1.Crowding: The teeth in the dental arch are not arranged in a natural and beautiful arc, but protrude forward or recess inward, or even overlap each other. The “tiger tooth lip protrusion” is a common crowding. 2, the upper front teeth protrude: commonly known as climbing teeth, that is, the teeth in the front section of the upper dental arch protrude forward, and drive the upper lip up, serious can lead to the lips can not be closed naturally. 3, the lower front teeth protrusion: commonly known as the ground, contrary to the normal bite, the lower front teeth bite in front of the upper front teeth, and drive the lower lip to protrude forward, so that the lower part of the face is “concave face type”, folk called “deflated mouth”. 4, upper and lower teeth protrusion: upper and lower teeth protrude forward at the same time, making the entire lip protrude forward, seriously leading to the upper and lower lips can not be closed naturally, forming “open lips and exposed teeth”.