Re: Grooves at Gumline, Recession and Sensitivity After Orthodontics

If you are having so many problems with your retainer, I would get it looked at. The retainer may have warped, your teeth may have moved beyond what the retainer can control comfortably, or you may just want to move to a nightguard.
Newer nightguard versions are now made with soft linings, so that they fit more comfortably on your teeth, should not cause headaches because the soft lining will not put pressure on your teeth. Options are worth discussing with a dentist who can treat you.

You cannot regrow enamel per say. You can remineralize enamel, but it cannot grow back. Your body creates enamel when the tooth is still inside the jaw. The tooth is surrounded by cells that excrete the enamel matrix and mineralize it. When the tooth erupts, these cells are lost permanently. Because you lose these cells, your enamel can never grow back.
Now, what you may have heard is about reminerlizing enamel. The way cavities start is bacteria releasing acids as waste. These acids leech out the calcium and phosphate minerals inside the enamel matrix. When you lose enough minerals, the matrix collapses. As long as the matrix is still intact, your body can put minerals back in if the bacteria is removed. This process is called remineralization and it happens all the time inside the mouth. However, once you lose the matrix, its gone forever.

Hope this helps. Good luck with your treatment!