The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

Abstract

STATEMENT OF PROBLEMRecently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.PURPOSEThe objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning electron microscope (SEM).MATERIAL AND METHODSY-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Säckingen, Germany) were prepared in 40 mm (length) × 4 mm (width) × 3 mm (height) samples. Specimens were artificially aged in distilled water by heat-treatment at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface. To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model 3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute, USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant differences (α= .05).RESULTSThe mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃, the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related to temperature, the minimum flexural strength was above 700 MPa.CONCLUSIONThe monoclinic phase started to appear after aging treatment above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to decrease was between 12% and 54%.

Long-term stability of an injection-molded zirconia bone-level implant: A testing protocol considering aging kinetics and dynamic fatigue

“…However, increased strength after an accelerated aging treatment has to be considered specific for the evaluated prototype implant of the present investigation and cannot be taken as general rule for Y-TZP [16]. At some point when the degradation process penetrates deeper into the material, the contribution from the aging may instead cause the strength of the same sample to be decreased [8]. Moreover, mechanical treatment also resulted in increased strength.…”

“…Once started, phase transformation continuously progresses from the surface into the volume in a layer-by-layer manner, following a linear time law [7]. Aging can result in intergranular micro-cracking, surface-roughening and, up from a certain level, in reduced strength [8]. Finally, PTT and LTD are based upon the same phenomenon and using Y-TZP for the fabrication of biomedical implants, one might not exploit the advantage of the former without being exposed to the risk of the latter.…”

The effect of zirconia sintering temperature on flexural strength, grain size, and contrast ratio

“…Zirconia FDPs are feasible for molar region, due to their high flexural strength and fracture toughness [12][13][14][15]. Limited number of clinical studies reported seldom zirconia framework fractures but more often chipping of the veneering ceramic [16][17][18][19][20].…”

Effects of a convenient silica-coating treatment on shear bond strengths of porcelain veneers on zirconia-based ceramics

“…To maintain the tetragonal phase at room temperature, zirconia-based ceramics must be stabilized by adding oxides. Yttria is a popular stabilizing additive, giving Y-TZP 12,13,16) . This new ceramic is useful as a prosthetic frame material because of its high fracture toughness and its precision fabrication with dental CAD/CAM systems.…”

“…Since the beginning of the 21st century, zirconium dioxide (ZrO 2: zirconia), a new and tough ceramic material, has been receiving increasing attention in dentistry [12][13][14][15][16] . Initially, its use was restricted to metalfree fixed partial anterior dentures, but its use is being extended to a variety of applications, such as fixed partial posterior dentures, orthodontic brackets 19) and dental implant abutment or fixture 20,21) , as well as simple dental restoration or prostheses 17,18) .…”