denatal caries - tooth decay

Denatal Caries

Is defined as a bacterial disease of the calcified tissues of teeth characterized by demineralization of the inorganic and destruction of organic substance of the tooth.

It’s a complex and dynamic process involving , for example , physio-chemical processes associated with movement of ions across the interface between the tooth and the external environment as well as biological process associated with the interaction of bacteria in the dental plaque with the host defense mechanism

Etiology of dental caries :

There are various theories regarding the etiology of dental caries have been proposed , but there is now overwhelming support the acidogenic theory which proposed that acid formed from the fermentation of dietary carbohydrates by oral bacteria leads to progressive decalcification of the tooth substance with a subsequent disintegration of organic matrix

Role of bacteria and dental plaque :

Bacteria are essential for the development of dental carries. They are present in dental plaques which are found on most teeth surfaces.

Now , a plaque is a biofilm consists of variety of different species of bacteria embedded in a matrix derived from salivary mucin and extracellular polysaccharide polymers (glucose and fructose) synthesized by these organisms.

Dietary sugars diffuse rapidly through plaque where they are converted by bacterial metabolism to acids ,like: lactic acid , acetic acid, and propionic acid. But mainly lactic acid.

The pH may fall by as much as 2 units within 10 min. after ingestion of sugars , and then slowly rises back to it’s normal value during the next 30-60 min.

At critical pH of 5.5 mineral ions are liberated from the hydroxyapatite crystals of the enamel and diffuse into the plaque.

Ions may diffuse back into the enamel (fluoride).

Microbiology of dental caries :

No single bacteria.

Members of the ‘mutant streptococci’ group are the most efficient cariogenic organisms.

Cont.

Other bacteria for example lactobacilli may be important in further progression of the lesion.

Lactobacillic are also the pioneer organism in dentine caries.

Role of Carbohydrates :

The evidence of the relationship between carbohydrate and dental caries :

1. The increasing prevalence of dental caries in the developing countries and the increasing availability of sucrose in their diet.

2. The decrease in prevalence of caries during WWII because of sugar restriction followed by arise to previous levels when sucrose become available.

3. The Hopewood house study – a children home in Australia where sucrose and white bread were virtually excluded from the diet , the children had low caries rate which increased dramatically when they moved out of their house.

Pathology of dental caries :

Dental cries can be classified according to :

1. The site of the lesion.

2. The rate of the attack.

Site of the lesion

Pit or fissure : Occurs on the occlusal surface of molars

and premolars on the buccal and lingual surface of molars and lingual surface of maxillary incisors.

Early caries may be detected clinically by brown or black discoloration of a fissure in which a probe “stick” .

Smooth surface caries

Occurs on the approximal surface and on the gingival third of the buccal and lingual surface.

approximal caries begins just below the contact point as a well-demarcated chalky-white opacity of the enamel.

Cemental or root caries :This occurs when the root face is exposed

to the oral environment as a result of periodontal disease , usually shallow , saucer shaped with ill-defined boundaries.

Recurrent caries :This occurs around the margin of at the

base of a previously existing restoration.

Rate of attack

Rampant or acute caries :This is rapidly progressing caries involving

many of all of the erupted tooth. (rapid coronal destruction)

Slowly progressive or chronic caries :This type progresses slowly and involves

the pulp much later than in acute caries.

Cont.

Arrested caries:

This is caries of enamel or dentine , including root caries that becomes static and shows no tendency for further progression

Enamel caries

The early established lesion (white spot) in smooth surface enamel caries is cone shaped with the apex pointing towards the amelodentinal junction.

In ground section it consists of series of zones , depending on the degree of demineralization.

Zones:

1. Translucent zone The first recognizable histological

change.

More poruos than normal enamel , contain 1 % by volume of spaces compared with the 0.1 % pores volume in normal enamel.

Mg and carbonate when compared with normal enamel.

Some times missing.

Cont enamel zone

Dark zone : 2-4% by volume of pores.

It is thought that the dark zone is narrow in rapidly advancing lesion and wider in more slowly advancing lesions when more reminiralization may occur.

Body of the lesion :

5-25% by volume of pores.

Highly mineralized and having higher fluoride level and lower Mg level0

Surface zone

This is about 40 µm thick and shows surprisingly little change in early lesion.

Highly meniralized and having higher flouride level and lower Mg level.

Histopathologenesis of the early lesions

1. Development of a subsurface translucent zone which is unrecognizable clinically and radiologicaly.

2. The subsurface translucent zone enlarges and a dark zone develops in it’s center.

3.As the lesion enlarges more mineral is lost and the center of the dark zone becomes the body of the lesion ,the lesion is now clinically recognizable as a white spot.

4.The body of the lesion may become stained by exogenous pigments from food ,tobacco , and bacteria . The lesion is now clinically recognizable as a brown spot.

5. When the caries reaches the amelodentinal junction it spreads laterally , underminig the adjacent enamel , giving the bluish-white appearance.

6.With progressive loss of mineral a critical point is reached when the enamel is no longer able to withstand the loads placed upon it to form a cavity.

Dentine caries

Dentine differ from enamel is that it’s a living tissue as such can respond to caries attack (Reactionary . Tertiary)

Caries of dentine develops from enamel caries , when the lesion reaches the amelodentinal junction lateral extension results in the involvement of great numbers of tubules.

The early lesion is cone shaped with base at adj

Zone of dentine caries

Zone of sclerosis:Beneath the sides of the serious lesion.Sclerosed dentine has a higher mineral

content. Zone of demineralizationThe intertubular matrix in mainly affected

by a wave of acid produced by bacteria in the zone of bacteria invasion.

Zone of bacterial invasionBacteria extended down and multiply

within the dental tubules , some of which may become occluded by bacteria.

Zone of destructionCracks of clefts containing bacteria and

necrotic tissue also appears at right angles to the course of the denital tubules forming transverse clefts.