Components of the Teeth - Enamel Flashcards
what does cariogenic mean
this is something that creates caries - “cariogenesis” is the creation of caries
how does acid lead to the development of caries
it removes certain components of the tooth structure
what is the structure of enamel essential for
the development of caries
give a brief summary of the features of enamel
- it is the hardest tissue in the body
- resists abrasion
- brittle
- supported by dentine
- covers the crown of the tooth
- varies in thickness
- translucent
- transparency of enamel increases with mineralisation
why is enamel the hardest tissue in the body
it is often exposed to traumas like biting and chewing that it needs to be resilient for
what is attrition
this is the normal wear of a tooth throughout its lifetime.
what is abrasion
wear over a very strong activity in which there is a more pathological wear. this includes activities like grinding of teeth, or dents in a tooth where there is constant contact and wear.
how must teeth be restored in older invididuals
in such a way that looks natural, including colour and level of wear. designing to make them look like the teeth of a teenager will not look natural on them
explain what is meant by describing enamel as brittle
this means it is breakable, where without any support the enamel would break apart from force
why does the enamel not break apart from force if it so brittle
it is cushioned by the dentine underneath the surface. if left unsupported when doing a tooth restoration, it would certainly break apart if any force was applied to it
what does it mean to say enamel is translucent
the light can pass thrugh it. the colour of tooth is actually due to the dentine underneath, rather than the actual enamel on the top surface.
where do enamel and dentine grow from
the amelo dentino junction
what are the cells that produce enamel called
ameloblasts
in what structure is enamel produced in
rods, or otherwise known as prisms.
what is the thickness of enamel dependent on
the function of the tooth
describe the regional variations of enamel
the surface enamel is more mineralised and harder than deeper enamel due to long term wear
the hardness of enamel decreases from the cusp tip (posterior teeth) or incisal edge (anterior teeth) to the cervical region
these properties have both functional and clinical significance
give a brief outline of the enamel rods
these are the basic units of enamel, and run from the amelo dentino junction to the surface. they contain hydroxyapatite crystallites, and their orientation of these crystallites will vary within and along the rod
what does rod structure arise from in relation to crystallites
their orientation
breakdown the different components and their composition within enamel
- hydroxyapatite makes up 95% of the weight of enamel, and about 90% of its volume
- water makes up 4% of weight and around 5-10% volume
- the organic matric makes up 1% of the wight and around 1-2% of the volume
what can be found within the organic matrix of enamel
proteins, like amelogenins, enamelins, peptides and amino acids
what are the different surface types found on enamel
smooth surface
pits and fissures
is surface enamel always different to deeper enamel
no, they are exactly the same at the start point of their lifetime but over time changes as the tooth is exposed
what does the hardness of enamel depend on
its mineralising and demineralising
what defines crystallites
the proteins
when is enamel formed
it is made before the tooth erupts in the mouth, by ameloblasts, which die once the tooth erupts.
why does the tooth lose its ability to make enamel
the ameloblasts die as soon as the tooth erupts
what is responsible for giving bone much of its hardness
hydroxyapatite
which protein makes up most of the enamel proteins
amelogenins
what are the three stages of amelogenesis
presecretory, secretory, and maturation.
what is dental papilla
a condensation of odontoblasts
what happens to the translucency of teeth as people age
increases
what colour is young enamel
white
what composition of enamel is hydroxyapatite crystals
95%
describe the structure of the hydroxyapatite crystals in enamel
long flat ribbons that are rhomboidal in cross section analysis. some of them can be distorted by crowding during development.
are the hydroxyapatite crystals wtihin enamel larger or smaller than in dentine
larger
why are there incremental lines on enamel
due to the phasic way that enamel develops
what makes up enamel
the enamel rods/prisms. these are a basic structural unit of enamel and are keyhole shaped, and are formed by the hydroxyapatite crystals.
how can enamel be described in relation to its composition of cells
it lacks cells and is a calfified tissue
where is enamel thickest on the tooth
the cusp and incisal edge
where is enamel thinnest on the tooth
the cervical margin
why does the thickness of enamel vary depending on the location on the tooth
the areas that suffer more attrition has more enamel and will have a reduced risk of fracture
how does the hardness and density of enamel change through its depth
these features decrease as you go from the surface enamel to the interior, subsurface layer
how are incremental lines removed from enamel
attrition and abrasion
what are the different types of incremental lines
straie of retzius and cross striations
describe the straie of retzius
these are a type of incremental line found on the surface of enamel. they run obliquely along the enamel prisms to the surface, and when they reach the surface they form perikymata
describe cross striations
these are short period incremental lines on the enamel that are formed parallel to the secretory face of ameloblasts. they cross enamel prisms at right angles
what causes the small pits on perikymata
the impressions of the ends of ameloblasts
how many days does it take for enamel to reach its full thickness
625
how many crystallites are found within each enamel prism
several million
how many different patterns of enamel prisms are there
three
what is type 1 of enamel prisms
these form complete prism boundaries
what is type 2 and 3 of enamel prisms
the prism boundaries are incomplete, and have a keyhole pattern. the tail points cervically
give a description of surface enamel
this is the most clinically relevent form of enamel as it is susceptible to caries, erosion etc. it is harder, less porous and less soluble than subsurface enamel.
when does enamel restrict fracture the most effectively
in regions where prisms make an acute angle with the surface
give a description of the pores found within enamel
the pores are waterfilled spaces that are found between the crystallites.
where are the enamel pores that are accessible for larger molecules located
prism boundaries
what are some features that extend from the dentine into the enamel at the amelodentine junction
enamel spindles, tufts and lamellae
what are enamel lamellae
features that are hypomineralised and extend from the junction to the surface of the enamel.
what are enamel spindles
narrow tubules
what are enamel tufts
these are features that resemble tufts of grass, and they contain tuftelin
which area of enamel is more soluble
the core is more soluble than the periphery of enamel
what determines the strength and resistance to fracture of enamel
arrangement of crystallites and prisms
when is the effect of fluoride on enamel strength and remineralisation most effective
when it has replaced 50% of the hydroxyl groups
are there prisms on the narrow surface zone of enamel
no
presecretory stage of amelogenesis
- inner enamel epithelial cells differentiate to form ameloblasts by stretching and becoming tall columnar cells
secretory stage of amelogenesis
ameloblasts secrete organic matrix to form the full enamel thickness
maturation stage of amelogenesis
ameloblasts carry out activities that help with degradation of enamel matrix and replacement by minerals or inorganic material
