A chunk of my gum is missing? (Photo)

one of the reasons for gum recession is agressive brushing and using hard tooth brush. Other causes include orthodontic treatment ( braces), bite problems, smoking ...It is not very clear in your oicture ,but I think I see a cut in the gum as well. This is a gingival cleft that could be caused by wrong method of flossing and/ or bite problems on that specific tooth. Use a soft tooth brush from now on. And see a dentist to evaluate the situation. Recession will not correct itself. You might need to be referred for treatment.  

From your photos it appears trauma is what has caused this condition probably due to the hard bristles of the tooth brush. Use a rinse like Peroxyl to help it heal and it should be fine within a couple weeks. If not, then have your dental provider take a closer look.

Hi there,
That looks like abrasion trauma. Considering the things you mentioned, new brush, hard bristles, it is very likely that you may have traumatized your gum tissue when brushing along the gum line in that area. Other form of trauma like having the area poked or scraped by a piece of crunchy food may also cause that sort of tissue loss. From the looks of it though, it will recover with time and some conscious wound care. Try not to traumatized it further or poke at it, in about 6-8 weeks the tissue should heal, mature, and fill in if the remaining underlying gingival tissue has not been severely damaged by whatever caused this. At this point I do not believe you will need gingival grafting, however, should the area not heal and continue to recede and shrivel away, it can be treated with a free connective tissue graft harvested from the roof of your mouth. For now though, I would just wait, good luck!