Teeth become impacted (stuck or obstructed) when there is no space available, due to crowding, or when there is a mass blocking their path of eruption. The mass may be an extra tooth, abnormal small pieces of tooth material, or exceedingly thick, impenetrable gum. They can also become impacted if they are simply pointing the wrong way. Sometimes, developing adult teeth point the wrong way and erupt into the back of baby molar teeth, as shown in the image below in the upper jaw. These ectopic molar teeth can cause damage to the roots of the baby teeth, causing root resorption, so they should be corrected early.