Intrusion is when an orthodontist makes a tooth go further into your gums. It happens when you have a tooth that is too long or sticking out too much. The doctor puts something on your tooth called an attachment and this helps to move the tooth down, like a slide. Once the tooth is where it needs to be, the doctor takes off the attachment and the tooth stays in its new spot. Think of it like moving a toy car down a ramp to make it go lower. Intrusion helps make your teeth straight and also makes them fit together nicely when you bite or chew your food.