Which one of the following tooth types is only found in the secondary dentition?

The first premolars are indeed only found in the secondary dentition, which is the set of permanent teeth that replace primary (or deciduous) teeth. The secondary dentition typically includes 32 teeth in total, and the first premolars erupt after the primary molars are shed.

In contrast, the other tooth types mentioned have different associations with the human dental development process. Canines, lateral incisors, and second molars are present in both the primary and secondary dentitions. The primary dentition features primary canines and primary molars, which are eventually replaced by their permanent counterparts, including permanent canines and second molars. This highlights the distinct nature of the first premolars, as they do not appear in the primary set but only in the permanent set, marking them as unique to the secondary dentition.