1) Mandibular growth rotation (MGR) refers to the complex rotational movements of the mandible that occur during growth due to condylar growth and functional remodeling. MGR can be forward/upward or backward/downward depending on the direction. 2) MGR is influenced by factors like condylar growth, occlusal relationships, and soft tissue influences. It is important to consider a patient's pattern of MGR during treatment planning to determine if extrusive or intrusive mechanics are needed. 3) Forward MGR can contribute to the development of a deep bite skeletal pattern and late lower incisor crowding. Backward MGR can increase lower anterior facial height and cause an

1. 1
Dr. Mohammed Alruby
Mandibular growth rotations
Prepared by:
Dr. Mohammed Alruby

2. 2
Dr. Mohammed Alruby
Definition:
Mandibular growth rotation (MGR): defined by Bjork and coworker as: the complex system of
rotational mandibular movements resulting from condylar growth and functional remodeling that
take place during active growth periods and may proceeds after puberty
N: B:
Mandible consists of core and functional process:
1- Alveolar process: serving in function of mastication
2- Muscular process: serving as muscular attachment
3- Condylar process serving to articulate the bone with the rest of skull
Types of mandibular growth rotation MGR
I- According to direction: Bjork:
1- Forward and upward (counterclockwise) rotation:
This type occurs in most individuals during pre-pubertal and post-pubertal growth, can divided
into:
a- Forward rotation with fulcrum located at the incisal edge of lower incisors, occurs mainly
due to vertical condylar growth
b- Forward rotation with fulcrum located at the premolar area, occurs mainly due to vertical
condylar growth and lack of incisal stop ------ deep bite
2- Backward and downward (clockwise) rotation:
The mandible rotates backward and downward with the fulcrum located near the condyles.
This type is expected in certain pathological condition such as tonsillitis, adenoids, nasal
obstruction or abnormal habits such as tongue thrust, and mouth breathing
II- According to origin: Skiller:
1- Matrix rotation:
The mandible rotates as a whole by the influence of overlying soft tissue matrix, with center of
rotation located at the condyle. This type represents 1/3 of total MGR
2- Intra-matrix rotation:
Usually caused by condylar growth and functional remodeling, the direction of this type is usually
determined from the shape of lower border of mandible. This type represents 2/3 of total MGR
3- Total rotation:
It is the sum of the previous two types
III- Mandibular auto-rotation:
In which the mandible rotates as a whole without change in its morphology ------ clockwise rotation
N: B:
== Mandibular growth rotation is an important phenomenon in human facial growth, however the
changes in vertical height of dentition, the inclination of occlusal plane and subsequent mandibular
rotation during growth are poorly established
== the mandibular growth rotation is associated with occlusal plane rotation, which caused by
greater height increase in the posterior than anterior segment
IV- Other types of rotations:
1- Internal rotation:
Rotation of mandibular core relative to cranial base
Around condyle ------- matrix rotation

3. 3
Dr. Mohammed Alruby
Within body -----------intra-matrix rotation
2- External rotation:
Rotation of mandibular plane relative to the core of mandible and it is produced by surface changes
(Bjork 1969, Bjork and Skiller 1972, Mills 1978, Huston et al 1985)
V- Other types:
1- Forward rotation:
a- Type I forward rotation:
Center at joint that give rise to deep bite
Underdevelopment of anterior facial height
The cause may be occlusal imbalance due to loss of teeth or powerful muscular, may occur at any
age
b- Type II forward rotation:
= Center located at incisal edges of lower anterior teeth due to the combination of marked
development of posterior facial height and normal increase in the anterior height
= posterior part of mandible rotates away from maxilla increasing the height of ramus
= mandibular symphysis swing forward to make the chin more prominent
c- Type III forward rotation:
Center of rotation displaced backward to the level of premolars
Anterior facial height become underdeveloped
Posterior facial height increase
Chin more prominent than type II
Displace the path of eruption of all teeth in mesial direction
Mandibular posterior teeth more upright in relation to maxillary posterior teeth.
2- Backward rotation:
a- Type I backward rotation:
Center at joint, this case when bite raised by orthodontic means as, change inter-cuspal or bite
raising appliance
Increase anterior facial height ------- open bite
Occurs in case of flattening of cranial base or incomplete development of middle cranial fossa as
in oxycephaly.
b- Type II backward rotation:
Center of rotation situated at the most distal occluding molars
The lower incisors become retroclined, this induce crowding in lower anterior teeth
Premolars and molars are inclined forward in relation to the maxillary teeth because of their
proximity to the center of rotation
N: B:
In short face: the rotation also progressively upright the incisors displacing them lingually toward
crowding
In long face: anterior open bite will develop. The rotation of the jaws caries the incisors forward
creating dental protrusion
Mechanisms of mandibular rotation:
1- Displacement type of rotation:
Mandible rotate upward and downward at the condyle pivot
Mandible rotate upward and forward to meet a short mid face or closed basi-cranial flexure, and
it rotate

4. 4
Dr. Mohammed Alruby
Downward and backward to accommodate vertically long mid face and / or open basi-cranial
flexure
2- Remodeling type of rotation:
Remodeling occurs at the angle between corpus and ramus (but not at gonial angle)
The ramus become more upright.
This occurs due to the resorptive and deposit growth processes occurs at the ramus – corpus
junction
Prediction of mandibular growth rotation
Prediction of amount and direction of MGR in the individual pt is very important
consideration in orthodontic treatment planning. As this enable clinician to decide when extrusive
or intrusive mechanics should be used and when environmental factors to be modified.
Bjork introduce a simple method for predicting MGR from single cephalogram, he determines 7
morphologic criteria in the mandible developed as a result of bone remodeling in particular type
criteria forward Backward
Inclination of condylar head Slop forward Straight or slop backward
Curvature of mandibular canal curved Straight
Shape of lower border Curved downward Notch at angle
Inclination of symphysis Slop forward and strong
chin
Slop backward and weak
chin
Inter-incisal angle obtuse Acute
Inter-molar angle obtuse Acute
Inter-premolar angle obtuse acute
Lower anterior facial height Decrease Increase
Clinical consideration of MGR in treatment planning
1- Forward MGR:
a- Forward rotators should be treated as early as possible, treatment should be directed to
correct the incisor relationship and provides proper incisal stop to support the occlusion
during active growth, however the correction of over jet into the adult value is not advisable
at this early age, as this would have an adverse effect on the future mandibular incisor
alignment.
In such instance a maxillary anterior bite plate is recommended to stabilize the anterior
occlusion
b- Posterior extrusive mechanics such as cervical headgear and inter-maxillary elastics
should be considered
c- Functional appliance that affect extrusion of posterior teeth is valuable in treatment as well
as in retention.
d- In the presence of moderate crowding, non-extraction approach such as distalization is
preferable. As extraction tend to close the bite and forward closure is very difficult of steep
cusps distalization tend to open the bite, thus aid in correcting the case
e- Non growing pt often require orthognathic surgery
f- Owing to the hyper active elevators, so high tendency to relapse which require especial
consideration in retention

5. 5
Dr. Mohammed Alruby
g- Natural anchorage is very good
h- Maxillary bite plate is mandatory, and retention in lower arch should be extended until
growth is completed
2- Backward MGR:
a- Special consideration should be given to control the vertical dimension:
- Avoid any extrusive mechanics, select mechanics that help intrusion on posterior teeth
as: high pull head gear, posterior bite blocks, open face activator
- In the presence of crowding, extraction therapy is preferable as it tend to close the bite
b- Anchorage requirement is very high because of higher tendency to anchorage loss
c- Non growing pt often require orthognathic surgery
d- Habit control is the key for success
e- Owing to hypoactive elevator and defect on muscle activity of orofacial musculature, higher
degree of relapse should be expected
f- Retention should be done with part time high pull headgear or functional appliances until
growth is completed. Retention in lower arch should be fixed for unlimited time
Two approaches were recommended for early treatment:
First:
1- If case require extraction, the U and L 1st
premolars should be extracted as it just emerge
to the level of gum
2- High pull chin cup exerting light force (16 ounce/side) should worn at least 12 hours / day.
Anterior open bite is completely closed before the insertion of fixed appliances
3- Full appliance is inserted after the remaining teeth erupt
Second:
1- High pull headgear is used to intrude maxillary posterior teeth
2- After 1st
molars intruded about 2 –3mm, the remaining deciduous teeth is removed to allow
the mandible to close
In both approaches:
Habit braking appliance should be used together with fixed appliance
Retention should be done by using functional appliances such as: Frankel, Mandibular bite block
to control the habit
Hazards of MGR
1- Forward MGR:
a- Contribution to skeletal dysplasia:
= The potential risk for the forward growth rotation during the active growth periods is the
development of skeletal deep bite.
= This is largely influenced by incisor relationship: for example: if there is proper incisor relation
and adequate incisal stop, there will be a great chance deep bite will not develop.
= Bjork reported that, under ideal circumstances, the fulcrum for anterior MGR will located at
incisor, the incisal stop will act as safety valve against deepening the bite
= for any reason there is a lack of incisal stop, the pt develops skeletal deep bite, because the
fulcrum of rotation will move further back to the premolar area
= growth related skeletal deep bite is often developing early and continuous to increase throughout
the active growth

6. 6
Dr. Mohammed Alruby
b- Contribution to dental malposition:
Bjork suggested a role for closing MGR in late lower incisor crowding, he stated that MGR
increase the mesial component of force and causes packing of lower incisor with resultant
retroclination and crowding, this view was supported by Richardson who concluded that, ((the
lower jaw grows forward more than the upper jaw, if the lower incisors were not free to move
forward because of restraining of upper incisors, then it is more likely to become retroclined and
consequent crowded))
2- Backward MGR:
a- Contribution to skeletal dysplasia:
Backward rotation may result in:
- Increase LAFH -------- skeletal open bite
- More posterior position of chin
- Worsen class II pt with associated functional problems such as: tongue thrust, mouth
breathing, weak elevator muscles
These functional problem often complicate treatment and contribute higher percentage of failure
b- Contribution to dental malposition:
Sakuda anf Belfast suggested that, opening rotation of the mandible causes retroclination of lower
incisors while the posterior teeth are not guided distally which lead to the development of crowding
Thanks: