GROWTH AND DEVELOPMENT OF MANDIBLE www.indiandentalacademy.com
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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INTRODUCTION The human mandible has no one design for life. Rather it adapts & remodels through the seven stages of life, from the slim arbiter of things to come in infant, through a powerful dentate machine & even weapon in the full flesh of maturity, to the pencil thin, porcelain like problem that we struggle to repair in the adversity of old age.� “
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prenatal growth of mandible
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PRENATAL GROWTH OF MANDIBLE
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prenatal growth of mandible °Nerve→osteogenesis(Neurotrophic factors) Ectomesenchyme interacts(36-38days iul) Epi of 1st Arch
Osteogenic Memberane www.indiandentalacademy.com
Trough for acc dev Tooth buds
1 centre of ossification(6th week) below
around
Inferior Alv Nerve Incisive branch
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prenatal growth of mandible • spread of IM ossification dorsally and ventrally →body and ramus of the mandible
presence of neuromuscular bundle→Mandibular foramen and canal and mental foramen
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Fate of Meckel`s cartilage
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PRENATAL GROWTH OF MANDIBLE SECONDARY ACC CARTILAGES (10TH -14TH WEEK I U L) -condylar cartilage -coronoid cartilage -Mental ossicle cartilage
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PRENATAL GROWTH OF MANDIBLE • Secondary cartilage of coronoid process • Develop within temporalis muscle • Incorporated into IMB of ramus • Disappear before birth www.indiandentalacademy.com
PRENATAL GROWTH OF MANDIBLE • 1/2 Cartilages Ossify (7th month of IUL)
Mental ossicles syndesmosis
Intramembranous bone
→
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synostosis
PRENATAL GROWTH OF MANDIBLE • CONDYLAR CARTILAGE(10TH WEEK IUL) • Grow interstitially and oppositionally
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CONDYLAR CARTILAGE • 1ST Evidence of endochondral bone (14th week iul) • Much of cartilage replaced with Bone by middle of fetal life • Upper end →Growth cartilage and Articular cartilage • Changes Mand position and form • Growth ↑ at puberty peak b/n 12 ½ -14yrs • Ceases →2o yrs of life www.indiandentalacademy.com
NEONATAL MANDIBLE Ramus→Low & wide coronoid→large & above the condyle Body→open shell containing tooth buds Mand canal→low in the body www.indiandentalacademy.com
DIFFERENTIAL GROWTH During fetal life 8weeks - MANDIBLE> MAXILLA 11weeks -MANDIBLE= MAXILLA 13-20weeks-MAXILLA>MANDIBLE
AT BIRTH Mandible tends to be retrognathic Early postnatal life -orthognathic www.indiandentalacademy.com
POST NATAL GROWTH & DEVELOPMENT OF MANDIBLE
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MECHANISMS OF GROWTH Growth Of The Mandible Primarily Involve Bone remodeling Process Of Bone Deposition And Resorption Cortical drift Combination of bone deposition and resorption resulting in growth movement towards deposition surface Displacement Movement of whole bone as a unit I) Primary displacement II) Secondary displacement www.indiandentalacademy.com
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THEORIES OF GROWTH • GENETIC THEORY
Bone ̶ primary determinent Cartilage̶ primary determinent The softwww.indiandentalacademy.com tissue matrix
SUTURAL THEORY • Craniofacial growth→sutures • Suture transplanted • Sutures pulled apart • Sutures compressed • Sutures are sites that react ̶ not primary dereminants www.indiandentalacademy.com
CARTILAGINOUS THEORY • Growth of maxilla ̶ Nasalseptum cartilage • Transplantation Epiphyseal plate Nasalseptal cartilage Condylar cartilage Removal of condyle
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FUNCTIONAL MATRIX THEORY OF GROWTH • Skeletal growth occur as a response to functional needs & mediated by the soft tissue in which it is embedded
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ENLOW’S EXPANDING ‘V’ PRINCIPLE The growth movement & enlargement of these Bones occur towards the wide ends of the ‘V’ as a result of differential deposition & selective resorption
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ENLOW’S COUNTERPART PRINCIPLE • The growth of any given facial /cranial part relates specifically to other structural & geometric ‘counterparts’ in the face & cranium Diff parts & counter parts Maxillary & Mandibular arches Middle cranial fossa breadth of Ramus www.indiandentalacademy.com
Parts of Mandible derived From 1. INTRAMEMBRANOUS OSSIFICATION * Whole body of mandible except the anterior part * Ramus of mandible as far as mandibular foramen 2 . ENDOCHONDRAL OSSIFICATION * Anterior portion of the mandible (symphysis) * Part of ramus above the mandibular foramen * Coronoid process * Condylar process
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Timing of growth • Growth in width is completed 1st then growth in length finally growth in height
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Growth in width • Intercanine width does not ↑ much after 12yrs • Both molar & bicondylar width show small ↑ until the end of growth in length • Ant width stabilize earlier
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Growth in length • Continues through the period of puberty Girls – 14 -15 yrs Boys – 18 yrs
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POST NATAL GROWTH OF MANDIBLE • Mandible – Developmentally & Functionally divisible into skeletal subunits
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• Mandible undergoes largest amt of growth postnatally and exhibits largest variability in morphology • The main sites of postnatal growth ٭At condylar cartilages ٭Posterior border of rami ٭Alveolar ridges www.indiandentalacademy.com
THE RAMUS • Key role of ramus in placing the corpus & dental arch into ever changing fit with growing maxilla & the faces limitless strl variations • By Remodeling adjustments in Ramus length & Ant post width. www.indiandentalacademy.com
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THE RAMUS Relocates postly Resorption
Deposition posteriorly anteriorly
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LINGUAL TUBEROSITY • Direct Anatomic equivalent of Max tuberosity • Inaccessible to cephalometric studies • Major Growth & Remodeling site • Effective boundary b/n Ramus & corps
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LINGUAL TUBEROSITY • Deposition • Resorption
Postly & Medially Below (Lingual fossa )
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Lingual Tuberosity Remodels in post direction with slight lateral shift
Lingual shift of Ant part of Ramus
↑ Length of corpus www.indiandentalacademy.com
Ramus to carpus Remodeling • Making room last Molar
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Ramus to carpus Remodeling
Growth direction fallows‘V’PRINCIPLE ‘X’ arrows Remodeling activity does not occur only on ant & post barder www.indiandentalacademy.com
Coronoid process • Propellar like twist • Lingual side faces posteriorly superiorly medially
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Coronoid process Fallows ‘V’ PRINCIPLE
‘V’ oriented vertically
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Coronoid process ‘v’ PRINCIPLE ‘V’Oriented horizontally
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Coronoid process Coronoid process → medially to become post part of carpus
Buccal side → Resorptive
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Ramus • Superior part of ramus the area below sigmoid notch
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Ramus
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Antigonial notch Size of the notch ↑ed – downward rotation Of carpus relative to the Ramus
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The size of the notch depends upon Ramus – Carpus junction
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Post edge Ramus is a major growth site Condyle grows obliquely upward & backward The angle of growth is variable The gonial region is Anatomically variable
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Mand Foramen – midway b/n Ant & post borders of Ramus
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The Mandibular condyle • Secondary cartilage •
not a primary center of growth, but rather * Secondary in Evolution * Secondary in Embryonic origin * Secondary in adaptive responses
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condyle • Cartilage is special nonvascular tissue • firm matrix – unyielding to the pressure • Endochondral growth mechanism
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• Provides pressure tolerant articular contact • Multidimensional growth capacity in response to ever changing developmental conditions & variations
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• Capsular layer of poorly vascularised connective tissue –highly cellular • Chondroblasts –cellular proliferation • Chondroblasts – hypertrophy • Zone of resorptive & Bone deposition www.indiandentalacademy.com
• Proliferative process produces upward & backward growth movement • Multidirectional proliferative capacitythe arrangement of daughter cells does not reflect direction of growth www.indiandentalacademy.com
• The cortical layer of IMB continues on to the condylar neck Ant margin of condylar neck – depository grows supe’ly post margin - depository grows on to post barder www.indiandentalacademy.com
• Lingual & Buccal sides - Resorptive
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• V-shaped cone of condylar neck growing towards its wider end
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• The condyle can’t play king pin role of “Master center” in pace-setting the growth Bilaterally condyle-lacking mand occupy normal Anatomic position Condylar remodeling acts with displacement as co-participants but not as driving force www.indiandentalacademy.com
Current concept • Condylar cartilage does have some intrinsic genetic programming • But extracondylar factors are needed to sustain this activity 1)Intrinsic & extrinsic biomechanical forces 2)physiologic inductors ENLOW; ↑amt of pressure – inhibit the growth www.indiandentalacademy.com ↓ amt of pressure – stimulate the growth
• Mandible is less responsive to orthopedic forces than maxilla • Mand orthopedics must modify growth signals targeted at both ramus & condyle to be maximally effective www.indiandentalacademy.com
MENTAL FORAMEN
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ALVEOLAR PROCESS Adds ht & thickness to the body of the Mand Teeth absent fails to develop Resorbs after tooth extraction
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Alveolar process • Maintain occlusal relationship during differential mandibular & midfacial growth– buffer zones • Maintains vertical height • Adaptive remodeling makes orthodontic tooth movement possible
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Lingual movement of anteriors
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Mental protuberance Formed by mental ossicles from accessory cartilage and ventral end of Meckel’s cartilage Poorly developed in infants
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Mental protuberance Forms by osseous deposition during childhood Prominence is accentuated by bone resorption above it Reversal between 2 growth fields Concave ďƒ convex Reversal line could be High or www.indiandentalacademy.com low
Chin • Protrusive chin is unique human trait • More prominent in male • Less prominent in female
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Factors Affecting Growth Systemic Factors Genetic Hormonal imbalance Nutrition Systemic illness or chronic illness Localized alteration/ diseases of uterus Systemic illness in mother Drugs
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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 9. Habits www.indiandentalacademy.com
Anomalies of mandible Some of the syndromes associated with mandibular abnormality 1)Down’s syndrome 2)Marfan’s syndrome 3)Turners syndrome 4)Kleinfelter’s syndrome 5) Pierre-robin syndrome 6) Treacher- collin syndrome www.indiandentalacademy.com
Congenital • Agnathia • Micrognathia • Macrognathia • Facial hemihypertrophy • Facial hemiatropy
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Developmental • Infantile cortical hyperostosis • Achondroplasia • Torus mandibularis • Stafne’s cyst • Odontogenic cyst • Odontogenic tumor www.indiandentalacademy.com
Age changes of Mandible At birth
Adult
Old age
1 Mental foramen
Near the lower border
Midway b/n upper & lower border
Near the upper border
2 Angle of the mandible 3 coronoid & condyloid processes
Obtuse (180)
Right angle
Obtuse (140)
Coronoid is larger & above condyle
Condyle is above the coronoid
4 Mandibular canal
Runs little above the mylohyoid line Present;two halves united fibrous tissue
Runs parallel to the mylohyoid line
Condyle is above the coronoid but in extreme old age –bent backwards Runs close to the upper border
5 Symphysis menti
Reprasented by faint ridge only in the upper part
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Not recognisable or absent
References * Craniofacial embryology – SPERBER * Facial growth – ENLOW * Contemporary orthodontics – PROFFIT * Handbook of orthodontics – MOYERS * Principles and practice of orthodontics –GRABER
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