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INDIAN DENTAL ACADEMY Leader in continuing dental education

CONTENTS      


What is Growth?  

Growth refers to increase in size- Todd Growth usually refers to an increase in size and number – Proffit Self multiplication of living substance – J.S. Huxley Entire series of sequential anatomic and physiologic changes taking place from the beginning of prenatal life to senility Meridith

What is Development? ď Ž

ď Ž

It is the progress towards maturity – Todd Development refers to all the naturally occurring unidirectional changes in the life of an individual from its existence as a single cell to its elaboration as a multifunctional unit terminating in death Moyers


Prenatal Growth 

It’s the most dynamic phase and is divided as

•Preimplantation period •Embryonic period •Fetal period

Formation of the Pharyngeal Arches ď Ž

The mesoderm of the lateral plate of the ventral foregut becomes segmented to form a series of five distinct bilateral mesenchymal swelling called as the Pharyngeal Arches.

th week

4 week embryo

Contents of each arch

   

Skeletal element Striated muscle Nerve Artery

Internal view of pharyngeal floor and cut arches

Mandibular Arch

   

Meckel’s cartilage Musculature Mandibular nerve Artery- maxillary and external carotid

Meckel’s cartilage   

41th- 45th day of I.U.L Provides a template Extends from Otic capsule –Midline or Symphysis

Ossification of Meckel’s cartilage ď Ž

Mandibular division of trigrminal nerve

Neurotrophic factor


Ossification of Meckel’s cartilage 

In 6th week IU

Ossification of Meckel’s cartilage Trough Trough for for dev. dev. teeth teeth

1°centre 1°centre of of ossification ossification below

Infr Infr alv. alv. Nerve Nerve && Incisive Incisive branch branch


Ossification of Meckel’s cartilage 

Ossification spreads dorsally and ventrally •Body •Ramus Ossification stops at the site that will become mandibular lingula

Fate of Meckel’s cartilage   

 

Meckel’s cartilage lacks enzyme phosphatase It disappears by 24th week of conception A small part transforms into sphenomandibular and anterior malleolor ligaments Ventral end forms accessory endochondral ossicles Meckel’s cartilage dorsal to mental foramen gets resorbed on the lateral surface. Immediately lateral to resorbing cartilage,intramembranus bony trabeculae are being formed.

Fate of Meckel’s cartilage

Woven Woven bone bone 55thth month month

Lamellar Lamellar bone bone ++ haversian haversian system system

Fate of Meckel’s cartilage Coronoid cartilage

Condylar cartilage

10th & 14th week Sec. accessory cartilage

Angular cartilage Mental ossicle

Secondary cartilage of coronoid process

Develop within temporalis muscle

Incorporated into intramembranus bone of ramus Disappear before birth

 

Secondary cartilage at Mental region 1 or 2 small cartilage ossify mental ossicles(7th month) in fibrous tissue of symphysis It gets incorporated into intramembranous bone symphysis menti 1st postnatal year

synostosis syndesmosis

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

Types Of Ossification 

Mandible is the first bone to be ossified (6th week) There are two types of ossification :



Intramembranous bone formation Mesenchyme

Collagen fibre


Osteoid matrix Calcium salts

Osteoblasts Bone lamella

Intramembranous bone formation

Intramembranous bone formation

Endochondral bone formation Mesenchymal cells

Hyaline cartilage Alkaline phosphatase

Primary areolae

Calcified Blood vessels

Secondary areolae


Lamella of bone

Endochondral bone formation

Endochondral bone formation


Cartilage template is replaced by endochondrial bone


Direct deposition of osseous tissue in periosteal membrane

Indirect bone growth

Direct bone growt

Slow expansion

Rapid expansion

Parts Of Mandible Derived From 1. INTRAMEMBRANOUS OSSIFICATION i.

Whole body of mandible except the anterior part

ii. Ramus of mandible as far as mandibular foramen

2 . ENDOCHONDRAL OSSIFICATION i. Anterior portion of the mandible (symphysis) ii. Part of ramus above the mandibular foramen iii. Coronoid process iv. Condylar process

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

Neonatal mandible

Differential growth During During fetal fetal life life 88 weeks weeks -- mandible mandible >> maxilla maxilla 11 11 weeks weeks -- mandible mandible == maxilla maxilla 13 13 –– 20 20 weeks weeks maxilla maxilla >> mandible mandible At At Birth Birth Mandible Mandible tends tends to to be be retrognathic retrognathic Early Early post post natal natal life life -- orthognathic orthognathic

Post Natal Growth 

Mechanism of bone growth

Theories of growth


Mechanisms Of Bone Growth Growth Of The Mandible Primarily Involve

1. Bone remodeling Process Of Bone Deposition And Resorption

2. Cortical drift Combination of bone deposition and resorption resulting in growth movement towards deposition surface

3. Displacement Movement of whole bone as a unit

I) Primary displacement II) Secondary displacement

Theories of growth

Theories of growth

Other theories for growth 

ENLOW’S “V” PRINCIPLE The growth and enlargement of bones occur towards wide end of ‘V’ due to differential deposition and resorption

Enlow’s Counterpart Principle 

‘The growth of any given facial or cranial part relates specifically to other structural and geometric “counter” parts in the face and cranium’. Eg. Maxillary arch is counter part of mandibular arch.

Regional Regional part part

counter counter part part

Balanced Balanced growth growth


Growth timings 

The overall growth of mandible takes place at different stages. First there is increase in its  Width  Length  Height

Width 

Growth in width is completed before adolescent growth spurt Intercanine width does increase after 12 years Both molar and bicondylar width shows small increase until growth in length ends

Growth in length 

 

Growth in length continues through puberty Girls - 14-15 years Boys - 18-19 years

Growth in height 


Main sites of post natal growth in the Mandible 

Condylar cartilage

Posterior border of the Rami

Alveolar ridges

Condylar cartilage Site of growth for ramus and body of mandible Dual function articular articular

growth growth Not a primary Centre of growth but rather site of growth 2° 2° in in evolution evolution 2° 2° in in embryonic embryonic origin origin 2°to 2°to adaptive adaptive changes changes

Is the Condylar cartilage the principle force that produces the displacement of the mandible ?

For many years considered primary growth center Condyle absent yet mandible positioned normally Considered secondary cartilage -no intrinsic growth potential

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 changes compensatory contributions are enhanced

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 – stimulates growth

based mainly on animal experiments

Age changes in mandible

Ramus 

Moves progressively posterior by:POSTERIOR PART Deposition Resorption


Ramus Superior part of ramus below sigmoid notch



Lower part of ramus below the Coronoid process




Coronoid process ď Ž

Deposition on lingual side

ď Ž

Resorption on buccal surface

Coronoid process ‘’V’ PRINCIPLE OF ENLOW

Lingual surface

Body of mandible 

The increase in width of the mandible occurs primarily due to resorption on the inside and deposition on the outside Increase in length occurs due to drift of the ramus posteriorly Increase in height occurs due to eruption of the teeth

Body of mandible

Ramus corpus junction 

Inferior Border of junction - resorption Forms Antegonial notch

Antegonial notch Size depends upon ramus – corpus angle

Lingual Tuberosity ď Ž

ď Ž

Grows posterior and medial by deposition

Resorptive field belowLingual fossa

Alveolar Process 

Adds to the height and thickness of the mandibular body Teeth absent fails to develop Teeth extracted resorbs

Alveolar Process 

Maintain occlusal relationship during differential mandibular & midfacial growth– buffer zones

Maintains vertical height

Alveolar Process Lingual Lingual movement movement of of anteriors anteriors

Mental Protuberance 

Formed by mental ossicles from accessory cartilage and ventral end of Meckel’s cartilage Poorly developed in infants

Mental Protuberance ď Ž

ď Ž

Forms by osseous deposition during childhood Prominence is accentuated by bone resorption above it

Mental Protuberance 

Reversal between 2 growth fields Concave  convex Reversal line could be High or low

Chin 

Protrusive chin is unique human trait

More prominent in male

Less prominent in female

Symphysis Menti 

Limited growth till fusion

No widening after fusion

Mental Foramen

Growth rotation ď Ž

The ramus undergoes remodeling rotation this produces displacement rotation as a whole

Rotation is of two type ď Ž

Internal rotation Intramatrix

ď Ž

External rotation


Growth rotation 

 

 

The rotation is considered forward if growth is more posteriorly than anteriorly. The rotation is considered backward if growth is more anteriorly than posteriorly. Short face -forward growth Long face -backward growth Males-slight forward growth Females-slight backward growth

Factors Affecting Growth A) Systemic Factors 1. Genetic 2. Hormonal imbalance 3. Nutrition 4. Systemic illness or chronic illness 5. Localized alteration/ diseases of uterus 6. Systemic illness in mother

B) Local factors 1. Vascular abnormality

2. Lymphatic disturbance 3. Neurologic disease 4. Local infection 5. Ear infection or mastoiditis 6. Ankylosis 7. Trauma or fracture 8. Birth injury

Age changes in mandible

Radiographs of midsagital section’s of mandible Pre-extraction

High well-rounded


Knife edge

Low well rounded With out cortical layer on crest

Low well rounded with cortical layer on crest


Syndromes associated with mandibular abnormality •Pierre-Robin’s syndrome •Treacher-collins syndrome

Pierre-Robin’s syndrome

Treacher-collins syndrome


Congenital •Agnathia •Micrognathia •Macrognathia


Developmental •Torus Mandibularis •Achondroplasia •Stafne’s cyst •Odontogenic cyst

Torus mandibularis

Stafne’s cyst


Oral histology, development, structure and function – A.R. Ten Cate, 4th Edition The essentials of facial growth – Enlow and Hans, 1st Edition. Orthodontics principles and practice – Graber, 3rd edition Craniofacial Embryology- GH Sperber, 4th edition Textbook of oral pathology– William Shafer, 5th Edition



Orthodontics art and science-

Bhalajhi,3rd edition Human embryology- Inderbir singh,7th edition

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