Andrews' six keys to occlusion

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A definition of the optimal occlusion in the permanent dentition as defined by Lawrence F. Andrews in 1972.They have significant clinical implications for routine orthodontic therapy.

Further Reading:

Andrews L. F. The six keys to normal occlusion. Am J Orthod 1972;62:296–309.

Andrews' six keys to occlusion


Molar relationship: the distal surface of the disto-buccal cusp of the upper first permanent molar occludes with the mesial surface of the mesio-buccal cusp of the lower second molar.


Crown angulation (mesio-distal tip): the gingival part of the long axis of the crown is distal to the incisal part of the axis. The extent of angulation varies according to tooth type.


• Crown inclination (labio-lingual, bucco-lingual): the incisors are at a sufficient angulation to prevent overeruption.

• Upper posterior teeth: the lingual tip is constant and similar from canine to second premolar and increased in the molars.

• Lower posterior teeth: the lingual tip increases progressively from the canines to the molar.


Rotations are not present.


There are no interdental spaces.


There is a flat plane of occlusion.

Subjects: Dentistry.

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