Growth Rotation
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Transcript of Growth Rotation
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GROWTH AND DEVELOPMENT
Growth Rotation
Dr Syed Bazli Alwi B. Syed Bakhtiar
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Introduction
• Early cephalometric growth studies show that as the face enlarges progressively, it grows downwards and forwards.
• The direction of growth is curved, giving a rotational effect (Bjork,1983).
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Introduction
• Growth rotation on the maxilla:- effects are small.- almost completely masked by surface remodelling.
• Growth rotation on the mandible:- effects are significant.- vertical dimension.- determine the ratio of the posterior to anterior facial heights.
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Introduction
• Factors affecting the growth of the posterior facial height:
- direction of growth at the condyles.
- vertical growth at the spheno-occipital synchondrosis.
- masticatory musculature at the ramus.
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Introduction
• Factors affecting the growth of the anterior facial height:
- eruption of teeth.
- vertical growth of the soft tissues, suprahyoid musculature and fasciae, spinal column.
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Introduction
• Forward growth rotations are more common than backward growth rotations.
• Average - mild forward rotation which produces a well-balanced facial appearance.
• ↑ Forward growth rotation, ↓ anterior vertical facial proportions, ↑ overbite.
• Treatment plan considerations eg. Class II malocclusion will be helped by a forward growth rotation.
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Growth Rotation
1. Total Rotation• The rotation of the mandibul
ar corpus in relation to cranial base.
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2. Matrix Rotation
• Change in inclination of the tangential mandibular line
(ML) in relation to S-N line.
Growth Rotation
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3. Intramatrix Rotation• Change in inclination of a reference line in the corpus rel
ative to the ML (difference between total and matrix rotations).
• Reflects bony remodelling on the lower border of the mandible.
Growth Rotation
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Centre of Rotation
Forward/Anterior/Anti-clockwise rotation:• Condylar head• Lower premolars• Lower incisal edges
Backward/Posterior/Clockwise rotation:• Condylar head• Distal occluding molars
Bjork, 1969
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Centre of Rotation (Forward Rotation)
Type I• Growth rotation at a ce
ntre located at the condyle.
• Resulting in underdevelopment of anterior facial height.
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Centre of Rotation (Forward Rotation)
Type II• Growth rotation at a centr
e located at the incisal edges of the lower anterior teeth.
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Centre of Rotation (Forward Rotation)
Type III• Centre of rotation at the p
remolar area.• Anterior facial height bec
omes underdeveloped when the posterior facial height increases.
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Centre of Rotation (Backward Rotation)
Type I• Lies in the condyles.• Increase in anterior facial
height.
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Type II• Situated at the most distal occluding molars.
Centre of Rotation (Backward Rotation)
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Consequences of Excessive Rotation of Mandible
Short Facial Height:• Excessive forward rotation of mandible.• Reduced lower anterior facial height (LAFH), prominence
of chin point, deep overbite and incisors rotate toward the palate.
Long Facial Height:• Excessive backward rotation of mandible.• Increased LAFH, reduced lip competence, reduced the p
rominence of chin point, reduction of overbite/anterior open bite (AOB).
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Consequences of Excessive Rotation of Mandible
Altered Chin Prominence:• Backward rotation tends to decrease the prominence of chin point w
hereas forward rotation increases chin prominence.
Path of Incisors Eruption:• Backward rotation generates more anterior path of eruption whereas
forward rotation generates upright path, incisors crowding and reduction of arch length.
Relapse in Orthodontic treatment:• Backward rotation of mandible results in downwards and backwards
rotation of the incisors with a consequent relapse of anterior open bite and overjet correction. Forward rotation can result in relapse in deep overbite correction.
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References
1. Bjork, A. and Skieller, V. (1983). Normal and abnormal growth of the mandible. A synthesis of longitudinal cephalometric implant studies over a period of 25 years. European Jounal of Orthodontics, 5, 1-46.
2. Mitchell, L., Littlewood, S.J., Doubleday, B., and Nelson-Moon, Z.L. (2007). An Introduction To Orthodontics, 3rd edn, Oxford.
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THANK YOU