Final answer:
An adult with three maxillary incisor crowns, one being abnormally wide and notched, likely has a dental anomaly, which is an irregularity during tooth development.
Step-by-step explanation:
An adult with only three maxillary incisor crowns, where one of the crowns is doubled in width and notched, would most likely indicate a dental anomaly. This is not a normal variation or an age-related change, and while it could have a genetic predisposition, the anomalous double-width notched crown suggests a developmental disturbance during the formation of the teeth. Humans typically have eight incisors in total, with four on the top (maxillary) and four on the bottom (mandibular). The presence of an abnormal incisor suggests an anomaly in the usual dental development sequence.