Black discolouration on the backside of the teeth, along with bad breath, is commonly caused by plaque and tartar buildup, staining from food, tea, coffee, smoking, poor oral hygiene, or tooth decay. When tartar collects behind the teeth, especially near the gums, it can appear dark or black and may also cause gum infection and foul smell from the mouth. In some cases, cavities or gum disease can also lead to persistent bad breath and discolouration. The most effective treatment is usually professional dental cleaning, also called scaling, which removes tartar and plaque from the teeth and gums. If cavities or gum problems are present, the dentist may advise fillings or additional treatment. Brushing twice daily with a soft toothbrush, cleaning the tongue, flossing regularly, and rinsing the mouth after meals can help prevent further buildup. Avoiding smoking and reducing tea, coffee, and sugary foods may also improve oral health. Drinking enough water and maintaining good oral hygiene are important for controlling bad breath. If you notice gum bleeding, loose teeth, pain, swelling, or worsening discolouration, you should visit a dentist for a detailed examination and timely treatment. Early dental care usually gives very good improvement and helps keep the teeth and gums healthy.