Andrew’s Six Keys & Skeletal Pattern Awatif, Fatin, Huda, Diyana, Fatimah, Fadhila, Aimi

Andrew’s Six Keys

Andrew’s Six Keys 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

Andrews’Six Keys- Correct Molar Relationship 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

Andrews’Six Keys - Correct Crown Angulation All tooth crowns are angulated mesially

Andrews’Six Keys - Correct Crown Inclination Incisors are inclined towards the buccal or labial surface Buccal segment teeth are inclined lingually

Andrews’Six Keys - No Rotation 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

Andrews’Six Keys - No spacing ( tight proximal contact) 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

Andrews’Six Keys – Flat Occlusal Plane The mandibular curve of spee should not be deeper than 1.5 mm

SKELETAL PATTERN

Skeletal Pattern Anterior-posterior Vertical Transverse

ANTERIOR-POSTERIOR

ANTERIOR-POSTERIOR Patient has to be postured carefully with the head in a neutral horizontal position (Frankfort Plane horizontal to the floor). Sit the patient upright in the dental chair and ask them to occlude gently on their posterior teeth. Look at the patient in profile and identify the most concave points on the soft tissue profile of the upper and lower lips.

Class I Class II Class III The most anterior part of the maxilla and mandible can be palpated in the midline through the base of the lips. Class I Class II Class III 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)

ANTERIOR-POSTERIOR 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

ANTERIOR-POSTERIOR 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

VERTICAL

VERTICAL Different way to assess vertical skeletal pattern Lower anterior face height (LAFH) Frankfort mandibular plane angle (FMPA)

VERTICAL : LAFH

LOWER ANTERIOR FACIAL HEIGHT (LAFH) 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%

LOWER ANTERIOR FACIAL HEIGHT (LAFH) The face can be split into thirds. LAFH (subnasale-menton) should be approximately equal to middle face height (glabella-subnasale)

VERTICAL : FMPA

FRANKFORT MANDIBULAR PLANE ANGLE (FMPA) 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

TRANSVERSE RELATIONSHIP

TRANSVERSE RELATIONSHIP 2 components that should be assessed are : Facial symmetry Arch width

Facial Symmetry 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

Arch Width 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.

References Orthodontics at glance An introduction to Orthodontics Orthodontics. Part 2: Patient assessment and examination I; British Dental Journal 2003; 195:489–493