Structural formula

Molecular weight: 74.094

calcium hydroxide, Ca(OH)2 slaked lime or "fluff" - a chemical substance, a strong base. Is a powder white color, poorly soluble in water.

Trivial names

• Hydrated lime - as it is obtained by "extinguishing" (that is, interacting with water) "quicklime" (calcium oxide).
• Lime milk is a suspension (suspension) formed by mixing an excess of slaked lime with water. It's like milk.
• Lime water is a clear solution of calcium hydroxide obtained by filtering milk of lime.

Receipt

Obtained by the interaction of calcium oxide (quicklime) with water (the process is called "lime slaking"). This reaction is exothermic, with the release of 16 kcal (67 kJ) per mole.

Properties

Appearance - white powder, slightly soluble in water. Calcium hydroxide is a fairly strong base, which is why the aqueous solution has an alkaline reaction. Solubility decreases with increasing temperature. Like all bases, it reacts with acids; as an alkali - is a component of the neutralization reaction (see neutralization reaction) with the formation of the corresponding calcium salts. For the same reason, a solution of calcium hydroxide becomes cloudy in air, since calcium hydroxide, like other strong bases, reacts with carbon dioxide dissolved in water. If you continue the treatment with carbon dioxide, the precipitate will dissolve, since an acidic salt is formed - calcium bicarbonate, and when the solution is heated, the bicarbonate is again destroyed and calcium carbonate precipitates. Calcium hydroxide reacts with carbon monoxide at about 400 °C. How a strong base reacts with salts, but only if the reaction results in a precipitate.

Application

• When whitewashing rooms.
• For the preparation of lime mortar. Lime has been used for building masonry since ancient times. The mixture is usually prepared in the following proportion: three to four parts of sand (by weight) are added to one part of a mixture of calcium hydroxide (slaked lime) with water. Water is released during the reaction. This is a negative factor, since in rooms built with lime mortar, high humidity. In this regard, and also due to a number of other advantages over calcium hydroxide, cement has practically replaced it as a binder for mortars.
• For the preparation of silicate concrete. The composition of silicate concrete is similar to the composition of lime mortar, however, its hardening occurs several orders of magnitude faster, since the mixture of calcium oxide and quartz sand it is processed not with water, but with superheated (174.5-197.4 ° C) water vapor in an autoclave at a pressure of 9-15 atmospheres.
• To eliminate carbonate hardness of water (water softening).
• For the production of bleach.
• For the production of lime fertilizers and the neutralization of acidic soils.
• Caustification of sodium and potassium carbonate.
• Leather tanning.
• Obtaining other calcium compounds, neutralizing acidic solutions (including industrial wastewater), obtaining organic acids, etc.
• It is registered in the food industry as a food additive E526.
• Lime water is a clear solution of calcium hydroxide. It is used to detect carbon dioxide. When interacting with him, she becomes cloudy.
• Lime milk is a suspension (suspension) of calcium hydroxide in water, white and opaque. It is used for the production of sugar and the preparation of mixtures for combating plant diseases, whitewashing trunks.
• In dentistry - for disinfection of root canals of teeth.
• In electrical engineering - when arranging grounding centers in soils with high resistance, as an additive that reduces resistivity soil.
• Lime milk is used as the basis for the preparation of a classic fungicide - Bordeaux liquid.

- inorganic compound, calcium alkali. Its formula is Ca(OH) 2 . Since this substance has been known to mankind since ancient times, it has traditional names: slaked lime, lime water, milk of lime, fluff.

Fluff is a finely divided powder. Lime milk is an aqueous suspension of alkali, an opaque white liquid. Lime water is a clear aqueous solution of alkali, obtained after filtering milk of lime.

Slaked lime was named after the method of production: quicklime (calcium oxide) is poured with water (quenched).

Properties

Fine white crystalline powder, odorless. Very poorly soluble in water, completely insoluble in alcohol, easily soluble in dilute nitric and hydrochloric acids. It is fireproof and even prevents fire. When heated, it decomposes into water and calcium oxide.

Strong alkali. Enters into neutralization reactions with acids to form salts - carbonates. When interacting with metals, explosive and combustible hydrogen is released. Reacts with carbon oxides (IV) and (II), with salts.

The reaction of obtaining calcium hydroxide by the “quenching” method occurs with a large release of heat, the water begins to boil, the caustic solution is sprayed in different directions - this must be taken into account when working.

Precautionary measures

Contact with the skin of dry powder particles or drops of calcium hydroxide solution causes irritation, itching, chemical burns, ulcers, severe pain. Eye damage can cause vision loss. Ingestion of the substance causes a burn of the mucous throat, vomiting, bloody diarrhea, a sharp decrease in pressure, damage internal organs. Inhalation of dust particles can lead to swelling of the throat that makes it difficult to breathe.

Before calling " ambulance»:
- in case of poisoning, give the victim to drink milk or water;
- if the chemical gets into the eyes or on the skin, then the damage sites should be washed with plenty of water for at least a quarter of an hour;
- if the reagent is accidentally inhaled, then the victim must be taken out of the room and provided with fresh air.

Work with calcium hydroxide should be in well-ventilated areas using protective equipment: rubber gloves, goggles and respirators. Chemical experiments must be carried out in a fume hood.

Application

- In the construction industry, a chemical reagent is added to binding solutions, plaster, whitewash, gypsum mortars; made on its basis silicate brick and concrete; with its help prepare the soil before laying road surfaces. Whitewash wooden parts structures and fences gives them fire-resistant properties and protects them from decay.
— For neutralization of acid gases in metallurgy.
- For getting hard oils and additives to oils - in the oil refining industry.
- In the chemical industry - for the production of sodium and potassium alkalis, bleach ("bleach"), calcium stearate, organic acids.
- In analytical chemistry, lime water serves as an indicator of carbon dioxide (absorbing it, it becomes cloudy).
- With the help of calcium hydroxide, sewage and industrial water; neutralize the acids of the water entering the water supply systems in order to reduce its corrosive effect; remove carbonates from water (soften water).
- With the help of Ca (OH) 2, the hair is removed from the skins in the leather business.
— Food additive E526 in the food industry: acidity and viscosity regulator, hardener, preservative. It is used in the manufacture of juices and drinks, confectionery and flour products, marinades, salt, baby food. Applied in sugar production.
— In dentistry, milk of lime is used to disinfect root canals.
- For the treatment of acid burns - in medicine.
- AT agriculture: means for regulating the pH of soils; as a natural insecticide against ticks, fleas, beetles; for the preparation of the popular fungicide "Bordeaux liquid"; for whitewashing tree trunks from pests and sunburn; as an antimicrobial and antifungal drug for storing vegetables in warehouses; how mineral fertilizer.
- Calcium hydroxide reduces the electrical resistance of the soil, so it is treated with soil when installing grounding.
— The chemical reagent is used in the production of ebonite, brake linings, hair removal creams.

You can buy slaked lime at a good price, retail and wholesale, with delivery or pickup at the PrimeChemicalsGroup chemical store.

Calcium oxide (CaO) - quicklime or burnt lime- a white fire-resistant substance formed by crystals. It crystallizes in a cubic face-centered crystal lattice. Melting point - 2627 ° C, boiling point - 2850 ° C.

It is called burnt lime because of the method of its production - the burning of calcium carbonate. Roasting is carried out in high shaft kilns. Limestone and fuel are laid in layers in the furnace, and then kindled from below. When heated, calcium carbonate decomposes to form calcium oxide:

Since the concentrations of substances in solid phases are unchanged, the equilibrium constant of this equation can be expressed as follows: K=.

In this case, the gas concentration can be expressed using its partial pressure, that is, the equilibrium in the system is established at a certain pressure of carbon dioxide.

Substance dissociation pressure is the equilibrium partial pressure of a gas resulting from the dissociation of a substance.

To provoke the formation of a new portion of calcium, it is necessary to increase the temperature or remove part of the resulting CO2, and the partial pressure will decrease. By maintaining a constant lower partial pressure than the dissociation pressure, a continuous calcium production process can be achieved. To do this, when burning lime in kilns, make good ventilation.

Receipt:

1) in the interaction of simple substances: 2Ca + O2 = 2CaO;

2) during thermal decomposition of hydroxide and salts: 2Ca(NO3)2 = 2CaO + 4NO2? +O2?.

Chemical properties:

1) interacts with water: CaO + H2O = Ca(OH)2;

2) reacts with non-metal oxides: CaO + SO2 = CaSO3;

3) dissolves in acids, forming salts: CaO + 2HCl = CaCl2 + H2O.

Calcium hydroxide (Ca (OH) 2 - slaked lime, fluff)- a white crystalline substance, crystallizes in a hexagonal crystal lattice. It is a strong base, poorly soluble in water.

lime water- a saturated solution of calcium hydroxide, having an alkaline reaction. It becomes cloudy in air as a result of the absorption of carbon dioxide, forming calcium carbonate.

Receipt:

1) is formed when calcium and calcium oxide are dissolved in the input: CaO + H2O \u003d Ca (OH) 2 + 16 kcal;

2) when calcium salts interact with alkalis: Ca(NO3)2 + 2NaOH = Ca(OH)2 + 2NaNO3.

Chemical properties:

1) when heated to 580 ° C, it decomposes: Ca (OH) 2 \u003d CaO + H2O;

2) reacts with acids: Ca(OH)2 + 2HCl = CaCl2 + 2H2O.

58. Water hardness and ways to eliminate it

Since calcium is widely distributed in nature, its salts are found in large quantities in natural waters. Water containing magnesium and calcium salts is called hard water. If salts are present in water in small quantities or absent, then water is called soft. In hard water, soap does not foam well, since calcium and magnesium salts form insoluble compounds with it. It doesn't digest food well. When boiling, scale forms on the walls of steam boilers, which poorly conducts heat, causes an increase in fuel consumption and wear of the boiler walls. Hard water cannot be used in a number of technological processes (dyeing). Scale formation: Ca + 2HCO3 \u003d H2O + CO2 + CaCO3?.

The factors listed above indicate the need to remove calcium and magnesium salts from the water. The process of removing these salts is called water softening, is one of the phases of water treatment (water treatment).

Water treatment– water treatment used for various household and technological processes.

Water hardness is divided into:

1) carbonate hardness (temporary), which is caused by the presence of calcium and magnesium bicarbonates and is eliminated by boiling;

2) non-carbonate hardness (constant), which is caused by the presence of sulfites and chlorides of calcium and magnesium in water, which are not removed during boiling, therefore it is called constant hardness.

The formula is correct: Total hardness = Carbonate hardness + Non-carbonate hardness.

General hardness is eliminated by adding chemicals or using cation exchangers. To completely eliminate hardness, water is sometimes distilled.

When applied chemical method soluble calcium and magnesium salts are converted into insoluble carbonates:

A more modern process for removing water hardness - using cation exchangers.

Cation exchangers- complex substances (natural compounds of silicon and aluminum, high-molecular organic compounds), the general formula of which is Na2R, where R- complex acid residue.

When water passes through a layer of cation exchanger, Na ions (cations) are exchanged for Ca and Mg ions: Ca + Na2R = 2Na + CaR.

Ca ions from the solution pass into the cation exchanger, and Na ions pass from the cation exchanger into the solution. To restore the used cation exchanger, it must be washed with a solution table salt. In this case, the reverse process occurs: 2Na + 2Cl + CaR = Na2R + Ca + 2Cl.

calcium hydroxide(Ca (OH) 2, slaked lime or "fluff") - a chemical, a strong base. It is a white powder, poorly soluble in water.

Trivial names

• Slaked lime- since it is obtained by "extinguishing" (that is, interacting with water) "quicklime" (calcium oxide).
• milk of lime- a suspension (suspension) formed by mixing an excess of slaked lime with water. Looks like milk.
• lime water- a clear solution of calcium hydroxide obtained by filtering milk of lime.

Receipt

Obtained by the interaction of calcium oxide (quicklime) with water (the process is called "lime slaking"):

$\backslash mathsf(CaO\; +\; H\_2O\; \backslash rightarrow\; Ca(OH)\_2)$

Properties

Appearance - white powder, slightly soluble in water:

Calcium hydroxide is a fairly strong base, which is why an aqueous solution has an alkaline reaction. Solubility decreases with increasing temperature.

Like all bases, it reacts with acids; as an alkali - is a component of the neutralization reaction (see neutralization reaction) with the formation of the corresponding calcium salts:

$\backslash mathsf(Ca(OH)\_2\; +\; H\_2SO\_4\; \backslash rightarrow\; CaSO\_4\backslash downarrow\; +\; 2H\_2O)$

for the same reason, a solution of calcium hydroxide becomes cloudy in air, since calcium hydroxide, like other strong bases, reacts with carbon dioxide dissolved in water:

$\backslash mathsf(Ca(OH)\_2\; +\; CO\_2\; \backslash rightarrow\; CaCO\_3\backslash downarrow\; +\; H\_2O)$

If you continue the treatment with carbon dioxide, the precipitate will dissolve, since an acidic salt is formed - calcium bicarbonate, and when the solution is heated, the bicarbonate is again destroyed and calcium carbonate precipitates:

$\backslash mathsf(CaCO\_3\; +\; H\_2O\; +\; CO\_2\; \backslash rightleftarrows\; Ca(HCO\_3)\_2)$

Calcium hydroxide reacts with carbon monoxide at about 400 °C:

$\backslash mathsf(Ca(OH)\_2\; +\; CO\; \backslash xrightarrow(400^oC)\; CaCO\_3\; +\; H\_2)$

How does a strong base react with salts, but only if the reaction results in a precipitate:

$\backslash mathsf(Ca(OH)\_2\; +\; Na\_2SO\_3\; \backslash rightarrow\; CaSO\_3\backslash downarrow\; +\; 2NaOH)$

Application

• When whitewashing rooms.

• For the preparation of lime mortar. Lime has been used for building masonry since ancient times. The mixture is usually prepared in the following proportion: three to four parts of sand (by weight) are added to one part of a mixture of calcium hydroxide (slaked lime) with water. Water is released during the reaction. This is a negative factor, since in rooms built with lime mortar, high humidity remains for a long time. In this regard, and also due to a number of other advantages over calcium hydroxide, cement has practically replaced it as a binder for mortars.
• For the preparation of silicate concrete. The composition of silicate concrete is similar to the composition of lime mortar, however, its hardening occurs several orders of magnitude faster, since the mixture of calcium oxide and quartz sand is treated not with water, but with superheated (174.5-197.4 ° C) water vapor in an autoclave at a pressure of 9 -15 atmospheres.
• To eliminate carbonate hardness of water (water softening).
• For the production of bleach.
• For the production of lime fertilizers and the neutralization of acidic soils.
• Caustification of sodium and potassium carbonate.
• Obtaining other calcium compounds, neutralizing acidic solutions (including industrial wastewater), obtaining organic acids, etc.
• It is registered in the food industry as a food additive E526.
• Lime water is a clear solution of calcium hydroxide. It is used to detect carbon dioxide. When interacting with him, she becomes cloudy.
• Lime milk is a suspension (suspension) of calcium hydroxide in water, white and opaque. It is used for the production of sugar and the preparation of mixtures for the control of plant diseases, whitewashing of trunks.
• In dentistry - for disinfection of root canals of teeth.
• In electrical engineering - when arranging grounding centers in high-resistance soils, as an additive that reduces soil resistivity.
• Lime milk is used as the basis for the preparation of the classic fungicide Bordeaux liquid.

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Notes

Sources and literature

• Monastyrev A. Production of cement, lime. - M., 2007.
• Johann Stark, Bernd Wicht. Cement and lime / per. with him. - Kyiv, 2008.

Links

• Krupsky A. K., Mendeleev D. I.// Encyclopedic Dictionary of Brockhaus and Efron: in 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.

An excerpt characterizing calcium hydroxide

- Your will! - Sonya cried out with despair in her voice, looking at Natasha's dress, - your will, again long!
Natasha stepped aside to look around in the dressing-glass. The dress was long.
“By God, madam, nothing is long,” said Mavrusha, who was crawling along the floor after the young lady.
“Well, it’s a long time, so we’ll sweep it, we’ll sweep it in a minute,” said the resolute Dunyasha, taking out a needle from a handkerchief on her chest and again set to work on the floor.
At that moment, shyly, with quiet steps, the countess entered in her toque and velvet dress.
- Wow! my beauty! shouted the Count, “better than all of you!” He wanted to hug her, but she pulled away, blushing, so as not to cringe.
“Mom, more on the side of the current,” Natasha said. - I'll cut it, and rushed forward, and the girls who were hemming, who did not have time to rush after her, tore off a piece of smoke.
- My God! What is it? I don't blame her...
“Nothing, I notice, you won’t see anything,” said Dunyasha.
- Beauty, my darling! - said the nanny who came in from behind the door. - And Sonyushka, well, beauties! ...
At a quarter past eleven we finally got into the carriages and drove off. But still it was necessary to stop by the Tauride Garden.
Peronskaya was already ready. Despite her old age and ugliness, exactly the same thing happened with her as with the Rostovs, although not with such haste (for her it was a habitual thing), but her old, ugly body was also perfumed, washed, powdered, also carefully washed behind the ears. , and even, and just like at the Rostovs, the old maid enthusiastically admired the outfit of her mistress when she went into the living room in a yellow dress with a cipher. Peronskaya praised the Rostovs' toilets.
The Rostovs praised her taste and dress, and, taking care of their hair and dresses, at eleven o'clock they got into the carriages and drove off.

Natasha had not had a moment of freedom since the morning of that day, and had never had time to think about what lay ahead of her.
In the damp, cold air, in the cramped and incomplete darkness of the swaying carriage, for the first time she vividly imagined what awaited her there, at the ball, in the illuminated halls - music, flowers, dances, sovereign, all the brilliant youth of St. Petersburg. What awaited her was so wonderful that she did not even believe that it would be: it was so inconsistent with the impression of cold, crowdedness and darkness of the carriage. She understood everything that awaited her only when, having walked along the red cloth of the entrance, she entered the hallway, took off her fur coat and walked beside Sonya in front of her mother between the flowers along the illuminated stairs. Only then did she remember how she had to behave at the ball and tried to adopt that majestic manner that she considered necessary for a girl at the ball. But fortunately for her, she felt that her eyes were running wide: she could not see anything clearly, her pulse beat a hundred times a minute, and the blood began to beat at her heart. She could not adopt the manner that would have made her ridiculous, and she walked, dying from excitement and trying with all her might only to hide it. And this was the very manner that most of all went to her. In front and behind them, talking in the same low voice and also in ball gowns, the guests entered. The mirrors on the stairs reflected the ladies in white, blue, pink dresses, with diamonds and pearls on open hands and necks.
Natasha looked into the mirrors and in the reflection she could not distinguish herself from others. Everything was mixed in one brilliant procession. At the entrance to the first hall, a uniform rumble of voices, steps, greetings - deafened Natasha; the light and brilliance blinded her even more. The master and hostess, who had been standing by the front door and those who said the same words to those who came in: “charme de vous voir,” [in admiration that I see you] also met the Rostovs and Peronskaya.
Two girls in white dresses, with identical roses in their black hair, sat down in the same way, but the hostess involuntarily fixed her gaze longer on thin Natasha. She looked at her, and smiled at her alone, in addition to her master's smile. Looking at her, the hostess remembered, perhaps, her golden, irrevocable girlish time, and her first ball. The owner also looked after Natasha and asked the count, who is his daughter?
- Charmante! [Charming!] – he said, kissing the tips of his fingers.
Guests were standing in the hall, crowding at the front door, waiting for the sovereign. The Countess placed herself in the front row of this crowd. Natasha heard and felt that several voices asked about her and looked at her. She realized that those who paid attention to her liked her, and this observation calmed her somewhat.
“There are people like us, there are worse than us,” she thought.
Peronskaya called the countess the most significant persons who were at the ball.
“This is a Dutch envoy, you see, gray-haired,” Peronskaya said, pointing to an old man with silver gray curly, abundant hair, surrounded by ladies, whom he made laugh at something.
“And here she is, the Queen of Petersburg, Countess Bezukhaya,” she said, pointing to Helen entering.
- How good! Will not yield to Marya Antonovna; see how both young and old follow her. And good, and smart ... They say the prince ... crazy about her. But these two, although not good, are even more surrounded.
She pointed to a lady passing through the hall with a very ugly daughter.
“This is a millionaire bride,” said Peronskaya. And here are the grooms.
“This is Bezukhova’s brother, Anatole Kuragin,” she said, pointing to the handsome cavalry guard, who walked past them, looking somewhere from the height of his raised head through the ladies. - How good! is not it? They say they will marry him to this rich woman. .And your sousin, Drubetskoy, is also very entangled. They say millions. “Well, it’s the French envoy himself,” she answered about Caulaincourt when asked by the countess who it was. “Look like some kind of king. And yet the French are very, very nice. There is no mile for society. And here she is! No, everything is better than all our Marya Antonovna! And how simply dressed. Charm! “And this one, fat, with glasses, is a worldwide freemason,” said Peronskaya, pointing to Bezukhov. - With his wife, then put him next to him: then that jester of peas!

L.A. Kazeko, I.N. Fyodorova

Calcium hydroxide: yesterday, today, tomorrow

Calcium hydroxide Ca(OH) 2 is a strong base, slightly soluble in water. A saturated solution of calcium hydroxide is called lime water and is alkaline. In air, lime water quickly becomes cloudy due to the absorption of carbon dioxide and the formation of insoluble calcium carbonate.

Calcium hydroxide ("slaked lime") is a white, very fine powder, slightly soluble in water (1.19 g/l), the solubility can be increased by glycerin and sucrose. Hydrogen index (pH) - about 12.5. Calcium hydroxide is very sensitive to contact with atmospheric carbon dioxide, which transforms it into calcium carbonate. The drug should be stored in a sealed container away from light; it can be stored in a supersaturated aqueous solution (distilled water) in a sealed vial.

The basis for the use of calcium hydroxide in endodontics was information about the etiology and pathogenesis of pulpitis and apical periodontitis. The most common cause of these diseases is microorganisms in the root canal system of the tooth. Kakehashi et al. (1965), Moller et al. (1981) showed in experiments that periapical inflammation and destructive processes around the tooth apex develop only with the participation of root canal microorganisms. Favorable factors for the existence of microflora are the complex anatomy of root canals, the ability of bacteria to penetrate into dentinal tubules to a depth of 300 microns, anaerobic development conditions, the ability to feed on live or necrotic pulp, saliva proteins, and periodontal tissue fluid. Thus, the quality of endodontic treatment is determined by the quality of the disinfection of the root canal system.

Endodontic instrument breakage, root perforation, ledges, overfilling or underfilling are considered to be the main causes of endodontic failure. However, in most cases, these errors do not affect the outcome of endodontic treatment until co-infection occurs. Of course, gross errors prevent or make it impossible to complete intracanal procedures, but the chances of successful treatment increase significantly if the infectious-toxic contents of the root canals are effectively removed before filling.

Microorganisms remaining after instrumentation and irrigation multiply rapidly and repopulate root canals that remain empty between visits. The probability of reinfection depends on the quality of the root canal filling and the usefulness of the crown restoration. However, in all cases where bacteria remain in the root canal system, there is a risk further development peri-apical changes.

In untreated teeth with a primary intracanal infection, one or more species of bacteria usually occur, with no apparent predominance of facultative or anaerobic forms. With secondary infection with unsuccessful treatment, a mixed infection is present, gram-negative anaerobic strains dominate.

There are different opinions regarding the necessary number of stages in the treatment of patients with periapical problems. Thus, some authors substantiate the need to treat infected root canals in several visits, using temporary intracanal dressings, which allows you to gradually and controlledly achieve the destruction of microorganisms in them. Others propose to prevent the growth of the remaining microorganisms by depriving them of food and living space through a complete cleaning, disinfection and three-dimensional filling of the root canals during the first and only visit.

Anti-inflammatory and antibacterial activity of calcium hydroxide

Instrumental processing of the root canal reduces the number of microorganisms by 100-1000 times, but their complete absence is observed only in 20-30% of cases. Antibacterial irrigation with 0.5% sodium hypochlorite solution increases this effect to 40-60%. Achieve complete disinfection of infected root canals even after complete mechanical cleaning and irrigation with antiseptic solutions is very difficult in practice. Bacteria remaining in the root canal can be destroyed by temporarily filling the root canal with antimicrobial agents until the next visit. Such drugs should have a wide spectrum of antibacterial activity, be non-toxic and have physical and chemical properties allowing them to diffuse through the dentinal tubules and lateral canals of the root system of the tooth.

As a temporary intracanal agent in endodontics, calcium hydroxide is widely used, which decomposes into calcium ions and hydroxide ions in an aqueous solution. The main biological properties of hydroxide: bactericidal activity, anti-inflammatory properties, tissue solubility, hemostatic effect, inhibition of tooth tissue resorption, stimulation of bone regeneration processes.

Calcium hydroxide has bactericidal activity due to its high alkalinity and the release of hydroxide ions, highly active free radicals, in the aquatic environment. Their effect on bacterial cells is explained by the following mechanisms:

- damage to the cytoplasmic membrane of a bacterial cell, playing an important role in cell survival. It is the cell membrane that provides selective permeability and transport of substances, oxidative phosphorylation in aerobic strains, production of enzymes, and transport of molecules for the biosynthesis of DNA, cellular polymers, and membrane lipids. Hydroxide ions from calcium hydroxide cause lipid oxidation, which leads to the formation of free lipid radicals and the destruction of phospholipids, which are structural components of cell membranes. Lipid radicals initiate a chain reaction, resulting in the loss of unsaturated fatty acids and cell membranes are damaged;

- protein denaturation due to the fact that the alkaline environment of calcium hydroxide causes the destruction of ionic bonds that provide the structure of proteins. In an alkaline environment, the polypeptide chains of enzymes randomly combine and transform into disordered formations. These changes often lead to the loss of the biological activity of enzymes and disruption of cellular metabolism;

- microbial DNA damage with which hydroxide ions react, causing its splitting and leading to damage to genes due to impaired DNA replication. In addition, free radicals themselves can cause destructive mutations.

The bactericidal action of calcium hydroxide depends on the concentration of hydroxide ions, which is high only in the zone immediate drug contact. When calcium hydroxide diffuses deeper into the dentin, the concentration of hydroxide ions decreases due to the action of buffer systems (bicarbonate or phosphate), acids, proteins and CO 2, the antibacterial activity of the drug may decrease or slow down. Neutralization of high pH calcium hydroxide can also occur as a result of coronal microleakage, leakage of tissue fluid through the root apex, the presence of necrotic masses in the canal, and the production of acidic substances by microbes. In the root canal, the pH is 12-12.5, in the adjacent dentin, where there is close contact with the hydroxide, the pH varies from 8 to 11, and in the depth of the dentin, the pH values ​​are 7-9. The highest pH values ​​were obtained between 7 and 14 days after the introduction of an aqueous suspension of calcium hydroxide into the canal.

Microorganisms differ in resistance to changes in pH, most of them multiply at pH 6-9. Some strains can survive at pH 8-9 and are usually the cause of secondary infection. Enterococci ( E. faecalis), resistant to pH 9-11, are not normally found in root canals or are present in small amounts in untreated teeth. They play an important role in endodontic failure and are often (32-38% of cases) present in teeth with apical periodontitis.

One of the important components of the effective disinfectant action of the drug in endodontics is its ability to dissolve and penetrate into the root canal system. Alkalis (NaOH and KOH) are highly soluble and can diffuse deeper than calcium hydroxide. These substances have a pronounced antibacterial activity. But high solubility and active diffusion enhance the cytotoxic effect on the cells of the body. Due to their high cytotoxicity, they are not used in endodontics. Calcium hydroxide is biocompatible, because due to its low water solubility and diffusion, a slow increase in pH occurs, which is necessary for the destruction of bacteria localized in the dentinal tubules and other hard-to-reach anatomical formations. Because of these features, calcium hydroxide is classified as an effective but slow-acting antiseptic.

The time required for optimal disinfection of the root canal with calcium hydroxide has not yet been precisely determined. Clinical studies give conflicting results. Cwikla et al. (1998) found that in 90% of cases after 3 months of hydroxide use bacterial growth not noted. In a study by Bystrom et al. (1999) calcium hydroxide effectively destroyed microorganisms in 4 weeks of application. Reit and Dahlen used the drug for 2 weeks - the infection persisted in 26% of the root canals. In an experiment by Basrani et al. after one week of calcium hydroxide application, bacteria remained in the canals in 27% of cases.

Mechanisms of resistance of microorganisms to the action of intracanal disinfectants

Factors determining the resistance of microorganisms to the action of disinfectants, the ability to survive after the use of intracanal (temporary and permanent) filling materials:

Neutralization of the drug with buffer systems or products of bacterial cells;

Insufficient disinfectant exposure in the root canal to kill microorganisms;

Low antibacterial efficacy of the drug in relation to microorganisms of the root canal;

The effect of the drug on microorganisms is limited for anatomical reasons;

The ability of microorganisms to change their properties (genes) after a change in the environment.

An important mechanism of bacterial resistance is their existence in the form of a biofilm. A biofilm is a microbiological population (bacterial ecosystem) associated with an organic or inorganic substrate, surrounded by bacterial waste products. Various strains of microorganisms collected in a biofilm are capable of organizing associations for joint survival, have increased resistance to antimicrobial agents and protective mechanisms. Over 95% of naturally occurring bacteria are found in biofilms.

Killing bacteria in biofilms is more difficult than in planktonic suspensions unless the disinfectant has tissue-dissolving properties. When re-treating infected teeth, calcium hydroxide cannot 100% kill resistant bacteria ( E. faecalis) that are able to multiply between dental visits. Of great importance is the full preparation, cleansing the canal from all microorganisms on the first visit (using abundant washings with sodium hypochlorite). Prevention of re-infection of the root canal is achieved by complete sealing of the tooth crown with high-quality temporary fillings.

Effect of solvents on the antibacterial activity of calcium hydroxide

Substances used as a medium for calcium hydroxide have different water solubility. The optimal environment should not change the pH of the calcium hydroxide. Many solvents do not have antibacterial activity, such as distilled water, saline, and glycerin. Phenolic derivatives such as paramonochlorophenol, camphor phenol have strong antibacterial properties and can be used as a hydroxide medium. Calcium hydroxide with paramonochlorophenol has a large radius of action, destroys bacteria in areas remote from the places where the paste is applied.

Siqueira et al. found that calcium hydroxide in saline does not destroy E. faecalis and F. nucleatum in the dentinal tubules within a week of application. And the calcium hydroxide paste with paramonochlorophenol and glycerin effectively destroyed bacteria in the tubules, including E. faecalis, for 24 hours of application. That is, paramonochlorophenol enhances the antibacterial activity of calcium hydroxide.

The results of a study of disinfection of dentinal tubules using three preparations of calcium hydroxide (Ca(OH) 2 in distilled water, Ca(OH) 2 with potassium iodide and Ca(OH) 2 with iodoform (Metapex)) showed that Ca(OH) 2 in pure form less effective at killing microbes in dentinal tubules. Growth of some microorganisms was observed in channels with calcium hydroxide ( E. faecalis, C. albicans) to a depth of 250 µm for 7 days. This is explained by the fact that Ca(OH) 2 has a low degree of permeability and its high pH (12) is partially neutralized by dentine buffer systems. Ca(OH) 2 with potassium iodide is more effective than pure hydroxide. But Metapex paste (Ca (OH) 2 with iodoform) turned out to be the most effective: except for E. faecalis it neutralized other microbes and penetrated into the tubules to a depth of more than 300 microns (Cwikla et al.).

Abdullah et al. (2005) studied the effectiveness of various intracanal agents (calcium hydroxide, 0.2% chlorhexidine, 17% EDTA, 10% povidone-iodine, 3% sodium hypochlorite) against strains E. faecalis contained in bacterial biofilms. In the biofilm E. faecalis in 100% of cases it was destroyed by 3% sodium hypochlorite after 2 minutes and 10% povidone-iodine after 30 minutes. Calcium hydroxide partially eliminated these bacteria.

Since some microorganisms, especially E. faecalis, resistant to calcium hydroxide, it is justified to combine it with other antimicrobial agents that increase its activity, for example, with idoform, camphor paramonochlorophenol. Having a low surface tension, fat-soluble phenols penetrate deep into the tissues of the tooth.

In endodontics, chlorhexidine is recommended for widespread use as an irrigant and intracanal dressing, effective against many bacteria that determine endodontic infection. The chlorhexidine molecule, interacting with the phosphate groups of the bacterial cell wall, penetrates into the bacterium and has an intracellular toxic effect.

Calcium hydroxide in combination with 2% chlorhexidine gel has increased antimicrobial activity, especially against resistant microorganisms. Chlorhexidine in the form of a gel has such positive properties as low toxicity to periodontal tissues, viscosity, which allows you to keep the active substances in constant contact with the walls of the root canal and dentinal tubules, and water solubility. The combination of chlorhexidine gel and calcium hydroxide was found to be highly effective against E. faecalis in infected root dentin. High pH (12.8) in the first two days increases the penetrating power of the preparations.

Effective against E. faecalis after 1, 2, 7 and 15 days of application of chlorhexidine 2% gel. According to Gomes et al., 2% chlorhexidine gel has greater antibacterial activity against E. faecalis than calcium hydroxide, but this ability is lost when used for a long time. This is confirmed by other studies, even when using chlorhexidine in the form of a solution or gel at concentrations of 0.05%, 0.2% and 0.5%. The combination of chlorhexidine and calcium hydroxide 100% inhibits growth E. faecalis after 1-2 days of contact .

Calcium hydroxide as a physical barrier

Secondary intracanal infections are caused by microorganisms that enter the canal during treatment, between visits, or after dental treatment. The main sources of secondary infection are dental deposits on the teeth, caries, infected endodontic instruments. The causes of infection between visits may be microleakage through a temporary filling due to its destruction; tooth fracture; delay in replacing a temporary filling with a permanent one when the tooth is left open for drainage. Secondary infection allows the emergence of new, virulent microorganisms that cause acute periapical inflammation.

Intracanal preparations destroy the bacteria remaining after chemomechanical treatment of the canal, and are also used as a physicochemical barrier that prevents the reproduction of microorganisms and reduces the risk of reinfection from the oral cavity. Reinfection of the canal is possible due to the fact that the drug dissolves with saliva, saliva seeps into the space between the drug and the walls of the canal. However, if the drug has an antibacterial effect, it will first be neutralized and only then bacterial invasion.

To prevent reinfection, the sealing ability of calcium hydroxide is more important than its chemical activity, since it has low water solubility, slowly dissolves in saliva, and remains in the canal for long term, delaying the progress of bacteria towards the apex. Despite the use of solvents, calcium hydroxide acts as an effective physical barrier, destroying some of the remaining bacteria and preventing their growth, limiting the space for reproduction.

As a reliable insulating barrier for various endodontic problems (perforation of the bottom of the cavity, the root of the tooth, root resorption, etc.), a new class of materials has been proposed - the mineral trioxide aggregate (ProRoot MTA). The basis of MTA is calcium compounds.

Effect of calcium hydroxide on the quality of permanent root canal filling

Before permanent obturation, calcium hydroxide is removed from the root canal using sodium hypochlorite, saline, and endodontic instruments.

Lambrianidis et al. (1999) investigated the possibility of removing some calcium hydroxide preparations from root canals: Calxyl (42% calcium hydroxide) and an aqueous suspension (95% calcium hydroxide). The percentage of calcium hydroxide did not affect the effectiveness of cleaning the walls of the root canal. Paste residue can affect the mechanical properties of the sealer and impair apical sealing. There is an opinion about the impossibility of completely removing the paste from the walls of the root canal.

Residual calcium hydroxide adversely affects the hardening of zinc-oxide-eugenol sealers, as it interacts with the eugenol of the paste to form calcium eugenolate. In the clinic, this can be manifested by blocking the progress of the gutta-percha pin for the entire working length of the canal. If calcium hydroxide residues are not completely removed, they compact apically or in canal recesses, which mechanically interferes with effective canal filling, impedes apical sealing, and may affect the outcome of endodontic treatment. The calcium hydroxide apical plug is preferably removed.

Calcium hydroxide is effectively removed from the canal walls hand tools with rinsing with sodium hypochlorite and 17% EDTA. Difficulties in cleaning root canals after temporary filling are due to paste-forming substances and fillers, and not calcium hydroxide. Calcium hydroxide preparations for water based(especially upcoming ex tempore) are completely devoid of these shortcomings. Moreover, sealers based on calcium hydroxide should be considered as materials of choice for permanent obturation of root canals after their temporary filling with calcium hydroxide.

Indications for temporary filling of root canals

The use of non-hardening pastes based on calcium hydroxide is indicated as a temporary intracanal agent for the treatment of acute forms of apical periodontitis, destructive forms of chronic apical periodontitis, cystogranulomas, radicular cysts, progressive root resorption, teeth with an unformed root tip in pediatric practice.

How to use calcium hydroxide:

1) calcium hydroxide in the form of a powder is kneaded to a paste-like state in distilled water or glycerin;

2) the paste is introduced into the thoroughly instrumentally and medically treated root canal using a canal filler;

3) to ensure adherence to the root dentin, the paste is compacted with a paper pin, closed with an airtight bandage.

Features of the use of calcium hydroxide in different conditions of the apical periodontium. At acute forms of apical periodontitis temporary filling with calcium hydroxide aims to have an anti-inflammatory and antimicrobial effect. Calcium hydroxide is introduced into the root canal loosely, without compaction, first for a day, then again for 1-3-7 days, depending on the clinical picture. In acute periapical abscess, a periostotomy is performed according to indications.

At chronic destructive processes in the apical periodontium the goal is to have not only anti-inflammatory and antimicrobial effects, but also to stimulate reparative processes in the bone. Calcium hydroxide is injected into the root canal with a seal against the walls, for 3-8 weeks, the time for updating the material depends on the clinical picture. Treatment is designed for a period of 0.5 to 1 year, its duration depends on the degree of infection of the root canal, the resistance of the organism, the age of the patient, and the motivation for cooperation. Restoration of the zone of destruction of the apical periodontium continues after permanent filling of the root canal with a calcium hydroxide-based sealer for 3-5 years.

Filling teeth with apical periodontitis on the first visit does not lead to the elimination of acute inflammation. Resorption of cement and dentin is maintained even 9 months after filling. In this case, in 80% of cases, a chronic process is formed. If the canal was filled with calcium hydroxide after drainage for 7 days before obturation, the periapical defect was replaced with new bone tissue, although inflammation progressed in 18.8% of cases.

Acute reactions with hermetic closure of the coronal cavity persisted only in 5% of the teeth in the presence of a periapical abscess. Temporary dressing and airtight filling prevent re-infection of the canal and increase the success of conservative treatment to 61.1% (compared to 22.2% without an antibacterial dressing) .

When calcium hydroxide is used as a temporary dressing, complete bone regeneration of 82% of even large periapical lesions is observed after 3 years. In 18% of cases, bone defects persisted or slightly decreased in size. The most active reduction in the size of the defect was noted in the first year of treatment. The first positive signs were found on radiographs 12 weeks after the introduction of the Ca(OH) 2 dressing, and on digital radiographs already after 3-6 weeks.

"Yesterday" calcium hydroxide. Information materials, scientific articles about calcium hydroxide preparations 20-30 years ago convinced (and convinced) us of its unique abilities: calcium hydroxide-based pastes have a strongly alkaline reaction, unlimited bactericidal action, and the ability to stimulate reparative processes in bone tissue.

The use of calcium hydroxide in endodontics has expanded indications for conservative treatment destructive processes in the apical periodontium. It became possible to fully preserve teeth that were previously considered hopeless. "The biocompatibility of calcium hydroxide has made it a multivalent preparation adapted to almost all clinical situations encountered in endodontics". Recommendations appeared on the obligatory stage of temporary filling of root canals in endodontic treatment: "It's useful!".

“Today” has accumulated a baggage of clinical observations that confirm the very high efficiency calcium hydroxide (Fig. 1-4; from the authors' own observations). High-quality performance of all stages of endodontic treatment in combination with temporary filling of root canals with calcium hydroxide allows us to recognize this method of treatment as organ-preserving.

But today, in the dental literature, the issues of the breadth of the antibacterial action of calcium hydroxide preparations, the targeted effect on the most resistant and aggressive strains of microorganisms that cause the development of periapical foci of destruction, re-infection and the development of exacerbations are being discussed.

So, A.A. Antanyan writes: "Multilateral analysis of scientific literature recent years(2003-2006) showed that calcium hydroxide has many disadvantages that cast doubt on its routine and mass use in endodontics. In modern endodontics essential has a full preparation, cleansing the canal from infection on the first visit (using abundant washings with sodium hypochlorite) and preventing re-infection of the canal by fully sealing the tooth crown using high-quality temporary fillings. Therefore, in many clinical situations, additional disinfection with calcium hydroxide is not necessary.”

"Tomorrow" calcium hydroxide. The experience of clinical use of calcium hydroxide shows that the need for its use in endodontics cannot be justified only by its antimicrobial efficacy, which in past years was given the main responsibility for the result of treatment. With the advent of sensitive methods of microbiological research, with the expansion of the range of highly effective means for irrigation of root canals, the possibilities and properties of calcium hydroxide as a material for temporary filling can be rethought and overestimated. But not discounted! In difficult clinical situations for endodontic treatment and retreatment of teeth, thanks to calcium hydroxide preparations, it is possible to save the patient's teeth and health.

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