Bone Grafts – Synthetic Hydroxyapatite

The first reports of successful bone grafting date from the last century, when Walker (1820), apud Shena (85), transplanted autogenous bone (tissue belonging to own receiver) in man. In the early twentieth century marrow transplantation has become very popular in medicine, with questionable success. The Second World War stimulated the interest on autografts (the donor is the own receiver), allograft (donor of the same species) and xenograft (donor of a different species from the receptor) (23). Since the publication of the first successes with allogenic bone grafts in humans at the end of the 60’s (31), hits and misses occurred in the selection of biomaterials in surgical techniques and prosthetic rehabilitation, in mechanical analysis of materials and problems, and in periodontal therapy. Over the past 10 years, extensive scientific documentation has been published on experimental clinical implants in dentistry and orthopedics. New materials have been developed and tested in numerous and complex ways (3, 14, 22). Among them we can cite: dura mater, cartilage, dentin, bone, freeze-dried or not, and biomaterials based on calcium phosphate.

Among bone substitutes are used marine corals of the Goniopora and Poritidae families, which by hydrothermal reactions with ammonium phosphate dibasic are converted into hydroxyapatite (36, 55). However, the hydroxyapatite of natural origin has limitations, such as small variation in quantity, size and shape of the product in relation to the original coral exoskeleton, the material produced being of low mechanical resistance (70). On the other hand, the hydroxyapatite obtained by the reaction of inorganic reagents can be prepared by different methods and has provided good results, with no significant obstacles as the natural hydroxyapatite. (23,54).

Autografts are widely used to repair fractures with loss of bone tissue, reconstruction after removal of invasive bone tumors, or to accelerate the reconstruction of fractured bones in special cases. The obvious advantage of autografts in orthopedic reconstructive surgery is the fact that the matrix grafted is not immunogenic. Among the disadvantages (82) it can be mentioned: complications at the donor site (12), limited availability of tissue, inability to replace a joint surface (79), unsatisfactory temporary storage methods (79).

Allografts and xenografts present several difficulties, including rejection, risk of strong antigenic reaction, transmission of infectious diseases, and requirement of matching between donor and receiver of bone tissue. Problems with biological grafts have stimulated interest in the potential of synthetic and bio-inert materials as bone graft substitutes. Researchers have aimed at obtaining biomaterials which meet the biomechanical requirements for an implant, and at the same time compatible with the surrounding biochemical / cell environment. Because of the similarity in chemical composition between the synthetic hydroxyapatite and the bones and teeth of vertebrates, it has been the primary material studied as a biomaterial intended for bone implantation (14, 74). When placed in contact with the bone, it acts initially as a prosthesis and then as a support for tissue regeneration. Hydroxyapatites obtained by different methods have been evaluated in animals and humans (23, 54). In all documented cases, this material has been found to have a high biocompatibility degree with hard and soft tissues.

Hydroxyapatite is indicated for recovering bone loss in general, bone deformities, filling alveoli after extraction, regularization of the alveolar ridge as direct pulp protector, and other clinical applications in human and veterinary medicine (including surgery for cosmetic and functional correction) and in dentistry.

The hydroxyapatite obtained by JHS – registered as HAP-91® – is absorbable, which means that once implanted in a bone defect it gives rise to the formation of new bone tissue, favoring the nutritional support within the pores and producing continuity with the surrounding bone. Histological evaluation reveals that the bone developed within the implant has normal appearance in all meanings.

A strong partnership with the Orthopedics Department of the Schools of Veterinary Medicine of UFMG and UFV, since the beginning of the research in 1990, has given the opportunity to JHS not only to prove the good performance of HAP-91® in recovering bone defects, but also to develop modifications in granulation, texture, and combination with other biological materials, meeting the demand for specific problems presented by researchers from the areas of orthopedics, neurosurgery, dentistry, oral-maxillofacial, and other.

(Text extracted from the Master’s dissertation of Ângela Leão Andrade (UFMG) – Found also in our book about HAP-91)