Dental Enamel Flashcards
In healthy gums which part of the tooth is visible
Only the enamel of the tooth crown
Describe enamel
The white, hard outer covering of the tooth
What is the anatomical crown
The part of the tooth covered in enamel
What is the part of the tooth covered in enamel called
The anatomical crown
Why do teeth appear yellower as you age
As the enamel wears away with age giving teeth a yellower appearance as more dentin is visible
What is the main disease that affects enamel
Dental caries
Does enamel have a cell population
No
What is the name of the group of non syndromic genetic defects that can affect enamel
Amelogenesis imperfecta
What percentage (by weight) of enamel is mineral?
95%
What is the name of the main mineral that makes up enamel
Inorganic hydroxyapatite crystals
What else makes up enamel apart from minerals? And state the percentage (by weight) of these other components in enamel
The other 5% is made up of unique enamel proteins, water and lipid material
In mature enamel 1-3% by weight is organic matrix (ie proteins but NOT collagen)
2% is water
How thick are hydroxyapatite crystallises in enamel?
25-30nm thick
How wide are hydroxyapatite crystallises in enamel?
60-90nm in width
What is the nature of the origin of enamel?
Enamel has ectodermal origin. It develops from the internal enamel epithelium of the tooth germ
Name the 4 proteins in enamel
Amelogenin
Ameloblastin
Enamelin
Tuftelin
State the possible functions of amelogenin
It may stabilise the amphorous Ca-P phase
May control crystal morphology and organisation
May control enamel thickness
State the possible functions of ameloblastin
May be a cell adhesion protein
May control cell differentiation
May maintain the integrity of the enamel rods/prisms
State the possible functions of enamelin
May control mineral nucleation and elongates growth (possibly with the help of amelogenin)
State the possible functions of tuftelin
May be involved in cell signalling
Why can enamel withstand both shearing and impact force?
As it is highly mineralised
As enamel is highly mineralised it can….
Withstand shearing and large impact force
It is the hardest biological tissue
List the physical properties of enamel
Has a high abrasion resistance Is brittle Has a low tensile strength Has a high modulus of elasticity Enamel can not undergo repair or replacement
What is the benefit of enamel having a high abrasion resistance
It wears down slowly
What is the benefit of enamel having a high modulus of elasticity
It minimises the chances of fractures
From which process does all secretion and modification of the matrix undergo
Tomes process
What appearance do mineralised surfaces of enamel have
Pit like appearance
The pits are surrounded by inter rod (inter prismatic) enamel
Which region between two processes secretes first:
The proximate region or the distal region
The proximal region between two processes always secrets ahead if the distal region
This forms a wall that represents the periphery of the prism and inter prismatic regions
What gives enamel its prismatic structure
The infilling of the pits as AMELOBLASTS retreat to form the main core (head) of the enamel prism
What is a prism?
The basic unit of enamel
Why are prism boundaries visible
Due to the sudden changes in crystallite orientation between the prism cores (heads) and inter prismatic enamel (tail) of adjacent prism
By how many degrees do prisms at the boundary deviate from the core
60°
How many ameloblasts make up each prism
One
How many ameloblasts make up the inter prismatic enamel
Four
Enamel prisms run from the ________ to the _________
What is the diameter and length of these prisms
Enamel dentine junction (EDJ)
Surface
Diameter: 5-6 micrometers
Length: 2-5 micrometers
Give the definition of diazones
Within longitudinal sections, areas where the prisms are sectioned transversely are termed diazones
Give the definition of parazones
Within longitudinal sections, areas where the prisms are sectioned longitudinally are termed parazones
What is gnarled enamel?
Area under the cusps of teeth where prisms appear to be disordered
Name the 4 lines visible in enamel
Hunter Schreger Lines
Striae of Ritzius
Incremental lines: cross striations and enamel striae
What are cross striations?
Lines that cross enamel prisms at right angles to their long axis
What is the reason for incremental lines forming
As there is a circadian rhythm in enamel production which produces regular crossed striations called incremental lines
How many types of incremental lines are there and what are they called?
2 types:
Cross striations
Enamel striae
Cross striations are described as ________ period incremental lines
Short
Give 5 features of cross striations
They are transverse to prisms Appear throughout the enamel Are 4 micrometers apart Represents DAILY increments Prisms vary in width
Enamel striae are describes as _______ period incremental lines
Long
Give 5 features of enamel striae
Are oblique to prisms Found throughout the enamel Are 25-40 micrometers apart Represent WEEKLY increments Reach the surface at the perikymate
What are the striae of Retzius
Prominent brown lines that run obliquely across the enamel surface to the surface
What are perikymate grooves?
Over the lateral surfaces of the crown enamel striae reach the surface in a series of grooves running circumferentially to the crown known as perikymate grooves
What are perikymate grooves separated by?
Perikymate ridges
What are the Hunter Schreger lines?
Prisms appear to travel in layers in a sinusoidal direction from the EDJ to the surface. These periodic changes in prism direction in alternating sheets results in alternating reflecting bands on the cut surface called the Hunter Schreger bands
(Ie prisms are arranged in alternating directions from layer to layer)
In what area of the enamel are no Hunter Schreger bands visible and why?
In the outer 1/4 of enamel all prisms run in the same direction so no bands are visible
How are Hunter Schreger bands an adaptation to enamel
They are an adaptation to try and break up lines of sheer within enamel to minimise chances of a fracture
Where are enamel trufts and lamellae seen?
In touch ground sections of enamel
What are tufts
They are structures radiating from the amino dentine junction for about 2/3 the thickness of enamel
Where do lamellae run in enamel
Lamellae run through the full thickness of enamel
What does scalloping aid
Scalloping aids the retention of the enamel on the dentine surface and helps resist shearing
What are enamel spindles
They are dark cigar shaped structures found in the cusps of teeth. They penetrate up to 50 micrometers of the enamel
What is the purpose of the Tomes process?
To secrete enamel
Where do rods extend from in the tooth?
The dentine to the outer surface of enamel
Where are the 2 rodless areas in the tooth?
Outermost 30-50 micrometres of enamel
Area immediately adjacent to dentine
What are enamel lamellae and why are they bad?
Enamel lamellae is a crack extending towards the enamel dentine junction
It contains abnormally high levels of organic material
This defect provides a pathway of entry for bacterial that may initiate caries
How and why are enamel tufts formed?
Formed due to a change in the orientation of the rods
They appear as branched dark short lines
They exhibit a high level of protein
These tufts extend from the enamel dentine junction into about 1/10 of the enamel thickness
What do enamel spindles represent?
Trapped odontoblast processes that failed to withdraw during enamel mineralisation
They appear as short dark finger like extensions from the enamel dentine junction into the enamel
What does the neonatal line in enamel represent?
It represents the border between the enamel formed before and after birth
It can also be formed due to a sudden change in in the environment after birth which causes a metabolic disturbance in the ameloblasts
What happens to the enamel as you age and why
- The enamel becomes less permeable due to a reduction in the spaces the crystals
- Teeth can become more sensitive due to attrition and wear
- Enamel becomes harder with age as the hydroxyapatite crystals become more mineralsied
- Teeth get yellower as enamel wears and dentine is visible
- Risk of caries decreases with age due to certain ion exchanges between the tooth and the oral environment
What percentage of immature developing enamel is made up of amelogenin?
90%
What percentage of immature developing enamel is made up of ameolblastin?
5%
What percentage of immature developing enamel is made up of enamelin?
5%
Which proteins and in what percentages make up the developing enamel?
Amelogenin 90%
Ameolblastin 5%
Enamelin 5%
What is 1% of the mature enamel composed of and why?
In mature enamel, the remaining 1% by weight of protein is comprised mainly of the nonamelogenin proteins This is because the amelogenins are selectively reabsorbed during enamel maturation.
