A naturally occurring mineral, hydroxyapatite is actually a form of the calcium apatite, which comprises calcium, oxygen and phosphorus. Hydroxyapatite is found growing in the form of hexagonal crystals. The color of unadulterated hydroxyapatite is white and most part of the human bone structure is made up of hydroxyapatite. In addition, this naturally occurring mineral also puts up tooth enamel, besides collecting in petite amounts in specific part of the human brain. While scientists have known hydroxyapatite for quite some time now, in recent times, developments in nano technology and materials science have made it possible to produce hydroxyApatite for medical uses in laboratory settings. In fact, hydroxyapatite is a very exceptional material, especially because it is also a bioactive material. Hence, it is among the few materials that are prepared in laboratories for to aid the growth of our teeth as well as bones. Precisely speaking, hydroxyapatite is a mineral belonging to a cluster of minerals containing phosphorus and called apatite. From the thermodynamic aspect, hydroxyapatite is known to be most stable when it is in the form of calcium phosphate under various physiological conditions, for instance, pH, temperature and proportion of the fluids in one's body. As nanotechnology as progressed, people have become more aware of materials science and the various applications of different materials. Since then there has been considerable focus on absorption, catalysis as well as optical applications of none-materials, especially when it involves biomaterials. More and more people are being attracted to nano-hydroxyapatite (nano-HAp) for its use in the form of a biomaterial in various prosthetic applications. This is because of this nano-material�s crystallography, size and chemical composition, which are quite similar to the hard tissues found in the human body. To a large extent, our teeth enamel and bones are made up of a variety of this material. While calcium hydroxyapatite is mainly composed of calcium and phosphate, the third element of this material is hydroxide. This hydroxide comprises one hydrogen atom that is linked to oxygen in a chemical bonding where the atoms share electrons among themselves. In fact, the presence of the hydrogen atom makes this mineral different from others in the entire Apatite group. For instance, it is possible to form other types of apatites like chlorapatite or fluorapatite provided the hydrogen atom is substituted by chloride or fluoride atoms respectively. It is well known that among other substances, our bones comprise as high as 50 percent of calcium hydroxyapatite. In our bones, calcium hydroxyapatite works as an inorganic compound known as bone mineral. It is also known as bone Apatite. In the human teeth, hydroxyapatite is found in the enamel as well as calcified dentin, which envelopes the teeth. They form two of the four major tissues in our teeth. Calcium hydroxyapatite found in human teeth and bones are present in a crystallized form that contributes to the firmness of these two structures. In actual fact, calcium hydroxyapatite not only makes the teeth enamel the strongest component of our body, but it also contributes to making the teeth the most mineralized part of our body. In the absence of calcium hydroxyapatite or even calcium, we may suffer the risk of suffering from specific diseases. One main example of the absence of calcium or calcium hydroxyapatite is development of osteoporosis, a condition wherein out bones are at risk of increased fractures because lack of calcium results in poor bone mineral density (BMD). In the case of another disease known as hydroxyapatite crystal disease, we suffer from inflammation as the crystallized mass of the mineral is wrongly directed in the human skeletal system, for instance it goes to the joints causing inflammation. In this case, the inflammation not only affects the joints or nearby areas, but it also affects the tendons and ligaments too causing great discomfort and pain.
There has been reasonable research as well as development aimed at growing and ascertaining the best possible utilities for hydroxyapatite. This has been possible in the wake of the recent developments in nano materials and material science. It has been found that apart from therapeutic benefits, hydroxyapatite has the potential to be of various non-medical uses. Some of the potential non-therapeutic uses hydroxyapatite include air filtration to remove carbon dioxide from the air and in a filter that helps to get rid of fluoride from saturated soil. However, all said and done, hydroxyapatite is most useful as a therapeutic material. Since nano hydroxyapatite aids in promoting growth of bones, surgeons use this material very frequently when they undertake surgeries that involve the tooth enamel as well as the bones. Even joint replacement implants are usually coated with nano hydroxyapatite with a view to stimulate bone growth. There is another advantage of using nano hydroxyapatite as our body is unlikely to reject such implants. This aside, the material promotes new bone growth in the region of the implant, thereby securing it more successfully. It has been found that calcium supplements containing hydroxyapatite have the potential to promote bone health better compared to carbonate supplements. However, more studies are needed in this regard to ascertain this particular attribute of hydroxyapatite. Generally, physicians use calcium hydroxyapatite to cure bone related problems in patients. This material can also be used in the form of an amputated bone replacement. Actually, a number of medical scientist have recommended that artificial bone implants made from hydroxyapatite can be used effectively to blend living bones, thereby restoring the structure's functional as well as aesthetic characteristics completely. In scientific terms, this process is called osseointegration. Hence, hydroxyapatite materials have been utilized to cover bones to promote the bones to fuse with the artificial implants. This use of hydroxyapatite is generally related to dental implants as well as hip replacements. In the case of people who suffer from deficiency of calcium, especially those who are vulnerable to develop osteoporosis or are already suffering from this condition, surgeons administer microcrystalline hydroxyapatite to promote sluggish bone loss. Our tooth enamel almost entirely comprises of hydroxyapatite. It has been found that people using oral care products containing hydroxyapatite have benefited greatly, especially they have helped to improve the dental health of such people. These days, all dental implants are also covered with nano hydroxyapatite to promote growth of new bone as well as make the implant more effective compared to the non-coated implants. Moreover, hydroxyapatite can also be included in dental filling agents that are employed to mend serious dental cavities. It has also been found that this material helps to decrease or even get rid of tooth sensitivity following whitening. In addition, hydroxyapatite can also help to enhance the results in the case of dental implants - very similar to the application of this material in bone implants in other parts of the human body. Therefore, it is not surprising that hydroxyapatite has turned out to be an crucial tool in oral and periodontal surgeries. It is not necessary to undergo oral surgery to obtain the therapeutic benefits of nano hydroxyapatite. Any product that incorporates this material is beneficial for the teeth, especially those that lack the vital mineral from the enamel and are beginning to show pre-cavity lesions. Using products containing hydroxyapatite on a regular basis can be helpful in maintaining healthy teeth and, at the same time, prevent the teeth from being demineralized. Aside from the ability of hydroxyapatite to aid in restoring the minerals on the surface of the damaged teeth, this material has also shown the aptitude to aid in checking bacteria that are responsible for most of caries diseases. This is especially true in the case of mutants streptococci, bacteria that are closely related to formation of caries, which is unable to stick to the teeth in the presence of nano hydroxyapatite. This results in considerable reduction in the presence of harmful bacteria in the oral cavity and, simultaneously, promotes resistance to formation of caries. With the advancement in nano material science, these days surgeons are using hydroxyapatite (also known as Hap or HA) of biological origin (such as coral-, marine algae- or bovine-derived) or synthetic origin for both bone repair and bone generation as hydroxyapatite granules, scaffolds and even blocks, by itself or in combination of polymers or various ceramics in the form of coatings on dental or orthopedic implants. In fact, these days they are available commercially for use as bone substitution, bone repair and also augmentation. They are also used in the form of scaffolds in the field of tissue engineering for regeneration of bones. The underlying principle for developing them in the form of a material that substitutes bones is that the composition of hydroxyapatite is quite akin to that of human bone mineral. Hydroxyapatite is also employed in the form of abrasives with a view to make the surface of the implant metal rougher and also as a source material to deposit bioactive coatings on dental and orthopedic implants. In addition, these materials can be employed in the form of drug carriers, transfection and percutaneous devices. Biomaterials based on hydroxyapatite having advanced attributes are incorporated in substituted apatites. In fact, this article is an update on the earlier reviews on apatites and it concentrates on the materials properties, preparation, and response of the cells and tissues to it as well as the material's application in medicine as well as dentistry. A lot of attention is now on hydroxyapatite materials as it has been found that this substance helps in regeneration of soft tissues. This is attributed to hydroxyapatite materials' outstanding biocompatibility with the soft tissues in the human body like the skin, gums and muscle. Several studies have suggested that Hap materials possess the ability to set off fibroblasts and, at the same time accrue vessel endothelial cells. In this way, this material supports the wounds to heal fast and properly. It has been found that Hap (hydroxyapatite) bioceramics contact firmly and they hold fast strongly with the skin tissues to put off any exit-site as well as tunnel bacterial infections. This explains why Hap materials may be used in the form of percutaneous devices. Deficiency of calcium in the body results in a bone density disorder known as osteoporosis. It has been found that about 33 percent of all adult females and 20 percent of males suffer from this condition in their lifetime in the form of osteoporotic fracture. In such cases, compared to taking calcium carbonate, taking supplements containing any hydroxyapatite helps to put off bone loss more effectively. This was revealed by the findings of a 20-month-long study undertaken on patients suffering from osteoporosis. It was found that after 1400 mg of a supplement was administered to them every day, the bone density due to use of hydroxyapatite supplement was just 0.8 percent less compared to 1.8 percent bone density loss in the subjects who were administered calcium carbonate supplements for 20 months.