Understanding Normal Occlusion: Andrew’s Six Keys Explained
Write short note on Andrew’s six keys to normal occlusion.
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Write about factors responsible for development of normal occlusion.
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Briefly discuss Andrew’s keys of occlusion.
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Write short note on six keys for normal occlusion.
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Write briefly on Andrew’s six keys of normal occlusion.
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Discuss Andrew’s keys to occlusion.
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Write short note on 6keys for normal occlusion.
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Write short note on Andrew’s six keys of occlusion.
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Write short note on keys to normal occlusion
Answer. Lawrence F Andrew’s six keys of normal occlusion are:\
- Key l: Molar Relationship (lnter-arch Relationship).
- Key 2: Crown Angulations (Mesiodistal Crown Angulations/Mesiodistal Tip).
- Key 3: Crown Inclination (Labiolingual Crown Inclination, the Labiolingual or Buccolingual Torque).
- Key 4: Absence of Rotations.
- Key 5: Presence of Tight Contacts.
- Key 6: Flat Occlusal Plane.
Key 1: Molar Relationship (Interarch Relationship)
- Mesiobuccal cusp of the maxillary fist permanent molar falls within the groove between the mesial and middle cusps of the mandibular fist permanent molar.
- Distal surface of the distal marginal ridge of the maxillary first permanent molar contacts and occludes with the mesial surface of the mesial marginal ridge of the mandibular second permanent molar.
- Mesiolingual cusp of the maxillary fist permanent molar seats in the central fossa of the mandibular fist permanent molar.
Key 2: Crown Angulations (Mesiodistal Crown Angulations/Mesiodistal Tip)
In the normal occluded teeth, the gingival portion of the long axis of each crown is distal to the occlusion portion of that axis. The degree of the angulation varies with each tooth type.
Key 3: Crown Inclination (Labiolingual Crown Inclination, Labiolingual or Buccolingual Torque)
- Angle between a line is 90° to the occlusal plane, as well as a line tangent to the middle of the labial or the buccal surface of clinical crown, which is referred to as crown inclination.
- Lingual crown inclination occurs in maxillary and mandibular posteriors.
- Positive or labial inclination in maxillary incisors.
Key 4: Absence of Rotations
- 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 affct esthetics and may lead to occlusal interference.
- There should be absence of rotation in both of the dental arches to be called as normal occlusion.
Key 5: Presence of Tight Contacts
There should be tight contacts and absence of any spacing. Tight contacts are an essential part to maintain the integrity of any arch form, especially the dental arches.
Key 6: Flat Occlusal Plane
- Curve of Spee should be relatively slight or flt.
- Vertical distance between any tooth and a line joining the most prominent cusp tip of the mandibular molar and central incisor (curve of Spee) should not exceed 1.5 mm.
- An excessive curve of Spee restricts the amount of space available for the upper teeth, which must then move toward the mesial and distal, thus, preventing correct intercuspation.
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