Final answer:
The screw is the component of the universal matrix retainer that secures the matrix band in place during dental restorative procedures.
Step-by-step explanation:
The component of the universal matrix retainer that holds the matrix band securely in the device is known as the screw. The matrix band is a thin, flexible band that is placed around a tooth to provide a temporary wall during restorative procedures, such as filling a cavity. The screw mechanism allows for the tightening or loosening of the band to ensure it fits snugly against the tooth, preventing any dental material from spilling out during the procedure.