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Arch forms


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Arch forms

  1. 1. ARCH FORMS
  3. 3. INTRODUCTION The achievement of a stable, functional & esthetic arch form has long been one of the prime objectives of orthodontist from the period of Edward Angle.
  4. 4. SEARCH FOR IDEAL ARCH FORM 1. Bonwill –1885  Tripod shape of lower jaw  Equilateral triangle Base – Condyle to Condyle Sides – Condyle to midline  Bicuspids & molars formed a straight line from cuspid to condyle 2. Hawley
  5. 5. Bonwill -Hawley Arch Formula  Anterior teeth should be made to lie along a circle whose radius equaled their combined widths  Equilateral triangle Base – Intercondylar width  Should be used only as a guide in establishing arch form
  7. 7. 3. Black -1902  Upper teeth are arranged in a semi-ellipse & lower teeth were arranged on a smaller curve.
  8. 8. 4. Broomel -1902 The teeth are arranged in the jaws in the form of two parabolic curves, the superior arch describing the segment of a larger circle than the inferior , as a result of which the upper teeth slightly overhang the lower.
  9. 9. 5. Angle –1907 – Line of occlusion Definition The line with which, in form & position according to type, the teeth must be in harmony if in normal occlusion. • This line resembles parabolic curve but varies due to Race Type Temperament of the individual
  10. 10. LINE OF OCCLUSION •Upper Molar – central fossa Anterior- cingulum •Lower Molar – buccal cusps Anterior –incisal edges
  11. 11. Angle -1907 Bonwill –Hawley Arch form- General approximation of the true line of occlusion Objected the straight line from cuspid to third molar Straight line existed from the cuspid to the MB cusp of the I molar,however, there was a natural curvature needed in the molar region.
  12. 12. 6. Grays Anatomy -1942 Maxillary dental archform- Elliptical curve Mandibular dental archform- Parabolic curve
  13. 13. 7. Chuck, 1934-AO –Ideal arch form Square Round Oval Tapering •BH archform – not suitable for every patient, can be used as a template •Bicuspid region should be wider than the cuspids to prevent excessive expansion of the
  14. 14. 8. Boone AO-1963 Similar superimposition of the BH archform on a mm template. 9. Mac Conaill & Scher 1949 It is impossible for an ellipse & a parabola to meet one another at every point.
  15. 15. Mac Conaill 1949 Catenary curve – Ideal curve of common occlusion Catenary curve is formed by suspending a chain or flexible cable of appropriate length from two points of varying width
  16. 16. Broodie & Lillie 1966 Basic bony arch is established as early as 9.5 weeks in utero & the arch was of a catenary design Scott 1957 Shape of the human arch - Catenary curve
  17. 17. Disadvantage of Catenary curve Does not give a good fit in the II & III molar region
  18. 18. 10. Musich –1973, AJO Catenometer –Device for construction of arch perimeter 11. Brader –1972-AJO Dental arch form was made up of teeth which assume unique positions along a compound curve representing an equilibrium at all points and delimited by the counterbalancing forces of the tongue and circumoral tissues.
  20. 20. Brader arch form The geometry of the dental arch form was best represented by a Trifocal ellipse, with the teeth occupying the portion at the constricted end of the curve.
  22. 22. Brader arch form  Arch guide with 5 arch forms  Selection of proper form –Arch width at the II molars  Maxillary arch form is selected one size larger than the mandibular arch form Drawback – Excessive narrowing in the cuspid region & excessive wear of the incisal portion of the
  23. 23. 12. Rocky mountain Data systems – Computer derived Arch design • Inter molar width • Inter cuspid width • Arch depth • facial type
  25. 25. LINGUAL ORTHODONTICS Mushroom archwire
  27. 27. Functional anatomy Although bone is the hardest tissue in the body, it is one of the most responsive to change when there is an alteration in the musculature. The dental arch form is initially shaped by the supporting bone & following eruption of teeth, by the musculature & intraoral functional
  28. 28. Buccinator mechanism Tongue
  29. 29. Buccinator mechanism
  30. 30. Balance of muscle forces & Arch form •Between the tongue and perioral musculature, there is no balance of force • During swallowing tongue pressures are considerably greater than those exerted by the cheeks & lips
  31. 31. EQUILIBRIUM ???
  32. 32.  Buccal forces operate constantly throughout the day.  Occlusal forces also help to maintain the equilibrium. Dental equilibrium – Dynamic equilibrium Posterior teeth may be moving buccally during swallowing, but the forces of the cheeks return them to a more lingual position, occlusal forces also produce buccolingual
  33. 33. Facial form Vs Arch form  Leptoprosopic – Narrow dental arches  Euriprosopic - Broad, round arches  Mesoprosopic – Average/ parabolic arches
  35. 35. Malocclusion Class II – Narrow & Tapered maxillary arch form - Ovoid mandibular arch form. Class III- Tapered mandibular arch form - Ovoid maxillary arch form.
  36. 36. Stanley Braun et al –AO, 1998 Class II Maxillary arch – Narrower Mandibular arch – width & Depthz Class III Maxillary arch – Arch width Mandibular arch - Arch width Arch
  37. 37. Habits Thumb sucking – Narrow dental arches Tongue thrusting – Narrowing of the maxillary arch
  39. 39. Basic components • The anterior curvature • Inter cuspid width • Inter molar width • Curvature from cuspids to II molars
  40. 40. VARI SIMPLEX DISCIPLINE ARCH FORM •Not based on clinical examination •Result of research by Dr. Garland McElvain
  41. 41. Final arch form •Fitted to the original study model of the mandibular arch • cuspids should not be expanded. • Wax bite of the maxillary arch is examined • Mandibular II molars – toe in
  42. 42. Roth – Tru Arch form •Modified catenary curve •5 separate radii •Over correction concept
  43. 43. MBT ARCH FORMS Arch forms – Tapered [Chuck-1934 ] Square Ovoid MBT - 3 Archforms in early treatment Individual archform in final stages These archforms vary mainly in interPm, intercanine width of 6mm.
  44. 44. TAPERED ARCH FORM •Narrowest intercanine width •Indications narrow arches gingival recession single arch Rx
  45. 45. SQUARE ARCHFORM •Indications Broad arches Buccal uprighting & expansion of post To maintain expansion
  46. 46. OVOID ARCHFORM •Most preferred •Good stability & •Minimum relapse
  47. 47. CUSTOMIZING ARCHWIRES  Done according to the lower arch  Upper archform –3mm wider in all areas After the rectangular HANT wires in approximate form for the patient as determined using the clear template.
  48. 48. PROCEDURE Wax template is molded over the lower arch 19x25 ss arch wire is bent to the indentations Compared with starting lower model Checked for symmetry Xerox copy of the wire is made & stored INDIVIDUALIZED ARCHFORM
  49. 49. 3M UNITEK • Tapered archform –Orthoform I • Square archform –Orthoform II • Ovoid archform -Orthoform III
  50. 50. Nojima et al – AO, 1971 Caucasian sample Japanese sample
  51. 51. The normal variation in arch form, are not reflected in the preformed arch wires presently available & it is important to keep in mind during orthodontic treatment that if preformed arch wires are used, their shape should be considered a starting point for the adjustments necessary for proper individualization. PRE FORMED ARCHWIRES
  52. 52. DIAGNOSIS OF ARCHFORM 1. Clear templates - Early indication TAPERED SQUARE OVOID
  53. 53. 2. Hassan Noroozi et al, AO-2001 Defined arch forms using the following parameters •Inter II molar width •Inter canine width •II molar depth •Canine depth
  54. 54. Square archform Inter canine width/ Inter IImolar width Canine depth / Molar depth Tapered archform Canine depth / Molar depth Intercanine width / Intermolar width
  56. 56. Riedel- 1969 Arch form, particularly in the mandibular arch, cannot be permanently altered during appliance therapy.
  57. 57. Strang , AO- 1949, AJO- 1946 Howes, AJO- 1960 Inter molar width was normally decreased during extraction Rx, however, that if cuspids were moved distally into extraction sites, they could be expanded buccally to limits offered by their new distal
  58. 58. Amott-1962, Arnold-1963,Welch-1956 Bishara AJO-1973 With regard to extraction cases, intermolar width decreased post Rx, but inter cuspid width which retained its original dimension did not show an increased arch width as was previously thought.
  59. 59. Shapiro AJO-1974 Mandibular intercuspid width demonstrated a strong tendency to return to its pre Rx dimension in all groups except cl II, div 2.  Mandibular arch length decreased substantially in every group during post- retention period.
  60. 60. Gardner , AJO-1976 Inter cuspid width was expanded during Rx but had a strong tendency to return to its original pre Rx width in both ext & nonext cases. Inter I pm width showed the greatest Rx increase in width with only a minimal post Rx reduction II pm width for nonext cases showed a significant increase with slight tendency for post- retn
  61. 61. II pm width for ext cases showed a decrease with Rx & a slight continued decrease post- retention Inter molar width Non ext cases –increase in width with Rx Extraction cases – decrease with Rx Post retention - no change
  62. 62. Felton et al, AJO- 1987 70% of the dental arches returned to their original shape during the post Rx period.
  63. 63.  Patients pre Rx arch form appeared to be the best guide for future arch form stability. De La Cruz et al, AJO 1995  Arch form tended to return toward the pre Rx shape after retention & that the greater the Rx change, the greater the tendency for post- retention change.
  64. 64. CONCLUSION The search for an ideal arch form, suitable for every patient, has been an unrealistic goal because of the wide individual variation. The basic principal of arch form in orthodontic Rx is that within reason, the patients original arch form should be preserved. Retention should certainly be an important consideration when original arch form is changed during
  65. 65.