Table 1. The means and standard deviations of microhardness values in the two groups at different time intervals .

Group	N	Mean ± SD
Before acid exposure
NHA toothpaste	40	70.3 ± 3.4
F toothpaste	40	63.6 ± 3.1
After acid exposure
NHA toothpaste	40	32.9± 1.0
F toothpaste	40	36.2± 1.0
After the intervention
NHA toothpaste	40	46.9 ± 1.3
F toothpaste	40	42.4 ± 1.7