While brushing my sons teeth I noticed a grey spot on the inside of one of his top teeth. It’s the tooth next to his 2 front teeth. He isn’t bothered by it AT ALL but I feel like such a failure and I try my best to do all the right things. I am calling his dentist in the morning but in the meantime...what could it be? He is 2 and a half btw. (And also, he hasn’t had any trauma to it which i know could cause it to turn a different color)