Prophylaxis and therapy of dental malpositioning are the tasks of the specialist orthodontal area. Well-formed dentition with the correct number of teeth is called "eugnathic". Deviations are called dysgnathia. Especially the normal number of teeth, regular teeth and regular interrelation of the upper and lower jaws to each other may be modified. Deviations from the ideal form of the jaws and their malformation are also called dysgnathia.

As dysgnathias may occur isolated or in combinations, it would be expedient to structure orthodontal clinical pictures into groups with certain position abnormalities. The following groups will be discussed:

• Narrow jaw (transversal tightness)
• Distal occlusion (enlarged sagittal step)
• Open occlusion
• Deep/closed occlusion
• Lack of space (sagittal tightness)
• Mesial occlusion
• Buccal occlusion/laterognathia
• Excess space
• Missing teeth (aplasia)
• Loss of teeth (trauma, caries)
• Retention and relocation of teeth
• Cleft lip and palate