The Effect of Airborne-particle Abrasion on the Surface Characteristics of Monolithic Zirconia and the Shear Bond Strength

Abstract

Purpose. This study was designed to evaluate the effects of several airborne-particle abrasion protocols on the surface characteristics of monolithic zirconia and to examine the effect of protocol choice on the shear bond strength of resin cement.

Material and Methods. Two forms of monolithic zirconia specimens, 375 bar-shaped (45 × 4 × 3 mm) and 500 disc-shaped (Ø 9 × 1 mm), were divided into 25 groups. All specimens were abraded with one of three different sizes of alumina particles (25, 50 or 125 μm), two different pressures (2 or 4 bar), two distinct application times (10 or 20s) and two distinct incidence angles (45 or 90°). The bar-shaped specimens were used for a 3-point bending test and determination of flexural strengths

Weibull parameters were calculated for these specimens. The transformed monoclinic phase (XM) was examined with X-ray diffractometry and Raman spectrometry. Surface characteristics were investigated with SEM, confocal laser scanning microscopy and AFM. The disc-shaped specimens were used to determine the shear bond strength of resin cement (Panavia F2.0) before and after thermocycling (5000 cycles). The fractured surfaces were examined with SEM. All data were analyzed using 4-way ANOVA and a multiple comparisons Scheffé test (α = .05).

Results. Specimens abraded with the 25 μm particles showed significantly increased flexural strength compared to the control group

however, differences between specimens abraded with 50 and 125 μm were insignificant. The particle size and abrasion pressure and time significantly affected the flexural strength, while the incidence angle was insignificant. The XM and surface roughness were proportional to the size, pressure, time and incidence angle. The Raman spectrum analysis showed a higher proportion of the monoclinic phase as the depth of the specimen was closer to the abraded surface. Under SEM and AFM observation, the larger particle groups showed a more substantial roughening effect. In bonding with resin cement, the highest shear bond strength after thermocycling was obtained by the abrasion with 50 μm particles at 4 bar for 20s, regardless of incidence angle.

Conclusion. Airborne-particle abrasion causes modification of the specimen flaw distribution, transformation of the crystal structure, and an increase in the shear bond strength of resin cement. Based on this study, the recommended protocol for airborne-particle abrasion is a 50 μm particle surface at 4 bar for 20s using an angle of either 45° or 90°.