Enamel and Dentine Caries Flashcards
Why is it important to understand the caries process in enamel and dentine?
Dentine caries is the most common disease to affect the dentition
Define dental caries
It is a localised, chemical dissolution of tooth surface brought about by metabolic activity in a microbial deposit (a dental biofilm) covering a tooth surface at any given time.
What is dental caries promoted by?
a frequent dietary supply of fermentable carbohydrates.
What does a high carbohydrate diet lead to?
It is thought to induce an ecological imbalance within the dental biofilm with acidogenic bacterial plaque species dominating
Where do dental caries lesions develop?
at relatively ‘protected sites’ in the dentition,
For example pits, grooves, and fissures in occlusal surfaces
Wha is the principal component of enamel?
Calcium hydroxyapatite
What is the chemical formula for calcium hydroxyapatite?
Ca10(PO4)6(OH)2
What percentage of enamel is made up of minerals?
95%
Whereis mineral content highest in he tooth?
At the surface
Where is mineral content at its lowest?
th enamel closest to the ADJ
What forms the bulk of the tooth?
Dentine
What is more mineralised dentine or enamel?
Enamel
What percentage of he dentine is made up of proteins?
20%
What percentage of he dentine is made up of water?
10%
What is the mineral content by weight of dentine?
70%
What percentage of he enamel is made up of proteins?
1%
What percentage of he enamel is made up of water?
3%
What are the crystal dimensions of enamel?
68 x 26nm
What are the crystal dimensions of dentine?
35 x 10nm
The fact enamel is highly mineralised means what?
Means enamel can withstand both shearing and impact face well
Also its abrasion resistance is high but it is brittle
Wha can happen of enamel is unsupported by dentine?
Can lead to fracture resulting in cavitation at the tooth surface
How can dentine be lost?
Due to the progression of caries in dentine
Generally what trend do the hardness and density follow in the tooth?
Hardness and density decrease from the surface of the tooth to the ADJ
dentine is F_______ and is c_______ ….
Flexible
Compressible
Why is dentine flexible and compressible?
To support the overlying enamel
How is dentine flexible and compressible?
Due to its organic matrix and tubular architecture
What qualities does dentine not possess?
- Has a poor abrasion resistance
- Poor resistance to crack propagation
- Presents a poor barrier to diffusion of bacterial by products under caries lesions
What quality does the outermost enamel possess?
It is porous
How can dental enamel be described?
It can be considered to be microporous soli composed of tightly packed crystals
What development defects can we see in enamels microstructure?
Small irregular fissures and micro pores can be seen within the surface Zone
How big are the tiny micro channels in enamel and what are they involved in?
they are about 0.5-1.5 micrometers in diameter
They are involved in the lesion development playing a role in the diffusion processes
What acts as a larger diffusion pathway in enamel?
The openings of the he Striae of Retzius
Where are the opens of the Striae of Retzius?
At the surface via the perikymata grooves
Where is packing slightly looser in the enamel?
The packing of crystals is slightly looser along the prism periphery/ boundary
What are crystal separated by in enamel?
Tiny inter crystalline spaces filled with water and possibly some organic material
What do the inter-crystalline spaces in enamel form?
They form a fine network of diffusion pathways which are often referred ti as micropores and open onto the surface enamel
How are the crystals arranged in enamel?
They are arranged in 5 micro metre rods
What is the basic structural unit in enamel?
Hydroxyapatite crystals
Describe hydroxyapatite crystals?
It is roughly hexagonal n cross section Crystals are larger than the crystals seen in dentine and bone
Where do the prisms run in enamel?
Runs from he dentine to just below the tooth surface
How does enamel dissolution occur?
By exposure to acid
How is acid formed on the enamel surface?
By the overlying plaque biofilm and by the proteolytic action of bacteria on the protein content
Where does and penetrate more easily?
Will penetrate more readily where there is greater porosity
Where may acid penetration occur the most?
Down paths provided by prism boundaries
What do prism boundaries provide?
A “highway” though the enamel allowing diffusion of molecules from the surface
What does acid dissociation produce?
Irregular crystal outlines
Crystal demineralization and destruction in the prism cores is also seen
What is the basic rule regarding caries progress?
Caries wilfl progress more rapidly along relatively hypomineralised areas within enamel including the Prism Boundaries, Cross Striations and Striae of Retzius.
What is the initial caries lesion formation related to?
initial caries lesion formation is related to the organization and ultrastructure of enamel.
When examining the structure of enamel what can we find it consists of?
It consists of large numbers of small, parallel dentinal tubules in a mineralised collagen matrix
What do the inner part of dentinal tubules contain?
They contain the long processes of the cells
What are the long processes found in the inner part of dentinal tubules responsible for?
They are responsible for forming the tissue, the odontoblasts and a small volume of extracellular fluid
At a superficial level how many dentinal tubules are there?
10,000-25,000 per mm2
with a diameter of 0.5-1.2 micro metres
At a deep dentinal level how many dentinal tubules are there?
30,000-52,000 per mm2
with a diameter of 1-3 microns
At a cervical dentinal level how many dentinal tubules are there?
10,000-25,000 per mm2
How much of the dentine is occupied by superficial dentinal tubules?
1%
How much of the dentine is occupied by deeper dentinal tubules?
30%
Why does the deeper dentinal tubules occupy more dentine space than superficial dentinal tubules?
As deeper dentine is approximately 22% by volume of free fluid but superficial dentine is only 1%.
The fact that deeper dentinal tubules are 22% by volume of free fluid means what?
The deeper dentine is more porous and permeable to bacteria and chemicals than superficial dentine
What can happen to plaque biofilm under suitable conditions?
Plaque biofilm can shift ecologically to become cariogenic
What does it mean when plaque biofilm is described as cariogenic?
It means it produces an retains a low pH at the tooth surface
What can give rise to initial caries lesions?
The periods of repeated de an remineralisation if the equilibrium tips toward acid dissociation and mineral loss