The integration of tactile sensors in dexterous robotic hands contributes greatly to creating autonomous robots capable of interacting with their environment and manipulating various types of objects. The shape of these objects may not be previously known to the robot. In this work we realize the manipulation of unknown objects that are grasped with two fingers of the SCHUNK SDH 2 robotic hand. The fingers manipulate the object changing its orientation with the use of the tactile information provided by the fingers' tactile sensors. The different contact points in the fingertip's surface are modelled by introducing a virtual joint that adds an extra degree of freedom to each finger.