请牙医帮帮忙

My son is 7 year old. Three days ago I notice he't got a bumper on the gum of his third tooth on the left side. It is hard, like a tooth going to erupt out. But I feel it's too early for him to have adult tooth in that position. I took him to see a dentist who didn't take x-ray for him, just told me it is probably a tooth coming out. Anyway I took my son to see another dentist, who took an x-ray for that tooth. No adult tooth coming out. The tooth is fine. The x-ray result is good. But but the doctor asked me to watch it, or it may be the way the gum is. Can x-ray tell if something is going wrong with the gum? Other than a little bumping on the gum, his gum is healthy.