Mandibular Growth Rotation (2) / orthodontic courses by Indian dental academy

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aim of the paperto dispel the controversies around this fundamental conceptdeals with basic etiology of mandibular growth rotation, effect of various pathologies and orthodontic treatmentglimpse of mandibular growth prediction and its clinical utilization


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


basic terminologies rotation- angular movement of one rigid body relative to another

angular change single body change


terminologiestrue rotation (angle between AA’)

apparent rotation (angle between BB’)

angular remodeling of the mandibular border (angle between BB’ when AA’ are overlapped)


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


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’

http://catholique-rouen.cef.fr/vie-consacr%E9e/pages/indexbis.htm


example from 4 years to adulthood -150 is internal rotationout 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


etiology Differential growth in anterior and posterior facial heightposterior facial height- sum of the vertical component of the descent of the middle cranial fossa and growth of the mandibular condyle


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


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 maxillarythus mandibular arch length decrease is more and so mandibular anterior crowding


natures compensation dentoalveolar compensation

periosteal remodeling by medial pterigoid and masseter


Pathologies affecting rotation digit sucking or extrusion of molarsopen bitefibrous ankylosis or juvenile rheumatoid arthritis of TMJfactors affecting the adequacy of the nasal airway

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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


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% prognosticationbut any variant significance alone is not more than 60%only applicable for extreme cases is disadvantage


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)


prediction of mandibular growth rotation by Todd Aki and Ram S. Nanda (1994)

symphysis ratio=height/widthlarge 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


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


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 allmultilevel prediction shown to be valid for independent variables


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.


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


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


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


effect of class II orthodontic treatment with fixed appliance on mandibular rotation

more vertical growth direction of treated cases as compared to untreated casesgreater occlusal movement of mandibular molars no great change in mandibular rotation due to treatment


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


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


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 fairbut future efforts are needed to establish mandibular growth prediction

Mandibular Growth Rotation (2) / orthodontic courses by Indian dental academy

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