Andrews' Six Keys to Normal Occlusion Lecture 7

Andrews' Six Keys

• In Andrews' Six Keys, significant occlusal characteristics do not include rotation.
• The distal surface of the distal marginal ridge of the upper first permanent molar contacts the mesial surface of the mesial marginal ridge of the lower second molar.
• The mesio-buccal cusp of the upper first permanent molar should fit into the embrasure between the lower first permanent molar and the lower second permanent molar.
• The maxillary canine should overlap and guide the mandibular canine and 1st premolar.

Curve of Spee

• The ideal range for a flat curve of Spee is 0-2mm.
• The average inter-incisal crown angle is 130°.
• The facial axis of the clinical crown (FACC) forms a 90° angle with the occlusal plane.
• The primary goal for the depth of curve of Spee is to prevent excessive wear of the teeth.

Tooth Alignment and Size

• If the lower anterior teeth are forced back and up, it is due to an excessive curve of Spee.
• The best intercuspation of teeth is when they fit together like a lock and key.
• According to Bennett & McLaughlin (1993), the correct tooth size is when the mandibular teeth are 0.5-1.5mm smaller than the maxillary teeth.
• A rotated molar occupies more space than normal, causing tooth-size discrepancies.
• Serious tooth-size discrepancies should be corrected with jackets or crowns to prevent future orthodontic problems.
• The facial axis of molar crowns is identified by the long axis of the crown.
• The goal for the depth of curve of Spee is to maintain a smooth, even plane of occlusion.

Test your knowledge of Andrews' six keys to normal occlusion with this quiz based on Dr. Basma alzubaidy's Lecture 7. Explore the concepts of interarch relationships, crown angulation, crown inclination, rotations, contact points, and the curve of Spee.