Teeth that don’t have enough space to erupt into the correct spot end up getting stuck in awkward positions. Again, let’s look at the classic example of wisdom teeth.
They are at the back of the jaw, and therefore, usually do not have sufficient space in the jaw to erupt into a functional, healthy position. So invariably, the tooth will get stuck in a position that has it partially covered by gum tissue.
Teeth are not supposed to be partially covered by gum tissue. It’s unhygienic. The gum tissue forms kind of a pocket that is not easily cleansible, and so food gets stuck there, and bacteria follows. Since you cannot clean there effectively with a toothbrush or floss, the bacteria flourishes there, and causes inflammation. This inflammation of the tissue makes the pocket deeper, and thus more bacteria accumulates. Over time, this becomes more and more painful. What makes it worse, Is that this is an area near the back of the jaw, where this swollen tissue becomes easily trapped between the teeth when you chew. This just exacerbates the situation.