Is it ok in the Islamic law to have a gold tooth. A Muslim dentist told me that a porcelain tooth will breaks easily.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

There is disagreement among Muslim scholars concerning making use of a tooth of gold.
According to the schools of Malik, al-Shafi'e and Ibn Hanbal, it is lawful to use a tooth of gold. They based their opinion on the Hadith (reported by al-Tirmizi) of 'Arfajah Ibn 'As'ad (Radiya Allahu Anhu) who used a nose of silver when it (his nose) was cut on the day of Kilab. But, when such a nose of silver became bad-smelling, the Prophet (Sallallahu Alaihi wa Sallam) ordered 'Arafajah to use a nose of gold.
Al-Athram reported from Musa Ibn Talha, Abu Jamrata al-Dub'i, Abu Rafi' Ibn Thabit al-Banani, Ismael Ibn Zaid Ibn Thabit and al-Mughirah Ibn 'Abdullah (Radiya Allahu Anhum) that they tied their teeth with gold.
According to the school of Imam Abu Hanifa, it is not lawful to use a tooth of gold except in case of need. This opinion is based on the Hadith that prohibit to use gold by men in general. It is also added that the narration of 'Arfajah was for a dire-need as stated by the Hadith. Here, it is safer to avoid such a use of gold as long as an alternative is available in silver, platinum or porcelain.
Allah knows best.