What is the primary reason that endodontically treated teeth are considered weak?

Endodontically treated teeth are considered weak primarily due to the loss of coronal tissues. The process of root canal therapy often involves the removal of the affected pulp tissue, which can also necessitate the removal of significant amounts of tooth structure above the gum line, particularly if decay or structural damage has occurred. This loss of coronal tooth structure compromises the tooth's overall integrity and strength, making it more susceptible to fracture under normal chewing forces.

While the loss of blood supply does occur and can influence healing and vitality, it is not the main reason for the weakness of the tooth itself. The presence of root canal materials is a critical aspect of the treatment and does not inherently weaken the tooth; these materials are designed to seal and protect the remaining structures. Overly aggressive endodontic treatment can lead to additional complications, but the fundamental issue revolves around the structural loss due to the removal of coronal tissues. Hence, the weak state of endodontically treated teeth is primarily attributed to the loss of coronal tissues during the treatment process.