1019DOH - Applied Oral Biology (ORAL HISTOLOGY)

hello! this is for the real ones lmao:) please study these in flashcard mode, unshuffled! they're meant to be in sequence. we got this YEAHH

what is the stomodeum?

the small distance between the heart and head in an embryo of 5-6 weeks in utero

stomodeum alternative name

primitive oral cavity

3 germ layers of the 5-6 WIU embryo (WIU = weeks in utero)

1. ectoderm

2. mesoderm

3. endoderm

ectoderm germ layer of the embryo

• external lining of the body and oral cavity later on

• epithelial in origin

• anything we can touch (eg. eyes, hair, nails, skin) is this

mesoderm germ layer of the embryo

• connective tissue in origin (eg. blood, bone, cartilage, muscle)

• anything inbetween guts and epithelium is this

endoderm germ layer of the embryo

• lines internal organs (guts)

• not supposed to be exposed to the external environment

• anything related to the GI (gastrointestinal) system is this

• starts from pharynx and travels down

all 3 ____ ______ are needed for an embryo to develop

germ layers

what are the different embryonic origins of the tissues found in the oral cavity?

• enamel) external layer, epithelial in origin ∴ ectoderm

• dentin, pulp, cementum, PDL, alveolar bone) connective tissue ∴ mesoderm

• NO ENDODERM (no guts in teeth lol)

what 2 layers form the ectoderm? (think microscopically)

what does the ectoderm lay above?

• a layer of superficial flat cells

• a layer of lower columnar cells

• ectoderm rests on a basement membrane and then a lower layer of connective tissue (mesoderm)

what does it mean if the basement membrane breaks?

• early signs of malignancy

• mixture of ectoderm and mesoderm is very bad (except in some embryological events)

from both ectoderm and mesoderm, the ____1___ (derived from mesoderm) is formed, which all __2___ and ___ ___3______ are formed from.

1. mesenchyme

2. teeth

3. oral structures

the development of ______ ____ ______ is the only development that precedes tooth development

neural crest cells

when do neural crest cells appear….

• during embyrological development?

• physically on the embryo?

• during CNS development (CNS = central nervous system)

• at the top of neural grooves (at the crest of the groove)

neural crest cell properties

(note: neural crest cells will be referred to as NCC’s from now on)

1. ectodermal in origin

2. ability to migrate to other tissues

3. can differentiate into other cell types

4. can send signals to neighbouring tissues and tissues they migrate to

why are NCC’s important?

• act as a leader during embryological development

• have different abilities (eg, ectodermal in origin like nervous tissue and can move and migrate like stem cells)

• when they move, they send signals to migrated to and surrounding tissues

NCC’s migrate from the __1__ surface of the embryo to the ___2____, where they reside in the ____3____ to change it to the _____4______.

1. dorsal

2. stomodeum

3. mesenchyme

4. ectomesenchyme

after NCC’s migrate to the mesenchyme, where will they reside?

below the basement membrane

when NCC’s migrate to the mesenchyme, why does the name change from mesenchyme to ectomesenchyme?

• NCC’s are ectodermal in origin - ‘ecto’ in ectomesenchyme refers to this

• mesoderm (mesenchyme) is pure connective tissue

• but because the NCC’s have travelled there it isn’t pure connective tissue anymore

• this is why the name changes

ectomesenchyme is needed to develop a tooth. why?

• enamel is ectodermal in origin

• PDL, alveolar bone, periodontal ligament, cementum, pulp and dentin are all mesodermal (connective tissue) origin

• ectomesenchyme is both ectoderm and mesoderm which is why it is needed to develop all above structures

once NCC’s reside in the ectomesenchyme, what do they do and what does this affect?

• start sending signals to migrated to and surrounding tissues

• signals therefore affect not only the mesenchyme but the ectoderm on top too

the embryo is flattened ____-_______

dorso-ventrally

what are branchial arches?

• six finger-like projections that extend from the ectoderm of the foregut to the outer ectodermal lining

• lined by ectoderm on outside, endoderm on inside and mesoderm inbetween

• ONLY FIRST BRANCHIAL ARCH LINED BY ECTODERM ON THE INSIDE AND OUTSIDE

• contain all information for developing organs

why is the first branchial arch lined by ectoderm on the inside and outside?

• because the first branchial arch develops into all structures in the head

• endoderm is for guts, and the head doesn’t need it

• this is why its lined by ectoderm on the inside and outside

what do the 2nd, 3rd/4th, 5th/6th branchial arches contain the information for?

• 2nd: neck

• 3rd/4th: thorax

• 5th/6th: anything below (guts/lower limbs)

what are clefts in branchial arches? what are they lined by?

• depressions between branchial arches from the outside

• lined by ectoderm

what are pouches in branchial arches? what are they lined by?

• depressions between branchial arches form the inside

• lined by endoderm (except between 1st and 2nd arches where lined by ectoderm - no need for endoderm in the whole head area including the oral cavity)

flip card over for transverse section of a branchial arch

6 derivatives of the first branchial arch (mandibular arch)

1. mandible and maxilla

2. lower lip, part of upper lip and cheek

3. all teeth

4. all salivary glands

5. all masticatory muscles

6. anterior 2/3rds of the tongue

all structures derived from the same branchial arch will share the same…

nerve and blood supply

how many branchial arches (and therefore, how many nerve supplies) form the tongue?

• 3 branchial arches form the tongue

• therefore, there are 3 nerve supplies

structures from the first branchial arch are supplied by the ____1____ nerve or a branch of this nerve, therefore, the first branchial arch can also be called the _______2_ ____

1. mandibular

2. mandibular arch

the first branchial arch is directly below the…

stomodeum (primitive oral cavity)

the anterior 2/3rds of the tongue is formed from the first branchial arch. which nerve is its sensory nerve supply?

• the lingual nerve (branch of mandibular nerve)

• what is Meckel’s cartilage?

• runs from where to where

• guides development of…

• remnants will leave how may ligaments and bones behind?

• Meckel’s cartilage is the cartilage within the mesodermal part (centre) of the mandibular arch

• runs from the middle ear to the mandible ( ∴ follows shape and structure of mandible)

• guides development of mandible but doesn’t contribute that much to it (can still develop a mandible without Meckel’s cartilage)

• remnants will leave 2 ligaments and 4 bones behind

list the structures derived from Meckel’s cartilage remnants

1. incus and malleus

2. lingula of the mandible (spiky bit on inner side of mandible - guards entrance of mandibular foramen)

3. mental ossicles (at midline, aka genial tubercles, are 4 little bones on lingual side of mandible)

4. sphenomandibular ligament

fill this in:

1st branchial arch (_____1____ arch) → ____2__ nerve (or branch of)

2nd branchial arch (__3___ arch) → __4___ nerve (or branch of)

1. mandibular

2. mandibular

3. hyoid

4. facial

name the stages in tooth development in order

1. dental lamina

2. bud

3. cap

4. bell

5. eruption

describe the formation of dental lamina

(this is step 1 of tooth development)

• note: phrase highlighted in yellow is something you need to include when you start any stage of tooth development (will appear from this card onward when describing tooth formation steps, so keep an eye out 👀)

• under influence of the NCC’s, downward proliferation of ectoderm forms two dental laminae

• dental laminae appear as band-like structures

• NCC’s do this by sitting in the mesenchymal area and signalling to the ectoderm to proliferate downwards

• one lamina carries the upper deciduous teeth

• the other lamina carries the lower deciduous teeth

describe the bud stage

(this is step 2 of tooth development)

• under influence of the NCC’s, 10 rounded projections/buds (enamel organs) appear on the labial surface of the dental lamina (corresponding to 10 deciduous teeth!)

• each bud is surrounded by a mesenchymal condensation (which is the dental papilla and the dental sac)

• each lamina (from step 1) have 10 tooth buds each

the enamel organ in the bud stage of tooth formation is the __1_dermal part, and eventually forms the ___2___

1. ecto

2. enamel ;)

in the bud stage, the dental papilla (mesenchymal condensation) eventually forms what under the influence of the NCC’s?

the dental papilla forms dentin and pulp of the tooth

the dental sac in the bud stage is ________/________ in origin, and forms what 3 structures to connect the tooth to the outside environment?

• mesenchymal/mesodermal

• cementum, PDL and alveolar bone

the tooth germ is formed of three parts. what are they? what are their dermal origins?

• enamel organ (ectoderm in origin)

• dental papilla (mesodermal in origin)

• dental sac (mesodermal in origin)

what is the difference between the enamel organ and the tooth germ?

• the enamel organ is 1 of 3 parts forming the tooth germ

• the tooth germ is all 3 parts

which tissue in the tooth germ (bud stage) is ectodermal in origin?

• the enamel (derived from the enamel organ)

describe the early cap stage

(this is step 3 of tooth development)

• note: there’s 2 parts to this stage and this is the first. the second part of this stage will be called the ‘late cap stage’

• under influence of NCC’s, the enamel organ of the bud stage undergoes unequal growth to change in shape from a bud to a cap

• enamel organ during this stage has its inner surface lined by columnar cells, called inner enamel epithelium or the inner dental epithelium

• the outer surface is lined by cuboidal cells and is called the outer enamel epithelium or the outer dental epithelium

• inner and outer dental epithelium meet at the cervical loop

what structures form above and below the cervical loop?

• above the loop: crown of the tooth

• below the loop: root/s of the tooth

true or false?

the inner and outer epithelium have the same functions as each other (cap stage)

false

• they have different functions

in the cap stage of tooth formation, are the tissues hard or soft?

• all tissues are soft tissue in this stage

what is morphal differentiation? (cap stage)

• the convexity of the outer surface and the overall morphological change to a cap shape

what is histo-differentiation? (cap stage)

• in bud stage, you have 2 layers of ectoderm (flat and columnar cells)

• but in cap stage, there are more layers. the inner surface is lined by different cells than the outer surface

in the early cap stage, which surface grows at a lower rate?

• the inner surface grows at a slightly lower rate than the outer surface

describe the late cap stage

(this is step 3.2 of tooth development)

• note: this is the second and final part of the cap stage

• polyhedral cells in the middle of the enamel organ change into star-shaped cells called stellate reticulum, due to secretion of a hydrophilic substance called glucosaminoglycans (GAG’s) produced by polyhedral cells

• lots of cytoplasm/tissue fluids will be attracted to the polyhedral cells

• with no escape route for the fluid, cells change shape to star-like forms (stellate reticulum cells) and form long processes to occupy space and prevent bursting.

• desmosomes connect stellate reticulum cells and form a tight network between them

• note: the enamel organ is still surrounded by dental papilla and dental sac like in the bud stage

3 functions of the stellate reticulum cells (cap stage)

1. resist against physical trauma (as filled with tissue fluid/cytoplasm)

2. help enamel mineralisation/maturation

3. distribution of calcium to newly formed enamel

list and describe the 2 transient structures in the cap stage

• note: these structures appear in this stage only!

1. enamel knot and enamel cord

   • rounded cells that connect inner and outer enamel epithelium

   • KNOT) thought to determine the future site of the cusp/incisal ridge

   • CORD) may give rise to another type of cells called stratum intermedium

1. cell free zone

   • thin area between enamel organ and dental papilla

   • separates dental papilla from inner surface of enamel organ

   • helps cells perform their function

   • elongate during early and late bell stage

enamel knot and cord and stratum intermedium cells (late cap stage and transient structures)

• the enamel knot and cord will eventually disappear (as they are only present in the cap stage)

• after the enamel knot and cord pull the inner enamel epithelium to the future site of the cusp/ridge, they will leave remnants

• these remnants are called stratum intermedium cells

• these cells appear rounded and flat

• they appear on top and work with the inner enamel epithelium and help it perform its function

flip card over for a visualiser of the cap stage