OCB02 - Oral and Craniofacial Biology :skull: (Enamel and Dentine (Enamel…
OCB02 - Oral and Craniofacial Biology :skull:
Enamel and Dentine
Enamel is the hardest known biological material and is able to last long periods of time so is seen in many fossils and is used to find many interesting facts about dead/extinct organisms.
It is designed to be structurally strong and to withstand occlusal forces.
It is a unique tissue as it is not able to 'turnover', once it has formed - this is what remains and must be managed.
Caries is the demineralisation of this hard tissue due to plaque acids. Plaque is able to generate a bio-film which can produce acidic secretions which cause the erosion of enamel. These carious areas appear
on a radiograph.
Teeth have many
as a result of their development.
Fissures are grooves in surface of teeth, primarily the posterior dentition.
Cusps are the 'peaks' on the occlusal surface of the teeth and occur either side of fissures.
The enamel thickness varies over the crown. The enamel thickness is greatest over the cusps as these areas are prone to the most wear.
Teeth are made mainly from enamel and dentine. Enamel is the outer surface and tends to be almost translucent and clear. The 'yellow' colour of a tooth comes from the dentine beneath.
Teeth also have
features which tend to be less obvious as they become more worn.
are grooves on the surface of teeth which manifest themselves as a surface representation of retzius lines whilst
Tomes process pits
are little indentations into the tooth surface.
There are also enamel
which are swellings of enamel near the cervical margin.
On the incisal edge of newly erupted incisors, they may have small swellings making the edge seem wavy - these are called
Enamel is 98% hydroxyapatite which should be very brittle nonetheless, enamel is very strong due to having a interweaving structure giving it strength as force is dissipated.
Enamel is made from hydroxyapatite crystallites which then form enamel prisms ~7 micrometers and 10,000 crystallites per prism.
The prisms pack tightly together which allows for mechanical stresses to be applied. This structure creates points of interest:
lines are formed as a result of the differential secretion of enamel matrix every week - this changes the direction of the prisms.
neonatal retzius line
is important forensically. During birth, a child's matrix will stop being laid down so there is a prominent retzius line which confirms whether a baby survived birth or not.
lines are daily increments in the tooth. The matrix creates a 'cross striation' where the prisms are different in size leading to the line.
Enamel is formed from the epithelial lining of the mouth whilst dentine is formed from the connective tissue. Therefore, dentine is collagenous whilst enamel is not.
The matrix of enamel is secreted by ameloblasts - two proteins are laid down; amelogenins and enamelins (non-amelogenins) from Tomes process.
Ameloblasts lay down protein matrix, which is replaced with water and then by mineral. This step is sensitive to
. Cells coalesce to make REE (reduced enamel epithelium) and fuses with the oral epithelium to form a junctional epithelium.
As matrix is deposited, the ameloblasts move away from the dentine.
The sinuous course of prisms from the enamel-dentine junction to the surface are called Hunter-Schreger bands. These bands can be diazones or parazones and important for adhesives.
Teeth have lamellae and tufts. Tufts are spaces between sheets of prisms. Lamellae are cracks from enamel-dentine junction to the surface which contain organic material.
Enamel is the hardest known biological material which is virtually made entirely from mineral.
A summary of how enamel is laid down:
The first enamel matrix to be laid down is at the enamel-dentine junction after some initial dentine has been laid down.