Effect of pH of Suspension and Mechanical Treatment on Nanosized Zirconia Dispersion / Noor Faeizah Amat...[et al.]

Understanding zirconia 3YSZ powder dispersion is crucial in achieving colloidal stability in order to produce high-strength and translucent structures required for dental applications. In this work, pH adjustment (pH 1–11) and mechanical treatment (ball milling, ultrasonic treatment, and centrifugation) were employed to remove agglomeration. As-received zirconia 3YSZ powder was characterized by transmission electron microscopy, Brunauer–Emmett–Teller method, and laser light scattering technique to identify the primary particle size and to verify the presence of powder agglomeration. Particle dispersion of nanosized zirconia 3YSZ in aqueous suspension at various pH and different mechanical treatments were investigated by measuring the particle size distribution and zeta potential. The particle size of zirconia powder after adjustment to pH 2 was found to decrease (195 nm) compared with that of the as-received powder (388 nm), thus indicating the occurrence of powder de-agglomeration. A higher zeta potential value was also observed at pH 2. The isoelectric point of the suspension was at pH 10.7, where agglomeration was found to occur. This result is in good agreement with the average particle size result, in which larger particle sizes were observed at pH 10 to 11. In addition, ball milling was found to be an effective method to remove weak agglomeration given that small particle sizes measuring 164 nm were produced, whereas ultrasonic and centrifugation treatments worsened the powder dispersion. Zirconia suspension at pH 2 and prepared via ball milling was well-dispersed and suitable for further consolidation process

Influence of Presintering Parameters on the Mechanical Properties of Presintered Dental Zirconia Block

This study aimed to investigate the effects of presintering parameters on the mechanical and microstructural properties of presintered zirconia block. The zirconia block was prepared using colloidal and cold isostatic pressing techniques and subsequently subjected to various presintering procedures at 850 °C, 900 °C, and 950 °C with two different heating rates (3 and 10 °C/min). All samples were evaluated in terms of hardness, density, and morphology. Results showed that the sample porosity decreased with increment in the presintering temperature. On the contrary, the Vickers hardness increased from 1.8 GPa at 850 °C to 2.7 GPa at 950 °C at 10 °C/min heating rate. The sintering temperature of 950 °C with 3 °C/min heating rate was considered the most suitable parameter among presintering procedures, with high theoretical density (96.2%) and appropriate hardness (1.27 GPa) that are within the range of commercial zirconia block hardness values for restoration milling procedure. Furthermore, to sinter the block samples successfully without considerable failure, the heating and cooling rates should be lowered to ≤3 °C/min. Therefore, on the basis of these results, the forming methods and the sintering temperature influence the resultant mechanical and microstructural properties of the final sample

Kesan agen penyerak dan pH ampaian dalam pemprosesan berkoloid serbuk nano zirkonia

Serbuk seramik bersaiz nano cenderung mengalami masalah aglomerat semasa pemprosesan serbuk disebabkan oleh kewujudan daya van der Waals pada permukaan zarah halus yang menggalakkan zarah untuk saling bergumpal. Pemprosesan berkoloid merupakan kaedah yang dapat membantu mencegah pengaglomeratan zarah halus dan membolehkan penyebaran zarah menjadi lebih terkawal. Pengaruh agen penyerak dan pH ampaian dalam pemprosesan berkoloid serbuk nano zirkonia (3Y-TZP) telah diuji dalam kajian ini. Agen penyerak Polyethylene Imine (PEI) dan Polydiallyldimethyl Ammonium Chloride (PDADMAC) telah digunakan dalam ujikaji ini dengan kuantiti agen penyerak masing-masing adalah sebanyak 0.0%, 0.3%, 0.4%, 0.5%, 0.6% dan 0.7 % daripada jumlah berat zirkonia. Jenis dan jumlah optimum agen penyerak yang boleh memaksimumkan penyebaran serbuk dalam ampaian zirkonia ditentukan menggunakan alat meter kelikatan. Kesan pH ampaian diuji terhadap ampaian zirkonia yang mengandungi agen penyerak dan tanpa agen penyerak. Jasad anum dihasilkan melalui proses penuangan buburan dan dipra-sinterkan pada suhu 600 oC selama 45 minit sebelum disinter pada suhu 1100 oC selama 2 jam. Kajian ini secara keseluruhannya menunjukkan agen penyerak PEI sesuai digunakan pada keadaan pH berasid. Ketumpatan dan kekerasan sampel adalah tinggi pada pH 4 dengan penambahan PEI iaitu dengan peratus ketumpatan 98% daripada nilai teori dan nilai kekerasan adalah 4.35GPa. Sifat mekanik zirkonia didapati mampu ditingkatkan sekiranya penyerakan zarah ampaian zirkonia berlaku dengan baik berikutan penambahan agen penyerak yang menepati kuantiti optimumnya serta penyesuaian pH ampaian yang tepat

Effect of sintering temperature on the aging resistance and mechanical properties of monolithic zirconia

This study aimed to investigate the effect of final sintering temperature and grain size on the aging resistance and mechanical properties of zirconia fabricated through colloidal and cold isostatic pressing. Zirconia samples appearing as cylindrical discs were prepared and subjected to five different sintering temperatures ranging from 1400 °C to 1600 °C. Grain pullout and rough surfaces were detected on the micrographs of aged samples sintered at more than 1500 °C, indicating surface degradation. The highest flexural strength of non-aged and aged samples was obtained at 1500 °C, whereas excellent fracture toughness was demonstrated by the sample sintered at 1550 °C under non-aged and aged conditions. The hardness properties of all of the samples sintered at various temperatures did not significantly differ. Under the aged conditions, their hardness properties slightly decreased. Overall, the mechanical performance of the aged zirconia slightly deteriorated but remained acceptable for use in an oral environment for 15–20 years. Mechanical performance evaluation after aging revealed that 1500 °C was the appropriate sintering temperature. The mechanical properties and aging resistance of the zirconia samples were greatly dependent on sintering temperature during fabrication. Keywords: Monolithic zirconia, Aging, Biaxial flexural strength, Fracture toughness, Monoclinic transformatio

Bonding stability of a novel nano-zirconia and commercial veneering ceramics

Nano-zirconia is commonly used in dentistry as a framework material over which feldspathic porcelain is layered to form an aesthetic and strong bi-layered restoration. Sufficient bonding strength between zirconia frameworks and veneering porcelains is crucial for the longevity of zirconia-based dental restorations. This study aims to determine the shear bond strength (SBS) of a colloidal-processed slip-casted novel nano-zirconia (NZ) and veneering ceramics, namely Cercon® Ceram Kiss (CK), VITA VM®9 (VM9), and IPS e.max® Ceram (e. max). Twenty-four cylindrical samples of each NZ and CZ were prepared and veneered with the veneering ceramics. Six groups of core–veneer assemblies, which are denoted as NZ-CK, NZ-VM9, NZ-e. max, CZ-CK, CZ-VM9, and CZ-e. max, were prepared for shear bond testing using the universal testing machine. Results of the shear test showed that NZ-VM9 recorded the highest shear strength value of 149.48 MPa, whereas NZ e. max showed the lowest SBS value of 71.56 MPa. A similar trend was also observed in the CZ groups, with the highest mean bonding strength (123.38 MPa) when bonded to VM9 (CZ-VM9), while the lowest mean value (44.07 MPa) was registered by the CZ-e. max groups. Scanning electron micrographs revealed that groups with high core–veneer bond strength values mostly displayed cohesive failure. By contrast, a mixed-mode of adhesive and cohesive failures was observed in the low SBS groups. The NZ showed similar performance based on the bonding property analysis. Therefore, NZ could potentially be used as an alternative to CZ