17. Histology of Tooth Development Flashcards
1
Q
Embryological origin and function of inner enamel epithelium?
A
- columnar epithelial cells that become preameloblasts which differentiate into enamel-forming ameloblasts (late bell stage)
- folding of IEE maps out shape of future crown
- IEE signalling to dental papilla induce odontoblast differentiation (late bell stage)
- at the end of enamel maturation stage, reduce enamel epithelium formed by IEE and other remnants of enamel organ (mainly OEE) to protect enamel from degradation and functions during eruption by fusing with oral epithelium
2
Q
Embryological origin and function of stratum intermedium?
A
- 2-3 layers of flat epithelial cells that support ameloblasts
- control transport of nutrients and removal of metabolic waste products
- production of alkaline phosphate involved in enamel mineralisation
3
Q
Embryological origin and function of stellate reticulum
A
- star-shaped epithelial cells separated by extracellular glycosaminoglycans that hydrate tissue
- protective function as a hydroskeleton
- mechanically supports developing tooth germ and maintains shape
4
Q
Embryological origin and function of outer enamel epithelium
A
- cuboidal epithelial cells that exchange substances with dental follicle (control nutrient transport, removal of metabolic waste products)
- maintains tooth shape
5
Q
Where is cervical loop? What does it do?
A
- where IEE and OEE meet
- it’s the growing end of enamel organ and forms precursor to future root/HERS
6
Q
Neural crest cells emerge from the …
What does this mean?
A
- neuroectoderm
- neural crest-derived mesenchymal cells of dental papilla and dental follicle termed ectomesenchyme
7
Q
2 types of mesenchymal cells that come from neural crest cells
A
- dental papilla
- dental follicle
8
Q
What is the dental papilla?
A
- mesenchymal cells that form cells of dental pulp - mainly fibroblasts
- condensed mesenchymal cells located adjacent to IEE are induced by epithelial signals to differentiate into dentine-forming odontoblasts
9
Q
What is the dental follicle?
A
- connective tissue sac consisting of inner layer (elongated, fibrous cells associated with OEE) and outer layer (mesenchymal cells, associated with alveolar bone)
- inner and outer layer separated by avascular, loose connective tissue
- it nourishes and protects developing tooth germ maintaining its correct shape.
- later the DF cells form tooth-supporting periodontal tissues (cementoblasts, periodontal ligament-forming fibroblasts and osteoblasts)
10
Q
What happens to the stellate reticulum of the enamel organ overlying the mineralised region of the cusp? How is this related to its function?
A
- stellate reticulum is absent around the mineralising cusp, has relocated to lower regions of crown that are still unmineralised and require physical protection
- mechanically supports and protects the developing tooth germ and maintains shape.
- relocation of SR is associated with cellular areas of developing tooth that require physical protection
11
Q
What is the functional relationship between capillaries located in dental follicle and enamel organ surrounding mineralised region?
A
- capillaries in dental follicle are associated with OEE and supply nutrients to stratum intermedium and ameloblasts
- required since enamel and dentine formation blocks access of ameloblasts to blood supply of dental papilla
12
Q
Function of Tome’s processes for
- enamel matrix secretion
- enamel crystallite orientation
A
- enamel formation starts by secretion of enamel proteins. in contrast to predentine, enamel matrix is immediately mineralised to 15-30%. First enamel is aprismatic (has no prisms) and formed against mantle dentine
- Tomes’ process is formed and proximal portion produces interprismatic enamel. Distal portion develops as an outgrowth of proximal portion, penetrates newly formed interprismatic enamel and starts to secrete prismatic enamel
- configuration of enamel secretion from proximal and distal portions results in staggered formation of interprismatic or interrod and prismatic enamel
- composition of interprismatic and prismatic enamel is identical and only differs in orientation of crystallites
13
Q
Name key enamel proteins in enamel matrix and describe their function
A
- amelogenins form 90% and remainder consist of non-amelogenin proteins like ameloblastin and enamelin
- amelogenins have low molecular weight, hydrophobic proteins generated by alternative splicing and proteolytic processing
- form nanospheres surrounding crystals preventing them from fusing and providing scaffold for future structure of mature enamel. Eventually removed to allow crystal growth but overall, regulate growth and thickness of enamel crystals
- non-amelogenins are rapidly processed after secretion (by proteinases such as enamelysin or kallikrein) and have short half lives. forms enamel sheath at periphery of enamel prism. basis of remaining organic material in enamel
- ameloblastin found in mainly newly formed enamel and facilitates adhesion of ameloblasts to forming enamel surface
- enamelin largest and least abundant of enamel protein
- non-amelogenins in general promote and guide formation of enamel cystals
14
Q
What tissues comprise Hertwig’s epithelial root sheath?
A
- after crown formation complete, epithelial cells of IEE and OEE proliferate downwards from cervical loop
- form double layer of epithelial cells (HERS)
15
Q
What happens to HERS after root dentine has formed?
A
- HERS becomes stretched by root dentine generation and forms meshwork of epithelial cells around developing root
- eventually disintegrates and most cells die by apoptosis
- remaining cells appear as epithelial rests of Malassez or sometimes incorporate in cementum
- rests can undergo epithelial-mesenchymal transition and contribute to periodontal ligament or cementoblast formation`
