Growth of cranial complex oral biology.pptx

dental

1. Growth and Development of Craniofacial Complex By: Ramesh Lal

2. Learning Objective Prenatal and Post Natal Growth of Craniofacial Complex Cranial Vault Cranial Base Nasomaxillary Complex

3. Growth and development of an individual can be divided into PRENATAL & the POSTNATAL periods. The pre-natal life can be arbitrarily divided into three periods. Period of the Ovum Period of the Embryo Period of the Fetus

4. Period of the ovum : This period extends for a period of approximately two weeks from the time of fertilization. During this period the cleavage of the ovum and the attachment of the ovum to the intra-uterine wall occurs.

5. Period of the embryo : This period extends from the fourteenth day to the fifty sixth day of intra-uterine life. During this period the major part of the development of the facial & the cranial region occurs. .

6. Period of the fetus : This phase extends between the fifty sixth day of intra-uterine life till birth. In this period ,accelerated growth of the cranio-facial structures occurs resulting in an increase in their size. In addition, a change in proportion between the various structures also occurs

7. Prenatal Growth of Cranial Vault Growth of cranial vault is specialized form of intramembranous ossification that begins prenatally as blastemas of bone tissue that arise de novo within the middle layer of desmocranial membrane

8. Prenatal Growth of Cranial Vault First sign of development appears during 6 to 7 week of gestation Frontonasal process which forms the dense desmocranial membrane, covers the entire forebrain . The inner portion of the membrane contains neural crest cells and give rise to dura mater covering the brain. The outer portion of desmocranial membrane is called ectomeninx which is comprised of surface ectoderm. Patterning of frontonasal prominence to form cranial vault and elements of nasal region is induced by expression Sonic Hedgehog and FGF-8.

9. Pre-Natal Growth of Cranial Vault By 8 th week of gestation of gestation initial blastemas of bone becomes apparent within the ectomeninx first for the frontal bone and squameous part of temporal bone, then followed by parietal and squameous part of occipital bone. As the growth continues the developing bone plates comes closer and end up with formation of fibrous joint called sutures.

10. Post Natal Growth of Cranial Vault At birth cranial vault is disproportionately relatively large relative to rest of the face and body due to precious nature of brain development. At birth, all cranial vault bones and sutures are present including the metopic sutures between the right and left frontal bone. At birth the flat bones of the skull are widely separated by loose connective tissue these open space called fonantanelles allows considerable amount of deformation of skull at birth. Metopic sutures fuses to form single frontal bone within first year of life.

11. Growth of Cranial Vault

12. Post Natal Growth of Cranial Vault Post nataly cranial vault continue to enlarge primarily as a result of compensatory growth of sutural bone fronts stimulated by expansion of the brain. By 4 years of age brain and the associated cranial vault will have achieved approximately 80% of adult size and 95 % by age 10. The growth at cranial sutures continues up to second decade of life then slows onward and by the third decade of life major cranial sutures stop growing. Later in life enlargement of cranial vault occurs through periosteal deposition of extracranial surface.

13. Prenatal Growth of Cranial Base The first sign of cranial base formation is seen during 4 -8the week of gestation. The cranial base arises from the ectomeningeal capsule or ectomeninx (a part of desmocranial Membrane) From around 40 th day onward the ectomeninx is slowly converted into cartilage. This chondrification occurs in four regions: parachordal, hypophyseal, nasal, otic .

14. Pre-natal Growth of Cranial Base Chondro-cranial ossification Once cartilaginous template is formed the cranial base undergoes both endochondral as well as intramembranous ossification Occipital, sphenoid and temporal bone ossifies both endochondrally and intramembranous while ethmoid bone shows completely endochondral ossification. The growth of cranial base is highly uneven and this attributed to uneven growth of ventral part of the brain.

15. Post Natal Growth of Cranial Base Cranial base grows post- natally by interaction of following three processes. Extensive cortical drift and remodeling Elongation at synchondrosis Sutural Growth

16. Cortical Drift and Remodeling The cranium is divided into a number of compartment by bony elevations and ridges, present in the cranial base. These ridges and elevations shows bone deposition while floor of the base shows bone resorption. This intracranial resorption of the bone helps in increasing the volume of cranial cavity to accommodate growing brain

17. Role of Synchondrosis These are bands of cartilage and important growth sites of cranial base. Spheno -occipital synchondrosis Spheno -ethmoid synchondrosis Inter-sphenoid synchondrosis Intra-occipital synchondrosis

18. Spheno -occipital synchondrosis It is considered to be principal growth cartilage and important growth site of cranial base during childhood. Active up to the age of 12-15 yrs , and completely fused by the age of 20 years. Spheno -occipital synchondrosis provides a pressure or compression adapted bone growth. The direction of growth of spheno -occipital synchondrosis is upward, it therefore carries the anterior part of cranium bodily forward.

19. Other synchondrosis Spheno -ethmoid Synchondrosis – ossifies by 5 to 25 years of age. Inter-sphenoid: ossifies at birth Intra-occipital Synchondrosis: ossifies by 3-5 years of age.

20. Sutural Growth As the brain enlarges during growth bone formation occurs at the level of suture. Sheno -frontal Fronto -temporal Spheno -ethmoid Fronto -ethmoid Fronto -zygomatic

21. Timing of cranial base growth By Birth: 60% of adult size is achieved By 4-7 years : 94% of adult size is achieved By 8-13 years : 98% adult Size is achieved

22. Pre-natal Growth of Maxilla

23. Around the fourth week of intra-uterine life, a prominent bulge appears on the ventral aspect of the embryo corresponding to the developing brain. Below the bulge a shallow depression which corresponds to the primitive mouth appears called “ STOMODEUM”. The floor f o r m e d b y membrane o f t h e s t o m o d e u m i s t h e b u cco p h a r y n g ea l w h i c h s ep a r a t e s t h e stomodeum from the foregut.

24. By around the 4th week of intra-uterine life, five branchial arches form in the region of the future head & neck. Each of these arches gives rise to muscles, connective tissue, vasculature, skeletal components & neural components of the future face.

25. The first branchial arch plays an important role in the development of the naso- maxillary region. The mesoderm covering the developing forebrain proliferates & forms a downward projection that overlaps the upper part of stomodeum .This downward projection is called “FRONTO- NASAL PROCESS”.

26. The stomodeum is thus overlapped superiorly by the fronto- nasal process. The mandibular arches of both The sides form the lateral walls of the stomodeum. The mandibular arch gives off a bud from its dorsal end called the “MAXILLARY PROCESS”.

27. The maxillary process grows ventro-medio-cranial to the main part of the mandibular arch which is now called the “MANDIBULAR PROCESS”. Thus at this stage the primitive mouth or stomodeum is overlapped from above by the frontal process,below by the mandibular process & on either side by the maxillary process.

28. The ectoderm overlying the fronto-nasal process shows bilateral localized thickenings above the stomodeum. These are called the “NASAL PLACODES”.These placodes soon sink and form the nasal pits. The formation of these nasal pits divides the fronto-nasal process into two parts: The medial nasal process & The lateral nasal process

29. The two mandibular processes grow medially & fuse to form the lower lip & lower jaw. As the maxillary processes become narrow so that the two nasal pits come closer. The line of fusion of the maxillary process & the medial nasal process corresponds to the naso- lacrimal duct.

30. OSSIFICATION OF MAXILLA STARTS AROUND THE 8 TH WEEK OF IUL INTRAMEMBRANOUS TYPE The centre of ossification appears in the angle between the division of a nerve i.e. where the anterosuperior dental nerve is giving off from the inferior branch of infra orbital nerve, above that part of the dental lamina from which develop the enamel organ of the canine. From this centre, the bone spreads :- Posteriorly: - Below the orbit toward the developing zygoma anteriorly: - Towards the future incisor region Superiorly: - To form the frontal process Enlow’s ; Essentials of Facial Growth, 4 th Edition

31. POST NATAL GROWTH OF MAXILLA

32. The growth of naso-maxillary complex is produced by the following mechanisms: Displacement (Translation) Growth at sutures (Translation) Surface remodeling (Transposition)

33. Displacement It is the movement of the whole bone as a unit. Displacement can be of two types:-

34. PRIMARY DISPLACEMENT 1 . P r i m a r y di s pla c e m en t : It o c cu r s b y g ro w th of m a x i ll a y t uber o s i ty i n a po s t e ri o r d i re c t ion . T hi s results in whole maxilla being carried anteriorly. The amount of this forward displacement equals the amount of posterior lengthning. This is primary type of displacement as the bone is displaced by its own enlargement.

35. 2. Secondary displacement: A passive or secondary displacement of the naso-maxillary complex occurs in a downward and forward direction as the cranial base grows .

36. G R O W T H A T S U T U R E S The maxilla is connected to the cranium and cranial base by a number of sutures. These sutures include: Fronto-nasal suture Fronto-maxillary suture Zygomatico-maxillary suture Zygomatico-temporal suture Pterygopalatine suture

37. Sutures are oblique and parallel to each other. This allows the downward and forward repositioning of maxilla as growth occurs at these sutures. As growth of surrounding soft tissue occurs, the maxilla is carried downwards and forward. This leads to opening up of space at the sutural attachments. New bone is formed on either side of the suture. Thus the overall size of the bones on either side increases.

38. SURFACE REMODELING Remodeling occurs by bone deposition & resorption to bring about: Increase in size Change in shape Change functional relationship

39. Changes associated with bone remodeling Resorption occurs at the lateral wall of orbital rim leading to lateral movement of the eyeball. To compensate there is bone deposition on medial orbital rim and external surface of lateral orbital rim. Bone deposition occurs along the posterior margin maxillary tuberosity. This causes lengthening of dental arch and enlargement of anterio -posterior dimension of entire maxillary body. This helps to accommodate erupting molars. Bone resorption occurs on lateral wall of the nose leading to increase in the size of nasal cavity.

40. Changes associated with bone remodeling Bone resorption is seen on the floor of nasal cavity and to compensate there is deposition on the palatal side. As a result there is net downward shift of leading to increase in maxillary height. Bone resorption occurs on the anterior surface of the maxilla and deposition on the facial surface of alveolar process.

41. Bone remodeling seen in the midfacial region

42. B on e re m o d e li n g o f th e p a l a t e res u l t i n g in its downward displacement

43. Growth of the palate exhibiting V pattern of growth

44. Any Question