This is a term that is used to describe Dens Invaginatus or Dens Evaginatus. Both are unusual developmental abnormalities that result to unsual folding of the enamel and risk the dental pulp becoming diseased.
These teeth can sometimes develop large lesions (abscess or cyst) without necessarily causing any prior symptoms.
Root canal treatment is often necessary and sometimes a decompression technique as well. If the dens is spotted early the internal or external folding of the enamel can be fissure sealed to protect the dental pulp within the root.