Skeletal changes in cl.ii & cl.iii /certified fixed orthodontic courses by Indian dental academy


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Skeletal changes in cl.ii & cl.iii /certified fixed orthodontic courses by Indian dental academy

  1. 1. Skeletal changes in class II and class III malocclusion INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2.  Skeletal changes.  Why study skeletal changes? -how and where? -how much growth remaining? -in which direction and when growth will express? -what role genetic and environmental factors play? -how we can influence these factors?
  3. 3. “Orthodontics is a 6mm profession.” - Melvin Moss
  4. 4.  Within dentofacial complex, changes in its various parts do not follow similar patterns (Bishara. AJO; Mar ’84).  Meredith – indices of upper face depth to upper face width is practically constant (73%) between 5-11yrs, but average constancy is not in all individuals.  Corresponding indices for lower face increases from 80% at 5yrs to 82% at 11yrs.  Thus changes in facial dimensions and relationships do not proceed at a constant rate in the various parts of the face.
  5. 5. Definitions  Mandibular growth rotations are a reflection of differential growth in the anterior and posterior facial heights.  Growth rotations usually refer to the mandible , maxilla is also shown to rotate during growth. - Houston, 1988.
  6. 6. Terminology – Solow and Houston, 1988  True rotation of the mandible – the rotation of the mandibular body relative to the anterior cranial base as registered by the implants or stable trabecular structures in the mandible – it is the fundamental rotation between the mandible and cranial base.
  7. 7. Terminology – Solow and Houston, 1988  Angular remodeling of the lower border – the angular change of the mandibular line when the mandible is registered on implants or stable mandibular structures.
  8. 8. Terminology – Solow and Houston, 1988  Apparent mandibular rotation – the angular change in the orientation of the mandible’s lower border relative to the cranial base and is the result of true mandibular rotation and lower border remodeling which masks 50% of the true rotation of the mandible – rotation apparent from conventional lateral cephalometric radiograph.
  9. 9. Rotational changes of jaws Condition Bjork Solow, Houston Proffit Rotation of mand. Core relative to cranial base Total rotation True rotation Internal rotation Rot. Of mandr. plane relative to cranial base Matrix rotation Apparent rotation Total rotation Rot. Of mandr. plane relative to core of mand. Intramatrix rotation Angular remodeling of lower border External rotation
  10. 10. The puzzle of growth rotation  Björk & Skieller(1983): concept of intramatrix rotation based on metallic implants in the mandible.  Intramatrix rotation is an expression of remodeling at lower border of the mandible and rotation occurred in the corpus of the mandible. (Dibbets,AJODO:1985 jun.)
  11. 11. Lavergne and Gasson  They contended that the rotation affected the ramus and the gonial angle and, consequently, the length of the condylion pogonion diagonal.  No enlargement & maximal rotation Vs maximal enlargement & minimal rotation.
  12. 12.  The direction of growth of the chin, is absolutely unpredictable from the direction of growth of the condyle. Nevertheless, both of these directions may be described in terms of rotation. (Dibbets).  The phrase growth rotation was introduced by Björk in 1955.
  13. 13. Superimposition of two consecutive tracings of a child's mandible registered upon metallic implants
  14. 14.  Björk divided the rotation phenomenon into the 3 components: 1. Total rotation. 2. Matrix rotation (inferred solely from osteologic considerations). 3. Intramatrix rotation.
  15. 15. Total rotation  The rotation of the mandibular corpus measured as a change in inclination of an implant line in the mandibular corpus relative to the anterior cranial base.
  16. 16. Matrix rotation  A rotation of the soft tissue matrix of the mandible relative to cranial base. The soft tissue matrix is defined by the tangential mandibular line.  Matrix rotation has its center at the condyles.
  17. 17. Intramatrix rotation  The difference between the total rotation and the matrix rotation is an expression of the remodeling at the lower border of the mandible.  It is identified by the change in inclination of an implant or reference line in the mandibular corpus relative to the tangential mandibular line.  The intramatrix rotation has its center somewhere in the corpus.
  18. 18. Intramatrix rotation
  19. 19.  ―Intramatrix rotation'' is based upon the local behavior of sites of deposition and resorption within a single bone during the growth period.  This analysis refers only to one specific element of the head, not to the pattern of growth of the head as a whole.  Intramatrix rotation represents the rotation of the mandibular corpus inside its matrix with a center somewhere in the corpus and not in the condyles.
  20. 20. 3 contentions 1. The mandible "wiggles" within its matrix. 2. This ''wiggling'' is associated predominantly with the corpus but is caused by the growing condyle. 3. Rotation results from, or compensates for, a genetically determined program.
  21. 21.  Lavergne and Gasson, define rotations within the range of the "intramatrix" definition.  They define rotation as "positional" and ''morphogenetic.―  Morphogenetic rotation of the mandible concerns the shape of the mandible itself.  Positional rotation deals with the position of the mandible within the head.
  22. 22.  According to Lavergne and Gasson's reasoning, a maxillary-mandibular sagittal discrepancy is minimized by opening or closing the gonial angle.  The external configuration of the mandible need not change its form or its position within the head in order to allow " intramatrix rotation" of the bony element to occur.  Any depositional or resorptive activity at the periosteum has served to preserve or to maintain the original contours.
  23. 23. Intramatrix rotation
  24. 24.  Growth of the condyle has at least two effects: ''intramatrix rotation" and enlargement.  Every millimeter of condylar growth along the pogonion— condylion diagonal will inevitably enlarge the mandible along that diagonal by 1 mm.
  25. 25.  Björk and Skieller speculate that the "intramatrix rotation" reflected in the rotation of the mandibular corpus relative to the lower border is a result of genetically determined condylar growth (both in magnitude and in direction).
  26. 26.  Lavergne and Gasson, using their own "morphogenetic rotation'' which is essentially the same phenomenon as "intramatrix rotation," postulate that this phenomenon is a compensating mechanism which is capable of enlarging or reducing mandibular length as measured along the condylion-pogonion diagonal.
  27. 27.  Hypothetical construction of two possible divergent patterns of mandibular growth:  a circular growth pattern, resulting only in ''intramatrix rotation" and marked by the absence of actual enlargement of the mandible, and  a linear condylar growth-pattern characterized by the absence of ''intramatrix rotation" but evidencing mandibular enlargement.
  28. 28.  Counterbalancing rotation pertains to circular condylar growth, accompanied by selective coordinated remodeling, which does not contribute to the incremental growth of the mandible.
  29. 29. Forward rotation
  30. 30. Backward rotation
  31. 31. Forward Backward Rotation Rotation typeIII Basal Basal Openbite Deep backward Bite condylar growth
  32. 32. Structural signs of growth rotation/prediction  inclination of the condylar head,  curvature of the mandibular canal,  shape of the lower border of the mandible(antegonial notch indicating a posterior growth rotator),  inclination of the symphysis,  interincisal angle,  interpremolar or intermolar angles, and  anterior lower face height. Björk, 1969
  33. 33. Mandibular remodeling  On average matrix rotation is approximately 50% of total rotation.  At its posterior border the figure is 20% which demonstrates the more efficient ―counter remodeling‖ process. - Solow & Houston, 1988
  34. 34. Direction of rotation  80% of people are ―forwards‖ or anterior rotators, that is with the patient facing right the jaws rotate anti clockwise and are assigned with a negative sign.  20% of the people are ―backwards‖ or posterior rotators. - Björk & Skieller, 1972
  35. 35. Degree of rotation  -15° of ―true rotation‖ occurs on average from age 4years to adulthood which is favorable in class II cases as point B will tend to move forwards as the jaws rotate.  On average the mandible rotates -7° ± 22°  On average the maxilla rotates -2.8° ± 7° Björk and skieller, 1972
  36. 36. Clinical relevance of growth rotations posterior rotation  Increased anterior vertical face height & ―long face appearance‖, with high MMP angle.  Patients become more class II with rotation as point ―B’’ moves backwards.  Increased lower incisor crowding may develop.  Overbite reduces with growth – may progress to a skeletal anterior open bite and progressively retrusive chin.  Excessive posterior rotation and increased lower anterior face height increases need for extractions for arch leveling. Björk and skieller, 1972
  37. 37. Clinical relevance of growth rotations anterior rotation  Overbite deepens with growth rotation & is difficult to reduce, a developing deep overbite and class II/2 incisal relationship.  May mask any slight maxillary antero-posterior growth inhibition achieved with headgear.  May develop increasing lower incisor crowding.  Deep overbite and forward growth rotation will mean slower space closure. Björk and skieller, 1972
  38. 38. Effects of treatment  Intermaxillary elastics, anterior bite planes can produce a temporary posterior rotation. Houston, 1988  Space closure is more favorable in growing patients as about 50% of the closure is due to jaw rotation. Stephens and Houston, 1985
  39. 39.  There is no such single entity as a ―normal‖ facial pattern, and that dentofacial anomalies are in a large measure occasioned by a random combination of facial parts, no one of which is abnormal in size when taken by itself, but each one of which may fit badly with the other parts to produce a condition which may be called dysplasia.
  40. 40. Wylie’s analysis Variables measured by Elsasser and Wylie:  The critical portion of the cranial base is divided into two parts by taking first the distance from the posterior surface of the head of the condyle (calling it glenoid fossa) to the projection of sella, and secondly, from the projection of sella to the pterygo-maxillary fissure.
  41. 41.
  42. 42.  Overall maxillary length is the distance between the projection of pterygomaxillary fissure and anterior nasal spine, and  The anteroposterior position of the maxillary first permanent molar is the distance between pterygomaxillary fissure and the buccal groove of the maxillary first permanent molar as projected to Frankfort.  Overall mandibular length was taken by drawing a line tangent to the lower border of the mandible and projecting to it the most posterior point on the head of the condyle and the most anterior point on the chin.
  43. 43.  Good facial balance obtained if these various facial dimensions were combined in a face as indicated: Dimension Male (mm) Female (mm) Glenoid fossa to sella 18 17 Sella to Ptm 18 17 Maxillary length 52 52 Ptm - 6 15 16 Mandibular length 103 101
  44. 44.
  45. 45.
  46. 46.
  47. 47.
  48. 48.  Class II and Class III relationships, based on mandibular displacement rather than disproportion between facial structures, are not uncommon.  When this method of assessment is applied to cases of mandibular displacement falling into either Class II or Class III the score is usually inconsistent with one which is to be expected from models in centric occlusion.
  49. 49.
  50. 50.
  51. 51.  The assessment of anteroposterior dysplasia is not based upon the relative position of facial parts in either centric or rest, but instead takes each part independently and assesses them with respect to their relative size.  One may expect better results when the dysplasia is localized under ―maxillary length‖ or ―Ptm-6‖ than when it is to be attributed to insufficiency of mandibular length or to excessive length in the cranial base.
  52. 52. Skeletal features – ClassII/1  76% have class II skeletal base, if skeletal class I, incisor relation is usually due to a habit.  Obtuse cranial base angle – mandibular retrognathia.  Longer cranial base – prognathic maxilla.  May have small mandible and large maxilla.  Average or decreased lower face height.
  53. 53. Skeletal features – ClassII/2  Usually skeletal class II base, can be skeletal class I or class III.  Obtuse cranial base angle – mandibular retrognathia.  Longer cranial base – prognathic maxilla.  Maxilla short, broad and forward relative to mandible.  Decreased lower face height.  Decreased gonial angle.  Decreased maxillomandibular plane angle.
  54. 54. Skeletal features – ClassIII  Usually skeletal class III base relationship.  Acute cranial base angle – forward position of mandible.  73% of cases have a large mandible, small maxilla or a combination of both.  Sometimes a short cranial base.  Maxilla short, small and narrow relative to mandible which tends to be broad, therefore, crossbites likely.  Obtuse gonial angle.  Normal or increased MMP angle and lower face height.
  55. 55. Headform and Malocclusion Tendencies Dolichocephalic headform:  Brain – horizontally long & relatively narrow.  Flat basicranium.  Flexure between middle & anterior parts of cranial floor is more open – horizontally longer.
  56. 56. Dolichocephalic head form
  57. 57. Consequences for pattern of face  Whole nasomaxillary complex is placed in a more protrusive position relative to mandible because of forward basicranial rotation.  Horizontally longer anterior & middle segments of cranial floor.  Whole nasomaxillary complex lowered relative to mandibular condyle causing downward and backward rotation of mandible.  Occlusal plane rotates to a downward inclined alignment.
  58. 58.  2 way forward placement of maxilla and backward placement of mandibular corpus – tendency towards mandibular retrusion.  Class II molar position.  Resultant profile – retrognathic.
  59. 59. Open cranial flexure
  60. 60. Retrognathism
  61. 61. Brachycephalic headform:  Rounder & wider brain.  Basicranial floor – upright, more closed flexure.  Decreased anterioposterior dimension of middle cranial fossa.  Horizontally nasomaxillary complex is relatively short.  More posterior placement of maxilla.  Nasomaxillary complex is shorter(A-P) but wider, following the anterior cranial fossa template.
  62. 62. Brachycephalic head form
  63. 63. Closed flexure
  64. 64. Brachycephalic
  65. 65.  Resultant effect is relative retrusion of the nasomaxillary complex & forward relative placement of entire mandible.  Tendency towards prognathic profile.  Class III molar relationship.
  66. 66. Intrinsic compensatory structural features Example:  Retrusive mandible due to open type cranial base flexure (&/or vertically long nasomaxillary complex)  Mandibular ramus can compensate by an increase in its horizontal dimension.  Mandibular arch positioned more anteriorly beneath maxilla establishing class I molar relationship.
  67. 67. Ramal compensation
  68. 68.  Downward placement of dental arch caused by downward-backward mandibular rotation is offset by upward drift of mandibular anterior teeth and downward drift of maxillary anterior teeth (curve of spee).  Facial development is one’s own personal orthodontist. Donald H. Enlow
  69. 69. Horizontally mandibular corpus (b) is short relative to its counterpart, the bony maxillary arch (a), causing mandibular retrusion (probably anterior crowding).
  70. 70. This does not necessarily cause a class II molar relationship, as the posterior parts of upper & lower bony arches can still be properly positioned.
  71. 71. These are relative comparisons between two contiguous parts within the same individual.
  72. 72.  If effective A-P breadth of ramus is narrow relative to its counterpart, which is the effective horizontal dimension of the middle cranial fossa, a mandibular retrusive effect is produced.
  73. 73.  Mandibular arch is in offset position relative to its counterpart, the maxillary arch, because parts behind them are imbalanced.
  74. 74.  Even if upper and lower arches are matched in dimensions, profile is retrognathic.  This is one basic skeletal cause that underlie a class II molar relationship.
  75. 75.  Effective horizontal dimension of ramus is broad relative to middle cranial fossa, or, the cranial fossa is horizontally narrow relative to ramus (either way as this is a relative comparison).
  76. 76.  Effect is mandibular protrusion, due to offset positions between the arches, even though the horizontal dimensions of the arches themselves can match.  This is one of the basic skeletal causes for a class III molar relationship.
  77. 77. Vertically long and short midface
  78. 78.  Vertically long nasomaxillary region.  Mandible as a whole has downward backward alignment.  Effect is mandibular retrusion.  Expression of vertical ramus dimension increases, while horizontal is decreased.
  79. 79.  Thus mandibular arch becomes offset relative to upper arch.  This causes retrognathic profile and class II molar relationship.  Downward inclined mandibular occlusal plane.
  80. 80.  Vertically short midface.  Forward and upward inclined alignment.  Effect is mandibular protrusion.  Arches are offset, molars are in class III relationship.  Occlusal plane has upward inclination relative to vertical posterior maxillary
  81. 81.  Posterior maxillary teeth can drift inferiorly, &/or gonial angle can open (compensatory adjustment) to provide proper occlusal fit.  Otherwise, a posterior open bite results.
  82. 82.  If closed gonial angle – mandibular retrusive effect is produced.  If open gonial angle – mandibular protrusive effect is produced.
  83. 83. Forward or backward inclined middle cranial fossa
  84. 84.  A forward inclined middle cranial fossa has 2 way, maxillary protrusive and mandibular retrusive effect.  Expression of effective horizontal dimension of middle fossa is increased.  Maxilla is offset anteriorly with respect to mandibular
  85. 85.  Midface is lowered causing whole mandible to rock down and back.  Mandibular retrusion results, even though the arch lengths of the upper and lower jaws can have equivalent dimensions.  Class II molar relationship results.
  86. 86.  A backward inclined middle cranial fossa has mandibular protrusive effect.  This contributes to a class III type of molar relationship.  Maxilla is placed backward, and the mandible rotates forward into protrusive position.
  87. 87.  Mandibular occlusal plane is rotated into an upward inclined position.
  88. 88. Deep overbite Morphologic characteristics Dentoalveolar Skeletal
  89. 89. Dentoalveolar deep overbite
  90. 90.  Infraocclusion of molars.  Supraocclusion of incisors.  Growth pattern – average or vertical.
  91. 91. Deep overbite due to infraocclusion of molars  Partially erupted molars.  Large interocclusal space.  Lateral tongue posture and thrust present.  Distance between maxillary and mandibular basal plane and occlusal plane are short.
  92. 92. Deep overbite caused by overeruption of incisors  Incisal margins of the incisors extend beyond the functional occlusal plane.  Molars are fully erupted.  Curve of spee is excessive.  Interocclusal space is small.
  93. 93. Skeletal deep overbite
  94. 94. Skeletal deep overbite  Characterized by the horizontal type of growth pattern.  Short anterior facial height (lower third particularly).  Long posterior facial height.  AUFH:ALFH = 2:3  In skeletal deep overbite ratio is reduced to 2:2.5 or 2:2.8
  95. 95. Skeletal deep overbite  Horizontal cephalometric planes (e.g. SN, Palatal, occlusal, mandibular, etc.) are approximately parallel to each other.  Small interocclusal clearance.
  96. 96. Open bite malocclusion  Simple open bite (Moyers, 1964): tongue thrust causing anterior deformation i.e. anterior open bite. May occur with bilateral narrowing of arch and posterior cross bite.  Complex open bite (Moyers): combined tongue thrust, causing both anterior and posterior open bite. More difficult to treat.
  97. 97. Dentoalveolar open bite  Extent depends on eruption of teeth.  Supraocclusion of molars and infraocclusion of incisors.
  98. 98. Skeletal openbite  Excessive anterior face height (lower third).  Posterior face height (ramus height) is short.  Narrow mandibular base with antegonial notching present.  Narrow and long symphysis.  Short ramus.  Gonial angle (particularly lower section), is large and growth pattern is vertical.
  99. 99. Variations observed  Depending on inclination of maxillary base or palatal plane: 1. Vertical growth pattern with upward tipping of forward end of maxillary base (severe skeletal open bite).
  100. 100. 2. Vertical growth pattern with downward tipping of anterior end of maxillary base (can compensate the open bite).
  101. 101. 3. Horizontal growth direction with an open bite caused by upward and forward tipping of maxillary base. Designated as a decompensated deep overbite by orthodontic practitioners.
  102. 102. Morphology of Mandible A.Orthognathic B.Retrognathic C.Prognathic
  103. 103.  In orthognathic face, ramus and body are fully developed.  Width of ascending ramus is equal to the height of body of mandible.  Condylar and coronoid processes are almost on the same plane.  Symphysis is well developed.
  104. 104.  In prognathic type, the corpus is well developed and wide in the molar region.  Symphysis is wider in the sagittal plane.  Ramus is wide and long.  Gonial angle is acute or small.  Mandible grows horizontally. Or shifting to a horizontal growth direction can be expected in the following years.
  105. 105.  In retrognathic facial type, the corpus is narrow, particularly in the molar region.  Symphysis is narrow and long.  Ramus is narrow and short.  Coronoid process is shorter than the condylar process.  Gonial angle is obtuse or large.  Shifting of the growth pattern in the opposite direction is less likely and produces much less expressivity.
  106. 106. Increments of mandibular base length between 6 and 19 years in patients with class III malocclusions. Broken line – average length.
  107. 107. Increments of maxillary base length between 6 and 19 years in patients with class III malocclusions.
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