Preprocess function to add filtered node body and teaser to template variables.

teaser_preprocess.php

<?php

/**
 * Implement hook_preprocess_node().
 */
function example_preprocess_node(&$vars) {

  // The node is reloaded from the static cache to generate new template
  // variables that contain just the filtered body and teaser. node_view()
  // unsets the node object's teaser or body property depending on the build
  // mode, so the node must be reloaded to get these values.
  $node = node_load($vars['nid']);
  $vars['node_body'] = check_markup($node->body, $node->format, FALSE);
  $vars['node_teaser'] = check_markup($node->teaser, $node->format, FALSE);

  // This node object has been loaded, prepared and altered. This is the one
  // originally passed to the theme. Any further operations on the node in this
  // preprocess function should probably use this object instead of the one
  // reloaded above.
  $node = $vars['node'];
}