Presentation on theme: "Demineralization and remineralization processes in enamel"— Presentation transcript:
1Demineralization and remineralization processes in enamel From UNIT 2 Etiology of Dental Diseases and Conditions, 3 Carious Lesions, p , PRIMARY PREVENTIVE DENTISTRY - 7th Ed. (2009) Norman O. HarrisProf. d-r R. Kabaktchieva- 2014
2It was the first step in dental decay In 1890 W. D. Miller, an American dentist teaching in Germany, published his chemico-parasitic theory of cariesMiller believed that extraction of the lime salts from the teeth was a result of bacterial acidogenesisMiller's work failed to identifydental plaque as the source of the bacteria and the bacterial acidsIt was the first step in dental decay
3G. V. Black, described the gelatinous microbial plaque as the source of the acids.
4Influence of MO, carbohydrates Dental caries is a multifactorial disease process, often represented by the interlocking circlesInfluence of MO, carbohydratesover time
54 conditions must occur simultaneously: There must be a susceptible tooth and host;(2) Cariogenic microorganisms must be present in a sufficient quantity;(3) There must be frequent excessive consumption of refined carbohydrates;(4) This process must occur over a sufficiently long period of time.For caries to develop,4 conditions must occur simultaneously:
6the bacteria produce acid. When a tooth covered with cariogenic bacteria is exposed to a suitable substrate, such as a refined carbohydrate, =If these conditions persist over a sufficiently long period of timethe bacteria produce acid.an incipient lesion develops
7The lesion looks like a white spot on the enamel. The incipient lesion is the initial stage of tooth decay that has not penetrated the outer surface of the tooth.The lesion looks like a white spot on the enamel.incipient lesioncaries
8Physical and Microscopic Features of Incipient Caries The incipient lesion in her earliest stage, is characterized byThese changes include demineralizationhistological changes of the enamelwhich represents the loss of calcium and phosphate and other ions from the enamel
9then continues into the dentin. Physical and Microscopic Features of Incipient CariesThe second stage includes the progress of demineralizationThe final phase of caries development is the development of the open or visible lesionthat is actually a really cavitationtoward the dentinoenamel junction (DEJ),then continues into the dentin.We can also say overt, or frank, lesion
10can be arrested or reversed!!! The early identification of the incipient lesion is extremely important,because it is during this stage that the carious processcan be arrested or reversed!!!
11The incipient lesion is macroscopically visible on the tooth surface by the appearance of an area of opacity, the white spot lesion.At this earliest clinically visible stage,the subsurface demineralization at the microscopic level is well established.
12The incipient lesion has been extensively studied and is best described by Silverstone. Тhe observations of the incipient lesion have been based on the use of a polarizing microscope.
13This microscope permits precise measurements of the amount of space, called pore space, which exists in normal enamel andto a greater extent in enamel defects.
14more pore space occurs; If demineralization progressesin contrast, during remineralization,more pore space occurs;less pore space is present.
15Direct Connection of the Bacterial Biofilm to the Body of the Lesion Tooth enamel is composed of interlocking structures calledenamel rods, which containbillions of crystals.The pores present betweenthe crystals and the rodsform a network of channels that allow diffusion of fluid, ions and small molecules found in the enamel
16The striae of Retzius extend this network into deeper layers of the enamel. This diffusion network allows:remineralization of the tooth throughout its lifeThe channels also allowplaque acids to enter the interior enamel, causing demineralization.
17In demineralization of the surface enamel: the initial attack may be on the ends of the enamel rods,between the rodsor both.Result from this:widening of the areas between adjacent rods (inter-rod space)
18When conditions are optimum ragged interface between surface and subsurfacecan be remineralized:1. by the body defenses, such as calcium and phosphate and other ions from the saliva,2. through preventive strategies , such as fluoride therapy3. By reduction of fermentable carbohydrates in the diet.When conditions are optimum
19Reaching the enamel-dentin border, whether any liquid causes demineralization or remineralization can move in 3 directions:1-2. along the hypomineralized EDJ in both direction – move lateralli3. into the dentinal tubules to the pulp chamber
20Diagram of a trichotomized lesion (go in three directions ) attributable to diffusion of acids: in both directions under the enameldirectly into the body of the lesion in the dentin.T, translucent zone;B, body of the lesion;R, reactionary dentin;P, pulp.(From Silverstone L. M., & Hicks, M. J. (1985).
21all of them continually changing. ,-The speed of progression of the caries front depends on such factors as:ion concentration,pH,saliva flowbuffering actionsall of them continually changing.
22Any chemical changes in the plaque can soon be reflected throughout the enamel and dentin as part of the incipient lesion.
23The initial acid attack preferentially : The pores allow plaque acids to be directed directly to the subsurface region.dissolves the magnesium and carbonate ions,the less-soluble calcium, phosphate, and other ions that are part of the crystal.The initial acid attack preferentially :followed by removal of:
24The undermined surface zone collapses. At the same time, the more soluble proteins are lost from the subsurface matrix.
25Cariogenic BacteriaAs a general rule, the cariogenic bacteria metabolize sugars to produce the energy required for their growth and reproduction.The byproducts of this metabolism are acids, which are released into the plaque fluid.The damage caused by MS is mainly caused by lactic acid, although other acids, such as butyric and propionic, are present within the plaque.
26Measuring Plaque pH, the Stephan Curve There is a continuous pH change in the plaque every time food is consumed.There is an almost immediate drop in pH when sugar or sugary snacks are eaten, followed by a longer recovery period than when other foods are eaten.
27This drop-and-recovery curve has been termed the Stephan curve; Different individuals have different capabilities to buffer acid production (see next fig.);Studies have identified foods that are accompanied by a drop the critical pH of 5.5 to 5.0,such as dried fruits,white bread, cereals,starchy foods
28Fig. Stephan curves. These curves show the typical plaque pH response to an oral glucose rinse . An immediate fall in the pH is followed by a gradual return to resting values after about 40 minutes.The upper curve was obtained from milk and the lower one from an apple- drink, showing a large difference in the acidogenicity of these two drinks.
29The Relationship of Saturation to pH The concentration of calcium and phosphate ions in the plaque fluid bathing the tooth at the plaque-tooth interface is extremely importantbecause these are the same elements that compose the hydroxyapatite crystal found in the enamel.If the fluid adjacent to the tooth is supersaturated with calcium and phosphate ions at a given pH,the enamel cannot undergo demineralization.
30The saliva in contact with the teeth is normally supersaturated with calcium and phosphate, compared with the levels of these minerals in enamel.The bacterial plaque can concentrate these ions to an even greater extent.For instance, the number of calcium and phosphate ions in plaque is 3 times greater than the number in the saliva.
31This increased concentration is of practical importance because calcium and phosphate levels tend to be inversely related to the caries score.
32As the pH drops in an acid attack, the level of supersaturation also drops, and the risk of demineralization increases.There is no exact pH at which demineralization begins, only a general range of 5.5 to 5.0.
33Demineralization is a function of both: a drop in pH , the length of time that the enamel surface is exposed to the acidic environment.Different plaques have:different initial pHs,different buffering potentials,different concentrations of calcium and phosphate in different parts of the mouth.A change in any of these variablesresults in a different level of supersaturation in the tooth environment.
34Demineralization and Remineralization Principles Demineralization is caused by plaque acids, which dissolve the tooth minerals making up the basic calcium, phosphate, and hydroxyl crystals of the enamel, dentin, and cementum.Remineralization, requires the availability of the same ions, preferably with fluoride as a catalyst to reconstruct the missing or damaged rods, a process that ten Cate called non-restorative repair.
35The crystals and fluoride compound of most dental interest in the demineralization and remineralization process are:hydroxyapatite (HAP),fluorhydroxyapatite (FHA),calcium fluoride (CaF2).
36Enamel mineralThe mineral of enamel is a salt formed from calcium phosphates.Basic calcium phosphate in enamel is hydroxyapatite.
37Enamel mineral Apatite - a mineral with chemical formula Са10(РО4)6 (F, OH)2FHA Ca10(PO4)6(F,OH)2FA Ca10(PO4)6 F2hydroxyl group
38Enamel mineral Са 8(РО 4) 4(НРО 4) 2.5Н 2О. Other calcium phosphates: Brushite СаНРО4.2Н 2О,ß-tricalcium phosphate- Са 3(РО 4) 2Octacalcium phosphate-Са 8(РО 4) 4(НРО 4) 2.5Н 2О.
39Dissociation equilibrium of hydroxyapatite НА in liquid medium undergoes electrolytic dissociationHA dissociates to :10 calcium ions6 trivalent phosphate ions2 hydroxide ionsСа 10(РО 4) 6 (ОН)2 ←→ 10Са РО ОН -
40Calcium and phosphate ions from the enamel get into plaque : - serve for buffering of the medium; - if the environment is alkaline the iones canreenter in enamel;- part of the ions get into the saliva,
41Between enamel and saliva is situated the plaque biofilm Processes of de-and remineralization of enamel in the oral environmentBetween enamel and saliva is situated the plaque biofilmIons entering the food diffuse plaque and saturate it;Within each eating into the plate enter acid, and other acids are formed from microbial metabolism.
42hydrogen ions + acid anions The acid is salt, and also in the liquid medium as well as the crystal starts to dissociate.Dissociation equilibrium of plaque acidshydrogen ions + acid anionsThe active part of an acid is the hydrogen ion, and its strength is dependent on the quantity thereof.
43The carious process is a process of acid demineralization
44When in the solution around HA acid is dissociate , begins the active effect of hydrogen ions; The hydrogen ions pass into the enamel and move in competitive reaction with calcium.
45form a monohydrogen phosphate ion (НРО42+) and (Н2О). The hydrogen ions move into contact with the hydroxyapatite and combined with the phosphate and hydroxide ions of the crystal–form a monohydrogen phosphate ion (НРО42+) and (Н2О).They quickly leave the crystal and move in solutionТеСа 10(РО 4) 6(ОН) 2 ←→ Са РО ОН -↓ Н+НРО Н20monohydrogen phosphateН2РО 4-dihydrogen phosphate ion
46Processes of de-and remineralization of enamel in the oral environment Enamel constantly washind from saliva. The concentration of Ca2 + and PO4 ions in the saliva varies - under normal conditions - 1,5 mmol / l. At neutral pH in the mouth the amount of Ca2 + and PO4 ions is sufficient to saturate the medium. These conditions provide balance in the process of de-and remineralization and no significant ion motion.
47Starts quickly extracting of ions from enamel for her saturation. Processes of de-and remineralization of enamel in the oral environmentBy acidification of the medium saturation with inherent apatite ions decreased sharplyStarts quickly extracting of ions from enamel for her saturation.Critical pH = 5,5 - direction of movement of the ions only in the direction from the enamel to the solution performed only under demineralizationPerformed only process of demineralization
48as a result of the action of saliva begins alkalization of the medium By dissolving apatite:over the enamel in the solution increases the concentration of Ca 2 +, Mg2 + PO 43 -, HPO4 -, CO 32 - / HCO 3 - ions. + Ions from salivaas a result of the action of saliva begins alkalization of the mediumions are directed to the enamel, enter it and precipitate to: - dicalcium phosphate dihydrate (DCPD) or oktakaltsiev phosphate (OCP)in a favorable environment, they pass into the hydroxyapatite and, in the presence of fluoride ions – to fluorhidroksiapatit Thus is realize the remineralization of tooth enamel
49The long-term exposure of teeth to low concentrations of fluoride (as found in fluoridated water) results in the gradual incorporation of fluoride into the existing hydroxyapatite (HAP) crystals to form fluorhydroxyapatite (FHA), which is more resistant to acid damage.Ендогенна Ф профилактика
50(as seen in electron microscope images). Conversely, a higher concentration of fluoride (as occurs with the use of topical fluoride applications, fluoride dentifrices, foams, and varnishes, etc.) results in the formation of surface globules of CaF2(as seen in electron microscope images).If phosphates and proteins of the saliva coat these globules, the globules become more insoluble.Локална Ф профилактика
51When the fluoride is incorporated into HAP to form FHA, it is said to be firmly bound, Fluoride in the form of CaF2, is loosely bound and adsorbed onto the surface of HAP and FHA crystals.
52The Relationship between HAP, FHA, and CaF2 After an attack by plaque acid(s),CaF2 dissolves first,followed in sequence by HAP,and finally, FHA (with its fluoride substitutions).As the attack continues, the dissociated ions increase the saturation level of the immediate fluid , sufficiently to slow crystal dissolution and eventually arrest further solution of the crystals.
53As the pH begins to return to normal, crystals begin to re-form from the complex pool of dissolved ions;some as HAP,some as FHA(with many of the fluoride ions coming from the previous CaF2).
54Any deficiencies are subsequently replaced, in time, by calcium, phosphate, and fluoride from sources such as the saliva, water, and toothpastes.
55The system “breaks down” (state of equilibrium -homeostasis)when the attacks are too frequent and too prolonged.