How to access to a control encapsuled in a style

Hello I have a style with some control in my style.  The style do this : A user will select a territory and the disposition of the control will change.

The style work.  The style do what I want to do.

My problem is : I'm not able to access to a control txtNom1.  This textBox was encapsuled in my Style.

Xaml of my style :

Xaml where I call my Style :

      


      
      

Thanks