Tessica Brown, the woman whose hair's been Gorilla Glued for more than a month, finally has sweet relief -- and we have video of the surgery that saved the day.

As we first reported, Tessica took up Bev Hills plastic surgeon Dr. Michael Obeng on his offer to perform the $12,500 procedure for free, and it was a pretty grueling process. ... about 4 hours long!

We shot the whole thing, from start to finish, and it's wild to see it play out -- and to see the relief on Tessica's face when it was all said and done.

Tessica was under a light anesthesia during the procedure, you've gotta see her reaction as she came out of it, and immediately reached for her hair. She got pretty choked up once she realized she could once again run her fingers through it.

We asked if she's done with home styling after the Gorilla Glue nightmare, and let's just say she's got big plans for this weekend.

As we reported ... Tessica had flown into L.A. from Louisiana Wednesday morning hoping Dr. Obeng could do what she'd tried, unsuccessfully, to do for more than a month now.

Remember ... in a pinch, she had swapped out her normal hair spray for Gorilla Glue Spray Adhesive, thinking she'd be able to wash it out a few hours later.

Since then she's been through the wringer ... suffering severe headaches, trying at-home remedies and even went to the ER, but everything just made her scalp burn intensely.

Dr. Obeng broke down his secret recipe for us, explaining it was all just basic chemistry. We're no scientists, so watch the video for his explanation -- but in a nutshell, he combined medical grade adhesive remover, aloe vera, olive oil and a dash of acetone.

He said that's all it took to break down the polyurethane -- the main ingredient in Gorilla Glue. BTW, he didn't go in cold. You gotta see the dummy scalp Dr. Obeng used to test his solvent.

The only small relief Tessica had gotten before her Bev Hills visit, came last weekend when she and her sister used superglue remover to chop off her ponytail.

Speaking of that ponytail ... she says she can't wait to get her hair back to that length, and it is pretty amazing how much of her hair Dr. Obeng was able to save.

Tessica had told us she was prepared to wear wigs for the rest of her life -- but after this procedure, she won't need them for too long.