Using “tattoo” to describe these ornamental designs is a bit of a misnomer, as a tattoo is, by definition, a pigment mark made by piercing the skin. In the case of dental tattoos, the teeth are not actually pierced or even touched with a needle, and the material which covers teeth is enamel, not skin. However, the end effect is much the same, especially in the case of an artfully produced dental tattoo.
Dental tattoos are usually applied by the dental lab which makes the crowns. After a dentist takes a mold and confirms that it is correctly sized for the tooth, he or she sends it to a lab to be manufactured into a crown, or produces the crowns in-house, depending on personal preference. If the customer wants a dental tattoo, the mold may be sent to a lab which specializes in such things, and a skilled artist typically does the tattoo work, carefully painting a miniature design onto the tooth before it is sealed. Because the work is sealed in, clients generally do not have to take any special steps to maintain their dental tattoos, beyond caring for the crown itself.
Labs which make custom crowns with dental tattoos say that the tattoos can be removed by grinding away the upper layers of the crown, for people who later sour on their dental tattoos, but do not want to replace the entire crown. For even more temporary options, people can apply specialized decals to their teeth, although care should be taken when removing such decals to make sure that all residue is removed from the teeth, and to avoid swallowing the decal.