Final answer:
The tooth commonly with two root canals is the first premolar or bicuspid. This type of tooth is used for mashing food and is located posterior to the cuspids with a flatter shape.
Step-by-step explanation:
The tooth that commonly has two root canals is a premolar, specifically the first premolar, often referred to as a bicuspid. Posterior to the cuspids, premolars are used for mashing food, with an overall flatter shape and two rounded cusps on their surface. While not all premolars may have two root canals, it is a common configuration, especially for the maxillary first premolars. The pulp cavity within these teeth extends down into the root canal(s), surrounded by dentin and cementum, with the latter anchoring the tooth in place.