Growth Rotation

GROWTH AND DEVELOPMENT

Growth Rotation

Dr Syed Bazli Alwi B. Syed Bakhtiar

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).

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.

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.

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.

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.

Growth Rotation

1. Total Rotation• The rotation of the mandibul

ar corpus in relation to cranial base.

2. Matrix Rotation

• Change in inclination of the tangential mandibular line

(ML) in relation to S-N line.

Growth Rotation

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

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

Centre of Rotation (Forward Rotation)

Type I• Growth rotation at a ce

ntre located at the condyle.

• Resulting in underdevelopment of anterior facial height.

Centre of Rotation (Forward Rotation)

Type II• Growth rotation at a centr

e located at the incisal edges of the lower anterior teeth.

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.

Centre of Rotation (Backward Rotation)

Type I• Lies in the condyles.• Increase in anterior facial

height.

Type II• Situated at the most distal occluding molars.

Centre of Rotation (Backward Rotation)

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).

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.

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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