MCQs on Oral Histology : Dental Pulp

# Which of the following structure is not found in a living pulp ?
A. Collagen fibers
B. Haversian fibers
C. Non myelinated nerve fibers
D. Reticulum

# The dental pulp contains nerve endings / receptors for:
A. Pain
B. Pressure
C. Proprioception
D. Temperature

# The dental pulp is derived from :
A. Dental papilla
B. Dental Sac
C. Odontoblasts
D. Stellate reticulum

# Pulp responds to all stimuli by pain because it has only:
A. Free nerve endings
B. Krause end bulbs
C. Pacinian corpuscle
D. Ruffini corpuscle

# All of the following are true about functions of dental pulp EXCEPT:
A. Formation of dentin
B. Nerve supply to dentin
C. Sends impulse to CNS
D. Nerve supply to enamel through fibers

# Odontoblasts are derived from :
A. Undifferentiated mesenchymal cells
B. Histocytes
C. Macrophages
D. Lymphocytes

# The primary function of the dental pulp is:
A. Nutritive
B. Production of dentin
C. Production of enamel
D. Vascular supply to the teeth

# The radicular pulp is continuous with tissues of the periapical area via the :
A. Pulp canal
B. Pulp chamber
C. Mental foramen
D. Apical foramen

# Weil's zone of pulp is :
A. Cell degenerated zone
B. Cell rich zone
C. Cell regenerated zone
D. Cell free zone

# The cells of the dental pulp which are responsible for the deposition of reparative dentin are:
A. Osteoblasts
B. Odontoblasts
C. Ameloblasts
D. Osteocytes

# Histologically, the dental pulp most closely resembles:
A. Nerve tissue
B. Vascular tissue
C. Granulation tissue
D. Loose connective tissue

# Pericytes are found:
A. In thymus
B. Around capillaries of pulp
C. In gall bladder
D. Along with Heparin on surface of mast cells

# The odontoblasts killed during cavity preparation are derived from :
A. Unaffected odontoblasts from the pulp
B. Undifferentiated cells
C. Histocytes
D. Osteoblasts

# Proprioceptors are seen in all EXCEPT:
A. Skeletal muscle
C. Pulp
D. None of the above

# Cells occurring in greatest number in pulp are :
A. Cementoblasts
B. Fibroblasts
C. Osteoblasts
D. Ameloblasts

# Pulp tissue contains all except:
A. Fibroblast
B. Capillary
C. Collagen
D. Cell rests of Malassez

# The cell free zone in pulp lies:
A. Above odontoblast
B. Below odontoblast
C. In radicular pulp
D. In pulp horn

# Aging process affects pulp tissue by:
A. Decreasing the size and shape of pulp tissue and cellular component
B. Increase cellular component at the expense of fibrous componenet
C. Increases vascularity of the pulp
D. Decreases the calcific component of the pulp

# The number of pulp organs in a person is :
A. 32
B. 20
C. 52
D. 62

# The total volume of all permanent pulp organ is:
A. 0.38 cc
B. 0.58 cc
C. 0.02 cc
D. 3.8 cc

# The size of apical foramen of maxillary teeth in adult is:
A. 0.4 mm
B. 0.3 mm
C. 0.2 mm
D. 0.7 mm

# The second most prominent cells in the pulp are:
A. Fibroblasts
B. Defense cells
C. Odontoblasts
D. Histocytes or resting wandering cell

# The fibroblasts associated with capillaries are:
A. Plasma cell
B. Histocytes
C. Lymphocytes
D. Pericytes

# Which of the following is true ?
A. Pulpal pressure is highest among body tissues
B. Majority of nerve that enter the pulp are non myelinated and are sympathetic in nature
C. Plexus of Rashkow or parietal layer of nerves is formed by network of peripheral axons located adjacent to cell rich zone
D. All of the above

# The average life time of primary pulp in oral cavity is:
A. 8.3 years
B. 5 years
C. 7 years
D. 2 and half years

# Regressive changes in pulp include :
A. Increased fibrotic component
B. Decreased cellular component
C. Calcification in blood vessels near apical foramen
D. All of the above

# Which of the following is not correct ?
A. Free denticles are entirely surrounded by pulp tissue (free of dentin)
B. Embedded denticles are entirely surrounded by dentin (embedded in dentin)
C. Attached denticles are partly fused with dentin
D. False denticles contain many dentinal tubules

# The development of pulp begins :
A. 6th week of IU
B. 8th week of IU
C. 10th week of IU
D. 18th week of IU

# Size of pulp chamber :
A. Increases with age
B. Decreases with age
C. Increases in some cases and decreases in some cases
D. None of the above

# Protein secreted by odontoblast :
A. Chitin
B. Keratin
C. Collagen
D. Elastin

# The primary response of the pulp to tissue destruction is :
A. Necrosis
B. Ulceration
C. Calcific degeneration
D. Inflammation

# Unmyelinated nerve fibers of pulp are:
A. Sensory in nature
B. Respond to hot and cold
C. Carry pain sensation
D. Associated with blood vessels and are sympathetic in nature

# Vitality of pulp depends upon:
A. Blood supply
B. Nerve supply
C. Lymphatic supply
D. All of the above

# Dystrophic calcification is seen most commonly in which of the following oral tissues?
A. Enamel
B. Pulp
C. Dentin
D. Periodontal ligament

# The Plexus of Rashkow is present in which of the following zones in the pulp ?
A. Cell free zone
B. Cell rich zone
C. Odontoblastic zone
D. Pulp core

# The diameter of the largest arterial vessels in the pulp range from:
A. 50-100 miocrometers
B. 101-150 micrometers
C. 151-200 micrometers
D. 201-250 micrometers

# Pain originate in dental pulp due to :
A. Free nerve ending in cell rich zone
B. Free nerve ending at sub odontoblastic layer
C. Krause bulb at the center of the pulp
D. Meissner's corpuscles at cell rich zone

# The pulp stem cells are :
A. Pluripotent in nature
B. Totipotent in nature
C. Multipotent in nature
D. None of the above

Dental MCQs - Multiple Choice Questions in Dentistry

*** AIIMS May 2011


*** Restorative Resins





*** Growth and Development


*** Epidemiology
*** Biostatistics


Different Types of Pathological Calcification

Q. Discuss the types of calcification.

The mineralisation of body tissues with calcium is a normal physiological process in tissues like bones and teeth, termed as physiological calcification. However, sometimes the visceral tissues and other soft tissues may also get calcified in many diseased states, which is called pathological calcification. In addition to the calcium salts, smaller amounts of iron, magnesium and other minerals may also be deposited.

Pathological calcification can be broadly classified into two types: Dystrophic Calcification and Metastatic Calcification.

Dystrophic calcification: When the deposition takes place in dead or dying tissues, then it is termed as dystrophic calcification. The serum calcium levels are normal and the calcium metabolism is not deranged. Though hypercalcemia is not a prerequisite for dystrophic calcification, hypercalcemia can exacerbate it. It is seen in areas of tissue necrosis of any type. It is almost always present in the atheromas of advanced atherosclerosis, associated with intimal injury in the aorta and large arteries and characterized by the accumulation of lipids. Sometimes dystrophic calcification may also indicate organ dysfunction, e.g. calcification can develop in damaged heart valves, resulting in severely compromised valve motion. Pathogenesis involves initiation and propagation where crystalline calcium phosphate is formed as the final product.

Metastatic Calcification: Due to hypercalcemia, metastatic calcification may occur in normal tissues.

 The causes of hypercalcemia may be:
- increased secretion of parathyroid hormone (due to either primary parathyroid tumors or production of parathyroid hormone–related protein by other malignant tumors)
- destruction of bone (e.g. Paget's disease, Myeloma, Leukemia, etc.)
- Vitamin D - related disorders and sarcoidosis
- renal failure, in which phosphate retention leads to secondary hyperparathyroidism

Metastatic calcification can occur widely throughout the body but principally affects the interstitial tissues of the vasculature, kidneys, lungs, and gastric mucosa.

Necrosis Vs Apoptosis

Q. Mention differences between necrosis and apoptosis.

Ans : Though both necrosis and apoptosis are events of cell death, they do differ in various ways. The differences can be observed under following parameters :

a) Cell Size
The cell is enlarged (swelling) in necrosis whereas the cell is reduced (shrinkage) in apoptosis.

b) Fate of Nucleus
In necrosis, nucleus undergoes series of changes like pyknosis ( irreversible condensation of chromatin in the nucleus of a cell ) , karyorrhexis (fragmentation of nucleus) and karyolysis (complete dissolution of the chromatin of a dying cell due to the enzymatic degradation). But, in Apoptosis, nucleus undergoes fragmentation into nucleosome size fragments

c) Plasma Membrane
The plasma membrane is disrupted and is full of leakages in case of necrosis but, it is intact in cells undergoing apoptosis. Only the orientation of lipids in plasma membrane is altered in apoptosis.

d) Cellular contents
Due to ruptured plasma membrane, cellular contents undergo digestion and may leak out of the cell in necrosis. But, the cellular contents are intact in case of apoptosis. However, they may be released in apoptotic bodies.

e) Adjacent inflammation
There is no any adjacent inflammation seen in apoptosis whereas adjacent inflammation can be seen in necrosis.

f) Physiologic or pathologic role
Apoptosis is often physiologic but necrosis is always pathologic.

Necrosis : Definition, Types and Examples

Q. Define Necrosis. Enlist its types with an example of each.

Ans: Necrosis is the type of cell death that is associated with loss of membrane integrity and leakage of cellular contents culminating in dissolution of cells, largely resulting from the degradative action of enzymes on lethally injured cells.

Types of Necrosis:
i) Coagulative Necrosis
- underlying tissue architecture is preserved,

- affected tissues take on a firm texture

- characteristic of infarcts in all of the solid organs except the brain

ii) Liquefactive Necrosis
- seen in focal bacterial or fungal (occasionally) infections

- the dead cells are digested completely, transforming the tissue into a liquid viscous mass

- seen often in hypoxic death of cells within CNS

iii) Caseous Necrosis (Caseous = Cheese like)
- Encountered most often in foci of tubercular infection

- friable yellow white appearance of the necrotic region

- area of caseous necrosis is often enclosed within a distinctive inflammatory border; this appearance is characteristic of a focus of inflammation known as a granuloma

iv) Fat Necrosis
- focal areas of fat destruction

- seen in Acute Pancreatitis

- grossly visible chalky white areas can be seen

v) Fibrinoid Necrosis
- special form of necrosis visible by light microscopy

- usually in immune reactions in which complexes of antigens and antibodies are deposited in the walls of arteries.

- a bright pink and amorphous appearance on H&E preparations called fibrinoid (fibrin-like) by pathologists

- seen in  immunologically mediated diseases (e.g. polyarteritis nodosa)

vi) Gangrenous Necrosis
- mostly the affected organ has lost its blood supply and has undergone coagulative necrosis involving multiple tissue layers

- When bacterial infection is superimposed, coagulative necrosis is modified by the liquefactive action of the bacteria and the attracted leukocytes (resulting in so-called wet gangrene)

- e.g. necrosis of a limb (mostly lower)

World Oral Health Day - 20th March 2017 - Live Mouth Smart

Poster for Oral Health Awareness : World Oral Health Day 2017 , Designed By: Raman Dhungel, BPKIHS,Dharan, Nepal.
FDI World Dental Federation (Federation Dentaire Internationale), has decided to celebrate 20th March 2017 as the world oral health day with a theme "Live mouth Smart".

The first World Oral Health Day was celebrated on 20th March 2013 by FDI World Dental Federation. Since then, every year , on 20th March it is celebrated across the globe by organising various campaigns and programs to raise Oral health awareness.

The themes for World Oral Health Day till date are:
2013: Healthy Teeth for Healthy Life
2014: Brush for a Healthy Mouth!
2015: Smile For Life!
2016: It all Starts Here. Healthy Mouth. Healthy Body
2017: Live Mouth Smart.

Good oral health leads to good overall health.
Share the message of World Oral Health Day and spread Oral Health Awareness.

MCQs on Oral Histology - Dentin Part 5

# During the formation of primary teeth:
A. Enamel forms more cervically than dentin
B. Enamel forms faster than dentin
C. Dentin forms faster than enamel
D. Processes of their cells remain in content with each other

# Matrix vesicles :
A. Are found in mantle dentin
B. Contain collagen
C. Produce alkaline phosphatase
D. Inhibit mineralization

# Transmission of stimulus across dentin is:
A. Direct activation of nerve endings
B. Correlated with the innervation density of the dentin
C. Stimulus induced fluid flow
D. There is no transmission of stimulus across dentin

# During hydrodynamic theory movement of fluids in dentinal tubules cause:
A. Movement of odontoblasts
B. Touch the nerves of the pulp to cause pain
C. Minimum effect on odontoblast
D. Stimulation of odontoblastic process

# Which of the areas of the tooth is most sensitive during cavity preparation :
A. Enamel (anterior teeth)
B. Enamel (posterior teeth)
C. Dentin
D. Dentinoenamel junction

# Matrix vesicles play important role in the mineralization of :
A. Dentin
B. Enamel
C. Pulp
D. Periodontal ligament

# False statement regarding interglobular dentin is :
A. The term interglobular dentin refers to organic matrix that remains unmineralized because the mineralising globules fail to coalesce
B. This occurs most often in the circumpulpal dentin just below the mantle dentin
C. Where the pattern of mineralization is likely to be appositional than globular
D. Large areas of interglobular dentin is a characteristic feature of childhood hypophosphatasia

<<View Part 4       PRACTICE MORE >>>

MCQs on Oral Histology - Dentin Part 4

# S-Shape of dentinal tubule is due to:
A. Incremental deposition
B. Peritubular dentin
C. Crowding of odontoblasts
D. Due to excess amount of organic component

# The formation of which of the following does not represent normal physiological process of dentin formation?
A. Primary and secondary dentin
B. Secondary dentin and Circumpulpal dentin
C. Tertiary dentin and Sclerotic dentin
D. All of the above

# All of the following is true about dentinal tubules except:
A. Inner pulpal layer contains more dentinal tubules than outer dentin layer
B. The diameter of dentin tubules ranges from 5 to 7 micrometer
C. The diameter of dentinal tubule is more at pulpal layer than outer layer
D. The bonding is more difficult is more difficult on the inner layer of dentin compared to outer surface

# Fluid flow , in and out of the dentinal tubules is proportional to the tubule diameter by:
A. Third power of the diameter
B. Sixth power of the diameter
C. Square of the diameter
D. Fourth power of the diameter

# The average diameter of coronal dentinal tubules near the pulp is :
A. 0.2-0.5 microns
B. 2-3 microns
C. 0.2-0.3 microns
D. 7 microns

# In adult teeth , the type of dentin present underlying dentino-enamel junction is:
A. Predentin
B. Mantle dentin
C. Interglobular dentin
D. Tertiary dentin

# All are the factors governing dentin permeability except:
A. Smear layer
B. Fluid Convention
C. Length of Dentinal tubules
D. Diffusion coefficient

# The most accepted theory for dentin sensitivity is :
A. Transduction theory
B. Direct neural stimulation
C. Hydrodynamic theory
D. Hydrostatic theory

# Compared to intertubular dentin , peritubular dentin is characterized by which of the following ?
A. Greater stainability
B. Lesser content of the inorganic salts
C. Greater content of the inorganic salts
D. Greater content of large collagen fibers

# One of the following statement is unique about circumpulpal dentin :
A. Collagen fibers are oriented perpendicular to DEJ
B. Von Korff fibers are present
C. Contain Phosphophoryn
D. Requires matrix vesicle for mineralisation

<<View Part 3      View Part 5>>>

MCQs on Oral Histology - Dentin Part 3

# Formula of hydroxyapatite crystal is :
A. Ca3(Po4)2.CaCO3
B. 3Ca3(Po4)2. Ca(OH)2
C. CaPo4. Ca(OH)2
D. None of the above

# The type of dentin that is formed prior to root completion is :
A. Inter tubular dentin
B. Peritubular dentin
C. Circumpulpal dentin
D. Secondary dentin

# Accentuated incremental lines in dentin due to disturbances in matrix and mineralisation process is:
A. Incremental lines of Retzius
B. Incremental lines of von Ebner
C. Contour lines of Owen
D. None of the above

# The pain transmission through dentin is :
A. Direct neural stimulation
B. Fluid or hydrodynamic theory
C. Transduction theory
D. All of the above

# Which of the following is correct ?
A. Reparative dentin is characterized by having fewer and more twisted tubules than normal dentin and may include odontoblasts
B. Dead tracts appear black in transmitted and white in reflected light
C. Sclerotic/transparent dentin appears transparent or light in transmitted light
D. All of the above

# First formed dental tissue :
A. Enamel
B. Dentin
C. Cementum
D. Bone

# Dentinal tubules are calcified in:
A. Sclerotic dentin
B. Secondary dentin
C. Primary dentin
D. Interglobular dentin

# Dentin formed throughout the life is:
A. Sclerotic dentin
B. Secondary dentin
C. Repartive dentin
D. All of the above

# Regarding teeth which statement is wrong ?
A. Enamel is harder than dentin
B. Enamel has no cells
C. Ameloblast secrete enamel and dentin
D. Odontoblast produce dentin

<<View part 2       View part 4>>>

MCQs on Oral Histology - Dentin Part 2

# The dentin receptors are unique because:
A. They elicit pain to hot and cold
B. They elicit pain to touch and pressure
C. They elicit pain to chemicals
D. Elicit only pain as a response

# The main bulk of dentin is formed by :
A. Peritubular dentin
B. Mantle dentin
C. Inter tubular dentin
D. Predentin

# The zone of dentin most recently formed and uncalcified is known as:
A. Mantle dentin
B. Circumpulpal dentin
C. Predentin
D. Secondary dentin

# Inter globular dentin results due to:
A. Failure of coalescence of calcospherites
B. Fracture of the dentin
C. Artifact in light microscopy
D. Disturbance in dentinal tubules

# Dentinogenesis by odontoblasts first behins at :
A. Pulpal end
B. Cusp tip
C. Tooth bud stage
D. Cervical area

# Sclerotic dentin has following features :
A. Caries susceptible
B. Insensitive
C. Hypersensitive
D. Resistant to caries

# The microhardness of dentin is about:
A. 1/2 that of enmel
B. 1/7 that of enamel
C. 1/4 that of enamel
D. 1/5 that of enamel

# Shape of the crown and the size of the roots is determined by:
A. Pulp
B. Dentin
C. Enamel
D. Cementum

# Physically and chemically, the dentin is closely related to:
A. Bone
B. Acellular cementum
C. Enamel
D. None of the above

# Organic portion can be separated from the mineral by :
A. Incineration / Organic chelation
B. Decalcification
C. Devitrification
D. Combustion

<<View Part 1      View part 3 >>>

MCQs on Oral Histology - Dentin

# Dentinal tubules are :
A. Concave
B. Straight
C. S-Shaped
D. None of the above

# The cells that form secondary dentin are:
A. Cementoblasts
B. Fibroblasts
C. Odontoblasts
D. Osteoblasts

# Dead tracts in ground section appears as:
A. Dentinal tubules
B. Coarse fibril bundles arranged at right angle to the dentinal surface
C. Black in transmitted light and white in reflected light
D. White in transmitted light and dark in reflected light

MCQs on Dental Caries Part 4

# Chemico-parasitic theory of dental caries is proposed by :
A. G.V. Black
B. Miller
C. Gottlieb
D. Schwartz

# Which of the following organisms is found in deep carious lesions rather than in incipient lesions ?
A. Streptococci
B. Lactobacilli
C. Veillonella
D. Bacteroides

# Pioneer bacteria in dental caries are in:
A. Enamel
B. Dentin
C. Pulp
D. Cementum

# The most pronounced effect on the oral microflora of a reduction in rate of salivary flow is a :
A. Significant increase in number of oral bacteria
B. Shift towards more acidogenic microflora
C. Significant decrease in number of oral bacteria
D. shift towards more aerobic microflora

# Ammonia causes:
A. increase in plaque formation
B. increase in calculus formation
C. decrease in plaque formation
D. precipitation of salivary proteins

# Cavity formation in a tooth, due to dental caries is due to:
A. Destructive potential of Streptococcus mutans
B. Destructive potential of Lactobacillus acidophilus
C. Lateral spread of caries along DEJ and weakening of the outer covering enamel
D. Mastectomy force and unrelated to the extent of carious process

# Animals maintained in a germ free environment did not develop caries fed on a high carbohydrate diet is given by:
A. Gottlieb
B. Miller
C. Snyder
D. Orland and Fizgerald

# Which of the following factors in the Stephan's curve is related to the caries incidence and sugar intake ?
A. Physical form of sugar
B. Frequency of sugar intake
C. pH of plaque
D. Quantity of sugar intake

# Initiation of caries by Streptococcus mutans is by the production of the :
A. Dextranase and soluble dextran
B. Insoluble dextran and glycosyl transferase
C. Soluble dextran and glycosyl transferase
D. None of the above

# The attachment of Actinomyces species to the tooth surface is facilitated by:
A. Fimbriae
B. Cilia
C. Flagella
D. Pseudopodia

# Caries associated with pre-eruptive enamel hypoplasia:
A. Secondary caries
B. Chronic caries
C. Occult caries
D. Incipient caries

# Bacteria free zone of dentinal caries is :
A. Zone of decomposed dentin
B. Zone of bacterial invasion
C. Zone of decalcification
D. Zone of dentinal sclerosis

# The legend of worms, endogenous theories, chemical theories and parasitic theory are early theories explaining:
A. Dental caries
B. Gingivitis
C. Periodontitis
D. Osteomylitis



MCQs on Dental caries Part 3

# Streptococcus mutans is considered to be a principal etiologic agent of caries because it produces acid and it:
A. forms a gelatinous matrix
B. metabolizes substrate from saliva
C. derives energy from enamel constituents
D. lives symbiotically with lactobacillus

# Miller put forth the acidogenic theory of dental caries in the year:
A. 1890
B. 1920
C. 1924
D. 1980

# For a bacterium to be seriously considered in the etiology of dental caries, it must :
A. exist regularly in the dental plaque
B. produce extracellular amylopectins
C. be lethal for gnotobiotic animals
D. produce intracellular dextrans

# Initiation of dental caries depends upon:
A. formation of large amount of acid
B. availability of carbohydrate food
C. viscosity of saliva
D. Localisation of acid over tooth surface

# Caries, all are true except:
A. Lactobacillus is the main causative organism in plaque
B. Smooth surface caries occur due to streptococcus mutans
C. Pit and fisssure caries can be prevented by using pit and fissure sealants
D. Fluorides help in reducing caries incidence

# The enzyme glucosyl transferase secreted by Streptococcus mutans synthesizes glucans from:
A. Glucose
B. Fructose
C. Sucrose
D. Lactose

# The lateral spread of dental caries is facilitated mostly by the :
A. Enamel spindles
B. Dentinoenamel junction
C. Enamel lamellae
D. Striae of Retzius

# The probable reasons for a high incidence of dental caries in the teenage population relates most directly to:
A. Rapid growth
B. Frequency of sucrose intake
C. Negligence in visiting the dentist
D. Carelessness in oral hygiene habits

# In a caries free individual, the saliva has:
A. low buffering capacity for acids
B. medium buiffering capacity for acids
C. High buffering capacity for acids
D. Buffering capacity of saliva is independent of caries incidence

# Early invading bacteria in carious lesions are called:
A. Microcosm
B. Pioneer bacteria
C. Advancing bacteria
D. Anaerobic bacteria



MCQs on Dental caries Part 2

# Streptococcus mutans is involved in dental caries initiation. Other bacteria also involved is:
A. S. sarcinus
B. S. macae
C. S. sanguis
D.S. salivarius

# The dietary carbohydrate most likely involved in etiology of dental caries is :
A. Glucose
B. Sucrose
C. Dextran
D. Polysaccharide

# Bacteria responsible for initiation of caries is :
A. Actinomyces
B. Streptococcus mutans
C. Lactobacillus
D. Streptococcus viridans

# What is the pH at which initiation of caries begins?
A. 4.3-4.5
B. 5.2-5.5
C. 4.9-5.1
D. 3.5-4.5

# Oral foci of Miller's are seen in :
A. Dental caries
B. Lichen planus
C. Herpes simplex
D. Syphilis

# In the earliest stages of carious lesion, there is loss of :
A. Enamel cuticle
B. Interprismatic substance
C. Organic matrix
D. Enamel lamellae

# Smooth surface caries is characterized by spread of caries in enamel and dentin as cones. These alignment in enamel and dentin is:
A. Base to base
B. Apex to base
C. Apex to apex
D. None of the above

# Least cariogenic among these:
A. Raw starch
B. Cooked starch
C. Sucrose
D. Fructose

# Which tooth in the permanent dentition is the most susceptible to dental caries ?
A. Maxillary first premolar
B. Maxillary second molar
C. Mandibular first molar
D. Mandibular second molar

# Turbid dentin in carious tooth is all EXCEPT:
A. Zone of bacterial invasion
B. Zone which cannot be remineralised
C. Zone in which collagen is irreversibly denatured
D. Zone that need not be removed before restoration