How much time will dna stay on a swab or a toothbrush?

Preservation: If the swab or toothbrush is preserved under ideal conditions, a very, very long time. See below link: http://crev.Info/2013/07/longevity-of-dna-estimated/.

For a long time: as long as the swab stays dry the DNA is preserved for a long time. You can use cotton-tipped swabs or a brand new toothbrush, because the toothpaste on a used brush will compromise the DNA results.