Andrew's six keys to occlusion
Andrews' Six keys of Occlusion is a proposition put forward by Lawrence F. Andrews, which plays an important role in the field of dentistry. In 1970, after a detailed study and research on one hundred and twenty patients, Andrews' six keys of occlusion were put forward. In his proposition, Andrew stated that these six keys are essential for a complete and proper occlusion. These six keys of occlusion are Molar inter-arch relationship, Mesio-distal crown angulation, Labio-lingual crown inclination, Absence of rotation, Tight contacts and Curve of spee.
According to the first key, Molar inter-arch relationship, the upper first molar's mesio-buccal cusp should essentially occlude into the groove, in between the lower first molar's mesial and medial buccal cusp. The first upper molar's mesio-lingual cusp must occlude into the central of lower first molar's fossa.The distal marginal ridge must be occluded with mesial marginal ridge of lower second molar by angulating the upper first molar.
As for the second key, it uses a line that passes from the long axis of the crown via the most important part in the middle of the buccal or labial surface. The line is discussion is known as long axis of the clinical crown.
According to the third key, distal or mesial view determines the crown inclination. It is known as positive crown inclination if the gingival area of crown is lingually placed than the occlusal part.
In fourth key, absence of rotation characterizes normal occlusion. More space is occupied in the dental arch by the rotated posterior teeth. On the other hand, less space is occupied by the rotated incisors.
Fifth key states that there should be tight contact between adjacent teeth to call it a normal occlusion.
And lastly, Andrews states that normal occlusal plane must be flat, with curve of spee not crossing 1.5mm.
See also
- Dental anatomy
- Occlusion (dentistry)