Effect of surface topography and wettability on shear bond strength of Y-TZP ceramic

Abstract

Zirconia ceramics have been widely used as dental restorations due to their esthetic appearance and high flexural strength. The bonding of zirconia with resin cement should rely on both mechanical and chemical bonds. This study was performed to investigate the effect of zirconia surface topography and its wettability after surface pretreatments on the microshear bond strength (μSBS) of a resin cement. Zirconia slabs were prepared and randomly divided into 5 groups based on the surface treatment as follows: no treatment (control), air abrasion (AB), etching with hydrofluoric acid (F), the mixture of hydrofluoric acid and nitric acid (FN), or the mixture of hydrochloric acid and nitric acid (CN) for 10 min. The specimens were subjected to investigation of surface roughness characteristics [average roughness (Ra), peak-to-valley average distance (Rpv), skewness (Rsk), and kurtosis (Rku)] using atomic force microscopy (AFM) and measurements of surface contact angle (θ_c) and μSBS of a resin cement. In addition, the area % of the nanoscale surface irregularity (nSI%) was calculated from the AFM images. The effects of nSI%, Ra and θ_c on the μSBS were analyzed by multiple linear regression analysis (p < 0.05). Multiple regression analysis revealed that the nSI% was the most predominant factor for the μSBS (p < 0.001). A surface with larger nSI%, higher Ra and relatively lower θ_c was essential for establishing a reliable resin-zirconia bond.

Figure 1

Schematic illustrations demonstrate the meaning of parameters Rsk (a) and Rku (b).

Figure 2

The representative 5 × 5 µm zirconia surface in a 2D image, showing the counting from a hundred-square grid. Blue squares (a) show smooth grain surface grids, and red squares (b) show nanoscale surface irregularity (nSI) grids.

Figure 3

Representative AFM images (upper) and line-scan profiles (lower) of the control (a), AB (b), F (c), FN (d), and CN (e) groups. Grain boundaries (white arrow) were clearly observed in the control group, whereas surface irregularities on grains (black arrows) were observed in all treated groups.

Figure 4

Frequency of failure modes after µSBS testing in each group (n = 12). The numbers in each bar are the numbers of specimens in each failure mode. There were significant differences in the failure mode distribution among the groups (p < 0.05). The majority of the failure mode of the control was adhesive failure, whereas it was mixed failure in the AB, F, FN, and CN groups.