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the Growth-of-Mandible in orthodontics ppt
1. Growth of Mandible
Guide:
Dr. Rajiv Yadav (Associate Professor)
Dr. Sanjay P. Gupta (Assistant Professor)
Presented by:
Dr. Mukti Ranabht
Resident (First year)
Orthodontic PG section
Dental Teaching Hospital, MMC
Institute of Medicine, Kathmandu
11. Growth of Mandible, Orthodontic PG program, IOM-2020
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Prenatal Development
12. Pharyngeal arch
• Development of pharyngeal
arches -4th & 5th week of IUL.
• Mandibular arch -1st arch
• Appears at about 6th week of
IUL
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13. Meckel’s Cartilage
• Each embryonic mandibular
process contains a rod-like
cartilaginous core, Meckel’s
cartilage, which is an extension of
the chondrocranium into the
viscerocranium
• Template for growth of mandible
• Extends from cartilaginous otic
capsule to symphysis
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14. Meckel’s Cartilage
• Distally accompanied by mandibular division of the
trigeminal nerve (CN V), as well as the inferior alveolar
artery and vein.
• Proximally, articulates with the cartilaginous cranial
base in the petrous region of the temporal bone.
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15. Meckel’s Cartilage
• Mandibular division of trigeminal nerve- 1st structure
to develop
• Precedes mesenchymal condensation forming
mandibular arch: laterally
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16. Ossification
• 6th week of IUL- single ossification centre
• At the bifurcation of inferior alveolar nerve
• Appears in the perichondrial membrane lateral to
Meckel’s cartilage
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17. Ossification
• Spread of ossification below & around IAN & its
incisive branch
• Upward to form trough for the developing teeth
• Dorsally & ventrally: to form corpus & ramus
• Prior presence of neurovascular bundle ensures
formation of mandibular foramen and mental foramen
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19. Ossification
• Intramembranous Ossification: Distally toward the
mental symphysis and proximally up to the region of
the mandibular foramen
• Stops at a point, mandibular lingula
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20. Secondary cartilage
Between 8th and 14th weeks secondary cartilage appear
at :
• Condyle
• Coronoid
• Mental region
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21. Condylar Process
• Appears separately between mandibular foramen and
developing temporal bone
• Articulation becomes apparent as TMJ by about 12
weeks gestation
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22. Condylar Process
• Cartilage cells differentiate from the centre and
condylar head increases by interstitial and
appositional growth
• 14th week: first evidence of endochondral ossification
• Fuses with mandibular ramus by 4th months
• Much part replaced with bone but upper end persists
into adulthood
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23. TMJ
• 8th weeks of pc
• From condylar blastema (first arch derivative)
• Temporal blastema (from otic capsule, a component of
basicranium which form pterous temporal bone)
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24. Coronoid Process
• Secondary accessory cartilage appears at about 10- 14
week of IUL
• Grows as a response to developing temporalis
• Gets incorporated into bone of ramus
• Disappears before birth
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25. Mental Region
• One or two cartilage appear on either side
• Mental ossicles ( after ossification , at 7th months of
IUL)
• Incorporated into membranous bone
• Replaced by bone by 1st year
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27. Mandible at birth
• Small
• Short ramus
• Large gonial angle
• Flat mandibular fossa
• Low mandibular canal
• Coronoid process above
condylar process
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28. Postnatal growth
• Subunits: basal bone and processes, alveolar, coronoid,
angular, condylar process and chin
• Right and left body of mandible united between 4-12
months postnatally
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30. Postnatal growth
• Whole mandible displaced "away" by
the growth enlargement of the
composite of soft tissues
• Condyle and ramus grow upward and
backward (relocate) into the "space"
created
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31. Postnatal growth
• Ramus becomes longer and wider to accommodate
Increasing mass of masticatory muscles inserted
onto it,
Enlarged breadth of the pharyngeal space,
Vertical lengthening of the nasomaxillary part of the
growing face,
Increases corpus length which provides room for
erupting molars
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32. The Ramus
Remodelling growth by:
• Resorption - anterior border
• Deposition - posterior border
• Called Hunterian growth
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33. Body of the Mandible
Relocation of ramus posteriorly – converts former ramal
bone into body
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34. Body of the mandible
• Lower border of corpus is depository except at
antegonial notch
• Increase in height of alveolar bone accompanies
eruption of teeth
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35. Antegonial notch
• A single field of surface
resorption is present on the
inferior edge of the mandible
at the ramus-corpus junction.
• This forms the antegonial
notch by remodeling from
the ramus just behind it as
the ramus relocates
posteriorly
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36. Antegonial notch
• Size of antegonial notch is determined by
ramus-corpus angle and also by the
extent of bone deposition on the
underside (inferior margin) just posterior
or anterior to the notch
• Less prominent : closed ramus corpus
angle
• Prominent notch: opened angle
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37. Ramus uprighting
• Remodeling" rotation of ramus alignment
• To match the continued vertical growth of the midface
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38. Mental foramen
• Mental foramen during infancy : right angle to body of
mandible
• Directed backward due to the forward growth of body
of mandible while dragging along with it
• Clinical implication: while injecting mental block,
applied obliquely from behind to achieve entry
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40. The Chin
• Underdeveloped in infancy
• Becomes significant as age advances
• Prominent in males compared to females
• Prominence accentuated by resorption in alveolar
region
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41. The Chin
• By 1st year the symphyseal
cartilage replaced by bone
• Superior aspect of symphysis
becomes wider due to superior
and posterior drift of posterior
aspect
Buschang et al, 1992
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42. The Chin
Changes in symphysis:
• Resorption of the anterior aspect
of symphysis above the bony
chin
• The cortical region at or just
above the chin is the only place
on the entire surface of the
mandible that remains stable(no
remodelling)
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43. Coronoid Process
• Enlow’s V principle
• Propeller like twist
• Lingual side faces 3
directions all at once
• Posteriorly
• Superiorly
• Medially
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44. Lingual Tuberosity
• Important anatomic site in mandible at the junction
of corpus and ramus at the medial aspect.
• Counterpart of maxillary tuberosity.
• Deposits on the tuberosity will cause a definitive
posterior growth of the posteriorly facing tuberosity
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45. Lingual Tuberosity
• If viewed from the occlusal aspect,
lingual tuberosity appears to be in
line with the dental arch whereas
ramus is slightly away along the
arms of the expanding V.
• The region below lingual tuberosity
is resorptive thereby accentuating
the prominence of tuberosity.
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46. Lingual Tuberosity
• When viewed from the lateral aspect,
the lingual and maxillary tuberosity
appear to be positioned along the same
vertical line called the posterior
maxillary plane or PM plane.
• Key anatomic plane forms the
reference basis for Enlow's counterpart
principle or principle of growth
equivalents
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48. Alveolar Process
• Develops in response to presence of tooth buds
• As the teeth erupt the alveolar process develops and
increases in height by bone deposition at the margins.
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49. Angle of the Mandible
• On the lingual side
• Resorption : postero-inferior aspect
• Deposition : antero-superior aspect
• On the buccal side
• Resorption : antero-superior aspect
• Deposition : postero-superior aspect
• Results in flaring of angle as age advances
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50. Growth of Condyle
Superior and posterior growth of
condyle presses against the
glenoid fossa/cranial base
Anterior thrust to displace the
lower jaw forward
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51. Condylar Cartilage
• Secondary cartilage
• Specialization of fibrous layer of periosteum
• Highly responsive to mechanical, functional, and
hormonal stimuli both at the time of development and
throughout the growth period
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53. Mechanisms of Condylar Growth
• 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, par-
ticularly the maxilla.
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55. Condylar neck
Growth on neck:
• Buccal & lingual surface of neck : resorptive
• Coupled with the deposition on head
• V-shaped cone of condylar neck growing towards its
wider end
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56. Timing of Mandibular growth
• Growth in width completed first, then growth in
length, and finally height
• Width - tends to be completed before adolescent
growth spurt
• Length and height - continues through puberty
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58. Mandibular growth changes
On average, ramus height increases 1 to 2 mm and body
length increases 2 to 3 mm per year
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60. Overall mandibular length (Co–Gn): Graber
• Early years: condylar growth and modeling of the
superior aspects of the ramus directed posteriorly and
superiorly
• After 1st few postnatal years: changes orientation
toward a predominant superior direction.
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Timing Growth increase
First year 15-18 mm
Second year 8-9 mm
Third year 5 mm or less
61. Peak of mandibular growth
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Baccetti et al, 2005
62. Peak of mandibular growth
• Peak mandibular growth corresponds with CVMI- III,
where functional appliances are best used
(Baccetti et al. 2002)
• Mandible grows at greater rate than cranial base but
lesser rate than cervical vetebra
(Scott et al. 1958)
• The peak increase in mandibular length, along with
greatest bone apposition at condylion, was observed
during the interval CS3–CS4
(James & Mc Namara, 2007)
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63. Differences
Maxillomandibular growth:
• Initially mandible >> maxilla
• 8 week pc: maxilla overlaps mandible
• 11th week: equal size
• Mandible lags behind maxilla
• At birth: retrognathic
• In postnatal life: rapid mandibular growth
• Mandible can grow much longer than maxilla
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65. Growth Rotation: Bjork
• The phrase “Growth Rotation” was
introduced in 1955 by Dr. Arne
Bjork
• He described it a particular
phenomenon occurring during the
growth of the head.
• Reflection of differential growth in
AFH & PFH.
• Houston, 1988
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66. Implant radiography
• A. Bjork started his study in 1951
• Had a sample size of 100 children between the age
group of 4 – 24 yrs.
• Used metal implants to find the sites of growth and
resorption in individual jaws.
• Also examined individual variation in direction and
intensity.
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68. Termnologies and Classification of Growth Rotations
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• Confusing??
• Authors using different terms to describe the same, or si
milar entities
• Buschang & Jacob (2014) summarised the most popular
terms
69. Bjork and Skeiller Proffit Solow, Houston
Rotation of mandibular
core relative to cranial
base(A)
Total Internal (15°) True
Surface Remodeling(B) Intramatrix External (11-12°) Angular Remodeling
of lower border
Net rotation of
mandibular plane
relative to cranial base
(C)
Matrix Total (3-4°) Apparent
C = A-B Matrix = total -
Intramatrix
Total= internal-
external
Apparent= true –
angular remodeling
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70. Growth Rotation- Bjork and Skeiller, 1983
Average individual with normal
vertical facial proportions -
• 15° internal (true) forward
rotation
25% - matrix : 3- 4°
75% - intra-matrix : 11-12°
• 3 to 4° decrease in mandibular
plane
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73. Growth Rotation- Bjork, 1969
Rotation of
mandible
Forward
Type 1
Type 2
Type 3
Backward Type 1
Type 2
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74. Forward Rotation
Type I Type II Type III
Centre: at TMJ
• Underdeveloped
anterior facial height
• Deepbite
• Lower dental arch
pressed into upper
• Cause: occlusal
imbalance, powerful
muscles, maxillary
impaction
Centre: at Incisal edges of
lower incisors
• Increased posterior, normal
anterior
• Cranial base bending or
inferior relocation of middle
cranial fossa
• Increase in ramus height
due to vertical condylar
growth
Centre: at premolars
• In cases of large anterior
overjet
• Increased posterior,
underdeveloped anterior
• Incisors displaced
backwards
• Increased anterior
crowding (packing)
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75. Backward Rotation
Type I Type II
Center: at TMJ
• Raised bite, change in intercuspation
• Flattening of cranial base
• Open bite
Centre: Most distal occluding molars
• Posteriorly directed condylar growth &
because of attachment to muscles & ligaments
• Double chin appearance
• Open bite
• Lip strain present
• Reduced alveolar prognathism
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76. Growth Rotation-Schuddy (1965)
Rotation of
Mandible
Clockwise
Counter- clockwise
Vertical growth at the molar area > at the
mandibular condyles
Condylar growth > vertical growth at molars
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78. Growth rotation
• Although both internal and external rotation occur in
everyone, variations from the average pattern are
common.
• Greater or lesser degrees of both internal and external
rotation often occur, altering the extent to which
external changes compensate for the internal rotation.
Houston et al, 1988
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79. Growth rotation
• There are significantly greater rates of true rotation
during the transition from late primary to early mixed
dentition than during the transition from early mixed
to permanent dentition
Wang et al, 2009
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80. True mandibular rotation (degrees per year) during
childhood and adolescence
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81. Structural Signs Of Rotation (Bjork)
• Inclination of the condylar head
• Curvature of the mandibular canal
• Shape of lower border of mandible(antegonial notch)
• Inclination of the symphysis
• Interincisal angle
• Interpremolar or intermolar angles
• Anterior lower face height
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88. Clinical implications
• Both forward & backward rotation greatly influences
paths of eruption
• Serious risk of extreme migration after extractions
• Extractions should be avoided until the beginning of
pubertal growth spurt
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89. Cranial base angle
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• Anterior inclination of the
middle cranial fossa/ Large
angle:
Mandibular retrusive/ maxillary
protrusive
Anteriorly and inferiorly
positioned maxillary complex
Long nasomaxillary complex
Downward and backward
alignment of the ramus
Posterior and inferior positioning
of B point
Closing of the gonial angle
90. Cranial base angle
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• Posteriorly inclined middle cranial
fossa/ Low angle:
Mandibular protrusive/ maxillary
retrusive effects
Posteriorly and superiorly
positioned nasomaxillary complex
Short nasomaxillary complex
Forward and upward alignment of
the ramus
Anteriorly and superiorly
positioned B point
Opening of the gonial angle
92. Angles used to measure mandibular rotations
• Basal plane angle
• Angle of inclination
• Mandibular plane angle
• Gonial angle
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93. Base plane angle
• Mean angle is 25°
• Inclination of mandible to the maxillary base
• Large, mandible rotated backwards
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94. Angle of inclination
• Angle between PN line
(perpendicular to sella-
nasion) and the palatal
plane
• Mean is 85°
• Gives assessment of
inclination of maxillary
base
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95. Mandibular plane angle
• Mean value is 32°
• Inclination of mandible to
anterior cranial base
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96. Gonial angle (Ar-Go-Me)
• Mean value is 128±7°
• Upper large, horizontal
• Lower large, vertical
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97. Corelation Between Growth Rotation
and Tooth Eruption
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98. • The eruption path of mandibular
teeth is upward and somewhat
forward.
• The normal internal rotation of the
mandible carries the jaw upward in
front.
• This rotation alters the eruption
path of the incisors, tending to
direct them more posteriorly
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100. Backward rotation
• Lower anterior lean against lip
• Increased lip pressure & decreased
tongue pressure
• Backward tipping of incisors
• Distal tipping of molars
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101. Symphyseal changes with rotation
• Forward rotation: forward relocation of chin together
with resorption in alveolus makes chin prominent &
vice versa
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102. Role of muscle activity in
mandibular rotation
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103. • The variation of masticatory muscle strength with
facial type is known from measurements of bite force
in adults
Ringqvist(1973)
Helkiroo and Ingervall(1978 )
Profit et al (1983)
• Low bite force values in children with the long face
morphology and high bite force with short face
Proffit and Fields (1983)
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104. Role of muscle activity in mandibular rotation
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106. Clinical implications
• Thicker masseter muscle is found to significantly
correlate with reduced gonial and mandibular plane
angles and increased ramus height implying its role in
the more horizontal development of face
• Training the jaw muscles of long-faced children by
having them chew daily on tough material to
strengthen the muscles and to induce a more favorable
anterior mandibular growth rotation
Ingervall et al, 1987
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107. Growth of Mandible, Orthodontic PG program, IOM-2020
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Congenital and
Developmental Anomalies
108. What are the potential disturbances of normal jaw
development?
• Failure of neural crest cells to form from margins of
neural tube.
• Slowed migration of crest cells away from neural tube
• Defective mitotic division of neural crest cells
• Increased neural crest cells adhesion
• Unusually high rate of neural crest cell death
• Failed epithelial- mesenchymal interaction
• Defect of influence of related nerve, vessels or muscles
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109. Agnathia
• Characterized by hypoplasia or
aplasia of mandible
• Partial absence of mandible is
more common
• Due to failure of migration of
neural crest mesenchyme into
maxillary prominence at 4th to
5th week of gestation
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110. Micrognathia
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• Deficient mandibular growth
• May be : congenital or acquired
• Congenital is associated with:
o congenital heart disease
o pierre robin syndrome, Treacher
Collins syndrome etc
111. Treacher Collins Syndrome
Results from altered development of structures
derived from neural crest
Features
Downward slanting eyes
Micrognathia
Underdeveloped zygoma
Malformed ears
Conductive hear loss
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113. Acquired micrognathia
• Post-natal origin
• Due to disturbance in TMJ area
or ankylosis
• Clinically characterized by severe
retrusion of chin, steep
mandibular angle and deficient
chin button
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114. Macrognathia
• Often associated with:
Acromegaly
Pagets disease of bone
• Clinically characterized by
prognathic mandible
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115. General factors which would influence and favor
mandibular prognathism are:
• Anterior positioning of the glenoid fossa
• Posterior positioning of the maxilla in relation to the
cranium
• Prominent chin button
• Increased height of the ramus
• Increased mandibular body length
• Increased gonial angle
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116. Aplasia of mandibular condyle
• Failure of development of
mandibular condyle
• Bilateral or unilateral
• If unilateral- obvious facial
asymmetry
• Occlusion and mastication is
altered
• Shift of mandible at affected
side during mouth opening
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117. Condylar hyperplasia
• Enlargement of condylar
head
• Cause facial asymmetry
• May be due to: endocrine
disorder, trauma etc
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118. Bifid condyle
• Persistence of septa dividing the fetal condylar
cartilage
• Trauma
• Usually asymptomatic
• Diagnosed radiologically
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119. References
1. Contemporary Orthodontics, Proffit, Fields, Sarver, Fifth Edition
2. Essentials of facial growth, Donald H. Enlow, Mark G. Hans
3. Craniofacial development, Geoffrey H. Sperber
4. Text book of Orthodontics, Samir E. Bishara
5. Hand book of orthodontics, Robert E. Moyers, Fourth Edition.
6. Langman’s medical Embryology, Ninth Edition
7. Nilton Alves, Study About the Development of the Temporomandibular Joint in the
Human Fetuses, Int. J. Morphol., 26(2):309-312, 2008.
8. Baume L. J. Ontogenesis of the human temporomandibular joint development of the
condyles. J. Dent. Res., 41:1327-39, 1962.
9. Carranza M. L.; Carda C.; Simbrón A.; Quevedo M C; Celaya, G. & de Ferraris, M. E.
Morphology of the lateral pterygoid muscle associated to the mandibular condyle in
the human prenatal stage. Acta Odontol. Latinoam., 19(1):29-36, 2006.
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120. 10. Steinberg R. A longitudinal study of mandibular growth rotation. University of Connecticut Health
Center. 1977
11. Bremen JV, Pancherz H. Association between bjork’s structural signs of mandibular growth
rotation and skeletofacial morphology. Angle Orthodontist; 75(4), 2005.
12. Liu YP, Behrents RG, buschang PH. Mandibular growth, remodeling, and maturation during infancy
and early childhood. Angle Orthodontist; 80,(1); 2010.
13. Bjork A. Prediction of mandibular growth rotation. Copenhagen, Denmark. Am J Ortho.1969.
14. Lewis AB, Roche AF, Wagner B. pubertal spurts in cranial base and mandible. The Angle
Orthodontist. 1975.
15. Moss ML, Rankoe RM. The role of the functional matrix in mandibular growth. The Angle
Orthodontist. 38(2);1968.
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The mandible greek word mandere: to masticate or chew (from Latin mandibula, "jawbone") or inferior maxillary bone is the largest, strongest and lowest bone in the face.
Horseshoe shaped and holds the lower teeth in place.
Movable bone and has no bony attachment with the skull instead the condyles rest on mandibular fossa of temporal bone forming TMJ
Has a horizontal portion – body
Two vertical portion – rami
Body: consists of two lateral halves which are joined at the median line shortly after birth marked by slight ridge called symphysis
two surfaces- external and internal
two borders- superior and inferior
Processes: condylar, coronoid and alveolar
The ramus (Latin: branch) of the human mandible has four sides, two surfaces, four borders, and two processes.
Processes
The coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size.
The condyloid process is thicker than the coronoid, and consists of two portions: the mandibular condyle, and the constricted portion which supports it, the neck.
The mandibular notch, separating the two processes, is a deep semilunar depression and is crossed by the masseteric vessels and nerve.
Foramina
Nerves
To the right and left of the symphysis, near the lower border of the mandible, are two prominences called mental tubercles
A prominent triangular surface made by symphysis and these two tubercles is called the mental protuberance
The external surface of the mandible from a lateral viewpoint presents a number of important areas
The oblique ridge(oblique line, radiographically) extends obliquely across the external surface of the mandible from the mental tubercle to the anterior border of the ramus, with which it is continuous. It lies below the mental foramen.
The internal surface of the body of the mandible is divided into two portions by a well-defined ridge, the mylohyoid line- origin of the mylohyoid muscle
On the inside at the center there is an oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. The margin of this opening is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lingula of the mandible, which gives attachment to the sphenomandibular ligament
Attachment for muscles of mastication and facial expersiion
On either side of the symphysis, just below the incisor teeth, is a depression, the incisive fossa, which gives origin to the mentalis and a small portion of the orbicularis oris
Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus; it affords attachment to the depressor labii inferioris and depressor anguli oris; the platysma is attached below it.
Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the genioglossus. Immediately below these is a second pair of spines for the origin of the geniohyoid.
Below the mental spines, on either side of the middle line, is an oval depression for the attachment of the anterior belly of the digastric.
mylohyoid line, which gives origin to the mylohyoid muscle
In specific areas of the developing embryo, the migrating and rapidly proliferating ectomesenchymal cells develop elevations between ectoderm and endoderm.
In the somite period, 4th week IUL, such elevations are seen in the ventral foregut resulting in the formation of six pharyngeal arches or branchial arches bilaterally, the fifth arch perishes; finally only five arches remain
The cartilage of the first pharyngeal arch. It is developed on the 41st to 45th day of intra-uterine life. It extends from the cartilaginous otic capsule into the midline or the symphysis and provide a template for guiding the growth of the mandible
Throughout its course
Meckel’s cartilage completely disappears by approximately 24 weeks’ gestation
A major portion of the Meckel’s cartilage disappears during growth (24 weeks gestation) and remaining part develops into; Mental ossicles, Incus and Malleus , Spine of sphenoid, Anterior ligaments of malleus ,Spheno-mandibular ligament
The first structure to develop in the primordium of the lower jaw which is mandibular division of the trigeminal nerve.
This is followed by mesenchymal condensation forming the first branchial arch.
A single ossification center for each half of the mandible arises in the 6th week of intra uterine life in region of the bifurcation of the inferior alveolar nerve into mental and incisive branches
As ossification continues the Meckel’s cartilage becomes surrounded and invaded by the bone
Meckel’s cartilage ossify in 7th week and ossification continues until the posterior aspect is covered.
At 8th- 12th week- Mandibular growth accelerates , as a result mandibular length increases
Forms sphenomandibular ligament & spinous process of sphenoid
Endochondral bone formation is seen only in : these regions
Arises secondarily within a skeletogenic membrane and apart from the primary embryonic cartilaginous anlagen,
Secondary cartilage formed in areas of precocious stresses and strains within intramembranous bones, as well as in areas of rapid development and growth of bone. Within the craniofacial complex, the angular and the coronoid processes of the mandible also may exhibit the presence of secondary cartilage because these are sites of very rapid bone growth associated with the function of the muscles of mastication
By 8 weeks gestation : The condylar cartilage appears as a separate carrot-shaped blastema of cartilage
Blastema is a mass of cells capable of growth and regeneration into organs or body parts,
Acting both as growth cartilage and articular cartilage
Articulation complete by 12 week
Blastema is a mass of cells capable of growth and regeneration into organs or body parts,
The only portion of the developing lower jaw that appears to be derived from endochondral ossification of Meckel’s cartilage is the mental ossicles,
which are two very small sesamoid bones that are formed in the inferior aspect of the mandibular symphysis.
These bones are no longer present at the time of birth.
Greatest postnatal growth potential of any component of the craniofacial complex
Ascending ramus of neonatal mandible is low and wide……Coronoid process is relatively large & projects above the condyle…….Body is just a small shell containing buds & partial crowns of deciduous teeth……………Mandibular canal low in body
Condyle at the level of occlusal plane
Although the mandible appears as a single bone in the adult, it is developmentally and functionally divisible into several skeletal subunits
The growth pattern of each of these skeletal subunits is influenced by a functional matrix that acts upon the bone.
The teeth act as a functional matrix for the alveolar unit;
The action of the temporalis muscle influences the coronoid process;
The masseter and medial pterygoid muscles act upon the angle and ramus of the mandible
The lateral pterygoid has some influence on the condylar process.
The functioning of the related tongue and perioral muscles and the expansion of the oral and pharyngeal cavities provide stimuli for mandibular growth to reach its full potential.
Displacement
Remodelling
The significance of the ramus of the mandible is mostly that it provides an attachment base for masticatory muscles, which, of course, is a basic function.
But, the key role of the ramus is placing the corpus and dental arch into ever-changing fit with growing maxilla and the face's limitless structural variations by critical remodeling and adjustments in ramus length and ant. post width
bone at the tip of the condylar process at an early age can be found at the anterior surface of the ramus some years later. The ramus remodeled in posterosuperior manner while mandible as a whole becomes displaced anteriorly and inferiorly.
This allows posterior lengthening of the corpus and dental arch.
Finally, the whole ramus becomes relocated posteriorly by resorptive and depository remodeling
In infancy the ramus is located at about the spot where the primary first molar will erupt. Progressive posterior modeling and remodeling create space for the second primary molar and then for the sequential eruption of the permanent molar teeth. More often than not, however, this growth ceases before enough space has been created for eruption of the third permanent molar, which becomes impacted in the ramus.
Growth of the mandible, as viewed from the perspective of a stable cranial base: the chin moves downward and forward.
B. Mandibular growth, as viewed from the perspective of vital staining studies, reveal minimal changes in the body and chin area, while there is exceptional growth and remodeling of the ramus, moving it posteriorly . Carry away phenomenon
The correct concept of mandibular growth is that the mandible is translated downward and forward and grows upward and backward in response to this translation, and maintainins its contact with the skull.
Transverse rotation of left and right corpus
So that increase in angle between two corpora
The notch itself is also increased in size owning • to its resorptive periosteal surface
To achieve this, condylar growth may become more vertically directed, and a different pattern of ramus remodeling can also become operative
The "gonial angle" thus must undergo change
(close) in order to prevent change in the occlusal relationship between
the maxillary and mandibular arches.
Lateral view of the mandible in infancy, adulthood, and senility, illustrating the influence of alveolar bone on the contour of the mandibular body.
Note the changing obliquity of the angle of the mandible.
In dentulate mandible mental foramen lies midway between upper & lower border …………Edentulous mandible: appears near upper margin
Growth of chin becomes significant in adolescence.
The mental protuberance forms by bone deposition during childhood. Its prominence is accentuated by bone resorption that occurs in the alveolar region above it, creating a concavity.
Remodeling changes of the symphysis between 6 (T1), 10 (T2), and 15 (T3) years of age.
Suprapogonion (PM) is the point where no remodeling changes occur
So taken as stable landmark for superimposition
Inferior aspect of anterior border is depository but limited or variable
The growth of coronoid process follows the enlarging “V” principle.
It has a Propellar like twist: fan like
Even thgough bone added on lingual side, it grows in all 3 directions
When the sections of the region of coronoid process are taken and bone at various stages of development superimposed, the coronoid process is
seen to grow in length (height), with increase in thickness due to deposit on the medial side; also posteriorly relocated.
Resorption on buccal surface
The combination of resorption in the region below tuberosity and deposition on the medial surface of the tuberosity itself accentuates the prominence of the lingual tuberosity.
When juvenile and adult mandibles are compared with the view from occlusal surface, the tuberosity is greatly relocated in a posterior direction yet the mediolateral growth is meager when compared to the posterior shift.
Enlow points out that it is due to the stable bicondylar width established early in childhood.
Bicondylar width in turn is related to the width of the cranial base that completes early.
this plane extends from the junction of anterior and middle cranial fossa and extends downward in a direction perpendicular to the vertical axis of the orbit.
In case of absence of teeth, the alveolar bone fails to develop and it resorbs in the event of tooth extraction.
The angle of mandible, as already mentioned becomes upright with age and subsequently becomes more acute
Frost
Growth of the mandible was thought to occur principally by growth at condyle.
cartilage has pressure adapted bone growth)
Primary displacement
Here physical force of displacement is condyle itself
In new concept : soft tissue is responsible for displacement
Can be divided into two general layers: an articular layer and a growth layer
The growth layer of the condylar cartilage is organized into an additional series of layers typical of growing cartilage that blend into each other
Articular layer: joint surface of the mandibular condyle and temporal portion of the TMJ consist of an avascular dense fibroelastic connective tissue whose collagen fibers are oriented parallel to the articular surface
Growth layer: immediately deep to the articular layer is comprised of a series of cellular zones representing the various stages of chondrogenesis in secondary cartilage
The zone of endochondral ossification is characterized by the initiation of mineralization of the intercellular matrix within the distal-most three to five layers of hypertrophying cells. This matrix is subsequently eroded away by osteoclastic activity and replaced by bone.
Provide multidirectional regional adaptive growth
Does not establish the rate or amount of overall mandibular growth
Petrovic and colleagues developed a “cybernetic” model of mandibular growth regulation referred to as the “servosystem hypothesis of mandibular growth
Independent growth of the maxilla (A) creates a minor occlusal deviation between the upper and lower dentition (B). This occlusal deviation is perceived by proprioceptors (C), which provide a signal to the muscles responsible for jaw protrusion to be tonically more active (D), which causes the mandibular condyle to become slightly more anteriorly located within the temporomandibular joint, thus stimulating condylar growth (F). Muscle function and the adaptive capacity of the condyle for growth are enhanced by expression of hormonal factors (E), and thus condylar growth may vary depending on the maturational and hormonal
status of the individual
Multidirectional proliferative capacity- the arrangement of daughter cells does not reflect direction of growth i.e. nonlinear arrangement
Neck of condyle is resorptive on buccal & lingual surface coupled with the deposition on head contributes V configuration…….
Bone resorption subjacent to the condylar head accounts for the narrowed condylar neck
Juvenile vs pubertal growth spurts
While an adolescent spurt in vertical mandibular growth certainly occurs, a pronounced spurt for the anteroposterior and transverse growth has not been established
4-17 yrs
Ramus height: 15 mm
Body: 20mm
Total mand. length: 30mm
During
these early years, condylar growth and modeling of the superior
aspects of the ramus are directed posteriorly and superiorly,
with roughly equal amounts of growth in each direction. This
orientation is important because it rapidly increases corpus
length to make room for the rapidly developing dentition. After
the first few postnatal years, growth of the condyle and superior
ramus slows down dramatically and changes orientation
toward a predominant superior direction.
Growth modification effective and more efficient to do it during adolescence growth spurt than prior to adolescence
Swedish dentist, Arne Bjork (1911-1996)
metallic implants have been inserted in the jaws to serve as fixed reference point
Analyzed mechanism of changes in intermaxillary relations during growth
Tantalum inert pins which are 1.5 mm long and have 0.5 mm diameter are used.
These metal pins get fused to the bone
Osseo-integrated implants serve as reference points and serial cephalometric radiographs are taken repeatedly over a period of time and compared.
Rotation of jaw bones was estimated using implant radiography
Mandibular inclinations drastically affects facial morphology, and treatment planning, treatment outcome
Implants were placed in the anterior aspect of symphysis
2 pins on the right side of the mandibular body
One pin on the external surface of the ramus
By superimposing two consecutive tracings, mandible found to be rotated slightly forward
Average individual with normal vertical facial proportions from age 4 to adult
External: surface changes and alteration in rate of eruption of teeth
Internal (total) rotation has 2 components: Matrix rotation: soft tissue matrix: rotation of mand plane with cranial base: rotation centered on the condyle
Intramatrix rotation: rotation of mand plane with core of lower jaw: rotation centered within the body of mandible
25% at the condyle
75% results from rotation within the body of the mandible
During the time that 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 to 4 degrees on average.
The reason that the internal rotation is not expressed in jaw orientation due to surface changes tend to compensate.
This means that the posterior part of the lower border of the mandible must be an area of resorption, whereas the anterior aspect of the lower border is unchanged or undergoes slight apposition.
Internal rotation: Rotation of mandibular core relative to cranial base
External rotation: Rotation of mandibular plane relative to core of mandible
Total rotation rotation of mandibular plane relative to cranial base
(
Forward rotation
More posterior development
Short midface
Mandibular protrusive effect
Upward inclination of mandibular plane angle
Backward rotation:
Less frequent than anterior rotation
More anterior development
Type I: Occlusal imbalance due to loss of teeth
Reduced depth of antegonial notch
Type II: alternatively: primary failure of eruption of posterior teeth; excessive loading of mastc muscles lead to of anterior teeth wearing; loss of anterior fac hght; forward rttn
Type II & III: symphysis typically swings forward to reveal a characteristically prominent chin.
Less frequent
Type II: smaller vertical height of ramus
Condylar growth: AP / horizontal growth
Here posterior growth means vertical growth at molars
they are not rotation
Greater rate during childhood than adolescence
Bjork gave 7 structural signs of extreme growth rotation to find the direction of mandibular growth
These signs are not clearly developed before puberty
In horizontal growing individuals:
1) The condyles are inclined forward.
2) The mandibular canal curvature greater than mandibular contour.
3) The lower border pronounced apposition below the symphysis and the anterior part of the mandible produces an anterior rounding, with a thick cortical layer, while the resorption at the angle produces a typical concavity.
4) The symphysis swings forwards in the face, and the chin is prominent.
5) The difference in the inter incisal angle is evident; in spite of the compensatory tipping of the lower incisors is more when compared to vertical growing individuals.
6) The difference in the interpremolar and inter molar angles in the two growth types is also clear is more in horizontal growth than vertical type growth pattern.
7) A compressed or reduced lower anterior face height.
Forward rotation: curves forward
Backward: straight or slopes back
Forward: curves downward
Backward: notched
symphysis swings forwards in the face, and the chin is prominent.
Forward: slopes backward
Backward : slopes forward
The lower border pronounced apposition below the symphysis and the anterior part of the mandible produces an anterior rounding, with a thick cortical layer, while the resorption at the angle produces a typical concavity.
The
Forward: vertical or obtuse
Backward: acute
forward: curved
Downward: straight
Forward: decreased
Downward: increased
He concluded on the structural signs
It is important to detect extreme types of mandibular rotation occurring during growth
Not all of them will be found in a particular individual , but the greater the number which is present the more reliable the prediction will be.
increased flexion of the skull base promotes a clockwise rotation of the sphenoid bone. This rotation transfers a downward vertical force, through the vomer bone to the maxillary complex, leading to the vertical elongation of this complex. This vertical elongation limits the antero-posterior growth of the maxillary complex, causing posterior discrepancy (crowding), which in turn motivates an excessive eruption of the maxillary molars, creating an excessively horizontal maxillary (upper) posterior occlusal plane. The mandible then has to adapt to this occlusal plane in order to keep occlusal function, and does so by anterior rotation. This anterior rotational adaptation of the mandible promoted by the neuromuscular system has two effects. On one hand, it leads to a decompression of the condyles, which then grow secondary, and at the same time it diminishes the compression exerted on the mandibular fossa of the temporal bone, which in combination with the traction effect exerted by the chewing muscles (masseter and temporal) suffers external rotation. The skull thus assumes a greater transverse dimension. This
external rotation of the temporal bone, through its direct connection with the sphenoid and occipital bones near the midline, influences flexion of the spheno-occipital synchondrosis. This bending of the midline bones determines a smaller anterior–posterior skull base, while influencing further clockwise rotation of the sphenoid bone, which again drives this cycle.
An increased extension of the cranial base would have the reverse effect on the craniofacial complex: a steeper upper posterior occlusal plane, lower vertical dimension, a more retrognathic mandible and internal rotation of the temporal bones, accompanied by an anterior– posteriorly longer and transversally narrower skull base.
The soft tissue matrix is defined by the tangential mandibular line(ML1)
Dental compensation
Growth of the mandible away from the maxilla creates a space into which the teeth erupt.
The rotational pattern of jaw growth obviously influences the magnitude of tooth eruption.
To a surprising extent, it can also influence the direction of eruption and the ultimate anteroposterior position of the incisor teeth
This rotation alters the eruption path of the incisors, tending to direct them more posteriorly than would otherwise have been the case
Because the internal jaw rotation tends to upright the incisors, the molars migrate further mesially during growth than do the incisors, and this migration
is reflected in the decrease in arch length that normally occurs
Modern view places relatively greater importance on lingual movement of the incisors and relatively less importance on the forward movement of molars
Lower anterior thrust forward relative to the mandible
The rotation of maxillary and mandibular jaw bases is a major factor in etiological assessment
Of all the patterns of growth , growth rotations assume an important role in orthodontics because of its major impact on treatment strategies.
Certain rotational patterns of jaw bases can be manipulated quite effectively by means of functional and orthopedic devices while certain extreme rotations are very difficult to treat and surgical correction has to be performed at a later stage
Broad dental arches
Jaw bones are dense; ortho tooth movement difficult esp in adult cases.
Individuals of the short-face type, who are characterized by short anterior lower face height, have excessive forward rotation of the mandible during growth, resulting from both an increase in the normal internal rotation and a decrease in external compensation.
The result is a nearly horizontal palatal plane, a low mandibular plane angle, and a large gonial angle (Fig. 4.18).
A deep bite malocclusion and crowded incisors usually accompany this type of rotation
Narrower dental arches
Jaw bone density relatively less
In long-face individuals, who have excessive lower anterior face height, the palatal plane rotates down posteriorly, often creating
a negative rather than the normal positive inclination to the true horizontal.
The mandible shows an opposite, backward rotation, with an increase in the mandibular plane angle
The mandibular changes result primarily from a lack of the normal forward internal rotation or even a backward internal rotation.
The internal rotation, in turn, is primarily centered at the condyle.
This type of rotation is associated with anterior open bite malocclusion and mandibular deficiency (because the chin rotates back as well as down).
Backward rotation of the mandible also occurs in patients with abnormalities or pathologic changes affecting theTMJs. In these individuals, growth at the condyle is restricted.
The interesting result in three cases documented by Björk and Skieller was backward rotation centered in the body of the mandible,
rather than the backward rotation at the condyle that is seen in individuals of the classic long-face type
Jaw orientation changes in both the backward-rotating types, however, are similar, and the same types of malocclusions develop.
Similar formula will be used for ramus asymmetry and condyle +ramus asymmetry
If >6% asymmetry is present..
Congenital disease : present at or before birth but is not necessarily inherited i.e. transmitted through the genes.
Developmental anomaly; unusual sequelae of development; a deviation from normal shape or size
In some case may be illusion due to retrognathic mandible or prognthaic maxilla
Seen in:
Pierre Robin
Cat’s cry (cri du chat) syndromes,
)
Progeria
Down syndrome (trisomy 21 syndrome)
also called mandibulofacial dysostosis and Franceschetti-Zwalen-Klein syndrome…In general, individuals with TCS may have underdeveloped or absent cheekbones, an underdeveloped or smaller-than-normal jaw bone, underdeveloped or malformed ears, and small or obstructed nasal passages. They often have an unusually large mouth and a large beak-like nose. An opening in the roof of the mouth, called a cleft palate, is common. Patients may also have misaligned teeth, eyes that slant downward, sparse eyelashes, and a notch in the lower eyelids, called a coloboma.
Complication: sleep apnoea, speech problem…chance of aspiration during GA
PRS is not a syndrome in itself, but rather a sequence of disorders
Intrauterine molding (fetus head tightly flexed against chest in utero) :
Mechanical theory: ……The smaller mandible displaces the tongue upward (cleft palate) and posteriorly, resulting in obstruction of the airway…glossoptosis., delineate the source of airway obstruction, and address airway and feeding issues…. nasopharyngeal tube, nasogastric tube, tracheostomy
Anterior positioning of the glenoid fossa
Other authors support the theory that bifid condyle is an embryological malformation. When the fetus is about 20 weeks old, a septum of vascular fibers appears in the cartilage of the condyle, extending all the way to the interior of the bone. This septum disappears at about the nine-teenth week of life, such that if one suffers an injury or there continues to be a shortage of blood supply, it may affect the proper ossification of the condyle and end up producing a bifid condyle.
Result of disturbance in early embryonic dev.
deficiencies of midline tissue of the neural plate very early in embryonic development caused by exposure to very high levels of ethanol
