GROWTH AND DEVELOPMENT OF THE MANDIBLE
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INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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GROWTH AND DEVELOPMENT OF THE MANDIBLE ANATOMY PRE NATAL GROWTH POST NATAL GROWTH ANOMALIES OF DEVELOPMENT
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Prenatal growth of the mandible
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Neural crest cells
Ist brachial arch Mandibular process
Mandibular bone www.indiandentalacademy.com
CT tissue
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36 – 38 DAYS Ectomesenchymal condensation
mandible
Lateral to Meckels cartilage
Osteogenic membrane
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6
th
week
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10 – 12 weeks
Secondary accessory cartilages appear
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10 week - condylar cartilage ď Ž
Appears in the Ramal region
ď Ž
Endochondral bone (14 week)
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Condylar Cartilage
Serves as a growth site Brings changes in the mandibular position and form Growth increases during puberty Peak 12 – 14 years Ceases by 20 years www.indiandentalacademy.com
7
th
month IUL
1 or 2 small cartilages appear in the future mental region
Mental ossicles
Incorporated into the intramembranous bone of symphsis
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Features of neonatal mandible
Ascending Ramus low and wide
Large Coronoid process Body – open shell containing tooth buds and partially formed deciduous teeth Mandibular canal that runs low in the body
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Features of neonatal mandible High Coronoid process
Wide Ramus www.indiandentalacademy.com
Differential growth During fetal life
8 weeks - mandible > maxilla 11 weeks - mandible = maxilla 13 – 20 weeks maxilla > mandible
At birth
Mandible tends to be retrognathic Early post natal life orthognathic www.indiandentalacademy.com
Post natal growth of the mandible
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Main sites of post natal growth in the Mandible
Condylar cartilage
Posterior border of the Rami Width
Height
length
Alveolar ridges
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Symphysis Menti
Limited growth till fusion
No widening after fusion
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Mental Foramen
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Mental Foramen ď Ž
Vertical relation within the body of the mandible
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Mental Protuberance
Formed by mental ossicles from accessory cartilage and ventral end of Meckel’s cartilage
Poorly developed in infants www.indiandentalacademy.com
Mental Protruberance ď Ž
ď Ž
Forms by osseous deposition during childhood Prominence is accentuated by bone resorption above it
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Mental Protuberance
Reversal between 2 growth fields
Concave
Reversal line could be High or low
convex
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Alveolar process
Adds to the height and thickness of the mandibular body
Teeth absent fails to develop
Teeth extracted resorbs www.indiandentalacademy.com
Alveolar process
Acts as buffer zone Maintains vertical height Adaptive remodeling makes orthodontic tooth movement possible
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Alveolar process Lingual movement of anteriors
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Condylar cartilage ď Ž
Secondary cartilage
ď Ž
Important contribution to the overall length of the mandible
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Condylar cartilage
‘ v ‘ principle of Enlow
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Is the Condylar cartilage the principle force that produces the displacement of the mandible ?
For many years considered primary growth center
FMH
-
Condyle absent yet mandible
positioned normally
Considered secondary cartilage -no intrinsic growth potential www.indiandentalacademy.com
PETROVIC ET AL – role of hormones
Experiments involving transplantation of the condyle
JOHNSTON ETAL
detached condyle from the body
of mandible in guinea pigs
Injection of papain –inhibition of chondrogenesis
RANCHOW MOSS
- Condylectomy – immediate
resumption of growth www.indiandentalacademy.com
Condylar cartilage and functioning muscles translate the mandible and in the absence of one the other does best to compensate
Integrity of periosteum is important
When environment is changed compensatory contributions are enhanced www.indiandentalacademy.com
CURRENT CONCEPT
Condylar cartilage does have a measure of intrinsic genetic programming But extra condylar factors are needed to sustain this activity
Physiologic inductors
Intrinsic and extrinsic biomechanical forces
ENLOW :
Increase pressure – growth inhibition Decrease pressure –www.indiandentalacademy.com stimulates growth
based mainly on animal experiments
Lingual Tuberosity
ď Ž
Grows posterior and medial by deposition
ď Ž
Resorptive field belowLingual fossa
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Coronoid Process
POSTERIOR
Lingual surface
SUPERIOR MEDIALLY
Follows ‘v’ principle
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Coronoid Process
‘’V’ PRINCIPLE OF ENLOW
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Coronoid Process
Deposition on lingual side MEDIAL
Resorption
INCREASES VERTICAL LENGTH
POSTERIOR GROWTH
- buccal surface
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RAMUS
Posterior border deposition
Anterior border resorption
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Ramus
Superior part of ramus below sigmoid notch
Lower part of ramus below the Coronoid process
LINGUAL -DEPOSITION BUCCAL RESORPTION BUCCAL DEPOSITION
LINGUAL RESORPTION www.indiandentalacademy.com
Ramus
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Posterior border of Ramus
Depository and keeps pace with condylar growth
Angle of growth vertical
horizontal
Posterior margin below condyle --resorptive field www.indiandentalacademy.com
Ramus Uprighting Posterior border – deposition Inferior > superior Anterior border – resorption Inferior >superior
Condylar growth more vertical
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Age related differences in mandibular growth MARK HANS , DONALD ENLOW AJO DEC 1995
30 well preserved human mandibles from dental ages 1 – 13 years Ground and polished microscopic sections were obtained from the Ramus Distribution of various types of resorptive vs depository surfaces were recorded 2 additional patterns of Ramal remodeling were noted www.indiandentalacademy.com
Type A – Classical Pattern
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Type B – Vertical Variation
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Type C - Rotation Variation
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Conclusions
All 3 patterns cause downward & forward displacement but to varying degree
ENLOW’S original description of general body growth & remodeling type A most common but one pattern of remodeling is incomplete
The difference in pattern were large enough to influence orthodontic treatment www.indiandentalacademy.com
Ramus corpus junction
Inferior Border of junction resorption
Forms Antegonial notch www.indiandentalacademy.com
Gonial region
Anatomically variable B - Resorption
Gonial flares
inwardly outwardly
L - deposition B -deposition L - resorption
Depends upon growth direction of ramus and condyle www.indiandentalacademy.com
Mandibular foramen
Ramus -- posterior and superior direction Mandibular foramen drifts in backward & upward direction Maintains constant position -[A-P] www.indiandentalacademy.com
Condylar neck
Anterior margin
Posterior margin
Lingual and buccal margin
Rotation – posterior border resorption
deposition
Periosteal
resorption Endosteal deposition
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Ramal growth
Backward transportation of entire ramus – elongation of mandibular body Displacement of corpus –anterior direction Vertical lengthening of ramus as mandible is displaced Movable articulation during various growth changes
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Role of muscles in Mandibular growth MOSS
CORONOID
Temporalis
GONIAL ANGLE Medial
Masseter & pterygoid
CONDYLE
internal pterygoid www.indiandentalacademy.com
Skeletal units of mandible
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Role of muscles in Mandibular growth ď Ž
Decrease muscle activity
Flattening of Gonial angle
Reduction of Coronoid process
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Growth of mandible during pubescence ARTHUR LEWIS , ALEX ROCHE AJO OCT 1982
Spurts in the mandible were analyzed in 67 subjects from Fels longitudinal study
Spurts in Ar-Go , Ar-Gn , Go-Gn
A spurt was defined as an annual increment exceeding the immediately preceding annual increment by at least 1 mm www.indiandentalacademy.com
Growth of mandible during pubescence
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Growth of mandible during pubescence conclusion
Spurts in mandibular dimensions are common but not universal More common in boys 1.5 yrs earlier in girls 1st pubertal spurt usually occurs before PHV Almost all 1st pubertal spurts occur one year after US ossification and before menarche
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Anomalies of development
AGNATHIA – deficiency of neural crest cells in lower part of the face
DOWNS
MICROGNATHIA -
TREACHER COLLINS PIERRE ROBIN
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Anomalies of development
BIFID /DOUBLE CONDYLE
MACROGNATHIA
MICROGENIA
TORUS MANDIBULARIS www.indiandentalacademy.com
References
Craniofacial embryology – SPERBER Facial growth – ENLOW Contemporary orthodontics – PROFFIT Handbook of orthodontics – MOYERS Principles and practice of orthodontics – GRABER Growth of mandible during pubescence – ROCHE,LEWIS AO OCT 1982 Age related differences in Ramus growth – ENLOW,HANS AJO www.indiandentalacademy.com DEC 1995
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