The black line in the fossa of a six-year-old tooth is a sign of caries and it is advisable to seek medical attention for restoration of the caries. The six-year-old teeth (clinically known as the first permanent molars) are the first permanent teeth that erupt around the age of six; their position is behind the milk molars, and because of their similarity in shape, they are often mistaken for milk teeth and not taken seriously, and are prone to caries when oral care is not in place. When the six-year-old teeth just erupted, the fossa is deeper, easy to caries due to food congestion, that is, the teeth fossa black line symptoms; must be timely medical caries restoration, the specific steps are the physician first with a special tool will be caries black part of the abrasion, and then with oral restorative materials such as tooth powder or resin and other parts of the defective parts of the repair can be. These cases should be treated promptly.