Dentine, unlike enamel, has the ability to react to the progression of caries due to the presence of odontoblasts. Odontoblasts can respond to irritation by depositing minerals in the dentinal tubules

1. PROGRESSION OF DENTAL
CARIES IN DENTINE
Makerere University BDS3

2. BRIEF INTRODUCTION
Caries Progression
Caries progression is caused by an imbalance favouring demineralization. The magnitude of this
imbalance will in turn affect not only the progress, but it will also determine the rate at which the caries
progress. Naturally, a larger imbalance would imply a faster progress of caries while a smaller
imbalance will lead to a much slower caries progression
Imbalance
Caries progression is a continuum resulting from many cycles of mineralization and demineralization. It
begins at the atomic level on both the enamel and dentine. Enamel and dentine contain carbonate and
hydroxyapatite that are acid soluble and result in loss of mineral structure when exposed to acids
Pathological factors that favour the progression of caries are:
· Acid producing bacteria
· Frequent eating/drinking of fermentable carbohydrates
· Subnormal saliva flow and function

3. INTRODUCTION CONT’D
Before we can truly appreciate the changes that dentine undergo due to caries, it is necessary
for us to first understand the dentine structure of a healthy tooth. Then only can we truly
understand and comprehend both the histological and physiological changes that a dentine
undergoes from caries.
Dentine comes from the cells of the dental papilla (EMBRYONICALLY)
Dentine is one of the calcified connective tissue within the body. The inorganic part of it is
made out of calcium hydroxyapatite. The inorganic part is deposited on a type 1 collagen
framework radiating from the pulp to the enamel. The collagen forms fibrils that have many
cross-links to provide a stable framework that is resistant to degradation

4. DENTINE STRUCTURE
Dentine is made up of very small (smaller than those found in enamel) 10 nm calcium
hydroxyapatite crystals with a carbonate ion in 1 out of 5 the phosphates ions. The carbonate
ions makes the dentine more susceptible to be dissolved by acids.
Half of the dentine by volume is made up of hydroxyapatite and it is arranged to form tubules
that radiate outwards. Within the dentinal tubules lie an odontoblast process along with
dentinal fluid (consisting of albumins, transferrins, tenascins and proteoglycans)
Dentine, unlike enamel, has the ability to react to the progression of caries due to the
presence of odontoblasts. Odontoblasts can respond to irritation by depositing minerals in the
dentinal tubules.

5. PICTORIAL STRUCTURE &
COMPOSITION
Content
Percentage
present (%)
Inorganic
molecules
(calcium
hydroxyapatite)
- Calcium
- Phosphorus
- Magnesium
- Sodium
- Chloride
- Ash
- Carbon dioxide
(75)
27
13
1
0.5
0.1
30
3
Organic
molecules
- Collagen
- Citric acid
- Insoluble
protein
-
Mucopolysacchari
de
- Lipid
(19-21)
18
0.2
0.2
0.2

6. TYPES OF DENTINE
Primary dentine
It is the most prominent dentine in the tooth and lies between the pulp and
enamel. It is more mineralized than mantle dentine and has a more compact
array of type 1 collagen fibres
Secondary (regular)
dentine
Secondary dentine is formed after root completion and the tooth is
functional. It is responsible for the slow but incremental growth of the
dentine (0.8 micrometer a day) in the direction of the pulp
Tertiary dentine
(also known as
secondary irregular
dentine)
Tertiary dentine refers to irregular secondary dentine and reparative dentine
that is formed as a result of caries. It is produced at a rate of 2.9
micrometers per day (Wennberg et al, 1982)
Circumpulpal
dentine
The inner portion of dentine that is adjacent to the pulp and consists of
thinner fibrils
Mantle dentine
Mantle dentine is formed from the pre-existing ground substances that
made up the dental papilla. It is only about 5-30 micrometres thick and is a
result of the odontoblast process secreting calcium hydroxyapatite in the
early stages of tooth development. It is considered part of primary dentine
Intertubular dentine This refers to the dentine that is found between adjacent tubules
Peritubular dentine This refers to the dentine that is found within the tubules
Interglobular This refers to the dentine that is found between 2 globules (globules are the

7. CARIES PROGRESSION PROCESS
Caries progression is governed by the intensity of the bacterial acid challenge, the
structure of the dentine and the response of dentine. Dentine caries is mainly the result of
slow chronic caries.
The acids produced by carious bacteria dissolve away the inorganic calcium hydroxyapatite
crystals. As a result the crystals become smaller and areas that are porous form

8. CARIES PROGRESSION PROCESS
CONT’D
Histologically, the carious process may be in dentine before an enamel cavity forms. On an
occlusal surface the lesion widens as it approaches the enamel–dentine junction, guided by
prism direction. Eventually a cavity forms and now the hole is filled with plaque and the
biofilm sits directly on the exposed dentine. At this stage demineralization spreads laterally
along the enamel -dentine junction, undermining the enamel. Undermined enamel is brittle
and will in due course fracture if subjected to occlusal forces, producing a large cavity.

9. CARIES PROGRESSION PROCESS
CONT’D
The increased porous nature of the calcium hydroxyapatite lattice and the dentine tubules allow the
acids/bacteria to move further into the tooth and do extensive damage. The first group of bacteria is
called pioneer bacteria like lactobacilli.
Underlying dentine is necessary to support the enamel. If the underlying dentine is degraded, it will
cause the enamel to be easily broken.
Advanced dentinal changes include the decalcification of the walls and the joining of the tubules. The
tubules get filled with necrotic debris and adjacent tubules get distorted.
The exposed collagen fibres that form as a result of the acid attack convert reversibly to their precursor
form. Therefore, remineralisation can occur the collagen fibres can reorganize and form a structural
framework.
However extensive damage to the collagen fibres results in permanent loss of the collagen framework
and irreversible loss of the dentine structure. This is due to the fact that as the caries continues, the
exposed collagen becomes increasing less resistant to the bacterial acids

10. DENTINE CARIES
Dentine caries is differentiated into early and advanced carious lesions.
In the early dentinal carious lesions;
-Histological changes occur without enamel cavitation
- Plaque toxins diffuse through the enamel and cause secondary
(reparative) dentine formation
- Early accumulation of inflammatory cells
- If the cause of the caries is eliminated, partial regression of caries can occur at this
stage ie the caries is arrested.

11. CONT’D
In the advanced dentine carious lesions;
-Enamel cavitation has already occurred
-The bacterial destruction expands along the mantle dentine
-The lesion becomes more extensive, undermining the enamel
- Initially there will be a defence mechanism to impede the progress of caries. Later on the
bacteria may progress unhindered
-Demineralization of dentine, destruction of the organic matrix, and damage and death of
odontoblasts.
6 zones can be differentiated
1. Softening and liquefication with excavatable dentine
2. Demineralization with multiple areas of destruction
3. Advancing bacteria penetrate the dentine tubules
4. Hypermineralization
5. The transparent zone is clinically hard
6. Reparative secondary dentine forms on the pulpal walls

12. CONT’D

13. PULP-DENTINE DEFENCE
REACTIONS
Dentine is a vital tissue containing the cytoplasmic extensions of the odontoblasts and must be
considered together with the pulp since the two tissues are so intimately connected. The pulp–
dentine complex, like any other vital tissue in the body, is capable of defending itself. The state
of the tissue at any time will depend on the balance between the attacking forces and the
defence reactions. The important defence reactions are tubular sclerosis within the dentine,
reactionary dentine at the interface between dentine and pulp, and inflammation of the
pulp.
Tubular sclerosis occurs through precipitation of minerals in the tubular space and is protective
in that it reduces the permeability of the dentine, inhibiting the penetration of acids and
bacterial toxins. Reactionary dentine is formed by the odontoblasts beneath the carious
stimulus.

14. RESPONSE OF DENTINE TO CARIES
PROGRESSION
Formation of secondary
dentine
•Dentine is made up of microscopic channels called dentinal tubules
which radiate outwards to the cementum and enamel
•The carious process continues through dentinal tubules to reach
the depths of the tooth (The tubules actually allow caries to
progress at a much faster rate)
As a result, immunoglobulins are carried inside the fluid (within the
tubules) to fight the bacterial infection
Simultaneously, there is an increased mineralization in surrounding
tubules to restrict the passage of caries by constricting the affected
tubules
More calcium and phosphate are released to allow for more crystals
to form a barrier deeper within the dentinal tubules and slow the
advancement of caries

15. CONT’D
Formation of
tertiary dentine
•Tertiary dentine refers to the additional dentine that is
produced towards the direction of the pulp as a result of
caries. It is produced in response to protect the pulp
from the advancement of the caries
•If the odontoblasts still remain it is referred to as
reactionary dentine and if the odontoblasts are destroyed
it is referred as reparative dentine
In reparative dentine, growth factors initiate production
of reparative dentine by the cells of the pulp
Reparative dentine results in the production of irregular
tubules, which diminishes the progress of the caries
within the dentinal tubules

16. CONT’D
Odontoblasts
•Odontoblasts lie between the pulp and dentine and continually produce
dentine at the dentinal-pulpal junction.
•Presence of caries can trigger a biological defence mechanism that leads
to the formation of sclerotic and tertiary dentine.
•If the odontoblasts still remain it is referred to as reactionary dentine and
if the odontoblasts are destroyed it is referred as reparative dentine
Odontoblast-like
cells
•When the odontoblasts die, pulpal cells are tasked with
maintenace/repairing dentine.
•Reparative dentine is produced from the newly differentiated odontoblast-
like cells (that differentiated from pulpal cells)

17. NEW ADVANCES AND
REFERRANCES
Pickard_s_Manual_of_Operative_Dentistry