PRE-NATAL & POST-NATAL GROWTH OF CRANIAL BASE www.indiandentalacademy.com
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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Introduction Functions of cranial base Anterior,middle and posterior cranial fossae Individual bones of cranial base Pre-natal growth Various foramina Ossification in individual basicranial bones Cranial base flexure Post-natal growth Clinical implications References www.indiandentalacademy.com
INTRODUCTION The cranial base is of considerable importance to the orthodontist as it serves as a reasonably stable reference structure in roentgen-cephalometric analysis.
Growth and development of face and the cranial base are intimately related to each other, and has been a focus of interest to many researchers. www.indiandentalacademy.com
For orthodontists, biologists and anthropologists, the patterns of normal development should be known to serve as a basis for comparing and understanding abnormal growth patterns. www.indiandentalacademy.com
FUNCTIONS OF CRANIAL BASE: Basicranium supports and protects the brain and spinal cord. It articulates the skull with the vertebral column, mandible and maxillary region. It acts as an adaptive or buffer zone between the brain, face and pharyngeal region whose growth are paced differently. www.indiandentalacademy.com
ď ˇ Internal surface of the cranial base shows a natural division into anterior, middle and posterior cranial fossae. ď ˇ The duramater is firmly adherent to the whole area, and through the numerous foramina and fissures its outer layer, the endocranium is continuous with the periosteum on the exterior of the skull. www.indiandentalacademy.com
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The anterior cranial fossa ď ˇ Limited in front and on each side by frontal bone. Its floor is formed by: 1. Orbital plate of frontal bone. 2. Cribriform plate of the ethmoid 3. Anterior part of the body and lesser wing of sphenoid. www.indiandentalacademy.com
The anterior cranial fossa
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1. Orbital plate of frontal bone ď ˇ Forms the greater part of the floor of the fossa on each side of the median plane ď ˇ Separates the orbit and its contents from the inferior surface of the frontal lobe of the brain. ď ˇ In its antero-medial part it is split into two laminae to contain part of an airspace, the frontal sinus.www.indiandentalacademy.com
2. Cribriform plate of ethmoid ď ˇ Separates the fossa from nasal cavity and forms the roof of the latter. ď ˇ Anteriorly it presents a median crest like elevation CRISTA GALLI which projects upwards in between the two cerebrals hemispheres (which is a land mark in frontal/anteroposterior cephalograms). www.indiandentalacademy.com
ď ˇ The numerous small foramina which perforate the cribriform plate of ethmoid transmit the minute olfactory nerves from the nasal mucosa to the olfactory bulb.
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3. The sphenoid bone Completes the fossa’s floor from behind.Centrally is the anterior part of the upper surface of its body termed the jugum sphenoidale. This separates the fossae from bilateral air spaces in the body of the sphenoid named the sphenoidal sinuses. www.indiandentalacademy.com
ď ˇ Lateral to the jugum the floor of the anterior fossa is formed by lesser wing of sphenoid. ď ˇ Optic canal is located at the junction of lesser wing and body of the sphenoid bone.
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The middle cranial fossa Deeper than the anterior. In front it is bounded by posterior borders of the lesser wings of sphenoid and body of sphenoid, Behind by superior borders of the petrous parts of the temporal bone and dorsum sella of sphenoid bone,laterally by the temporal squamae,parietal bone and sphenoidal greater wings. www.indiandentalacademy.com
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Centrally the floor is narrower and formed by sphenoid body. Optic canal is present between roots of a lesser wing and lateral to the body of the sphenoid. It contains the optic nerve, ophthalmic artery and meninges. The chiasmal sulcus connects the optic canals. www.indiandentalacademy.com
ď ˇ Behind the sulcus the upper sphenoidal surface is the sella turcica,whose ant. slope bears a median tuberculum sellae,behind which is the hypophyseal fossa. Posterior to it the dorsum sellae projects up & forwards. www.indiandentalacademy.com
ď ˇ Hypophyseal fossa is present in the middle cranial fossa, which contain the hypophysis cerebri.
ď ˇ Laterally the middle cranial fossa is deep and supports the temporal lobe of cerebrum. www.indiandentalacademy.com
ď ˇ Communicates anteriorly with the orbit through the superior orbital fissure, which is bounded above by the lesser wing ,below by the greater wing and medially by the body of the sphenoid. ď ˇ Transmits the terminal branches of ophthalmic nerve, ophthalmic veins, occulomotor, trochlear and abducent nerves. www.indiandentalacademy.com
ď ˇ Foramen Rotundum pierces the greater wing of the sphenoid and leads forwards into the pterygopalatine fossa to which it conducts maxillay nerve.
ď ˇ Foramen ovale lying post. to F.rotundum leads downwards into the infra-temporal fossa and transmits the mandibular nerve. www.indiandentalacademy.com
ď ˇ Foramen spinosum transmits the
middle meningeal artery and is located near the posterolateral margin of foramen ovale.
ď ˇ Foramen lacerum is located at the posterior end of the carotid groove and posteromedial to the foramen ovale. It contains the internal carotid artery and its accompanying sympathetic and venous plexuses. www.indiandentalacademy.com
The Posterior cranial fossa The largest and deepest of the cranial fossa. Surrounded by dorsum sella, posterior part of the body of the sphenoid and basilar part of the occipital bone anteriorly; Behind by the lower portion of the occipital squamae. www.indiandentalacademy.com
ď ˇ On each side by the petrous and mastoid parts of temporal bone and lateral parts of occipital ď ˇ Above & behind by the mastoid angles of the parietal bones. ď ˇ It contains the cerebellum,pons and medulla oblongata. www.indiandentalacademy.com
The posterior cranial fossa
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The foramen magnum – It is in the floor of the fossa and surrounded by the parts of the occipital bone. Somewhat ovoid in shape communicates with the vertebral canal where the medulla oblongata becomes continuous with the spinal cord. www.indiandentalacademy.com
ď ˇ The jugular foramen sited at post. end of petro-occipital fissure, provides a passage to the glossopharyngeal, spinal accessory and vagus nerves and internal jugular vein,.
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ď ˇ Above the anterior part of the jugular foramen the internal acoustic meatus runs transversely in a lateral direction. It allows facial and vestibulocochlear nerves, the nervus intermedius and labyrinthine vessels. ď ˇ Hypoglossal canal is present lateral to the foramen magnum and contains hypoglossal nerve. www.indiandentalacademy.com
BONES FORMING THE CRANIAL BASE
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The occipital bone It forms much of the back and base of the cranium. Trapezoid in shape,concave internally. Contains 3 parts: Squamous part. Basillar part. Lateral / condylar part.
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The sphenoid bone ď ˇ It is in the base of the skull,wedged between the frontal and the temporal bones and basilar part of occipital bone. ď ˇ Has a shape of a bird with wings stretched out . www.indiandentalacademy.com
The sphenoid consists of: 1. 2. 3. 4.
Central portion or body Greater wings (2) Lesser wings (2) Pterygoid processes (2) Each has: Lateral pterygoid plates (2) Medial pterygoid plates (2) www.indiandentalacademy.com
The temporal bones This paired bone forms the sides and base of the skull. Each consists of 4 parts: • • • •
Squamous part. Petromastoid part. Tympanic. Styloid process
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The frontal bone It is an irregular cap like bone which forms the region of the forehead On each side it has a horizontal orbital part which forms most of the roof of the orbital cavity. The portion of the bone which projects downwards between the supraorbital margins is named as the nasal part. www.indiandentalacademy.com
The ethmoid bone It is cuboidal and extremely light in build. Situated at the anterior part of the basicranium and assists in forming the medial walls of orbits, the nasal septum and roof and lateral walls of nasal cavity. It consists of 3 parts: Cribriform plate (perforated one) A perpendicular plate Lateral masses (labyrinths) www.indiandentalacademy.com
The Inferior nasal conchae ď ˇ These are curved laminae, which lie horizontally in the lateral walls of nasal cavity.
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PRENATAL DEVELOPMENT OF CRANIAL BASE
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Cranium can be divided into 2 parts: ď ˇ Neurocranium: It protects and supports the brain and sense organs. ď ˇ Viscerocranium: Which is related to alimentary, respiratory tracts, face, maxilla and mandible. www.indiandentalacademy.com
Basicranium or cranial base is related to the both neural and visceral components. At cellular level, bones of cranial base develop by the following processes: Hyperplasia (Prominent feature of all forms of growth) Hypertrophy(sec. Factor) Secretion of extracellular material www.indiandentalacademy.com
ď ˇChondrification: Earliest evidence of formation of cranial base is seen in the late somite period i.e. 4th – 8th week of intrauterine life.
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Mesenchyme derived from primitive streak,neural crest and occipital sclerotomes condenses around the developing brain “ectomeningeal capsule� basal portion
future cranial base .
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During this period:
The occipital sclerotomal mesenchyme Concentrates around the notochord underlying the developing hindbrain Cephalic extension Floor of the brain. www.indiandentalacademy.com
ď ˇ Approximately 40th day of intrauterine life mesenchyme starts converting into cartilage marking the onset of cranial base formation. ď ˇ Chondrification centers form in the following regions: 1. 2. 3. 4.
Parachordal Hypophyseal Nasal Otic
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Parachordal region ď ˇ Chondrification centers forming around the cranial end of the notochord are appropriately called the parachordal cartilages. ď ˇ Fuse with the sclerotomes arising from occipital somites.
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ď ˇ The sclerotome cartilage is considered to be the first part of the skull to develop and it forms the boundaries of foramen magnum, providing the anlagen for basilar and condylar parts of the occipital bone.
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Hypophyseal region Oropharyngeal membrane closes off the stomadeum. Just cranial to this membrane the hypophyseal pouch (Rathke’s pouch) arises from the stomodeum.
Anterior lobe of pituitary gland (Adenohypophysis) lying cranial to notochord termination. www.indiandentalacademy.com
Two hypophyseal or polar or post sphenoid cartilages Either side of the hypophyseal stem
Sella turcica and posterior part of the body of the sphenoid bone. www.indiandentalacademy.com
Cranial to the pituitary gland fusion of the two presphenoid or trabecular cartilages Precursor to the presphenoid bone Anterior part of the body of the sphenoid bone. www.indiandentalacademy.com
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ď ˇ Laterally the chondrification centers of the orbitosphenoid (lesser wing) and alisphenoid (greaterwing) contribute later to the sphenoid bone. ď ˇ Most anteriorly, the fused presphenoid cartilage forms a vertical cartilaginous plate called the mesethmoid cartilage Perpendicular plate of the ethmoid bone and crista galli. www.indiandentalacademy.com
ď ˇ The capsules surrounding the nasal, otic sense organs chondrify and fuse to the cartilages of the cranial base.
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Nasal capsules: Formed around the nasal sense organ Chondrify in the 2nd month IU Box of cartilage with a roof and lateral walls divided by a median cartilage septum. The cartilaginous nasal capsules Ossification www.indiandentalacademy.com
Ethmoid and inferior nasal concha.
The chondrified nasal capsules Cartilages of the nostrils & median nasal septum NS remains cartilaginous except posteroinferiorly, Intramembraneous ossification Vomer bone www.indiandentalacademy.com (paired initially,2 halves uniting before birth)
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In the foetus, the septal cartilage intervenes between the cranial base above and the premaxilla, vomer and palatine processes of maxilla Postnatally the nasal septal cartilage acts as a functional matrix in the downward and forward growth of the midface. It helps in transferring compressive forces from incisor region to the sphenoid bone. www.indiandentalacademy.com
Otic capsules: ď ˇ Formed around the vestibulocochlear sense organs, Chondrify & fuse with the parachordal cartilages Ossification Mastoid and petrous portions ofwww.indiandentalacademy.com the temporal bones.
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Initial separate centers of cranial base chondrification Fusion A single, irregular and much perforated basal plate. ď ˇ This cartilaginous basal plate has numerous perforations formed by the establishment of blood vessels, cranial nerves and spinal cord between the developing brain and its extracranial contacts. www.indiandentalacademy.com
The height of cartilaginous skeletal development occurs during the 3rd month IU. A continuous plate of cartilage extends from nasal capsule posteriorly all the way to the foramen magnum During the 4th month IU there is an ingrowth of vascular elements into the various points of chondrocranium. These areas become centers of ossification, at which cartilage is transformed into bone. www.indiandentalacademy.com
Various foramina
Related nerves and vessels
1) Perforations in Fibres of olfactory the cribriform plate nerve (I) of ethmoid bone. 2) Optic foramen (Formed by extensions of orbitosphenoid cartilage around II N. fused with cranial part of basal plate)
Optic nerve (II) Ophthalmic artery.
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3) Superior orbital fissure (space between the orbitosphenoid and alisphenoid cartilages)
Occulomotor (III) Trochlear (IV) Opthalmic (VI) Abducens (VI) nerves and Ophthalmic veins.
4) Foramen rotundum
Maxillary (V2)
nerve
5) Foramen ovale
Mandibular (V3)
nerve
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6) Foramen spinosum (Junction between thealisphenoid and polar cartilages)
Middle artery
meningeal
7) Foramen lacerum (At the junction of alisphenoid and postsphenoid cartilages and otic capsule)
Internal artery
carotid
8) Internal acoustic Facial (VII) meatus (Nerves Vestibulocochlear passes through otic (VIII) www.indiandentalacademy.com capsule)
9) Jugular foramen (Passage of nerves and vessels between the otic capsule and the parachordal cartilage)
Glossopharyngeal (IX) Vagus (X) Spinal accessory (XI) Internal jugular vein
10) Hypoglossal / anterior condylar canal (Nerve passing between the occipital sclerotomes)
Hypoglossal (XII)
11) Foramen magnum
nerve
Lower end of medulla,meninges, www.indiandentalacademy.com spinal arteries,
Ossification in individual basicranial bones:
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Occipital bone: ď ˇ Ossified from 7 centres, which are 2 intramembranous 5 endochondral. ď ˇ The supranuchal squamous portion ossifies from a pair of intramembranous ossification centers in the 8th week of intrauterine life. www.indiandentalacademy.com
ď ˇ The Infranuchal squamous portion ossifies from a pair of endochondral ossification centers at the 10th week.
ď ˇ The basilar part ossifies appearing in 11th wk IU Anterior portion of occipital condyle & ant. boundary of foramen magnum. www.indiandentalacademy.com
A pair of endochondral ossification centres appears in the 12th wk forming the lateral boundary of foramen magnum & posterior portion of occipital condyles. An occasional centre appears in the post. Margin of the foramen magnum in 16th wk-KERCKRING’s CENTRE which unites with the rest of squamae before birth. www.indiandentalacademy.com
The temporal bone Ossifies both endochondrally and intramembraneously from 21 ossification centres. Squamous and tympanic elements Intramembranous ossification Petrosal and styloid elements Endochondralwww.indiandentalacademy.com ossification
ď ˇ The squamous portion ossified intramembranously from a single center appearing in the 8 week, the zygomatic process extends from this ossification center. ď ˇ The tympanic ring surrounding the external acoustic meatus ossifies from 4 intramembranous centers starting in the 12th week I.U. www.indiandentalacademy.com
ď ˇ The petrosal part ossifies endochondrally in the otic capsule from about 14 centres, these centers start to appear in the 16 th week and fuse during the 6th month I.U. when the contained inner-ear, labyrinth has reached its final size. ď ˇ Styloid process ossifies from 2 centres in the hyoid (2nd) branchial arch cartilage; the upper center appears just before birth and the lower center just after birth. www.indiandentalacademy.com
ď ˇ At 22 weeks of I.U. the petrous and tympanic ring fuse incompletely, leaving the petrotympanic fissure. ď ˇ At birth the tympanic ring fuses incompletely with the squamous part of temporal bone.
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ď ˇ The petrous, squamous and proximal styloid process-parts fuse during the 1 st year of life. ď ˇ The mandibular (Glenoid) fossa is only a shallow depression at birth facing laterally, deepening with development of articular eminance and ultimately facing downwards. www.indiandentalacademy.com
Ethmoid bone:
This wholly endochondral bone, which forms the median floor of the anterior cranial fossa and forms parts of the roof, lateral walls and median septum of the nasal cavity, ossifies from 3 centres. www.indiandentalacademy.com
ď ˇA pair of centers for the lateral labyrinths appears in the nasal capsular cartilages at the 4th month I.U. ď ˇA single median center in the mesethmoid cartilage forms the perpendicular plate and cristagalli just before birth. At two years of age the perpendicular plate unites with the lateral labyrinths to form a single ethmoid bone. www.indiandentalacademy.com
Inferior nasal choncha: Single center in the cartilage of lateral part of the nasal capsule (5thmonth I.U) Endochondral ossification Inferior nasal concha Detaches from the capsule www.indiandentalacademy.com Independent bone.
The sphenoid bone: ď ˇ Sphenoid bone has up to 14 ossification centers (intramembranous and endochondral) ď ˇ Until the 7th or 8th month IU,sphenoid body has a presphenoid part anterior to tuberculum sellae,with which the lesser wings are continuous ; and a postsphenoid part ,comprising sella turcica and dorsum sellae,and integral with the greater wings www.indiandentalacademy.com & pterygoid processes.
ď ˇ Lesser wing: Endochondral ossification in the orbitosphenoid cartilage. ď ˇ Greater wing and lateral pterygoid plate: 2 intramembraneous ossification centres seen in alisphenoid cartilage.A part of G.wing ossifies endochondrally. ď ˇ Medial pterygoid plate:Ossifies endochondrally from a secondary cartilage in the hamular process. www.indiandentalacademy.com
Anterior part of body of sphenoid: Ossifies endochondrally from 5 centres(2 paired &1 in midline) in the presphenoid cartilage. Posterior part of body of sphenoid: Ossifies endochondrally from 4 centres in the postsphenoid cartilage. The midsphenoidal synchondrosis between the pre and post sphenoid fuses shortly before birth. The sphenooccipital synchondrosis fuses in www.indiandentalacademy.com adolescence.
CRANIAL BASE FLEXURE ď ˇ During the embryonic and early fetal periods,the enormous human cerebrum expands around a much smaller enlarging midventral segment(the medulla,pons, hypothalamus,optic chiasma). ď ˇ This causes a bending of the whole underside of the brain.And the flexure of the cranial base results, in the region of the pituitary fossa,at the spheno-occipital junction,so that the developing face becomes tucked in under the cranium. www.indiandentalacademy.com
Cranial Base Flexure
Early embryo (Cranial base straight)
Fetus (Cranial base flexed)
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This relates to two key features: 1. The spinal cord is now aligned vertically,a change that permits upright,bipedal body stance with free arms and hands 2. As the forehead is rotated in a vertical plane with the growth of the frontal lobe,the superior orbital rim is carried with it.This aligns the eyes so that they point in the forward direction of upright body movt. www.indiandentalacademy.com
ď ˇ The body has become vertical,but the neutral visual axis is still horizontal ,as in other mammals. ď ˇ This cranial base flexure effectively enlarges the neurocranial capacity and causes downward rather than forward displacement of face during its growth from the cranial base. www.indiandentalacademy.com
Cranial base angulation ď ˇ The central region of the cranial base is composed of prechordal and chordal parts which meet at an angle at the hypophyseal fossa (sella turcia). ď ˇ The lower angle, formed by lines from nasion to sella to basion in the sagittal plane varies following the growth of embryo. www.indiandentalacademy.com
Initially highly obtuse = 150° in 4 week old embryo (precartilage stage). Reduces approximately = 130° in 7-8 week old embryo (cartilage stage). Becomes more acute = 115-120° at 10 weeks embryo (pre-ossification stage). Widens to 125-130° at 10-20 weeks (ossification stage) and maintains this angulation postnatally. www.indiandentalacademy.com
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Uneven nature of cranial base growth ď ˇ Growth of the cranial base is highly uneven. ď ˇ The uneven growth of the parts of the brain is reflected in the related parts of the cranial base adapting as compartments or cranial fossae. www.indiandentalacademy.com
ď ˇ Unevenness is also seen in rate of growth ď ˇ Eg. the anterior cranial base increases in length and width by evenfold between the 10th and 40th weeks I.U. whereas, The posterior cranial base grows only 5 fold. www.indiandentalacademy.com
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Postnatal growth of cranial base
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ď ˇ Cranial base has a potent role in the development of structure, dimensions, angles and placement of various facial parts. ď ˇ Floor of the cranium is a template from which face develops. ď ˇ Any difference in the development of basicranium will be reflected in the facial growth. www.indiandentalacademy.com
ď ˇ Growth of the central ventral axis of the brain and of the related body of the sphenoid and basioccipital bones is slow, providing a comparatively stable base. ď ˇ Laterally,cranially and caudal to this base, the anterior,middle and posterior fossae expand enormously in keeping with the growth of related parts of the brain. www.indiandentalacademy.com
ď ˇ The cranial base grows postnatally by complex interaction between the following growth processes: 1. Extensive cortical drift and remodelling 2. Growth of the cartilage remnants of the chondrocranium that persist between the basicranial bones. 3. Expansive forces emanating from the growing brain displacing the bones at the suture lines (capsular functional www.indiandentalacademy.com matrix).
Cortical drift and remodelling Endocranial surface of cranial floor has a different mode of development when compared with the culvaria because of its complex structure and curvature. The endocranial or neural surface of the basicranium in contrast to the roof is resorptive in most areas www.indiandentalacademy.com
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ď ˇ The reason is that the sutures do not have the capacity to provide for the multiple directions of enlargement and the complex magnitude of remodeling required. ď ˇ Remodeling is required to accommodate the massively enlarged human brain. www.indiandentalacademy.com
ď ˇFossa enlargement: The unidirectional sutural growth occurs at locations 1 and 2, which is not sufficient to accommodate the brain expansion.
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ď ˇFossa enlargement is accomplished by direct remodeling involving deposition on the outside with resorption from the inside. ď ˇThis is the key remodeling process that provides for the direct expansion of the various endocranial fossae in conjunction with sutural growth and growth at synchondrosis. www.indiandentalacademy.com
Various endocranial compartments are separated from one another by elevated bony partitions: ď ˇ The olfactory fossae are separated by CRISTA GALLI. ď ˇ Middle and posterior fossae are divided by the petrous elevation. www.indiandentalacademy.com
ď ˇ Right and left middle cranial fossae are separated by the longitudinal midline sphenoidal elevation. ď ˇ Right and left anterior and posterior cranial fossae are divided by a longitudinal midline bony ridge.
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ď ˇ All these elevated partitions, unlike of the remainder of the cranial floor are depository in nature because as fossae expand outward by resorption, the partitions between them must enlarge inward by deposition to maintain the proportions.
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ď ˇ The mid ventral segments of cranial floor grow more slowly than the floor of the laterally located fossae. This accommodates the slower development of the medulla, pons, hypothalamus, optic chiasma in contrast to the massive rapid expansion of the hemispheres. www.indiandentalacademy.com
ď ˇ A markedly decreasing and tapering gradient of sutural growth occurs as the ventral midline is approached but direct remodeling also occur to provide for the varying extents of expansion required among the different midline parts themselves and much faster growing lateral regions.
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ď ˇ Unlike the roof, the floor of the cranium provides the passage of cranial nerves and major cerebral vessels. ď ˇ The process of remodeling growth in the basicranium provides for the stability of these nerves and vascular passageways. www.indiandentalacademy.com
ď ˇ The foramen moves by deposition and resorption keeping pace with corresponding movement of nerve/vessel. ď ˇ The foramen enclosing each cranial nerve and major blood vessel also undergoes its own drift process to constantly maintain the proper position (Relocation) www.indiandentalacademy.com
ď ˇ Growth in the posterior cranial fossa is more when compared with growth of the spinal cord and foramen magnum. ď ˇ Differential remodeling process maintains the proportionate placement of spinal cord, even though the floor of the posterior cranial fossa, which surrounds the spinal cord expands to a considerably greater extent than the circumference of the foramen magnum. www.indiandentalacademy.com
The resorption occurs from the lining side of the forward walls of the middle cranial fossa (1). Deposition on the orbital face of the sphenoid and in the sphenofrontal suture (2). Forward displacement of the anterior cranial fossae occurs as the frontal lobes are displaced anteriorly (3). www.indiandentalacademy.com
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The petrous elevation (4) increases by deposition on the endocranial surface. Lengthening of clivus occurs by growth at SOS (5). The foramen magnum is progressively lowered by resorption on the endocranial surface and deposition on the ectocranial side. Endocranial fossa enlarge by a combination of endocranial resorption and ectocranial deposition. www.indiandentalacademy.com
2. Synchondroses: The midline part of the basicranium is characterized by the presence of synchondroses. They are the “left over� from the primary cartilages of the chondrocranium after the endocranial ossification centers appear during fetal development. www.indiandentalacademy.com
ď ˇ By their interstitial growth,the interposed cartilages or “synchondrosesâ€? can separate the adjacent bones as appositional bone growth adds to the sutural edges of the bones. www.indiandentalacademy.com
Different synchondroses seen in cranial base
Spheno-occipital Spheno-ethmoidal Intra occipital Inter-sphenoidal www.indiandentalacademy.com
The sphenooccipital synchondrosis ď ˇ It is the principal growth cartilage of cranial base During childhood ď ˇ As all growth cartilages are associated with (directly) bone development, the SOS provides a pressure adapted bone growth mechanism unlike the sutural areas which show tension adapted mechanism. www.indiandentalacademy.com
Pre s
Post sphenoid Basi occipital
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Because cranial base supports the mass of the brain and face, SOS in the midline is subjected to craniofacial muscular forces. As endochondral bone growth occurs at the SOS,the sphenoid and the occipital bones become moved apart by the 1° displacement process. www.indiandentalacademy.com
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ď ˇ At the same time new endochondral bone is laid down by the endosteum within each bone (Medullary fine cancellous bone). Compact cortical (Intramembranous) bone is formed around this core of endochondral bone tissue. . ď ˇ Each bone thereby becomes lengthened. Both bones also increase in girth by periosteal and endosteal remodeling. www.indiandentalacademy.com
ď ˇ The interior of the sphenoid bone eventually becomes hollowed to form the sizable sphenoidal sinus. ď ˇ Sphenoidal sinus expansion does not push the maxilla. The sinus grows secondarily as the body of the sphenoid bone expands around it keeping constant junction with the moving nasomaxillary complex. www.indiandentalacademy.com
ď ˇ The synchondrosis has a series of zones like primary cartilage :
1. 2. 3. 4.
Familiar reserve zone. Cell division zone. Hypertrophic zone. Calcified zone. www.indiandentalacademy.com
Similar to an epiphyseal plate, but unlike the condylar cartilage, the chondroblasts in the cell division zone are aligned in distinctive columns that point along the line of growth Unlike the epiphyseal plate the synchondrosis has 2 major (Bipolar) directions of linear growth. Structurally the synchondrosis is essentially 2 epiphyseal plates positioned back to back and separated by a common zone of reserve cartilage. www.indiandentalacademy.com
ď ˇ SOS is the last of all synchondrosis to fuse and starts fusing at 12-13 years in girls, and 14-15 years in boys and completing ossification of the external aspect by 20 years of age. ď ˇ This prolonged growth period allows for continued posterior expansion of the maxilla to accommodate last erupting molar teeth and provides space for growing nasopharynx. www.indiandentalacademy.com
Spheno-ethmoidal synchondrosis A cartilaginous band between the sphenoid and ethmoid bones. Believed to ossify after 5yrs of age. Inter sphenoidal synchondrosis Between 2 parts of sphenoid Ossifies at birth Intra occipital synchondrosis This ossifies by 3-5 yrs of age. www.indiandentalacademy.com
ď ˇ The size, shape and characteristics of cranial floor have evolved in direct phylogenetic association with the brain it supports, but the basicranium itself has presumably developed a genetic capacity of its own growth that is some how independent of the brain. ď ˇ Extrinsic control factors are also involved; but to what extent they are involved is not fully understood, since the cranial floor can develop to a greater or lesser extent, www.indiandentalacademy.com even though the brain is malformed or
3. Expansive forces from brainGrowth at sutures. Some of the sutures of cranial base: Spheno-frontal Fronto-temporal Spheno-ethmoid Fronto-ethmoid Fronto-zygomatic www.indiandentalacademy.com
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. ď ˇ The expansion of the middle cranial fossa and its neural contents
ď ˇ Secondary displacement effect on the anterior cranial floor , underlying nasomaxillary complex and mandible.
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ď ˇ Because the posterior boundary of nasomaxillary complex is developmentally positioned to exactly coincide with the boundary between the anterior and middle cranial fossae some amount of forward displacement of both the anterior cranial fossa and the nasomaxillary complex occurs. www.indiandentalacademy.com
ď ˇ The temporal and frontal lobes have fibrous attachments to the middle and anterior cranial fossa. ď ˇ As both lobes expand these 2 fossae are thus pulled away from each other. ď ˇ This set up tension fields in various frontal, temporal, sphenoidal, and ethmoidal sutures and this also presumably triggers sutural bone responses. www.indiandentalacademy.com
ď ˇ At about 5 years of age, frontal lobe growth and anterior cranial fossae expansion are largely complete. ď ˇ The temporal and middle cranial fossa, however continue to enlarge for several more years
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ď ˇ The expansion of each temporal lobe continues to displace the frontal lobe forward and this in turn causes tension in the osteogenic suture systems between these 2 areas. ď ˇ The anterior fossae and the maxillary complex are carried anteriorly by the frontal lobes, which is moved forward because of temporal lobe enlarging behind it. www.indiandentalacademy.com
Timing of cranial base growth 1. By birth,55-60 % of adult size is attained. 2. By 4-7 yrs,94 % of adult size is attained. 3. By 8-13 yrs,98 % of adult size is attained. www.indiandentalacademy.com
Clinical implications
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Study:Cranial base growth for Dutch boys and girls (AJO 1994 November)) - Monique Henneberke and Birte Prahl Andersen In this study growth and development of the cranial base in children who were treated orthodontically were compared with children who were not. www.indiandentalacademy.com
The hypothesis tested was that there is no difference in cranial base growth between children with and without orthodontic treatment. This is a mixed longitudinal study of *153 boys and 167 girls samples for S-N *116 boys and 116 girls for N-Ba and S-Ba, * All were of 7-14 years of age. www.indiandentalacademy.com
ď ˇ Cephalometric points used in this study. www.indiandentalacademy.com
Results: ď ˇ The effect of orthodontic therapy on cranial base growth was apparently so limited that no significant differences could be demonstrated between children with or without treatment. ď ˇ The cranial base displayed sexual dimorphism in absolute size, timing and amount of growth. www.indiandentalacademy.com
ď ˇ All C.B. dimensions examined in this study were greater in boys than in girls.
ď ˇ Girls did not show adolescent growth spurts, where as all boys showed that for S-N and N-Ba. www.indiandentalacademy.com
Anencephaly Characterizd by chondrocranium anomalies.
a short, narrow with notochordal
Anencephaly patients retain the acute cranial base flexure typical of early fetuses. This suggests that brain growth contributes to flattening of the cranial base. www.indiandentalacademy.com
ď ˇ Certain forms of dental malocclusions may be related to defects of the chondrocranium eg. The defects that minimize the space available for maxillary dentition (diminished maxilla) may lead to impacted teeth viz.third molars.
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Afflictions of cartilage growth produce a reduced cranial base resulting in a ‘dished’ deformity of middle 1\3 of face which is seen in conditions like achondroplasia, cretinism and Down’s syndrome (Trisomy 21). All these produce a similar characteristic facial deformity by their inhibiting effect on chondrocranial growth. www.indiandentalacademy.com
Achondroplasia:
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ď ˇ The C.B. does not lengthen normally because of deficient growth at the synchondroses; the maxilla is not translated forward to the normal extent, and a relative midface deficiency occurs
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ď ˇ Premature ossification or synostosis of the suture between the presphenoid and post sphenoid parts and of the sphenooccipital suture produces a characteristic apearance. ď ˇ This is seen in profile, and consists of an abnormal depression of the bridge of the nose
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ď ˇ Hypertelorism. Anomalous development of the presphenoidal elements excessive separation between the orbits and abnormally broad nasal bridge.
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ď ˇ Craniopharyngeal tumours Coalescence of the ossification centers in the body of sphenoid obliterates the orohypopharyngeal track. Persistence of the track as a craniopharyngeal canal in the sphenoid body gives rise to craniopharyngeal tumours.
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ď ˇ Premature fusion of sphenooccipital synchondrosis in infancy results in a depressed nasal bridge and dished face. ď ˇ Cleidocranial dysostosis patients with CCD exhibit high frequencies of anomalous traits in the cranial base. www.indiandentalacademy.com
ď ˇ CCD is characterized by abnormalities of the skull, jaws and shoulder girdle as well as by occasional stunting of long bones. ď ˇ In the skull, frontanelles remain open or atleast exhibit delayed closing. ď ˇ Frontal, parietal and occipital bones are prominent and the paranasal sinuses are underveloped and narrow. www.indiandentalacademy.com
Study: (AJO May 1981) ď ˇ Kreiborg,Jensen, Bjork and Skieller conducted a qualitative screening for abnormal morphological traits in the cranial base. ď ˇ The sample comprised 17 patients with CCD (8 males and 9 females) 1646 yrs of age. www.indiandentalacademy.com
Results: ď ˇ The anterior and posterior cranial base was significantly shorter and the C.B. angle smaller in the syndrome groups than in the control groups. ď ˇ Clivus was distorted in 82 % of patients. www.indiandentalacademy.com
ď ˇ All patients showed bulbous dorsum sellae and many had small pituitary fossae. ď ˇ The amount of bone resorption was lesser than normal, so abnormalities in remodeling pattern is seen. www.indiandentalacademy.com
ď ˇ Lateral roentgenocephalometric film of adult male patient with cleidocranial dysostosis. ď ˇ Poor visualization of posterior cranial base. www.indiandentalacademy.com
ď ˇ Midsagittal tomogram of posterior cranial base in a patient of CCD. ď ˇ Bulbous dorsum sellae and flexion of clivus. www.indiandentalacademy.com
ď ˇ Tracings of the posterior cranial base from midsagittal tomograms of three patients with cleidocranial dysostosis. Note shallow pituitary fossa in Patient 1065Z. ď ˇAll three patients exhibited bulbous dorsum sellae, flexion of clivus, and bulbous anterior margin of foramen magnum. www.indiandentalacademy.com
Distortion of clivus in the syndrome group could have arisen in a number of ways: • First, it could be related to an abnormal remodeling pattern. • Second, it could be primary anomaly comparable to the other midline anomalies found in the syndrome.. www.indiandentalacademy.com
ď ˇ Third, it could result from displacement of the bone of the cranial base during the development caused by delayed or defective ossification in the region ď ˇ It could result from any combination of these mechanisms www.indiandentalacademy.com
References 1. Craniofacial Embryology - G.H.SPERBER 2. Essentials Of Facial Growth - D.H.ENLOW 3. Gray’s Anatomy - Gray 4. Contemporary orthodontics - W.R.PROFFIT www.indiandentalacademy.com
5. Orthodontics-The art and science-- S.I.Bhalajhi 6.Abnormalities Of Cleidocranial Dysostosis – Kreiborg,bjork& Skeiller (AJO May; 1981) 7. Cranial Base Growth For Dutch Boys & Girls – M.Herneberke,b.P. Andersen (AJO November; 1994) www.indiandentalacademy.com
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