Probably it is recession of gingiva from a particular tooth region but the underlying cause is not known. There are so many possible reasons like very commonly plaque n calculus accumulation or it may be due to faulty tooth brushing or mal positioning of tooth. No need to worry.. Just visit a dental clinic..

There are many reasons for gum recession.most common are gum disease and faulty tooth brushing. The recessed gums can't be brought back to their original position in most cases but you can already prevent further recession if you know the cause .

Hi dear . It is important to know the underlying cause that caused the Gum to recede or gone & since you're mentioning just one particular tooth region, possibly the placement of the tooth might be one of the reasons of many reasons to the same . Seeing the condition in person will help Dental Surgeons evaluate the problem & hence the treatment options more efficiently. Nevertheless there are a lot of options to bring the condition back to normal if not perfect, depending upon the age and systematic conditions of the body . It's important for you to see a dentist. Hope this was helpful. Warm Regards.