Enamel And Dentine Caries

Question 1

Why is it important that we understand the caries process?

Answer 1

So we can request appropriate radiographs, implement effective preventative measures and make informed decisions in selecting minimally invasive treatment options.

Question 2

Definition of dental caries

Answer 2

Localised chemical dissolution of tooth surface brought on by metabolic activity in a dental biofilm, promoted and supplied by a frequent supply of fermentable carbohydrates.

Question 3

Physical properties of enamel

Answer 3

Highly mineralised
Withstands shearing and impact forces
High abrasion resistance
Brittle
Hardness and density decrease from the surface towards ADJ.

Question 4

Physical properties of dentine

Answer 4

Flexible because of proteins
Compressible to support enamel due to tubules
Poor abrasion resistance and crack propagation

Question 5

What is the microstructure of enamel?

Answer 5

Tightly packed crystals
Openings of striae of retzius act as larger diffusion pathways
Packing of crystals is slightly looser at the periphery
Each crystal separated by intercrystalline spaces filled with water, make up diffusion pathways
In longitudinal sections prisms are approximately perpendicular to the ADJ.

Question 6

What is the microstructure of caries?

Answer 6

Acid will penetrate more readily where there is greater porosity, down paths provided by prism boundaries
Caries will progress more readily along hypomineralised areas including prism boundaries, cross striations and striae of retzius.

Question 7

What are the different types of dentinal tubules?

Answer 7

Superficial
Deep dentinal tubules
Cervical

Question 8

Why do white lesions appear white?

Answer 8

Sub surface enamel has become porous as a result of mineral being dissolved.

Question 9

What are the different zones of lesion?

Answer 9

Translucent zone - deepest and least affected
Body of lesion - most affected with greatest porosity
Underneath biofilm - intact surface zone
Dark zone separates body of lesion from the translucent zone

Question 10

What are pore sizes like in different zones?

Answer 10

Translucent - small uniformly sized pores
Dark - unequal and high protein content, reprecipitation of carbonate and magnesium
Body of lesion has >20% mineral loss may have up to 70 before cavitation occurs

Question 11

How does the surface layer of the lesion act as a barrier to remineralisation?

Answer 11

Remineralisation requires calcium and phosphate ions to diffuse into the porous subsurface enamel through the surface zone. With slow diffusion it is difficult to maintain supersaturation so remineralisation is not obtained to a significant degree.

Question 12

What is the caries process in dentine?

Answer 12

Mineral removed by bacterial acid
Ground substance by enzymes
Enzymatic removal of collagen

Question 13

What is the difference between intertubular and peritubular dentine?

Answer 13

Intertubular - needle like crystals, contain less calcium and more carbonate so is more soluble
Peritublar - less soluble, lacks a collagenous matrix, small crystals in a non fibrillar matrix and laid down in ageing.

Question 14

What is the pulps response to caries?

Answer 14

Activated by acids, lipopolysaccharides and soluble plaque metabolic products diffusing to the pulp. Reacts by a combination of inflammation and promotion of mineralisation.
Odontoblasts produce tertiary dentine under the area of challenge.

Question 15

What is reactionary dentine?

Answer 15

Forms in response to milder irritation

Regulation of existing odontoblasts forms dentine with an irregular appearance

Question 16

What is reparative dentine?

Answer 16

Formed in response to stronger stimuli in which odontoblasts have been destroyed and calcified tissue formed by odontoblast like cells which is more irregular than circumpulpal dentine.
Pulp exposure healing can occur via this.

Question 17

What is sclerotic dentine?

Answer 17

Formed when dentinal tubules fill in response to an external stimulus, reduces permeability of dentinal tubules which communicate with the pulp.

Question 18

How does loss of pulp vitality occur?

Answer 18

Bacterial infiltration of dentinal tubules causes inflammation of pulp tissue, penetration into pulp space.

Question 19

When placing a restoration what steps do we take to avoid bacterial infection?

Answer 19

Place a rubber dam to isolate the tooth, protect against salivary contamination
Restorations provide an adequate coronal seal to prevent micro leakage.

Question 20

Steps in caries spreading to dentine

Answer 20

1) plaque + time + fermentable carbohydrates no fluoride causes release of acids
2) dissolution occurs at prism boundaries and cores, loss of mineral allows acid attack to advance through enamel
3) spreads along the adj laterally
4) dentinal tubules decrease in volume as sclerotic dentine is deposited and reactionary on pulpal wall
5) enamel surface cavitates, bacteria invade the lesion and penetrate tubules (infected dentine)

Question 21

What are occult caries?

Answer 21

Spread of enamel lesions producing larger hidden lesions, frequent in pits and fissures.

Question 22

Why do we restore teeth?

Answer 22

Aid biofilm control
Protect dentine pulp complex and arrest lesion activity by sealing coronal part with adhesive
Restore form and function of tooth
Maximise longevity of restoration by removing enough soft dentine to place a restoration but enough left for support
Leaving enough soft dentine minimises risk of pulp exposure

Question 23

What is soft dentine

Answer 23

Necrotic and contaminated zone
Deforms with pressure easily scooped up with excavator
Caries infected dentine

Question 24

What is leathery dentine

Answer 24

Does not deform when an instrument is pressed but can be easily lifted with excavator
Caries affected dentine
Demineralised zone

Question 25

What is firm and hard dentine?

Answer 25

Firm is physically resistant to hand excavation requiring pressure
Hard is sound dentine a scratchy sound should be heard when taken across.

Question 26

What are the different layers of dentine that have caries?

Answer 26

1) infected - coronal layer of dentine that has been exposed to oral environment through cavity allowing bacteria in. Disruption of organic matrix so is not seen to have dentinal tubules, peritubular and intertubular dentine, heavily infiltrated with bacteria. Bacteria use type 1 collagen as their food substrate, deeper into the infected layer recognised structure of dentine is more visible.
2) affected - much closer to pulp, recognisable structure, dentine is slightly demineralised, softer than normal dentine, not heavily infiltrated with bacteria.
3) Normal dentine - sclerotic dentine and tubules reduced in size.

Question 27

What is the difference between deep caries an extremely deep caries?

Answer 27

Deep - radio graphic evidence reaching the inner third or quarter of dentine but still a well defined zone of radiopaque dentine separating infected dentine from the pulp.
Extremely - radiographic evidence penetrating the entire thickness of the dentine without a radiopaque zone separating the lesion from the pulp.

Question 28

What is non selective removal to hard dentine?

Answer 28

Only hard sound dentine remains so demineralised dentine is completely removed

Question 29

Selective removal to firm dentine definition

Answer 29

Leaves leathery dentine pulpally, cavity margins and peripheral dentine including adj are scratchy after excavation is complete.
Treatment of choice in shallow or moderately deep cavitated dentine (radiographs less than pulpal 1/3 or 1/4 of dentine)

Question 30

What is selective removal to soft dentine?

Answer 30

Deep cavitated lesions

Soft carious tissue left over the pulp whilst peripheral enamel and dentine are prepared to hard dentine.

Question 31

What is stepwise excavation?

Answer 31

Involves carious removal in two stages or visits
First some soft carious tissue is left over the pulp and peripheral dentine prepared to hard.
A provisional restoration of 6-12 months is placed and lesion is re entered and further excavation on pulpal aspect is carried out to firm dentine prior to restoration.