Mandibular growth rotation (2)/certified fixed orthodontic courses by Indian dental academy


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Mandibular growth rotation (2)/certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. aim of the paper to dispel the controversies around this fundamental concept deals with basic etiology of mandibular growth rotation, effect of various pathologies and orthodontic treatment glimpse of mandibular growth prediction and its clinical utilization
  3. 3. review of literature concept introduced by Lande (1952) Bjork (1955) Odegard (1970) Bjork and Skieller (1972)- dentoalveolar adaptation Lavergne and Gasson (1977)- positional rotation, morphogenetic rotation Bjork and Skieller (1983)- ‘total rotation’, ‘matrix rotation’, ‘intramatrix rotation’ Dibbets (1985)- ‘counter balancing rotation’ for intramatrix rotation
  4. 4. basic terminologies rotation- angular movement of one rigid body relative to another angular change single body change
  5. 5. terminologies true rotation (angle between AA’) apparent rotation (angle between BB’) angular remodeling of the mandibular border (angle between BB’ when AA’ are overlapped)
  6. 6. condition Bjork Solow & Houston Proffit rotation of mandibular core relative to cranial base total rotation true rotation internal rotation rotation of mandibular plane relative to cranial bases matrix rotation apparent rotation total rotation rotation of the mandibular plane relative to core of mandible intra- matrix rotation angular remodel- ing external rotation relation of terminologies
  7. 7. condition Bjork Shudy Solow & Houston anterior growth greater than posterior forward rotation ‘-ve’ clockwise rotation backward rotation ‘+ve’ posterior growth greater than anterior backward rotation ‘+ve’ counter clockwise rotation forward rotation ‘-ve’
  8. 8. example from 4 years to adulthood -150 is internal rotation out of which 25% is matrix rotation (A) and 75% intramatrix rotation (B) 11-120 external rotation so only –(3-40) total rotation or decrease in mandibular plane angle
  9. 9. etiology Differential growth in anterior and posterior facial height posterior facial height- sum of the vertical component of the descent of the middle cranial fossa and growth of the mandibular condyle
  10. 10. cont… anterior facial height- primary determinant is upper cervical vertebral growth, this acts through differential growth in the muscles and fascia that are attached to the mandible and pass to the cranium above and to the hyoid bone and shoulder girdle below
  11. 11. normally occurring mandibular growth rotation forward internal rotation of mandible is greater than the maxilla because vertical condylar growth exceeds growth at the maxillary sutures so mandibular incisors become more upright, mandibular molar moves mesially more compared to maxillary thus mandibular arch length decrease is more and so mandibular anterior crowding
  12. 12. natures compensation dentoalveolar compensation periosteal remodeling by medial pterigoid and masseter
  13. 13. Pathologies affecting rotation digit sucking or extrusion of molars open bite fibrous ankylosis or juvenile rheumatoid arthritis of TMJ factors affecting the adequacy of the nasal airway
  14. 14. Prediction of mandibular growth rotation Riketts (up to 1978) facial axis open 10 -/5 mm of convexity reduction, /3 mm molar correction, /4 mm overbite correction facial axis opens 1- 11/2 0- cross bite correction condyle will move 1 mm/year along DC-Xi Pm will move 2 mm/year along Xi-Pm fixed values are added so less accurate
  15. 15. prediction of mandibular growth rotation Bjork and Skieller (1984) 44 morphological variants 20 variants prognostication lies between 23%-60% stepwise regression leads to 4 variants with 86% prognostication but any variant significance alone is not more than 60% only applicable for extreme cases is disadvantage
  16. 16. four variants inter-molar angle (a) shape of the lower border of the mandible (b) inclination of the mandibular symphysis (c) inclination of mandible (d) (a) (b) (c) (d)
  17. 17. prediction of mandibular growth rotation by Todd Aki and Ram S. Nanda (1994) symphysis ratio=height/width large anterior facial height is produced when large symphysis ratio, receding chin and high mandibular plane angle small symphysis ratio will produce large chin, low mandibular plane, lower facial height men posses stronger relation with symphysis morphology than women
  18. 18. prediction of mandibular growth rotation by Chvatal, Behrents, Ceen & Buschang (2005) longitudinal cephalograms provides information on growth pattern, maturation status, growth velocity, growth potential construction of multilevel model
  19. 19. Contd… horizontal movement of mandible dose not have adolescence growth spurt, vertical growth follows sigmoid growth pattern leads to greater decrease in MPA in childhood & slight increase of Me-0 during adolescence Me-Y is good predictors of all multilevel prediction shown to be valid for independent variables
  20. 20. clinical consideration clockwise rotation induced by orthodontic treatment, particularly associated with the use of class II elastics, anchorage bends and anterior bite plates are often transient.
  21. 21. contd… treatment induced increase in anterior face height exceeds that which would normally have occurred with growth, there will often be a gradual anticlockwise rotation associated with intrusion of teeth under the occlusal forces
  22. 22. contd… clockwise mandibular rotation associated with obstruction leads to changes in head posture to maintain airway, auto correction is always expected after removal of cause
  23. 23. contd… anticlockwise mandibular rotation associated with reduction in anterior face height and deepening of overbite is not a growth rotation- it may follow a treatment which has raised the occlusal plane unduly or it may be a consequence of loss of posterior teeth
  24. 24. effect of class II orthodontic treatment with fixed appliance on mandibular rotation more vertical growth direction of treated cases as compared to untreated cases greater occlusal movement of mandibular molars no great change in mandibular rotation due to treatment
  25. 25. class II case treated with functional appliance posterior and upward growth direction of condyle with clockwise growth rotation of mandible can improve the sagittal discrepancy
  26. 26. treatment of class III patient with chin cup the principle effect of chin cup appliance is downward and backward rotation of mandible (clockwise) so symmetric low mandibular plane angle patient with short normal anterior facial height are preferred
  27. 27. conclusion mandibular growth rotation plays important role in orthodontic treatment planning so mandibular growth prediction becomes equally important currently available data based prediction models are fair but future efforts are needed to establish mandibular growth prediction
  28. 28.