Questions and Answers
According to Andrews' Six Keys, which of the following is not one of the significant occlusal characteristics?
Protrusion of the upper first permanent molar
What is the relationship between the distal surface of the distal marginal ridge of the upper first permanent molar and the mesial surface of the mesial marginal ridge of the lower second molar according to Andrews' Six Keys?
They contact and occlude
What type of relationship should the mesio-buccal cusp of the upper first permanent molar have with the lower first permanent molar according to Andrews' Six Keys?
It should fall within the groove between mesial and middle cusps of the lower first permanent molar
What type of relationship should the maxillary canine have with the mandibular canine and 1st premolar according to Andrews' Six Keys?
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What is the ideal relationship between the mesio-lingual cusp of the upper first molar and the central fossa of the lower first molar according to Andrews' Six Keys?
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What is the range for a flat curve of Spee according to Andrews' Six Keys?
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What is the average inter-incisal crown angle?
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Which angle is formed by a line which bears 90° to the occlusal plane and facial axis of the clinical crown (FACC) as viewed from the mesial or distal?
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What is the primary goal for the depth of curve of Spee according to the text?
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What causes the lower anterior teeth to be forced back and up according to the text?
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What is the best intercuspation of teeth according to the text?
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What is the correct tooth size according to Bennett & McLaughlin, 1993?
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What does a rotated molar occupy more than normal according to the text?
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"Serious tooth-size discrepancies should be corrected with jackets or crowns" according to the text. Why is this recommended?
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What is the facial axis of molar crowns identified by according to the text?
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What is the goal for the depth of curve of Spee according to the text?
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Study Notes
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.
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