HA decomposition unless a special sintering method is applied.

Type of Failure of Zirconia-Based Ceramics in Dental Laboratory in Misurata, Libya

Zirconia (ZrO2) is used to fix restorations as a core material because of its mechanical properties, aesthetics, and compatibility. This study aims to analyze the failure types in ZrO2-based restoration fabricated in a dental laboratory in Misurata, Libya. Data were collected from laboratory records for a 30-day period with follow-up for five months. About 6% of the total restorations had defects with different percentages, 46% of which were fractures, 29% of which had weak bonding between ZrO2 frameworks and veneers, 18% of which had cracks, and 7% of which had shade defects. Although ZrO2 is a suitable material for dental restorations, defects may occur and lead to the failure of dental restorations. A thorough study is necessary to analyze the cause of failurein zirconia-based restorationsand to improve the properties to produce a versatile dental restorative material.

A review of the low-temperature degradation of dental zirconia

The use of tetragonal zirconia as a dental restorative material has recently increased because of its unique mechanical and optical properties, as well as high biological compatibility with the oral cavity environment. However, the mechanical properties of zirconia can be severely degraded, which leads to the failure of dental restorations. This review focuses on the low-temperature degradation of dental zirconia and its effects on the properties of zirconia and on the oral environment. The purpose is to show the importance of this negative phenomenon and suggest guidelines for minimizing the aging of zirconia that is used as a dental restoration material.

Influence of Sintering Temperature on the Translucency of Sintered Zirconia by Cold Isostatic Pressing

Zirconia-based ceramics exhibit excellent mechanical properties and biocompatibility in dental applications. However, the production of translucent zirconia that offers resemblance to real teeth remains a challenge. This study aims to fabricate zirconia compacts by cold isostatic pressing (CIP) and investigate the influence of sintering temperature on translucency, microstructure, hardness, and density of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). Zirconia stabilized with 3 mol% yttria (3Y-TZP) was pressed by uniaxial pressing and later by CIP to produce green bodies in pellet form. Subsequently, the green bodies were sintered at different temperatures (1100 °C to 1300 °C). The specimens were then investigated in terms of translucency, density, and hardness. X-ray diffraction was also performed and the microstructure of the specimens was observed under a scanning electron microscope (SEM). Density and light transmittance tests results showed that zirconia sintered at 1200 °C exhibits the highest density (5.957 g/cm3) and light transmittance intensity. Vickers hardness test showed that higher sintering temperatures result in higher hardness of the sintered zirconia. SEM micrographs illustrate the effect of microstructural changes on the translucency of zirconia. A temperature of 1200 °C is found to be the recommended sintering temperature at which zirconia exhibiting optimum translucency and mechanical properties is produced. CIP is found to be a suitable consolidation method to produce high-density translucent zirconia.

Properties and survival rate of all ceramics dental crown: A review

All-ceramic dental crown restoration is popular because it results in better aesthetic quality than metal alloy restoration. Ceramics also show superior biocompatibility and inertness to human biological systems. However, clinical experience indicates that all-ceramic crowns are not as durable as their porcelain-fused-to-metal counterparts, particularly on molar teeth. New ceramic biomaterials that combine durability with excellent aesthetic qualities have been developed. In this study, several promising bioceramics for dental crown applications are evaluated and compared. The evaluated parameters include strength of the material, survival rate in clinical performance, and aesthetic quality.

Effect of Sintering Temperature on the Mechanical Properties of Nanostructured Zirconia Fabricated via Colloidal Processing

This study aims to evaluate the effects of sintering temperature on the density and hardness of tetragonal zirconia polycrystals stabilized with 3 mol% 3Y-TZP dental ceramic type. Five cylindrical specimens were fabricated from zirconia powder of particle size 50 nm via colloidal processing. The specimens were sintered densely at the final sintering temperatures of 1000, 1100, 1200, and 1300 °C, respectively. The sintered density and hardness of the sintered specimen were then examined. The results showed that the sintered densities and hardness of the specimen increased as the temperature increased from 1000 °C to 1300 °C. Zirconia 3Y-TZP could gain near full density and reach hardness of as high as 11.30 GPa at the final sintering temperature of 1300 °C. The density and hardness of zirconia structured from 3Y-TZP can be improved by controlling the final sintering temperature.

Effect of Dispersant Agent Amount in Colloidal Processing of Zirconia Dental Ceramic

The effects of a polyelectrolyte dispersant agent, polyethyleneimine (PEI), on the rheology of zirconia 3Y-TZP suspensions and the densification characteristics of sintered zirconia were investigated. The colloidal processing technique was used to minimize the agglomeration of nanoparticles during the fabrication of the samples. Five batches of 10% zirconia suspensions containing different amounts of PEI at 0.3, 0.4, 0.5, 0.6, and 0.7 wt% were prepared. The rheological properties of the zirconia suspensions were determined using a rotational viscometer. The optimum amount of PEI that can maximize powders dispersion was determined. The green samples were then prepared using the slip casting process. The samples were densely sintered at a final sintering temperature of 1300 °C. The result revealed that the zirconia suspension with 0.5 wt% PEI was the most optimum amount to obtain a well-dispersed suspension. The sintered density of zirconia 3Y-TZP reached its maximum by adding 0.5 wt% PEI.