Group 9 - Zirconia in Dentistry.pdf - Advanced Material...

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.Advanced Material (MECH 6501 X 2202)Group 9Written ProjectZirconia in DentistryInstructor: Professor Dmytro KevorkovSubmitted By:Arman Kamranianfar40169241Dolapo Adeoya40161456Reza Farajdadian40174180Zahra Aboonasr Shiraz40165323November 2020
11.IntroductionThe zirconia is a biomaterial used in biomedical applications since the 1960s. Among the dental ceramics, zirconia orzirconium dioxide (ZrO2) has approximately 96%-99% crystalline content with no glassy phase, presenting highphysicochemical properties, such as flexural strength, fracture toughness, and hardness, increased mechanical properties,excellent biocompatibility, and satisfactory esthetic. These zirconia properties lead to a wide range of indications, includingPFZ (Porcelain fused to zirconia) core, monolithic crown, FPD (fixed dental prosthesis) frameworks, implants, implantabutments, orthodontic brackets, posts, veneers, and dentures. Although there are many types of zirconia-based ceramicsystems available, currently, only two types are commonly used in dentistry: Yttrium-stabilized tetragonal zirconia (Y-TZP)and zirconia-toughened alumina (ZTA)Yttrium-stabilized tetragonal zirconiaZirconia is obtained by minerals such as baddeleyite and zircon(ZrSIO4), and it has both basic and acidic chemical properties.Unalloyedzirconiaisapolymorphthatassumesthreecrystallographic forms depending on the temperature (Fig. 1). Thezirconia has a monoclinic crystalline structure at room temperatureand is stable up to 1170֯C. In this form, the zirconia shows reducedmechanical properties as well as cohesive strength (low density).Between 1170֯C and 2370֯C, the zirconia has a tetragonal structureand allows a ceramic with improved mechanical properties. Above2370֯C, the zirconia crystals have a cubic shape with intermediate mechanical properties. The zirconium oxide can bestabilized with the addition of approximately 2-3 mol.% of yttrium oxide (Y2O3) (Fig. 2). After its processing, during thecooling, the tetragonal phase again becomes monoclinic, and this transformation results in a substantial volume expansionof approximately 3%-4.5%.Zirconia exposure to water and humidity also triggers spontaneous phasetransformation,creatingresidualcompressionstressevenwithoutmechanical surface change or load application. Thus, yttrium oxide is addedto zirconia in order to maintain a metastable phase at temperatures belowthe tetragonal-to-monoclinic transformation temperature, creating a fullytetragonal zirconia ceramic made of small metastable tetragonal grains (Y-TZP). This procedure depends on the processing temperature, the yttriumoxide content, and the grain size, and it improves the mechanical strength ofthe zirconia because when the Y-TZP is induced by tensions that initiate thepropagation of a crack, the tetragonal crystals close to the crack become thestable monoclinic phase (Fig.3). The metastable phase exhibits good crackpropagation resistance since it is associated with a volume expansion of 3%-5% of the particles that cause stresses of compression that oppose the

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Term
Fall
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Tags
Materials Science, Ceramic materials, Zirconium dioxide, Alumina, ZTa, Feldspathic Porcelain

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