Andrew’s six keys of occlusion Key 1 : Molar relation Mesiobuccal cusp of upper 1 st molar rests in the mesiobuccal groove of lower 1 st molar. Distal surface of the distobuccal cusp of upper 1 st molar should occlude with mesial surface of the mesiobuccal cusp of lower 2 nd molar Mesiolingual cusp of the upper 1 st molar should occlude in the central fossa of lower 1 st molar. Key 2 :Crown angulations(Tip) The gingival portion of the long axis of each crown should be distal to the incisal portion. Measured by the inclination of long axis of the crown to a line perpendicular to the occlusal plane. Key 3 :Crown inclinations (Torque) Determined by the resulting angle between a line perpendicular to the occlusal plane and one tangent to the middle of the labial or buccal clinical crown. Maxillary and mandibular anteriors :+ve inclination(labial) Maxillary and mandibular posteriors : -ve inclination(lingual) Key 4:Rotation Absence of rotation( arch should be devoid of any rotated tooth) A rotated incisor occupies less space. A rotated molar occupies more mesiodistal space. Key 5 :Interproximal contact Proximal contacts should be tight. Absence of spacing. Key 6:Curve of Spee Flat curve of spee is most receptive for normal occlusion. Deep curve results in more crowding. Reverse curve results in spacing. Key 7: Bolton’s discrepancy The sum of the mesio-distal dimension of the lower teeth must be equal to 91% of the sum of the mesio-distal dimension of the upper teeth. The presence of a tooth size discrepancy between the maxillary and mandibular dental arches would otherwise result in either crowding or spacing, or compensatory angulations or inclination of the anterior teeth.
Andrews six keys of occlusionKey 1 : Molar relationMesiobuccal
cusp of upper 1st molar rests in the mesiobuccal groove of lower
1st molar.Distal surface of the distobuccal cusp of upper 1st molar
should occlude with mesial surface of the mesiobuccal cusp of lower
2nd molarMesiolingual cusp of the upper 1st molar should occlude in
the central fossa of lower 1stmolar.
Key 2 :Crown angulations(Tip)The gingival portion of the long
axis of each crown should be distal to the incisal portion.Measured
by the inclination of long axis of the crown to a line
perpendicular to the occlusal plane.Key 3 :Crown inclinations
(Torque)Determined by the resulting angle between a line
perpendicular to the occlusal plane and one tangent to the middle
of the labial or buccal clinical crown.Maxillary and mandibular
anteriors :+ve inclination(labial)Maxillary and mandibular
posteriors : -ve inclination(lingual)Key 4:RotationAbsence of
rotation( arch should be devoid of any rotated tooth)A rotated
incisor occupies less space.A rotated molar occupies more
mesiodistal space.Key 5 :Interproximal contactProximal contacts
should be tight.Absence of spacing.
Key 6:Curve of SpeeFlat curve of spee is most receptive for
normal occlusion.Deep curve results in more crowding.Reverse curve
results in spacing.Key 7: Boltons discrepancyThe sum of the
mesio-distal dimension of the lower teeth must be equal to 91% of
the sum of the mesio-distal dimension of the upper teeth.The
presence of a tooth size discrepancy between the maxillary and
mandibular dental arches would otherwise result in either crowding
or spacing, or compensatory angulations or inclination of the
anterior teeth.
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