Wednesday, February 24, 2010

DENTAL CARIES: INTRODUCTION AND THEORIES OF CARIES FORMATION

DENTAL CARIES


def.

Dental caries is defined as the irreversible multi-factorial disease of microbial origin affecting the calcified tissues of the teeth, which is characterized by demineralization of the inorganic portion and destruction of the organic constituents of the tooth, often leading to cavitation.





etiology

Various theories have been proposed trying to explain the etio-pathogenesis of dental caries, which are-

a)Early theories
1) the legend of worms (5,ooo B.C.)
2) endogenous theory
3) chemical theory
4) parasitic theory

b)Miller’s chemicoparasitic theory
(acidogenic theory)

c)Proteolytic theory
d)Proteolysis-chelation
e)Sucrose-chelation theory
f)Current concept of caries etiology


The legend of worms
In the past, dental caries was thought to be caused by living worms inside the tooth structure.


Endogenous theories
Includes 1) humoral theory- according to which an imbalance
between the humors of body caused tooth decay.
2) vital theory- according to which tooth decay
originated from within the tooth itself, like a bone
gangrene.


Chemical (acid) theory
On the basis of findings of Robertson, this theory proposed that tooth decay was caused by the fermentation of food particles around the teeth.


Parasitic (septic) theory
This was the first theory that related microorganisms with caries on a causative basis (by ERDLE, 1843)Accordingly, it was proposed that even though caries starts purely as a chemical process BUT microorganisms continued the disintegration in both enamel and dentin.






Miller's chemico-parasitic theory(the acidogenic theory)

Proposed by Willoughby D Miller.
This theory is a blend of both chemical and parasitic theory proposed earlier.
a/c to this theory, dental caries is a chemico-parasitic process consisting of 2 stages:
first, decalcification of enamel and dentin (preliminary stage)
second, dissolution of the softened residue (later stage)
and the acid causing primary decalcification is produced by the fermentation of starches and sugar from the retained corners of teeth.

Hence Miller advocated an essential role of 3 factors in the caries process: the oral microorganisms,
the carbohydrate substrate, and
the acid.
Even though, at that time, this theory couldn’t explain
1) predilection of specific sites on a tooth
2) initiation of smooth surface caries
3) why some populations are caries free
4) the phenomenon of arrested caries.
This theory is still considered as the backbone of current knowledge and understanding of the etiology of dental caries.




The proteolytic theory
By Gottlieb and Gottlieb.
a/c to this theory,
the organic or protein elements of tooth (not the inorganic constituents of enamel ) are the initial pathways of invasion by microorganisms;
And, caries is essentially a proteolytic process , in which the microorganisms invade the organic pathways and destroy them while advancing through them by forming acids.
Hence certain structures of enamel having high organic material composition, like enamel lamellae and enamel rod sheaths, could serve as a pathway for microorganism invasion through the enamel .


Drawbacks of this theory
1)It couldn’t provide sufficient evidences to support the claim that the initial attack on enamel is proteolytic;
2)also 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.






Current concept of caries etiology

a/c to the current concept , caries occurs as a result of interplay between 3 primary factors:
the host,
the microorganism,
the substrate.
In addition a fourth factor- the time , is also taken into consideration.

(TO BE CONTD/...)

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