Dental caries development

The term dental caries (tooth decay or cavity) is used to describe the results (
the signs and symptoms) of a localized chemical dissolution of the tooth surface
caused by metabolic events taking place in the biofilm (dental plaque) covering the
affected area.
It is a multifactorial disease characterized by “demineralization of the
mineral components and dissolution of the organic matrix”. The destruction can
affect enamel, dentin and cementum.
Carious process is the result of an interaction of the following:

1- Host.

2- Plaque.

3- Diet.

4- Time.

The multifactorial complexity of dental caries can be explained simply by

the following figure:

Tooth
Time
substrate Flora

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Factors affecting caries process:
Host Factor: This involves susceptible tooth and saliva.
✓ The tooth: Several factors affecting tooth susceptibility are:

1- Morphology of teeth: Dental caries lesions may develop at any

tooth site in the oral cavity where a biofilm develops and remains for a
period of time. Such sites include pits, grooves and fissures in occlusal
surfaces, proximal surfaces cervical to the contact point/area and along the
gingival margin. These are the sites where lesion development is more
likely to occur because the biofilm is allowed to stagnate there for
prolonged time. Other areas in the oral cavity are relatively protected from
dental caries due to the mechanical influence from the tongue, the cheeks,
abrasive foods and tooth brushing but the insertion of foreign bodies to the
dentition (e.g. fillings with inappropriate margins, dentures, orthodontic
bands) may also result in dental caries in these protected sites.
Certain surfaces of a tooth are more prone to caries whereas other surfaces
rarely show caries. For example, in mandibular 1st molars the caries in descending
order is occlusal, buccal, mesial, distal and lingual. The differences in caries rates
of various surfaces on the same tooth are in part due to morphology.

2- Position of teeth: Anterior teeth are less affected by dental caries

compared to posterior teeth. The most susceptible permanent teeth are the
mandibular first molars, followed by the maxillary first molars and the
mandibular and maxillary second molars. The second premolars, maxillary
incisors and first premolars are the next in sequence. While the mandibular
incisors and canines are the least susceptible teeth to develop caries.

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 3- Composition of teeth: The tooth is composed mainly of
inorganic elements (96% in enamel and 70% in dentin) and the remaining
are organic materials and water. Composition of teeth is affected by
environmental factors (water, diet and nutrition).

Inorganic components involve:

➢ Major elements: calcium, phosphorous, hydroxyl group
{Ca10 (PO4)6(OH)2} hydroxyapatite crystals.
➢ Minor elements: Zinc, copper, strontium, magnesium,
fluoride, etc. These elements may incorporate the tooth during tooth
formation or incorporate the outer enamel surface later after
eruption. Furthermore, these elements may incorporate the enamel
crystal in substitutions with one of its major elements. Some of these
elements may increase the resistance to caries like fluoride, zinc and
others. While other elements such as magnesium may increase the
susceptibility of teeth to caries. It had been found that substitution of
hydroxyl group by fluoride ion results in formation of fluoroapitite
crystals {Ca10 (PO4)6F2} that increase tooth resistance to caries. The
accumulation of these elements will results in changes of the enamel
(decrease in density and permeability, an increase in fluoride
content) with age.

The organic constituents and water of both enamel and dentin may act as a
diffusion pathway for bacterial acids increasing the tooth destruction. In other way,
they permit the penetration of ions for physiological remineralization-
demineralization process. Such voids in enamel as well as proteins act as a caution
for intense biting pressure to prevent fracture.

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 ✓ Saliva: through its secretion and composition affects dental
caries development. It can affect the number of microorganisms through cleansing
action (oral clearance), While buffer system in saliva affects the integrity of teeth
as well as calcium and phosphate.

• Dental plaque: The cariogenic bacteria in plaque consist of mutans

streptococci, lactobacilli and other types. Bacteria ferment carbohydrate causing
release of acid lead to demineralization of tooth surface. Plaque accumulation may
show individual variations and affected by many factors such as age and practices
of oral hygiene.

• Diet: It may exert an effect on caries locally in the mouth by reacting

with the enamel surface and by serving as a substrate for cariogenic microorganisms.
Frequent consumption of sweets between meals lead to continuous drop of pH, thus
demineralization will occur.

Terminology of caries

Dental caries may be classified in a number of ways, according to their anatomical

sites.

- Primary caries is used to differentiate lesions on natural, intact tooth surfaces

from those that develop adjacent to a filling material.

- Recurrent or secondary caries is a lesion developing at a tooth surface

adjacent to a filling.

- Pits and fissures caries is a lesion affected pits and fissure sites of tooth
surfaces.

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 - Smooth surfaces caries is lesion that may start on smooth enamel as
buccal/labial or interproximal surfaces

- Arrested caries is a lesion that may have formed years previously and then
stopped further progression.

- Rampant caries is the name given to multiple active carious lesions

occurring in the same patient.

- Nursing bottle caries is one type of rampant caries in the primary dentition
of infants and young children, result from a sleep sucking bottle.

- Root caries is lesion on the exposed root cementum and dentin.

Dynamics Process of De-/Remineralization

Dental caries is a disease that is manifested as a dynamic process of

de/remineralization in the mouth (Enamel sieve concept).
The first stage of demineralization is occurring at the atomic level far before it
can be seen visually as gross demineralization. During this step, fermentable
carbohydrates are metabolized by bacteria in dental plaque to produce organic acids.
The acids diffuse into the dental hard tissue through the water among the crystals
and could reach a susceptible site on a crystal surface. Calcium and phosphate are
dissolved into the surrounding aqueous phase between the crystals. This is
considered as the first step in the progress of the dental caries process which can
eventually lead to cavitation.

The oral fluids (saliva, biofilm fluid) have calcium (Ca) and phosphate (P) in
supersaturated concentrations with respect to the mineral composition of enamel. At
physiological conditions (a neutral pH of 7), low ion concentrations are sufficient to
keep dental hard tissues in equilibrium. If the pH drops because of acid produced by

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the dental plaque, higher ion concentrations are needed to prevent dissolution of
dental hard tissue. Calcium (Ca) and phosphate (P) ions are continually deposited
on the enamel surface or redeposit in enamel areas where they were lost. At a pH of
5.5, under saturation begins, that is, the calcium and phosphate ion concentrations in
the plaque fluid are not sufficient to maintain the enamel in stable equilibrium; thus,
the enamel starts to dissolve.
Demineralization is a continual imbalance between pathological and protective
factors that results in the dissolution of apatite crystals and the net loss of calcium,
phosphate, and other ions from the tooth.

The term “remineralization” is used to describe mineral gain. Remineralization

is the body’s natural repair process for subsurface non-cavitated carious lesions. In
the process of remineralization, calcium and phosphate ions are supplied from a
source external to the tooth to promote ion deposition into crystal voids in
demineralized enamel to produce net mineral again.

De-/remineralization cycles continue in the mouth as long as there are factors

including cariogenic bacteria, fermentable carbohydrates, and saliva. The balance
between pathological factors and protective factors determines whether
demineralization or remineralization is proceeding at any one time.

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The development of a carious lesion occurs in three distinct stages:

- The earliest stage is the incipient lesion; macroscopically evidenced on the tooth surface by
the appearance of an area of opacity (the white spot lesion), which is accompanied by
histologic changes of the enamel at the microscopic level and is well established with a
number of recognizable zones.

- The second stage includes the progress of the demineralization front toward the
dentinoenamel junction and/or into the dentin; the affected dentin displays discoloration
from brown to dark brown or black, microscopic changes of dentin showed different zones.

- The final phase of caries development is the development of the overt or frank lesion, which
is characterized by actual cavitation.

References
• Textbook of clinical cariology (1996)
(book).
• Comprehensive preventive dentistry (2012)
(book).
• Primary preventive dentistry (2014)
(book).

• Dental caries, principles and management (2016) (book).