Altering nodes title value
You need to implement both 


template_preprocess_page() : this will take care of node full view mode.
temaplte_proprocess_node() : this will take care of node teaser view mode


In your theme template.php

function mythemename_preprocess_page(&amp;$variables) {
  if(isset($variables['node']) &amp;&amp; $variables['node']-&gt;type == "your content type") {
    drupal_set_title("your_title");    
  }
}

/**
 * Override or insert variables into the node template.
 */
function mythemename_preprocess_node(&amp;$variables) {
  if($variables['type'] == "your content type") {
    $variables['title'] = "your title";
  }
}


Note: 


  
  only changing in template_preprocess_node(), will now reflect on node teaser view as it will be overridden by page template.
  in order to change  you should use drupal_set_title() instead of $variables['title'].