Andrew’s Six Keys & Skeletal Pattern
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Transcript of Andrew’s Six Keys & Skeletal Pattern
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Awatif, Fatin, Huda, Diyana, Fatimah, Fadhila, Aimi
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• The six keys to normal occlusion, serve as a goal
•Can be used to evaluate why good class I occlusion failed to be achieved at the end of treatment
• They are:–Correct molar relationship
–Correct crown angulation
–Correct crown inclination
–No rotations
–No spaces
–Flat occlusal plane
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*The MB cusp of upper first molar occludes with the groove between the MB and middle buccal cusp of lower first molar
*DB cusp of upper first molar contacts the MB cusp of lower second molar
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• All tooth crowns are angulated mesially
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*Incisors are inclined towards the buccal or labial surface
*Buccal segment teeth are inclined lingually
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•None of the teeth should be rotated to achieve normal occlusion•Rotated molars and
premolars occupy more space•Rotated incisors occupy less
space•Rotated canines adversely
affect aesthetics and may lead to occlusal interferences
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*If there is no anomalies in the
shape of the teeth or
intermaxillary discrepancies in
the mesiodistal tooth size, the
contact points should be next
to each other in normal
occlusion
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*The mandibular curve of spee
should not be deeper than 1.5 mm
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*Anterior-posterior
*Vertical
*Transverse
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1. Patient has to be postured carefully with the head in a
neutral horizontal position (Frankfort Plane horizontal
to the floor).
2. Sit the patient upright in the dental chair and ask
them to occlude gently on their posterior teeth.
3. Look at the patient in profile and identify the most
concave points on the soft tissue profile of the upper
and lower lips.
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*Class I: mandible lies 2-3 mm posterior to maxilla. (straight profile)
*Class II: mandible is retrusive to the maxilla. (convex profile)
*Class III: maxilla is retrusive to the mandible. (concave profile)
• The most anterior part of the maxilla and mandible can be palpated in the midline through the base of the lips.
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*Determine the position of
jaw relative to the cranial
base.
*Vertical imaginary line:
through soft tissue nasion in
the neutral head position.
*Zero meridian: represent the
anterior limit of the cranial
base.
*Assess by soft tissue A point
and B point
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• Class I: A point lie 2-3 mm ahead and B point 0-2 mm behind zero meridian
• Class II: B point lie more than 2mm behind zero meridian
• Class III: B point lie ahead than zero meridian
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*Different way to assess vertical skeletal pattern
*Lower anterior face height (LAFH)
*Frankfort mandibular plane angle (FMPA)
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*Is used to assess vertical dimension
*Ratio of the LAFH to the total face height gives an indication if the LAFH is within normal limits
*Facial proportion (LAFH %)
= MxPl to Me x 100
MxPl to Me + MxPl to N
= 55% ± 2%
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*The face can be split into
thirds.
*LAFH (subnasale-menton)
should be approximately
equal to middle face
height (glabella-
subnasale)
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*It measures the relationship between LAFH and posterior face height
• Normal: mandibular and frankfort lines intersect in occipital region
• Increased:anterior to occipital region
• Reduced:posterior to occipital region
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*2 components that should be assessed are :
*Facial symmetry
*Arch width
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•Assessed by constructing a facial midline between soft tissue nasion and middle part of the upper lip at vermillion border
•Chin should be coincident with this line
• If there is assymetry, check for compensatory cant in max.occ plane
• Lateral mandibular displacement can produce facial asymmetry
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*If maxilla is narrow, it will cause crossbite at the buccal segment if there is inadequate dentoalveolar compensation
*Transverse max.discrepancy may exist due to incorrect AP positioning of max/mand.
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*Orthodontics at glance
*An introduction to Orthodontics
*Orthodontics. Part 2: Patient assessment and examination I; British Dental Journal 2003; 195:489–493