It is the negative replica of the teeth and surrounding structure in the oral cavity, introduced as a gel form then becomes relatively hard or set while in contact with these tissues.
It is the negative registration of the entire denture bearing, stabilizing and border seal areas present in the edentulous mouth.
The success of dental prostheses rests directly on exact dental impressions, for this there are techniques that allow the precise copy of the supporting tissues that will allow the retention we seek.
This video describes use of two mirrors with the operator seated and the patient in a supine positon for making complete denture impressions.