You might have a loose tooth due to severe gum problem on that particular area with black deposits.
Next Steps
Do visit a dentist and find out the reason behind this loose tooth. Dental cleaning/scaling may help you in this case to reduce looseness and if any cavity on that tooth, then filling will require. By these you might save this or the adjacent teeth
Health Tips
Check the inner surface(tounge side surface) of your front teeth, if this black traces are there on other teeth as well. Do brush twice a day and visit your dentist every 6 months once.