Skeletal changes in cl.ii & cl.iii /certified fixed orthodontic courses by Indian dental academy

Skeletal changes in class II and
class III malocclusion
www.indiandentalacademy.com
INDIAN DENTAL ACADEMY
Leader in continuing dental education

 Skeletal changes.
 Why study skeletal changes?
-how and where?
-how much growth remaining?
-in which direction and when growth
will express?
-what role genetic and environmental
factors play?
-how we can influence these factors?

“Orthodontics is a 6mm profession.”
- Melvin Moss

 Within dentofacial complex, changes in its various
parts do not follow similar patterns (Bishara. AJO;
Mar ’84).
 Meredith – indices of upper face depth to upper face
width is practically constant (73%) between 5-11yrs,
but average constancy is not in all individuals.
 Corresponding indices for lower face increases from
80% at 5yrs to 82% at 11yrs.
 Thus changes in facial dimensions and relationships
do not proceed at a constant rate in the various parts
of the face.

Definitions
 Mandibular growth rotations are a reflection of
differential growth in the anterior and posterior
facial heights.
 Growth rotations usually refer to the mandible ,
maxilla is also shown to rotate during growth.
- Houston, 1988.

Terminology – Solow and Houston,
1988
 True rotation of the mandible – the rotation of
the mandibular body relative to the anterior
cranial base as registered by the implants or
stable trabecular structures in the mandible – it
is the fundamental rotation between the
mandible and cranial base.

Terminology – Solow and
Houston, 1988
 Angular remodeling of the lower border – the
angular change of the mandibular line when the
mandible is registered on implants or stable
mandibular structures.

Terminology – Solow and Houston,
1988
 Apparent mandibular rotation – the angular
change in the orientation of the mandible’s
lower border relative to the cranial base and is
the result of true mandibular rotation and lower
border remodeling which masks 50% of the true
rotation of the mandible – rotation apparent
from conventional lateral cephalometric
radiograph.

Rotational changes of jaws
Condition Bjork Solow,
Houston
Proffit
Rotation of mand.
Core relative to
cranial base
Total
rotation
True rotation Internal
rotation
Rot. Of mandr.
plane relative to
cranial base
Matrix
rotation
Apparent
rotation
Total
rotation
Rot. Of mandr.
plane relative to core
of mand.
Intramatrix
rotation
Angular
remodeling of
lower border
External
rotation

The puzzle of growth rotation
 Björk & Skieller(1983): concept of intramatrix
rotation based on metallic implants in the
mandible.
 Intramatrix rotation is an expression of
remodeling at lower border of the mandible and
rotation occurred in the corpus of the mandible.
(Dibbets,AJODO:1985 jun.)

Lavergne and Gasson
 They contended that the rotation affected the
ramus and the gonial angle and, consequently,
the length of the condylion pogonion diagonal.
 No enlargement & maximal rotation Vs maximal
enlargement & minimal rotation.

 The direction of growth of the chin, is
absolutely unpredictable from the direction of
growth of the condyle. Nevertheless, both of
these directions may be described in terms of
rotation. (Dibbets).
 The phrase growth rotation was introduced by
Björk in 1955.

Superimposition of two consecutive tracings of a
child's mandible registered upon metallic implants

 Björk divided the rotation phenomenon into
the 3 components:
1. Total rotation.
2. Matrix rotation (inferred solely from osteologic
considerations).
3. Intramatrix rotation.

Total rotation
 The rotation of the mandibular corpus measured
as a change in inclination of an implant line in
the mandibular corpus relative to the anterior
cranial base.

Matrix rotation
 A rotation of the soft tissue matrix of the
mandible relative to cranial base. The soft tissue
matrix is defined by the tangential mandibular
line.
 Matrix rotation has its center at the condyles.

Intramatrix rotation
 The difference between the total rotation and
the matrix rotation is an expression of the
remodeling at the lower border of the mandible.
 It is identified by the change in inclination of an
implant or reference line in the mandibular
corpus relative to the tangential mandibular line.
 The intramatrix rotation has its center
somewhere in the corpus.

Intramatrix rotation

 ―Intramatrix rotation'' is based upon the local
behavior of sites of deposition and resorption
within a single bone during the growth period.
 This analysis refers only to one specific element
of the head, not to the pattern of growth of the
head as a whole.
 Intramatrix rotation represents the rotation of
the mandibular corpus inside its matrix with a
center somewhere in the corpus and not in the
condyles.

3 contentions
1. The mandible "wiggles" within its matrix.
2. This ''wiggling'' is associated predominantly
with the corpus but is caused by the growing
condyle.
3. Rotation results from, or compensates for, a
genetically determined program.

 Lavergne and Gasson, define rotations within
the range of the "intramatrix" definition.
 They define rotation as "positional" and
''morphogenetic.―
 Morphogenetic rotation of the mandible
concerns the shape of the mandible itself.
 Positional rotation deals with the position of the
mandible within the head.

 According to Lavergne and Gasson's reasoning,
a maxillary-mandibular sagittal discrepancy is
minimized by opening or closing the gonial
angle.
 The external configuration of the mandible need
not change its form or its position within the
head in order to allow " intramatrix rotation" of
the bony element to occur.
 Any depositional or resorptive activity at the
periosteum has served to preserve or to maintain
the original contours.

 Growth of the condyle has at least two effects:
''intramatrix rotation" and enlargement.
 Every millimeter of condylar growth along the
pogonion— condylion diagonal will inevitably
enlarge the mandible along that diagonal by 1
mm.

 Björk and Skieller speculate that the "intramatrix
rotation" reflected in the rotation of the
mandibular corpus relative to the lower border is
a result of genetically determined condylar
growth (both in magnitude and in direction).

 Lavergne and Gasson, using their own
"morphogenetic rotation'' which is essentially
the same phenomenon as "intramatrix rotation,"
postulate that this phenomenon is a
compensating mechanism which is capable of
enlarging or reducing mandibular length as
measured along the condylion-pogonion
diagonal.

 Hypothetical construction of two possible
divergent patterns of mandibular growth:
 a circular growth pattern, resulting only in
''intramatrix rotation" and marked by the
absence of actual enlargement of the
mandible, and
 a linear condylar growth-pattern characterized
by the absence of ''intramatrix rotation" but
evidencing mandibular enlargement.

 Counterbalancing rotation pertains to circular
condylar growth, accompanied by selective
coordinated remodeling, which does not
contribute to the incremental growth of the
mandible.

Forward rotation

Backward rotation

Forward Backward
Rotation Rotation
typeIII Basal
Basal Openbite
Deep backward
Bite condylar
growth

Structural signs of growth
rotation/prediction
 inclination of the condylar head,
 curvature of the mandibular canal,
 shape of the lower border of the mandible(antegonial
notch indicating a posterior growth rotator),
 inclination of the symphysis,
 interincisal angle,
 interpremolar or intermolar angles, and
 anterior lower face height.
Björk, 1969

Mandibular remodeling
 On average matrix rotation is approximately
50% of total rotation.
 At its posterior border the figure is 20% which
demonstrates the more efficient ―counter
remodeling‖ process.
- Solow & Houston, 1988

Direction of rotation
 80% of people are ―forwards‖ or anterior
rotators, that is with the patient facing right the
jaws rotate anti clockwise and are assigned with
a negative sign.
 20% of the people are ―backwards‖ or posterior
rotators.
- Björk & Skieller, 1972

Degree of rotation
 -15° of ―true rotation‖ occurs on average from
age 4years to adulthood which is favorable in
class II cases as point B will tend to move
forwards as the jaws rotate.
 On average the mandible rotates -7° ± 22°
 On average the maxilla rotates -2.8° ± 7°
Björk and skieller, 1972

Clinical relevance of growth rotations
posterior rotation
 Increased anterior vertical face height & ―long face
appearance‖, with high MMP angle.
 Patients become more class II with rotation as point ―B’’
moves backwards.
 Increased lower incisor crowding may develop.
 Overbite reduces with growth – may progress to a skeletal
anterior open bite and progressively retrusive chin.
 Excessive posterior rotation and increased lower anterior
face height increases need for extractions for arch leveling.

Clinical relevance of growth rotations
anterior rotation
 Overbite deepens with growth rotation & is
difficult to reduce, a developing deep overbite
and class II/2 incisal relationship.
 May mask any slight maxillary antero-posterior
growth inhibition achieved with headgear.
 May develop increasing lower incisor crowding.
 Deep overbite and forward growth rotation will
mean slower space closure.

Effects of treatment
 Intermaxillary elastics, anterior bite planes can
produce a temporary posterior rotation.
Houston, 1988
 Space closure is more favorable in growing
patients as about 50% of the closure is due to
jaw rotation.
Stephens and Houston, 1985

 There is no such single entity as a ―normal‖
facial pattern, and that dentofacial anomalies are
in a large measure occasioned by a random
combination of facial parts, no one of which is
abnormal in size when taken by itself, but each
one of which may fit badly with the other parts
to produce a condition which may be called
dysplasia.

Wylie’s analysis
Variables measured by Elsasser and Wylie:
 The critical portion of the cranial base is divided
into two parts by taking first the distance from
the posterior surface of the head of the condyle
(calling it glenoid fossa) to the projection of
sella, and secondly, from the projection of sella
to the pterygo-maxillary fissure.

 Overall maxillary length is the distance between the
projection of pterygomaxillary fissure and anterior
nasal spine, and
 The anteroposterior position of the maxillary first
permanent molar is the distance between
pterygomaxillary fissure and the buccal groove of the
maxillary first permanent molar as projected to
Frankfort.
 Overall mandibular length was taken by drawing a line
tangent to the lower border of the mandible and
projecting to it the most posterior point on the head
of the condyle and the most anterior point on the
chin. www.indiandentalacademy.com

 Good facial balance obtained if these various
facial dimensions were combined in a face as
indicated:
Dimension Male (mm) Female (mm)
Glenoid fossa to
sella
18 17
Sella to Ptm 18 17
Maxillary length 52 52
Ptm - 6 15 16
Mandibular length 103 101

 Class II and Class III relationships, based on
mandibular displacement rather than
disproportion between facial structures, are not
uncommon.
 When this method of assessment is applied to
cases of mandibular displacement falling into
either Class II or Class III the score is usually
inconsistent with one which is to be expected
from models in centric occlusion.

 The assessment of anteroposterior dysplasia is
not based upon the relative position of facial
parts in either centric or rest, but instead takes
each part independently and assesses them with
respect to their relative size.
 One may expect better results when the
dysplasia is localized under ―maxillary length‖ or
―Ptm-6‖ than when it is to be attributed to
insufficiency of mandibular length or to
excessive length in the cranial base.

Skeletal features – ClassII/1
 76% have class II skeletal base, if skeletal class I,
incisor relation is usually due to a habit.
 Obtuse cranial base angle – mandibular
retrognathia.
 Longer cranial base – prognathic maxilla.
 May have small mandible and large maxilla.
 Average or decreased lower face height.

Skeletal features – ClassII/2
 Usually skeletal class II base, can be skeletal class I or
class III.
 Obtuse cranial base angle – mandibular retrognathia.
 Longer cranial base – prognathic maxilla.
 Maxilla short, broad and forward relative to mandible.
 Decreased lower face height.
 Decreased gonial angle.
 Decreased maxillomandibular plane angle.

Skeletal features – ClassIII
 Usually skeletal class III base relationship.
 Acute cranial base angle – forward position of
mandible.
 73% of cases have a large mandible, small maxilla or a
combination of both.
 Sometimes a short cranial base.
 Maxilla short, small and narrow relative to mandible
which tends to be broad, therefore, crossbites likely.
 Obtuse gonial angle.
 Normal or increased MMP angle and lower face
height. www.indiandentalacademy.com

Headform and Malocclusion
Tendencies
Dolichocephalic headform:
 Brain – horizontally long & relatively narrow.
 Flat basicranium.
 Flexure between middle & anterior parts of
cranial floor is more open – horizontally longer.

Dolichocephalic head form

Consequences for pattern of face
 Whole nasomaxillary complex is placed in a
more protrusive position relative to mandible
because of forward basicranial rotation.
 Horizontally longer anterior & middle segments
of cranial floor.
 Whole nasomaxillary complex lowered relative
to mandibular condyle causing downward and
backward rotation of mandible.
 Occlusal plane rotates to a downward inclined
alignment.

 2 way forward placement of maxilla and
backward placement of mandibular corpus –
tendency towards mandibular retrusion.
 Class II molar position.
 Resultant profile – retrognathic.

Open cranial flexure

Retrognathism

Brachycephalic headform:
 Rounder & wider brain.
 Basicranial floor – upright, more closed flexure.
 Decreased anterioposterior dimension of middle
cranial fossa.
 Horizontally nasomaxillary complex is relatively
short.
 More posterior placement of maxilla.
 Nasomaxillary complex is shorter(A-P) but
wider, following the anterior cranial fossa
template.

Brachycephalic head form

Closed flexure

Brachycephalic

 Resultant effect is relative retrusion of the
nasomaxillary complex & forward relative
placement of entire mandible.
 Tendency towards prognathic profile.
 Class III molar relationship.

Intrinsic compensatory structural
features
Example:
 Retrusive mandible due to open type cranial
base flexure (&/or vertically long nasomaxillary
complex)
 Mandibular ramus can compensate by an
increase in its horizontal dimension.
 Mandibular arch positioned more anteriorly
beneath maxilla establishing class I molar
relationship.

Ramal compensation

 Downward placement of dental arch caused by
downward-backward mandibular rotation is
offset by upward drift of mandibular anterior
teeth and downward drift of maxillary anterior
teeth (curve of spee).
 Facial development is one’s own personal orthodontist.
Donald H. Enlow

Horizontally mandibular corpus (b) is short
relative to its counterpart, the bony maxillary
arch (a), causing mandibular retrusion (probably
anterior crowding).

This does not
necessarily cause a
class II molar
relationship, as the
posterior parts of
upper & lower bony
arches can still be
properly positioned.

These are relative comparisons between two
contiguous parts within the same individual.

 If effective A-P
breadth of ramus is
narrow relative to its
counterpart, which is
the effective
horizontal dimension
of the middle cranial
fossa, a mandibular
retrusive effect is
produced.

 Mandibular arch is in
offset position
relative to its
counterpart, the
maxillary arch,
because parts behind
them are imbalanced.

 Even if upper and
lower arches are
matched in
dimensions, profile is
retrognathic.
 This is one basic
skeletal cause that
underlie a class II
molar relationship.

 Effective horizontal
dimension of ramus
is broad relative to
middle cranial
fossa, or, the cranial
fossa is horizontally
narrow relative to
ramus (either way as
this is a relative
comparison).

 Effect is mandibular
protrusion, due to
offset positions
between the arches,
even though the
horizontal dimensions
of the arches
themselves can match.
 This is one of the
basic skeletal causes
for a class III molar
relationship.

Vertically long and short midface

 Vertically long
nasomaxillary region.
 Mandible as a whole
has downward
backward alignment.
retrusion.
 Expression of vertical
ramus dimension
increases, while
horizontal is
decreased.

 Thus mandibular arch
becomes offset relative
to upper arch.
 This causes
retrognathic profile
and class II molar
relationship.
 Downward inclined
mandibular occlusal
plane.

 Vertically short
midface.
 Forward and upward
inclined alignment.
protrusion.
 Arches are
offset, molars are in
class III relationship.
 Occlusal plane has
upward inclination
relative to vertical
posterior maxillary line.www.indiandentalacademy.com

 Posterior maxillary
teeth can drift
inferiorly, &/or gonial
angle can open
(compensatory
adjustment) to provide
proper occlusal fit.
 Otherwise, a posterior
open bite results.

 If closed gonial angle –
mandibular retrusive
effect is produced.
 If open gonial angle –
mandibular protrusive
effect is produced.

Forward or backward inclined
middle cranial fossa

 A forward inclined
middle cranial fossa has
2 way, maxillary
protrusive and
mandibular retrusive
effect.
 Expression of effective
horizontal dimension
of middle fossa is
increased.
 Maxilla is offset
anteriorly with respect
to mandibular corpus.www.indiandentalacademy.com

 Midface is lowered
causing whole
mandible to rock down
and back.
 Mandibular retrusion
results, even though
the arch lengths of the
upper and lower jaws
can have equivalent
dimensions.
 Class II molar
relationship results.

 A backward inclined
middle cranial fossa has
mandibular protrusive
effect.
 This contributes to a
class III type of molar
relationship.
 Maxilla is placed
backward, and the
mandible rotates
forward into protrusive
position.

 Mandibular occlusal
plane is rotated into an
upward inclined
position.

Deep overbite
Morphologic characteristics
Dentoalveolar
Skeletal

Dentoalveolar deep overbite

 Infraocclusion of
molars.
 Supraocclusion of
incisors.
 Growth pattern –
average or vertical.

Deep overbite due to infraocclusion
of molars
 Partially erupted molars.
 Large interocclusal space.
 Lateral tongue posture and thrust present.
 Distance between maxillary and mandibular
basal plane and occlusal plane are short.

Deep overbite caused by
overeruption of incisors
 Incisal margins of the incisors extend beyond
the functional occlusal plane.
 Molars are fully erupted.
 Curve of spee is excessive.
 Interocclusal space is small.

Skeletal deep overbite

 Characterized by the horizontal type of growth
pattern.
 Short anterior facial height (lower third
particularly).
 Long posterior facial height.
 AUFH:ALFH = 2:3
 In skeletal deep overbite ratio is reduced to 2:2.5
or 2:2.8

 Horizontal cephalometric planes (e.g. SN,
Palatal, occlusal, mandibular, etc.) are
approximately parallel to each other.
 Small interocclusal clearance.

Open bite malocclusion
 Simple open bite (Moyers, 1964): tongue thrust
causing anterior deformation i.e. anterior open
bite. May occur with bilateral narrowing of arch
and posterior cross bite.
 Complex open bite (Moyers): combined tongue
thrust, causing both anterior and posterior open
bite. More difficult to treat.

Dentoalveolar open bite
 Extent depends on eruption of teeth.
 Supraocclusion of molars and infraocclusion of
incisors.

Skeletal openbite
 Excessive anterior face height (lower third).
 Posterior face height (ramus height) is short.
 Narrow mandibular base with antegonial
notching present.
 Narrow and long symphysis.
 Short ramus.
 Gonial angle (particularly lower section), is large
and growth pattern is vertical.

Variations observed
 Depending on inclination of maxillary base or
palatal plane:
1. Vertical growth pattern with upward tipping of
forward end of maxillary base (severe skeletal
open bite).

2. Vertical growth pattern with downward
tipping of anterior end of maxillary base (can
compensate the open bite).

3. Horizontal growth direction with an open bite
caused by upward and forward tipping of
maxillary base.
Designated as a decompensated deep overbite
by orthodontic practitioners.

Morphology of
Mandible
A.Orthognathic
B.Retrognathic
C.Prognathic

 In orthognathic face, ramus
and body are fully developed.
 Width of ascending ramus is
equal to the height of body of
mandible.
 Condylar and coronoid
processes are almost on the
same plane.
 Symphysis is well developed.

 In prognathic type, the corpus
is well developed and wide in
the molar region.
 Symphysis is wider in the
sagittal plane.
 Ramus is wide and long.
 Gonial angle is acute or small.
 Mandible grows horizontally.
Or shifting to a horizontal
growth direction can be
expected in the following years.

 In retrognathic facial type, the
corpus is narrow, particularly in
the molar region.
 Symphysis is narrow and long.
 Ramus is narrow and short.
 Coronoid process is shorter
than the condylar process.
 Gonial angle is obtuse or large.
 Shifting of the growth pattern
in the opposite direction is less
likely and produces much less
expressivity.

Increments of mandibular base length between 6
and 19 years in patients with class III
malocclusions.
Broken line – average length.

Increments of maxillary base length between 6
and 19 years in patients with class III
malocclusions.

Thank you
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Skeletal changes in cl.ii & cl.iii /certified fixed orthodontic courses by Indian dental academy

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