1. Lawrence F. Andrews observed 120 non-orthodontic patient casts and identified six keys that define normal occlusion: molar relationship, crown angulation, crown inclination, rotations, spaces, and occlusal plane. 2. The six keys provide objective standards to diagnose optimal occlusion and proper treatment planning. They include specifications for the interarch relationship of molars, distal angulation and lingual inclination of crowns, lack of tooth rotations, tight contact points between teeth, and a flat occlusal plane. 3. Achieving all six keys through orthodontic treatment results in optimal occlusion and orofacial harmony according to Andrews' research. The keys establish natural occlusion standards to guide orthodont

1. JOURNAL CLUB
ANDREWS SIX KEYS OF NORMAL OCCLUSION
PREPARED AND PRESENTED BY
DR. MAHIPAL SINGH CHUNDAWAT
JUNIOR RESIDENT I,
DEPT OF ORTHODONTICS,
GOVT. DENTAL COLLEGE ,
KOTTAYAM.
ON

2. ANDREWS SIX KEYS OF NORMAL
OCCLUSION (1972)
Lawrence F. Andrews, D.D.S. San Diego, Calif.

3. Lawrence F. Andrews, D.D.S. San Diego, Calif.
He is the first orthodontist to clarify the
importance of addressing both facial and
dental harmony from the beginning of
treatment to achieve the best facial form and
head and neck function for each patient.
Father of “PRE ADJUSTED BRACKET SYSTEM”

4. •Lawrence F. Andrews is the inventor of the Straight-Wire Appliance System, discoverer of the Six
Keys to Normal (Optimal) Occlusion™, and the Six Elements of orofacial Harmony.
•The Andrews Foundation for Orthodontic Education and Research is an organization dedicated to
the advancement of orthodontic research, teaching, and treatment. It was founded in San Diego,
California in 1970 by Dr. Lawrence F. Andrews.
BACKGROUND

5. STUDY DESIGN
• Observational study.
• Observed in a study of 120 casts of non-orthodontic patients with
normal occlusion.

6. PRINCIPLES
They are:-
Each normal tooth type is similar in shape from one individual to another.
The size of normal crowns within a dentition has no effect on their optimal angulations,
inclination or prominence of their facial surface.
Most individuals have normal teeth regardless of whether their occlusion is flawed or optimal.
Jaws must be normal & correctly related to permit the teeth to be correctly positioned & related.
Dentitions with normal teeth and in jaws that are or can be correctly related can be brought to
optimal occlusal standards.

7. IMPORTANCE OF THE SIX KEYS
• They are a complete set of indicators of optimal occlusion.
• They can be judged from tangible landmarks.
• Proper diagnosis and treatment planning.
• Consistent with nature’s plan aesthetically and functionally.

8. SIX KEYS OF NORMAL OCCLUSION
1. Molar relationship.
2. Crown angulations.
3. Crown inclination.
4. Rotations.
5. Spaces.
6. Occlusal plane

9. KEY 1: INTERARCH RELATIONSHIP
This key consist of seven points:
1. The mesiobuccal cusp of permanent maxillary first molar occludes in
the groove between the mesial and middle buccal cusp of lower
permanent 1st molar.(angle)
2. The distal marginal ridge of the maxillary 1st molar occludes with
mesial marginal ridge of lower 2nd molar.
3. The mesiolingual cusp of the maxillary 1st molar occludes in the central
fossa of the mandibular 1st molar.

10. 4. The buccal cusp of the maxillary premolar have a cusp-embrasure relationship
with the mandibular premolars.
5. The lingual cusp of the maxillary premolar have cusp relationship with lower
premolar.
6. The maxillary incisors overlaps the mandibular incisor.
7. The maxillary canine has a cusp –embrasure relationship with lower canine and
premolar.

11. Improper molar
relationship.
More improved
molar relationship.
Improved molar
relationship.
Proper molar
relationship.

12. • The closer the distal surface of the distobuccal cusp of the upper first
permanent molar approaches the mesial surfaces of the mesiobuccal
cusp of the lower second molar.

13. KEY 2: CROWN ANGULATION
• The gingival portion of the long
axis of all crowns are more
distal than the incisal portion.
• Crown tip is expressed in
degrees, (+) or (-).

14. • The degree of crown tip is the
angle between long axis of the
crown & a line drawn 90 degree
from occlusal plan.
• POSITIVE – when gingival portion
is distal to incisal portion.
• NEGATIVE- when gingival portion is
mesial to incisal portion.
• All the non orthodontic models
had a distal inclination of the
gingival portion of the
crown.(positive reading)

15. KEY 3- CROWN INCLINATION (LABIOLINGUAL OR BUCCOLINGUAL INCLINATION)
• Crown inclination is determined
from mesial or distal perspective.
• Angle form by a line 90 degree to
occlusal plan & a line tangent to
bracket position.
• “POSITIVE” when gingival portion
of tangent line is lingual.
• “NEGATIVE” when gingival portion
of tangent line is labial or buccal.
+7 -7

16. ANTERIOR CROWN INCLINATION
• The contact points move distally in concert with the increase in
positive (+) upper anterior crown inclination.
Improperly inclined anterior
crowns result in all upper
contact points being mesial,
leading to improper occlusion.
anterior crowns are properly
inclined the contact points
move distally, allowing for
normal occlusion.

17. A lingual crown inclination generally occurs in normally
occluded upper posterior crowns. The inclination is
constant and similar from the canines through the
second pre- molars and slightly more pronounced in the
molars.
The lingual crown inclination of normally occluded lower
posterior teeth progres- sively increases from the canines
through the second molars.

18. WAGON WHEEL EFFECTS
For every 4 degree of lingual crown torque there is
1 degree of mesial convergance of the gingival
portion of lateral and central crown, that makes a
ratio of 4:1

19. KEY 4: ROTATIONS
• The teeth should be free of rotations.
• Because if molar rotated, would occupy
more space then normal. So it will create
a situation unreceptive to normal
occlusion.
• If incisor rotated less space.

20. KEY 5 : TIGHT CONTACTS
• Contact points should about unless there is a tooth size discrepancy
in mesiodistal crown diameter.

21. KEY 6 : OCCLUSAL PLANE
• The planes of occlusion found in the non
orthodontic models ranged from flat to slight
curve of spee.
• Andrew believes that a flat plane should be
treatment goal as a form of over treatment
since there is natural tendency for the curve
of spee to deepen with time.

22. BOLTONS ANALYSIS
• TOOTH SIZE ARCH LENTH DISCREPANCE
• Bolton not directly related to tooth size arch length discrepance.
• This analysis is an important analysis to determine the discrepancy in
the mesiodistal width of mandibular and maxillary teeth.
SPACE
AVAILABLE
SPACE
REQUIRED

23. MEASURMENT BOLTON ANALYSIS
LOWER MOLAR
WIDGTH IS MORE
SO THIS MUCH
GAP BETWEEN
ANTERIOR RATIO
AND OVERALL
RATIO

24. CONCLUSION
• Successful orthodontic treatment involve many disciplines, not all of
which are always within our control.
• Compromise treatment is acceptable when patient cooperation or
genetic demands it.
• Achieving the final desired occlusion is the purpose of attending to
the six keys to normal occlusion.