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Clinical skills 2 > Enamel and dentine caries > Flashcards

Enamel and dentine caries Flashcards

1
Q

What is the definition of dental caries?

A

a localised, chemical dissolution of the tooth surface

caused by the metabolic activity in a microbial deposit.

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2
Q

What promotes dental caries?

A

fermentable carbohydrates

which cause a ecologic imbalance within the dental biofilm

with acidogenic and aciduric bacterial plaque species dominating.

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3
Q

What is acidogenic?

A

organisms capable of producing acidic metabolites and reducing environmental pH

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4
Q

What is aciduric?

A

organisms capable of growth at acidic pH levels that are often toxic to other bacteria

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5
Q

What relatively protected sites do these lesions occur?

A

pits, grooves, fissures on occlusal surfaces

approximal surfaces

along the gingival margin

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6
Q

What is the mineral component by weight in enamel?

A

95%

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7
Q

What impurities does Ca10(PO4)6(OH)2 contain?

A

carbonate and magnesium

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8
Q

Where is the mineral content the highest and lowest?

A

highest at surface and decreases towards ADJ

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9
Q

What is the mineral content by weight of dentine?

A

70%

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10
Q

What is the water content by weight of enamel?

A

3%

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11
Q

What is the water content by weight of dentine?

A

10%

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12
Q

What is the protein content by weight of enamel?

A

1%

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13
Q

What is the protein content by weight of dentine?

A

20%

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14
Q

What are the physical properties of human enamel and dentine

A

withstands shearing and impact forces

abrasion resistance is high but is brittle

Hardness and density decrease towards the ADJ

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15
Q

What happens when there is a loss of dentine support?

A

unsupported enamel can fracture

resulting in cavitation

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16
Q

What properties of dentine allow it to support enamel?

A

flexible and compressible

due to organic matrix and tubular structure

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17
Q

What happens when dentine is exposed?

A
  • Has poor abrasion resistance
  • Poor resistance to crack propagation
  • Presents poor barrier to diffusion of bacterial by-products under caries lesions
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18
Q

Describe the outermost enamel

A

porous

has thin outer aprismatic layer (5-15 μm) covering prismatic bulk

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19
Q

What development defects does outer enamel have?

A

small irregular fissures and micropores

micro channels are approx 0.5-1.5 μm in diameter

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20
Q

What acts as a larger diffusion pathway on enamel surface?

A

Openings of Striae of Retzius at surface via perikymata grooves

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21
Q

Describe the relation between crystals, water and organic content on the enamel surface

A

Each crystal is separated by tiny inter-crystalline spaces filled with water and some organic material

these spaces act as a diffusion pathway ie micropores that open up onto enamel surface

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22
Q

How does caries affect enamel structure?

A

Acid penetrates more readily where there is greater porosity

will progress down paths provided by prism boundaries

Acid dissolution produces irregular prism outlines

central demineralisation and destruction is seen

Caries will progress more rapidly along these hypomineralised areas inc prism boundaries and incremental lines (cross striations and striae of retzius)

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23
Q

What does dentine contain a large number of?

A

small, parallel dentinal tubules in a mineralised collagen matrix

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24
Q

What do the inner part of dentine tubules contain?

A

long processes of odontoblasts as well as a small volume of extracellular (dentinal) fluid

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25
How do tubules change from ADJ to pulp?
they become wider and greater in number superficial dentinal tubules occupy approx. 1% of dentine volume compared to 30% of deeper dentine volume. deeper dentine is more porous and permeable to bacteria and chemicals than superficial
26
When is it best to visualise a white spot lesion?
when tooth is clean and dried under compressed air
27
When does the white spot lesion become brown?
as the porosity has increased, the lesion may stain and become a brown
28
What characteristic shape does lesion have when reached dentine?
wedge
29
When viewed under polarised light with imbibition media, what are the 4 zones of the cavitation lesion?
1. Translucent zone is the deepest and least affected 2. Body of lesion is the most affected part with the greatest porosity 3. Right underneath the plaque biofilm there is an intact surface zone 4. Finally, a dark zone separating the body of lesion from the translucent zone
30
Describe the translucent zone
<1% of minerals have been lost relatively large, uniformly sized pores translucent optical effect due to uniform pores
31
Why does the dark zone have its appearance?
as it diffracts/reflects the light due to unequal pore size possibly the relatively high protein content
32
Why is the pore size unequal in the dark zone?
smaller pores are caused by the reprecipitation of mineral occurs as the magnesium and carbonate rich minerals will have been dissolved from the translucent zone 5% mineral loss
33
Describe the mineral loss in the body of lesion
>20% mineral loss and may have up to 70% before cavitation occurs
34
What is the mineral loss in the surface zone?
1-10%
35
What is pore volume in the surface zone?
<5% of space
36
Why does the surface zone have greater resistance?
due to the greater degree of mineralisation or greater fluoride concentration in surface enamel may also be calcium and phosphate ions that are released and reprecipitate
37
How do active white spot lesions appear?
matt and has a loss of lustre
38
How do white spot lesions feel with probe?
rough
39
How do inactive white spot lesions appear?
less opaque, smaller smoother with probe
40
What is the 3 stage process of dentine caries?
1. Mineral is removed by bacterial acid 2. The ground substance is created by enzymes 3. There is an enzymatic removal of collagen meshwork which forms the scaffold around the dentinal tubules
41
Describe the content of intertubular dentine
apatite crystals are small, contain less calcium and more carbonate than in enamel so are more soluble
42
Describe the content of peritubular dentine
less soluble than intertubular - Lacks a collagenous fibrous matrix - consists of small crystals in an amorphous matrix - Is about 5-12% more mineralised than intertubular dentine
43
How is tertiary dentine formation stimulated?
dentine matrix components are released during caries breakdown bioactive molecules migrate down the dentinal tubules hence stimulating tertiary dentine formation and other pulpal regenerative processes
44
How does the pulp and dentine complex communicate?
odontoblast processes dentinal tubules
45
What is the initial pulpal response to caries activated by?
- Bacterial acids - Their cell wall components eg lipopolysaccharides - Soluble plaque metabolic products These diffuse towards the pulp against the natural direct of pulp tissue fluid movement
46
What is tertiary dentine?
hard tissue deposited on the pulpal surface in response to an external stimulus
47
What external stimulus causes tertiary dentine to be formed?
caries, attrition, cavity preparation, microleakage at restoration margins and trauma
48
Where is tertiary dentine restricted to?
region beneath the irritation and provides a barrier to progress of caries and toxins.
49
What are the 3 types of tertiary dentine?
- Reactionary dentine - Reparative dentine - Sclerotic dentine
50
When does reactionary dentine form?
milder irritation in which some damage has been sustained and odontoblasts die up-regulation of existing odontoblast activity occurs
51
Describe the appearance of reactionary dentine
irregular fewer tubules than circumpulpal dentine
52
When does reparative dentine form?
stronger stimuli in which the original odontoblasts die
53
What happens when reparative dentine forms?
calcified tissue has been formed by newly differentiated ‘odontoblast-like’ cells much more irregular than circumpulpal dentine
54
What happens if the pulp is exposed?
Pulp exposure healing can occur via reparative dentine forming a mineralised bridge
55
What is sclerotic dentine?
tissue formed when dentinal tubules fill in response to external stimulus - slow advancing caries - severe attrition
56
What effect does sclerotic dentine have?
reduce permeability of dentinal tubules which communicate with the pulp
57
What happens without preventative treatment and/or restorative intervention?
reversible inflammation of pulp tissue eventual loss of vitality bacterial colonisation of pulp
58
What type of bacteria can colonise the pulp?
proteolytic gram negative facultative anaerobic bacteria.
59
What happened when the pulp were mechanically exposed in gnotobiotic rats?
Pulp tissue remained vital New dentine was laid down at exposure site There was no pulpal infection or periapical lesions formed So, pulps die due to bacterial infection
60
What happens in stage 1 smooth surface caries?
plaque layer forms fermentable carbohydrates and no fluoride causes the release of organic acids
61
What happens in stage 2 smooth surface caries?
acid dissolution of enamel prisms at prism boundaries and cores loss of mineral increase in porosity
62
What happens in stage 3 smooth surface caries?
spreads along ADJ laterally
63
What happens in stage 4 smooth surface caries?
dentinal tubules decrease in volume due to sclerotic dentine reactionary dentine on pulpal wall
64
What happens in stage 5 smooth surface caries?
enamel surface cavitates plaque bacteria invade the lesion and penetrate dentinal tubules
65
Where does occlusal fissure caries start?
both sides of fissure wall rather than the base
66
What is the shape of occlusal caries?
cone-shaped lesions penetrate nearly perpendicular toward the ADJ
67
How can deep dentine caries be defined?
inner third or inner quarter of dentine but still with a well-defined zone of radiopaque dentine separating the infected demineralised dentine from pulp
68
How can extremely deep dentine caries be defined?
caries penetrating the entire thickness of dentine without a radiopaque zone separating the lesion from the pul
69
What treatment is extremely deep dentine caries excluded from?
selective caries removal and a strategy based on avoiding pulp exposure pulp exposure is unavoidable
70
What is non-selective caries removal?
Only sound dentine remains so that demineralised dentine is completely removed This is considered over-treatment
71
What is selective removal to firm dentine?
Leaves leathery dentine pulpally Cavity margins and peripheral dentine including ADJ are left hard after excavation treatment of choice in shallow or moderate cavitated dentine lesions
72
What is selective removal to soft dentine?
in deep cavitated lesions soft carious tissue is left over the pulp, whilst peripheral carious dentine is prepared to hard dentine
73
What happens in the first visit of stepwise excavation?
ADJ has been made hard by removing demineralised dentine with slow speed round bur Top layer of soft, wet dentine on cavity floor has been removed with excavator but some remains restored with glass ionomer or composite interim restoration
74
What happens in the second visit of stepwise excavation?
Interim restoration has been removed after a few months dentine is now dry, dark and harder urther excavation on pulpal aspect is carried out to firm dentine prior to definitive restoration.
75
Why is it argued if reentry for further excavation is necessary?
carries a risk of pulp exposure albeit smaller than at first visit
76
What materials be used under interim restorations?
Calcium hydroxide setting cement protected with lining of resin-modified glass ionomer suggested that a bioactive silicate cement on cavity floor
77

Clinical skills 2 (13 decks)

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