Chemical formula of hydroxyapatite. Physical properties of hydroxyapatite (HA) crystals

Lately there has been a lot of talk about a unique filler filler – calcium hydroxyapatite. Faced with an incomprehensible term, many patients prefer to bypass it without trying to understand the essence. But this drug is predicted to become a leader among filler fillers.

Calcium hydroxyapatite is an inorganic component present in our body and is the main component of our bone tissue. It is part of bones, cellular and acellular cement and tooth enamel. It is isolated from corals of the genus Porites, which are mined in the sea.

Completely safe for humans and inert to human tissues. For this reason, it is widely used in medicine: dentistry, maxillofacial surgery, orthopedics. In cosmetology it is used as a filler in fillers to replenish lost volumes.

Calcium hydroxyapatite in biological tissues is organized into crystalline structures. It is used in microspheres in the form of white crystals. According to manufacturers, calcium hydroxyapatite stimulates collagen synthesis in the skin. After some time, calcium hydroxyapatite is completely eliminated from the body, and the improvement of skin characteristics continues.

Why is calcium hydroxyapatite used?

It is generally accepted that wrinkles are the first sign of skin aging, but this is not entirely true. Wrinkles are indeed considered a serious sign of aging skin, but there is a more obvious sign that makes the skin truly aged. These are lost volumes. What does it mean? This means that as you age, the skin loses its elasticity and simply “slides” down.

In youth, skin density is concentrated in the upper part of the face in the cheekbone area. She looks elastic and toned. Over the years, the skin loses its former firmness and elasticity, and the entire volume moves from the upper part of the face to the lower part to the chin area. This process is called deformational ptosis. Why does facial deformation occur? There are several factors contributing to this process:

• gravity;
• destruction of collagen and elastic fibers;
• decreased synthesis of hyaluronic acid;
• reduction of fibroblasts in connective tissue.

As a result, the skin becomes flabby, inelastic, with poor turgor, and a “floating” oval of the face. And most importantly, the face becomes old and tired, and its expression is forever mournful and sad. It turns out that eliminating only wrinkles or only nasolabial folds will not rejuvenate the face to the extent that it is truly considered young: with volume, good turgor and tissue elasticity.

Modern women are incredibly lucky. Now you can replenish skin volumes without resorting to radical measures of the past. And here the leading role is given to calcium hydroxyapatite. Basically, fillers based on calcium hydroxyapatite are used to replenish lost volumes. In this case, they have no equal. But unlike fillers based on hyaluronic acid, they do not promote skin hydration and do not restore metabolic processes in it.

Advantages of calcium hydroxyapatite fillers

Fillers based on calcium hydroxyapatite have their advantages. At the moment, this is a popular component in fillers, and the popularity of procedures based on it is growing every day. What are these benefits?

Firstly, calcium hydroxyapatite is a biodegradable drug. This means that it is removed from the body after its expiration date.

Secondly, calcium hydroxyapatite is part of our body. That is, for the body it is not a “stranger” that can cause drug rejection or an allergic reaction. It is completely biocompatible with our tissues. Although the risk of allergic reactions still exists, the body's behavior is sometimes unpredictable, but this risk is minimal.

Thirdly, it triggers the synthesis of endogenous collagen.

Fourthly, fillers with calcium hydroxyapatite have a longer lasting effect. Compared to hyaluronic acid fillers, calcium hydroxyapatite lasts twice as long.

Mechanism of action of calcium hydroxyapatite

As mentioned above, calcium hydroxyapatite is introduced into the body in the form of microspheres. Along with it, a carrier gel is also introduced. After introducing the drug into the skin, the carrier gel instantly smoothes out wrinkles. A wrinkle is a deep groove in the skin.

When filler is injected, the wrinkle is lifted by a carrier gel that fills the cavity underneath. The jelly-like structure of the gel does not allow the wrinkle to return to its original position.

Thus, the wrinkle is smoothed out, and the skin around it becomes elastic. After some time, macrophages (cells of the body that devour bacteria, particles foreign to the body and toxins) absorb the gel carrier. Microspheres of calcium hydroxyapatite remain, which form new collagen. Collagen, in turn, forms a new skin matrix that envelops the microspheres.

In this way, a new structure of connective tissue is formed, which lasts for almost two years. The formation of a new connective structure gives a good long-term effect from the procedure.

What can calcium hydroxyapatite fillers fix?

The range of application of fillers is quite wide. With their help:

• replenish lost volume (on the cheekbones, chin, cheeks);
• fill nasolabial folds;
• eliminate marionette wrinkles in the mouth area;
• correct the oval of the face;
• allow for correction of the hands.

Side effects and complications

Let us immediately note that fillers based on calcium hydroxyapatite are completely safe. Three years of research have fully confirmed their reliability. There are practically no contraindications, except for individual intolerance to the drug. Allergic reactions most often develop in allergy sufferers.

Before the procedure, it is necessary to carry out skin tests to identify allergies, since sometimes the patients themselves do not always realize that they have such an intolerance.

Side effects are very minor and manifest themselves in a classic way:

• swelling;
• microhematomas at puncture sites;
• bruises.

Within a few days, all side effects completely disappear on their own. Complications are not so simple; they do not disappear on their own. To eliminate them, they sometimes resort to medical intervention. Most often, complications indicate low professional training of a cosmetologist. What complications can there be?

• White streaks may appear on the face at the injection site. This usually happens due to insufficiently deep filler injection;
• administration of the drug in places not intended for this type of filler (for example, lips, tear trough) As a result, lumps on the skin, its unevenness and even the development of asymmetry may occur;
• penetration of the gel under the skin (Tyndall effect). It also occurs as a result of shallow injection of the drug, or into the wrong layer of skin;
• development of a bacterial infection on the face in case of gross violations of septic and antiseptic measures;
• the formation of gel clots at the injection sites and the formation of granulomas.

The professionalism and skill of a cosmetologist lies in following the precise injection technique. They are able to minimize side effects and complications.

Hydroxyapatite is an inorganic mineral that is the main component of human tooth enamel and bone tissue.

Ceramics made on the basis of hydroxyapatite bind to healthy human bone tissue and do not cause rejection. This property of the mineral allows it to be actively used to restore damaged bones. In addition, the biologically active layer of the drug with hydroxyapatite is used to improve the ingrowth of implants in dentistry.

Pharmacological action

The drug based on calcium hydroxyapatite stimulates the formation of bone tissue, does not cause a rejection reaction and is characterized by biological compatibility with human tissues. After introducing the drug into the bone cavities, it does not harden or dissolve, but over time is replaced by full-fledged and healthy bone tissue.

Indications for use

Calcium hydroxyapatite is used as one of the components of filling pastes, which are used in the following cases:

Filling root canals for the treatment of inflammatory dental diseases (pulpitis, periodontitis);

Therapy of periodontitis (inflammation of the bone tissue surrounding the tooth root);

Treatment of bone defects using aplografts (donor bone);

Restoration of bone tissue after cyst removal;

Restoration of a tooth after resection of the apex of its root;

Filling intraosseous cavities of various origins, etc.

Instructions for use (method and dosage)

Calcium hydroxyapatite powder is mixed with ethylene glycol, an oil solution of retinol acetate or sterile saline until a paste-like mixture is formed. This manipulation must be carried out in compliance with all rules of aseptic technique.

Calcium hydroxyapatite paste, intended for filling tooth root canals, is prepared on the basis of eugenol. If filling materials are incompatible with eugenol, saline solution must be used instead of eugenol. 50% zinc oxide can be added to the paste, allowing for a more accurate X-ray contrast examination. All subsequent therapeutic manipulations after applying hydroxyapatite paste are traditional.

When treating periodontitis, the bone pocket is filled with sterile hydroxyapatite granules to the level of healthy preserved bone, then the wound is sutured. Postoperative management of the disease remains traditional.

Filling bone cavities with hydroxyapatite granules during resection of the apex of a tooth root or removal of dead bone tissue is carried out in the same way as when using other materials used for this purpose.

Hydroxyapatite is also used during surgical operations involving bone grafting, in particular when working with transplants. So, in order to enhance the process of replacing the transplanted bone tissue with the patient’s own bone tissue, to prevent rapid resorption of the transplant, as well as to reduce the inflammatory reaction, irregularities or places of loose fit between the transplant and the patient’s bone tissue are filled with a preparation based on the mineral in question.

The preparation for surgical operations is prepared as follows: sterile granules or hydroskiapatite powder must be moistened with sterile saline until a mixture is obtained that resembles a thick paste in consistency. The drug is sterilized in a drying cabinet for 10-15 minutes at a temperature of 150 °C. Using the prepared paste, the places where the graft does not adhere tightly to the patient’s own bone tissue are filled. After which the wound is sutured layer by layer. Further postoperative therapy remains traditional.

Application in cosmetology

Cosmetologists have not ignored hydroxyapatite either. Based on it, an innovative injection drug has been created that is used to correct wrinkles. Unlike other cosmetic preparations that provide wrinkle correction for 4-8 months, injections based on hydroxyapatite help achieve a longer-term correction effect, up to 13-15 months or more.

The product is absolutely biologically compatible with the tissues of the human body.

Used for the following cosmetic procedures:

Correction of nasolabial folds;

Correction of severe and moderate facial folds;

Correction and tightening of the oval face;

Enlargement of cheeks and chin.

Article for the “bio/mol/text” competition: Diseases associated with an increased rate of bone tissue degradation in older people are increasingly felt by the population. This is largely due to an increase in life expectancy in general and the aging of the so-called “golden billion”. New materials based on calcium phosphates, suitable for implantation in patients with osteoporosis, can partially solve this problem.

Modern science sets one of its main goals to extend the duration of human life. New methods of treating diseases are being developed, the lives of the elderly are being made easier, many diseases that were previously considered incurable have been almost completely defeated by humanity. However, some age-related changes are genetically embedded in the body, and it is almost impossible to combat them using conventional methods.

Bone diseases occupy one of the first places in the ranking of the most common problems among older people. Loss of bone mass increases with age. Women especially suffer from this - due to the more active leaching of calcium cations from the body, which serves as the basis of our skeleton. Bone loss can reach 40% in women over 70 years of age!

This disease is called osteoporosis. The bones affected by it become fragile, having difficulty coping with the load placed on them. In the event of a fracture, such a bone will take much longer to heal than a healthy one. As mentioned above, the main reason for such changes is the gradual leaching of calcium from the body. Throughout our lives, two equilibrium processes occur in our body: the continuous formation of new bone tissue and the resorption (dissolution) of old bone tissue. With old age, the balance shifts towards resorption, and new tissue simply does not have time to take the place of dissolved tissue. And excess calcium cations, which is the main product of this process, are eliminated from the body naturally.

What is a human bone? Figure 1 schematically shows the structure of human bones. The base consists of a composite (a material made up of other materials and having properties different from those of the “parents”), which are crystals of non-stoichiometric hydroxylapatite with the chemical formula:

Ca 10−x−y/2 (HPO 4) x (CO 3) y (PO 4) 6−x−y (OH) 2−x,

Thus, complete replacement of bone with artificial material is undesirable. The most preferred way to regenerate bone tissue today is to replace the damaged part of the tissue with a bioactive prosthesis, which will fuse with the surrounding tissues, then accelerate natural regeneration and gradually dissolve without a trace, leaving new tissue on the bone defect.

Figure 2. Individual prosthesis of a fragment of the lower jaw for a patient with sarcoma of the lower jaw. The prosthesis is made of polymer and hydroxyapatite.

Traditionally in orthopedics it is used for these purposes. hydroxylapatite. Stoichiometrically, hydroxylapatite (hereinafter, for brevity, we will call it HAP) is the closest in composition to the mineral component of bone (compared to other calcium phosphates). Its formula:

What is hydroxyapatite?

For a long time it was believed that hydroxylapatite Ca 10 (PO 4) 6 (OH) 2 is an ideal material in terms of biocompatibility for restoring damaged bones and teeth. The first documented attempt to use HAp as a bone replacement material dates back to the 1920s. However, the successful use of HAP for these purposes occurred only after 60 years. Hydroxylapatite is perfectly compatible with muscle tissue and skin; Once implanted, it can directly fuse with bone tissue in the body. The high biocompatibility of hydroxyapatite is explained by the crystal chemical similarity of the artificial material to the bone “mineral” of vertebrates.

The name of the mineral comes from the Greek “apatao” - I’m deceiving, since the beautifully colored natural varieties of apatite were often confused with beryl and tourmaline. Despite the very wide range of colors of natural apatites caused by various impurities, the low hardness (it is the standard value of 5 on the 10-point Mohs scale) does not allow it to be considered as a semi-precious ornamental stone.

It is known that bone mineral contains noticeable amounts (~8% by weight) of carbonate ions; There is also a natural mineral of similar composition - dallit. It is believed that carbonate ions can occupy two different positions in the structure of HAP, replacing hydroxyl and/or phosphate ions to form A- and B-type carbonate hydroxylapatite (CHAP), respectively. Apatite of biological origin belongs to the B-type. The replacement of phosphate ions with carbonate ions leads to a decrease in the crystal size and degree of crystallinity of HAP, and this greatly complicates the study of natural biominerals. An increase in the proportion of carbonate ions in the composition of hydroxyapatite causes natural changes in the equilibrium shape of the crystal. The needle-shaped crystals "flatten" into plates that are very similar to the crystallites of existing apatite in the body. Thus, by introducing a small proportion of carbonate ions into the synthesized mineral, it is possible to obtain a material similar to the biogenic one both in chemical composition and geometrically.

An important characteristic of HAP is the stoichiometry of its composition, which is usually expressed by the Ca/P ratio. The variable composition is due to the fact that when synthesizing HAP from solution, it is impossible to protect against H 3 O + and HPO 4 2 − ions, which can replace Ca 2+ and PO 4 3 − ions, respectively, in the crystal structure of hydroxylapatite.

How is hydroxylapatite used?

There are various methods for the synthesis of hydroxyapatite. They can be roughly divided into high- and low-temperature. High-temperature methods are not of great interest to us, since the materials obtained in this way are practically not bioactive. Low temperature methods can be divided into two large groups: hydrolysis(including the so-called hydrothermal synthesis methods) and precipitation from solution. Also interesting is the combined method of the so-called sol–gel synthesis. In it, the dry residue of the gel undergoes decomposition at a relatively low temperature of 400–700 ° C (compared to high-temperature synthesis). The materials obtained in this way are hard, porous ceramics, whose chemical composition and physical properties resemble bone mineral.

How does the body react to calcium phosphate ceramics?

Bioactivity- comprehensive characterization of materials compatible with the body, taking into account, in addition to the impact on the biological processes of cell growth and differentiation, also:

• the rate of dissolution of the material in environments created by certain groups of cells (bioresorbability);
• the rate of deposition of material from the interstitial fluid onto the surface of the material.

Among the requirements that apply to bioactive materials used in medical practice to restore the integrity of bone tissue, the first place is occupied by a relatively high dissolution rate (of the order of tens of microns per year) - the so-called bioresorbability. The surface plays an active role in the biochemical reactions occurring at the bone/implant interface with the participation of cells specific to the process of osteosynthesis. When talking about the rate of resorption of material located in the interstitial fluid, it is customary to compare new materials with those already used in medicine - ceramics based on hydroxyapatite or β-tricalcium phosphate. Coarse-crystalline ceramics based on HAp are resorbed slowly, so inclusions of artificial material can be detected in the bone even after many years. Ceramics produced using β-Ca 3 (PO 4) 2 dissolve so quickly that the growing bone does not have time to fill the resulting cavities. The rate of dissolution of the material depends on many factors: surface area, structure, composition, defectiveness of the material. These characteristics determine the body's response to a foreign implant. Bioactive materials are characterized by rapid fusion with bone tissue through the formation of an intermediate layer of HAP, which is formed in two possible ways:

1. Dissolution of calcium phosphate - precipitation of hydroxyapatite.
2. Precipitation of HAP from a supersaturated solution in tissue fluid.

An important procedure for assessing bioactivity involves testing in vivo. It is expensive and time-consuming, and also carries risks. However, active development of methods is underway that makes it possible, already at an early stage of preclinical testing, to rank materials according to the degree of bioactivity in the course of relatively simple experiments in vitro, simulating processes in the human body - dissolution of material and deposition of HA on the surface of the material from solutions similar to body fluids.

The study of the bioactivity of materials is carried out using a solution that imitates the ionic composition of human interstitial fluid. Compact samples of the test material are placed in the solution for several days at 37 °C. The process of deposition of carbonate hydroxylapatite from a model solution onto the surface of the material is controlled by X-ray phase analysis, IR spectroscopy and scanning electron microscopy.

There is a need to regulate the bioresorbability of artificial materials, depending on their purpose. This possibility exists due to the different properties of materials with different compositions. To make a sample more resorbable, it is necessary to increase the proportion of carbonate and silicate ions in the crystal lattice of the material.

Figure 3. Openwork layer of partially resorbed ceramic. Scanning electron microscope image. Shown here is a fragment of material subjected to dissolution in a model solution in vitro. Right you can see what the material was like before resorption began.

Silicon-containing material exhibits the best bioactivity in such studies. Silanol (-SiOH) groups are formed on its surface, actively participating in the mineralization of the outer layer of the implant. Such a material intensively exchanges ions with the solution: silanol groups firmly bind calcium ions, promoting the formation of a layer of amorphous calcium phosphate on the surface, the separation and crystallization of which leads to the formation of an openwork layer consisting of HAP particles ~10 nm in size (Fig. 3). Differences in the thickness of such a layer can serve as a measure of the bioactivity of the material: the thicker it is, the easier it will be for the bone to integrate this material into its structure.

Another of the most important properties of modern implantation materials is osteoinductivity- the ability to support the vital activity of osteoblasts and stimulate ectopic (outside the bone) formation of bone tissue de novo. This is the most important property for artificial implants. The fact is that to initiate bone formation around the implant, a microenvironment with living bone particles is necessary. The newly formed bone gradually fuses with the surrounding implanted particles, “jumping” from one to another.

It is believed that the most active from the point of view of osteosynthesis is the amorphous modification of hydroxyapatite. However, sufficiently crystalline HAP with crystallite sizes approaching those of crystals in bone tissue (20–40 nm3) can show results an order of magnitude higher than the amorphous cements currently used.

Bioinert materials do not affect the osteosynthesis process in any way. On the surface of implants made from them, fibrous tissue is formed, which prevents the formation of a connection between the implant and the bone. There is a significant likelihood of rejection of such materials by the body, often accompanied by inflammatory processes. However, it is not yet possible to completely abandon these materials, since they are cheap and easy to process. The main problems that are solved when designing implants from bioinert materials are bringing the elastic characteristics of the implant closer to the characteristics of bone, as well as reducing the rate of corrosion processes.

Unlike bioinert synthetic materials based on polymers and metals, ceramics based on calcium phosphates are biocompatible and bioactive, and therefore are the most promising material for bone implants. Its main disadvantage is fragility. So far, the best solution is the use of composites made of metals or polymers coated with calcium phosphate ceramics (Fig. 4). They provide good integration of the material into bone tissue, preventing the formation of fibrous tissue around the bioinert metal. Over time, the prosthesis will fuse very firmly with the surrounding bone, which will replace the layer of HAPA. The failure rate of such prostheses is significantly lower than that of metal and plastic analogues.

Figure 4. Bioactive ceramic coating on a hip joint prosthesis. A - Porous structure of the ceramic coating. b - X-ray of the prosthesis implanted in place of the hip joint. The prosthesis itself is made of titanium and polymers.

How to give new properties to GAP?

Not all properties necessary for prosthetics are inherent in hydroxyapatite by nature. However, some therapeutic effects can be added to the materials by complicating the composition of the composite with additional substances. However, this is not very convenient, as it will complicate clinical trials, and it is much more difficult to develop such material. But progress can be made and unique properties obtained by slightly modifying the composition and introducing impurities of other cations and anions into the hydroxyapatite lattice. By changing the composition of ceramics, you can vary its strength, size and shape of crystallites, dissolution rate and many other parameters.

Calcium phosphate ceramics can be modified by introducing many components. The possibilities for choosing such a modifier (doping component) are quite wide: depending on the size of the replaced ion, you can change the composition by either fractions or tens of percent. For example, low concentrations of silicon ions activate bone tissue regeneration, playing the role of an antigen for the corresponding cells.

Interesting, for example, are the biological properties of lanthanide cations. The use of lanthanide ions in oral medications is limited by their low ability to pass through the walls of the stomach and intestines. To improve the availability of lanthanide cations, lipophilic shells of complexes can be used. Substances that can penetrate cell membranes are called ionophores. (You can read more about them in the article “Unknown peptides: the “shadow” system of bioregulation”.) Such a shell will allow them to penetrate the cell membrane. This method of delivering ions to osteoblasts could become a fundamentally new approach to the treatment of a number of bone diseases.

Due to their high affinity for phosphates, lanthanides are firmly bound in the structure of minerals that form the basis of bone tissue, without disturbing their structure. Lanthanides can even replace calcium in bones, while simultaneously suppressing the development of cells responsible for the rupture and resorption of bone tissue. This ability to “mimic” the functions of calcium ions allows lanthanides to be considered as a component for the treatment of bone diseases.

Partial exchange of calcium cations for lanthanide cations opens up broad prospects for a number of different materials based on calcium phosphates. With the help of lanthanides, it is possible to influence the physical properties of the resulting ceramics, regulate the rate of resorption, and even use this material as a drug for the treatment of osteoporosis.

In practice, HAP is used in the form of cement or porous inlays to fill cracks, cavities and other defects in orthopedics and maxillofacial surgery. In the form of a film, it is applied to prostheses made of other materials (most often metal or polymer) to reduce the risk of rejection and better fixation due to the formation of new tissue around the prosthesis. As a rule, these are hip joint prostheses and various dentures.

Of course, artificially synthesized hydroxyapatite is far from ideal, and it cannot yet be used as an implantation material to create full-fledged prostheses for large bones or joints. But the use of its remarkable properties, such as relatively simple regulation of the composition and morphology of crystallites, bioactivity and the ability to accelerate natural regeneration, makes it possible to make drugs based on it for the correction and prevention of bone defects right now. This means that in the foreseeable future we will be able to significantly simplify the treatment of osteoporosis, speed up the healing of fractures, and, perhaps, even return lost limbs using artificial bones.

Literature

1. Larry L. Hench. (2005). Bioceramics. Journal of the American Ceramic Society. 81 , 1705-1728;
2. Veresov A.G., Putlyaev V.I., Tretyakov Yu.D. (2000). Advances in ceramic materials. “Rus. Chem. Journal." 6 , 32–46;
3. Larry L. Hench. (2006). The story of Bioglass®. J Mater Sci: Mater Med. 17 , 967-978;
4. Dorozhkin S.V. & Agathopoulous, S. (2002). Biomaterials: Market overview. "Chemistry and Life". 2 , 8;
5. E. D. Eanes, A. W. Hailer. (1998). The Effect of Fluoride on the Size and Morphology of Apatite Crystals Grown from Physiologic Solutions. Calcif Tissue Int.. 63 , 250-257;
6. Qinghong Hu, Zhou Tan, Yukan Liu, Jinhui Tao, Yurong Cai, et. al.. (2007). Effect of crystallinity of calcium phosphate nanoparticles on adhesion, proliferation, and differentiation of bone marrow mesenchymal stem cells. J. Mater. Chem.. 17 , 4690;
7. Cheri A. Barta, Kristina Sachs-Barrable, Jessica Jia, Katherine H. Thompson, Kishor M. Wasan, Chris Orvig. (2007). Lanthanide containing compounds for therapeutic care in bone resorption disorders. Dalton Trans.. 5019;
8. Unknown peptides: “shadow” bioregulation system;
9. G. Renaudin, P. Laquerrière, Y. Filinchuk, E. Jallot, J. M. Nedelec. (2008). Structural characterization of sol–gel derived Sr-substituted calcium phosphates with anti-osteoporotic and anti-inflammatory properties. J. Mater. Chem.. 18 , 3593.

/ mineral Hydroxylapatite

Hydroxylapatite- mineral, calcium phosphate from the apatite group of the apatite supergroup. Hydroxyl analogue of fluorapatite and chlorapatite, phosphate analogue of jonbaumite. Hexagonal polymorph of clinohydroxylapatite.
Soluble in HCl and HNO3.
Hydroxylapatite as a biomineral
Up to 50 wt.% of bones consist of a specific form of hydroxyapatite (known as bone tissue). Hydroxyapatite is the main mineral component of tooth enamel and dentin (non-stoichiometric hydroxyapatite with plate-shaped crystals measuring 40x20x5 nm and the “c” axis of the crystal structure lying in the plane of the crystal). Hydroxylapatite crystals are found in small calcifications of living organisms (in the pineal gland and other organs). Also included in pathogenic biominerals (dental, salivary, kidney stones, etc.).
It is relevant to create biomaterials based on hydroxyapatite to replace damaged bone tissue, etc. It is often used as a filler in place of amputated bone or as a coating to promote bone ingrowth into prosthetic implants (many other phases, albeit with similar or even identical chemical composition, are responded to very differently by the body). It has been shown that not only the chemical composition, but also the morphology of synthetic hydroxylapatite crystals is an important characteristic that determines the body’s response to foreign material (Puleo D.A., Nanci A., 1999).

report an error in the description

Properties of the Mineral

Color	white, green, blue-green, blue, purple, rarely red
Stroke color	white
Origin of the name	Named as the hydroxyl end member of the apatite group, and from the Greek apatao - misleading
IMA status	valid, first described before 1959 (before IMA)
Chemical formula	Ca5(PO4)3(OH)
Shine	glass fatty
Transparency	transparent translucent
Cleavage	very imperfect by (0001) very imperfect in (1010)
Kink	conchoidal uneven
Hardness	5
Thermal properties	Under item tr. difficult to fuse around the edges
Strunz (8th edition)	7/B.39-30
Hey"s CIM Ref.	19.4.2
Dana (8th edition)	41.8.1.3
Molecular weight	502.31
Cell Options	a = 9.41Å, c = 6.88Å
Attitude	a:c = 1: 0.731
Number of formula units (Z)	2
Unit cell volume	V 527.59 ų
Twinning	Rarely twins fused by (1121)
Point group	6/m - Dipyramidal
Space group	P63/m
Density (calculated)	3.16
Density (measured)	3.14 - 3.21
Refractive indices	nω = 1.651 nε = 1.644
Maximum birefringence	δ = 0.007
Type	single-axis (-)
Optical relief	moderate
Selection form	in the form of prismatic crystals and needles; short-columnar or tabular crystals are less common. Main simple forms: (1010), (1120), (0001), (10l2), (1011), (1121), (2021), (3142), etc.
Classes on taxonomy of the USSR	Phosphates, arsenates, vanadates

Tooth enamel is the outer protective shell of the crown of the teeth. This is the hardest tissue of the human body, which is 97% composed of hydroxyapatite crystals. The enamel structure also contains a small amount of water (2-3%) and organic substances (1-2%).

Enamel demineralization is the loss of minerals and salts from the tooth enamel, primarily calcium salts. The demineralization process begins with prolonged contact of the enamel with acids that are secreted by bacteria living in the mouth. Constant consumption of foods high in carbohydrates and poor oral hygiene contribute to the deposition of plaque in which these bacteria live and multiply. If plaque is not removed in time, demineralization of the enamel continues, leading after some time to the appearance of a chalky stain, and then to the appearance of caries.

At the white spot stage, caries is reversible. Timely measures to strengthen the enamel help reduce and even completely eliminate the stain. Strengthening enamel (remineralization) is the saturation of enamel with missing minerals, promoting its restoration and increasing resistance to acids. It can be performed either in the dentist's office or at home.

Indications for strengthening enamel

• Presence of caries.
• Childhood.
• Pregnancy and breastfeeding period.
• The initial stage of caries (white spot stage).
• Increased sensitivity of teeth.
• Periods before and after teeth whitening.
• Availability of installed orthodontic structures (brackets).

Ways to strengthen enamel

Another effective way to strengthen enamel is remineralization using medical nano-hydroxyapatite (nano"mHAP"), which is identical in composition to the main component of tooth enamel and dentin. Medical nano-hydroxyapatite is used as a component of toothpastes, the regular use of which helps restore and strengthen enamel. Being embedded in the crystal lattice of tooth enamel, medical hydroxyapatite seals microcracks, reduces tooth sensitivity and eliminates caries at the white spot stage. This unique component is found in pastes Apadent, Apagard, Biorepair, Miradent, etc.

You can also strengthen the enamel and prevent caries using products containing amorphous calcium phosphate. Interacting with saliva and hydroxyapatite, it forms a biofilm on the surface of the teeth, which protects the enamel from the harmful effects of acids. Also, thanks to this film, bioavailable calcium penetrates the enamel - its remineralization occurs. Amorphous calcium phosphate is the main active component of GC Tooth Mousse and Mi Paste Plus pastes, which are used as a tooth cream - applied to the enamel surface for a few minutes. This drug should not be used in patients with milk protein intolerance, since amorphous calcium phosphate is extracted from cow's milk casein.

The newest way to strengthen enamel is to use theobromine– cocoa bean extract. The effectiveness of theobromine in strengthening enamel is based on the ability of this substance to stimulate the formation of its own hydroxyapatite crystals, as a result of which the enamel becomes more acid-resistant. Strengthening toothpastes with theobromine are produced by Theodent and belong to luxury cosmetics.