Impact of different pretreatments and aging procedures on the flexural strength and phase structure of zirconia ceramics

Abstract

OBJECTIVE To test the impact of zirconia pretreatment and aging on flexural strength and phase structure. METHODS For flexural strength measurements, 180 3Y-TZP 0.25 specimens were fabricated and pretreated: (i) air-abraded (105-m alumina, 0.25MPa), (ii) air-abraded (50-m alumina, 0.25MPa), (iii) air-abraded (30-m silica-coated alumina, 0.28MPa) (iv) non-pretreated. Each pretreated group (n=15) was aged: (a) hydrothermal (134°C, 0.23MPa, 2h) (b) in a mastication simulator (1,200,000×, 5/55°C) and (c) not aged. The fractured specimens were stored dry for 5 years (23°C) for analysis of phase transformation. Additionally, specimens were fabricated from 3Y-TZP 0.25 (n=12) and 3Y-TZP 0.05 (n=8), pretreated (i, ii, iii, iv), and hydrothermally aged. Each air-abrasion method was alternated using 0.05, 0.25 and 0.4MPa pressure. The phase transformation was examined by Raman spectroscopy and surface topography by scanning electron microscope. Data were analyzed using univariate ANOVA with the Scheffé post hoc test and partial-eta-squared (p ²) (=0.05). RESULTS The highest impact on flexural strength was exerted by the pretreatment (P ²=0.261, p<0.001), followed by interactions between pretreatment and aging (P ²=0.077, p=0.033). Non-pretreated and non-aged specimens showed the lowest monoclinic percentage. Hydrothermal aging and 5 years of storage at room temperature increased the monolithic percentage of 3Y-TZP 0.25. The highest phase transformation was observed in groups air-abraded with 105-m alumina particles. Increasing pressure during the air-abrading process increased the content of the monoclinic phase in zirconia surfaces. SIGNIFICANCE Air-abrasion with 30m silica-coated alumina powder can be recommended for pretreatment of 3Y-TZP 0.25 and 3Y-TZP 0.05. For air-abrasion using alumina powder lower pressure should be used.

Effect of air‐abrasion at pre‐ and/or post‐sintered stage and hydrothermal aging on surface roughness, phase transformation, and flexural strength of multilayered monolithic zirconia

“…Cotic et al 42 determined a more than two‐fold slower aging rate at initial stages of aging in air‐abraded specimens compared with as‐sintered ones. Similar results were also revealed by other studies that emphasized the possible protective effect of the compressive layer 17,41 . Consequently, it is possible to say that the immediate zirconia surface is a deciding factor of susceptibility to LTD 42 …”

“…15,16 However, in dental literature, the effect of air-abrasion on the mechanical strength of zirconia is still controversial. After this treatment, some reports stated an increase in flexural strength, probably because of the residual compressive stress at the surface as a result of phase transformation, [17][18][19][20][21] yet others concluded an unfavorable effect because of substantial surface damage. [22][23][24] Unlike the earlier studies that concentrated on evaluating the effects of pretreatments after zirconia sintering, recent studies have focused on airborne-particle abrasion before sintering.…”

Effect of shading and hydrothermal aging on optical properties of partially and fully stabilized zirconia

“…The present results also come in agreement with De souza et al, [41] and Kelch et al, [42] , who analyzed the influence of hydrothermal aging on zirconia and stated that hydrothermal aging affects monoclinic phase content and surface topography.…”

Effect of Pressure and Particle Size During Aluminum Oxide Air Abrasion on the Flexural Strength of Disperse-Filled Composite and Polymer-Infiltrated Ceramic Network Materials

“…Similar to the CAD/CAM polymers DFC and PICN evaluated in this study, zirconia requires surface treatment to obtain reliable adhesion [ 30 , 31 , 32 , 33 ]. In the zirconia material, several changes in material properties occur on varying the pressure intensity; two contradictory results have been reported on the effect of air abrasion pressure on zirconia material.…”

“…In the zirconia material, several changes in material properties occur on varying the pressure intensity; two contradictory results have been reported on the effect of air abrasion pressure on zirconia material. Some studies reported that surface treatment using air abrasion caused tetragonal–monoclinic transformation toughening and formation of a compressive layer on the surface of the zirconia material that improved its flexural strength [ 30 , 31 , 32 ]. Other studies have reported that the flexural strength decreased as flaws (e.g., cracks) formed on the surface [ 33 , 34 ].…”