enamel and dental caries Flashcards
to outline the mechanism of underlying progression of enamel and dentine to examine the microstructure of both enamel and dentine and how it affects the carious process to draw comparison between two tissues to outline the physiocochemical process by which caries cause destruction to outline the pulp-dentine complex and how it provides a limited defence mechanism to examine the structure of a typical tooth surface enamel caries lesion and an occlusal pit lesion
what is the definition of dental caries
it is a localised, chemical dissolution of the tooth surface bought about by metabolic activity in a microbial deposit coving the tooth surface at any given time
what is the dental caries promoted and maintained by
by frequently dietary supply of fermentable carbs
where can dental caries attack
pits
fissures
grooves
especially during eruption and approximate surfaces
what is the percentage of mineral component of the tissue by weight
95%
where is the mineral content the highest
highest at the surface and decreases as it reaches the ADJ
what is the water content in volume in enamel
10%
what is the water content in volume in dentine
20%
what is the residual content by weight in enamel of water
3%
what is the residual content by weight in dentine of water
10%
what is the residual content by weight in enamel of protein
1%
what is the residual content by weight in dentine of protein
20%
what are the crystal dimensions in enamel (w x t)
68 x 26nm
what are the crystal dimensions in dentine ( w x t)
35 x 10 nm
what is the length of the crystal in enamel
7mm
what is the crystal length in dentine
indeterminate
what are the physical properties of human enamel
highly mineralised
withstands shearing forces
abrasion resistance is high
BUT brittle
what happens with the loss of the dentine support
unsupported enamel can fracture resulting in cavitation
what happens to hardness of enamel as we move towards the ADJ
DECREASES
what happens to the density of the enamel as we move towards the ADJ
DECREASES
what re the physical properties of dentine
flexible
poor abrasion resistance
why is dentine flexible
due to its organic matrix and tubular architecture
how is enamel considered
it is considered as microporous
what is the structure of the outermost enamel
it is rather porous
what developmental features can be seen in the enamel microstructure
irregular tissues and micropores
what is the diameter of irregular tissues and mirco pores
0.5-1.5micro metres
the irregular tissues and micropores can take part in
diffusion processes
what to the striae of retzius and perikymata act as
larger diffusion pathways
what is the crystals separated by in the enamel microstructure
tiny inter-crystalline spaces filled with water and organic materials
how can we clinically tell that enamel is microporous
the teeth start to dry out and become lighter in colour therefore shade check at the start
where does acid penetrate more readily
where there is greater porosity
what type of crystals do acid dissolution occur
irregular crystal outlines although demineralisation and destruction in the prism core is also seen
where does caries progress more rapidly
prism boundaries
cross striations
striae of retzius
how many cervical dentinal tubules are in the dentine cross section
10-25000 tubules per mm2
how many superficial tubules are found in the cross section of dentine
10-25000 tubules per mm2
what is the diameter of superficial tubules
0.5-1.2 microns in diameter
how many deep dentinal tubules are there in the cross section of dentine
30-52000 tubules per mm2
what is the diameters of the deep dentinal tubules
1-3 microns in diameter
what do the middle of the dentinal tubules contain
they contain odontoblasts and a small amount of extracellular dentinal fluid
how much % of the dentine volume do the superficial dentinal tubules occupy
approx 1 %
how much % of the deeper dentine volume do the superficial dentinal tubules occupy
30%
is the deeper dentine more porous and permeable to bacteria chemicals than superficial dentine
YES
what is the chemical equation that can be used to represent the reaction which takes place when enamel mineral dissolves
Ca10(PO4)6(OH)2 ⇌ 10Ca2+ + 6PO43– + 2OH–
what happens under suitable conditions
the biofilm can shift ecologically to become cariogenic so it produces a low pH
clinically what do the lesions look like as they first appear
opaque white spots- and the tooth needs to be dry with 3-in-1
why does the carious lesion appear white
because the sub surface enamel has become porous as a result of dissolution by acid
why does the carious lesion turn Brown
due to the fact the lesion might take up stain and may end up exposing dentine
what shape is the lesion shown on an x ray
a wedge shaped lesion
what is the pore volume of the surface zone
less than 5%
what is the pore volume of the body of lesion
5-25%
what is the pore volume of the dark zone
2-4%
what is the pore volume of the translucent zone
1%
what is the pore volume of the sound enamel
0.1%
what is the mineral per unit volume loss of the surface zone
1-10%
what is the mineral per unit volume loss of the body of the lesion
24%
what is the mineral per unit volume loss of the dark zone
6%
what is the section of enamel stained with to make the different zones visible
chloronaphthalene
what is the translucent zone like
deepest and least area affected
what is the body of the lesion like
most affected part and the greatest porosity
what lies underneath the plaque
the intact surface zone
what separates the body of the lesion and the translucent zone
the dark zone
what is found in the translucent zone
small number of uniform sized pores.
what do these small pores form in the translucent zone
produces the translucent optical effect which is seen in the lesion
why does the dark zone look dark
it diffracts light due to unequal pore sizes and also due to high protein content in this zone
why are there different size pores in the dark zone
due to the fact that some pores remineralise and some do not
how much mineral loss does the body of the lesion have
greater than 20% and may have 60-70% before cavitation occurs
what is now important in clinical settings
Preserving the integrity of the fragile surface zone enamel overlying the lesion
which minerals are needed to remineralise the tooth surface
CALCIUM AND PHOSPHORUS which diffuse into the porous zone
where are dentine HA crystals found
in an organic matrix of type 1 collagen
what is dentine composed of
mineral and protein
how many stage process is caries in dentine
three stages
what’s the first stage of caries in dentine
mineral is removed by the bacterial acid
what is the second stage of caries in dentine
then the ground substance by enzymes( including 8% component of the organic matrix; the non-collagenous proteins NCPs
what is the third stage of caries in dentine
enzymatic removal of collagen
where do bioactive molecules migrate
down the dentinal tubules and stimulate tertiary formation and the other purple reparative processes
what are the dimensions of the intertubular dentine
5nm x 35 nm x 100 nm ( length and width
what minerals do intertubular dentine
less calcium and more carbonate
how is peritubular dentine different than intertubular dentine
lacking a collagenous fibrous matrix
5-12% more mineralised than intertubular dentine
laid down as a physiological response to ageing
less soluble
how does the initial plural response to caries activated
by bacterial acids and their cell wall components such as lipopolysaccharides
what does the dental pulp complex react to
irritation
inflammation and the promotion of mineralisation
what do odontoblasts produce beneath the area of challenge
tertiary dentine
what are defence mechanisms produced by
odontoblasts or their replacement cells from progenitor cells within the pulp tissue
describe tertiary dentine
All hard tissue deposited on the pulpal surface in response to an external stimulus. It is restricted to the region beneath the irritation and provides a barrier to the progress of caries and toxins.
describe reactionary dentine
dentine forming in response to milder irritation in which, although some damage is sustained and some odontoblasts die
this dentine has an irregular appearance with fewer tubules than circumpulpal dentine
what does reparative dentine describe
dentine formed in response to stronger stimuli in which the odontoblasts in the region have destroyed and the calcified tissue has been formed by newly differentiated by odontoblast like cells.
much more irregular than circumpulpal dentine
if the pulp is exposed this can cause pulp exposed healing by reparative dentine forming a mineralised bridge
describe sclerotic dentine
when dentinal tubules fill in a response to external stimulus such as slow caries or beneath severe attrition
it appears translucent
what happens as the inflammatory response moves towards the pulp
intensifies
what happens if there is irreversible inflammation of the pulp
loss of vitality
bacterial colonisation of the pulp by proteolytic gram -ve facultative anaerobic bacteria
How do smooth surface caries spread into dentine
In five stages which are called
Plaque layer forms on the enamel due to the fact that sugar+ time + fermentable carbohydrates
Stage 2: acid dissolution occurs on enamel prisms and loss of the mineral and increases the porosity allows acid attack
Stage 3: spreads laterally along the EDJ
stage 4: dentinal tubules increase in volume as sclerotic dentine is deposited and reactionary dentine
Stage 5: enamel surface caries plaque bacteria invade the lesion and penetrate dentinal tubules
What is found in deep fissures and pits
Food debris and dental plaque
Where does the various lesion form
Starts at both sides of the fissure wall NOT at the base
The one shaped lesion moves perpendicularly toward the ADJ - precede cavitation and occur without apparent break
What are occult caries
The spread of the lesion which can reveal a large hidden dentine lesion below the smaller enamel lesion
Why do occult caries form
Due to the enamel having a high fluoride conc
Why do we restore mildly symptomatic or asymptomatic teeth
To restore the function and aesthetics
Maximise the longevity of the tooth restoration complex by removing soft dentine to place a durable restoration
Protect the pulp dentine complex and arrest the lesion activity
What is the ICCC
The international caries consensus collaboration
How can we clinically test for sound dentine
Scratching sound when scraping with dental probe
What are the clinical characteristics for soft dentine
Deforms with pressure and can be easily scooped with the excavator tool
It is described as caries inffected dentine and appears moist
What are the clinical characteristics of leathery dentine
Does not deform when pressure is applied to it with a excavators probe
Often described as caries affected dentine
What are the clinical characteristics of firm dentine
Physically resistant to hand excavation and requires a lot of pressure to lift it
What are the clinical characteristics of hard dentine(sound dentine)
A scratchy sound cAn be heard when a probe is taken across
What are the three layers of a deep various lesion. Into dentine
Infected dentine
Affected dentine
Sound dentine
What is the infected dentine consist of
Most coronal layer
There is gross disruption of the organic fibrillation matrix of the dentine so that it is not recognisable as possessing dentinal tubules, peritubular or inter tubular dentine
In the infected dentine stage what are the proteolytic bacteria using as food source
Collage type 1
What are the characteristics of the caries affected dentine
Recognisable dentine structure but starting to be damaged by the wave of demineralisation
Slightly softer than normal dentine
Is shown in the normal dentine structure
There will be evidence of the dentinal tubules reducing in size due to the fact that odontoblasts are laying down sclerotic dentine
As the caries gets deeper the layer of the pulp becomes more thin so there is a greater risk of direct pulpit exposure
How can the depth of the carious lesion be estimated
Using a bite wing radiograph
How can deep caries be defined
As radiography
If evidence of the carious lesion reaching the inner third or inner quarter of dentine but still with a well defined zone of radio opaque dentine separating the dentine from the pulp
How is extremely deep caries defined as
Radiographic evidence of caries penetrating the entire thickness of the dentine without a radio opaque zone of dentine separating it from the pulp
How do we manage non Selective removal to hard dentine
Complete caries removal
Only hard sound dentine remains so that demineralised dentine is completely removed
This is OVER TREATMENT
How do we manage selective removal to firm dentine
Leaves leathery dentine pulpally- resistance feeling in the hand excavator
What is the treatment for shallow or moderately deep cavitation lesions
Selective removal of firm dentine
Explain the treatment of selective removal to soft dentine
Recommended in deep cavitation lesions- extending into pulpal third or quarter of the dentine
Soft carious dentine left at the top of the pulp
What is stepwise excavation
This involves carious tissue removal in two stages
The first one some soft carious tissue is left over the pulp
Why do we selectively remove soft dentine
A number of biological reactions underpin this approach:
- The two defence reactions of tubular mineralization and tertiary dentine reduce the permeability of the dentine, walling off the pulp from the bacteria invading the dentine in the lesion.
- Once a restoration is placed that seals the cavity, any remaining bacteria either die or change to reflect a non-cariogenic flora and the lesion will arrest.
- Note that the residual demineralised (affected) dentine may remineralise to some extent but will appear as a radiolucency under the new restoration on future radiographs so inform the patient and document this in your clinic outcome.
- Teeth treated this way require carful monitoring for possible failures such as continuing caries activity and may not be advisable under full coverage restorations which would obscure radiographic and clinical evaluation.
What does a caries first look like
Soft discoloured and wet tissue
What does the active deep carious environment become
Darker harder and drier appearance
