## 3 Results
### Xrd  
Through analysis of the XRD pattern (Figure 4) on zirconia, we found that strong diffraction peaks of the tetragonal phase were identified in both the NT and APA groups. The zirconia surface with no treatment was completely tetragonal-phase (Figure 4a). Compared with the APA group, the diffraction peaks of the tetragonal phase for the NT group were dominant. The tetragonal phase ratio of the surface treated with APA was low, with a small amount of monoclinic phase (about 9.23%) and cubic phase (4.10%), as shown by the  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multirow{2}{*}{\(N\)} & \multirow{2}{*}{**Mean**} & \multirow{2}{*}{**SD**} & \multirow{2}{*}{**SE**} & \multicolumn{3}{c}{**95\% Confidence Interval of the Mean**} & \multirow{2}{*}{**Minimum**} & \multirow{2}{*}{**Maximum**} \\ \cline{5-6}  & & & & & & **Lower Bound** & & **Upper Bound** \\ \hline NT & 12 & 0.9820 & 0.1821 & 0.0526 & 0.8663 & 1.0977 & 0.71 & 1.28 \\ APA & 12 & 1.1248 & 0.2813 & 0.0812 & 0.9461 & 1.3035 & 0.89 & 1.81 \\ FSL & 12 & 1.4237 & 0.1613 & 0.0466 & 1.3213 & 1.5262 & 1.22 & 1.69 \\ \hline \multicolumn{8}{l}{The mean difference is significant at the 0.05 level. NT: no treatment group; APA: airborne particle abrasion group; FSL: femtosecond laser} \\ \multicolumn{8}{l}{group.} \\ \end{tabular}
\end{table}
Table 1: Statistical description of surface roughness of the three surface treatment groups (\(\upmu\)m).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Group**} & \multirow{2}{*}{\(N\)} & \multirow{2}{*}{**Mean**} & \multirow{2}{*}{**SD**} & \multirow{2}{*}{**SE**} & \multicolumn{3}{c}{**95\% Confidence Interval of the Mean**} & \multirow{2}{*}{**Minimum**} & \multirow{2}{*}{**Maximum**} \\ \cline{5-6}  & & & & & **Lower Bound** & & **Upper Bound** \\ \hline NT & 12 & 665.4604 & 82.2518 & 23.7441 & 613.2001 & 717.7207 & 563.78 & 825.14 \\ APA & 12 & 577.0494 & 150.0842 & 43.3256 & 481.6905 & 672.4083 & 415.92 & 927.46 \\ FSL & 12 & 727.7890 & 71.7360 & 20.7084 & 682.2101 & 773.3678 & 611.99 & 887.62 \\ \hline \hline \end{tabular}  
* The mean difference is significant at the 0.05 level. NT: no treatment group; APA: airborne particle abrasion group; FSL: femtosecond laser group.  
\end{table}
Table 2: Statistical description of the flexural strengths of the three surface treatments (Mpa).  
Figure 3: (**a**) The mean surface roughness values (R\({}_{\text{a}}\)), where the R\({}_{\text{a}}\) value for the FSL group was significantly the highest (\(p\) < 0.05); (**b**) the mean flexural strength values (\(p\) < 0.05), where the result in the FSL group was significantly higher than that in the APA group (\(p\) < 0.05). NT: no treatment group; APA: airborne particle abrasion group; FSL: femtosecond laser group.  
small peaks of monoclinic crystal and cubic phases (Figure 4b); however, the XRD of the sample treated with FSL suggested that there may be an amorphous phase, as it was also possible to form salt crystals on the surface of the ceramic treated by FSL (Figure 4c).  
Figure 4: XRD images of zirconia surface from different groups: (**a**) For NT (no treatment group), the zirconia surface for NT was completely tetragonal-phase; (**b**) for APA (airborne particle abrasion group), the tetragonal phase ratio of the surface was low, with a small amount of monoclinic and cubic phases; and (**c**) for FSL (femtosecond laser group), there may be an amorphous phase, as it was also possible to form salt crystals on zirconia surfaces treated with FSL.