Crown Formation

Question 1

When does crown formation commence and at what stage?

List the stages of moving from one stage into the next:

Answer 1

Crown formation - week 14 - late bell stage to crown stage

• cervical loop cells divide
• signal dental papilla to IEE: IEE cells mature, elongate and polarise
• signal IEE-DP: DP cells mature - DP cells invade acellular zone
• signal DP-IEE: IEE cell mature
• DP cells mature into odontoblasts - form predentine then dentine
• IEE cells mature into ameloblasts - form enamel

Question 2

What is the driver for hard tissue formation?

What is the cervical loop?

What cells do they interact with?

Answer 2

• epithelial cells of the cervical loop

Cervical loop: where outer enamel epithelial cells meet inner enamel epithelial cells at the most apical part of the enamel organ - responsible for root development

Interact with cells which will form the dental follicle, and dental papilla

Question 3

What signals occur during cervical loop proliferation?

How do odontoblasts mature?

Answer 3

• signal from DP to IEE - control number of cell divisions
• signal from IEE to DP - induce papilla cells to mature
• signal from DP to IEE - induce IEE cells to mature
• signal from dentine to IEE - appearance of dentine signals start of enamel secretion

Odontoblast maturation occurs due to an interaction between ameloblast and odontoblast

Question 4

Explain odontoblast differentiation:

Answer 4

• all cells become columnar - lots of RER and golgi
• matrix produced is mainly collagen
• lag phase before mineralisation of matrix –> pre-dentine then dentine
• dentine formed throughout life
• producing regions such as mantle, granular and hyaline layers

Question 5

Exlain the stages of life as an ameloblast:

• pre-secretory:
• secretory:
• transition:
• maturation:
• postmaturation:

Answer 5

• pre-secretory: cytodifferentiation, morphodiff, resorption of basal lamina, epi-mes interaction
• secretory: initial layer of aprismatic enamel formed, develop tomes processes, matrix secretion to final thickness, initiation and mineralisation, crystallite elongation, matrix degradation, development of prismatic structure
• transition: ameloblasts shorten, 50% die, vascular invagination, reformation of basal layer, cessation of matric secretion, matrix degradation and selective matrix withdrawal
• maturation: cycling of ruffled and smoothed ameloblasts, final degradation and withdrawal of matrix, crystal growth and final third mineralised
• postmaturation: enamel organ dgenerates, enamel coverings established, eruption, exposure to oral cavity

Question 6

When does tooth shape determination take place?

How is it determined?

What can happen at bud stage?

What transcription factors are important in tooth development?

Which transcription factors are needed for incisors and molars?

Answer 6

• late cap stage and early bell stage
• difference between rapid growth and cell division throughout IEE
• tooth shape comes from signal from dental papilla

Bud stage: can separate epithelium from molar region, put into incisor mesenchyme and will develop incisiform shape

PITX-2 must be switched on for any tooth development to occur.

• MSX1, MSX2, DLX1, 2, Barx1 and Alx-3 determine what sort of tooth is found where

MSX1 - drives incisor development

DLX-1, 2, RX-1 - responsible for molars

Question 7

What is the reduced enamel epithelium?

What is its role?

Answer 7

• forms when enamel formation is complete

Derived from:

• reduced ameloblasts
• other remnants of the enamel organ: OEE, SR, SI

Role: protection of enamel surface from resorption, prevention of cementum formation

• provide an epithelial lined pathway for eruption

forms initial junctional epithelium

Question 8

What is the successional dental lamina?

Where is it usually developed?

What is a tooth gland lamina?

Name some terms for missing teeth:

Answer 8

Successional dental lamina - development of the permanent dentition

• usually goes to lingual side of tooth

Tooth gland lamina: successional lamina goes to the labial side

Missing teeth:

• hypodontia: tooth loss except 3rd molars
• oligodontia: more than 6 teeth missing
• anodontia - all missing teeth, extremely rare

Question 9

What is supernumerary?

List its sub types:

What can occur in the cap stage?

Answer 9

Supernumerary - overexpression of a gene to get extra layers of teeth developing

• microdontia - small teeth
• macrodontia - unusually large teeth - developmental disorder during bud stage

Cap stage:

• dens in dente - enamel organ invaginates into dental papilla, deep lingual pit forming
• fusion - two teeth become one
• gemination - splitting of the tooth