Agenesis of permanent teeth has an important impact on orthodontic diagnosis and therapy. It is related to clinical symptoms which are not commonly known. This short overview deals with epidemiology, symptomatology of micromanifestations, and specific possible tissue reactions during the treatment of patients with hypodontia. Palabras clave: Hypodontie, Oligodontie, ectopic tooth germ position, reduction of tooth shape, agenesis