Stephanie's brace had affected her immune system
Stephanie Fender, 15, from Mount Pleasant, Swansea suffered 18 months of illness which made her feel sick and permanently lethargic.
She missed months of school, was not able to see her friends, and at times could not even get out of bed.
Doctors were unable to diagnose what was wrong with the schoolgirl, suggesting she was suffering from chronic fatigue or ME.
But a breakthrough came when her mother Donna, 31, read of a similar illness, apparently triggered by a dental brace, and realised Stephanie might be suffering from the same problem.
A dental specialist in Bristol has since confirmed that Stephanie's long illness was caused by her brace.
The brace had played havoc with the teenager's immune system by effectively blocking passages which allow vital fluid to circulate around her brain and body.
"He said the brace which caused the problem forced her teeth to grow in such a way that it locked off the fluid in her brain which became stale," said Mrs Fender.
"The whole of her body was out of alignment and she was in a weak state the whole time - she became like a zombie."
In January - after seeing the specialist - Stephanie threw out the brace which had caused her all the problems.
"Since I have taken the brace out I feel much better.
"I am doing school work at home now for the first time in a year.
"Before, I would occasionally go out with friends but I constantly felt tired and spent more and more time at home in bed."
Stephanie is now being treated by a dentist in Bristol and is being given two transparent plastic splints to hold her jaw in the correct position.
However, the dental treatment is costing £2,000 and the family are receiving no help from the NHS, said Donna Fender.