Which of the following is considered a cause of endogenous intrinsic stains?

Endogenous intrinsic stains originate from within the tooth and are often linked to internal factors that affect the tooth's structure and color. Pulpless teeth, or teeth that have undergone endodontic treatment, can develop intrinsic stains due to the breakdown of pulp tissue and changes in the dentin. These changes can lead to discoloration in the tooth structure, resulting in a darker appearance.

In contrast, excessive fluoride exposure, while it can lead to intrinsic staining, generally causes a different type of discoloration known as dental fluorosis, which is more about the alteration of enamel during development rather than a direct intrinsic stain related to pulpal health. External whitening agents typically affect the outer layer of the teeth and are designed to improve tooth color without causing intrinsic stains. Dental caries can lead to discoloration but are typically more associated with external factors rather than being classified under intrinsic stains from within the tooth structure like pulpless teeth.