Ans. Having yellowish teeth does not come under any pathological dental problem. There are various causes of yellow teeth:

• Teeth become slightly yellow with the age because the enamel wears off. It is a natural procedure. Sometimes it can happen due to plaque build-up too and this can be reducing by brushing and cleaning.
• Some people have genetically yellow teeth. It cannot be corrected by whitening agent or toothpaste.
• Some of the teeth like canines withstand more tear and wear; they contain thick layer of dentine and thin layer of enamel. Due to more dentine it appears yellowish then other teeth. It is an intrinsic stain.
• Thin enamel layer of the tooth gives it a yellow hue, because of underlying dentine.
• Some stains are due to some food and beverages or tobacco product, certain medicines, or poor oral hygiene etc.
• Fluoride is a chemical, which is good for teeth as it protects from decay, but excess fluoride  in either in water or food may cause yellow or brownish yellow spots on teeth called as fluorosis.