Normally, human have 32 teeth (including wisdom teeth). However, some people have more than that. The extra one is called supernumerary tooth. Most of the time, the supernumerary tooth failed to erupt so it is not noticeable in general dental check-up. The x-ray is the best way to check if there is one. This extra tooth sometime causes problems, for example, preventing permanent tooth to erupt, causing root resorption of permanent tooth and it might develop into a cyst. In the most cases, the extra tooth should be removed.