Teeth are primarily mineral in content. The
enamel is rich in calcium and is more than 95% hydroxyapatite,
while dentine contains less hydroxyapatite than enamel. There
is in constant demineralization and remineralization in the oral
environment and saliva. As such, optimum pH and minerals should
be maintained for the processes to be balanced.
Types of dental caries
There four types of caries. These are pits and fissures caries
found generally in posterior teeth and maxillary incisors, smooth
surface caries found on all intact enamel surfaces of the tooth
except those of pits and fissures, root surface caries occurring
anywhere on the root surface and secondary or recurrent caries
found on tooth surface adjacent to a restoration.
Causes of dental caries
Dental caries is an infectious and transmissible disease. Various
factors play a role in the transmission of the cariogenic bacteria
and the propagation of the colonies in the susceptible host.
As with any infection, when the agent is transmitted, first be
able to colonize the host before the disease can be established.
Caries and tooth decay more commonly occur in the rear teeth,
which are pitted and fissured – the molars and premolars.
The uneven surfaces of these teeth aid in chewing and mastication
however, food particles get stuck in them. Since they are in
the back of the mouth, they are harder to reach when brushing
and so the bacteria in the mouth work on these trapped food particles,
turning them into acids, thus dropping the pH of the mouth. When
brushing is not done frequently and properly, plaque build up
occurs and the acids in it attack the teeth enamel.
Mature tooth enamel is harder than deciduous tooth enamel, hence
the increased incidence of dental caries in young children. Aside
from this, diet and oral hygiene are other factors that contribute
to this distribution.
The acids first attack the minerals of the enamel, the outer
stronger barrier. Since the pH of the mouth has dropped and become
acidic, tooth demineralization is hastened and remineralization
is slowed down. Once the acids have eroded the enamel, cavities
are formed. These cavities are the weaker points in the tooth
surface and continued demineralization will eventually expose
the inner, softer dentin to the acids. As dentin is less resistant
to acids, the tooth decay process is hastened, especially when
it is left untreated.
The acids will continue to eat away through the layers of the
tooth, until finally reaching the inner material of the tooth –the
pulp. Because of the opening, bacteria are also able to work
their way into the pulp. The presence of acid and bacteria inside
the tooth causes inflammation, which in turn causes the tooth
pain. When this happens, most patients seek medical advice.
Enamel and dentin structures
To further understand dental caries, the compositions of the
enamel and dentin must be understood.
The enamel is the hardest and most mineralized tissue in the
body. It contains 96% inorganic material, most of which is the
hydroxyapatite and calcium, and only 4% of it is organic material,
which include water. The enamel has a protein –rich matrix,
which allows the diffusion of fluids, ions, and small-sized molecules.
In dentin, only inorganic material comprises only 70%, which
is mainly composed of calcium phosphate. Unlike enamel, dentin
contains collagen and is not as hard as enamel.
Amelogenesis, or enamel formation occurs before the tooth erupts,
after the establishment of the dentin. There are 2 stages of
enamel formation: the secretory stage, when cells, known as the
ameloblasts, secrete enamel proteins, and the maturation stage,
when the ameloblasts now transport substances used in the formation
of the enamel. Before the tooth erupts, these ameloblasts are
broken down hence there is no way to regenerate enamel once it
Dental plaque formation
The formation of dental plaque occurs naturally and is of benefit
to the host as it helps prevent teeth colonization by exogenous
bacteria. The plaque has a constant composition of bacteria which
is maintained by their constant synergistic and antagonistic
activities. However, changes in the environment also affect the
homeostasis of these bacteria, permitting the activity certain
species over the others. For example, when there is prolonged
exposure to an acidic environment, aciduric bacteria (e.g. Lactobacillus
spp, Streptococcus mutans) flourish and produce more acids, thereby
initiating enamel erosion.
The dental plaque is also supersaturated with calcium phosphate
at normal oral pH. When the pH becomes acidic or drops below
the critical level, it loses its calcium phosphate content, allowing
further destruction of the enamel by the acids.
The cariogenic bacteria
Normal oral flora consists of various organisms, of which the
Lactobacillus species and Streptococcus mutans are the ones of
interest in caries development. When diet is rich in carbohydrates
and sugars, these microorganisms ferment the available sources,
producing lactic acid. This drops the pH enviroment in the mouth,
promoting faster demineralization and slows down remineralization.
This process leads to the formation of dental caries and tooth
decay by weakening the enamel.
Mutans Streptococci (MS)
Studies have shown that MS play a major role in the transmission
of dental caries. Out of all the bacteria, MS strain GS-5 shows
the greatest sucrose-dependent adherence to smooth surface. Thus
it is more able to colonize the tooth and this plays an important
role in the development of caries. However, a study done in 2006
claimed that sucrose level in the diet is not correlated with
the bacterial count.
Determination of levels of MS may be done using various tests.
Levels detected by these test relate to the levels of bacterial
colonization in teeth, and correlated with dental health status
Lactobacillus species (LB)
Lactobacillus species’ role in caries formation has been
refuted. Instead, it is now known that LB levels in saliva corresponds
to the prevalence of dental caries. LB is both acidophilic and
aciduric, meaning, it thrives in acidic environment and it also
produces acids, and so it aids in the demineralization of the
enamel once a lesion has been formed. Increased bacterial count
is seen in patients with clinical caries, although it is part
of the “normal” flora. As such, tests for LB detection
are not good for caries detection. Instead, LB tests are good
indicators of cavitation, sugar intake, and oral health status
since strong association has been noted between caries and high
or increasing LB counts.