Take calcium supplements. Calcium is essential to forming healthy teeth and bones. The two most popular forms of calcium supplements are calcium citrate and calcium carbonate. Taking vitamin D and magnesium supplements with calcium can help your body absorb and use the calcium more efficiently. Calcium supplements should be taken in very small doses, no more than 500 mg at any given time, in divided doses with six to eight cups of water to avoid constipation.
Make a paste of baking soda and lemon juice. It will likely fizz and foam a bit. Wait for it to settle down and use this solution to brush your teeth. Rinse well. You don’t need to follow with your regular toothpaste, but you can if you wish. Lemon juice contains citric acid, so it can damage your teeth if used too often. Only do this once a week for best results.
Rinse your mouth with water. Rinsing with water after meals or drinking caffeinated beverages will help remove any leftover food or residue from your teeth will help prevent stain and decay.  This method is especially useful if you’re away from home and don’t get a chance to brush or floss after eating. Drinking water throughout the day and rinsing with clean water after meals is the most underrated method of overall oral health.
Español: blanquear los dientes de forma natural, Português: Clarear os Dentes Naturalmente, Русский: отбелить зубы натуральными средствами, Italiano: Sbiancare i Denti in Modo Naturale, Français: avoir des dents plus blanches naturellement, Deutsch: Zähne natürlich aufhellen, 中文: 自然美白牙齿, Čeština: Jak přirozeně vybělit zuby, Bahasa Indonesia: Memutihkan Gigi Secara Alami, 日本語: 自然に歯を白くする, العربية: تبييض الأسنان بطرق طبيعية
Avoiding smoking cigarettes, drinking too much coffee and/or soda, improving your oral hygiene overall, and eating a healthy diet can all also help prevent yellow teeth. If you do regularly drink staining beverages, do so through a straw and try to cut back. Try to drink more plain water after eating or drinking something staining or acidic to help reduce the negative effects.