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Lab talk, the good, the bad, and the ugly
Zirconium
Y3, y4, y5 zirconia?
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<blockquote data-quote="Patrick Coon" data-source="post: 310460" data-attributes="member: 11366"><p>As everyone has stated it has to do with the mole % of yttria. We add yttria to increase translucency by allowing the zirconia crystal to be stable in the cubic phase at room temperature, this increases the translucency. Generally speaking 3y is 100% Tetragonal phase, 4y is 75% tetragonal and 25% cubic, and 5y is about 50/50.</p><p></p><p>We also have to think about strength between these different y's. 3y is ~ 1100+MPa, 4y ~ 750-850MPa, and 5y ~ 550-650MPa. This is due to the loss of transformation toughening. Tetragonal phase zirconia when damaged goes through a phase transformation back to it's monoclinic phase crystal. When it does this it increases in volume by about 2.5%, this compresses the crack and stops it from propagating. Cubic phase crystals do not go through this phase transformation, thus allowing the crack to propagate through the restoration. This is why you see much lower flexural strength and fracture toughness values as the mole % increases.</p></blockquote><p></p>
[QUOTE="Patrick Coon, post: 310460, member: 11366"] As everyone has stated it has to do with the mole % of yttria. We add yttria to increase translucency by allowing the zirconia crystal to be stable in the cubic phase at room temperature, this increases the translucency. Generally speaking 3y is 100% Tetragonal phase, 4y is 75% tetragonal and 25% cubic, and 5y is about 50/50. We also have to think about strength between these different y's. 3y is ~ 1100+MPa, 4y ~ 750-850MPa, and 5y ~ 550-650MPa. This is due to the loss of transformation toughening. Tetragonal phase zirconia when damaged goes through a phase transformation back to it's monoclinic phase crystal. When it does this it increases in volume by about 2.5%, this compresses the crack and stops it from propagating. Cubic phase crystals do not go through this phase transformation, thus allowing the crack to propagate through the restoration. This is why you see much lower flexural strength and fracture toughness values as the mole % increases. [/QUOTE]
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Lab talk, the good, the bad, and the ugly
Zirconium
Y3, y4, y5 zirconia?
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