Andrews Six keys of occlusion

Am J Orthod. 1972 Sep;62(3):296-309

•The of the upper first molar should occlude in the groove between the mesial and medial buccal cusp of the lower first molar.

•The crown of the upper first molar must be angulated so that its occludes with the mesial marginal ridge of the lower second molar.

•The of the upper first molar should occlude in the central fossa of the lower first molar.

distal marginal ridge

Molar interarch relationship

Mesio-distal crown angulation

Labio-lingual crown inclination

No rotations

Tight proximal contacts

Flat occlusal plane(curve of Spee)

Class I Molar relationship

(Andrews,1972)

mesiobuccal cusp

mesiolingual cusp

(Andrews,1972)

Mesio-distal crown angulation

•The gingival part of the long

axis of the crown must be distal

to the occlusal part of the axis.

Molar interarch relationship

Mesio-distal crown angulation

Labio-lingual crown inclination

No rotations

Tight proximal contacts

Flat occlusal plane(curve of Spee)

Anterior:

•The interincisal angle between the crown tangents of the upper and lower incisors is 132o for normal occlusions

Posterior:

•The gingival portions of the teeth are

more pronounced buccally than the

occlusal portions.

(Andrews,1972)

Labio-lingual crown inclinationMolar interarch relationship

Mesio-distal crown angulation

Labio-lingual crown inclination

No rotations

Tight proximal contacts

Flat occlusal plane(curve of Spee)

•In order to achieve correct occlusion, none of the

teeth should be rotated.

•Rotated molars and premolars occupy more space in

the dental arch than normal.

•Rotated incisors may occupy less space than those

correctly aligned.

•Rotated canines adversely affect esthetics and may

lead to occlusal interferences.

(Andrews,1972)

RotationsMolar interarch relationship

Mesio-distal crown angulation

Labio-lingual crown inclination

No rotations

Tight proximal contacts

Flat occlusal plane(curve of Spee)

•If there are no anomalies in the shape of the teeth,

or intermaxillary discrepancies in the mesiodistal

tooth size, the contact points should abut in normal

occlusion.

(Andrews,1972)

Tight proximal contacts

(no spacing)Molar interarch relationship

Mesio-distal crown angulation

Labio-lingual crown inclination

No rotations

Tight proximal contacts

Flat occlusal plane(curve of Spee)

•A normal occlusion has a flat occlusal plane (the

mandibular curve of Spee should not be deeper than

1.5mm).

(Andrews,1972)

Flat occlusal plane

(curve of Spee)Molar interarch relationship

Mesio-distal crown angulation

Labio-lingual crown inclination

No rotations

Tight proximal contacts

Flat occlusal plane(curve of Spee)