GROWTH AND DEVELOPMENT OF MANDIBLE

1. PRE-NATAL AND POST-NATAL
DEVELOPMENT OF MANDIBLE
JB
PG 1ST YEAR MDS
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2. INTRODUCTION
 The mandible is an osteological component of the viscerocranium, the lower
face and the oral apparatus.
 It has an important anatomic and functional role to play and its growth and
development and the effect, treatment can have on its development and
function is of crucial importance to the clinician.
 Mandibular development provides the basis for normal occlusion relationships
and significant masticatory forces.
 The growth of the mandible occurs in parallel with that of the nasomaxillary
complex and dentition. This reciprocal growth is necessary if proper occlusion
is to be achieved.
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4. EMBRYOLOGY AND PRENATAL
DEVELOPMENT
 Mandible develops bilaterally within the mandibular processes of the first
branchial arch, where it is preceded by Meckel’s cartilage.
 Each embryonic mandibular process contains the rod like cartilaginous
Meckel’s cartilage core, and it accompanies inferior alveolar artery, vein and
nerve.
 MC takes no direct part in the formation of the corpus of the mandible.
 Proximally, MC articulates with the cartilaginous cranial base in the petrous
region of the temporal bone.
 It completely disappears by approximately 24 weeks gestation
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5. DEVELOPMENT BY
INTRA-MEMBRANOUSOSSIFICATION
 By 6 weeks’ gestation, a center of ossification appears in the
perichondrial membrane lateral to Meckel’s cartilage.
 The mandible develops and subsequently grows by means of
intramembranous ossification and not through endochondral
ossification and replacement of Meckel’s cartilage.
 Intramembranous ossification of the body of the mandible
proceeds distally toward the mental symphysis and proximally
up to the region of the mandibular foramen.
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MC
M
MST

6.  The spread of membrane bone encloses the mental nerve in a groove and forms a plate
extending laterally to the inferior alveolar nerve.
 The groove containing the mental nerve becomes the mental foramen by the extension of
bone over the nerve.
 With the formation of bone over the incisive nerve, the incisive canal is formed.
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7.  The ramus of the mandible develops by a rapid spread of ossification
posteriorly into the mesenchyme of the first arch, turning away from
Meckel’s cartilage. This point of divergence is marked by the lingula..
 Bone formation spreads backwards, resulting in a plate lateral to the
inferior dental nerve. At this stage, the developing dental lamina is
remote from the bone of the mandible.
 The tooth germs become enclosed in a trough which is later divided by
septa extending mediolaterally to form crypts or alveoli.
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8.  The bone of the two halves of the mandible comes into close relationship
in the midline where they are separated by fibrous tissue to form a
symphysis in which nodules of the remnants of Meckel's cartilage may be
seen until birth.
 Complete bony union to form a synostosis is not complete until the end
of the first year after birth.
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9. DEVELOPMENT OF SECONDARY
CARTILAGES
 By approximately 10 ‐12 weeks gestation, secondary cartilages appear.
These are the symphysial, angular, coronoid and condylar cartilages.
 The symphysial and coronoid cartilages disappear before birth.
 The most important cartilage in relation to the development and growth of
the mandible is the condylar cartilage.
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10.  By approximately 8 weeks’ gestation, the condylar
process appears as a separate carrot-shaped
blastema of cartilage.
 Formation of the joint cavity between the condylar
process and the squamous portion of the temporal
bone is essentially completed as the TMJ by about
12 weeks’ gestation.
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CONDYLAR CARTILAGE CC
MCC

11.  As the cartilage comprising the mandibular condyle arises “secondarily”
within a skeletogenic membrane and apart from the primary embryonic
cartilaginous anlagen, it is referred to as a secondary cartilage.
 Secondary cartilage has the characteristics of both intramembranous bone
and certain histologic and functional features of hyaline growth cartilage.
 Secondary cartilage is formed in areas of precocious stresses and strains
within intramembranous bones, as well as in areas of rapid development and
growth of bone.
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12.  The condyle grows rapidly at its distal end both appositionally and
interstitially.
 By 14 weeks, endochondral ossification is taking place.
 condylar cartilage is converted quickly to bone by endochondral
ossification, so that at 20 weeks only a thin layer of cartilage remains
in the condylar head.
 Histologic analysis of the human TMJ has demonstrated progressive
changes in the thickness of cartilage and as such the growth activity of
the condyle cartilage throughout development.
 These changes appear to be coordinated with functional changes
associated with occlusal development.
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13. HISTOMORPHOLOGY OF THE GROWING
CONDYLE
 The secondary cartilage composing the condyle during growth
can be divided into two general layers: an articular layer and
a growth layer.
 The more superficial articular layer is continuous with the
outer fibrous layer of the bilaminar periosteum encapsulating
the condylar neck and temporal bone, respectively.
 A subarticular growth layer, the growth layer of the condylar
cartilage is organized into an additional series of layers or
zones typical of growing cartilage that blend into each other.
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14.  The mandibular condylar cartilage was initially considered to be a growth
center with an intrinsic capacity for tissue‐separating growth. However, it is
now generally understood that growth of the mandibular condylar cartilage is
highly adaptive and responsive to growth in adjacent regions, particularly the
maxilla.
 Petrovic and colleagues developed a “cybernetic” model of mandibular
growth regulation referred to as the “servosystem hypothesis of mandibular
growth”
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15. SERVOSYSTEM HYPOTHESIS OF MANDIBULAR
GROWTH
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16. PRE-NATAL REMODELLING OF THE
MANDIBLE
 The fetal mandible initially has outside surface that are entirely depositary in
character.
 At about 10 weeks, however, resorption begins around the rapidly expanding
tooth buds and is present thereafter.
 By 13 weeks, distinct resorptive fields are becoming established:
• on the buccal side of the coronoid process,
• on the lingual side of the ramus, and
• on the lingual side of the posterior part of the corpus.
• The anterior edge of the ramus is already resorptive,
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17.  The posterior border is depository.
 By 26 weeks, the basic growth and remodelling pattern that continues into
postnatal development is seen except, notably, in the incisor region.
 In the fetal and early postnatal mandible, the entire labial side of the
anterior part of the corpus is depository.
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18. ANATOMY OF MANDIBLE
Each half of the mandible is characterized anatomically by:
 a condyle, which articulates with the temporal bone to make up the TMJ;
 a ramus, which extends roughly vertically‐inferiorly from the TMJ and
provides insertions for the muscles of mastication; and
 a corpus, or body, which extends roughly horizontally anteriorly to provide a
base for the mandibular dental arch and house the inferior alveolar
neurovascular bundle.
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19. FUNCTIONAL UNITS
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The anatomic structures of the mandible can also be considered in terms of 5 overlapping
functional units.

20. 1. The mandibular condyle is closely related to the articular function of the TMJ and movements of
the mandible. At the same time, the condylar cartilage also plays a significant role in mandibular
growth.
2. The gonial region of the mandible, at the inferior aspect of the ramus, is related to the function
of the masseter and medial pterygoid complex of muscles.
3. The coronoid process is primarily related to the temporalis muscle.
Variation in the growth and form of each of these regions is due in large part to variation in the
function of the muscles of mastication.
4. The alveolar process of the mandible functions to provide support for the dentition.
5. The body of the mandible, extending from the mandibular foramen to the mental process,
provides support and structural connection between the various functional components of the
mandible.
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21. POST-NATAL DEVELOPMENT OF
MANDIBULAR GROWTH
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22. POST-NATAL DEVELOPMENT OF
MANDIBULAR GROWTH
 The mandible, at birth is small, with short ramus,
large gonial angle, and flat mandibular fossa with
no articular eminence. The condyles are at the
level of the occlusal plane.
 It appears as if mandibular growth is forward and
downwards, and as such one could suppose that
the mandible enlarges by growth at the anterior
end.
 Studies by Brash and Brodie, has however shown
that growth mainly happens in a posterior
direction, with forward and downwards
displacement.
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23.  Growth of the mandible was thought to occur principally by growth at
condyle. Superior and posterior growth of condyle presses against the glenoid
fossa/ cranial base providing an anterior thrust to displace the lower jaw
forward (similar to growth of maxilla).
 The concept of posterior growth and anterior displacement leads to primary
displacement.
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24. THE CONDYLAR HEAD
The cartilaginous covering on the condyle serves a dual function:
1. It represents an articular cartilage (although covered by a fibrous membrane),
and
2. It functions as a growth cartilage.
 The condyle is a major site of growth involved in the upward and backward
elongation of the ramus, in combination with coordinated growth activity by
the periosteum and endosteum in cortical parts of the condyle, neck, and
ramus.
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25.  The condylar growth mechanism represents a means for providing direct
linear growth in a field involving pressure, and it is a composite of articular
endochondral (pressure adapted) growth and membranous (cortical) growth.
 The endochondral and membranous growth are mutually interdependent
processes of enlargement and produces a movement of the entire condyle
that results in the elongation of the ramus.
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26. CONDYLAR NECK
 As growth progresses, bone from one level in the
condyle‐upper ramus region, gets incorporated into
the next level lower down.
 In sequence: Condylar head parts incorporated into
new upper Condylar neck >> Upper parts of the
neck undergo remodelling conversion into the new
lower parts >> The lower portions receive direct
remodelling changes into the ramus proper.
 The condylar head is much broader than the neck
beneath it. Because the neck is sequentially
derived from the head by remodelling, a marked
reduction in width takes place.
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27.  The growth and remodelling processes in the condylar
neck follow the V principle. New bone is added to the
inner side of the V ‐shaped neck while bone is removed
from the outer (periosteal) surface at the same time.
The V mechanism of remodelling provides three simultaneous
growth functions.
1. It moves the entire structure in a progressive course
toward its free (wide) end,
2. Second, it produces an overall enlargement of the whole
V‐shaped region proportionate to the increasing size of
the mandible as a whole.
3. Third, it results in a sequential reduction of the tapering
wide part of the head and neck into more narrow areas .
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28. THE POSTERIOR MARGIN OF
THE RAMUS
 As the condyle moves obliquely in a posterior and
superior direction, the posterior border of the ramus
becomes lengthened vertically.
 At the same time, it receives proportionate additions of
bone along its entire backward facing margin, keeping
pace with the posteriorly moving condyle.
 This process involves rapid deposition of relatively large
amounts of new fine cancellous, nonlamellar bone
because it produces one of the dominant growth
movements in the mandible.
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29. THE SIGMOID NOTCH
 An outward periosteal reversal occurs on the antero-
lingual side of the neck so that a zone of periosteal bone
extends downward from a level just below the condylar
head. This periosteal reversal on the anterior face of the
neck takes place much higher than on the buccal side.
 Periosteal bone is added onto the lingual surface of the
ramus in the region just below the sigmoid notch. These
periosteal deposits continue down from the condylar
head around the lingual side of the sigmoid notch
 This results in a shift of the anterior base of the neck in a
lingual direction. This surface faces lingually and
cephalically
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30. THE CORONOID
PROCESS
 To produce a backward movement of the
ramus in toto, it is apparent that its anterior
margin, including coronoid process, must
undergo progressive removal.
 The basal part of the process moves laterally,
but the forward portion of each base shift
toward the midline as it joins the mandibular
body.
 These complex, multidirectional growth
movements all occur simultaneously.
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31.  Note also that the greater portion of the lingual face of the process is
depository, and that its cortex is composed of periosteal bone.
 The entire buccal surface, however, is resorptive in nature, and the
inward growing cortex on this side of the coronoid process is composed
of endosteal bone.
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32. Schematic showing the V‐principle of
growth of the Coronoid process.
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• the two coronoid processes become larger and higher and that they grow farther apart at
their apices (3)
• by additions on the lingual surface (4’)
• with contralateral removal from the buccal side (4).
• this same mechanism of lingual deposition brings their bases toward each other (5).

33. BUCCAL SIDE OF THE RAMUS
 The upper part of the mandibular ramus on its lateral
side possesses a resorptive periosteal surface. Its cortex
is of endosteal bone, continuous with the condylar neck,
the sigmoid notch, and the coronoid process on their
lateral (buccal) sides.
 A reversal occurs on a line marked by the prominent
change in contour along the ridge that projects downward
from the neck across the upper portion of the ramus.
Below this line, the entire remainder of the ramus has an
outer periosteal surface that is depository.
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34. An important remodelling transition occurs at the junction between ramus
and body. This is a key process because it involves conversion of one major
portion of the mandible directly in to another.
In the superimposed mandibles pictured in Figure, several contrasting
relationships are seen between the two growth stages.
 The mandible has enlarged in all dimensions.
 The right and left condyles have become only slightly separated.
 The body has increased proportionately in breadth,
 Both the body and the ramus have become significantly lengthened.
 In this figure, the coronoid process and most of the ramus of the
younger bone are within the area occupied by the body of the older
bone.
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THE MANDIBULAR BODY

35.  The body of the mandible is growing continuously into
areas previously occupied by the posteriorly moving
ramus, while the ramus in turn becomes progressively
relocated behind the backward moving condyles and
posterior edge of the ramus.
 The posterior portion of the body becomes
consecutively converted from the former ramus by
direct structural remodelling due to the V mechanism of
growth.
 New bone deposits are added onto the lingual surface of
the V‐shaped, anterior portion of the ramus and
posterior portion of the body as they both move
posteriorly toward the wide end of the V.
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36. THE TRIHEDRAL EMINENCE
 The depository type of surface on the buccal
side of the posterior body is a continuation of
the depository zone extending across the
ramus below the sigmoid notch and coronoid
process.
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37. THE CHIN AREA
 The diminutive chin of the young mandible becomes
progressively more prominent with increasing age.
 The alveolar region undergoes cortical regression and moves
posteriorly while at the same time the protuberance
continues to grow forward.
 The cortical region at or just above the chin is the only place
on the entire surface of the mandible that remains stable
during postnatal growth. This is the reason for it serving as a
useful site for superimposing successive radiographs.
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38. DIMENSIONAL CHANGES
 The teeth continue to migrate and erupt throughout childhood and
adolescence, even after they have attained functional occlusion. The
posteruptive movements of teeth are directly related to the spaces created
by growth displacements and movements of other teeth.
 Dentoalveolar compensation is the mechanism that coordinates their eruption
and migration relative to their jaw bases; it maintains the relationships of
teeth within and between the upper and lower dental arches.
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39.  Total mandibular length [Co–Me]) undergoes the greatest increases in
length: Approximately 25 mm and 30 mm for female and male,
respectively between 4 and 17 years of age,
 followed by corpus length [Go–Pg]; approximately 18 mm and 22 mm
for females and males, respectively and
 ramus height [Co–Go]; approximately 14 mm and 17 mm for females
and males, respectively. (Graber et al. 2011)
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42. EFFECT OF TREATMENT ON
MANDIBULAR GROWTH
The mandible is the bone in the craniofacial complex with the most post‐natal
growth potential. As such it would be of great value to be able to manipulate its
growth during orthodontic treatment.
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43. EFFECT OF REMOVABLE FUNCTIONAL
APPLIANCES
 One of the most controversial topics in orthodontics relates to the
effectiveness of functional appliances on mandibular growth.
 In skeletal Class II malocclusion, mandibular retrusion seems to be a major
contributing factor; it occurs in about one third of the population
(McNamara 1981).
 Evidence shows that favorable growth responses are not always achieved with
functional therapy; some authors reported increases in overall mandibular
length (Mills 1991) and changes in the amount of condylar
growth,(Baltromejus et al. 2002) but others believe that mandibular length
cannot be altered by such therapy (Creekmore & Radney 1983)
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44. EFFECT OF FIXED FUNCTIONAL
APPLIANCES
 The correction of Class II malocclusion due to mandibular retrognathia with
the use of Fixed Functional Appliances has also been investigated by various
researchers.
 The findings of various studies were contradictory, where some authors found
favorable treatment outcomes based on mandibular growth, attributed either
as a mandibular length augmentation or effective condyle growth (e.g.
Franchi et al), others dispute the magnitude of these effects (e.g. Cozza).
Moreover, existing evidence indicates that the dentoalveolar changes
produced by functional treatment outweigh the skeletal changes attained
(e.g. Cope).
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45. EFFECTS OF CHIN‐CUP THERAPY ON
MANDIBULAR GROWTH
 A major treatment strategy of skeletal Class III malocclusion with mandibular
overgrowth in growing patients is retardation or redirection of mandibular
growth and posterior positioning of the mandible.
 The chin cup has been used since the 19th century to control mandibular
growth in patients with excessive and/ or anteriorly positioned mandibles.
 Some studies indicated that the chin cup had no effect on retarding
mandibular growth but only produced a backward rotation of the mandible.
 Many studies have, however, reported a tendency of a return to the original
skeletal morphology and growth pattern after chin cup therapy was
discontinued and uncertainties existed in the efficacy of chin cup therapy in
Class III malocclusion (Liu et al. 2010).
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46. DEVELOPMENTAL ABNORMALITIES
 Developmental anomalies that affect the maxilla will usually also affect the
mandible as part of the same syndrome. This is due to the fact that the
neural crest cells that invaginate the region that will become the future
mandible comes from the same stream (first arch) as those that will become
the nasomaxillary complex.
 The diminutive mandible of micrognathia is characteristic of several
syndromes, including Pierre Robin, mandibulofacial dysostosis, progeria, Down
syndrome, oculomandibulodyscephaly, and Turner syndrome.
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47.  Agnathia: In this condition, the mandible may be grossly deficient or absent,
reflecting a deficiency of neural crest tissue in the lower part of the face.
 First‐and second‐arch syndrome: This is a lethal condition with multiple
defects of the orbit and maxilla. Aplasia of the mandible and hyoid bone, well
developed ears and auditory ossicles is seen in this syndrome. The probable
cause is ischemic necrosis of the mandible and hyoid bone occurring after the
formation of the ear.
 Pierre Robin syndrome: Mandibular micrognathia is the primary aetiological
factor. An excessively small mandible resulting in the tongue falling
downwards and backwards into the pharynx, being compressed between the
palatal shelves and preventing their closure.
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48.  Mandibulofacial dysostosis: (Cobourne & DiBiase 2010) Also known
as Treacher Collins Syndrome.
The regions of the face affected are those derived from pharyngeal arches 1
and 2.
 Usually a severely class II skeletal pattern with increased vertical
proportions, due to mandibular deficiency and posterior mandibular
growth rotation.
 Deficiency of the mandible is maintained throughout growth. In
unilateral agenesis of the mandibular ramus, the malformation increases
with age.
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49. CONCLUSION
 Knowledge of mandibular growth and development is of crucial importance to
the orthodontist.
 As the mandible is the part of the craniofacial skeleton that shows the
greatest post‐natal growth potential, but with questionable response to
growth modification, it is important to know the possible growth timing,
directions and magnitude it may exhibit.
 Armed with this knowledge the clinician can make informed decisions as to
possible treatment possibilities, be it orthodontic or surgical.
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50. REFERENCES
 ORTHODONTICS: CURRENT PRINCIPLES AND TECHNIQUES BY GRABER,
VANARDALL (5TH EDITION)
 ORTHODONTICS: CURRENT PRINCIPLES AND TECHNIQUES BY GRABER,
VANARDALL (6TH EDITION)
 ENLOW’S BOOK ON GROWTH
 CONTEMPORARY ORTHODONTICS: PROFITT 6TH EDITION
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