DS (7) has two adult teeth growing at the bottom. They have been coming through for awhile and are nearly fully grown I think. Yesterday I noticed they seem quite yellow in the middle of the teeth but white around the edges. He brushes twice a day and has recently started using Listerine for kids mouthwash too. He hasn't had any injury or trauma to them. I am worried as they are his adult teeth. Anyone know what could have caused this and if it is likely to be permanent now? Can too much/too little fluoride cause this? Is it likely to be the mouthwash? Thanks