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Lec. 4 Pathological feature of dental caries

الكلية كلية طب الاسنان     القسم التقويم والاطفال وطب الاسنان الوقائي     المرحلة 5
أستاذ المادة حسن فليح فرحان السلطاني       6/7/2011 1:01:06 PM

د. حسن الوطيفي                                          Preventive dentistry                                      Lec. 4 

 

Pathological feature of dental caries
The enamel surface appear macroscopically firm and light, normal and sound enamel consist of hydroxyapatite crystals so tightly packed that the enamel has a glass-like appearance, the enamel is translucent, the yellow- white color of teeth is therefore the result of the dentin shining through the translucent enamel cover. Each crystal is separated from its neighbors by tiny inter crystalline spaces that filled with water and organic material.
When enamel is exposed to acids, minerals is removed or dissolved from the solid mineral, even a slight removal of mineral from the crystal periphery reduces the crystal size, this result in enlargement of inter crystalline spaces, which can be observed as an increase in tissue porosity. Deminerilzed enamel is thus more porous.
A slight increase in enamel porosity leads to change in the optical properties of the enamel in such a way that light is scattered; with increasing tissue porosity the enamel gradually become less translucent which clinically can be observed as a whitish (opaque) ---------Why?
Since the enamel translucency is an optical phenomenon, which depend on the size of the inter crystalline spaces, so the content of the inter crystalline spaces plays a role in the observed degree of the translucency. The refractive index of hydroxylapatite is 1.62, if one imagines that that all spaces in porous enamel sire filled with watery solution with the same refractive index as hydroxyapatite, its easy to understand that existing inter crystalline spaces disappear or that the enamel maintain its translucency. If watery material is removed from the inter crystallin spaces then this are more or less filled with air which has a refractive index of 1.0, the difference between the refractive index of hydroxyaptite and that of empty spaces is now so large that the porous tissue has lost its translucency and hence appear opaque .

Carious lesion in enamel
The development of dental caries is a dynamic process; of demineralization of the dental hard tissue by the products of bacterial metabolism, alternating with periods of reminerilization, dental caries is not a continual cumulative loss of mineral but rather a dynamic process, characterized by alternating periods of demineralization and reminerilization, a lesion result when the cumulative negative mineral balance exceeds the rate of reminerilization over an extended perio.
The development of caries occur s in two distinct stages.
1- The earliest stages in the incipient lesion macroscopically evidenced by the appearance of an area of opacity the so called, white spot lesion.
2- The first sign of surface breakdown (overt or/rank lesion) are limited to the outer most enamel and presumably created by mechanical injuries, if such area are not kept free of dental plaque the process will continue because the bacteria harbored in the micro cavity will receive more protection than those on the surface which again will favor the ecological shift toward anaerobic and acid-producing bacteria, the gradual enlargement of the cavity is therefore the combined result of the continual acid production in the protected microbial biomass and the mechanical micro traumas.
At microscopical level the incipient lesion described by measurement of the amount of space (pore space) that exist in the enamel into four zone, these are usually present
from the deepest zone of penetration to the mature outermost layer:
1- Translucent zone: advancing front of lesion and first to recognize from enamel. Only seen in longitudinal section in clearing agent eg. Quinoline dye. It has a structure less and has a width of 5- 100 Micron. Explanation for translucency is that the initial dissolution of enamel mainly occurs along the gaps between rods.

2- The dark zone: is more constant feature of the advancing front of caries lesions than in the translucent zone. Thus, the dark zone occurs in 90-95 percent of lesions, and if the translucent zone is present the dark zone is located between this and the body of the lesion. The dark appearance of the zone indicates that large quinoline molecules have not penetrated all micropories. The act that quinoline is unable to penetrate the dark zone indicates that this contains very small pores in addition to the relatively larger ones which were present in the previous.
3-The Body of the lesion:
The body is the largest proportion o carious enamel in the small lesion it lies superficial to the dark zone and deep to the relatively unaffected surface layers.
When a longitudinal ground section is examined in quinoline in polarized light, the area appears translucent and the Striae of retizius may be well marked.
4-TheSurfacezone:
 One of most important characteristics of enamel caries is that the greatest degree of dernineralization occurs at a subsurface. The small lesion remains by a surface layer which appears relatively unaffected by the attack. This surface zone approximately 1% percent. If the lesion progresses this surface layer is eventually destroyed and a cavity forms. The most important fact is that the surface zone is intact although its much more porous than sound enamel, the implication is that the caries process can be retarded arrested before any physical cavitations requiring clinical intervention has occurred. Even though minerals have been removed from the enamel and the lesion such characterized as porous, the remaining mineral still preserves the structural composition of the enamel, we are not dealing with an empty space beneath the surface zone but with a certain degree of mineral loss in a still highly mineralized tissue.
Caries in dentin
The first reaction of the pulpo-dentinal organ was tubular sclerosis, following exposure of dentin to the mass of bacteria, the superficial zone of dentin undergoes demineralization (decomposed) due to the action of acids and proteolytic enzymes which clinically can be seen as yellow- brownish discoloration of the of the soft dentin , the discoloration is a result of the biochemical changes of the collagenous dentin due to demineralization .
Dentinal caries exhibit a somewhat different microbial ecology related to its location. Organisms growing here must be more anaerobic and derive mast of their food from the tooth itself
As mentioned before, bacterial communities in carious dentin occupy two closely associated habitats, the soft necrotic area and the partially deminenilized deeper areas. The impact of the environment on the composition of the flora is also evident from the community at the advancing front of the lesion where gram positive rods such as lactobacillus, Eubacterium and Propionibacterium predominate with fewer S. mutans and gram negative bacteria.
 The dentine caries lesion contains three recognizable zone: 
1-The Infected Zone:
It is the superficial area that comprise the body of the carious infection comparable to fully nature plaque. This zone contain about 108 viable microbial cells per-gram, if consists almost entirely of mature of bacteria with a predominance of proteolytic cells and a tow concentration of about 0.1 percent aciduric cells. Clinically this material is a soft, yellow mass of cheesy texture.
2- The Affected Zone:
In gradual transition from the infected zone, the affected zone in the dentine. This is an area of partially dernineralized dentin which retains much of its tubular structure.
 This zone contains about 105 viable microbial cells per gram.
Within this zone, there is a marked increase in the proportion of bacteria that are aciduric and a corresponding decrease in the proportion that are proteolytic. This observation is compatible with the interpretation that acid demineralization plays a predominant role in the affected zone, while proteolytic activity (collagen degradation) is more active in the infected zone. Clinically the affected zone becomes progressively more dark and leathery in texture.
3- The hypermineralized Zone:
Consisting of increased mineral content. The hypermineralized zone is found at the active front of the advancing carious lesion in dentin its thickness varies with the intensity and chronicity of the caries attack. This zone is narrow in cases of acute caries, but is considerable wide subjacent to the front of chronic, more slowly progressing caries.
Specific to dentin caries, its developmental mechanism is unknown. It’s considered probable that this zone occurs as a result of the precipitation of mineral salts at that site during each reversal of the demineralization-rernineralization equilibrium.

Root caries:
Differ from coronal caries in several aspects. A critical difference is that the tissue affected are fundamental dissimilar, Enamel is much more highly mineralized than cementurn because the lower mineral content and higher organic content. Histological studies of the surface of normal exposed cementium indicate that its hypermisveralized in relation to unexposed cementium due to calcium, phosphate and fluoride ions.
Root caries may progress both by acid demineralizadon and by proteolytic breakdown of organic component. In the earliest stages of root caries, the surface hyperminerilization can also result from the release of ions from the subsurface lesion much as happens with coronal caries. Clinically the lesion is initially non cavitated; its softened has a yellowish brown coloration.
Although many bacterial species exist in the community associated with root caries, strain of Streptococcus and Actinomyces comprise the major part of the microflora in established lesion. Demineralization of root tissue may occur at higher PH than enamel and consequently less aciduric and acidogenic Streptococcus strains than those causing enamel demineralization and also Actinomyces may contribute to the development and progression of root surface lesions.



المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .