Musannaf Ibn Abi Shayba 18:318

Abu Bakr narrated to us, he said: 'Abbad bin al-'Awwam narrated to us, from Hajjaj, from Husayn, from al-Sha'bi, from al-Harith, from 'Ali, regarding the tooth: If a portion of it is broken, its owner is given [compensation] according to the measure of what was diminished from it.