Which instrument is specifically used to disengage wire ties when removing an arch wire?

The ligature cutter is specifically designed to disengage wire ties when removing an arch wire in orthodontic procedures. It has a precise cutting edge that allows for the safe and effective removal of the small, tightly wound ties that hold the arch wire in place. This instrument ensures that the ties can be cut without damaging other components of the orthodontic appliance or causing harm to the surrounding tissues.

Each of the other instruments listed has a different primary function and is not suited for the specific task of cutting wire ties. A scalpel is used for making incisions in soft tissue, and while it is sharp, it is not designed for the delicate task of cutting ligatures. Forceps are generally used for grasping or holding objects but do not have the cutting capabilities needed for wire ties. A hematoma cutter, although not a common instrument in orthodontics, would similarly not relate to wire tie disengagement as it typically serves different surgical purposes. Thus, the use of a ligature cutter is the appropriate choice for this specific orthodontic task.