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Postnatal growth of the skull and jaws _  Dr. Nabil Al-Zubair
 

Postnatal growth of the skull and jaws _ Dr. Nabil Al-Zubair

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  • great presentation, could you please send it to me..(koki_jan26@yahoo.com).. thanks in advance..
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    Postnatal growth of the skull and jaws _  Dr. Nabil Al-Zubair Postnatal growth of the skull and jaws _ Dr. Nabil Al-Zubair Presentation Transcript

    • POSTNATAL GROWTHofTHE SKULL and JAWSDr. Nabil Al-Zubair
    • • What initiates growth?• What controls the extent & timing of growth?
    • What initiates growth?Somatotrophin hormone(growth hormone)released from the pituitary gland
    • What controls the extent & timing of growth?• Highly conserved homeobox genesprovide the genetic “blue print” forgrowth & development• These genes are the same in allanimals & are highly conserved• Gives rise to family resemblance – adisturb of the genes can causechromosome defects such as Trisomy21 (Down’s syndrome)Genetic control Environmental control
    • What controls the extent & timing of growth?• Psychological stress in emotionallydeprived children inhibit the releaseof growth hormone• Moss’s functional matrix theoryGenetic control Environmental control
    • Mechanisms of bone growthBone deposition & resorptionCortical driftDisplacement
    • (1) Bone deposition & resorption• Bone changes in shape & size by two basicmechanisms(1) bone deposition &(2) bone resorption• The process of bone deposition & resorptiontogether is called“Bone Remodeling”
    • Bone deposition & resorptionThe changes that bone deposition &resorption can produce are:a. Change in sizeb. Change in shapec. Change in proportiond. Change in relationship withadjacent structures
    • (2) Cortical drift• A combination of bone deposition &resorption resulting in:a growth movement towards the depositingsurface is called“cortical drift”Deposition = ResorptionThickness of the bone remains constantDeposition > ResorptionThickness of the bone increases
    • • PALATE, where bone isdeposited on the inferiorsurface and resorbed fromits superior surface. The change in the position of a bony structure owing toremodelling of that structure is called driftExamples
    • 1. Primary Displacement:2. Secondary Displacement(3) DisplacementIt is the movement of the whole bones as a unitDisplacement can be of two types:
    • a- if a bone gets displaced as a result ofits own growthb- For example growth of the maxilla atthe tuberosity region results in:pushing of the maxilla against thecranial base which results in:the displacement of the maxilla in aforward & downward direction1. Primary Displacement:
    • 2. Secondary displacement:a- if a bone gets displaced as aresult of growth &enlargement of an adjacentboneb- For example, the growth of thecranial base causesthe forward & downwarddisplacement of the maxilla
    • OsteogenesisEndochondral bone formationIntra-membranous bone formation
    • OSTEOGENESIS• Bone formation takes place in two ways:1. Endochondral bone formation2. Intra-membranous bone formationThe process of bone formation is called osteogenesis
    • Endochondral bone formationThe bone formation is preceded by formation of a cartilaginousmodel which is subsequently replaced by boneEndochondral bone formation occurs as followsCartilage Bone
    • Mesenchymal cellsChondroblastsHyaline cartilagealkaline phosphataseThe surrounding inter-cellular substance becomes calcifiedThus the nutrition to the cartilage cells is cut off leading to their deathPrimary areolaeSecondary areolaeThe blood vessels & osteogenic cellsfrom the preichondrium invade thecalcified cartilaginous matrixOsteoblastsOsteoidCalcified to form a lamella of bonePreichondriumEndochondral bone formationcondensed
    • Intra-membranous bone formation• Instead bone is laid down directly in a fibrous membrane• The intra-membranous bone is formed in the following manner:• The formation of bone is not preceded byformation of a cartilaginous model
    • Mesenchymal cellsCollagen fiberEnlarge & acquire a basophilic cytoplasm & form osteoblastsSecrete a gelatinous matrix called osteoid around the collagen fiberThey deposit calcium salts into theosteoid leading to conversion ofosteoid into bone lamellaosteoid bone lamellaNow another layer of osteoid is secreted & this goes on & on.Ca++aggregatedIntra-membranous bone formation
    • Theories of growthGenetic theorySutural theoryCartilaginous theoryThe functional matrix concept
    • What is the primary determinant of growth ?Structures thought to be involved:BoneCartilageSoft tissueWhat are the components which have innate growth potential over which there isgenetic & environmental influence ?‫فطري‬
    • • Simply states that all growth iscontrolled by genetic influence & ispre-planned• One of the earliest theories putforwardGenetic theory
    • • Sicher believed that cranio-facialgrowth occurs at the sutures• According to him :• The sutures had innate growthpotential & that the sutures pushapart the bones → an increase in sizeSutural theoryOld school of thought:
    • • Disproved by transplanting a suture→ no sutural growth was produced• Growth takes place in untreatedcases of cleft palate even in theabsence of suturesSome points against Sutural theory:
    • • This theory was put forward by JamesScott.• According to him:– intrinsic growth controlling factorsare present incartilage & periosteumwith sutures being only secondary• He viewed the cartilaginous sitesthroughout the skull as primary centersof growth• Growth of the maxilla is attributed to thenasal septal cartilageCartilaginous theory
    • 1. In many bones,cartilage growth occurs, while bonemerely replaces it2. Nasal septal cartilage also showinnate growth potential on beingtransplanted to another siteCartilaginous theoryPoints favour this theory include:
    • The functional matrix concept• The functional matrix concept of MelvinMoss revitalized the studies on growth &development at a time when the Suturalgrowth theory by Sicher & Cartilaginousgrowth theory of Scott were severelycriticized for their inadequacy• The functional matrix concept attemptsto comprehend the relationship b/wform & function
    • The functional matrix concept• The functional matrix hypothesis claimsthat:The origin, form, position, growth &maintenance of all(skeletal tissues & organs)are alwaysSecondary, compensatory & necessaryresponse toChronologically & morphologically prior eventsor processes that occur inspecifically related(non-skeletal tissues, organs or functionspaces)
    • • A number of relatively independent functionare carried out in the cranio-facial region of thehuman body• Some of the function carried out include:(1) respiration, (2) olfaction, (3) vision, (4) hearing,(5) balance, (5) chewing, (6) digestion, (7)swallowing, (8) speech & (10) neuralintegration• Each of these functions is carried out by afunctional cranial component
    • • Each functional cranial component consistof all of the tissues, organs, spaces &skeletal parts necessary to carry out agiven function• The functional cranial component isdivided into:1. Functional matrix2. Skeletal unit
    • Moss’s functional matrix theoryGenetic control is expressed in the softtissue& the cartilage & bone secondarilySoft tissueGenetic controlCartilage Bone State that : “growth of the face occursas a response to functional needs & ismediated by the soft tissue in whichthe jaws are embedded” Brain growth cranium size O2 demand Max. sinusdevelopment The orbit grows as a result of eyegrowth
    • Enlow’s expanding ‘V’ PRINCIPLE• Many of facial bones or parts of bonehave a ‘V’ shaped pattern of growth• The growth movements & enlargementof these bones occur towards the wideends of the ‘V’ as a result of(1 ) differential deposition &(2 ) selective resorption of bone
    • • Bone deposition occurs on the innerside of the wide end of the ‘V’ & boneresorption on the outer surface• Deposition also takes place at the endsof the 2 arms of the ‘V’ resulting ingrowth movement towards the ends• The ‘V’ pattern of growth occurs in anumber of regions such as the (1) baseof the mandible,(2) ends of long bones,(3) mandibular body,(4) palate etc.,.+ +- -++
    • POSTNATAL GROWTH OF THESKULL AND JAWS
    • MECHANISMS OF BONE GROWTHBone grows either by:1. Replacement of cartilage(endochondral ossification)2. Periosteal activity(intramembranous ossification)
    • Endochondral ossification-• This form of bone growth is under tight intrinsic control (genetic).1. The epihyseal plates of long bones &•This process is seen in both:2. The synchondroses of the cranial base.Spheno-occiptalSpheno- ethmoidalSpheno-occiptal
    • Intramembranous ossification-Bone is laid down and resorbedbyThe investing periosteumand endosteum.Periosteal remodellingalso needed toMaintain the overall shape of the bone as it grows
    • HeadCranial vault Cranial baseMandibleNaso-maxillary complex
    • Mechanisms of growthOssification Apposition at sutures Remodeling due to “ functional matrix” ofexpanding brainIntra-membranousCranialvault Growth centers at synchondrosesEndochondoralCranial baseGrowth is directed byorientation of the suturesforwards & downwards Apposition atsutures Remodeling Alveolardevelopment to alloweruption of teethIntra-membranousexcept fornasal cartilageNaso-maxillarycomplex Increase in ramalheight by condylargrowth Increase in bodyheight due to Alveolardevelopment to alloweruption of teeth 2/3 of jaw is completedat age 10 yearsApposition at sutures Remodeling due to “functional matrices” ofattached musclesIntra-membranousMandible
    • Mechanisms of growthOssification Apposition at sutures Remodeling due to “ functional matrix” ofexpanding brainIntra-membranousCranialvault Growth centers at synchondrosesEndochondoralCranial baseGrowth is directed byorientation of the suturesforwards & downwards Apposition atsutures Remodeling Alveolardevelopment to alloweruption of teethIntra-membranousexcept fornasal cartilageNaso-maxillarycomplex Increase in ramalheight by condylargrowth Increase in bodyheight due to Alveolardevelopment to alloweruption of teeth 2/3 of jaw is completedat age 10 yearsApposition at sutures Remodeling due to “functional matrices” ofattached musclesIntra-membranousMandibleSpheno-occiptalSpheno- ethmoidalSpheno-occiptal
    • Elongation at the synchondroses• Most of the bones of the cranialbase are formed by a cartilaginousprocess• Later the cartilage is replaced bybone• Certain bands of cartilage remainat the junction of various bones.• These areas called Synchondroses.They are important growth sites ofthe cranial base• The important synchondroses foundin the cranial base are:1. Spheno-occipital synchondroses2. Spheno-ethmoidal synchondroses3. Inter-sphenoid synchondroses4. Inter-occipital synchondroses
    • Growth centers(1) Spheno – occipital synchondrosis:Active until age 16 yearsCalcification completed at age 25 yearsSpheno-occiptalSpheno- ethmoidalSpheno-occiptal
    • Cranial Base• The SOS is anterior to the TMJ butposterior to the anterior cranialfossa and its growth influences thefacial skeletal pattern.• Growth at the SOS (1) Increases the length of the cranialbase, andsince the maxilla and mandible are bothrelate to this structure, the latter(2) plays an important part in howthe 2 jaws relate to each other.
    • Growth centers(2) Fronto – ethmoidal synchondrosis:Active until pubertySpheno-occiptalSpheno- ethmoidalSpheno-occiptal
    • Growth centers(3) Spheno – ethmoidal synchondrosis:Active until age 7 yearsSpheno-occiptalSpheno- ethmoidalSpheno-occiptal
    • Timing of cranial base growtha. By birth, 55-60% of adult size is attainedb. By 4-7 years, 94% of adult size is attainedc. By 8-13 years, 98% of adult size is attained
    • Mechanisms of growthOssification Apposition at sutures Remodeling due to “ functional matrix” ofexpanding brainIntra-membranousCranialvault Growth centers at synchondrosesEndochondoralCranial baseGrowth is directed byorientation of the suturesforwards & downwards Apposition atsutures Remodeling Alveolardevelopment to alloweruption of teethIntra-membranousexcept fornasal cartilageNaso-maxillarycomplex Increase in ramalheight by condylargrowth Increase in bodyheight due to Alveolardevelopment to alloweruption of teeth 2/3 of jaw is completedat age 10 yearsApposition at sutures Remodeling due to “functional matrices” ofattached musclesIntra-membranousMandible
    • The maxillary complex• The maxilla enlarges AP by(1) Deposition of bone posterioly at thetuberosities which enlarge the dentalarches.(2) Anterior displacement occurs as bone islaid down on its posterior aspect.• Downward growth occurs by(1) development of the alveolar process and(2) dental eruption, and also by(3) inferior drift of the hard palate.
    • The maxillary complex• Lateral growth in the mid-faceoccurs by displacement apart ofthe 2 halves of the maxilla,with deposition of bone at the midlinesuture.• Maxillary growth ceases at ;- 15 yrs (girls) &- 17 yrs (boys).
    • Mechanisms of growthOssification Apposition at sutures Remodeling due to “ functional matrix” ofexpanding brainIntra-membranousCranialvault Growth centers at synchondrosesEndochondoralCranial baseGrowth is directed byorientation of the suturesforwards & downwards Apposition atsutures Remodeling Alveolardevelopment to alloweruption of teethIntra-membranousexcept fornasal cartilageNaso-maxillarycomplex Increase in ramalheight by condylargrowth Increase in bodyheight due to Alveolardevelopment to alloweruption of teeth 2/3 of jaw is completedat age 10 yearsApposition at sutures Remodeling due to “functional matrices” ofattached musclesIntra-membranousMandible
    • • The basal bone or the body ofthemandible forms one unit, towhich is attached(1) the alveolar process,(2) the coronoid process,(3) the condylar process,(4) the angular process,(5) the ramus,(6) the lingual tuberosity &(7) the chin
    • • The ramus moves progressivelyposterior by: a combination ofdeposition & resorption• Resorption occurs on the anterior partof the ramus while bone depositionoccurs on the posterior region• This results in a ‘drift’ of the ramus ina posterior directionRamus
    • • The functions of remodeling of the ramusare:1. To accommodate the increasing mass ofmasticatory muscles inserted into it2. To accommodate the enlarged breadth ofthe pharyngeal space3. To facilitate the lengthening of themandibular body, which in turnaccommodates the erupting molarsRamus
    • • Alveolar process develops in responseto the presence of tooth buds• As the teeth erupt the alveolar processdevelops & increases in height by bonedeposition at the margins• In case of absence of teeth, thealveolar bone fails to develop & itresorbs in the event of tooth extractionThe alveolar process
    • • The chin is a specific humancharacteristic & is found in its fullydeveloped form in recent man only• In infancy, the chin is usuallyunderdeveloped• As the age advances the growth of chinbecomes significantThe chin
    • • Usually males are seen to haveprominent chins compared to femalesThe chin
    • The Mandible• Growth of the condylar cartilageelongates the mandible.• Most mandibular growth occurs asa result of periosteal activity whichmaintains the shape.Growth ceases at 17 yrs in girls and 19 yrs in boys.
    • Mechanisms of growthOssification Apposition at sutures Remodeling due to “ functional matrix” ofexpanding brainIntra-membranousCranialvault Growth centers at synchondrosesEndochondoralCranial baseGrowth is directed byorientation of the suturesforwards & downwards Apposition atsutures Remodeling Alveolardevelopment to alloweruption of teethIntra-membranousexcept fornasal cartilageNaso-maxillarycomplex Increase in ramalheight by condylargrowth Increase in bodyheight due to Alveolardevelopment to alloweruption of teeth 2/3 of jaw is completedat age 10 yearsApposition at sutures Remodeling due to “functional matrices” ofattached musclesIntra-membranousMandible
    • Overall facial growth1. Head occupies 30% of the bodylength & 12% in adulthood2.The face occupies less than30% of the skull height &60% in adulthood, thisdemonstrate how rapidly thebrain grows immediatelyafter birth3.The brain is fully grown at age8 years on average
    • Dr. Nabil Al-Zubair