In short, acrylic comes in powder form, then it is mixed with liquid chemicals and is cooked under pressure for a certain period of time under certain temperature. This process is called curing.
I don't want to scare you though, because a lab that does dentures all day long will cure dentures properly. Another thing you should look for in a denture is good polish, a denture that has rough spots and is not polished properly will attract bacteria. Bacteria does not stick to smoothly polished denture or crown. This is for the exterior of denture, the interior is not polished because it will fall off if otherwise.