Which of the following is NOT a way stains can occur on teeth?

Stains on teeth can arise from several factors, and understanding these mechanisms helps in both dental practice and patient education. The correct answer indicates that "filtered through saliva" is not a method by which stains form on teeth.

Teeth can develop stains through several processes. For example, stains can become embedded in calculus and plaque, which is a common occurrence. Calculus forms when plaque mineralizes and can retain various pigments from food and beverages, thereby leading to discoloration.

Additionally, certain stains can become incorporated into the tooth structure itself. This means that the intrinsic color of the tooth can change due to factors such as certain medications, systemic conditions, or developmental issues.

Stains can also adhere directly to the tooth surface, primarily from external sources like coffee, tea, tobacco, and other staining agents that physically stick to the enamel.

In contrast, the idea that stains are "filtered through saliva" does not align with the typical mechanisms of stain formation on teeth. Saliva plays a role in maintaining oral health and can aid in remineralization or in washing away food particles and bacteria; however, it does not actively contribute to the staining of teeth. Understanding the correct mechanisms provides clarity in dental hygiene practices and informs strategies for stain prevention and treatment.