What is the source of endogenous stains?

Endogenous stains originate from sources that impact the teeth during their development, leading to intrinsic discoloration. These stains can be the result of factors such as systemic conditions, medications taken during specific developmental stages (like certain antibiotics), or even excessive fluoride exposure. Because these influences occur internally during the formation of the teeth, the stains become part of the tooth structure itself, rendering them different from stains that come from external elements.

In contrast, the other options refer to extrinsic factors that can stain teeth after they have developed. For example, external sources involve dietary components that may cause discoloration after teeth have erupted. Habits such as smoking or chewing tobacco introduce pigments that adhere to the enamel's surface, while cosmetic products can also contribute to surface stains rather than intrinsic changes. Thus, the correct response highlights the unique nature of endogenous stains as tied to tooth development rather than later environmental influences.