User control binding in wpf

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C#

Hi,
I have a problem if any one can help me to solve it, the problem is.
i have a user control it is Rounded Text Box,composed from one text box only,
i did write some line of code to can bind this user control,it is worked but in one way if i change the source property the rounded text box show the modification by if i change from the text box the change do not appear in property bounded;
the code behind of rounded text box is :

public partial class  UCRTextBox : UserControl
{
  public static readonly DependencyProperty TextProperty = DependencyProperty.Register
  ("Text",typeof(string),typof(UCRTextBox), new FrameworkPropertyMetadata  
  (null,FrameworkMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallBach(textChangedCallBack),
  new CoerceValueCallback(coerceValue)));

  public string Text
  {
      get{return (string)GetValue(TextProperty);}
      set{SetValue(TextProperty,value);}
  }

  static void textChangedCallBack(DependencyObject property,DependencyPropertyChangedEventsArgs args)
  {
      UCRTextBox ucRounded=(UCRTextBox)property;
      ucRounded.TextBx.text=(string)args.NewValue;
  }

  static object CoerceValue(DependencyObject sender,object value)
  { 
      return (string)value;
  }

}

and the code in the window with i did use this control i did bind it by code behind:

private void SetTextBoxBinding(FrameworkElement target,DependencyProperty dp,string value)
{
   Binding b=new Binding(value);
   b.source=_editPatient.Patient;
   b.Mode=BindingMode.TwoWay;
   target.SetBinding(dp,binding);
}

Using for this function is :

on the windowLoad Events

this.SetTextbinding(this.txtFirstName,TextBox.TextProperty,"FirstName");

that is all .

can any one show me the correct way to solve this problem??
and thx for all