THE SIX KEYS TO NORMAL OCCLUSION seminar.pptx

The study of ideal natural occlusions, serve as a benchmark for successful orthodontic treatment to achieve optimal tooth alignment and function.

1. THE SIX KEYS TO NORMAL OCCLUSION DEPARTMENT OF ORTHODONTICS & DENTOFACIAL ORTHOPEDICS Presented By : DR RAVI RANJAN PGT 1 st YEAR 1 Guided By:- DR. SANTOSH KUMAR (ASSOCIATE PROFESSOR)

2. Dr. Lawrence F . Andrews completed orthodontic training at Ohio State University in 1958. He is the inventor of the Straight-Wire Appliance System and discoverer of the  Six Keys to Normal (Optimal) Occlusion and the Six Elements of Orofacial Harmony. THE SIX KEYS TO NORMAL OCCLUSION LAWRENCE F. ANDREWS, D.D.S. AJO-DO 1972 SEP (296-309 ) 2

3. introduction Six significant occlusal characteristics identified & first reported in 1972 by Lawrence F. Andrews “The six keys to Normal Occlusion ”. These six keys were found to be consistently present in a collection of 120 models of teeth with natural excellent occlusion (“non-orthodontic normal” models). 3

4. The six keys Andrews' Six Keys (1972) to normal (or optimal) are a widely quoted set of static occlusal goals for tooth relationships in the intercuspal position. Interarch Relationships Crown Angulation (Mesiodistal) Crown Inclination (Labiolingual / Buccolingual) Rotations Tight Contacts Occlusal Plane 4

5. 1. INTERARCH RELATION SHIP The distal surface of the distobuccal cusp of upper first permanent molar occluded with the mesial surface of the mesiobuccal cusp of the lower second molar. The mesiobuccal cusp of the permanent maxillary first molar occludes in the groove between the mesial and middle buccal cusps of the permanent mandibular first molar. 5

6. Improper molar relationship. Improved molar relationship. More improved molar relationship. Proper molar relationship. 6

7. 2. Crown Angulation The degree of crown tip is the angle between the long axis of the crown (as viewed from the labial or buccal surface) and a line bearing 90 degrees from the occlusal plane. 7

8. A “plus reading” is awarded when the gingival portion of the long axis of the crown is distal to the incisal portion. A “minus reading” is assigned when the gingival portion of the long axis of the crown is mesial to the incisal portion. 8

9. 3. Crown Inclination Crown inclination is determined by the resulting angle between a line 90 degrees to the occlusal plane and a line tangent to the middle of the labial or buccal clinical crown. 9

10. A + reading is given if the gingival portion of the tangent line (or of the crown) is lingual to the incisal portion. A - reading is recorded when the gingival portion of the tangent line (or of the crown) is labial to the incisal portion. 10

11. Tip and Torque Before continuing to the fourth key to normal occlusion, let us more thoroughly discuss a very important factor involving the clinical i mplications of the second and third keys to occlusion (angulation and inclination) and how they collectively affect the upper anterior crowns and then the total occlusion . 11

12. As the anterior portion of an upper rectangular arch wire is lingually torqued, a proportional amount of mesial tip of the anterior crowns occurs The ratio is approximately 4:l . For every 4 degrees of lingual crown torque, there is 1 degree of mesial convergence of the gingival portion of the central and lateral crowns. 12 The wagon wheel . Anterior arch wire torque negates arch wire tip in a ratio of four to one .

13. 4. Rotations 13 Teeth should be free of undesirable rotations. Rotated molar, would occupy more space than normal, creating a situation unreceptive to normal occlusion.

14. 5. Tight Contacts Contact points should be tight (no spaces). Serious tooth-size discrepancies should be corrected with crowns, so the orthodontist will not have to close spaces at the expense of good occlusion. 14

15. 6. CURVE OF SPEE C urve of spee ( Occlusal plane), depth of curve of Spee ranges from flat plane to slight concave surface ( 0 - 2.5 mm ). A- deep curve of Spee results in a more confined area for the upper teeths creating spillage of the upper teeth progressively mesially and distally. B- A flat occlusion is most receptive to normal occlusion. C - A reverse curve of Spee results excesive room for the upper teeth . 15

16. REFERENCE Straight Wire “The concept and Appliance”- Lawrence F. Andrews. Andrews LF. The six keys to normal occlusion. Am J Orthod . 1972 Sep ;62(3):296-309. doi : 10.1016/s0002-9416(72)90268-0. 16

17. 17