There tooth abnormalities can be classified into four major groups, depending on the depth of the invagination. A typical example from group four is described. Thorough röntgenological examination reveals a frequent occurrence. The great diversity in nomenclature and the variety of morphogenetic and etiological theories show that genetic factors are very important in the development of an invaginated tooth and that knowledge concerning the pathomechanisms is very inadequate. A detailed inspection of the inner tooth morphology on röntgennogram is necessary as the surface morphology generally does not reveal the existence of an invagination. The irreversible pathological evolution occurring when diagnosis is neglected. Should incite the practitioner to look for invaginations on every set of röntgenograms. Five thereapeutic techniques are described. If an appropriate endodontic technique is applied, a successful root canal filling can be achieved.