To answer this question, we have to first explain why you need to reline your dentures to begin with. When a tooth is extracted from your mouth, the area of the gums that used to support the tooth, called the edentulous ridge, begins to shrink. After all, with the tooth gone, then there's no reason to have so much tissue in place to support thin air. Our bodies know this, and so get rid of that excess gum. The initial shrinkage (about 90% of it) happens in the first 4 to 6 months after your tooth is extracted, after which it will stabilize somewhat. Obviously, after such a loss of volume, it's no surprise that you'll suddenly find your dentures rather loose. It's time for a reline.