Growth rotations of the jaws-Orthodontics

1. Dr Zahra Khalid

2.  Facial growth in terms of rotations is
important in terms of understanding the
development of craniofacial complex.
 The introduction of implant method by
Bjork(1955) made it possible to study the
rotations of maxilla and mandible.

3.  Hard palate behind deciduous canines (prior
to eruption of permanent maxillary incisors)
 Below the anterior nasal spine(after eruption
of maxillary incisors)
 Two implants on either side of zygomatic
process of maxilla
 Border between the hard palate and alveolar
process medial to the first molars

5.  Anterior aspect of symphysis
 Two pins on the right side of mandibular
body, one pin under the first premolar and
second under the second premolar or first
molar
 One pin on the external aspect of the right
ramus at the level of occlusal surface of
molars

7.  ROTATION
It is the angular movement of one body
relative to another
 FORWARD ROTATION
Posterior growth greater than anterior
Counterclockwise rotation
Negative rotation

8.  BACKWARD ROTATION
Anterior growth greater than posterior
Clockwise rotation
Positive rotation

10.  INTERNAL ROTATION
Rotation that occurs in the core of the jaw.
e.g in the mandible core is the bone that
surrounds the inferior alveolar nerve
Bjork and Skieller distinguished two
contributions to internal rotation
a)Matrix rotation
b)Intramatrix rotation

12.  MATRIX ROTATION
Rotation around the condyle
 INTRAMATRIX ROTATION
Rotation centered within the body of the
mandible

13. TOTAL ROTATION= MATRIX ROTATION+INTRAMATRIX ROTATION

14.  EXTERNAL ROTATION
Rotations caused by surface changes and
alterations in the rate of tooth eruption.
Surface and remodelling changes in
functional processes of the mandible
 Alveolar process
 Muscular process
 Condylar process

16.  INTERNAL ROTATION
For an average individual with normal vertical
facial proportions, there is about -15 degrees
internal rotation from age 4 to adult life
 Matrix Rotation 25%
 Intramatrix Rotation 75%

17.  EXTERNAL ROTATION
 During the time the core of the mandible
rotates forward an average of 15 degrees, the
mandibular plane angle representing the
orientation of the jaw to an outside observer
,decreases only 2-4 degrees on the average
 The reason that the internal rotation is not
expressed in jaw orientation,of course, is that
surface changes(external rotation) tend to
compensate

18.  This means that the posterior part of the
lower border of mandible must be an area of
resorption, while the anterior aspect of the
lower border is unchanged or undergoes
slight apposition

19. MANDIBULAR
ROTATION
INTERNAL
ROTATION
(-15 º)
INTRAMATRIX
ROTATION
(75%)
MATRIX
ROTATION
(25%)
EXTERNAL
ROTATION
11º-13º

20. INTERNAL
ROTATION
-15º
EXTERNAL
ROTATION
11º-12º
TOTAL
ROTATION
-2º to -4º

21.  INTERNAL ROTATION
Forward and backward
 EXTERNAL ROTATION
Remodelling of palate ,alveolar
process,variations in amount of eruption of
incisors and molars contribute to external
rotation
Opposite in direction and equal in magnitude
to internal rotation

22.  So the two rotations cancel and the net
change in jaw orientation(as evaluated by the
palatal plane) is zero.

24.  Short face type
 Short lower anterior
facial height
 Nearly horizontal
palatal plane
 Low mandibular plane angle
 Deep bite
 Crowded incisors

25.  Long face type
 Excessive lower anterior
facial height
 Negative inclination of
palatal plane
 Increased mandibular
plane angle
 Anterior open bite

26.  Forward rotation of maxilla
Proclination of incisors
 Backward rotation of maxilla
Upright incisors
 Forward rotation of mandible
Upright incisors and crowding
 Backward rotation of mandible
Proclination of incisors