Seminar on Human Embryology.

2. • Development of Mouth
• Development of the Tongue
• Development of Maxilla
• Development of Mandible
• Development of the Temporomandibular Joint
• Development of Facial Muscles
• Development of the Salivary Glands

3. • Bidermal in development.
• Derived partly from the stomodeum
(ectodermal) and partly from the
cranial part of the foregut
(endodermal).
• Epithelial lining: partly
ectodermal and partly endodermal
and the demarcartion between the
two is buccopharyngeal membrane.
• The buccopharyngeal membrane
disappears by 4th week.

4. PRIMITIVE ORAL CAVITY
STOMATODEUM
NASAL PART ORAL PART
Ectodermal Derivatives Endodermal Derivatives
• Epithelium lining inside of lips,
cheeks and palate
• Teeth and gums
• Epithelium of Tongue, Floor
and Soft palate
• Palatoglossal and
Palatopharyngeal folds

5. • Alveololabial sulcus is
ectodermal.
• Alveololingual sulcus is
endodermal.
• Floor of the mouth: In this region,
the mandibular processes take
part in the formation of three
structure.
1. Lower lip and lower part of cheeks
2. Lower jaw
3. Tongue
DEFINITIVE ORAL CAVITY

6. • Roof of the mouth:
- Formed by the palate.
- The alveolar process of upper jaw
is separated from the upper lip
and cheek by the appearance of
labiogingival furrow.

7. • Appears in the embryo at about 4
weeks
• Appears as two lateral lingual
swellings and a median swelling, the
tuberculum impar (origin: 1st
pharyngeal arch)
• A 2nd median swelling, the copula of
His or hypobranchial eminence, is
formed by 2nd, 3rd and 4th pharyngeal
arches.
• The caudal part related to the 4th arch
forms the epiglottis.

8. The Anterior two-thirds of the tongue:
• Derived from the mandibular arch.
• Formed by the fusion of tuberculum
impar and the two lingual swellings.
• Innervation:
‒ Lingual branch of Mandibular branch of
trigeminal nerve.
‒ Chorda tympani branch of the Facial nerve.

9. The posterior one-third of the tongue:
• Formed from the cranial part of the
hypobranchial eminence (copula)
• The 3rd arch mesoderm grows over the
2nd arch and fuses with the mesoderm
of the 1st arch.
• Innervation: Glossopharyngeal nerve and
vagus nerve.

10. The posterior-most part of the tongue
• Derived from the 4th arch.
• Innervation: Superior laryngeal nerve
(nerve of 4th arch)
• The tongue muscles (except palatoglossus)
are derived from myoblasts originating in
occipital somites.
• Tongue musculature is innervated by the
hypoglossal nerve
• The body of the tongue is separated from the
posterior third by a V-shaped groove, the
terminal sulcus.

11. TASTE BUDS:
• Formed in relation to the terminal branches
of the innervating nerve fibres.
MUCOSA:
• Anterior part contains numerous cone shaped
papilla.
• Mucosa is covered by keratinised filiform papillae.
• Fungiform papillae are found scattered between
filiform papillae and contain taste buds.
• Foliate papillae are found on the lateral parts of the
tongue. Taste buds are found in its non keratinised
regions.
• Circumvalate papillae develop from cranial part of
hypobrancial eminence and migrate to anterior
aspect of sulcus terminalis.

12. DEVELOPMENTAL DISTURBANCES OF THE
TONGUE
1. Macroglossia: Enlarged tongue. May
cause lateral displacement of the
open bite.
2. Microglossia: Underdevelopment of
the tongue. Leads to underdeveloped
3. Aglossia: Very rarely the tongue
may be absent.
4. Ankyloglossia: The apical part of the
tongue may be anchored to the floor
mouth by an overlapped frenulum.
5. Ankyloglossia superior: The tongue
may be adherent to the palate.
6. Glossoschissis: Bifid tongue or cleft
tongue.

13. Around 4th week of intrauterine lifet
Prominent bulge appears on ventral aspect of embryo
(Developing Brain)
Shallow depression below the bulge - STOMODEUM
1st Pharyngeal Arch
(MANDIBULAR ARCH)
FRONTONASAL PROCESS
5 Pharyngeal arches form
Mesoderm covering the developing forebrain grows
downward and overlaps upper part of stomodeum
Forms Nasomaxillary
process
Part of mandibular
arch

14. At this stage, the primitive mouth or
the stomodeum is overlapped from :
• above by the frontal process,
• below by the mandibular process
and
• on either sides by the maxillary
processes.
Formation of the nasal pits divides
the frontonasal process into two
parts:
1. The Medial Nasal Process and
2. The Lateral Nasal Process

15. The post natal growth of maxilla occurs by the following mechanisms:
• Displacement
• Growth at sutures
• Surface remodelling

16. DISPLACEMENT:
It is the movement of the whole bone as a unit and it can be of two types:
1. Primary displacement:
- occurs by growth of maxillary tuberosity
in a posterior direction.
2. Secondary displacement:-
- occurs in downward and
forward direction due to growth of
cranial base

17. GROWTH AT SUTURES:
The maxilla is connected to
the cranium and the cranial
base by a number of sutures.
These include:
• Fronto-nasal suture
• Frontomaxillary suture
• Zygomatico-maxillary suture
• Zygomatico-temporal suture
• Pterygopalatine suture

18. SURFACE REMODELLING:
Remodelling occurs by bone
deposition and resorption to bring
about
• Increase in size
• Change in shape
• Change in functional relationship
• Change in proportion

19. • By 4th week of IUL, the pharyngeal arches are
laid down on the lateral and ventral aspects of
the cranialmost part of the foregut that lies in
close approximation with the stomodeum.
• The mandibular arch forms the lateral wall of
the stomodeum.
• Its gives off a bud from its dorsal end, maxillary
process.
• Its grows ventro-medially, cranial to the main
part of the arch, which is called the mandibular
process.
• By 5th week of IUL, the mandibular processes
of both sides grow towards each other and fuse
in the midline, form the lower border of
stomodeum i.e, the lower lip and lower jaw.

20. Secondary cartilages like the condyle, the coronoid and the symphyseal cartilages
influence furthur growth of the mandible.

21. Of all the facial bones, the
mandible undergoes the largest
amount of growth post-natally and
also exhibits the largest variability
in morphology.

22. RAMUS:
• The ramus moves progressively
posterior by a combination of
deposition and resorption.
• Resorption occurs on the anterior
part of the ramus, while bone
deposition occurs on the
posterior region.
• This results in a 'drift' of the
ramus in a posterior direction.

23. BODY OF THE MANDIBLE
• Body of the mandible lengthens as
the ramus exhibits bone deposition
on the posterior aspect and
resorption on the anterior aspect.

24. ANGLE OF THE MANDIBLE
• On the lingual side of the angle ofhe
mandible, resorption takes places on
the postero-inferior aspect while
deposition occurs on the antero-
superior aspect.
• On the buccal sid, resorption occurs
on the antero-superior aspect while
deposition takes place in the postero-
inferior part.
• This results in flaring of the angle of
the mandible as the age advances.

25. THE ALVEOLAR PROCESS
• As the teeth erupt the alveolar
process grow in size by bone
deposition at the margins.
• The alveolar process adds to the
height and thickness of the body of
the mandible.
• In the absence of teeth, the alveolar
bone fails to develop and it resorbs
in the event of tooth extraction.

26. THE CONDYLE
• The mandibular condyle has been
recognised as an important growth
site. The head of the condyle is
covered by the condylar cartilage.
• The presence of the condylar cartilage
is an adaptation to withstand the
compression that occurs at the joint.

27. THE CORONOID PROCESS
• Its growth follows the enlarging “V”
principle.
• Deposition occurs on the lingual surfaces
of the left and right coronoid processes,
when viewd from the posterior aspect of
the longitudinal section.
• Viewing from the occlusal aspect, the
deposition on the lingual surfaces of the
coronoid processes brings about a posterior
growth movement in the “V” pattern

28. • TMJ development takes place
mostly between the 7th and 20th
week of intrauterine life.
• A particularly sensitive period is
morphogenesis between the 7th
and 11th week.

29. • There are three stages in TMJ
development:
1. Blastemic stage (7th-8th week;
development of the condyles,
articular fossa, articular disk and
capsule),
2. Cavitation (9th-11th week;
beginning of lower joint space
development and condylar
chondrogenesis), and
3. Maturation stage (after the 12th
week)

30. • From the 8th until the 16th week of
development, the primordial cartilages
function as the primary
temporomandibular or malleoincudal
joint; auditory ossicles develop from the
latter.
• This joint can perform only simple
rotation or buccal movements, which
appear in the 8th week of development.
• In the 9th week, chondrogenesis begins
from the mesenchyme cells, laterally from
Meckel’s cartilage, in the middle of the
condylar blastema.
• In the 10th week, the condylar head and
the entire conical condyle are apically
surrounded by the lower jaw body, which
is ossified intramembraneously.

31. • Enchondral ossification of the condylar
cartilage in the anterior part begins in the
17th week and after the 20th week the
cartilaginous form of the condyle is
present only on the surface.
• The existence of temporal bone is visible
from the 8th and 9th week.
• In the 10th week, there is medial
thickening of the disk with mildly
pronounced concave contours.
• The articular fossa spreads cranially from
the condyle in anterior direction and from
the 12th week it has a concave shape and
is in its permanent position between the
temporal bone and condyle.

32. • The mesenchymal development of the articular capsule starts in the 8th week and
stretches from the squamous part of the temporal bone towards the articular disk and
the condyle.
• In the 11th week, the capsule is positioned between the zygomatic arch of the temporal
bone and the condyle and it is attached to the outer portion of the articular disk.
• Lower articular space starts developing earlier but slower than the upper one, in the
9th week, and follows the condylar base shape.
• The upper articular space starts forming in the 11th week between the zygomatic
process of the temporal bone and the articular disk.
• The articular spaces are disproportionate until the 26th week.
• The secondary TMJ is fully developed after the 14th week of intrauterine growth,
anteriorly from the otic capsule, and after the 16th week it assumes the primary joint
function.

33. Postnatal development of the temporomandibular joint
• At birth, the articular surfaces of both the mandibular
condyle and temporal bones are covered with fibrous
connective tissue.
• Extensive remodeling occurs during postnatal life.
• Changes involving increases in the posterior slope of
the articular tubercle and in the depth of the mandibular
fossa are reported up to the 4th decade of life.
• Postnatal remodeling occurs in the bone adjacent to the
joint in harmony with the growth of the condyle and
temporal fossa.
• Neuromuscular changes and occlusal status are also
reflected in discrete bony and functional changes in the
joint region.

34. DEVELOPMENTAL ANAMOLIES OF THE JAWS
1. AGNATHIA:
• Defined as the complete or partial absence
of one or both jaws.
• A very rare condition.
• Autosomal recessive condition.
• Occurs due to failure of migration of the
neural crest cells into the maxillary
prominence in the 4th - 5th week of
gestation.

35. 2. MICROGNATHIA:
• It is a condition in which the jaw is
undersized.
• It can also result due to abnormal
positioning of the jaws (Apparent
Micrognathia)
• True micrognathia can be either congenital
or acquired.
• Congenital heart disease and Pierre Robin
Sequence are commonly associated
congenital abnormalities.
• Trauma, infection and ankylosis are some
of the acquired causes.

36. 3. MACROGNATHIA:
• It is a condition where the jaws are
abnormally large.
• Causes: Pituitary gigantism, Paget's disease
of bone, Acromegaly.
• Mandibular protrusion or prognathism is a
common occurance and a prominent chin is
seen.

37. 4. FACIAL HEMIHYPERTROPHY:
• Also called as Friedreich's disease,
Hemihyperplasia.
• Represents the hyperplasia of the tissue
rather than its hypertrophy.
• It can be genetic in nature or be caused due
to vascular abnormalities or due to
endocrine dysfunction.

38. 5. FACIAL HEMIATROPY:
• Also called as Parry Romberg Syndrome or
Progressive Facial Hemiatrophy.
• It is a rare disorder, characterised by slowly
progressive wasting of the soft tissues of half of the
face.
• The wasting is associated with the skin, cartilage,
connective tissue, muscle and bone.
• Causes: Localised scleroderma, malfunction of
sympathetic nervous system, loss of adipose tissue or
even a familial tendency.
• Coup de sabre: Some patients may show sharp line of
line of demarcation resembling large linear scar
scar between normal and abnormal tissue.

39. 6. TREACHER COLLINS SYNDROME
(MANDIBULOFACIAL DYSOSTOSIS)
• Rare syndrome characterized by bilaterally
symmetrical abnormalities derived from the 1st and
2nd branchial arches.
• An autosomal dominantly inherited disorder.
• Arises from aberrations in the development of the
facial structure during histodifferentiation
morphogenesis between approximately the 20th day
and 12th week of intrauterine life.
• These aberrations result from the destruction of neural
crest cells before they migrate to form the facial
processes.

40. • During the 5th and 6th weeks, myoblasts within the
mandibular arch begin proliferating and become
oriented to the sites of origin and insertion of the
muscles they form.
• By 7th week, the mandibular muscle mass enlarges
and beguns migration and differentiation into the 4
muscles of mastication : the masseter, temporal,
medial and lateral pterygoid muscles.
• The muscles within the hyoid arch and in the
occipital myotomes undergo proliferation and migrate
anteriorly towards the floor of the mouth to form
muscles of the tongue.
• Muscles of the 3rd and 4th arch form the pharyngeal
muscles : stylopharyngeus, cricothyroid, levator
palatini and constrictor muscles of pharynx.

41. • By 10th prenatal week, the mandibular
arch muscles become well organised
bilaterally.
• The masseter and medial pterygoid
muscle forms the vertical sling in the
developing coronoid process.
• The lateral pterygoid muscle fibres,
which also arise from the infratemporal
fossa, extend horizontally to the necks of
condyles and insert in the articular discs.
• The pharyngeal constrictor muscles
differentiate and enclose the pharynx.
• The face changes shape considerably as it
grows, and all its muscles develop to
meet the increasing fuctional demand.

42. There are 3 pairs of major salivary glands:
 the parotid glands,
 the submandibular glands, and
 the sublingual glands.
The development of salivary glands is a
result of a highly orchestrated complex
interaction between 2 distinct tissues, the
oral epithelium and the underlying
mesenchyme.

43. • The major salivary glands begin
development during the 6th to 8th
week.
• The parotid develops in the lateral
aspect of the stomodeum while the
submandibular and sublingual
glands develops in the floor of the
stomodeum.
• Each gland develops from a bud of
oral epithelium into the underlying
mesenchyme.

44. • The epithelial buds differentiate
into solid cords of cells which later
form lumen and get converted into
ducts.
• Minor salivary glands develop
during the 3rd month of prenatal
life and they remain as separate
acini scattered in the connective
tissue under the oral mucosa.
Oblique view of a developing
salivary gland acinus and ductal
system

45. DEVELOPMENTAL DISTURBANCES OF
SALIVARY GLANDS.
1. ABERRANCY
• It is defined as a situation in which salivary gland tissue
develops at a site where it is not normally found.
• Also called as Ectopic salivary gland.
• Most frequntly reported in the cervical region, near the
parotid gland or body of the mandible.
• Salivary tissue in neck lymph nodes are often mistaken for
metastatic disease.
• They may become site for development of retention cyst or
neoplasm.

46. 2. APLASIAAND HYPOPLASIA
• Aplasia is defined as the congenital
absence of salivary glands.
• Any one of the gland or group of glands
is missing either unilaterally or bilaterally.
• Patient complains of xerostomia and lack
of saliva results in rampant dental caries.
• The oral mucosa appears dry and there is
cracking of lips.
• Proper oral hygiene should be maintained
in order to decrease dental caries and
preserve teeth.

47. 3. HYPERPLASIA OF SALIVARY GLAND
• It is the increase in size of the salivary gland.
• It is more common in minor salivary glanof the
palate. These appear as small swellings of varying
size in the hard palate or at the junction of hard
and soft palate.
• They are usually asymptomatic and can be caused
due to hormonal and metabolic disorders.
• Management is often by surgical excision.

48. 4. ATRESIA
• It is a congenital occlusion or
absence of one or two major
salivary gland ducts.
• The submandibular gland is most
commonly affected.
• The newborn infant presents,
within 2 or 3 days of life, with
submandibular swelling on the
affected site due to retention.
• It produces a relatively severe
xerostomia.