Calcium oxide (CaO) – quicklime or burnt lime– a white, fire-resistant substance formed by crystals. Crystallizes in a face-centered cubic crystal lattice. Melting point – 2627 °C, boiling point – 2850 °C.
It is called burnt lime because of the method of its preparation - burning calcium carbonate. Firing is carried out in high shaft kilns. Layers of limestone and fuel are placed in the oven and then lit 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, equilibrium in the system is established at a certain pressure of carbon dioxide.
Substance dissociation pressure– 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 partial pressure lower than the dissociation pressure, a continuous calcium production process can be achieved. To do this, when burning lime in kilns, good ventilation is provided.
Receipt:
1) during 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. In air it becomes cloudy as a result of the absorption of carbon dioxide, forming calcium carbonate.
Receipt:
1) is formed by the dissolution of calcium and calcium oxide in the input: CaO + H2O = Ca(OH)2 + 16 kcal;
2) during the interaction of calcium salts with alkalis: Ca(NO3)2 + 2NaOH = Ca(OH)2 + 2NaNO3.
Chemical properties:
1) when heated to 580 °C, it decomposes: Ca(OH)2 = CaO + H2O;
2) reacts with acids: Ca(OH)2 + 2HCl = CaCl2 + 2H2O.
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 the water is called soft. In hard water, soap does not foam well, since calcium and magnesium salts form insoluble compounds with it. It does not cook 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 when carrying out a number of technological processes (dying). Scale formation: Ca + 2HCO3 = H2O + CO2 + CaCO3?.
The factors listed above indicate the need to remove calcium and magnesium salts from 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 calcium and magnesium sulfites and chlorides in water, which are not removed by boiling, which is why it is called constant hardness.
The correct formula is: 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 using the chemical method, soluble calcium and magnesium salts are converted into insoluble carbonates:
A more modern process for eliminating 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 acidic residue.
When water is passed through a layer of cation exchange resin, Na ions (cations) are exchanged for Ca and Mg ions: Ca + Na2R = 2Na + CaR.
Ca ions pass from the solution 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 of table salt. In this case, the reverse process occurs: 2Na + 2Cl + CaR = Na2R + Ca + 2Cl.
Calcium hydroxide – chemical substance having a strong foundation. What are its features and chemical properties Let's look at it in this article.
Crystalline calcium hydroxide is a powder white, which decomposes when heated, but is practically insoluble in water. The formula of calcium hydroxide is Ca(OH) 2. In ionic form, the equation for the formation of calcium hydroxide looks like this:
Rice. 1. Equation for the formation of calcium hydroxide.
Calcium hydroxide has other names: slaked lime, milk of lime, lime water
The molar mass of calcium hydroxide is 74.09 g/mol. This means that 74.09 g/mol of calcium hydroxide contains 6.02*10^23 atoms or molecules of this substance.
Calcium hydroxide is used for whitewashing in construction, disinfection of tree trunks, in the sugar industry, for tanning leather, and for producing bleach. A dough-like mixture of slaked lime with cement and sand is used in construction.
Rice. 2. Calcium hydroxide.
Calcium hydroxide, like all bases, reacts with acids:
Ca(OH) 2 (calcium hydroxide) + H 2 SO 4 (sulfuric acid) = CaSo 4 (salt - calcium sulfate) + 2H 2 O (water).
Calcium hydroxide is also capable of forming compounds with carbon dioxide. A solution of this substance in air becomes cloudy, since calcium hydroxide, like other strong bases, reacts with carbon dioxide dissolved in water:
Ca(OH) 2 +CO 2 (calcium hydroxide)=CaCO 3 (calcium carbonate)+H 2 O (water)
When heated to 400 degrees, calcium hydroxide reacts with carbon monoxide:
Ca(OH) 2 (calcium hydroxide)+CO (carbon monoxide)=CaCO 3 (calcium carbonate)+H 2 (hydrogen).
Calcium hydroxide can react with salts, resulting in the formation of a precipitate:
Ca(OH) 2 (calcium hydroxide) + Na 2 SO 3 (sodium sulfite) = CaSO 3 (calcium sulfite) + 2NaOH (sodium hydroxide).
At a temperature of 520-580 degrees, calcium hydroxide is susceptible to decomposition. As a result, calcium oxide and water are formed:
Rice. 3. Slaked lime.
Ca(OH) 2 (calcium hydroxide) = CaO (calcium oxide) + H 2 O (water).
Calcium hydroxide is produced by a chemical reaction of calcium oxide (quicklime) with water. This process is called "lime slaking". The equation for the lime slaking reaction is as follows:
CaO (calcium oxide) + H 2 O (water) = Ca (OH) 2 (calcium hydroxide).
Calcium hydroxide is a strong base, slightly soluble in water. Like anyone chemical element It has a number of properties - it is able to react with carbon dioxide, salts, and also decomposes at high temperatures. Calcium hydroxide is used in construction and industry.
Calcium hydroxide(Ca(OH) 2, slaked lime or “fluff”) is a chemical substance, a strong base. It is a white powder, poorly soluble in water.
Obtained by reacting calcium oxide (quicklime) with water (the process is called “slaking lime”):
Appearance: white powder, slightly soluble in water:
Calcium hydroxide is a fairly strong base, which is why the aqueous solution is alkaline. 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 to treat with carbon dioxide, the precipitate that has formed will dissolve, as an acidic salt is formed - calcium bicarbonate, and when the solution is heated, the bicarbonate is again destroyed and a precipitate of calcium carbonate precipitates:
Calcium hydroxide reacts with carbon monoxide at a temperature of about 400 °C:
How a strong base reacts with salts, but only if the reaction results in a precipitate:
Since the morning of that day, Natasha had not had a minute of freedom, and not once 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, dancing, the sovereign, all the brilliant youth of St. Petersburg. What awaited her was so beautiful that she did not even believe that it would happen: it was so incongruous with the impression of the cold, crampedness 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 entryway, took off her fur coat and walked next to 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 the majestic manner that she considered necessary for a girl at the ball. But fortunately for her, she felt that her eyes were running wild: she saw nothing clearly, her pulse beat a hundred times a minute, and the blood began to pound at her heart. She could not accept the manner that would make her funny, and she walked, frozen with excitement and trying with all her might to hide it. And this was the very manner that suited her most of all. In front and behind them, talking just as quietly and also in ball gowns, guests entered. The mirrors along the stairs reflected ladies in white, blue, pink dresses, with diamonds and pearls on their open arms and necks.
Natasha looked in the mirrors and in the reflection could not distinguish herself from others. Everything was mixed into one brilliant procession. Upon entering the first hall, the uniform roar of voices, footsteps, and greetings deafened Natasha; the light and shine blinded her even more. The owner and hostess, who had already been standing at the front door for half an hour and said the same words to those entering: “charme de vous voir,” [in admiration that I see you], also greeted 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 especially at her, in addition to her masterful smile. Looking at her, the hostess remembered, perhaps, both her golden, irrevocable girlhood time and her first ball. The owner also followed Natasha with his eyes and asked the count who was his daughter?
- Charmante! [Charming!] - he said, kissing the tips of his fingers.
Guests stood 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 just like us, and there are people worse than us,” she thought.
Peronskaya named the countess the most significant people who were at the ball.
“This is the Dutch envoy, you see, gray-haired,” said Peronskaya, pointing to an old man with silver gray curly, abundant hair, surrounded by ladies, whom he made laugh for some reason.
“And here she is, the queen of St. Petersburg, Countess Bezukhaya,” she said, pointing to Helen as she entered.
- How good! Will not yield to Marya Antonovna; Look how both young and old flock to her. She is both good and smart... They say the prince... is 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, Anatol Kuragin,” she said, pointing to a handsome cavalry guard who walked past them, looking somewhere from the height of his raised head across the ladies. - How good! isn't it? They say they will marry him to this rich woman. .And your sauce, Drubetskoy, is also very confusing. They say millions. “Why, it’s the French envoy himself,” she answered about Caulaincourt when the countess asked who it was. - Look like some kind of king. But still, the French are nice, very nice. No miles for society. And here she is! No, our Marya Antonovna is the best! And how simply dressed. Lovely! “And this fat one, with glasses, is a world-class pharmacist,” said Peronskaya, pointing to Bezukhov. “Put him next to your wife: he’s a fool!”
Instructions
Possessing all the characteristic properties of bases, hydroxide easily reacts with acids and acid oxides. Being a fairly strong base, it can also react with salts, but only if the result is a slightly soluble product, for example:
Ca(OH)2 + K2SO3 = 2KOH + CaSO3 (calcium, precipitates).
In the laboratory, calcium hydroxide can be obtained in several other ways. For example, since calcium is a highly alkaline earth metal, it readily combines with water, displacing hydrogen:
Ca + 2H2O = Ca(OH)2 + H2 This reaction proceeds, of course, not as violently as in the case of alkalies of the first group.
You can also get calcium hydroxide by mixing a solution of any of its salts with a strong alkali (for example, sodium or potassium). They more easily displace calcium, taking its place and, accordingly, giving it “their” hydroxide ions. For example:
2KOH + CaSO4 = Ca(OH)2 + K2SO4
2NaOH + CaCl2 = 2NaCl + Ca(OH)2
Calcium hydroxide is widely used, mainly in repair and construction work, as a component of plaster, cement, mortars, as well as in the production of fertilizers and bleach. Used in the leather industry, as a tanning agent, in the pulp and paper industry, etc. It is well known to gardeners as a component of “Bordeaux mixture”, used in the fight against various plant pests. Used as food additives.
Oxide calcium- This is ordinary quicklime. But, despite such a simple nature, this substance is very widely used in economic activity. From construction, as a base for lime cement, to cooking, as a food additive E-529, oxide calcium finds application. Both in industrial and at home conditions you can obtain oxide calcium from carbonate calcium thermal decomposition reaction.
You will need
Instructions
Prepare the crucible for annealing the carbonate. Mount it firmly on fireproof stands or special fixtures. The crucible must be firmly installed and, if possible, secured.
Grind the carbonate calcium. Grinding must be done for better heat transfer inside. It is not necessary to grind limestone or chalk into dust. It is enough to produce coarse, heterogeneous grinding.
Fill the annealing crucible with ground carbonate calcium. Do not fill the crucible completely, since when carbon dioxide is released, some of the substance may be thrown out. Fill the crucible about a third full or less.
Start heating the crucible. Install and secure it well. Heat the crucible smoothly from different sides to avoid its destruction due to uneven thermal expansion. Continue heating the crucible on the gas burner. After some time, the thermal decomposition of carbonate will begin calcium.
Wait for the thermal decomposition to complete. During the reaction, the upper layers of the substance in the crucible may not warm up well. They can be mixed several times with a steel spatula.
Video on the topic
Please note
Be careful when working with a gas burner and a heated crucible. During the reaction, the crucible will be heated to temperatures above 1200 degrees Celsius.
Useful advice
Instead of trying to produce large quantities of calcium oxide yourself (for example, for the subsequent production of lime cement), it is better to buy the finished product on specialized trading platforms.
Sources:
Hydroxides are compounds of substances and hydroxyl groups OH. They are used in many areas of industry and everyday life. The electrolyte in alkaline batteries and the slaked lime used to paint tree trunks in the spring are hydroxides. Despite the apparent complexity of chemical terms and formulas, you can obtain hydroxide at home. It's quite simple and quite safe. The easiest way to obtain sodium hydroxide.
You will need
Instructions
Prepare the dishes for baking. It is better if it is a refractory glass dish or a ceramic crucible. You can also use steel containers. As a last resort, a regular spoon or an empty tin can will do. A holder is required to prevent hand burns when using it.
Carry out thermal decomposition of sodium bicarbonate. Place some sodium bicarbonate in a baking dish. Heat the dishes on a gas burner. You can heat it over medium heat using a household gas stove - it will be sufficient. The progress of the reaction can be judged by some “boiling” of the powder in the container due to the rapid release of carbon dioxide. Wait for the reaction to complete. Sodium oxide has formed in the dishes.
Cool the sodium oxide container to room temperature. Simply place the cookware on a fireproof rack or turn off the gas burner. Wait until it cools down completely.
Obtain sodium in the form of an aqueous solution. While stirring constantly, add sodium oxide in small portions to the water. Stir with a glass or steel rod or spatula.
Please note
Do not use test tubes to calcinate sodium bicarbonate. Due to the rapid passage of the thermal decomposition reaction, part of the substance can be ejected from the test tube under the pressure of the resulting carbon dioxide. Wear gloves and safety glasses. Avoid contact of sodium oxide with your skin. It will react with skin moisture to form hydroxide. Possible burns. Avoid getting sodium hydroxide solution on your skin for the same reason.
Useful advice
In order to check the alkaline reaction of the resulting sodium hydroxide solution, you can use a phenolphthalein solution. Phenolphthalein tablets are freely sold in pharmacies. Dilute the tablet in a small amount ethyl alcohol, and you will receive an indicator of the alkaline state of the environment.
Sources:
Hydrogen is the first element of the periodic table. It is a colorless gas. Widely used in the chemical and food industries (hydrogenation of various compounds), and also as a component of rocket fuel. Hydrogen It is very promising as a fuel for cars, since it does not pollute the environment when burned.
You will need
Instructions
The test tube where the hydrogen is collected must be absolutely intact, even the slightest crack is unacceptable! Before conducting an experiment with a smoldering splinter, it is better to wrap the test tube with a thick cloth as a precaution.
Pour some water into a flat-bottomed flask, put a small piece in it and immediately close the stopper tightly. The curved “elbow” of the tube passing through the stopper should be in a “hydraulic seal” container with water, and the tip of the tube should protrude slightly above the surface of the water. Quickly cover this tip with an upside down test tube to collect the hydrogen (the edge of the test tube should be in the water).
To demonstrate that it is hydrogen that has been obtained, remove the stopper and hold a smoldering splinter to the edge of the test tube. A characteristic pop will be heard.
Video on the topic
Please note
Although calcium is less active than alkali metals, caution is also required when working with it. Store it in a glass container under a layer of kerosene or liquid paraffin and remove it immediately before the start of the experiment (best of all - with long tweezers). During the reaction, an alkali is formed, which is a caustic substance, beware of burns! If possible, use rubber gloves.
When mixed with air or oxygen, hydrogen is explosive.
Aluminum hydroxides in fine powder form
There is a method for obtaining aluminum in the form of a fine powder. The aluminum precursor is mixed with a substance that is used as a seed material for the formation of hydroxide crystals. The mixture is then calcined in an atmosphere containing hydrogen chloride. This method is inconvenient due to the need for filtration; in order to obtain a fine powder, grinding and extrusion must be carried out.
Preparation of hydroxide from aluminum metal
It is more convenient to obtain hydroxides by reacting aluminum metal with water, but the reaction slows down due to the formation of an oxide film on the metal surface. In order to avoid this, various additives are used. To activate the process of interaction of aluminum, as well as its compounds with hydrogen, I use an installation that includes a stirrer, a separator, a heat exchanger and a filter for separating the suspension. To form hydroxides, it is necessary to add substances that promote the interaction of the reactants, for example, organic amines in catalytic quantities. In this case, it is not possible to obtain pure hydroxide.
Preparation in boehmite form
Sometimes aluminum hydroxide is obtained in the form of boehmite. To do this, use an installation with a reactor and a stirrer, in which there is a hole for introducing powdered aluminum and water; a settling tank and a condenser for receiving steam gas are also needed. The reaction is carried out in an autoclave; water and fine aluminum particles are pre-loaded into it, after which the mixture is heated to 250-370°C. Then, at the same temperature, the mixture begins to be stirred under pressure sufficient to ensure that the water remains in the liquid phase. Stirring is stopped when all the aluminum has reacted, the autoclave is cooled, and then the resulting aluminum hydroxide is separated.
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, limewater 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), solubility can be increased by glycerin and sucrose. Hydrogen index (pH) is 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 sealed packaging away from light; it can be stored in a supersaturated aqueous solution (distilled water) in an airtight bottle.
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 apex of the tooth develop only with the participation of microorganisms root canal. Favorable factors for the existence of microflora are the complex anatomy of the root canals, the ability of bacteria to penetrate into the dentinal tubules to a depth of 300 microns, anaerobic development conditions, the ability to feed from living or necrotic pulp, salivary proteins, and periodontal tissue fluid. Thus, the quality of endodontic treatment is determined by the quality of disinfection of the root canal system.
Endodontic instrument breakage, root perforation, ledges, and 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 a concomitant 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 and toxic contents of the root canals are effectively removed before filling.
Microorganisms that survive instrumentation and irrigation quickly multiply and repopulate root canals that remain empty between visits. The likelihood of reinfection depends on the quality of root canal filling and the usefulness of the coronal 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 primary intracanal infection, one or more species of bacteria are usually present, with no apparent predominance of facultative or anaerobic forms. In case of secondary infection if treatment fails, a mixed infection is present, with gram-negative anaerobic strains dominating.
There are different opinions regarding the required number of treatment steps for patients with periapical problems. Thus, some authors justify the need to treat infected root canals in several visits, using temporary intracanal dressings, which allows for the gradual and controlled destruction of microorganisms in them. Others suggest preventing the growth of remaining microorganisms by depriving them of nutrition and living space by fully debridement, disinfection, and 3D filling of the root canals during the first and only visit.
Anti-inflammatory and antibacterial activity of calcium hydroxide
Instrumental treatment 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 antiseptic solutions in practice it is very difficult. Bacteria remaining in the root canal can be destroyed using temporary root canal filling. antimicrobial agents until next visit. Such drugs must have wide range antibacterial action, be non-toxic and have physical and chemical properties allowing them to diffuse through the dentinal tubules and lateral canals of the tooth root system.
Calcium hydroxide is widely used as a temporary intracanal agent in endodontics, 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 aqueous environment. Their effect on bacterial cells is explained by the following mechanisms:
- damage to the cytoplasmic membrane of the bacterial cell, playing an important role in the preservation of the cell. 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, as a result of which unsaturated fatty acids are lost 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 are chaotically combined and transformed into disordered formations. These changes often lead to loss of biological enzyme activity and disruption of cellular metabolism;
- damage to microbial DNA, with which hydroxide ions react, causing its splitting and leading to damage to genes due to disruption of DNA replication. Besides this, free radicals can independently cause destructive mutations.
The bactericidal effect of calcium hydroxide depends on the concentration of hydroxide ions, which is high only in the zone direct contact with the drug. When calcium hydroxide diffuses deeper into 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 be reduced or slowed 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 depths of the dentin the pH values are 7-9. The highest pH values were obtained in the period from 7 to 14 days after adding an aqueous suspension of calcium hydroxide to the channel.
Microorganisms differ in their resistance to changes in pH; most of them reproduce 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 quantities in untreated teeth. They play an important role in unsuccessful endodontic treatment and are often (32-38% of cases) present in teeth with apical periodontitis.
One of the important components of the effective disinfectant effect 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 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, since due to its low water solubility and diffusion, a slow increase in pH occurs, which is necessary to destroy bacteria localized in dentinal tubules and other hard-to-reach anatomical formations. Because of these features, calcium hydroxide is an effective but slow-acting antiseptic.
The time required for optimal root canal disinfection with calcium hydroxide has not yet been precisely determined. Clinical studies give conflicting results. Cwikla et al. (1998) found that in 90% of cases there was no bacterial growth after 3 months of hydroxide use. In a study by Bystrom et al. (1999) calcium hydroxide effectively killed microorganisms within 4 weeks of use. Reit and Dahlen used the drug for 2 weeks - infection persisted in 26% of root canals. In an experiment by Basrani et al. After one week of using calcium hydroxide, bacteria remained in the canals in 27% of cases.
Mechanisms of resistance of microorganisms to the action of intracanal disinfectants
Factors that determine the resistance of microorganisms to the action of disinfectants and the ability to survive after the use of intracanal (temporary and permanent) filling materials:
Neutralization of the drug buffer systems or products of bacterial cells;
Insufficient exposure of the disinfectant in the root canal to destroy microorganisms;
Low antibacterial effectiveness of the drug against root canal microorganisms;
The effect of the drug on microorganisms is limited for anatomical reasons;
The ability of microorganisms to change their properties (genes) after a change environment.
An important mechanism of bacterial resistance is their existence in the form of a biofilm. 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 and have increased resistance to antimicrobial agents and protective mechanisms. Over 95% of naturally occurring bacteria are found in biofilms.
It is more difficult to destroy bacteria in biofilms than in planktonic suspensions if disinfectant does not have the property of dissolving tissue. At re-treatment infected teeth, calcium hydroxide cannot kill stubborn bacteria 100% ( E. faecalis), which are able to reproduce between visits to the dentist. Of great importance is a complete preparation, cleansing the canal of all microorganisms on the first visit (using copious rinses with sodium hypochlorite). Prevention of re-infection of the root canal is achieved by completely sealing the tooth crown using 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. An optimal environment should not change the pH of calcium hydroxide. Many solvents do not have antibacterial activity, such as distilled water, saline, and glycerin. Phenol derivatives, such as paramonochlorophenol, camphor phenol, have pronounced antibacterial properties and can be used as a hydroxide medium. Calcium hydroxide with paramonochlorophenol has a long range of action and 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 use. And calcium hydroxide paste with paramonochlorophenol and glycerin effectively destroyed bacteria in the tubules, including E. faecalis, within 24 hours of use. That is, paramonochlorophenol enhances the antibacterial activity of calcium hydroxide.
The results of a study on the 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 has been observed in calcium hydroxide channels ( 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 dentin 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: in addition E. faecalis it neutralized other microbes and penetrated into the tubules to a depth of more than 300 µm (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, located in bacterial biofilms. As part of a 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, are resistant to calcium hydroxide, its combination with other antimicrobial agents that increase its activity, for example with idoform, camphor paramonochlorophenol, is justified. Having low surface tension, fat-soluble phenols penetrate deep into tooth tissue.
In endodontics, chlorhexidine, which is effective against many bacteria that cause endodontic infection, is recommended for widespread use as an irrigant and intracanal dressing. The chlorhexidine molecule, interacting with the phosphate groups of the bacterial cell wall, penetrates 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 gel form has the following positive properties, as low toxicity for periodontal tissues, viscosity that allows you to retain active substances in constant contact with the walls of the root canal and dentinal tubules, water solubility. The combination of chlorhexidine gel and calcium hydroxide has been found to be highly effective against E. faecalis in infected root dentin. High pH (12.8) in the first two days increases the penetration ability of the drugs.
Effective against E. faecalis after 1, 2, 7 and 15 days of use of 2% chlorhexidine 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 inhibits growth by 100%. 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: dental plaque on teeth, caries, infected endodontic instruments. Causes of infection between visits may include microleakage through a temporary filling due to its destruction; tooth fracture; delay in replacing a temporary filling with a permanent one, when the tooth remains open for drainage. Secondary infection allows the emergence of new, virulent microorganisms that cause acute periapical inflammation.
Intracanal preparations destroy bacteria remaining after chemomechanical treatment of the canal, and are also used as a physical and chemical barrier that prevents the proliferation 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 is dissolved by saliva, saliva seeps into the space between the medication and the walls of the canal. However, if a drug has an antibacterial effect, it will first be neutralized and only then will bacterial invasion occur.
To prevent reinfection, the sealing ability of calcium hydroxide is more important than its chemical activity, since it has low water solubility, dissolves slowly in saliva, remains in the canal for a long time, delaying the movement 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.
A new class of materials - a mineral trioxide aggregate (ProRoot MTA) - has been proposed as a reliable isolating barrier for various endodontic problems (perforation of the cavity bottom, tooth root, root resorption, etc.). The basis of MTA is calcium compounds.
The influence 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 solution and endodontic instruments.
Lambrianidis et al. (1999) investigated the possibility of removing certain 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 root canal walls. Paste residues can affect the mechanical properties of the sealer and impair the apical seal. There is an opinion that it is impossible to completely remove the paste from the walls of the root canal.
Residual calcium hydroxide negatively 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 may manifest itself as blocking the advancement of the gutta-percha pin along the entire working length of the canal. If calcium hydroxide residues are not completely removed, they become compacted apically or in the recesses of the canal, which mechanically interferes with effective canal filling, complicates apical sealing and can affect the outcome of endodontic treatment. It is preferable to remove the apical calcium hydroxide plug.
Calcium hydroxide is effectively removed from the canal walls with hand instruments and rinsing with sodium hypochlorite and 17% EDTA. Difficulties in cleaning root canals after temporary filling are caused by paste-forming substances and fillers, and not calcium hydroxide. Water-based calcium hydroxide preparations (especially those prepared ex tempore) are absolutely devoid of these shortcomings. Moreover, sealers based on calcium hydroxide should be considered the 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 apex in pediatric practice.
Method of using calcium hydroxide:
1) calcium hydroxide in powder form is mixed to a paste with distilled water or glycerin;
2) the paste is injected into a carefully instrumentally and medicinally treated root canal using a canal filler;
3) to ensure adherence to the root dentin, the paste is compacted with a paper pin and covered with an airtight bandage.
Features of the use of calcium hydroxide for different conditions of the apical periodontium. At acute forms 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 case of acute periapical abscess, periostotomy is performed according to indications.
At chronic destructive processes in the apical periodontium The goal is to provide not only an anti-inflammatory and antimicrobial effect, but also to stimulate reparative processes in the bone. Calcium hydroxide is injected into the root canal with compaction to the walls for 3-8 weeks, the time of renewal of 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 body's resistance, the patient's age, and motivation to cooperate. Restoration of the zone of destruction of the apical periodontium continues after continuous 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 elimination acute inflammation. Resorption of cement and dentin persists even 9 months after filling. Moreover, in 80% of cases a chronic process is formed. If, after drainage, the canal was filled with calcium hydroxide for 7 days before obturation, the periapical defect was replaced with a new one. bone tissue, although in 18.8% of cases the inflammation progressed.
Acute reactions with a hermetically sealed closure of the coronal cavity, only 5% of teeth were preserved in the presence of a periapical abscess. A temporary dressing and hermetic seal 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, after 3 years complete bone regeneration is observed in 82% of periapical lesions, even large ones. In 18% of cases, bone defects remained or slightly decreased in size. The most active reduction in the size of the defect was observed in the first year of treatment. The first positive signs were detected on radiographs 12 weeks after the introduction of the Ca(OH) 2 bandage, and on digital radiographs already after 3-6 weeks.
"Yesterday" calcium hydroxide. Information materials, scientific articles about calcium hydroxide preparations 20-30 years ago they convinced (and convinced) us of its unique abilities: pastes based on calcium hydroxide have a highly alkaline reaction, an unlimited bactericidal effect, and the ability to stimulate reparative processes in bone tissue.
The use of calcium hydroxide in endodontics has expanded the indications for conservative treatment of destructive processes in the apical periodontium. It is now 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 have appeared on the mandatory stage of temporary filling of root canals during endodontic treatment: “This is useful!”
“Today” baggage has accumulated clinical observations, which confirm very high efficiency calcium hydroxide (Fig. 1-4; from the authors’ own observations). High-quality implementation of all stages of endodontic treatment in combination with temporary filling of root canals with calcium hydroxide makes it possible to recognize this method organ-saving treatment.
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But today in the dental literature the issues of the breadth of the antibacterial action of calcium hydroxide preparations, targeted effects 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 discussed.
So, A.A. Antanyan writes: “Multilateral analysis of scientific literature recent years(2003-2006) showed that calcium hydroxide has many disadvantages that call into question its routine and widespread use in endodontics. In modern endodontics, the most important is complete preparation, cleansing the canal from infection on the first visit (using copious rinses with sodium hypochlorite) and preventing re-infection of the canal by fully sealing the tooth crown using high-quality temporary fillings. Consequently, in many clinical situations additional disinfection with calcium hydroxide is not necessary.”
"Tomorrow" calcium hydroxide. Experience in the clinical use of calcium hydroxide shows that the need for its use in endodontics cannot be justified solely by its antimicrobial effectiveness, which in past years was primarily responsible for the treatment outcome. With the advent of sensitive methods microbiological research, with the expansion of the range of highly effective root canal irrigants, the capabilities and properties of calcium hydroxide as a temporary filling material may be rethought and reevaluated. But not discounted! In difficult clinical situations involving endodontic treatment and re-treatment of teeth, thanks to calcium hydroxide preparations, it is possible to preserve the patient’s teeth and health.
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