Because wisdom teeth are the last to emerge, usually during the late teens or early 20s, there is often a lack of room in the jaw. Consequently, these teeth try to emerge underneath the adjacent teeth or even erupt sideways through the gum. Some wisdom teeth managed to erupt partially but remain partly covered with gum tissue. A partially erupted wisdom tooth is harder to keep clean and is more likely to become infected and decayed. The infection and decay can affect the adjacent teeth.