Final answer:
A tooth can have a post and crown if its root is strong enough to support it. The crown is the part of the tooth above the gum, while the root canal contains the pulp and is covered by dentin and cementum below the gum line.
Step-by-step explanation:
A post can be used as a retention aid for a crown, provided that the tooth has a remaining root structure that is strong enough to support the crown. In dental terminology, the crown refers to the portion of the tooth that is visible above the gum line. When a crown is required, it usually means that the natural crown has been damaged or decayed and needs to be covered with a restorative material to protect and restore its functionality.
The root canal is the region of the pulp cavity that runs through the root of the tooth, which is surrounded by dentin and cementum under the gum line. To use a post effectively, the remaining root structure must be intact and strong enough to support the mechanical forces that will be applied to the crown during ordinary activities like chewing. If the root is not adequate, alternative methods of tooth restoration will need to be considered.
To illustrate, a cuspid or canine tooth, which is pointed and used for tearing and shredding food, might be suitable for a crown with a post if its root is robust and healthy. In contrast, if a bicuspid is missing, and the adjacent teeth, such as a molar and another cuspid, have cavities, a dentist might consider creating a bridge to fill the gap using crowning and bridging techniques that would distribute the load across multiple teeth.