Dental Disease

One significant problem in dentistry is the progression of
carious lesions in the teeth. Carious lesions or dental
caries is defined as a localized, progressively destructive
disease of the teeth that starts at the external surface
with an apparent dissolution of the inorganic components by
organic acid.
 
The tendency to the development of dental caries depends on
specific surfaces of teeth and several other factors which
include: type of tooth, location and length of exposure to
the oral environment, oral hygiene practices, nutritional
status, previous fluoride exposure , and the oral status of
the patient.
 
Among the primary teeth, there are many more occlusal
cavities than any other type of lesion. Evidence shows that
caries is a more common occurrence on two surfaces of a
tooth rather than just one surface.
 
Occlusal caries is the most common type of caries on the
permanent teeth. Studies show that 43-75% of all caries
lesions are on the occlusal surfaces of posterior teeth. In
the entire dentition, there are more mesial cavities than
distal cavities and there are more buccal cavities than
lingual cavities. 

The cuspal, incisal, buccal, lingual, and palatal surfaces
are usually resistant to dental caries. This resistance is
related to external factors such as food retention and the
formation of dental plaque. The most susceptible areas for
dental caries are the fissures and proximal surfaces of the
teeth. 

The occlusal surface will usually start to decay soon after
tooth eruption. About 20% of the erupted teeth do not
develop decay. The reason for this is due to the anatomical
structure or chemical composition of the tooth. These
factors could include the shape and condition of the
gingival margin and papilla, the nearness of another tooth,
the width of the interdental space, and the degree of tooth
mobility. Fluoride also plays an important role in the
prevention of dental caries.
 
Dental caries is composed of three basic types of diseases:
Streptococcus mutans, Streptococcus sanquis, and
Lactobacillus species. Each has its own anatomical site on
the tooth and particular disease-causing microorganisms.
All three cause pit and fissure caries which are bacteria
that are forced into the bony structures of the tooth.
Streptococcus mutans is an organism that bonds to the tooth
surface because of its ability to produce dextrans which
will allow bacteria to bond to tooth surfaces. This
microorganism plays an important role in the initiation of
dental caries. The leading role of Streptococcus mutans is
determined by a composition of biochemical properties which
include the capability of growing and producing acids in an
acidic environment that initially causes dental caries in
enamel.
 
Enamel is defined as the hard substance covering the
exposed portion of the tooth. In its mature form, it is
composed of an inorganic portion made up of 90%
hydroxyapatite and 6-8% calcium carbonate, calcium
fluoride, and magnesium carbonate, and the remainder
comprising an organic matrix of protein and glycoprotein.
 
The basic unit of structure of enamel is called the enamel
rod. This rod is a column of enamel that runs all the way
from the dentinoenamel junction to the surface of the
tooth. The rod is generally perpendicular to the
dentinoenamel junction and to the surface. The ameloblast
is round or hexagonal in cross section and the enamel rods,
which fit tightly together, are keyhole shaped. The enamel
is composed of two parts: the rod and rod sheath. The rod
is made up of hydroxyapatite crystals. The rod sheath
outlines the rod and contains most of the organic fibrous
substance. 

Caries lesions in enamel can partially remineralize.
Differences in the fluoride and carbonate concentrations of
the remineralizing solutions are reflected in the
composition of the enamel. Fluoride present during the
remineralization period inhibits the progression of
demineralization. The influence of fluoride is the result
of the fact that the mineral deposited contained
fluorapatite, which is less soluble than hydroxyapatite.
Fluorapatite may be present as a result of remineralization
or as a result of transformation reactions occurring during
the secondary demineralization. The conclusion was that the
resistance to dental decay imparted by fluorine was the
result of an increase of fluorine in the tooth structure,
particularly the enamel, which added to the ability of the
tooth substance to resist decalcification by acids.
 
Caries of the enamel can be divided into progressive or
acute and arrested or chronic types of disease. Acute
enamel caries is characterized clinically by being white or
chalky in appearance. Arrested enamel caries is yellow to
dark brown in color.
 
Enamel caries depends upon its location. On smooth surfaces
the carious lesion tends to develop in a conical form with
the apex pointing towards the dentin. In fissural caries,
however, the apex points towards the enamel surface.
 
The first sign of dental caries is the presence of white
spots. The white spots are demineralized sub-surface areas
with a mostly intact surfaces. This is known as
hypocalcified enamel and is the result of an insuffient
growth of the enamel crystals or an insufficient number of
crystals originally deposited in the matrix. "Permanent
teeth are more susceptible to hypomineralization or "white
spot" defect."1 Thus a less dense enamel is produced, which
may make the enamel decay more rapidly.
 
Cracks in the enamel caused by developmental problems or
trauma are called enamel lamellae. The most common types
are those caused by trauma. Clinically they appear as
hairlike cracks in the enamel. These may extend all the was
through the enamel and eventually into the dentin. "The
differences between permanent and primary teeth extend to
the area of dental trauma."2 A developmental defect is a
less common type of lamella which results in preventing the
production of enamel and leaving a space between other
enamel rods. These provide an entrance through the enamel
for bacteria to enter which makes the tooth more
susceptible to dental caries or the early development of a
caries lesion. 

The early lesion of dental caries in permanent enamel is
divided into four zones: the translucent zone, the dark
zone, the body of the lesion zone, and the surface zone.
 
The translucent zone is the first sign of normal enamel
seen in enamel caries . It lies at the beginning part of
the lesion. The zone appears to be translucent because the
spaces, or pores, created in the tissue in this first stage
of caries are located at prism boundaries and other
junctional sites of enamel.
 
The dark zone is superficial to the translucent zone. It
constitutes a "molecular sieve" in the tissue and the
exclusion of large molecules from the micropores, which
remain filled with air or vapor.
 
The body of the lesion zone known as the third zone is the
bulk of the carious area. It extends superficially from the
dark zone but does not include "intact" enamel surface.
 
The surface zone of enamel caries contains the greatest
degree of demineralization which occurs at the sub-surface
level. The early lesion is in a sub-surface position and
remains covered by a surface layer, which is most affected
by a caries attack.
 
The structural resistance of teeth to caries lies mainly in
the enamel surface since this disease begins on the surface
of the enamel and extends to the deeper layers of the
tissue and dentin. Dentin is defined as the hard calcified
tissue forming the inside of the tooth, underlying the
cementum and enamel and surrounding the pulpal tissue.
About 20% of the mass is organic matrix, mostly collagen,
with some elastin and a small amount of mucopolysaccharide;
the inorganic fraction (70%) is mainly hydroxyapatite, with
some carbonate, magnesium, and fluoride. 

Dentin in cross section is composed of three distinct areas
microscopically: dentinal tubule, peritubular dentin, and
intertubular dentin. A dentinal tubule is a long tube,
running from the dentinoenamel junction or dentinocemental
junction to the pulp. This tube is filled with a cellular
extension of the odontoblast called the odontoblastic
process. The dentin that surrounds and is closest to the
tubules in the circumpulpal dentin is hypermineralized.
This dentin is peritubular dentin because it surrounds the
tubule. It has an area of higher crystalline content
surrounding the dentinal tubules. This dentin is formed
within the existing tubule and the term intratubular dentin
is more accurate. It is slightly more calcified than the
rest of the dentin. The intertubular dentin is the
remainder of the dentin matrix, that lies between the
tubules. However, increased formation and mineralization of
intratubular dentin, the tubule may eventually become
occluded. The resulting dentin is termed sclerotic,
transparent, and translucent dentin. These are all
microscopic structures. 

Dentin deposition begins with the formation of the pulp
chamber and continues as long as the pulp remains vital.
Primary dentin is developmental dentin that is formed from
the beginning of calcification until tooth eruption.
Secondary dentin is dentin that is formed throughout the
pulp chamber and pulp canal from the time of eruption. 

There is a considerable variation in the composition of
primary and secondary dentine. There is a change in the
course of the dentinal tubules in the shift from primary
dentin to secondary dentin deposition, the tubules are more
irregular in secondary dentin. Secondary deposits contain
less calcium, phosphorous, and collagenous matrix per unit
volume than the primary dentine. Secondary dentin is less
mineralized and contains 6-10 % more mineral than primary
dentin.
 
"Unlike secondary dentin, which is formed as a result of
normal physiological stimuli, tertiary or reparative dentin
is formed as a result of a pathological process, caries."
(3) A carious lesion involves the enamel and eventually can
enter into permanent dentinal deposits. These deposits do
not always prevent toxins from entering into the dental
pulp before becoming a carious lesion. The variations of
the mineral deposits are due to the differing proportions
of apatite and octocalcuim phosphate crystals in the
mineralized matrix of the teeth. Calcifications with
calcium/phosphorolar ratios of 1.47-1.68 suggested that
octocalcium phosphate crystals were located on collagen
fibers within the pulp enduring fibrotic and
arteriosclerotic age changes. However, in the mantle zone
there are increased amounts of collagen and mineral content
of the primary dentine, but were proportionately consistent
everywhere else. Secondary deposits contain less calcium,
phosphorous, and collagenous matrix per unit volume than
the primary dentine. 

Another type of dental caries, known as root caries may be
caused by filamentous organisms including Actinomyces
viscosus and Actinomyces naeslundi and Streptococcus
mutans. Root surface caries is a soft, progressive lesion
that can be found anywhere on the root surface that has
lost connective tissue attachment and is exposed to the
oral environment. Dental plaque and microbial attack are an
essential part of the cause and progression of the caries
lesion.
 
The carious lesion of the root is similar to that of
enamel, except that the microflora associated with the
lesion may be different. Root surface caries are usually
associated with filamentous organisms whereas coccal forms
are seen in enamel caries.
 
Dental plaque plays a major role in dental caries. Plaque
is a group of microbes that stick to the tooth surface. In
order for plaque to form it must have a form of energy. The
energy used are sugars which is known to be metabolized to
lactic acid, which acts as the demineralizing agent in
dental caries. As the glucose is metabolized to the lactic
acid, the cell transforms the glucose to adenosine
triphosphate (ATP), heat and lactic acid. It is these
materials in the plaque that cause decalcification and
cavitation of tooth structure.
 
Since plaque is the major cause of dental caries, it
affects the majority of the population of the United States
and other countries of the world. People need to be more
educated on the cause and prevention of dental caries to
keep their teeth more healthy and their overall oral
hygiene status healthy. Educating the population on plaque
and dental caries, could reduce many dental cavities,
periodontal disease, and reduce tooth loss.