Usually, your tooth will ache to tell you that something's wrong but that's before the days of the tooth tattoos.
If Mike McAlpine of Princeton University has his ways, we all will be sportin' a special sensor made of graphene tattooed to our teeth to tell us what's making us sick from the bacteria on our breath:
Graphene, a layer of carbon that’s one-atom thick, is a super-sticky, super-sensitive surface. By planting carefully constructed peptides (a short sequence of amino acids) onto the surface of graphene, McAlpine and his group have shown that the sensors can detect bacteria individually, picking them up like velcro.
Previously on Neatorama: Tooth Tattooing (for cosmetic reasons)