Zirconia Types
🧊 1. Monoclinic Phase (M)🔹 Characteristics: The natural crystal form of zirconia at room temperature.🛠️ Application: Found in the pre-sintered state (used during the milling of zirconia blocks).📏 Larger in volume: About 30% bigger than the final sintered phase — which leads to significant shrinkage during sintering.⚠️ Unstable at high temperatures, transforms into the tetragonal phase.🧱 Esthetics: Not relevant (not present in the final restoration).◻️ 2. Tetragonal Phase (T)🔹 Formation: Develops after sintering from the monoclinic phase.🏗️ Application: Main core phase in dental zirconia (especially in 3YTZP).🛡️ High mechanical strength – toughening effect due to stress-induced transformation.👁️ Drawback: Low translucency, appears opaque, less esthetic.🔬 Chemical designation:3Y-TZP (3 mol% yttria)3Y-TZP-HA (High Alumina)3Y-TZP-LA (Low Alumina)💎 3. Cubic Phase (C)🔹 Formation: Achieved through more intensive sintering and higher Y₂O₃ content.🌟 Esthetics: Highly translucent, ideal for anterior restorations.🧱 Drawback: Lower mechanical strength – lacks the transformation toughening of the tetragonal phase.⚗️ Higher stabilizer (Y₂O₃) content:4Y-PSZ → ~25% cubic phase5Y-PSZ → ~50% cubic phase6Y-PSZ → even higher translucency, lowest strength🧬 PSZ = Partially Stabilized Zirconia — a mix of cubic and tetragonal crystalsSummary of Ratios and Designations:LabelY₂O₃ contentCubic phase (%)Properties3Y-TZP-HA/LA3 mol%0%Maximum strength, opaque, for posterior use4Y-PSZ4 mol%~25%Higher translucency, slightly reduced strength5Y-PSZ5 mol%~50%Esthetic, moderate strength6Y-PSZ6 mol%>50%Maximum translucency, lowest strength📝 Note:Higher cubic content = better esthetics, lower strength.Tetragonal phase = ideal for posterior load-bearing areas,Cubic phase = ideal for anterior esthetic zones.
By Radek Mounajjed
Free course on Cicero dental education platform.
Topics: Zirconia, Tetragonal, Cubic, Polycrystal, Blank