The most frequent supernumerary tooth is a mesiodens, which occurs between the two maxillary central incisors. Often it fails to erupt, but creates a large anterior diastema, and would not be detected on physical examination (requires X-ray evaluation). This designation excludes coexistence of primary and permanent dentition due to delayed loss of the former. Note that this term does not refer to the situation in which two rows of teeth are seen at the time of eruption of permanent dentition before exfoliation of primary teeth, which can be a normal finding.