Comparison of Testing Designs for Flexural Strength of 3Y-TZP and 5Y-PSZ Considering Different Surface Treatment

Abstract

The aim of this study was to analyze the influence of different surface treatments and the corresponding surface roughness on the ball-on-three-balls test and piston-on-three-balls test for measuring flexural strength 3Y-TZP and 5Y-PSZ. Additionally, the influence of cutting the material into the specimens when pre-sintered or fully sintered was analyzed. A total of 120 specimens for each material group, 3Y-TZP zirconia (Katana HT, Kuraray) and the 4 different layers of multilayered 5Y-PSZ zirconia (Katana UTML, Kuraray), were produced. The used material was cut into half of the specimens in a fully sintered stage, the other half was cut when pre-sintered. Each subgroup was divided into 3 different surface treatment groups being air abraded with 50 µm alumina particles at 1 bar pressure, ground with 600 SiC paper or polished up to 1 µm with a polycristalline diamond suspension. These were then analyzed by X-ray diffraction (XRD) (N = 3) and tested for flexural strength using the ball-on-three-balls test (N = 10) or piston-on-three-balls test (N = 10). For 3Y-TZP groups different surface roughness did not result in statistically significant differences in flexural strength but cutting the specimens in fully sintered state significantly reduced flexural strength of 1133 ± 109 to 741 ± 81 MPa. For 5Y-PSZ groups air abrasion of the specimens with alumina particles significantly reduced the flexural strength of 562 ± 68 MPa to 358 ± 58 MPa. Cutting and surface treatment in pre-sintered or fully sintered state had no significant influence. Flexural strength testing with the ball-on-three-balls test resulted in about 20% higher strengths compared to the piston-on-three-balls test. Results of both tests showed the same tendencies when compared.

The Effect of Restoration Thickness on the Fracture Resistance of 5 mol% Yttria-Containing Zirconia Crowns

“…In a previous study, air particle abrasion did not significantly decrease the fracture resistance of 5Y-Z crowns cemented with RMGIC [18]. These results are in contrast with studies which report that air particle abrasion reduces the strength of 5Y-Z discs [22,25,26]. As air particle abrasion has not been shown to impact the bond strength with RMGIC, it is at the clinicians' and laboratories' discretion if 5Y-Z crowns are routinely air particle-abraded [27].…”

“…Without air particle abrasion, the bond strength to both 3Y-Z and 5Y-Z decreases significantly [22][23][24]. The flexural strength of 3Y-Z is not negatively affected by air particle abrasion; however, 5Y-Z can be weakened following air particle abrasion [22,25,26]. With the use of RMGIC on zirconia crowns, air particle abrasion has not been shown to improve the bond as it has with resin cement [27].…”

The Influence of Alumina Airborne-Particle Abrasion on the Properties of Zirconia-Based Dental Ceramics (3Y-TZP)

“…Our present findings are supported by those of other authors; however, previous studies have mainly evaluated Ra surface roughness. Nevertheless, they proved that the 3Y-TZP surface roughness increased with the size of alumina particles used for air abrasion and confirmed a significant increase when compared to untreated specimens [23,26,33,35,39,40,47,48].…”

Translucent Zirconia in Fixed Prosthodontics—An Integrative Overview

“…As a result, it is suggested that sandblasting particles of 110 µm be employed for 3Y-TZP, while 50 µm particles are recommended for 4Y-PSZ and 5Y-PSZ. Hergeroder et al found that different surface roughness has no significant differences in flexural strength but cutting the specimens in a fully sintered state reduced flexural strength, especially in 5Y-PSZ air abrasion [61]. Investigating the outcome of different technical tools on the surface temperature and phase composition of crowns, Wertz found that burs had no influence on the phase transformation but caused a shift in preferred orientation, whereas coarse polishers induced a phase transformation to the rhombohedral phase.…”