Summary: A classification of the extension defects ofendodontically anterior teeth is presented. This classification is based on the amount of remanentcoronal tooth after an essential treatment has been done, such as: root canal therapy, removal ofcarious tissue, periodontal surgery whenever needed and tooth preparation either for the placementof a direct restoration material such as composite or a post and core and full crown restoration.This classification is based on 3 specific variables: supragingival remaining coronal toothstructure or core height, diameter and root canal depth. Key words: Post and core. Root canaltreatment. Diagnostic.