Effect of air-particle abrasion protocols on the biaxial flexural strength, surface characteristics and phase transformation of zirconia after cyclic loading

Abstract

This study evaluated the effect of air-particle abrasion protocols on the biaxial flexural strength, surface characteristics and phase transformation of zirconia after cyclic loading. Disc-shaped zirconia specimens (Ø: 15mm, thickness: 1.2mm) (N=32) were submitted to one of the air-particle abrasion protocols (n=8 per group): (a) 50 m Al2O3 particles, (b) 110 m Al2O3 particles coated with silica (Rocatec Plus), (c) 30 m Al2O3 particles coated with silica (CoJet Sand) for 20s at 2.8bar pressure. Control group received no air-abrasion. All specimens were initially cyclic loaded (×20,000, 50N, 1Hz) in water at 37°C and then subjected to biaxial flexural strength testing where the conditioned surface was under tension. Zirconia surfaces were characterized and roughness was measured with 3D surface profilometer. Phase transformation from tetragonal to monoclinic was determined by Raman spectroscopy. The relative amount of transformed monoclinic zirconia (FM) and transformed zone depth (TZD) were measured using XRD. The data (MPa) were analyzed using ANOVA, Tukey's tests and Weibull modulus (m) were calculated for each group (95% CI). The biaxial flexural strength (MPa) of CoJet treated group (1266.3±158(A)) was not significantly different than that of Rocatec Plus group (1179±216.4(A,B)) but was significantly higher than the other groups (Control: 942.3±74.6(C); 50 m Al2O3: 915.2±185.7(B,C)). Weibull modulus was higher for control (m=13.79) than those of other groups (m=4.95, m=5.64, m=9.13 for group a, b and c, respectively). Surface roughness (Ra) was the highest with 50 m Al2O3 (0.261 m) than those of other groups (0.15-0.195 m). After all air-abrasion protocols, FM increased (15.02%-19.25%) compared to control group (11.12%). TZD also showed increase after air-abrasion protocols (0.83-1.07 m) compared to control group (0.59 m). Air-abrasion protocols increased the roughness and monoclinic phase but in turn abrasion with 30 m Al2O3 particles coated with silica has increased the biaxial flexural strength of the tested zirconia. 942.3±74.6 C ; 50 µm Al 2 O 3 : 915.2±185.7 B,C ). Weibull modulus was higher for control (m=13.79) than those of other groups (m=4. 95, m=5.64, m=9.13 for group a, b and c, respectively). Surface roughness (R a ) was the highest with 50 µm Al 2 O 3 (0.261 µm) than those of other groups (0.15-0.195 µm). After all air-abrasion protocols, F M increased (15.02-19.25%) compared to control group (11.12%). TZD also showed increase after air-abrasion protocols (0.83-1.07 µm) compared to control group (0.59 µm). Air-abrasion protocols increased the roughness and monoclinic phase but in turn abrasion with 30 µm Al 2 O 3 particles coated with silica has increased the biaxial flexural strength of the tested zirconia.

Could readily silanized silica particles substitute silica coating and silanization in conditioning zirconium dioxide for resin adhesion?

“…The loss of all bonded specimens of the control group in thermocycle signifies the importance of air-abrasion surface conditioning. The particle morphology of alumina particles presents a more amorphous pattern than silica coated alumina ones or silica particles only where the latter does not yield to subsurface damage [12,13]. Silica coating leaves a fresh, chemically reactive silica (silicon dioxide) layer embedded on the 9 conditioned surface [17], facilitating chemical covalent bonding with a silane coupling agent application.…”

“…Increased particle size and pressure may impair fatigue resistance or fit of the framework [12]. Thus, particles with small size and round morphology as in the case of silica particles are favorable.…”

“…In fact, abrasive particles vary in morphology and their impact on the zirconia surface works as a function of their morphology and other deposition parameters [11,13]. Small size silicacoated alumina particles with more favourable morphology was reported to result in less transformation of tetragonal phase into monoclinic [12,13]. Yet, bond strength results show dramatic decrease depending on the test type after hydrothermal aging which typically take place in thermocycling device at alternating temperatures between 5-55°C in water [10].…”

Adhesion to Zirconium Dioxide Used for Dental Reconstructions: Surface Conditioning Concepts, Challenges, and Future Prospects

“…To date, controversial opinions are present regarding the harmful effects of particle deposition methods on zirconia [38][39][40][41][42], in that momentum of particles on zirconia yield to local lattice distortions or create new phase by ferroelastic domain switching. In fact, the impact of particle deposition methods on zirconia is dependent on parameters such as particle morphology, pressure and duration [37] effecting residual compressive stress layer that stimulates phase transformation (t→m) and creates transformed zone depth (TZD) [9,40].…”

“…In fact, the impact of particle deposition methods on zirconia is dependent on parameters such as particle morphology, pressure and duration [37] effecting residual compressive stress layer that stimulates phase transformation (t→m) and creates transformed zone depth (TZD) [9,40]. TZD typically ranges from 0.59 to 1.6 µm and interestingly with the good combination of deposition parameters this zone may even increases mechanical strength of zirconia [38,[40][41][42]. ISO standard 13356 suggests 25% as the maximum acceptable amount of monoclinic phase [8].…”