الفهرس 
Evaluation of flexural strength of monolithic zirconia and zirconia core after
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Abstract
Polycrystal (Y-TZP) for monolithic zirconia and core zirconia. However, studies on effect of low temperature degradation on mechanical characteristics of zirconia were insufficient. Aim of study: The aim of the study was to assess the effect of low temperature degradation (LTD) on flexural strength of monolithic zirconia and zirconia core using hydrothermal aging in autoclave condition for 8 hours (relevant to around 30 years of clinical service). Materials and methods: 32 zirconia discs were cut from 2 zirconia blocks(monolithic zirconia and zirconia core) with isomet -1000, then were sintered according to manufacturer instructions to dimensions (12mm diameter and 1.2 mm thickness). Each group of zirconia was subdivided according to hydrothermal aging into aged subgroups and non-aged subgroups. Artificial aging was done in autoclave condition at (134{u00BA}c, 0.2 MPa) for 8 hours. Non aged subgroups representing control had no aging. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to analyze the microstructure of both Y-TZP types before and after aging. All samples were subjected to Biaxial flexural strength test with ball on ring in universal testing machine. Data from biaxial test were analyzed using Graph Pad Instat (Graph Pad, Inc.) software