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PRE NATAL GROWTH AND DEVELOPMENT

Dr MUHAMMED RAHEESH

SENIOR LECTURER

DEPT OF ORTHODONTICS

INTRODUCTION

• Man has inherited a complex of craniofacial bones and tissues that is hundreds of millions of years old.

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• The basic “bony” support of the cephalic complex in the early organisms was cartilage. This cartilage ultimately became bone, forming the cranial base and some of the midline structures of the face.

PRENATAL GROWTH

PRENATAL GROWTH OF NASOMAXILLARY COMPLEX

FUNCTIONS :-

• Mastication
• Adds resonance to the voice
• Airway

PRENATAL GROWTH:-

3 Phases:

a. Period of ovum (from fertilization to the 14th day)

b. Period of Embryo (From 14th – 56th day)

c. Period of foetus (56th day to Birth)

• Differentiation of the human face takes place early in prenatal life, specifically between the fifth and seventh weeks after fertilization occurs.

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• During this short period, a number of important events occur that determine the formation of the human face.

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• In the fourth week after conception, the future face and neck region located under the fore brain of the human embryo becomes segmented.

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• Five branchial arches are formed, appearing as rounded, tubular enlargements, and are bounded by clefts and grooves that help define each arch

Pre – natal embryology of mandible

• Around the fourth week of intra uterine life, a prominent bilge appears on the ventral aspect of embryo corresponding to the developing brain.

• By around the fourth week of intra-uterine life, Five branchial arches form in the region of the future head and neck.

• The first pharyngeal arch is called the Mandibular arch and plays an important role in the development of naso-maxillary region.

FORMATION OF FRONTONASAL PROCESS

• Head end of an embryo before formation of the frontonasal process

• Formation of frontonasal process
• Below the bulge a shallow depression which corresponds to the primitive mouth appears called Stomodeum

The mandibular arches of both the sides form the lateral walls of the stomodeum.

• The mandibular arch gives of a bud from its dorsal end called the Maxillary process.

• 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 is overlapped from above by the fronto-nasal process, below by the mandibular process and on either side by the maxillry process.

• The two mandibular processes grow medially and fuse to form the lower lip and the lower jaw i,e the Mandible.

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• The ectoderm overlying the fronto nasal process show bilateral localized thickening

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• Nasal placodes

• This placods soon sink and form nasal pits, this divides frontonasal process to

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• Lateral nasal process and medial nasal processc

DEVELOPMENT OF FACE

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• As the maxillary process undergoes growth, the frontonasal process becomes narrow and two nasal pits com close

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• The two medial nasal processes grow towards each other and fuse at the midline; from now on it is called globular process.

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• The derivatives of globular process are tip of the nose, columella, philtrum, prolabium, primary palate

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• The maxillary process joins also with the lateral nasal process, the junction being marked by the naso-optic furrow. The furrow develops into a canal called nasolacrimal duct

DEVELOPMENT OF PALATE

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• A primary intramembranous ossification center appease for each maxilla in the 8th week of IU life.
• Two further intra membranous premaxillary centers appear anteriorly on each side in the 8th week of IU life and rapidly fuse with the primary maxillary center.

• The mid and lower facial regions develop, in part, from the first two, named the mandibular and hyoid arches.

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• The third also contributes to the base of the tongue.

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• Within each of these branchial arches arise skeletal, muscular, vascular, connective tissue, epithelial, and neural elements that develop into the systems supplying the face and neck.

• 1^st arch (Meckel’s cartilage)

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• Gives rise to Malleus, Incus, Anterior ligament for malleus, sphenomandibular ligament & lays down the meshwork for formation of mandible & some part of it may be included in mandible

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• The mandible has its origin in the mandibular processes of the first branchial arches around the 40^th day of intrauterine life.
• It begins to form lateral to Meckel’s cartilage and then develops inward, medial to the dental and incisive nerves.
• With these as centers of ossification are formed the angle, coronoid process, condylar process.

Ossification

• During the 6^th week of intrauterine life, a center of ossification appears at the future metal foramen.
• Bone formation spreads rapidly beginning with the 7^th week and continues distally towards the mental symphisis and proximally upto mandibular foramen(intra membranous)

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• Meckel’s cartilage supports the mandibular processes prior to ossification and union of the two sides of the mandibular bone.
• Meckel’s cartilage completely disappear by 24 weeks gestation leaving behind sphenomandibular ligament which give rise to future incus and malleus

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• At 4 ½ months I.U. the adult form of the mandible can be recognized.
• Mandibular Symphysis : the mandible is originally formed in two halves which are joined at the mental symphysis by fibrocartilage at about the 6^th month of intrauterine life.

• coronoid : the coronoid cartilage develop at 14^th week of IUL, cartilage grows downward and forward into the ramus. At 4 ½ months I.U., the cartilage begins to ossify and the coronoid process joins the ramus.

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• Condylar cartilage: at 10^th week of IUL condylar cartilage condensation appear as cone shaped projection ,ossification starts at 14^th week ,the superior end of condyle persist as cartilage
• This cartilage may be a cause for the growth of condyle in later life

DEVELOPMENT OF TMJ

• ANATOMY OF TMJ

• Tmj develops as two separate surfaces on condyle and temporal bone
• Earlier movements are facilitated by joint between malleus and incus
• As growth proceed malleus and incus loose the contact with meckels cartilage

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• The condylar cartilaginous proliferation leads growth of cartilage towards temporal bone
• The mesenchyme between the two tissues proliferate to fibrous tissue
• By 12^th week of IUL two joint cavities are seperated by interviening fibrous articular disc

• Later synovial membrane invades and secrete synovial fluid,joint develops and compression in centre leads to biconcave shape
• At birth condyles and articular eminence are less developed,this helps in suckling
• As the decidous denttion develops the articular eminence starts its development