Air Abrasion Before and/or After Zirconia Sintering: Surface Characterization, Flexural Strength, and Resin Cement Bond Strength

Abstract

The purpose of this in vitro study was to evaluate the effect of air-abrasion/zirconia sintering order on the yttria partially stabilized tetragonal zirconia polycrystal (Y-TZP) surface characterization (roughness, morphology, and phase transformation), flexural strength (FS), and shear bond strength (SBS) to a resin cement. Y-TZP specimens were air abraded with 50-μm Al2O3 particles after (AS), before (BS), or before and after zirconia sintering (BAS). For roughness (Ra), 30 block specimens (12×12×3.0 mm; n=10) had their surfaces analyzed by a profilometer. Next, on the air-abraded surfaces of these specimens, composite resin discs (n=30) were bonded with RelyX ARC. The bonded specimens were stored for 24 hours in distilled water at 37°C before shear testing. Failure mode was determined with a stereomicroscope (20×). The surface morphology (n=2) was evaluated by SEM (500×). For the four-point flexural strength test (EMIC DL2000), 39 bar-shaped specimens (20×4.0×1.2 mm; n=13) were air abraded according to the three conditions proposed, and an additional group (nonabraded) was evaluated (n=13). The quantitative analysis of phase transformation (n=1) was completed with Rietveld refinement with X-ray diffraction data. Ra (μm) and SBS (MPa) data were analyzed by one-way analysis of variance (ANOVA) and the Tukey test (α=0.05). Pearson correlation analysis was used to determine if there was a correlation between roughness and SBS. For FS (MPa) data, one-way ANOVA and the Dunnett C-test (α=0.05) were used. The air-abrasion/zirconia sintering order influenced significantly (p<0.001) Ra, SBS, and FS. The BS and AS groups presented the highest (1.3 μm) and the lowest (0.7 μm) Ra. The highest SBS (7.0 MPa) was exhibited by the BAS group, followed by the AS group (5.4 MPa) and finally by the BS group (2.6 MPa). All groups presented 100% adhesive failure. A weak correlation (r=-0.45, p<0.05) was found between roughness and SBS. The air-abrasion/zirconia sintering order provided differences in the surface morphology. The nonabraded (926.8 MPa) and BS (816.3 MPa) groups exhibited statistically similar FS values but lower values than the AS (1249.1 MPa) and BAS (1181.4 MPa) groups, with no significant difference between them. The nonabraded, AS, BS, and BAS groups exhibited, respectively, percentages of monoclinic phase of 0.0 wt%, 12.2 wt%, 0.0 wt%, and 8.6 wt%. The rougher surface provided by the air-abrasion before zirconia sintering may have impaired the bonding with the resin cement. The morphological patterns were consistent with the surface roughness. Considering the short-term SBS and FS, the BAS group exhibited the best performance. Air abrasion, regardless of its performance order, provides tetragonal to monoclinic transformation, while sintering tends to zero the monoclinic phase content.

Structural and Morphological Evaluation of Presintered Zirconia following Different Surface Treatments

“…Results of this investigation were in agreement with a study that stated a statistically significant difference for presintered zirconia regarding the bond strength, 50 whereas was not in agreement with Abi-Rached et al, 38 which stated that the lowest bond strength value for the group abraded before sintering was due to its higher surface roughness value, which probably impaired the wettability of the zirconia by the resin cement.…”

“…A previous study confirmed that air abrasion performed before sintering using 50 μm Al 2 O 3 provided the highest Ra value, while air abrasion performed after sintering had the lowest Ra value. 38 This was also confirmed in this study, in which group III provided the highest Ra value (0.11 μm).…”

“…This was in agreement with studies that stated that the samples abraded before sintering have blunt and melted-round surfaces, whereas sandblasting after sintering showed surface with coarse and needle-like rough surfaces. 33,38 The crystalline structures of the presintered samples by XRD showed that the relative monoclinic phase of C1 was 0.15%, after surface polishing with silicon carbide paper; relative monoclinic phase of C2 became 0.17%. After sintering, the relative monoclinic phase of group I was 0.01%.…”

Influence of Particle and Air‐Abrasion Moment on Y‐TZP Surface Characterization and Bond Strength

“…Apart from the particle characteristics, the moment in which air‐abrasion is performed can also affect the bond strength between the zirconia and resin cements . Zirconia frameworks are usually air‐abraded before cementation, when the zirconia is already sintered.…”

“…With this modification, the sintering procedure, besides zeroing the monoclinic phase, could seal or, at least, tightly contain the microcracks created by the particle impact, as a result of the sintering‐induced shrinkage . Studies exploring the effect of this modification are scarce, and more data are needed to confirm the advantages that may arise from improvements of zirconia/cement bonding.…”