Final answer:
The matrix band should extend 1-2 millimeters below the gingival margin of the preparation when a posterior metal matrix band and retainer are placed for dental restoration.
Step-by-step explanation:
When a posterior metal matrix band and retainer are placed for a dental restoration, the seated matrix band should extend approximately 1-2 millimeters below the gingival margin of the preparation. It is crucial to ensure that the matrix band is properly positioned to recreate the natural contours of the tooth and to avoid overhanging restorations or gingival irritation.
The matrix band acts as a temporary wall to hold the dental restorative material in place and must be seated below the preparation margin to adequately contain the material and shape the restoration.