Which tooth type is found in both primary and secondary dentitions?

The first molar is indeed found in both primary and secondary dentitions. In primary (or deciduous) dentition, children have primary first molars that emerge around the age of 10 to 16 months. These primary first molars serve important functions in chewing and help guide the development of the dental arch.

In the secondary (or permanent) dentition, the first molars that replace the primary molars are known as the permanent first molars, commonly referred to as "six-year molars." These erupt around the age of 6 and serve a critical role in the adult dentition, contributing to the overall function of the teeth and the maintenance of proper occlusion.

The other tooth types mentioned do not appear in both dentitions. The first premolar only appears in permanent dentition, as primary teeth do not include premolars; instead, primary teeth are replaced by permanent premolars. Similarly, the second premolar, also known only in permanent dentition, and the third molar, which can erupt later in life, are not present in primary dentition.