Andrews Six key of occlusion
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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
Andrews Six key of occlusion
- 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.