Pre-natal and Post-natal Development of Maxilla Part 4 / orthodontic courses by Indian dental academy

Pre-natal and Post-Pre-natal and Post-natal Development of natal Development of MaxillaMaxillaContinued…..

www.indiandentalacademy.com

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

PALATOGENESISPALATOGENESIS


End of 5 TH

week IUL12 TH week IULEnd of 6th

Week IULBeginning of 9th week

CRITICAL PERIOD


The entire palate develops from two primorida –The primary palateThe primary palate, and

The secondary palateThe secondary palate


Week 6:Week 6:A cut between the maxillary and the mandibular prominences and tipping the top of the head back allows visualization of the developing palate.

•The secondary palatal shelves are considered to be part of the maxillary prominences.


Week 6:Week 6:The medial nasal prominences merge in the midline to smooth the median furrow.

This fusion produces a wedge-shaped mass of mesenchymal tissue known as the intermaxillary segment. www.indiandentalacademy.com

Week 6:Week 6:

After the oronasal membrane ruptures, The intermaxillary segment will form the anterior part of the palate, the primary palate (circled).

This section is cut like the last one (b/w maxillary & mandibular prominences)

1.2.

3.

4.

5.

6.


• A higher magnification view of the circled area illustrates the oronasal membrane that is beginning to break down.


Week 7:A parasagittal cut illustrates that the oronasal membrane breaks down to allow continuity between the nasal pit and the common oral and nasal cavities.


Secondary Palatal Shelves

Week 8:

A frontal cut illustrates that the tongue is initially interposed between the secondary palatal shelves.


The two lateral maxillary palatal shelves and the primary palate of the frontonasal prominence—are initially widely separated due to the vertical orientation of the lateral shelves on either side of the tongue.


Elevation of head and lower jaw


Mechanism of palatal shelf elevation

*Intrinsic Force within the shelf (accumulation and hydration of hyaluronic acid)

*Accumulation of Glycosaminoglycans*EGF(epidermal growth factor) andTGF (transforming growth factor h3)

stimulate production of Hyluronan*Increase in vascularity*Contraction of elastic fibres or muscle fibres.*Unequal division in the palatal and the oral epithelium*Neurotransmitters like Serotonin*Increase in MMP-3*Upregulation of Vimentin expression*Master controlling gene is FSP-1

(gene encoding a fibroblast-specific protein) ,ssh www.indiandentalacademy.com

Pressure differences between the nasal and oral regions due to tongue muscle contractions may account for the palatal shelf elevation. This occurs at about 8th and 9th week p.c.. It is possible that the nerve supply to tongue is sufficiently developed to provide neuromuscular guidance to the intricate activity of palatal elevation followed by closure.


Shelf elevation and fusion begin a few days earlier in male than in female embryos, possibly accounting for sex differences in the incidence of cleft palate.




During palate closure, the mandible becomes more prognathic and the vertical dimension of the stomodeal chamber increases, but maxillary width remains stable, allowing shelf contact to occur.

Also, forward growth of Meckel’s cartilage relocates the tongue more anteriorly, concomitant with upper-facialelevation.


The transition from vertical to horizontal is completed within hourswww.indiandentalacademy.com

Week 9:The palatal shelves become positioned above the tongue to allow for fusion in the midline.


Week 9: Fusion beginsThe secondary palatal shelves change their contours towards a midpoint from which they fuse anteriorly and posteriorly. At this point, the nasal septum grows downwardly from the fused medial nasal processes.


Medial Edge Epithelium. (M.E.E.)

During the initial stage of the fusion process, MEE cells form a midline epithelial seam (MES) separating mesenchymes of the two apposing shelves.


For the complete fusion of the palate, the MEE acts as a barrier:

Epithelium cells of MEE transforms into connective tissue cells.

Epithelium undergoes necrosis. (not supported as microscopic structure Doesn’t show any necrotic cells)

Epithelial cells migrate towards oral and nasal cells.


Release of MMP (Matrix metalloproteinase) causes disintegration of the cells and allows the connective tissue to mix up.

Balance between the MMP and TIMMP (Tissue inhibiting MMP)


The loss of epithelial continuity in the area of the shelf contact was originally described as a classic example of apoptosis (programmed cell death).

Two other mechanisms may also play a role in palatal shelf fusion.

Migration of the basal cells into the mesenchyme and differentiation of these cells into mesenchymal cells.

Cells near the periphery appear to migrate to the nearest epithelial surface, and then differentiate into either oral or nasal epithelium


Since the differentiation patterns of MEE cells in the cultured single palatal shelf is similar to that observed during palatal fusion (Mori et al. , 1994; Martínez-Álvarez et al. , 2000), it is clear that terminal differentiation of MEE cells is not necessarily dependent on palatal shelf contact and midline seam formation in vitro

Int. J. Dev. Biol. 48: 307-317 (2004)TOSHIYA TAKIGAWA and KOHEI SHIOTA


Week 10Fusion of the palatal shelves with each other and with the nasal septum separates the nasal cavities from the oval cavity.


Fusion of the three palatal components initially produces a flat unarched roof to the mouth.


OssificationOssification Ossification of the palate proceeds during the 8th

week post conception from the spread of bone into the mesenchyme of the fused lateral palatal shelves and from trabeculae appearing in the primary palate as “premaxillary centers,” all derived from the single primary ossification centers of the maxillae.


Posteriorly, the hard palate is ossified by trabeculae spreading from the single primary ossification centers of each of the palatine bones.

Most posterior part - no ossification - soft palate


Week 10Week 10The four maxillary incisors develop within the primary palate. Fusion completes at week 12.


Note: tongue has been removed.


MID PALATAL SUTURE Appears at 10 ½ wk IU Growth ceases b/w 1 - 2 yrs

But no synostosis till adulthood RME can be done

Obliteration starts in adolesence but complete fusion occurs by 30 yrs.


Palatal Vault Eruption of teeth – Deepening of palatal vault


Musculature of palate

Tensor veli palatini 40 days 1st arch

Palatopharangeous 45 days

Levator veli palatini 8th week 2nd arch

Palatoglossus 9th week Uvular muscle 11thweek 2nd

arch


MAXILLARY SINUS

First to develop at 10th week IU.

Develop from middle meatus by primary pneumatization in ecto-ethmoidal cartilage

Secondary pneumatization in ossifying maxilla starts at 5th

month IU.



Post natal growth of maxilla


Growth of maxilla occurs by two processes:

Extensive appositional and resorptional surface remodelling

Displacement


apposition

resorption

MOSS

Transformation

Translation

SUTURES

Displacement

Surface remodeling

CRANIAL BASE MAXILLAwww.indiandentalacademy.com

Enlow and Hans have described this by applying the principle of “Area Relocation”. (i.e. Specific local areas come to occupy new actual positions in succession, as the entire bone enlarges, involving both processes, translation and transposition)


Two methods have been used for precise assessment of remodelling process: Cross sectional study using histologic sections of

dried skulls

Longitudinal studies using implant markers and cephalometric radiographs.


Mechanism of growth Surface apposition and resorption Sutural growth Nasal septal growth Spheno-occipital synchondrosis Alveolar process


Maxilla develops postnatally entirely by intramembranous ossification.

During the different eras, different eras, different theories have been propounded to put forth the concepts (e.g.: Sutural theory or Scott’s septal cartilage theory etc.).


However none of these theories could answer all the questions and hence it is best to explain the growth of the different parts of maxilla based on a composite explanation.


Growth of maxilla can be viewed in three aspects: Growth in height

Growth in transverse direction.

Growth in the antero-posterior direction.


Height

In the coronal section, the palate is “V” shaped. Applying the Enlow’s “V” principle:

Deposition on the oral side.

Resorption on the nasal side. This increases the height of the nasal cavity.








Primary Pneumatization

Ethmoid air cells from the middle and superior meatus and sphenoethmoid recess invade the ectethmoid nasal capsule (primary pneumatization), from the 4th month post conception.


Secondary Pneumatization

Secondary pneumatization occurs between birth and 2 years as groups of 3 to 15 air cells grow irregularly to form the ethmoid labyrinth





Vimentin

Vimentin is a member of the intermediate filament family of proteins. Intermediate filaments are an important structural feature of eukaryotic cells. They, along with microtubules and actin microfilaments, make up the cytoskeleton


matrix metalloproteinase-3

Human fibroblast stromelysin (also called transin or matrix metalloproteinase-3) is a proteoglycanase closely related to collagenase (MMP1) with a wide range of substrate specificities. It is a secreted metalloprotease produced predominantly by connective tissue cells. Together with other metalloproteases, it can synergistically degrade the major components of the extracellular matrix (Sellers and Murphy, 1981). Stromelysin is capable of degrading proteoglycan, fibronectin, laminin, and type IV collagen, but not interstitial type I collagen.


DisplacementDisplacement

Primary displacementPrimary displacement

Secondary displacementSecondary displacement




Reversal line

Directions of growth sequentially undergo reversals

A reversal line showing the crossover between resorptive and depository growth fields seen in microscope

Factors affecting reversal shape of bone muscle attachments rotations growth fields


Mechanism of growth

Sutural Nasal septum Surface apposition and resorption on

periosteal and endosteal surfaces Alveolar process Spheno occipital synchondrosis


Surface apposition Sutural growth Nasal septum growth Spheno occipital synchondrosis


In contrast to cranial base maxilla is dominated by intra membranous ossification

Endochondral bone growth seen at the ethmoid bone and nasal septum


Surface apposition


Growth according to various theories

Sutural Theory (Weinman &Sicher)

Cartilagenous Theory ( Scott)

Functional Matrix Theory (Moss)


Sutural Theory

Bone growth in various maxillary sutures

Causes pushing apart of bone

Resultant thrust on whole maxilla in forward and downward direction



Shortcomings of sutural theory

Not pressure related - Tension adapted tissue.

No innate growth potential.

Crouzon’s syndrome


Cartilagenous Theory




Thank you

For more details please visit www.indiandentalacademy.com


Documents

Pre-natal and Post-natal Development of Maxilla Part 4 / orthodontic courses by Indian dental academy