Good morning madam Floss will work when you have relatively good contact between the teeth Here since your complaining of gap and no attachment with gum may be you have developed problem with gums or there might be slight gap from before which you have noticed after you gum is infected and tongue is reaching that area Kindly post a photo or radiograph to comment more

Probably pocket and possible interdental bone loss. Get an Xray of the region and a clinical examination for a more accurate picture.

Hi,,get an X-ray done and see a dentist,,there might be a decayed tooth that you are talking about.

There might be a periodontal pocket in the region. Consult a dentist and get a scaling and polishing done. Your dentist will advise you if anything further is required