DatePicker, how can I change the FontFamily for the contents?

hi,

<DatePicker x:Name="FechaNac" Grid.Column="1" FontFamily="Trebuchet Ms" FontSize="14" Grid.Row="6" Height="24" Margin="15,8,166,10" Grid.ColumnSpan="2">
                       
</DatePicker>

The above line only changes the font for the header of the control. Once you open the control you see the whole months in other font.

Thanks in advance,

Primary platform is Windows 7 Ultimate 64 bit along with VS 2012/Sql2k8 for WPF/SilverLight projects.