Andrews 6 keys /certified fixed orthodontic courses by Indian dental academy


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  • Andrews 6 keys /certified fixed orthodontic courses by Indian dental academy

    1. 1. Andrews’ Andrews’ Six Keys Six Keys of of Normal Occlusion Normal Occlusion
    2. 2. Introduction  There is no of diagnostic way to measure or accurately estimate malocclusion, nor to decide how closely trt. has approached good results, until we first know what normal (good) occlusion is.
    3. 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 (“nonorthdontic normal” models)
    4. 4. Introduction  The keys tell about the characteristic of static occlusion  Ronald H. Roth declared six keys to be “Consistent with desirable function occlusal goals, provided that the occlusal interdigitation occurs with the mandible in centric relation” (Five-Year Clinical Evaluation of the Andrews StraightWire Appliance,1976)
    5. 5. These keys believed by Andrews & others to be :  Consistent with nature’s plan esthetically & functionally.  Attainable in trt. of the great majority of N American orthodontic patients – the estimated 90% or more who present no trt. limiting abnormalities.
    6. 6. Study  A gathering of data (1960 to 1964)  120 nonorthodontic normal models  With the cooperation of Some Orthodontists & general dentists in San Diego University of Illinois (Dr. A..G Brodie )
    7. 7. Teeth of selected models  Never had orthodontic treatment  Were straight and pleasing in appearance  Had a bite which looked generally correct  Would not benefit from orthodontic treatment.
    8. 8. The crowns of Sample  Angle's molar cusp groove concept was validated still.  The molar relationship in these healthy normal models exhibited two qualities when viewed buccally  Angulation (MD tip) and inclination (buccolingual inclination) showed predictable natures as related to individual tooth types.
    9. 9. The crowns of Sample  Teeth had no rotations.  No spaces between teeth.  The occlusal plane was not identical in all models but with a limited a range of variation. Tentative conclusions were reached, and six characteristics were formulated in general terms.
    10. 10. The six keys  The six keys to normal occlusion contribute individually and collectively to the total scheme of occlusion and, therefore, are viewed as essential to successful orthodontic treatment.  Lack of even one of the six is a defect predictive of an incomplete end result in treated models.
    11. 11. Key I. Interarch relationships The nonorthodontic normal models consistently demonstrated that  The distal surface of the distal marginal ridge of the upper first permanent molar contacts and occludes with the mesial surface of the mesial marginal ridge of the lower second molar.
    12. 12. Key I. Interarch relationships
    13. 13. Key I. Interarch relationships  The mesio-buccal cusp of the upper first permanent molar falls within the groove between the mesial and middle cusps of the lower first permanent molar.  The mesio-lingual cusp of the upper first molar seats in the central fossa of the lower first molar.
    14. 14. Key I. Interarch relationships  The premolars enjoy a cusp-embrasure relationship buccally, and a cusp fossa relationship lingually.  Max. canine has a cusp-embrasure relationship with mand. canine & 1st PM. The cusp tip is slightly mesial to embrasure  Max. incisors overlap mand. Incisors & midlines of arches match
    15. 15. Key II. Crown angulation (tip) Facial axis of the clinical crown (FACC)  Best viewed from the labial or buccal perspective  For all teeth except molars, is located at the middevelopmental ridge that runs vertically and is the most prominent portion in the central area of the labial or buccal surface.  The facial axis of molar crowns is identified by the dominant vertical groove on the buccal surface.
    16. 16. Key II. Crown angulation (tip)  Viewed from mesial or distal perspective, the FACC is represented by a line that is parallel to the middevelopmental ridge (or with molars, the dominant groove), and tangent to the middle of the clinical crown on the labial or buccal surface
    17. 17. Key II. Crown angulation (tip) Crown angulation refers to angulation (or tip) of the long axis of the crown, not to angulation of the long axis of the entire tooth.  As orthodontists, we work specifically with the crowns of teeth and, therefore, crowns should be our communication base or referent.
    18. 18. Key II. Crown angulation (tip) Crown Angulation or Crown tip  The degree of crown tip is the angle formed by the FACC and a line perpendicular to the occlusal plane.  A “+ reading" when the gingival portion of the FACC is distal to the incisal portion.  A “- reading" when the gingival portion of the FACC is mesial to the incisal portion.
    19. 19. Key II. Crown angulation (tip) Each normal model had a distal inclination of the gingival portion of each crown, It varied with each tooth type, but within each type the tip pattern was consistent from individual to individual.
    20. 20. Key II. Crown angulation (tip)  Normal occlusion is dependent upon proper distal crown tip, especially of the upper ant. teeth ( longest crowns).  Degree of tip of incisors, determines the amount of MD space they consume & has a considerable effect on post. occlusion as well as ant. esthetics.
    21. 21. Key III. Crown inclination (torque)  Crown inclination angle formed by a line which bears 90°to the occlusal plane and FACC (as viewed from the mesial or distal).  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
    22. 22. Key III. Crown inclination (torque)
    23. 23. Key III. Crown inclination (torque) ANTERIOR CROWN INCLINATION. In upper incisors + crown inclination. In lower incisors - crown inclination The average inter-incisal crown angle - 174°.
    24. 24. Key III. Crown inclination (torque)  Properly inclined anterior crowns contribute to normal overbite and posterior occlusion,  when too straight-up and -down they lose their functional harmony and overeruption results.
    25. 25. Key III. Crown inclination (torque)
    26. 26. Key III. Crown inclination (torque)  If the inclination of the anterior crowns is not sufficient, space, in treated cases, is often incorrectly blamed on tooth size discrepancy.
    27. 27. Key III. Crown inclination (torque) POSTERIOR CROWN INCLINATION— UPPER.  A minus crown inclination for each crown from the U canine through the U-2nd PM.  A slightly more negative crown inclination existed in the U-1st & 2nd molars
    28. 28. Key III. Crown inclination (torque) POSTERIOR CROWN INCLINATION— LOWER. A progressively greater "minus" crown inclination existed from the lower canines through the lower second molars
    29. 29. Tip & torque  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 4:1. For every 4° of lingual crown torque, there is 1 ° of mesial convergence of the gingival portion of the central and lateral crowns.
    30. 30. Tip & torque Wagon wheel
    31. 31. Key IV. Rotations  Teeth should be free of undesirable rotations. Rotated molar, would occupy more space than normal, creating a situation unreceptive to normal occlusion.
    32. 32. Key V. Tight contacts  Contact points should be tight (no spaces).  Persons who have genuine tooth-size discrepancies pose special problems.  Serious tooth-size discrepancies should be corrected with jackets or crowns, so the orthodontist will not have to close spaces at the expense of good occlusion.
    33. 33. Key VI. Occlusal plane (curve of spee)  Depth of curve of spee ranges from flat plane to slight concave surface (0- 2.5 mm)  A flat plane should be a treatment goal as a form of over treatment.  There is a natural tendency for the curve of Spee to deepen with time.
    34. 34. Key VI. Occlusal plane (curve of spee)  L jaw's growth downward and forward sometimes is faster and continues longer than that of the U jaw.  This causes the L ant. teeth,, to be forced back and up,  crowded lower anterior teeth and/or a deeper overbite and deeper curve of Spee.
    35. 35. Key VI. Occlusal plane (curve of spee)  At the molar end of the lower dentition, the 3 rd molars are pushing forward, even after growth has stopped, creating essentially the same results.  If the lower anterior teeth can be held until after growth has stopped and the 3rd molar threat has been eliminated by eruption or extraction, All should remain stable, assuming that treatment has otherwise been proper.
    36. 36. Key VI. Occlusal plane (curve of spee)  Intercuspation of teeth is best when the plane of occlusion is relatively flat There is a tendency for the c.o.s to deepen after trt.  Trt.. the plane of occlusion until it is somewhat flat or reverse to allow for this tendency.
    37. 37. Key VI. Occlusal plane (curve of spee)  A deep curve of Spee results in a more contained area for the U teeth, making normal occlusion impossible.  Only the U- 1st PM is properly intercuspally placed.  The remaining upper teeth, ant. & post. to the 1 st PM, are progressively in error.
    38. 38. Key VI. Occlusal plane (curve of spee)  A reverse c.o.s is an extreme form of over treatment, allowing excessive space for each tooth to be intercuspally placed
    39. 39. Key VII. Correct tooth size  Bennett & McLaughlin  If Andrews’ non orthodontic models have shown tooth size discrepancy, it would have resulted in either spacing or crowding in either of arches, until compensated by tip & torque in ant. segment.  Prior to trt. by Bolton analysis
    40. 40. Key VII. Correct tooth size  Discrepancy may exist prior to trt. but frequently not noticed until the finishing stage  The potential need for interproximal reduction to ↓ tooth size in one arch or restorative procedure to ↑tooth size in opp. arch should be discussed with patient/parents before trt.
    41. 41. Treated occlusion  1150 treated cases of nation's most skilled orthodontists (on display at national meetings) were studied, from 1965 to 1971.  To learn to what degree the 6 keys were present  Whether the absence of any one permitted prediction of other error factors, such as the existence of spaces or of poor posterior occlusal relations.
    42. 42. Treated occlusion  Key I :- In 932 (80 % ) cases distal surface of the U-6 did not occlude with the mesial surface of the mesiobuccal cusp of the L-7.  Key II :- 91% of cases (if angulation of FACC varies more than ± 2°from optimum for that tooth type) – improper MD tip faulty contacts, or post. occ., or spaces. U-2 ,U-3, U-7 frequently undertipped.
    43. 43. Treated occlusion  Key III :- 78% of cases (if inclination of FACC varies more than ±2°from optimum for that tooth type) Insuff. torqued ant.  improper post. occ., or spaces, or ant. overbite Upper pos. also insuff. torqued  Key IV :-67% of cases (if line connecting contact point of crown varies >± 2°) U-6 & teeth adjacent to extn. frequently rotated.
    44. 44. Treated occlusion  Key V :- 43% of cases Extn. Site space due to insuff. closure & spaces due to improper ant. torque most common  Key VI :- 56% of cases excessive curve of spee(> 2.5 mm)
    45. 45. Treated occlusion  A comparison of the best in treatment results (the 1,150 treated cases) and the best in nature (the 120 nonorthodontic normals) revealed differences  This could provide significant insight on how we could improve ourselves orthodontically.
    46. 46. Conclusion  The 120 nonorthodontic normal models differed in some respects, but all shared the six characteristics.  Compromise treatment is acceptable when patient cooperation or genetics demands it, but should not be acceptable when treatment limitations do not exist.
    47. 47.  When possible, six keys should be our measure of the static relationship of successful orthodontic treatment.  Achieving the final desired occlusion is the purpose of the six keys to normal occlusion.
    48. 48. Leader in continuing dental education