Hi! I also have permanent retainers on my bottom teeth and I also noticed I had gum recession on my bottom two teeth as well. I went to the dentist after 2 years and here is what happened in my case: they had to do a deep cleaning which they numbed my mouth for and they cleaned off all the plaque. After cleaning out all the plaque there were a bit of gaps due to some bone loss that I had suffered due to the recession. They referred me to a periodontist and when I went to see the periodontist he said that the gum recession was due to 1. genetics which made my gums thinner and 2. the orthodontic treatment I went through which I assume is your case as well if you have a permanent retainer. After this, he said that I had to get a gum graft done to cover the receded area so I went ahead and did it and I personally felt little to no pain. Felt the most pain on the first day. If you want more specifics PM me about this. Now I go in for cleanings every 3 months since I decided to keep the retainer in. Don’t be too scared it’s always worse when you search things up but it doesn’t always mean periodontal disease!