February’s Tip

Do not memorize, understand – Dr. T. Mulligan

The Mulligan overlay arch is a one-couple intrusion or extrusion arch wire used for control of anterior deep overbite or open bite. It is commonly made with a round wire (a .020 or a .018 SS), inserted to the molar tubes only and ligature tied in two places – in the anterior sextant, to the cardinal arch wire.  The Overlay Arch is activated for incisor intrusion by a molar tip-back or incisor extrusion by a molar tip forward (off-center, gable bend).  In this fashion, there is only one moment of the couple on the molar and none in the anterior sextant, thus the expression – one couple system.

The Overlay Arch was designed for two main reasons:

1. It facilitates vertical control of the anterior sextants when the patient is already in the fixed orthodontic treatment.
2. There is no moment of the couple on the incisor teeth, thus preventing undesirable mesial movement of the roots after the insertion of the arch wire.

The resiliency and the bowing of the Mulligan intrusion arch (or Utility arch) creates an undesirable moment of the couple on the incisor teeth.  The roots are tipped mesially.  As soon as the energy of the Tip back (off-center bend, gable bend) expires and the incisor teeth are intruded, the arch wire becomes straight, and the roots will return to the original position.  This is referred to as “a Round-tripping” and it may cause root blunting and root resorption – Charles Burstone {1928- 2015)