INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
GROWTH Terms and Terminology in growth Embryology Pre and Post natal development of cranial vault www.indiandentalacademy.com
Terms and Terminology in growth Growth - The self multiplication of living substance. J.S. Huxley - Increase in size, change in proportion and progressive complexity. Krogman www.indiandentalacademy.com
- An Increase in size. Todd
- Entire series of sequential anatomic and physiologic changes taking place from the beginning of prenatal life to senility. Meridith www.indiandentalacademy.com
DEVELOPMENT According to Todd â€“ Progress towards maturity.
According to Moyers â€“ The naturally occurring unidirectional changes in the life of an individual from its existence as a single cell to its elaboration as a multifunctional 6 unit terminating to www.indiandentalacademy.com death.
DIFFERENTIATION It is the change from a generalized cell or tissue to one that is more specialized. Thus differentiation is a change in quality or kind. MATURATION Is a process by which an individual or system is fully grown or developed mentally or physically i.e. it has achieved itâ€™s full potential. www.indiandentalacademy.com
RHYTHM OF GROWTH
Human growth is not a steady and uniform process wherein all parts of the body enlarge at the same rate and the increments of one year are equal to that of the preceding or succeeding year. (Hooton) www.indiandentalacademy.com
RHYTHM OF GROWTH First wave of growth -Birth to 5-6th year Slow increase terminating in 10-12th year
Next period of accelerated growth terminating in14-16 years
Final period of growth terminating in18-20 years
DIFFERENTIAL GROWTH Different organs grow at different rates to a different amount and at different times.
DIFFERENTIAL GROWTH ďƒ˜ Lymphoid tissue proliferates rapidly in late childhood and reaches almost 200% of adult size. By 18 years, it undergoes involution to reach adult size. ďƒ˜ Neural tissue grows very rapidly and almost reaches adult size by 6-7 years of age. Intake of further knowledge is facilitated by the very little 12 growth that occurswww.indiandentalacademy.com after this age.
DIFFERENTIAL GROWTH General or visceral tissues exhibit or “S’ shaped curve with rapid growth up to 2-3 years, slow phase between 3-10 years and finally another rapid growth from tenth year to 18-20 years. Genital tissues grow rapidly at puberty reaching adult size after which growth ceases. www.indiandentalacademy.com
CEPHALO-CAUDAL GRADIENT OF GROWTH It means that there is an axis of increased growth extending from head towards the feet.
Head- Head takes up about 50% of the total body length around the 3rd month of I.U. life. At birth – 30% of body length In an adult – 12% of total body length www.indiandentalacademy.com
Lower Limbs – These are rudimentary around 2nd month of I.U. life In an adult - 50 % of total body length.
At Birth, cranium is proportionally larger than the face. Post-natally, the face grows more than the cranium. www.indiandentalacademy.com
CEPHALO-CAUDAL GRADIENT OF GROWTH
GROWTH SPURTS ďƒ˜ Period of accelerated,incremental,intermittent and sequential enlargement of skeletal structures associated with the homeostasis of the individual with the environment. ďƒ˜ Physiological alteration in hormonal secretion is the believed cause of growth www.indiandentalacademy.com
Timings of growth spurts 1. 2. 3. 4.
Just before birth One year after birth Mixed dentition growth spurt Boys : 8-11 Years Girls : 7-9 Years Pre-pubertal growth spurt Boys : 14-16 Years Girls : 11-13 Years www.indiandentalacademy.com
CLINICAL SIGNIFICANCE ďƒ˜
Growth modification by means of functional and orthodontic/orthopedic appliances elicit better response during growth spurts.
Surgical correction involving the maxilla and mandible should be carried out only after correction of growth spurts. www.indiandentalacademy.com
The trajectorial theory of face states â€œthe lines of orientation of the bony trabeculae correspond to the pathways of maximal pressure and tension and that bone trabeculae are thicker in the region where the stress is greaterâ€?. www.indiandentalacademy.com
Benninghoff studied the natural lines of stress in the skull by piercing small holes in fresh skull. Later as the skulls were dried, he observed that the holes assumed a linear form in the direction of the bony trabeculae. These were called Benninghoffâ€™s lines or trajectories which indicate the direction of the functional stresses. www.indiandentalacademy.com
TRAJECTORIES OF THE MAXILLA
STRESS TRAJECTORIES Vertical trajectories A. Fronto nasal buttress B. Malar Zygomatic buttress C. Pterygoid buttress
STRESS TRAJECTORIES A. Fronto Nasal Buttress-This trajectory originates from the incisors, canines and first maxillary premolar and runs cranially along the sides of the piriform aperture, the crest of the nasal bone and terminates in the frontal bone.
B Molar-Zygomatic Buttress-This trajectory transmits the stress from the buccal group of teeth in three pathways: a) Through the zygomatic arch to the base of the skull. b) Upward to the frontal bone through the lateral walls of the orbit. c) Along the lower orbital margin to join the upper part of fronto nasal buttress www.indiandentalacademy.com
Pterygoid Buttress-This trajectory transmits the stress from the second and third molars to the base of the skull.
STRESS TRAJECTORIES Vertical Trajectories
STRESS TRAJECTORIES Horizontal Trajectories A. Hard Palate B. Orbital ridges C. Zygomatic arches D. Palatal bones E. Lesser wings of sphenoid www.indiandentalacademy.com
STRESS TRAJECTORIES TRAJECTORIES OF THE MANDIBLE DENTAL TRAJECTORY ďƒ˜ The spongy trabeculae surrounding the apical part of the sockets unite as a trajectory that runs backward below the sockets and then diagonally upwards and backwards through the ramus to end in the condyle. In this way the masticatory pressure is finally transmitted to the base of the skull over the www.indiandentalacademy.com
This trajectory bulges on the inner surface of the ramus as a blunt crest, the crest or ridge of the mandibular neck continuous with the mylohyoid ridge.
Other trajectories are formed in response to the forces exerted by the muscles of mastication â€˘
in the region of mandibular angle
beginning of the coronoid process and fans out into the mandibular body. www.indiandentalacademy.com
in the chin trajectory of the spongiosa where the tracts of trabeculae cross each other at right angles, running from the lower border of the chin upward to the left into the alveolar process and vice versa.
STRESS TRAJECTORIES TRAJECTORIES OF THE MANDIBLE
FUNCTIONAL CIRCLES OF STRESS IN THE UPPER JAW COMPLEX (RICKETS) • One circle of stress in function is directed to support of the canine and incisor teeth. • A second circle of stress may be located from the molar teeth where the forces of a transpalatine nature take place through the palate. • A third circle of reinforcement runs around the nasal capsule to terminate as the frontal www.indiandentalacademy.com 34 process of the maxilla.
â€˘Force is also transmitted to a fourth, larger circle passing around the orbits and up through the frontal bone. â€˘Through the zygomatic arch and on to the temporal bone extending backward to the joint and finally downward into the mandible. www.indiandentalacademy.com
CLINICAL IMPLICATION AND PRINCIPLES OF THE UPPER JAW COMPLEX • A whole complex is involved. • This type of bone is laminated and passive in function. • Analysis of stress can be followed by reinforcements for transmission of force around the maxillary sinus. www.indiandentalacademy.com
• These bones, when connected form capsules. • The superstructure or base for the upper jaw complex does not come from the anterior cranial floor alone. • The scaffolding for the maxilla is principally through other bones transmitting force to the basal skull. www.indiandentalacademy.com
â€˘ The several intermediate bones between the maxilla and skull base provide a mechanism capable of slight movement by virtue of multiple sutures. â€˘ Forces tend to run perpendicular to sutures and the direction of sutures tends to parallel the Basion-Nasion plane. â€˘ These sutures provide areas of adjustment and 40 mechanisms forwww.indiandentalacademy.com adaptation.
â€˘ Critical cephalometric points are found in the upper jaw complex for orientation. Nasion (N), Orbital(O), Anterior nasal spine (ANS), Point A (A), Point Jugale (J), Nasal Cavity (NC), Posterior nasal spine (PNS), Pterygo-maxillary fissure (PTM)
• Growth of the maxillay complex is downward and forward from the Basion-Nasion plane. • The arrangement of bones within the complex protects the blood and nerve supply. • The arrangement of the bones in the upper jaw complex protects the respiratory tract. www.indiandentalacademy.com
â€˘ The upper jaw complex, while mainly passive for the forces of mastication, also gives support for certain functions. â€˘ The upper jaw is connected to the lower jaw directly through the muscles of mastication and the muscles of facial expression.
â€˘ The alveolar process has distinct architectural designs in its organization. The stresses from the teeth are carried through the alveolar processes into the basilar portion from which they are transmitted to the areas of muscle attachment, which provide the sources of the power for tooth contact. www.indiandentalacademy.com
• The upper jaw complex is important to the esthetics of the face • The maxillary complex is the target of Le Fort surgical procedures. It is considered as a nasal operation. • Early orthodontics has capability of orthopedic alteration of the upper jaw complex in three planes of space.www.indiandentalacademy.com 45
WOLFFâ€™S LAW It states that a bone grows and develops in such a manner that the composite of physiologic forces exerted on it are accommodated by bones developmental process, thereby adopting its structure to its complex of functions. Enlow (1899)
Thus not only is the quantity of bone tissues the minimum that would be needed for function requirements, but also its structure is such that it is best suited for the forces exerted upon it e.g. if a long bone such as the femur is cut open, it will be found that dense cortical bone is on the outside in such a way that they support its cortical bone along well defined paths of stress and strain. www.indiandentalacademy.com 47
Internal architecture of bone 1. Osteone, 2. Cortical and medullary bone 3. A long bone www.indiandentalacademy.com
ENDODERM The cells of the inner cell mass differentiate into flattened cells, that come to line its free surface. These constitute the endoderm (the first germ layer). It gives rise to living epethelium of alimentary canal between the pharynx & anus, lining epethelium of respiratory system, secretary cells of liver and pancreas. www.indiandentalacademy.com
ECTODERM The remaining cells of the inner cell mass become columnar. There cells form the second germ layer on the ectoderm. It gives rise to cutaneous system = skin + appendages , oral mucous membrane + enamel of teeth Neural system = CNS , PNS
MESODERM The cells of the trophoblast give origin to a mass of cells called extra embryonic mesoderm or primary mesoderm. These cells come to lie between the trophoblast and the flattened endodermal cells living the yolk . It gives rise to CVS, locomotor system, connective tissues + pulp , dentine, cementum, PDL www.indiandentalacademy.com
OSTEOGENESIS The process of bone formation is called osteogenesis. Bone formation takes place in two ways :1. Endochondral bone formation 2 Intra-membranous bone formation
ENDOCHONDRAL BONE FORMATION Undifferentiated Mesenchymal Cells Chondroblasts Hyaline Cartilage Cartilage Cells
Alk. Ph. Intercellular substance gets calcified
Primary Areolae Formation of Bars due to eating away of the calcified matrix Secondary Areolae www.indiandentalacademy.com
Secondary Areolae Osteogenic cells become osteoblasts Osteoid www.indiandentalacademy.com Lamella of bone
INTRAMEMBRANOUS BONE FORMATION Undifferentiated Mesenchymal Cells
Osteocytes Bone Lamella www.indiandentalacademy.com
INTRAMEMBRANOUS OSSIFICATION •Frontal •Parietal •Zygomatic •Palatine •Nasal •Lacrimal •Maxilla •Vomer www.indiandentalacademy.com
•Ethmoid •Inferior nasal conchae
•Occipital •Sphenoid •Temporal •Mandible
PRIMARY CARTILAGE – Cartilage of the pharyngeal arches such as Meckel’s cartilage and the definitive cartilages of the cranial base. SECONDARY CARTILAGE – It does not develop from the established primary cartilage of the skull e.g. condylar cartilage. www.indiandentalacademy.com
Primary Cartilage New cells are formed within existing tissues. (Interstitial growth)
e.g. epiphyseal, spheno-occipital, synchondrosis, nasal septal www.indiandentalacademy.com
Secondary Cartilage New cells are added from exterior.(Appositional growth)
e.g. condylar, coronoid, angular www.indiandentalacademy.com
TERMS & TERMINOLOGIES GROWTH DEVELOPMENT DIFFERENTIATION MATURATION RHYTHM OF GROWTH DIFFERENTIAL GROWTH www.indiandentalacademy.com GROWTH SPURTS
STRESS TRAJECTORIES ENDODERM, ECTODERM, MESODERM OSSIFICATIONENDOCHONDRAL INTRAMEMBRANOUS PRIMARY CARTILAGE www.indiandentalacademy.com SECONDARY CARTILAGE
FACTORS AFFECTING PHYSICAL GROWTH HEREDITY NUTRITION ILLNESS RACE SOCIO ECONOMIC FACTORS FAMILY SIZE AND BIRTH ORDER SECULAR TRENDS CLIMATIC AND SEASONAL EFFECTS PSYCHOLOGICAL DISTURBANCES EXERCISE www.indiandentalacademy.com
EARLY EMBRYONIC DEVELOPMENT The development of the embryo may conveniently be divided into three main periods during the 280 days of its gestation (10 lunar months of 28 days each). The period of the ovum extends from conception until the 7th or 8th day. . www.indiandentalacademy.com
The embryonic period, from the second through eighth week, may be subdivided into presomite, somite and postsomite periods. The final period of the foetus encompasses the 3rd to 10th lunar months www.indiandentalacademy.com
The presomite period extends from the 8th to the 20th days of development. The somite period covers the 21st to 31st days of development. During this ten-day period, the basic patterns of the main systems and organs are established
The postsomite period from the 4th to 8th week, is characterized by rapid growth of the systems and organs established in the somite period and by the formation of the main features of external body form. During the foetal period, from the 3rd month until birth, there is little organogenesis or tissue differentiation, but there is rapid growth of the www.indiandentalacademy.com 69 foetus.
PERIOD OF THE OVUM Sperm + Secondary Oocyte
Cleavage (30 Hrs.)
After 6 days Bastocyst Trophoblast
Attaches to the endometrial epithelium Inner Cytotrophoblast Outer Syncytiotrophoblast
After 7 days Blastocyst
Hypoblast (Primitive Endoderm)
Trophoblast differentiates into 2 layers www.indiandentalacademy.com
EMBRYONIC PERIOD Presomite Period Primiordium of amniotic cavity Aminoblast (from epiblast) Amnion (Membrane) www.indiandentalacademy.com
Amniotic cavity 77
Embryoblasts Embryonic disc Epiblasts (High Columnar Cells)
Hypoblasts (Cuboidal Cells)
Surrounds Hypoblast blastocyst cavity
Extraembryonic mesoderm Extraembryonic Coelom
Primary Yolk Sac ďƒŠin size
Secondary Yolk Sac
Extraembryonic Somatic Mesoderm
Extraembryonic Splanchic Mesoderm
+2 layers of trophoblast
At 14 th day Bilaminar embryonic disc Hypoblastic Cells Columnar Cells Prechordal plate www.indiandentalacademy.com (cranial end of embryo)
Third Week Gastrulation (Bilaminar embryonic disc
Trilaminar embryonic disc)
Addition of cells to Caudal end Cloacal membrane Anus
Cranial end Proliferates Primitive node or knot Primitive Pit
Cells of Primitive Streak
Form a loose network
Intraembryonic Intraembryonic Intraembryonic endoderm ectoderm Mesoderm www.indiandentalacademy.com
Primitive node Cells migrate cranially
Notochord Process Notochord canals reach
Prechordal Plate www.indiandentalacademy.com Oropharyngeal Membrane
Communication with yolk sac Notocanal disappears www.indiandentalacademy.com
Notochordal plate infolds
Notochord detaches from endoderm www.indiandentalacademy.com
Notochord Neural Plate 18thday Neuralation Neural Groove + Neural folds
Neural Crest Cells 96
SOMITE PERIOD Neural Tube
Lateral Plate Pleural, Pericardial cavities
Intermediate Gonads, kidneys, adrenal cortex www.indiandentalacademy.com
Paraxial Somites (42-44 paired) 103
Ventromedial (Sclerotome) Vertebral Column, Occipital Skull
Lateral Aspect (Dermatome) Dermis of Skin www.indiandentalacademy.com
Muscles of trunk, limbs, orofacial region 104
Most of the organ systems start to develop i.e. cardiovascular,alimentary,respiratory genitourinary and nervous systems develop. The part of yolk sac endoderm incorporated in cranial end is called foregut while that in the caudal end of the embryo is called hindgut.
-hepatic and pancreatic diverticula(liver,pancreas) -pharynx,pharyngeal pouches (oesophagus, stomach, 1st part of duodenum)
ďƒ˜Midgut-rest of the duodenum -small intestine -ascending and transverse colon of L.I ďƒ˜Hindgut -descending colon -terminal parts of the alimentary canal www.indiandentalacademy.com
THE POSTSOMITE PERIOD The predominance of the segmental somites as an external featureof the early embryo fades during the 6th week i.u.. The head dominates much of the development of this period. The earliest muscular movements are first manifest at this time. www.indiandentalacademy.com
ďƒ˜ Facial features become recongnizableears,eyes,nose and neck become defined. ďƒ˜ Body stalk condenses into a definitive umblical cord.
ďƒ˜Thoracic cavity enlarges as the developing heart is accompanied by rapidly growing liver. ďƒ˜The long tail at the beginning of embryonic period regresses.
NEURAL CREST CELLS www.indiandentalacademy.com
EMBRYOLOGY Characteristics of Neural Crest Cells: 1.Pleuripotent capability â€“ These cells are capable of giving rise to several types of precursor cell which are required in formation of different structures.
EMBRYOLOGY 2.Migratory property â€“ NCC break free during neuralization from neural folds by losing their lateral connections to adjacent epidermal and neural ectodermal cells and by dissolution of underlying basement membrane as these cells begin their migration away from the developing neural tube and towards future craniofacial regions of the embryo. www.indiandentalacademy.com
EMBRYOLOGY This migration is brought about by two means: Active (Cohen and Konigsberg 1975) Passive (Nuden, 1986)
EMBRYOLOGY Active â€“ Cells readily migrate away without the ectoderm which is present superficially. Passive â€“ In which lateral and ventral translocation of superficial ectoderm take place along with NCC. NCC migrates as a single cell dividing as they go, so that by the time they reach their final destination, they represent a much larger www.indiandentalacademy.com 131 population than was present at the outsets.
EMBRYOLOGY Factors affecting migration : Molecules â€“ Especially fibronectin which is encountered along the way are used by NCC to govern their migration. This is supported by work of (Rovasio et al 1983) â€“ in which they found out when NCC are confronted with either fibronectin coated or fibronectic free substrates in vitro, they preferentially with great precision choose the www.indiandentalacademy.com 132 fibronectin coated surface.
Vitamin A â€“ Acts as a teratogen, it is shown to slow the migration of neural crest cell maintained in vitro by inhibiting their interactions with extracellular matrix products. Administration of vit. A in pregnant mice leads to formation of craniofacial structures in abnormal position. Defects analogous to either Treacher Collins Syndrome or Hemifacial Microsomia can by produced by varying the dose of Vit. A www.indiandentalacademy.com 133 between 50,000-100,000iu
Drugs: Isotretenion â€“ cause severe facial malformation by effecting neural crest cell migration.
EMBRYOLOGY 3) Regulation Refers to ability of an embryo to compensate for the loss of cells. This compensation is brought about by two ways: â€˘ Either via migration of neural crest cell across the midline (if defect is unilateral). â€˘ By increasing proliferation of the remaining neural crest cells. www.indiandentalacademy.com
This was shown in study done by Bonner-Fraser (1986) â€“ in the CSAT antibody, which was used as an antibody to a cell surface receptor that recognizes fibronectin and laminin, both of which are involved in control of neural crest cells migration.
This antibody was injected in embryonic chicks just before initiation of NCC migration. 24 hours later she observed decrease in number of NCC (defective proliferation), accumulation of NCC within neural tube (defective initiation of migration) and neural crest cells in abnormal position (defective directionality of migration). However 36-48 hours of after injection of CSAT antibody, neural crest derivatives had developed normally. www.indiandentalacademy.com
4) Cessation: For neural crest derived craniofacial mesenchyme, which is migrating into the position of future craniofacial structure, some message must signal these cells to cease migration, which is a prerequisite for condensation. The best signal is type II collagen. Migrating NCC possess specific receptors for collagen which inhibit the further migration and they accumulates at site where later cytodifferentiation will take place. www.indiandentalacademy.com
STRUCTURES DERIVED BY THE NEURAL CREST CELLS Connective tissueEctomesenchyme of facial prominences and brachial arches Bones and cartilages of facial visceral skeleton. Dermis of face and neck Stroma of salivary, thymus, thyroid, parathyroid and pituitary gland. Corneal mesenchyme. Aortic arch arteries. Dental papilla Portions of periodontal ligament www.indiandentalacademy.com 139 Cementum
Muscle tissueCiliary muscles Covering connective tissue of branchial arch muscles
STRUCTURES DERIVED BY THE NEURAL CREST CELLS Nervous tissue Leptomeninges. Schwan sheath cells. Sensory gangliaAutonomic ganglia. Spinal dorsal root ganglia. ANS Sympathetic ganglia. Parasympathetic ganglia www.indiandentalacademy.com
STRUCTURES DERIVED BY THE NEURAL CREST CELLS Endocrine tissueAdrenomedullary cells Calcitonin ‘c’ cells Carotid body Pigment cellsMelanocytes Melanophores
STRUCTURES DERIVED BY THE NEURAL CREST CELLS Dental context The initiation of the tooth formation. The determination of the tooth's crown pattern. The initiation of dentinogenesis. The initiation of amelogenesis. The determination of the size,shape and number of the tooth roots. The determination of the anatomy of the dentogingival junction www.indiandentalacademy.com
EMBRYOLOGY Clinical Implications Mandibulofacial Dysostosis (Treacher Collins Syndrome): Maxillary and mandibular undercuts, Lack of mesenchymal fissures. Lt orbital and zygomatic area. Ears may be affected. www.indiandentalacademy.com
Etiology: excessive cell death in trigeminal ganglion www.indiandentalacademy.com
Hemifacial Microsomia: Lack of tissue of affected side. Both ramus & soft tissue is deficient / missing.
EMBRYOLOGY Etiology: Early loss of NCC. Limb abnormalities â€“ thalidomine. -Isotretenion
SUMMARY OF EVENTS ZYGOTE
MORULA (30 HRS.) NEURAL CREST CELLS
BLASTULA (4th Day)
NEURAL PLATE AND TUBE (End of 3rd Week) NOTOCHORD (Middle of 3rd Week)
PRIMITIVE STREAK (3rd Week)
GERM LAYERS (2-3 Weeks)
IMPLANTATION ( 7th Day)
BILAMINAR EMBRYONIC DISC
CHORIONIC SAC (End of 2nd week)
YOLK SAC (1-2 Weeks) 148
Pre and Post Natal Development of the Cranial Vault
Introduction Conventionally, the craniofacial region is divided into 4 major regions, in order to better understand growth. These regions are:1. The Cranial Vault 2. The Cranial Base 3. The Naso-maxillary complex 4. The Mandible www.indiandentalacademy.com
The growth of each region is further divided into:1. Pre natal 2. Post natal To understand how the growth occurs we need to pay attention to the following aspects:1. The sites and location of growth. 2. The type of growth. 3. The determinant and controlling factors. www.indiandentalacademy.com
Anatomy of the Cranial Vault Synonyms â€“ 1. 2. 3. 4.
Calvaria, and not Calvarium Cranial vault Desmocranium Calva
The skull may be viewed from different angles:1. 2. 3. 4. 5.
Above – Norma Verticalis Below – Norma Basalis Side – Norma Lateralis Behind – Norma occipitalis Front – Norma frontalis www.indiandentalacademy.com
The cranial vault spans from the superciliary ridges and glabella of the frontal bone, upto and including the squamous occipital bone. It also includes part of the squamous temporal bone, laterally. When seen from above:The vault is roughly ellipsoid, with the greatest width at its occipital end. The bones that make up the vault arewww.indiandentalacademy.com 154
The frontal bone â€“ It forms the forehead. It passes back to meet the two parietal bones at the coronal suture.
Anatomy of the Cranial Vault
At birth, a suture is seen between the 2 halves of the frontal bone â€“ the frontal or metopic suture. It usually closes early in life, but may persist into adulthood in 10-15% of cases. The parietal bones- form most of the cranial vault. They articulate in the midline at the saggital suture. Posteriorly, the parietal bones articulate with the occipital bone at the lambdoid suture (named after the Greek letter â€˜lambdaâ€™, which it resembles in shape). www.indiandentalacademy.com 157
Laterally, the parietal bones extend upto the greater wing of the sphenoid – anteriorly, and squamous temporal bone- posteriorly. The junction of the coronal and saggital suture is known as the ‘bregma’ and The junction of the lambdoid and saggital suture is known as the ‘lambda’. Also, there is a parietal eminence on each side and a frontal eminencewww.indiandentalacademy.com anteriorly. 158
The vault is covered by the SCALP which has 5 layers1. 2. 3. 4. 5.
Skin Subcutaneous tissue Aponeurosis of the occipito-frontalis Loose areolar tissue Pericranium. www.indiandentalacademy.com
Pre-natal Growth The cranial vault is a derivative of the mesenchyme, which is initially arranged in the form of a capsular membrane around the developing brain. The membrane has 2 parts:Endomeninx- derived from neural crest cells Ectomeninx â€“ derived from neural crest cells and paraxial mesoderm www.indiandentalacademy.com
The ectomeninx deferentiates into :ďƒ ďƒ
Inner dura mater Outer superficial membrane with osteogenic properties
The part of the superificial membrane which is over the dome of the brain ossifies intramembranously and forms the vault. The part that is below the brain, ossifies endochondrally and forms the cranial base. www.indiandentalacademy.com
The endomeninx differentiates into:ďƒ Piamater ďƒ Arachnoid. During their development, the 2 layers (ectomeninx and endomeninx) remain in close apposition, except in areas where the venous sinuses will develop. The duramater shows distinctly organized fiber bundles, which later develop into the various folds â€“ falx cerebri, falx cerebelli and tentorium cerebelli. www.indiandentalacademy.com
These bands also, to an extent , control the shape of the brain, which would expand as a perfect sphere if it were not for them.
Sites of ossification Type of Ossification Controlling factors
Sites of the future bones. Intra membranous. Brain
Ectomeninx gives rise to the following bones – Mesoderm – frontal, parietal, sphenoid, petrous temporal and occipital. Neural crest – lacrymal, nasal, squamous temporal, zygomatic, maxilla & mandible. The individual bones form from various primary and secondary ossification centers. www.indiandentalacademy.com
Frontal bone Single primary center in the region of the superciliary arch. This appears in the 8th week of intrauterine life. 3 secondary ossification centres appear in the zygomatic process, nasal spine and trochlear fossae. Parietal bones 1 primary center each in the region of parietal eminence. Thesewww.indiandentalacademy.com do not fuse with each other, and a 166
Occipital bones Squamous portion ossifies intramembranously â€“ primary center appearing just above the supranuchal lines. Squamous part of temporal bone Single ossification center appearing at the root of the zygoma. www.indiandentalacademy.com
Tympanic ring of the temporal bone 4 centres on the lateral wall of the tympanum. Also, the development of sutural bones occurs if any unusual ossification sites develop. Most centers of ossification appear during the 7 th or 8th week intrauterine, but ossification is not complete until after birth. Apart from fontanelles, the sutures themselves are wide, with syndesmotic www.indiandentalacademy.com 168 articulations.
The fontanelles are named according to ther relation with the parietal bonesAnterior, posterior, 2 â€“ antero-lateral, 2 â€“ posterolateral. These close at varied times between 2 months after birth (post. And ant.lateral) and 2 years (ant. And post.lateral). www.indiandentalacademy.com
www.indiandentalacademy.com 170 Sutures continue to ossify until they fuse, sometime in adult life.
Van Limbourgh poses 3 questions in relation to control of morphogenesis (prenatal growth)of the skull â€“ 1. Is there a relationship between development of the skull and presence of primordial of other organs? 2. How is endochongral and intramembranous growth coordinated? 3. How is growth of the skull and growth of other organs coordinated? www.indiandentalacademy.com
Three major controlling factors come to mind:1. Intrinsic Genetic factors â€“ or direct hereditary influence of genes 2. Epigenetic factors â€“ indirect genetic control through intermediary action on the associated structures (eye, brain etc) 3. Environmental factors www.indiandentalacademy.com
Earlier a totally genetic influence was thought to control the cranial differentiation But various observations have served to swing the pendulum more in favor of epigenetic influences. Example â€“ If the primordial of the eye does not develop, usually, the orbits do not develop. The number of orbits that develop correlates with the number of eyes that develop. â€˘If no brain develops, no cranial vault develops (anencephaly). www.indiandentalacademy.com
Role of genetics to a small extent. More acceptance to local epigenetics. Also consideration of general epigenetics and local and general environmental factors.
Post-natal Growth 1. Growth of the skull vault is closely related to growth of the brain. 2. Due to rapid growth of the CNS up to the 5 th year of life, it is seen that the calvaria is relatively bigger at birth than in adulthood. This reflects the cephalocaudal gradient of growth.
There is a different explanation of growth of the vault according to different theories of growth. In order to understand the site of growth of the cranial vault, the type of growth and controlling factors, it is important of look at some of the theories of growth and how different theories have interpreted cranial growth in different ways. www.indiandentalacademy.com
Theories of growth and how they relate to the growth of the cranial vault. Sutural growth theory Sicher said that skull growth was genetically determined that growth occurred at the sutures. Local factors, like muscle activity had only a mild effect.
Scottâ€™s Theory Scott gave importance to cartilage growth. He said that cartilage had inherent growth potential and sutures grew in response to cartilaginous growth. Therefore, sutures respond to growth at synchondrosis and to environmental factors.
Mossâ€™ FMH Moss postulated the role of functional matrices which are formed by non osseous tissue. Hence, this is an example of epigenetic control and environmental control.
Post-natal Growth Combination of the Theories Sicher claimed that the growth was under intrinsic genetic control, but from the work of Moss, we know that this is not a direct control, but epigenetic control. Hydrocephaly, microcephaly and anencephaly are testimony to this.
What Scottâ€™s experiments showed, is that cartilages are not responsive to pressure or tension, but intramembranous bone is. Therefore one could deduce that as the synchondroses grow, there is tension created at the sutures, and bone deposition occurs. This view is supported by others â€“ Sarnat, Burdi, Baume,, Petrovic etc. www.indiandentalacademy.com
This also explains why growth of the cranial base is influenced less by brain growth as compared to the cranial vault. We are familiar with Mossâ€™ explanation for control of bone growth by brain growth. He especially based his theory on the fact that in the synostosis syndromes, though the cranium cannot grow, the brain continues to grow. The growth is seen in many ways â€“ example, bulging of the eyes. www.indiandentalacademy.com
But it is interesting to see that if growth were to be explained entirely on the basis of the FMH, in hydrocephaly or anenchphaly, even the cranial base would be relatively large or small, as the growing brain would exert equal force in all directions.
But what is seen, is that the cranial base remains more or less normal. (Burdi, Van Limborgh, Sarnat, Latham, Baume, Petrovic & others.) Thus there is some support for Scottâ€™s theory, that cartilage growth is under genetic control.
So the modern view should be a rational amalgamation of these theories. This has been summarized by Van Limborgh as under:-
1. Intrinsic control of growth is exhibited at the synchondroses. 2. The intrinsic control of sutural growth is less 3. The Synchondroses should be considered as growth centres. 5. Sutural growth is controlled, in part, by growth at the synchondroses. www.indiandentalacademy.com
â€˘Some amount of periosteal growth also takes place in the cranial vault, this is controlled epigenetically. â€˘Growth of the cranial vault is also controlled, to some extent by local environmental factors (muscle forces inclusive).
Growth of the Cranial Vault Growth of the cranial vault is directly influenced by pressure from the neurocranial capsule.
As the brain expands the cranial vault bones are separated, at the sutures and the resulting space is closed by proliferation of connective tissue at the suture and its subsequent ossification. BUT the bones are NOT PUSHED outwards.
Each bone is enmeshed in a stroma, which is continuous with the meninges and skin. Hence, as the brain grows, this connective tissue stroma separates the bones at the sutures.
Another change taking place is periosteal growth. In general, deposition occurs both, at the inner table and outer table of the bones of the vault, and resorption occurs at the endosteal surface. The effect is twofold:-
1. To flatten the bones.At birth, the bones are quite curved. The remodeling serves to flatten the bones and hence arrange them along a bigger arc. There may be certain areas of reversal of the resorption â€“ deposition pattern mentioned earlier, in order to achieve this. www.indiandentalacademy.com
2. This also helps to increase the thickness of the bones. At birth the bones are thin and lack the spongy diploĂŤ between the inner and outer table. According to Sicher, the thickening is not uniform, as the inner table is influenced by the growth of the brain, while the outer table is influenced by mechanical force, especially of muscles in the supraorbital, otic and mastoid www.indiandentalacademy.com 196 regions
Another response to functional stresses is the development of the frontal sinus(Benninghoff). As the thickness of the bone increases, the supraorbital ridges develop due to more thickening of the outer table. Then, the spongy bone between the inner and outer table is slowly filled in by the developing sinus.
90% of the cranial vault growth of completed by the age of 5 â€“ 6 years, as has been shown by Davenport. This is in accordance with Scammons curve for brain growth as well as the cephalocaudal gradient.
Clinical Implications 1. Synostosis Syndromes These syndromes result from early closure of the sutures between the cranial and facial bones. This is obvious since growth occurs at the sutures, cranial growth will be extremely limited. Apart from limited cranial growth, maxillary growth is also limited due to synostosis of the circum-maxillary sutures. The orbits are bulging â€“ due to a combination of increased intracranial pressure and underdevelopment of the maxilla. www.indiandentalacademy.com
Treatment â€“ Surgery to release sutures
2. Hydrocephaly, Microcephaly and Anencephaly Change in the size of the vault due to increased CSF or absence of the brain. www.indiandentalacademy.com
3. Herniation of the dura into the nose. For some time, the dura covering the forebrain and the ectoderm remain in contact at the surface, in the region of the anterior neuropore. When the frontonasal process bends ventrally, the dura lies near the future frontonasal process. Then, the nasal capsule forms around it. A midline canal is formed, which later develops into the foramen caecum, when the dura separates from the www.indiandentalacademy.com 202 ectoderm.
â€˘The foramen caecum, then closes. If this fails to happen, it leaves an area from where the dura can herniated into the nasal cavity. It can also lead to the formation of dermoid cysts, sinus, or encephalocele.
4. Distortion of the head during birth which is possible due to the presence of Fontanelles.
5. Development of the outer superstructure of the vault due to muscular forces esp. mastoid, temporal and nuchal line, coronoid process etc. Direct www.indiandentalacademy.com 205 dependence on muscular activity.
6. In various conditions ,cretinism, progeria, trisomy 21, cleidocranial dysostosis – there is delayed – ossification of the frontal suture, and anterior fontanelles remain open into adult life. It results in a brachycephalic skull and ‘bossed’ forehead, and highly curved frontal and parietal bones and hypertelorism.
REFERENCES Craniofacial Embryology - G.H. Sperber Essentials of Facial Growth - D.H.Enlow Anatomy – Gray Abnormalities of Cleidocranial Dysostosis – Kreiborg,, Bjork & Skeiller (AJO May;1981) Cranial Base Growth For Dutch Boys & Girls – M. Herneberke, B.P. Andersen (AJO 208 November; 1994)www.indiandentalacademy.com
Contemporary Orthodontics - W.R. Proffit The Developing Human - Moore & Persaud Craniofacial Morphogenesis & Dysmorphogenesis â€“ Katherine and Alphonse Oral Histology â€“ Tencate
Provocation and Perception in Craniofacial Orthopaedics- Ricketts, Robert M. Orthodontics- Art And Science-Bhalaji
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