DEMINERALIZATION AND REMINERALIZATION PROCESSES IN

ENAMEL 

Prof. d-r R. Kabaktchieva- 2014

In 1890 W. D. Miller, an American dentist teaching in Germany, published his chemico-parasitic theory of caries

Miller believed that extraction of the lime salts from the teeth was a result of bacterial acidogenesis

Miller's work failed to identify

dental plaque as the source of the bacteria and the bacterial acids

It was the first step in dental decay

G. V. Black, described the gelatinous microbial plaque as the source of the acids.

Dental caries is a multifactorial disease process, often represented by the interlocking circles

Influence of MO, carbohydrates over time

For caries to develop,

4 conditions must occur

simultaneously:

(1) 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.

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 time

the bacteria produce acid.

an incipient lesion develops

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 lesion caries

Physical and Microscopic Features of Incipient Caries

The incipient lesion in her earliest stage, is characterized by

These changes include demineralization

which represents the loss of calcium and phosphate and other ions from the enamel

histological changes of the enamel

The second stage includes the progress of demineralization

The final phase of caries development is the development of the open or visible lesion

that is actually a really cavitation

Physical and Microscopic Features of Incipient Caries

toward the dentinoenamel junction (DEJ),

then continues into the dentin.

We can also say overt, or frank, lesion

The early identification of the incipient lesion is extremely important,

because it is during this stage that the carious process

can be arrested or reversed!!!

The 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.

The 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.

This microscope permits precise

measurements of the amount of space, called pore space,

which exists in normal enamel and

to a greater extent in enamel defects.

If demineralization progresses

in contrast, during remineralization,

more pore space occurs;

less pore space is present.

Direct Connection of the Bacterial Biofilm to the Body of the Lesion

Tooth enamel is composed of interlocking structures called

enamel rods, which contain

billions of crystals.

The pores present between

the crystals and the rodsform a network of

channels that allow diffusion of fluid, ions and small molecules found in the enamel

The striae of Retzius extend this network into deeper layers of the enamel.

This diffusion network allows:

•remineralization of the tooth throughout its life

The channels also allow

•plaque acids to enter the interior enamel, causing demineralization.

In demineralizati

on of the surface enamel:

• the initial attack may be on the ends of the enamel rods,•between the rods•or both.

Result from this:

•widening of the areas between adjacent rods (inter-rod space)

ragged interface

between surface and subsurface

can be reminerali

zed:

1. by the body defenses, such as calcium and phosphate and other ions from

the saliva,

2. through preventive strategies ,

such as fluoride therapy

3. By reduction of fermentable

carbohydrates in the diet.

When conditions are optimum

1-2. along the hypomineralized EDJ in both direction – move lateralli

3. into the dentinal tubules to the pulp chamber

Diagram of a trichotomized lesion (go in three directions ) attributable to diffusion of acids:-in both directions under the enamel - directly 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).

- ,- - The speed of progression of the caries

front depends on such factors as:

ion concentration,

pH,

saliva flow

buffering actions

-all of them continually changing.

Any chemical changes in the plaque can soon be reflected throughout the enamel and dentin as part of the incipient lesion.

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.

followed by removal of:

The initial acid attack preferentially :

The undermined surface zone collapses.

At the same time, the more soluble proteins are lost from the subsurface matrix.

Cariogenic Bacteria As 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.

Measuring 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.

This 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

Fig. 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.

The concentration of calcium and phosphate ions in the plaque fluid bathing the tooth at the plaque-tooth interface is extremely important

If the fluid adjacent to the tooth is supersaturated with calcium and phosphate ions at a given pH, the enamel cannot undergo demineralization.

The Relationship of Saturation to pH

because these are the same elements that compose the

hydroxyapatite crystal found in the enamel.

The 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.

This increased concentration is of practical importance because calcium and phosphate levels tend to be inversely related to the caries score.

As 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.

Demineralization 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 variables results in a different level of supersaturation in the tooth environment.

Demineralization 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.

The crystals and fluoride compound of most dental interest in the demineralization and remineralization process are:

- hydroxyapatite (HAP),- fluorhydroxyapatite (FHA), - calcium fluoride (CaF2).

Enamel mineral

The mineral of enamel is a salt formed from calcium phosphates.

Basic calcium phosphate in enamel is hydroxyapatite.

Enamel mineral

Apatite - a mineral with chemical formula

Са10(РО4)6 (F, OH)2

FHA- Ca10(PO4)6(F,OH)2 FA Ca10(PO4)6 F2

Enamel mineral

Other calcium phosphates:

Brushite - СаНРО4.2Н 2О,

ß-tricalcium phosphate- Са 3(РО 4) 2

Octacalcium phosphate-

Са 8(РО 4) 4(НРО 4) 2.5Н 2О.

Dissociation equilibrium of hydroxyapatite

НА in liquid medium undergoes electrolytic dissociation HA dissociates to :

10 calcium ions 6 trivalent phosphate ions 2 hydroxide ionsСа 10(РО 4) 6 (ОН)2 ←→ 10Са 2+ + 6РО4

3- + 2ОН -

Calcium and phosphate ions from the enamel get into plaque :

- serve for buffering of the medium;

- if the environment is alkaline the iones can reenter in enamel;

- part of the ions get into the saliva,

Between enamel and saliva is situated the plaque biofilm

Processes of de-and remineralization of enamel in the oral environment

Ions entering the food diffuse plaque and saturate it;

Within each eating into the plate enter acid, and other acids are formed from microbial metabolism.

The acid is salt, and also in the liquid medium as well as the crystal starts to dissociate.

hydrogen ions + acid anions

The active part of an acid is the hydrogen ion, and its strength is dependent on the quantity thereof.

Dissociation equilibrium of plaque acids

The carious process is a process of acid demineralization

When 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.

They quickly leave the crystal and move in solutionТе Са 10(РО 4) 6(ОН) 2 ←→ Са 2+ + 6РО 4

3- + ОН -

↓ Н+

НРО42+ Н20

↓ Н+monohydrogen phosphate Н2РО 4

-

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).

dihydrogen phosphate ion

Processes 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.

Processes of de-and remineralization of enamel in the oral environment

By acidification of the medium saturation with inherent apatite ions decreased sharply

Starts 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 demineralization

Performed only process of demineralization

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 saliva

as a result of the action of saliva begins alkalization of the medium

ions 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

Ендогенна Ф профилактика

The 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.

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

When 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.

The 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.

As 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).

Any deficiencies are subsequently replaced, in time, by calcium, phosphate, and fluoride from sources such as the saliva, water, and toothpastes.

The system “breaks down”

(state of equilibrium -homeostasis)

when the attacks are too frequent and too prolonged.

end