When there is not enough space.

existing spaces between teeth

When the lower teeth are much forward relatively to upper ones.

When the upper teeth almost completely cover the bottom ones.

Crossbite is a change in the occlusion where one or more teeth have a longer buccal or lingual position. For example, the tooth is closer to the lips or tongue more than normal, in relation to the corresponding opposing tooth in the higher or lower arch.

The anterior or lateral opening  area, existing between the upper and lower dental occlusal surfaces, when teeth are “closed”.

When the midline between the maxillary central incisors does not coincide with the midline of the face and / or the midline between the mandibular central incisors.