Teeth whitening tips. The antibiotic tetracycline causes gray teeth in children whose teeth are still developing. Antibacterial mouthwashes that contain chlorhexidine or cetylpyridinium chloride can also stain teeth. Some antihistamines, antipsychotic drugs, and blood pressure medications cause tooth stains, as can iron and excess fluoride. If bleaching doesn’t help, ask your dentist about dental bonding, in which a tooth-colored material is applied to teeth. Baking Soda & Lemon: Mix a tablespoon of toothpaste, a pinch of salt, a bit of baking soda, and 4-5 drops of lemon juice in a bowl. Brush your teeth with this mixture for 4-5 minutes. …