Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- Plastic surgery is permissible as a treatment to correct an actual abnormality, whether that abnormality is congenital or acquired.
2- If the gap between your two front teeth is excessive, causing a deformity, then it is allowable to fix it. The physician decides what is considered anomalous.
In responding to your question, Dr. Hatem Al-Hajj, Dean of the College of Islamic Studies at Mishkah University and a member of the Permanent Fatwa Committee for the Assembly of Muslim Jurists in America (AMJA), states:
Changing the creation of Allah: Forbidden?
Changing the creation of Allah is not permissible. The Messenger of Allah (blessings and peace be upon him) said,
“May Allah curse the one who does tattoos and the one who has a tattoo done, the one who plucks eyebrows and the one who has her eyebrows plucked, and those who file teeth for the purpose of beautification, changing the creation of Allah.” (Agreed upon)
We should be content with how Allah fashioned us. The Prophet saw a man dragging his garment because he was ashamed of his deformed legs, he (PBUH) said,
“Raise your garment for all of the creation of Allah is beautiful.” (Ahmad)
The Messenger of Allah allowed `Arfajah ibn As`ad (may Allah be pleased with him) to get a nose out of gold after his nose got cut off on the day of Al-Kulab. (At-Tirmidhi)
He also said,
“Seek proper cure [for your diseases] O, servants of Allah.” (At-Tirmidhi)
Is plastic surgery permissible?
Plastic surgery is thus permissible as a treatment to correct an actual abnormality, whether that abnormality is congenital or acquired.
Lastly, if the gap is excessive, causing a deformity, then it is allowable to fix it. The physician decides what is considered anomalous.
Almighty Allah knows best.
Source: www.amjaonline.org