Growth and devop/ dental implant courses by Indian dental academy by indiandentalacademy

Growth and development of cranium and maxilla

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ď&#x201A;§ Growth- Robert Moyers defines growth as the normal changes in amount of living substance. ď&#x201A;§ Development-refers to all naturally occurring unidirectional changes in life of an individual from its existence as a single cell to its elaboration as a multifunctional unit terminating in death. ď&#x201A;§ Development=growth+differentiation+translo cation www.indiandentalacademy.com

Controlling factors in craniofacial growth ď&#x201A;§ Natural genetic function general body growth neurotrophism

ď&#x201A;§ Disruptive forces orthodontic forces surgery malnutrition malfunctions gross craniofacial anomalies www.indiandentalacademy.com

pre-natal Growth proper

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ď&#x201A;§ Pre-natal life of an individual can be broadly divided into following three phases Period of ovum Period of embryo Period of fetus

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Pharyngeal arches www.indiandentalacademy.com

pre-natal Growth and development of cranium

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 Mesodermally derived ectomeninx gives rise to – – – – –

Frontal Parietal Sphenoid Petrous temporal Occipital

 Neural crest provides mesenchyme for – – – – – –

Lacrimal Nasal Squamous temporal Zygomatic Maxilla Mandible

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Calvaria

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Frontal Bone  Single primary ossification centre in the region of superciliary arch at 8th week i.u.  3 pairs of secondary centres in  Zygomatic processes  Nasal spine  Trochlear fossae  Fusion completes at 6-7 months i.u.  Metopic suture-synostic fusion starts at 2 nd year and completes by 7years www.indiandentalacademy.com

Parietal Bone ď&#x201A;§ Arises from two primary ossification centres at parietal eminence in 8th week i.u. ď&#x201A;§ Fuses in 4th month i.u. ď&#x201A;§ Delayed ossification in region of parietal foramina results in sagittal fontanelle at birth. www.indiandentalacademy.com

Temporal bone  Squamous portion ossifies intra membranously from 1 centre appearing at root of zygoma at 8th week i.u.  Tymphanic ring ossifies I.M. from 4 centres at 3rd month i.u. in the lateral wall of tympanum.  Pre-mastoid & styloid ossify endochondrally www.indiandentalacademy.com

Occipital bone  Supranuchal squamous part ossifies I.M. at 8 th week  Below superior nuchal line, basilar part, condylar part ossifies endochondrally at 10th ,11th, 12th week respectively.  Earliest centres of ossification first appear at 7 th & 8th week i.u. but ossification is not completed until well after birth  Unusual ossification centres develop between individual calvarial bones- sutural or wormian www.indiandentalacademy.com bones`

 Ultimate shape & size of cranial vault depends on internal pressure exerted on inner table of neurocranial bones.  Circumference of head is good indicator of brain growth.     

18cm at mid gestational period 33cm at birth 46cm at 1yr of age 49cm at 2yrs 50cm at 3yrs

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 Growth of calvarial bone is combination of – – –

Sutural growth Surface apposition & resorption Centrifugal displacement by expanding brain

 Bones of new born calvaria are unilaminar & lack diploe  Inner table is related to brain & intracranial pressures  Outer table more responsive to extracranial muscular & buttressing forces. www.indiandentalacademy.com

 Thickening of frontal bone at region of glabella results from separation of inner & outer tables with invasion of frontal sinus between cortical plates.  Inner plate becomes stable at 6-7 yrs because of cessation of cerebral growth. Used as stable reference point for growth studies.  Growth of external plate produces – – – –

Superciliary arches Mastoid processes External occipital protuberance Temporal & nuchal lines

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The cranial base ď&#x201A;§ Chondrocranium is important as a shared junction between neurocranial & facial skeletons. ď&#x201A;§ Formation of the cartilages of chondrocranium is dependent on presence of brain & other neural structures & an appropriately staged inducing epithelium. ď&#x201A;§ Chondrogenesis occurs only after an epithelialmesenchymal interaction has taken place. www.indiandentalacademy.com

Basicranial ossification centres

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Cranial base angulation

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 Anterior & posterior parts of cranial base grow at different rates  10th-40th week i.u. anterior cranial base increases its length & width sevenfold.  Posterior cranial base grows only 5 fold.  Growth of central ventral axis of brain is slow providing a comparatively stable base. www.indiandentalacademy.com

Cartilages of fetal chondrocranium & their derivatives

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post- natal development of cranium www.indiandentalacademy.com

Expansion of cranial base takes place as a result of :-Growth at synchondroses -Cortical drift & remodelling -Sutural growth

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synchondroses  These are important growth sites of cranial base. They are primary cartilages.  Spheno- occipital -ossifies by 20yrs  Spheno-ethmoidal -ossifies by 5-25yrs  Intersphenoidal

-ossifies at birth

 Intraoccipital

-ossifies 3-5yrs of age www.indiandentalacademy.com

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Spheno-occipital synchondroses  Believed to be principal growth cartilage of cranial base during childhood.  Active upto 12-15yrs.  Sphenoid & occipital segments become fused in mid-line by 20yrs.  Provides a pressure adapted bone growth.  Fusion begins on its cerebral surface at 12-13yrs in girls www.indiandentalacademy.com 14-15yrs in boys

Cortical drift & remodelling  Remodelling is a process where bone resorption & deposition occur to bring about change in size, shape & relationship of bone.  Clivus undergoes resorption on cerebral surface, apposition on nasopharyngeal surface of basioccipital bone & anterior margin of foramen magnum.  At birth, temporo-mandibular fossa is flat & lacks articular tubercle. www.indiandentalacademy.com

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Sutural growth

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Cranial vault  Fontanelles- areas of fibrous tissue membrane which forms primitive cranial vault before ossification begins.  Posterior fontanelle- closes at birth  Anterior - 1st yr  Anterolateral- 15 months  Posterolateral -18 months www.indiandentalacademy.com

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cranium at birth

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 At birth cranial vault is about 8 times larger than face.  In embryonic period ,cranium to face ratio is 40:1. At 4 months 5:1. At birth 8:1.  Post-natal facial growth causes it to reduce to 2:1.  Skull contains 45 separate bones at birth.  During birth skull is altered in shape & part of skull which lies more centrally in birth canal is temporarily swollen & oedematous due to interference with venous return– CAPUT SUCCEDANEUM.  By the end of 5th yr of life 90% of growth of brain vault haswww.indiandentalacademy.com been achieved.

Anomalies of development of cranium  Trisomy 13 syndrome  Chromosomal disorder in which extra chromosome 13 is present.  Cleft lip & palate  Micropthalmia  Microcephaly  Congenital heart defects  polydactyly www.indiandentalacademy.com

Apert syndrome      

Single gene disorder characterized by Pre-mature fusion of cranial sutures Bizzare craniofacial appearance Highly arched palate Syndactyly Congenital heart defects

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craniosynostosis  Condition resulting from premature fusion of cranial sutures.  Head shape depends on which sutures are pre- maturely synostosed.  Abnormal intra- uterine compression of cranium alters immature sutural tissue & initiates mineralisation of sutural ligament.  Dolicocephaly- sagittal suture is pre maturely synostosed  Brachycephaly- bilateral synostosis of coronal sutures  Plagiocephaly- premature synostosis of one side of coronal or lambdoidal suture causing obliquity of skull  Trigonocephaly- metopic suture closes pre-maturely www.indiandentalacademy.com

achondroplasia

 Characterized by unusual craniofacial configuration & dispropotional small stature.  Enlarged calvaria  Frontal bossing  Large frontal sinus  Occipital prominence  Normal anterior cranial base  Shortened posterior cranial base  Acute cranial base angle  Short nasal bone that is deformed & depressed  Short upper facial height  Recessed maxilla  Prognathic mandible  Bone that is preformed in cartilage is affected. www.indiandentalacademy.com

Cleidocranial dysplasia  Dominant mendelian characteristic of inheritance  Men & women equally affected  Abnormalities of skull,teeth,jaws,shoulder gridle,stunting of long bones.  Fontanelles exhibit delayed closure.  Paranasal sinuses are underdeveloped & narrow.  Head is brachycephalic with transverse diameter of skull being incerased.  Patient exhibits unusual mobility of shoulders . Maybe able www.indiandentalacademy.com to bring shoulders forwards till they meet in mid- line.

Marfan syndrome  Hereditary disease transmitted by autosomal dominant trait.  Disease of connective tissue related to defective organization of collagen.  Shape of skull & face is characteristically narrow & long.  Excessive length of tubular bones.  Arachnodactyly & high arched palatal vault. www.indiandentalacademy.com

Down’s syndrome / trisomy 21 syndrome         

Most common chromosomal abnormality Flat face, large anterior fontanelle open sutures small slanting eyes with epicanthal folds open mouth Frequent prognathism Sexual underdevelopment Hypermobility of jaws Cardiac abnormalities www.indiandentalacademy.com

hypothyroidism  Base of skull is shortened leading to retraction of bridge of nose.  Face is widened & fails to develop in longitudinal direction.  Mandible is underdeveloped.  Maxilla is overdeveloped.  Mental retardation. www.indiandentalacademy.com

development maxilla

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 Pharyngeal arches begin to develop early in 4 th week as neural crest cells migrate into future head & neck region.  1st pharyngeal arch develops two prominences  Maxillary prominence gives rise to maxilla, zygomatic bone & squamous part of temporal bone.  Mandibular prominence forms lower jaw.

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Development of face  Facial primordia appear early in 4 th week around large primordial stomodeum.  The 5 facial primordia that appears as prominences around stomodeum are: Single frontonasal prominence  Paired maxillary prominence  Paired mandibular prominence www.indiandentalacademy.com

 Facial development occurs mainly between 4 th & 8th weeks  By the end of 4th week bilateral oval thickenings of surface ectoderm –nasal placodes-have developed on inferolateral parts of fronto nasal process.  Each lateral nasal prominence is separated from maxillary prominence by cleft called nasolacrimal groove.  Nasolacrimal duct develops from rod like thickening of ectoderm in floor of nasolacrimal groove. www.indiandentalacademy.com

 Part of nasolacrimal duct fails to canalize resulting in – atresia of nasolacrimal duct.  By end of 5th week , primordia of auricles of ear begin to develop.  During 7th week there is shift in blood supply of face from internal to external carotid artery.    

Intermaxillary segment gives rise to:Philtrum of upper lip Pre maxillary part of maxilla & its associated gingiva Primary palate www.indiandentalacademy.com

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ď&#x201A;§ Recent clinical & embryological studies suggest upper lip is formed entirely from maxillary prominences. Lower parts of medial nasal prominences appear to have become deeply positioned & covered by medial extensions of the maxillary prominences to form philtrum.breitsprecher et al,2002.

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pre natal development of maxillary complex

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 Until bone formation occurs, the nasal capsule is the only skeletal support of upper face  Lateral & inferior to cranial base cartilages, ossification centers appear & face begins to develop in width.  Nasal, premaxillary, maxillary, Lacrimal, Zygomatic, palatine & temporal ossification centers appear & expand until they appear as bones separated only by sutures. www.indiandentalacademy.com

Development of palate  Palatogenesis begins at end of 5 th week & is not completed until 12th week.  Critical period of palate development is 6 th week until beginning of 9th week.  Bones of palate arise from several ossification centers.  In 8th week bilaterally located bony centers in anterior palate give rise to pre-maxilla & www.indiandentalacademy.com maxilla.

ď&#x201A;§ Three elements that make up secondary palate -2 lateral maxillary palatal shelves -primary palate of frontonasal prominence ď&#x201A;§ At 8th week I.U. life lateral shelves alter from vertical position to horizontal

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Mechanisms proposed for rapid elevation of palatal shelves  Biochemical transformations in physical consistency of connective tissue matrix of shelves  Variations in vasculature & blood flow to these structures  Sudden increase in tissue turgor  Rapid differential mitotic growth  An “intrinsic shelf force” generated by accumulation & hydration hyaluronic acid. www.indiandentalacademy.com

 Withdrawal of embryo’s face from against heart prominence by uprighting of head facilitates jaw opening.

 Pressure differences between nasal & oral regions due to tongue muscle contraction may account for palatal shelf elevation.

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ď&#x201A;§ Epithelium overlying edges of palatal shelves are thickened , & their fusion on mutual contact is crucial for intact palatal development ď&#x201A;§ Fusion seam forms initially anteriorly in hard palate region. ď&#x201A;§ Combination of degenerating epithelial cells & a surface coat accumulation of glycoprotiens & desmosomes facilitate epithelial adherence b/w contacting palatal www.indiandentalacademy.com shelves.

 Ossification of palate begins at 8th week I.U. by spread of bone into mesenchyme of fused lateral palatal shelves & from trabeculae appearing in primary palate as “pre-maxillary centres”.  Posteriorly hard palate is ossified by trabeculae spreading from single primary ossification centres of each palatine bone.  Ossification does not occur in most posterior part of palate ,giving rise to region of soft palate. www.indiandentalacademy.com

muscles of the palate

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 Muscles of soft palate are derived from myogenic mesenchymal tissue of first, second & fourth branchial arches.     

Tensor veli palatini – 1st arch Palatopharyngeus Palatoglossus Levator palatini – 4th arch Uvular - 4th arch

( 40 days) I.U. (45 days) (9 th week) (8th week) (11th week)

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 Palatoglossus attaches to soft palate during 11 th week I.U.  Hard palate grows in length, breadth, height to become arched shaped roof of mouth.  b/w 7 & 18 wks i.u. fetal palate increase in length more rapidly than in width.  From 4th month i.u. palate widens as a result of mid palatal sutural growth & appositional growth along lateral alveolar margins.  At birth length & breadth of hard palate are almost equal. www.indiandentalacademy.com

post â&#x20AC;&#x201C; natal development of palate

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 Palate increases in length due to appositional growth in maxillary tuberosity region & at transverse maxillopalatine suture.  Growth at mid-palatine suture ceases b/w 1 -2yrs of age.  Growth in width of mid-palatine suture is more posteriorly than anteriorly.  Obliteration in mid-palatine suture may start in adolescence, but complete fusion is rarely found before 30 yrs of age. www.indiandentalacademy.com

 Lateral appositional growth continues till 7yrs of age, by which time palate achieves ultimate anterior width.  Posterior appositional growth continues after lateral growth has ceased ,so that palate becomes longer than wider during late childhood.  During infancy & childhood , bone apposition occurs on entire inferior surface of palate , accompanied by resorption from nasal surface. www.indiandentalacademy.com

Factors in normal palatal development  Elevation of head to erect posture maybe related to elevation of palatal shelves.  Deficiencies of oxygen, various food stuffs or vitamins.  Excess of certain endocrine substances , drugs & irradiation.  Delay in the shift of blood supply of face & palate from internal to external carotid artery during critical period of palatofacial develoment. www.indiandentalacademy.com

post-natal development of maxilla

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Mechanisms & sites  Sutures  Nasal septum  Periosteal & endosteal surfaces  Alveolar bone www.indiandentalacademy.com

Amounts & direction  Maxillary height – classic implant studies of bjork & skeiller confirm that maxillary height increases by sutural growth towards frontal & zygomatic bones & appositional growth in the alveolar process.  Maxillary width – growth at median suture is more important than appositional remodeling .

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 Maxillary length – length increases in maxilla after second year by apposition on the maxillary tuberosity & by sutural growth toward palatine bone.  Maxilla rotates forward in relation to anterior cranial base  Timing – increase in alveolar process size is closely related with eruption of teeth.  Increase in overall maxillay height coincides with vertical growth in mandible www.indiandentalacademy.com

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anomalies of palatal development

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 Epstein’s pearls – entrapment of epithelial rests or pearls in line of fusion of palatal shelves.  Mucosal gland retention cysts or bohn’s nodules may occur on buccal & lingual aspects of alveolar ridges ,& dental lamina cysts composed of epithelial remnants of this lamina may develop on crests of alveolar ridges.  Torus palatinus www.indiandentalacademy.com

Cleft lip & palate  Delay in elevation of palatal shelves from vertical to horizontal while head is growing continuously results in widening gap between shelves so that they cannot meet & fuse.  Failure of medial edge epithelial cell death  Post –fusion rupture & failure of mesenchymal consolidation & differentiation. www.indiandentalacademy.com

 Cleft palate is a feature of many congenital syndromes  Mandibulofacial dysostosis/treacher collins’ syndrome  Pierre robin syndrome  Orodigitofacial dysostosis syndrome  Palate is narrower,shorter & lower than normal in down syndrome. High mid-line elevation ,horizontally flattened laterally along alveolar ridges , creating a “steeple palate”. www.indiandentalacademy.com

ď&#x201A;§ Conditions displaying high arched palate -Marfanâ&#x20AC;&#x2122;s syndrome -Cleidocranial dysostosis -Craniofacial dysostosis/ crouzan syndrome -Acrocephalosyndactyly / apert syndrome -Progeria -Turner syndrome -Oculodentodigital dysplasia www.indiandentalacademy.com

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The para-nasal sinuses

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ď&#x201A;§ 4 sets of paranasal sinuses -maxillary -sphenoidal -frontal -ethmoidal ď&#x201A;§ Begins development at end of 3rd month i.u. as outpouchings of mucous membranes of middle & superior nasal meatus & sphenoethmoidal recesses. www.indiandentalacademy.com

Primary Pneumatization ď&#x201A;§ Early paranasal sinuses expand into cartilage walls & roof of nasal fossae by growth of mucous membrane sacs into maxillary, sphenoid, frontal, ethmoid bones. Secondary Pneumatization ď&#x201A;§ Sinuses enlarge into bone from their initial small outpocketings, retaining communication with nasal fossae through ostia. www.indiandentalacademy.com

MAXILLARY SINUS  1ST to develop at 10 wks from middle meatus by primary pnumatization into ectethmoid cartilage.  Secondary pneumatization into ossifying maxilla starts in 5th month i.u.  At birth it is large enough to be clinically imp. & radiographically identifiable.  Sinus enlarges by resorption of cancellous bone except on medial wall. www.indiandentalacademy.com

 Rapid & continuous downward growth of sinus after birth brings its wall in close proximity to roots of maxillary cheek teeth.  As each tooth erupts ,vacated bone becomes pneumatized by expanding sinus.  In adulthood, roots of molar teeth commonly project into sinus lumen.

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 Absence of the development of frontal & shenoidal sinuses is characteristic of down syndrome.  Diminution or absence of sinuses is also found in Apert’s syndrome.  If a metopic suture persists ,the frontal sinuses are small or even absent.

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Coronal section of paranasal sinuses

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NEW INSIGHTS IN FACIAL DEVELOPMENT

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The fate of the neural crest mesenchymal precursors into differentiated facial tissue is strongly restricted by homeobox (HOX) gene expression. The HOX genes are expressed in a stepwise manner ,delineating the cascading streams of ectomesenchyme that migrate from their dorsal origin to their ventral destination to create six pharyngeal arches and five facial prominences. www.indiandentalacademy.com

 Five key secreted growth factors control facial growth by regulation of cell proliferation ,survival & apoptosis.     

Endothelins Fibroblast growth factor Sonic hedgehog Wingless Bone morphogenetic proteins

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New genetic lineage markers are identifying the expression changes occurring in the early embryonic face at different stages. 173 genes expressed in frontonasal prominence like TBX10, TBX21, BARX1, BAPX1, MNT, located of different chromosomes. During 4th week ,64 genes are upregulated. During 5th week further 26 genes upregulated in frontonasal prominence www.indiandentalacademy.com

COGENE CRANIOFACIAL AND ORAL GENE EXPRESSION NETWORK

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