All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
What is considered in this regard is whether the appearance is normal or abnormal. If it is normal, then it is not permissible to get braces in this case. If it is abnormal to the point that people often find it ugly and it often makes the person feel embarrassed, then it is permissible to get the braces.
Shaykh Ibn ‘Uthaymeen said when clarifying the ruling on orthodontics:
"If getting braces is due to a defect, then it is permissible to get them; some people may have protruding teeth (the two front teeth or otherwise) that appear abnormal to the point that those who see them would consider them ugly; so in this case, it is permissible for a person to fix them because this is removing a defect and not increasing one’s beauty. The evidence of this is that the Prophet ordered the man who had his nose cut off to wear a nose made of silver, and when his nose started to smell, he ordered him to replace it with a nose made of gold, because this is a removal of a defect, and it is not meant to increase beauty."
For more benefit, please refer to fatwas 88719 and 85149.
Allah knows best.