How to access a text within a Button programatically?

Hi i was using this for movie clips

LuzLetra is a MovieClip which contains a DynamicText inside with the name of texto

var nuevaLetra:LuzLetra = new LuzLetra();
nuevaLetra.texto.text = “sfsf”;
this.addChild(nuevaLetra);

this works for MovieClip but it doesn’t works if I use a Button so I would like to know if there’s a way to make it to work using Button.

Thanks for the advice.