altering form with hook_form_FORM_ID_Alter
You shouldn't reset the form completely by doing $form = array();, since you will delete some of the stuff Drupal expects to be there.

You should instead do something like this:

function dental_form_simplenews_block_form_2_alter(&amp;$form, &amp;$form_state)
{
    global $user;
    // Remove what you don't want..
    unset($form['fields']);
    // Add what you do want..
    $form['#attributes'] = array('class' =&gt; array('newsletter'));
   ...
}