What condition is characterized by 6 or more missing teeth?

The correct answer is based on the definition of the conditions listed. Oligodontia is specifically characterized by the congenital absence of six or more teeth, excluding third molars. This condition is a more severe form of hypodontia, which refers to the absence of one to five teeth.

In contrast, ankylosis involves the fusion of a tooth to the bone rather than missing teeth, making it unrelated to the question. Hypodontia, while also involving missing teeth, specifically denotes fewer than six absent teeth. Amelogenesis imperfecta is a genetic condition affecting the enamel of the teeth, leading to defects in enamel formation but does not directly relate to the number of teeth present or absent.

Thus, oligodontia accurately describes the situation of having six or more missing teeth, making it the correct choice.