Pharyngeal arches
Tongue and Salivary glands development
Permanent dentition
Defects
May 2024
Pharyngeal arches
https://www.youtube.com/watch?v=oP1-ejJdZyc
Pharyngeal arches
Phylogenetically conserved organ, serves as a carrier for gills (which work as a respiratory organ)
First appears in sharks, around the pharyngeal gut
In vertebrates, transforms and forms the basis of important organs - branchiogenic organs
Wikipedia
The pharyngeal apparatus starts to develop in human embryos in the neck region behind the frontal (frontonasal)
prominence in the second half of the 4th week
Pharyngeal arches 6
Pharyngeal pouches (entodermal) 5
Pharyngeal clefts (grooves) (ectodermal) 4
Membranae obturantes 4
All structures are paired
Pharyngeal arches
Pharyngeal (branchial) arches (6)
The first four - cause an obvious segmented structure of the neck (5th
and 6th are rudimentary)
Cells of the mesencephalic and rhombencephalic part of neural crest
migrate into the paraaxial mesoderm of the first cervical somites and
contribute to formation on arches and subsequently organs
The formation of pharyngeal arches is controlled by the endoderm of
the pharyngeal arches
Ectomesenchymal derivatives: ligaments, cartilages, bones
Paraaxial mesoderm derivatives: muscles of pharyngeal arches and
branchial arteries
Migration of neural crest (ectomesenchyme) in several
migratory pathways
Controled by Hox genes which regulate expression of
transcription factors with effectory function
Pharyngeal pouches - 5
The first starts to develop on the stage of 5 somites
The 5th is rudimentary and develops as a part of the fourth pouch at end of the 1st month
Endodermal origin
Pharyngeal clefts - 4
Form of shallow grooves
Ectoderm origin
Membranae obturantes - 4
Two-layer membranes that separate each ectoderm and entoderm groove (physiologically do not perforate in humans)
Frontal section through apparatus and branchial arch components
In each arch is: Cartilage
Skeletal muscle basis (mezoderm)
Arch artery
Branchial arch nerve
1. Pharyngeal arch (mandibular)
arch cartilage (Meckel´s cartilage) - malleus, incus, lig. mallei ant., sphenomandibulare lig.
muscles of mastication, mylohyoid and anterior belly of digastric, tensor tympani, tensor veli palatini
the 1st aortic arch - disappears (a small portion may persist and form maxillary artery)
the 1st branchial nerve - trigeminal
Derivatives of
pharyngeal
arches
2. Pharyngeal arch (hyoid):
arch cartilage (Reichert´s cartilage) - stapes, styloid process, lesser cornu of hyoid, upper part of body of the hyoid bone
muscles of facial expressions, stapedial and stylohyoid muscle, posterior belly of digastric
the 2nd aortic arch - disappears (small portions of this arch contributes to the hyoid and stapedial arteries)
the 2nd branchial nerve - facial
Derivatives of
pharyngeal
arches
Functional in the future is only the
1. pouch
2. - 4. obliterates and form a sinus
cervicalis
Pharyngeal clefts (ectodermal)
Defects caused by maldifferentiation of the pharyngeal
apparatus
1. Branchial (cervical) cysts
2. Branchial (cervical) fistulae
3. Branchial (cervical) vestiges (rudiments of branchial arches)
4. Preauricular cysts a fistulae
5. Syndrome of the 1. branchial arch
6. DiGeorge syndrome
7. Ectopia of thymus
Branchial cysts (lateral neck cysts)
Origin from persisting sinus cervicalis, positioned under angulus mandibulae
Subcutaneously or deep around the pharynx (possibly larynx)
When a cyst ruptures, communication occurs with the body surface or pharynx
Lined with stratified squamous epithelium
They may contain a liquid content with cholesterol crystals
Usually clinically not important
https://subent.com/removal-of-branchial-cleft-cyst
Abnormal communication of the pharyngeal cavity with the body surface
Between 2. pouch and cleft
(fossa tonsillaris - sternocleidomatoideus muscle)
Between 3. pouch and cleft
(tongue - art. sternoclavicularis)
Complete
at the surface of the skin
Incomplete
external, internal
Branchial fistula (lateral cervical fistula)
Koltsidopoulos et Skoulakis, CMAJ, 2018
Small grooves, pits or cysts in skin
in triangular area anteriorly to the
pinna (auricle)
Origin: by persistence of sulci
separating auricular hillocks
Residues of some components of the pharyngeal arches, usually cartilage.
Occurrence: in the subcutaneous ligament of the neck above the lower 1/3 m.sternocleidomastoid
Rare
Branchial vestiges (rudiments of branchial arches)
Preauricular cysts and fistulae
Isaacson, IJPO, 2019
Complex malformation of the skeleton of the face (both jaws, palate), eye and ear, caused by delay or non-migration of
crista neuralis into the 1st pharyngeal arch
Types:
1) Treacher-Collins syndrome - dysostosis mandibulofacialis – autosomal dominant hereditary malformation
anatomically: hypoplasia to aplasia of zygomatic bones, hypoplasia of the upper and lower jaw, macrostomy, gothic
floor, hypoplastic and sparse teeth, malocclusion - the face shows a characteristic physiognomy
The First pharyngeal arch syndrome
2) Pierre-Robin syndrom
Hypoplasia of the mandible, gothic floor or posterior cleft palate, glossoptosis, ear defects
Autosomal recessive inheritance, X chromosome - linked
The intellect of individuals is not affected
Symptoms: due to the shortened base of the oral cavity, individuals after birth have difficulty feeding and breathing
(stridor - caused by a disproportion between the lower jaw and the tongue)
Resnick et at, 2019
Agnathia
Incorrect development of the 1st pharyngeal arch. Caused by improper migration of neural crest cells.
Anatomically: hypoplasia of the mandible, shortened philtrum - nasal hypoplasia, congenital aplasia of the thymus and
parathyroid glands, hypoplasia of the thyroid gland, defects of the heart and large vessels (right aortic arch), external
ear defects
Clinically: hypoparathyroidism (hypocalcemic seizures), absence of cellular immunity, manifestations of heart defect
Incidence 1: 50 000
Etiology: Most frequently deletion on chromosome 22 - (22q11)
DiGeorge syndrome
The development of the tongue begins in the 5th week at the interface of the stomodeum and the beginning of the primitive pharynx
Anterior 2/3 of the tongue Apex and corpus linguae Formed from the mandibular process of the 1st pharyngeal arch
Posterior 1/3 of the tongue Radix linguae Formed from the 3rd and 4th pharyngeal arch
Apex and corpus
On the mandibular prominence are 3 mesenchymal protrusions covered with ectoderm:
Paired tuberculum linguale laterale (dx et sin) - distal lingual protrusion
Middle unpaired tuberculum impar (tuberculum linguale mediale) - middle tongue protrusion - more caudally
Tongue development
Radix linguae
2 foundations: copula - fused ectomezenchyme of the ventral ends of the hyoid arch
eminentia hypobranchialis - formed by fusion of ventral ends of 3rd and 4th pharyngeal arch
both the copula and the hypobranchial eminence are covered by the endoderm
Endoderm between the tuberculum impar and the dome very intensively proliferates and grows caudally, its luminization creates a
ductus thyreoglossus (see thyroid gland)
During the 6th week, the protrusions begin to fuse together
Lateral protrusions enwrap the unpaired tuberculum impar - a uniform apex and corpus linguae is formed
In definitive proportions, it resembles the original symmetrical origin of the tip and body of the tongue sulcus medianus linguae
(+septum linguae)
Only a small part of the body near the root of the tongue comes from the tuberculum impar)
The hypobranchial process merges with copula and
moves forward - approaching the base of the
corpus with which it merges
Radix - Pharyngeal part of the tongue
The fusion line is visible until
adulthood as a shallow "V" - shaped
groove - Sulcus terminalis
At the top of the "V" is a short channel:
Foramen caecum, remnant of the
proximal end of the ductus
thyreoglossus
The ectoderm and entoderm of the common base of the tongue differentiate into stratified squamous epithelium, taste bud cells, and
secretory compartments and ducts of the tongue glands
From ectomesenchyme of fused protrusions, the ligament of the tongue, blood and lymph vessels develop, incl. lymphatic tissue of
the root of the tongue
Muscles of the tongue come from the occipital myotoms, which move to its base and merge together.
During the fusion of myotomes, their motor nerves also merge (segmental arrangement) - the hypoglossus nerve is formed
Development of tongue papillae - in the 8th week – firstly papillae vallatae, foliatae (near the branches of the n. IX.), fungiformes
(branches of the n. Lingualis), filiformes (the 11th-12th week)
Taste buds - weeks 11-13
Sensitive innervation: Apex and corpus - trigeminal nerve (n. mandibularis)
Radix - n. Glossopharyngeus
Innervation of taste buds:
- Taste buds in papillae fungiformes fungal - n. facialis - chorda tympani
- Taste buds in papillae foliatae and circumvallatae - n. glossopharyngeus
- Taste buds in another location (radix lingue, isthmus faucium) - n. vagus
Tongue development
Ankyloglossia (lingua accreta) - short frenulum, limited mobility of the tip of the tongue, it is not possible to stick out the tongue
(difficulty breastfeeding), 1: 300 births. The frenulum usually lengthens spontaneously (surgery is not needed)
Congenital lingual cysts and fistulas - persistence of ductus thyreoglossus – clinically usually non important, causes problems only
when enlarged (discomfort in the pharynx or dysphagia)
Macroglossia - a rare, abnormally large tongue (associated with some syndromes, e.g. Down sy.)
Microglossia - a rare, abnormally small tongue (mostly associated with micrognathia; microglossia in combination with limb defects Hanhart's
syndrome)
Glossoptosis - displacement of the tongue dorsally. Pushes on the epiglottis, narrowing of the pharynx.
Lingua bifida (lingua fissa, glossoschisis) - a very rare anomaly, incomplete fusion of the tubercula lingualia lateralia
complete cleft - including the tip of the tongue (associated with the cleft of the lower lip and jaw)
partial cleft - deep longitudinal groove (groove) in the body of the tongue
Aglossia – tongue not developed
Overview of tongue development defects
Salivary glands as derivatives of the lining of the stomodea or other structures: the oral side of the palate, the tip
(ectoderm) and the root of tongue and the oral base (entoderm)
ectoderm: small salivary glands of lips and face, palate, gl. apicis lingue and parotid gland
entoderm: Weber's and Ebner's glands of the tongue, gl. submandibularis and gl. sublingualis
They all develop in a similar way:
From the epithelium (ecto- or entoderm) at the site of the future gland(s): cells begin to proliferate against
adjacent mesenchyme
They lengthen and branch - the basis for the glandular duct system is created, the last 6th generation form terminal
branches
Development of salivary glands
At the ends of the terminal branches (6th-7th generation) clusters of small spherical clusters of cells are subsequently
formed - singular acins
The secretion starts during the 5th month of development, followed by gradual lumen formation during the 6th month
of development
During this period, the division of the parenchyma into lobules begins, and thin septa are formed in glandular
parenchyma from the superficial mesenchyme.
Lobulization continues until birth when glands become fully functional and begin to excrete saliva
Basis for gl. parotis 4th - 6th week, at the upper edge of both corners of the mouth; after narrowing
of the rima oris, the ductus parotideus opens into the vestibule on the buccal side
Basis for gl. submandibularis 6th week
Basis for gl. sublingualis 8th week
Small salivary glands during 3rd month of development
Development of salivary glands
Permanent dentition
Development
Defects
Eruption
Eruption
Tooth eruption = growth process
It is manifested by the fact that the dental crowns protrude from the gingiva at a certain time, reach the oral cavity and eventually the
occlusion plane.
Primary dentition: 5. - 30. month after born
Growth and elongation of the root of the future tooth
Progress:
The root of the tooth grows to the bottom of the ossified alveolar bone
During further growth it rises and pushes the dental crown to the surface of the gingival wall
Gingival compression - vascular supply disorder and necrosis in the terminal phase
After the dead tissue is removed, a dental crown hole is created
During eruption, the crown is protected by the enamel residue: reduced enamel epithelium (REE)
When the crown reaches the gum wall, the reduced enamel epithelium fuses with the oral epithelium
During the crown eruption, the reduced enamel epithelium gradually separates from the enamel surface
Eruption
When the tooth crown reaches the occlusion plane, there is a 1-2 mm wide stripe around the cervical part of the crown
– dento-gingival epithelium
Eruption
Alveolar process development
It is established together with the other parts of the upper and lower jaw. Intramembranous ossification
Initially, it is low and develops with the development of tooth roots and during eruption of the dentition.
It is distinguished into
a) Cortical bone (lamina vestibularis, lamina oralis)
b) Proper alveolar bone (os alveolare)
c) Supporting bone (spongiosa)
Timeline of primary dentition eruption
Exfoliation (shedding)
i1 6. - 8. months 7 year
i2 7. - 12. months 8 year
c 15. - 20. months 12 year
m1 12. - 16. months 10 year
m2 20. - 30. months 11-12 year
Temporary dentition erupts between 5 - 30 months after birth
Temporary dentition is fully functional until 6. year, then is being changed with secondary dentition
Exfoliation of temporary dentition follows the eruption of secondary dentition
Permanent dentition development
Takes a substantially longer period than primary dentition
Starts in the middle of the 2nd trimester (approx. 4 months of prenatal development) and ends with eruption between 7. -
17. (40). year of age
Mechanisms and developmental stages similar to temporary dentition
I1,I2, C, P1,P2, develop from a successional dental lamina
Successional dental lamina is a derivative of primary dental lamina and is segmented (in contrast to primary dental lamina)
Permanent dentition development
M1, M2, M3 develop from the elongation of the primary dental lamina
Developmentally molars from the secondary dentition belong to the teeth of primary dentition
Permanent dentition development
Permanent dentition development
Timeline of primordia of permanent dentition formation
Prenatally:
M1 4. month – distal prolongation of the primary lamina
I1, I2 5 - 6. month
C 8. month
Postnatally:
M2 6. month – distal prolongation of the primary lamina
P1 10. - 12. month
P2 18. month (1,5 year)
M3 5. year – distal prolongation of the primary lamina
Permanent molars developmentally belong to teeth of primary dentition
foetus - 6 month old
The follicle of temporary and definitive tooth is initially at the same level, both surrounded by ectomezenchyme and sharing part of the
dental follicle
During development, the primary tooth grows and secondary takes place under the root of the temporary tooth
The follicles of both teeth separates the bony barrier
Permanent dentition development
I1/i1
Bucolingual crossections through incisors (newborn - 9 years)
Eruption of permanent molars are similar to temporary teeth
For permanent incisors, canines and premolars primary dentition needs to be removed
With the growth of the permanent root, the crown pushes the bone barrier, which separates both teeth. After
resorption of the bone, the crown cause pressure on root of primary dentition which initiate radix resorption
Role of „-clasts“
The result is a gradual shortening root of a temporary tooth
In parallel there are changes in dental pulp,
periodontium and epithelial tissue
Eruption of permanent teeth
Periodontium loses its ligamentous character
conversion into loose collagenous connective tissue (it still
retains the ability of redifferentiation because it provides
material for the definitive periodotium)
Epithelial junction is disintegrated and cementum is exposed.
Dental pulp - transformation into stripes of dense connective
tissue
… In case of increased load, when the ligaments are no longer
sufficient to fix and stabilize the tooth when biting and
chewing, the stripes break and the temporary tooth falls out
(exfoliation)
The channel formed after the temporary tooth has fallen out
(called gubernacular), will be used by a permanent crown for
easier eruption into the oral cavity
Eruption of permanent teeth
Gubernacular canal
tooth jaw dental calcifica end of eruption root
cap tion enamel dev. formation development
Mixed dentition
Dentition, in which temporary and permanent teeth are both present
Mixed dentition period - starts by eruption of the first permanent molar (M1) and ends by exfoliation of the
second temporary molar (m2)
Lasts between 6. - 12. year
Exfoliation (shedding) of deciduous teeth recapitulate their eruption
i1 6. – 8. month 7. year
i2 7. – 12. month 8. year
c 15. – 20. month 12. year
m1 12. – 16. month 10. year
m2 20. – 30. month 11. – 12. year
Mixed dentition
Congenital dental malformations
Teeth number anomaly
Increased number of teeth
Rudimentary
Suppmenental
Decreased number of teeth
Hypodontia
Oligodontia
Anodontia
Fused teeth
dentes confusi
dentes concreti
dental druse
Tooth shape anomalies
Size anomalies
Macrodontia
Microdontia
Anomalies in the hard tissues formation
Enamel
Dentin
Cementum
Tooth positions anomalies
protrusion
transposition
rotation
heterotopy
retention
Anomalies in eruption (related to time)
dentitio tarda
dentitio praecox
Odontomas
a) Dentes supernumerarii (hyperdontia)
more frequent in permanent dentition, the shape of teeth is a normal or garbled (odontoid)
paramolar - molars located labial to molars //distomolar - molars located distal to molars
parapremolars, distopremolars
mesiodens - the upper middle
incisor (maxillary central uncisor)
Numerical abnormalities
dysostosis cleidocranialis
Mesiodens - in the gap between the upper middle incisors (spherical or conical shape)
Dens parapremolaris - supernumerary tooth on the bucal or palatal side or dens distopremolaris (between P2 and M1)
Dens paramolaris - between the first and second molars on the vestibular side
Dens distomolaris - supernumerary 4th molar (located distally to the 3rd molar)
Dentes prelactales (dentes natales) - rare; small supernumerary teeth present at birth, with a small crown and no root
(occurring in the region of the lower incisors)
diferenc. dg.: dentitio precox
b) Hypodontia
number of lacking teeth is lesser than 6 - most often M3, I2, P2 (lower jaw)
Occurence: 0.7% (temporary), 2% (perm.) of individuals (M3, I2 , P2 /lower)
c) Oligodontia
number of lacking teeth is more than 6,
mostly teeth of the same type lack
familiar occurrence, AD inheritance
c) Anodontia
rare, associated with total dysplasia of the ectoderm and ectomesenchyme
Hypodontia Oligodontia
Fused teeth
Dentes concreti and dentes confusi (double teeth)
concreti - adjacent teeth coupled with their roots - A,B (separate dental cavities)
confusi - adjacent teeth coupled in the full length (from the crown to the apex) - C
have a common dental cavity
most often caused by a fusion of tooth buds
(rarely by division of one tooth bud - dentes geminati)
Common – manifested in a crown, neck or root
Caused by activity of aberrant ameloblasts or by defectly developed Hertwig´s epithelial sheath
Examples: conically shaped crowns of lateral incisors, reduced or increased length of the root, reduced or increased number of the root
branches etc.
Anomalies of tooth shape
Macrodontia and Microdontia - increased/decreased activity of individual parts or the entire dental bar (disproportion
between the size of teeth and jaws)
Isolated (microdontia, macrodontia)
Complete (macrodontism, microdontism)
Size of teeth
Enamel hypoplasia
occurs when activity of ameloblasts is finished earlier than should be
findings: crown shows usually abnormal shape; enamel is thinner; fissures, scratches, and holes
isolated teeth or group of teeth
Causes:
rachitis, hypoparathyroidism
syphilis congenita (Hutchinson incisors with semilunar edges, „mulberry“ molars)
Inflammatory affections of deciduous teeth connected with affections of tooth germs of permanent teeth - enamel of
permanent teeth crowns has fissures and is pigmented - Turner´s teeth)
treatment of tetracyklin antibiotics
Anomalies of hard tooth tissues
Amelogenesis imperfekta
Always hereditary cause, inheritance of AD, AR, but also linkage to the X chromosome
3 forms: hypoplastic, hypomaturation and hypomineralization
Hypoplastic: local defects (fissures, pitting) or overall thinned enamel, affecting both
dentition, temporary or permanent, AD inheritance
(ameloblasts are not functional throughout amelogenesis)
Hypomaturation: normal enamel thickness, but pigmented appearance and yellow-white
to brown colour compared to healthy enamel, softer and easily peels away from dentin
Occurrence temporary, permanent or both dentitions, AR inheritance
Hypomineralisation: the enamel is of normal thickness after eruption, but is very soft.
Soon disappears during natural attrition (it can also be removed with sharp objects)
patients complain of sensitivity to cold and heat
1 in 20 000 school-age children
Dentin
Dentinogenesis imperfecta
disorder in the development of dentin, which is pinkish to brownish and contains a reduced number of dentinal tubules
teeth are smaller, gray-blue color to brownish color
enamel is normal, but is easily separated
from dentin (fast abrasion), the in temporary
teeth are usual crown fracture
rare, AD inheritance
Sclerosis of dentin
caused by obliteration of dentinal tubules
Cementum
hypercementosis (hereditary)
aberrant cementum
in the periodontium cementicles
Anomalies of tooth position
Protrusion - longitudinal axis inclined labially
Retrusion - longitudinal axis inclined orally (into the oral cavity)
Transposition - exchange of space between 2 adjacent teeth in the dental arch (canine / incisor or first molar / canine)
Rotation - rotation of the tooth around the longitudinal axis (mesiorotation, distorotation)
Heterotopia (anomalous eruption) (heteros other, topos - site location)
the tooth was established and developed at an atypical site (isthmus faucium, hard palate) or cut outside the maxillary
arch (vestibularly or lingually)
Anomalies in eruption (time)
Dentitio tarda - no tooth is erupted until the end of the 10th month
Dentitio praecox - the first temporary tooth erupt before the 4th month of age