Growth Rotations Divya

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GOOD MORNINGt1

GROWTH ROTATIONSDR. DIVYA SWARUP 1st YEAR

CONTENTS Introduction Terminologies Concepts of Mandibular Rotations Concepts of Maxillary Rotations Tooth eruption and facial development Prediction of growth rotations Clinical implications of Rotations Conclusion3

INTRODUCTION First publication on the growth of the face- 18th century Hunter suggested that mandible lengthens due to resorption of the anterior surface of ramus and deposition posteriorly Growth was studied using stains and inserting metal wires

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Cephalometrics introduced in 1930s Originally used to reveal the anatomy of head Since longitudinal study is possible it was used to test various concepts concerning the mechanisms of postnatal enlargement of head

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Measurements and tracings showed little changes in the facial form

The development in the form of the face was considered static

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With the use of metallic implants as markers it was seen that mandibular corpus rotates during growth but the shape is kept stable by surface remodeling

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Lande in 1952 observed that the lower border becomes less steeply inclined with growth The phrase growth rotation was introduced by Bjork in 1955 Metallic implants were precise markers from which sites and amount of growth and resorption could be found Superimposing two consecutive tracings showed that the older mandible had rotated

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Study began in 1951 It comprised of a study of about 100 children of each sex covering the age period from 4 to 24 years The sample consisted of normal children with and without malocclusion and also children with pathologic conditions

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The mandible can be visualized as consisting of a core of bone surrounding the inferior alveolar neurovascular bundle, and a series of functional processes: the alveolar process, serving the function of mastication; the muscular processes, serving for muscle attachments; and the condylar process, serving to articulate the bone with the rest of the skull

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TERMINOLOGIES 1965-Schudy introduced clockwise and counterclockwise rotation 1969-Bjork discussed different directions of rotation of the mandibular implant line and the relation of these to mandibular form- forward & backward

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Counterclockwise (Schudy) 1965 / Forward rotation (Bjork) 1969

Clockwise (Schudy)1965 / Backward rotation (Bjork) 1969

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1970-Odegard described rotation as the change in the orientation that can occur between implant line and lower border of the mandible

1977-Lavergne and Gasson described the terms Positional and Morphogenetic rotations

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1983-Bjork and Skieller gave the termsTotal rotation Matrix rotation Intramatrix rotation 1985-Dibbets introduced the term Counterbalancing rotation

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1988-Solow,Houston True rotation Apparent rotation Angular remodeling of the lower border Proffit- used the terms Internal rotation Total rotation External rotation16

BJORKRotation of the mandibular core relative to cranial base

SOLOW,HOUSTON

PROFFIT

Total Rotation

True Rotation

Internal Rotation

Rotation of mandibular plane relative to cranial base

Matrix Rotation

Apparent Rotation

Total Rotation

Rotation of mandibular plane relative to core of the mandible

Intramatrix Rotation

Angular Remodeling of lower border

External Rotation

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Total / True / Internal Is the rotation of the mandibular corpus Is measured as a change in inclination of a reference line or an implant line in the mandibular corpus relative to the anterior cranial base

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If line anteriorly rotate towards the face then is known as forward rotating and signated as - i.e. posterior growth > anterior growth If line anteriorly rotate away from the face then is known as backward rotating and signated as + i.e. anterior growth > posterior growth

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Matrix / Apparent /Total Rotation of the soft tissue matrix of the mandible relative to the anterior cranial base Is shown by a tangential mandibular line It can rotate forward and backward in the same patient with condyles as the centre of rotation and is described by the term pendulum movement

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Centre of rotation at the condyle

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Intramatrix / Angular remodeling of lower border / External rotation Rotation of mandibular plane relative to core of mandible It is an expression of remodeling of the lower border of the mandible It is found out by the change in inclination of an implant line or reference line in the mandibular corpus to the tangential mandibular line

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Schematic illustration of "intramatrix rotation." A, Two mandibles superimposed on their external contours. Note divergence of the implant lines indicative of "intramatrix rotation" not reflected in dimensional change or alteration of mandibular contours. B, The same two mandibles superimposed on the implant markers. Note lack of concordance of mandibular contours, indicating extensive remodeling during development.Source: AJO-DO on CD-ROM (Copyright 1998 AJO-DO), Volume 1985 Jun (473 - 480): Puzzle of growth rotation - Dibbets. 24 --------------------------------

Rotation of the corpus inside the soft tissue matrix Centre of rotation some where in the corpus Dependent on the rotation of maxilla and occlusion of teeth

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TOTAL ROTATION

= MATRIX ROTATION + INTRAMATRIX ROTATION

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Forward Rotation

Posterior growth is greater than the anterior growth29

Backward Rotation

Anterior growth is greater than posterior growth30

Positional and Morphogenetic Rotation Introduced by Lavergne and Gasson

Positional Rotation Describes the position of mandible within the head

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Morphogenetic Rotation Concerns the shape of the mandible Superimposition done on line through condylion and pogonion The angle formed between the 2 implant lines-degree of morphogenetic rotation Similar to Bjorks intramatrix but not identical32

REFERENCES Contemporary orthodontics W.R. Proffit Prediction of mandibular growth rotation A. Bjork, AJO, June 1969, pg. 585-599 The puzzle of growth rotation J.M.H. Dibbets, AJO, June 1985, pg. 473-480

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THANK YOUt

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GOOD MORNINGt35

GROWTH ROTATIONSDR. DIVYA SWARUP 1st YEAR

CONTENTS Introduction Terminologies Concepts of Mandibular Rotations Concepts of Maxillary Rotations Clinical implications of Rotations Conclusion

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BJORKS CONCEPT Implant studies show-growth of the mandible occurs essentially at the condyles The anterior aspect of the chin-stable Lower border of the mandibleAt the symphysis-apposition At the angle -resorption

The appositional and resorptive areas may change-determining the type of growth38

The growth of the condyle occurs in a upward and forward curving manner The center of rotation may be located-posteriorly or anteriorly or somewhere in between The center may not always lie at the TMJ

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FORWARD ROTATION THREE TYPES: TYPE I

-center at the TMJ - deep bite - lower dental arch is pressed into the upper - underdevelopment of the anterior face height Cause: Occlusal imbalance due to loss of teeth or powerful muscular pressure41

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Type II

- center at the incisal edges of the lower anterior teeth - posterior face height - anterior face height Increase in posterior face height Lowering of the middle cranial fossa Increased height of ramus

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Increase in ramus height maybe due to vertical growth of the condyle But this vertical lowering manifestes as forward rotation muscular and ligamentous attachments Eruption of the molars keep pace with the rotation

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Type III

- center of rotation is at the premolars - anterior face height becomes underdeveloped when the posterior face height increases - basal deep bite occurs Cause: Anomalous occlusion-large overjets46

BACKWARD ROTATION TWO TYPES: Type I -center at the TMJ -increase in AFH -underdevelopment of the posterior face height occurs-open bite Causes: 1.middle cranial fossa is raised 2.orthodontic bite raising appliance 3.oxycephaly47

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TYPE II

-center at distal most occluding molars -growth in the sagittal direction at the mandibular condyle. The direction of this sagittal growth curves increasingly backward. As the mandible grows in the direction of its length it is carried forward more than it is lowered in the face, and because of its attachment to muscles and ligaments it is rotated backward49

- the eruption of lower molars was hindered-the rotation not due to overeruption

- seen in condylar hypoplasia

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STRUCTURAL SIGNS1. 2. 3. 4. 5. 6. 7. Condylar head inclination Mandibular canal curvature Shape of lower border of mandible Symphysis inclination Interincisal angle Intermolar angle Anterior lower face height52

CONDYLAR HEAD INCLINATION Characteristic sign- Forward or backward inclination of the condylar head

In forward growers backward growers

condyle is upright inclined backward

Is difficult to identify on the lateral cephalogram

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Condylar inclination

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MANDIBULAR CANAL The mandibular canal curvature remains the same throughout the life

Backward growers the curvature of the canal is more than that of the mandibular contour

Forward growers the canal may be flat or less curved

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Mandibular canal inclination56

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