There are several common causes of marks on teeth, including:

1. Stains from food and drinks: Certain foods and drinks, such as coffee, tea, red wine, and berries, can stain your teeth over time.

2. Plaque and tartar build up: Plaque is a sticky film of bacteria that forms on your teeth and can lead to tartar build up if not removed. Tartar is a hard, yellow or brown substance that can stain your teeth and contribute to tooth decay and gum disease.

3. Tooth decay: Cavities can cause discoloration or dark spots on your teeth.

4. Enamel erosion: The outer layer of your teeth, called enamel, can wear away over time from factors such as acid erosion from acidic foods and drinks, tooth grinding, or brushing your teeth too hard. This can cause your teeth to appear more yellow or expose the darker layer underneath, called dentin.

5. Medications: Some medications can cause tooth discoloration as a side effect.

If you're concerned about marks on your teeth, it's best to schedule an appointment with your dentist. They can examine your teeth and determine the cause of the marks, as well as recommend treatment options if necessary.