Fairies keep the teeth that are left out for them. They are so precious to fairies that they’re like trophies to them. Often fairies will keep them sitting on little silk cushions on the mantles in their homes for all to admire. Your teeth hold all your childhood memories and fairies are guardians of these and take this job very seriously. Teeth have no value in terms of human money but fairies know how much humans like it so that is why they leave some in exchange for your precious tooth.