Is there a surgery for flat nipples?

I have flat nipples which have a tiny indent in the middle. I have been using the advent nipplette and supple cups religiously for a year. I'm not sure if the stretching I have had is actually my 'nipple' or if the stretching is just creating me a nipple. Is the tissue stretching permanent over a long period? I have been using most days a week for a number of hours. I'm still not happy with the shape and I'm wondering if there is a surgery that isn't just for truly inverted & fixes flat instead. Thank u