L2 Histopathology of Caries

Question 1

What is meant by the term residual caries?

Answer 1

Demineralised tissue that has been left behind before a filling is placed.

Question 2

How can caries be classified by site?

Answer 2

• Pits and fissures
• Smooth surface (interproximal or cervical)
• Root surface

Question 3

How can caries be classfied by rate of progression?

Answer 3

• Rapidly progressive (acute or rampant caries)
• Slowly progressive (chronic caries)
• Arrested caries (progression ceased and remineralisation may have occurred)

Question 4

What type of sections are used to study enamel?

Answer 4

Ground sections

Question 5

Describe the appearance of an early smooth surface caries lesion.

Answer 5

• Cone shaped lesion
• Base at enamel surface (white spot)
• Apex pointing towards the ADJ

Question 6

Describe the appearance of caries of pits and fissures.

Answer 6

• Ring develops around wall of fissure
• Extends to base of fissure
• Produces cone with base towards dentine
• Much more dentine involved than in a smooth surface lesion

Question 7

What are the 4 zones in caries of enamel?

Answer 7

1. Translucent zone
2. Dark zone
3. Body of lesion
4. Surface zone

Question 8

Describe the translucent zone of a caries lesion.

Answer 8

• Aka advancing edge
• More porous than normal enamel
• Large pore spaces, uniform in size
• 1% pore volume
• Reduced magnesium and carbonate ions
• Not present in all lesions

Question 9

Describe the dark zone of a caries lesion.

Answer 9

• 2-4% pore volume, more demineralisaiton
• Mixture of large and small pore spaces
• Present in all lesions, narrow in rapidly progressing lesions, wide in slowly advancing lesions

Question 10

Describe the body of a caries lesion.

Answer 10

• Occupies the bulk of the lesion
• 5-25% pore volume
• Variable pore size spaces
• Increased prominence of striae of Retzius
• Presence of some large apatite crystals, evidence of reminerlisation

Question 11

Describe the surface zone of a caries lesion.

Answer 11

• 40microns thick
• 1% pore volume
• Suggested to be more acid resistant
• Surface enamel is usually more highly mineralised, more fluoride, less magnesium, aprismatic enamel
• Likely that surface zone is due to reprecipitation of mineral in quiescent periods

Question 12

Describe step 1 of caries development in enamel.

Answer 12

• No clinical or radiological change

- Seen histologically as development of a subsurface translucent zone

Question 13

Describe step 2 of caries development in enamel.

Answer 13

• Subsurface translucent zone enlarges and the dark zone develops in the centre

Question 14

Describe step 3 of caries development in enamel.

Answer 14

• Lesion enlarges and more mineral lost
• Centre of dark zone becomes body of lesion
• Clinically recognisable as a white spot

Question 15

Describe step 4 of caries development in enamel.

Answer 15

• Body of lesion becomes stained by exogenous pigments (from food or bacteria), now visible as a brown spot

Question 16

Describe step 5 of caries development in enamel.

Answer 16

• Caries reaches the ADJ, spreads laterally and undermines the enamel

Question 17

Describe step 6 of caries development in enamel.

Answer 17

• Enamel surface breaks down, produces a cavity

Question 18

What type of dentine forms near the pulpal chamber in response to caries attack?

Answer 18

Reparative dentine

Question 19

Describe caries progression once it reaches dentine.

Answer 19

• Dentinal tubules allow diffusion of acid from enamel, and extension of bacteria deep into dentine

Question 20

What are the 4 zones in caries of dentine?

Answer 20

1. Zone of sclerosis
2. Zone of demineralisation
3. Zone of bacterial invasion
4. Zone of destruction

Question 21

Describe the zone of sclerosis.

Answer 21

• At the advancing edge of the lesion
• Area of higher mineral content beneath and at sides of carious lesion
• Appears translucent in ground section because tubules are filled with mineral
• Formed by accelerated peritubular dentine deposition and mineralisation of odontoblast processes
• It is an essential reaction of odontoblasts to irritation by acid
• Occludes dentinal tubules

Question 22

Describe the zone of demineralisation.

Answer 22

• Intact organic matrix but mineral has been removed

- Contains acid diffusing ahead of bacteria, which dissolves HAP crystals

Question 23

Describe the zone of bacterial invasion.

Answer 23

• Bacteria penetrate down tubules towards pulp
• Only occurs after the tooth surface has cavitated, allowing bacteria to access ADJ
• First wave of acidogenic bacteria is lactobacilli
• Second wave of bacteria is mixed acidogenic and proteolytic bacteria
• Walls of tubules are softened, and some distended by proteolysis and increasing mass of multiplying bacteria

Question 24

What are liquefaction foci?

Answer 24

• Focal areas of significant dentine matrix damage due to proteolytic digestion by bacteria
• Multiple liquefaction foci produces a beaded appearance in the zone of destruction

Question 25

Describe the zone of destruction.

Answer 25

• Organic matrix of dentine being destroyed
• Liquefaction foci enlarge and increase in number
• Clefts containing bacteria and necrotic tissue appear at right angles to tubules- called transverse clefts
• Bacteria not confined to tubules
• Little normal dentine structure remains

Question 26

Describe the production and structure of reactionary dentine.

Answer 26

• Secreted by pre-existing odontoblasts
• Often formed at pulp surface beneath caries
• Fewer, irregular and more tortuous tubules
• Prominent incremental layers
• Variations in degree of mineralisation
• Fewer tubules, may act to slow advance of caries
• Poor structure and areas of reduced mineralisation may speed progress of caries