The document discusses various theories of dental caries development over time. It begins by classifying theories as new, early, exogenous, and endogenous. The acidogenic/chemicoparasitic theory proposed by Miller in 1890 that dental decay results from acid attack followed by bacterial dissolution is still the most accepted. Other theories discussed include the proteolytic, proteolysis-chelation, autoimmune, sucrose chelation, and Levine's ionic see-saw theories. Current concepts recognize dental caries as resulting from an interaction between plaque, tooth susceptibility, dietary substrates, and time for the factors to act and lower pH.

1. OPERATIVE DENTISTRY
GROUP 6
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2. Classification of theories of dental caries.
New theories
 Acidogenic theory
 Proteolytic theory
 Proteolysis chelation theory
Early theories
 Vital theory
 Humoral theory
 Septic theory
 Legend of the worm theory
 Chemical theory
Exogenous theories
 Acidogenic
 Proteolysis theory
 Proteolysis chelation theory
 Septic theory
 Chemical theory
Endogenous theories
 Vital theory
 Humoral theory
 OTHER THEORIES
 Enzymatic theory
 Acid –Enzymatic theory
 Levine’s Ionic see saw theory
 Auto immune theory
 Sucrose chelation theory
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3. Acidogenic Theory/Chemicoparasitic Theory
• It is the most accepted theory given by WD. Miller in 1890.
• Miller said, “Dental decay is a chemicoparasitic process consisting of two
stages, the decalcification of enamel, which results in its total destruction, as a
preliminary stage; followed by dissolution of the softened residue of the enamel
and dentin.
In the first stage there is a destruction which is done by the acid attack whereas the
dissolution of the residue is done by the proteolytic action of the bacteria
• This whole process is supported by the presence of carbohydrates, microorganisms
and dental plaque.
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4. Conts….
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5. Role of the factors
 Role of carbohydrates
 According to Miller’s observations, teeth decalcify when incubated in saliva and
bread/sugar mixture and show no change when incubated with fat. His simple
experiment demonstrated the cariogenic effects of carbohydrates.
However, the cariogenic potential of dietary carbohydrates varies on their physical
form, chemical composition and frequency of intake. It is a well known fact that
carbohydrates which have a slow clearance rate from the oral cavity are more
cariogenic than those which have a higher clearance rate. The risk of caries incidence
increases greatly if the dietary sugar is sticky in nature, and when there is increased
frequency of ingestion of the sugars.
Polysaccharides are less easily fermented by plaque bacteria than monosaccharides
and disaccharides. Glucose, sucrose and fructose which are highly fermentable have a
greater role to play in the causation of dental caries. These sugars are readily broken
down by the bacteria to produce acids that in turn cause the dissolution of the
hydroxyapatite crystals of the enamel and dentin.
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6. Continuation on role of carbohydrates
Sucrose is readily fermented by the cariogenic bacteria (mainly Streptococcus mutans)
to produce acids, which can demineralize the tooth. S. mutans use sucrose to
synthesize an extracellular insoluble polysaccharide with the help of the enzyme
‘dextran’, which helps in adhering the plaque firmly on to the tooth surface.
The pH of plaque falls to 4.5–5 in about 1–3 minutes of sugar intake. It is estimated
that pH returns to neutral levels in approximately 30 minutes.
 The physical nature of the diet intake also has a bearing on the incidence of carious
lesions. Coarse fibrous foods aid in greater clearance rate from the oral cavity thereby
minimizing the carious incidence. However, sticky refined food and sweetened soft
drinks predispose to debris accumulation and the increased likelihood of carious
lesions
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7. Role of microorganisms
 Lactobacillus acidophilus along with a combination of other bacteria such as S.
mutans and Actinomyces species are closely associated with the causation of dental
caries. It is believed that a few types of bacteria may be intimately involved in the
initiation of the carious process whereas some may be involved in the progression
of the carious process.
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8. Role of acids
 Miller in his observations reported that many of the microorganisms in
the oral cavity were capable of producing acids and these acids were
usually present in deeper carious lesions. In many of the lesions studied,
lactic acid was identified in carbohydrate saliva combined mixtures. A
specific microorganism, Leptothrix buccalis, was isolated from the dentinal
tubules, suggesting that the microorganisms and the acids may have a
synergistic action to dissolve the organic portion of the tooth
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9. Role of dental plaque
 Plaque as described by GV Black is a ‘gelatinous plaque of the caries fungus in a
thin, transparent film that usually escapes observation, and which is revealed
only by careful search’. It generally consists of salivary components such as
mucin and desquamated epithelial cells and of microorganisms. However, long-
standing plaque may accumulate to a perceptible degree in 24–48 hours. It is
estimated that cariogenic plaque contains 2 × 108 bacteria/mg weight.
The pH of plaque also varies in caries free and individuals with high caries
activity. The pH is about 7.1 in caries free individuals and approximately 5.5 in
individuals with high caries activity.
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10. Sucrose Chelation Theory
 This theory proposes that if there is a very high concentration of sucrose
in the mouth of a caries-active individual, there can be formation of
complex substances like calcium saccharate and calcium complexing
intermediaries by the action of phosphorylating enzymes. These
complexes cause release of the calcium and phosphorus ions from the
enamel and thereby resulting in tooth decay.

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11. Autoimmune Theory
 According to this theory few odontoblasts, within the pulp of few certain
teeth are damaged by the autoimmune mechanisms, leading to a
compromised Défense mechanism and the loss of integrity of enamel or
dentin. These targeted sites are potential sites for the development of
carious lesions.
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12. Proteolytic Theory
• Heider, Bodecker (1878) and Abbott (1879) thrown considerable light to this
theory
• According to this theory, organic portion of the tooth plays an important role in the
development of dental caries
• It has been recognized that enamel contains 0.56 percent of organic matter out of
which 0.18 percent is keratin and 0.17 percent is a soluble protein
• Enamel structure which are made of the organic material such as enamel lamellae
and enamel rods prove to be the pathways for the advancing microorganisms
• Microorganisms invade the enamel lamellae and the acid produced by the
bacteria's causes damage to the organic pathways.
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13. Proteolysis theory (Gottlieb in 1944)
 Gottlieb in 1944 suggested that the initial lesion of the carious process is due to
the proteolytic enzymes attacking the lamellae, rod sheaths, tufts and walls of
tubules. He believed that the yellow pigmentation that is characteristic of caries
was due to pigment produced by the proteolytic organisms. He also proposed that
the Staphylococcus plays a vital role in initiating proteolytic activity.
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14. Proteolytic theory (pincus in 1949)
 Pincus in 1949 proposed that the proteolytic breakdown of the dental cuticle is
the first step in the carious process.
 He proposed that the Nasmyth’s membrane and the enamel proteins are
mucoproteins, which are acted upon by the sulfatase enzyme of the bacilli
yielding sulfuric acid.
 The sulfuric acid thus produced combines with the calcium of the hydroxyapatite
crystal and destroys the inorganic component of the enamel.
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15. Conts…….
Draw back of the proteolytic theory
 It couldn’t provide sufficient evidences to support the claim that the initial attack
on enamel is proteolytic
 Experimental studies have shown the occurrence of caries even in the absence of
proteolytic microorganisms. However, this theory is still helpful in explaining the
progression of a more advanced carious lesion
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16. Proteolysis-Chelation Theory
 Some of the minor flaws of the acidogenic and the proteolytic theories
were addressed in the proteolysis-chelation theory. This theory was put
forward by Schatz and co-workers in 1955.
 Chelation is a process in which there is complexing of the metal ions to
form complex substance through coordinated covalent bond which
results in poorly dissociated and/or weakly ionized compound.
Chelation is independent of the pH of the medium.
 The proteolysis-chelation theory considers dental caries to be a bacterial
destruction of organic components of enamel and the breakdown
products of these organic components to have chelating properties and
thereby dissolve the minerals in the enamel even at the neutral/alkaline
pH. Mucopolysaccharides, lipids and citrates may also act as secondary
chelators.
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17. Continuation of proteolysis chelation
 Schatz and co-workers observed that there is a simultaneous microbial
degradation of organic component by proteolysis and the dissolution of
inorganic part by the process of chelation.
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18. “Caries Balance Concept” (Proposed by
Featherstone)
• According to this theory, caries does not result from a single factor; rather, it is the
outcome of the complex interaction of pathologic and protective factors
 • Pathological factors involved in a carious lesion are bacteria, poor dietary
habits, and xerostomia.
 Protective factors include saliva, antimicrobial agents (chlorhexidine, xylitol),
fluoride, pit and fissure sealants and an effective diet.
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19. Conts….
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20. Endogenous theories
1. Humoral theory
The relative proportion of the four elemental fluids of the body determines the
persons physical and mental constitution(blood, phlegm, black bile ,yellow bile)
Its suggests that ‘’An imbalance in humours of the body causes tooth decay’’
2. Vital theory
It suggests that ‘’ tooth decay originated from with in the tooth its self , like a bone
gangrene’’
(gangrene is a dead part of the body tissue due to lack of blood or serious bacteria
infection)
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21. Conts….
Legend of the worm theory
 The theory dates back as far as 5000BC .
 It was believed that dental caries were caused by a tiny worm inside the tooth.
And that the activity of the worm corresponded to the pain afflicted by it.
The parasitic or septic theory
 This was the first theory that related microorganisms with caries on a causative basis.
 Accordingly, it was proposed that even though caries starts purely as a chemical
process, but microorganisms continued the disintegration in both enamel and dentin
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22. Conts…….
The chemical /Acid theory
 In the 17 -18th century, there immerge a concept that the teeth are destroyed by
acids formed in the oral cavity by fermentation of food particles around the teeth.
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23. Current Concept of caries
 Introduction
The current concept on caries suggests that caries have a multi-factorial synthesis. It
suggests that these factors interact with each other in a specific period of time in such
a way which increases demineralization of the tooth structure with resultant caries
formation.
There are 3 prerequisite factors for the development of dental caries i.e
1.plaque,
2. tooth
3. substrate (keye’s triad) .
Later Keye’s triad was modified to include the time factor.
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24. Tooth
The variation in tooth morphology, its composition and position contributes to caries
formation
i. Susceptible areas on tooth for caries are deep and narrow occlusal fissures, deep
buccal and lingual pits, exposed root surface, margins of existing restorations.
ii. Lack of enamel maturation or presence of developmental defects increase plaque
retention, bacterial colonization and make the tooth more to tooth demineralization.
iii. Tooth position also affects the initiation of dental caries, if a tooth is out of
position, rotated or in any abnormal position, it becomes difficulty to clean, and
hence retains more food and debris.
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25. Substrate
This refers to environmental factors with in the oral cavity that necessitate the
development of caries.
These include; saliva, diet
Saliva;
The composition, quantity, pH, viscosity and antimicrobial factors of saliva
affect the development of caries
 Saliva contains calcium, phosphate and fluoride and normal conditions the tooth is
continually in touch with saliva. These minerals help in remineralization of the
early stages of carious lesions.
 When saliva flow is reduced or absent, there occurs the increased food retention.
Since salivary buffering capacity is lost, an acid environment is encouraged which
further promotes the growth of aciduric bacteria.
(cause of hyposalivation; medication, dehydration, pathological conditions, mouth
breathing etc).
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26. Cont……
Diet;
More refined and less fibrous foods stick stubbornly to the teeth and are not removed
easily due to lack of roughages.
Streptococcus mutans makes use of sucrose to produce the extracellular
polysaccharide glucan. Glucan polymer help the S. Mutans to adhere to teeth.
Frequency of carbohydrate intake; the greater the time lapse between acid attacks,
better are the chances for repair( remineralization) to occur.
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27. Plaque /bacteria
 The main etiological agent in occlusal and pit and fissure caries is the S.
mutans. Deep dentinal caries is commonly associated with lactobacilli,
certain gram-positive anaerobes and filaments such as Eubacterium and
Actinomyces.
 Root caries or cemental caries is predominantly associated
with Actinomyces viscous. However other species of Actinomyces such
as A. naeslundii and A. nocardia have also been isolated.

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28. Time/ period
 The time period during which all above three direct factors, i.e tooth,
microorganisms and substrate are acting jointly should be adequate to produce
acidic pH which is critical for dissolution of enamel to produce a carious lesion.
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29. conclusion
The current concept on caries suggests that the 4 factors mentioned above are the
primary factors required for development of caries.
However there are many other factors affecting the interplay between these primary
factors.
These include; age, sex, race, hereditary, systemic health, occupation, geographical
area.
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30. OTHER THEORIES
 Enzymatic Theory
 This theory is based on the fact that plaque bacteria produces enzymes. Enzymes
involved may include phosphatase (dissolves apatite), chondroitin sulfatase
(dissolves dentinal chondroitin sulphate), hyaluronidase (dissolves dentinal
hyaluronic acid) and proteases (dissolve dentinal collagen). All these enzymes are
produced by plaque bacteria.
 Acid-enzyme Theory
 This theory is a combination of the acidogenic and the enzyme theories. It is
believed that the acids produced have a major role in enamel dissolution and the
enzymes probably play a greater role in dentinal dissolution.
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31. Levine’s Ionic See-saw Theory
 This theory was proposed by Levine in 1977. According to this theory, there is a
chemical relationship between enamel plaque and the factors which determine
the movement of minerals from saliva/plaque to enamel and vice versa, which
was termed as the ionic see-saw mechanism.
Levine proposed that the demineralization and remineralization of enamel is a
continuous process. If in a given interval of time, more ions leave the enamel than
enter it, then there is a net demineralization, which heralds the beginning of the
carious process. It was proved that the ions are constantly exchanged between
enamel and plaque. This theory emphasizes the importance of pH of plaque,
calcium and phosphate ion concentration at the interphase and fluoride ion
concentration.
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