Hey Jullasana,

Well,yes the candidates are allowed to wear the tooth braces as this is something that one wears because of Medical problems just like the spectacles .To be on the safer side,just carry the prescription of the dental you are under treatment with,in case the officials ask questions you can show it to them.
For detailed information about the dress code of NEET,follow the link given below:
https://medicine.careers360.com/articles/neet-dress-code
Hope this helps.
Good luck.