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
Describe how caries lesions may appear in their early stages?
Lesions may appear as opaque white spots
Why do initial lesions appear white?
Because the sub surface enamel has become porous as a result of the mineral being dissolved by acid (produced by bacteria)
What happens to the lesion as porosity increases?
May begin to take up a skin becoming a brown spot lesion
Can eventually cavitate exposing dentine
State the formula for the dissociation of calcium hydroxyapatite
Ca10(PO4)6(OH)2 ⇌ 10Ca2+ + 6PO43– + 2OH–
Name the zones that are visible when we look at a wedged shaped lesion under polarisedlight
- The translucent zone
- The body of the lesion
- The Intact surface son
- The dark zone
Where is the translucent zone found
It is the deepest layer
Describe the translucent layer?
It is the least affected layer
It is made up of 1% pore volume
Where is the body of the lesion found?
It is the subsurface zone
Describe the body of the lesion
It is the most affected part with lesion
Has the greatest porosity with a pore volume of 5-25%
Where is the intact surface zone?
Right underneath the plaque biofilm/
What does the dark zone separate?
It separates the body of the lesion from the translucent zone
How much mineral has been lost in the translucent zone?
Less than 1%
What is produced in the translucent zone?
Small number of relatively large uniformly sized pores
Why is the translucent zone called this?
Due to the uniformed sized pores In this zone
They give the zone a translucent optical effect
Why does the dark zone look dark?
Because to diffracts/refracts the light due to unequal pore sizes
Also possibly because of a relatively high protein content in this zone
Why does the dark zone have pores of varying sizes?
Results from some pores growing bigger whilst others become smaller because of some re-precipitation of mineral.
Why does re precipitation o minerals orrin the dark zone?
Because in the translucent zone it is likely that the magnesium and carbonate rich mineral will preferentially dissolved
These ions will then diffuse away leaving mineral ions relatively depleted in these areas and therefore less soluble and some re-precipitation will occur.
How much mineral loss does the body of the lesion exhibit?
More than 20% mineral loss
May have up to 60-70% mineral loss before cavitation occurs
What does surface zone indicate?
Indicates partial de mineralisation equivalent to about 1-10% loss of mineral salts
What is the greater resistance of the surface layer due to?
- May be due to greater degree of mineralisation or greater concentration fo fluoride in the surface enamel
OR - It is the site where calcium and phosphate ions released by subsurface dissolution re precipitates (Re-mineralisation)
When is the surface zone disrupted?
Usually at the late stage when the lesion has penetrated some way into the dentine
Preserving which zone of a carious lesion is of great clinical value?
Preserving the integrity of the fragile surface zone enamel overlying the lesion has great clinical zone
Which type of enamel carries may be arrested?
Non caveatted enamel caries lesions may be arrested
Why might changes be seen clinically in enamel caries?
Due to changed at the surface layer of the lesion
A combination of abrasion of the porous enamel,el and slow re deposition of mineral in and onto the partly dissolved crystals
What is required to remineralise enamel subsurface caries?
Requires that calcium and phosphate ions are able to diffuse into the porous subsurface enamel usually through the relatively intact surface zone
Which layer in the tooth protects the underlying lesion body?
The surface layer of the lesion protects the underlying lesion body from demineralization but also from remineralisation
What is dentine a composite of?
Minerals and proteins
How does caries from in the dentine?
- The mineral is removed by the bacterial acid
- then by the ground substance by enzymes
- There is enzymatic removal of the collagen
What is released during caries breakdown of the dentine matrix
Dentinal matrix components
Some bioactive molecules migrate down the dentinal tubules and stimulate tertiary dentine formation and other pulpal reparative processes.
How big are the apatite crystals n intertubular dentine?
5nm x 35nm x 100nm
Describe intertubular dentine
Contains less calcium
Contains more carbonate hydroxyapatite
Therefore is more soluble
Which type of dentine is more soluble Intertubular or peritubular?
intertubular
How does peritubular dentine differ from intertubular dentine?
- It lacks a collagenous fibrous matrix. It consists of small crystals in an amorphous (non-fibrillar) matrix.
- is about 5–12% more mineralized than intertubular dentine.
- It is laid down as a physiological response to ageing
Why are the dentine and pulp considered as one entity?
Since their physiological processes during development; pathology and repair are intertwined and reliant upon one another.
What is the initial pulpal response to caries activated by ?
Activated by bacterial acids
What is the initial pulpal response to caries?
their cell wall components such as lipopolysaccharide (LPS) and soluble plaque metabolic products diffuse towards the pulp against the natural direction of pulp tissue fluid movement.
How does the dentine-pulp complex react to irritation?
By a combination of inflammation and the promotion of mineralisation
What do odontoblasts produce?
Tertiary dentine locally beneath the area of challenge
Why is the situation in dentine more complicated compared to enamel?
Due to the presence of potential defence mechanism
Which cells raise a problem in dentine due to their defensive properties ?
Odontoblasts
Where and why is tertiary dentine deposited?
On the hard tissue on the pupal surface
Due to an external stimulus
Give examples of external stimuli that may result in the production of tertiary dentine?
1 .Caries
- Attrition
- Cavity prep
- microleakage at restoration margins
- Trauma
What does tertiary dentine create a barrier to?
It provides a barrier to the progress of caries and toxins
What does reactionary dentine refer to?
Refers to dentine forming in response to milder irritation in which some damage has ben sustained and some odontoblasts die
Which cells die in the reactionary dentine?
Odontoblasts
Describe reactionary dentine
Has an irregular appearance
Has fewer tubes that circumpulpal dentine
What does reparative dentine relate to?
Relates to dentine coming in repose to stronger stimuli.
What happens reparative dentine?
Th original odontoblasts in the region have bee destroyedand calcified tissue has been formed by newly differentiated ‘odontoblast-like’ cells
Describe reparative dentine?
It is much more irregular than circumpulpal dentine
How dos pulp exposure healing occurs?
Happens vis reparative dentine forming a mineralised bridge
What is sclerotic dentine?
It is tissue formed whendentinal tubules fill in as a response to an external stimulus
Give examples of an external stimuli that may give rise to sclerotic dentine
Slowly advancing caries
Severe attrition
Wha colour does sclerotic dentine look?
Transparent
What dos the presence sclerotic dentine lead to?
The presence of this tissue under a carious lesion can reduce the permeability of the dentinal tubules which communicate with the pulp.
What follows caries lesion progression?
Bacterial invasion of the dentinal tubules
What happens as a bacterial stimuli moves towards the pulp?
The inflammatory response intensifies However, the dental pulp has an innate ability to heal if the challenge is removed and the tooth is suitably restored.
What may happen if a bacterial invasion is not prevented/restored in tooth?
Damage may progress further into irreversible inflammation of the pulp tissue, and eventually loss of vitality and subsequent bacterial colonization of the pulp by proteolytic gram negative facultative anaerobic bacteria.
What can lead to pulp death?
is bacterial infiltration of the dentine tubules and subsequent penetration into the pulp space
Wha does avoiding exposing the pulp lesion reduce the risk of?
bacterial infection and preserves the odontoblasts to facilitate reactionary (or reparative) dentinogenesis.
What is it important t do when treating a deep carious lesion?
it is important to isolate the tooth using rubber dam to prevent salivary bacterial contamination.
What all a successful restoration achieve
It will provide an adequate coronal seal to prevent microleakage and pulpal pathology.
Talk through the steps of how smooth surface caries spreads Ito the dentine
- Plaque layer forms on the enamel
- Acid dissolution of enamel prisms at prism boundaries and cores, loss of mineral & increase in porosity allows acid attack to advance through the enamel.
- Acid dissolution of enamel prisms at prism boundaries and cores, loss of mineral & increase in porosity allows acid attack to advance through the enamel.
- Dentinal tubules decrease in volume as sclerotic dentine is deposited, and reactionary dentine on the pulpal wall.
- Enamel surface cavitates, plaque bacteria invade the lesion and penetrate dentinal tubules (infected dentine)
What can bacterial infiltration of the dentine tubules and subsequent penetration into the pulp space lead to?
Pulp death
How do occlusal or pit caries spread into the enamel
1 The carious lesion often starts at both sides of the fissure wall
- The cone-shaped lesion penetrates nearly perpendicularly toward the ADJ.
- lesions precede cavitation and occur without apparent break in the enamel surface.
What MAY the spread of occlusal or pit caries lead to?
may produce a large ‘hidden’ dentine lesion below a smaller enamel lesion.
What are occult caries?
Large hidden dentin lesions below a smaller enamel lesions
Where are occult caries often found?
Below the fissure caries
Why do occult caries often form?
As the enamel has a high fluoride content and is relatively resistant to caries
What do adhesive restorative materials reduce the need for?
dental hard tissues removal for retention and resistance cavity form.
What do we restore teeth?
- Aid biofilm control on a restored tooth surface
- Protect the pulp-dentine complex and arrest lesion activity by sealing the coronal part with an adhesive dental material.
- Restores the function, form and aesthetics of the tooth
4,Maximise longevity of the tooth-restoration complex
What does dealing the coronal pat of the tooth with an adhesive dental material do?
can remove the symptoms of an acute, reversible pulpitis.
And protects the pulp dentine complex
How dow e reduces he viability of bacteria and action tissues in the tooth?
by having a good peripheral seal of the adhesive restorative material to sound dentine and/or enamel cavity walls (caries-free ADJ)
What do we sometimes do to minimise the risk of pulp exposure when resting a tooth?
We leave behind softer affected dentine in close proximity to the pulp
When I a lesion considered active?
When it has surface cavitation that cannot be managed by cleaning
What is is important to take into consideration when making decisions regarding operative intervention vs non-operative control measures.?
The patient’s caries risk assessment and response to preventive management
What does the Knowledge of the correlation between the histological states and subjective hardness levels allow us to do?
Allows us to make decisions in removing or maintaining carious dentine at different points within the lesion
What characteristics should peripheral dentine have?
should ideally be hard
similar tactile characteristics to sound dentine, such as a scratching noise when scraping the surface with a sharp hand excavator or dental probe.
Describe soft dentine
deforms with pressure and can be easily scooped up with a sharp hand excavator with little force being applied
Consistency can appear moist
Describe leathery dentine
does not deform when an instrument is pressed onto it but can still easily be lifted using an excavator without much force
Describe firm dentine
is physically resistant to hand excavation requiring some pressure to be exerted through an instrument to lift it.
Describe hard dentine
is sound dentine
a scratchy sound can be heard when a straight probe is taken across the
dentine.
Name the 3 layers that form when he caries process enters into dentine.
- Cross infected dentine
- Caries affected dentine
- Normal dentine layer
Where is cross infected dentine found?
It is the most coronal layer of the dentine
Describe cross infected dentine
There is gross disruption of the organic fibrillar matrix of the dentine so that it is not recognisable as possessing dentinal tubules, peritubular and intertubular dentine, and it is heavily infiltrated with bacterial colonies.
How can we What are the proteolytic bacteria doing in the ross infection stage?
They are using predominantly type 1 collagen protein as their food substrate.
Where is the caries affected dentine found?
Closer to the pulp
Describe caries affected dentine
there is a recognisable dentine structure, although it is affected by acid waves of demineralisation
This acid demineralisation means that the dentine is slightly demineralised therefore slightly softer in comparison to normal dentine
How can we estimate of the depth of a carious lesion ?
By using bitewing radiograph
Define deep caries
radiographic evidence of caries reaching the inner third or inner quarter of dentine but still with a well-defined zone of radiopaque dentine separating the infected demineralized dentine from the pulp
Define extremely deep caries
radiographic evidence of caries penetrating the entire thickness of the dentine without a radiopaque zone separating the lesion from the pulp.
caries extends the entire thickness of the dentine
What happens if a patient has Extremely deep caries
They are excluded from selective caries removal and a strategy based on avoiding pulp exposure.
Where do micro organisms penetrate in extremely deep carious lesions?
microorganism penetrating into the critical zone of tertiary dentine including the pulp.
