Patient: Recently, I noticed that my child’s teeth have a black substance growing near the gums, and most of the teeth have it. The child brushes his teeth twice a day, morning and evening, and has always paid close attention to oral hygiene since he was a child. I would like to know why there is still this black stuff on the teeth and how to brush it off, and whether it needs to be treated on the teeth. Doctor: From the description it may be food pigmentation on the tooth surface, which may be related to the calcification of the teeth and recent medication or drinks. 6 year olds can go to the hospital to remove the pigment and then brush their teeth carefully.