Table 2.

Mean and standard deviation (SD) of surface roughness (SR) in 5 and 10% hydrofluoric acid (HF) with different etching times

Time (s)	5% HF	10% HF
20	58.40±27.07 aA	112.92±56.78 aB
60	64.24±25.15 aA	137.81±80.78 aB
120	63.48±14.07 aA	150.45±70.90 aB
Control	16.47±6.70 b

Different lowercase letters indicate a significant difference (P<0.05) among etching times with the same acid concentration. Different capital letters show a significant difference (P<0.05) among acid concentrations at the same time point