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ePaper created 2015-05-22, 12:38:27 | version 1.38.0
January 201418 Implant Tribune United Kingdom Edition T he human body contains over 200 different types of cells, which are or- ganised into tissues and organs that perform all the tasks re- quired to maintain the viability of the system, including repro- duction. In healthy adult tis- sues, the cell population size is the result of a fine balance be- tween cell proliferation, differ- entiation, and death. Following tissue injury, cell proliferation begins to repair the damage. In order to achieve this, quiescent cells (dormant cells) in the tis- sue become proliferative, or stem cells are activated and dif- ferentiate into the appropriate cell type needed to repair the damaged tissue. Research into stem cells seeks to understand tissue maintenance and repair in adulthood and the derivation of the significant number of cell types from human embryos. It has long been observed that tissues can differentiate into a wide variety of cells, and in the case of blood, skin and the gastric lining the differenti- ated cells possess a short half- life and are incapable of renew- ing themselves. This has led to the idea that some tissues may be maintained by stem cells, which are defined as cells with enormous renewal capacity (self-replication) and the ability to generate daughter cells with the capacity of differentiation. Such cells, also known as adult stem cells, will only produce the appropriate cell lines for the tissues in which they reside (Fig 1). Not only can stem cells be isolated from both adult and embryo tissues; they can also be kept in cultures as undif- ferentiated cells. Embryo stem cells have the ability to produce all the differentiated cells of an adult. Their potential can therefore be extended beyond the conventional mesodermal lineage to include differentia- tion into liver, kidney, muscle, skin, cardiac, and nerve cells (Fig 2). The recognition of stem cell potential unearthed a new age in medicine: the age of regen- erative medicine. It has made it possible to consider the regen- eration of damaged tissue or an organ that would otherwise be lost. Because the use of embryo stem cells raises ethi- cal issues for obvious reasons, most scientific studies focus on the applications of adult stem cells. Adult stem cells are not considered as versatile as em- bryo stem cells because they are widely regarded as multi- potent, that is, capable of giving rise to certain types of specific cells/tissues only, whereas the embryo stem cells can differ- entiate into any types of cells/ tissues. Advances in scientific research have determined that some tissues have greater diffi- culty regenerating, such as the nervous tissue, whereas bone and blood, for instance, are considered more suitable for stem cell therapy. In dentistry, pulp from pri- mary teeth has been thorough- ly investigated as a potential source of stem cells with prom- ising results. However, the re- generation of an entire tooth, known as third dentition, is a highly complex process, which despite some promising re- sults with animals remains very far from clinical applicability. The opposite has been observed in the area of jawbone regen- eration, where there is a high- er level of scientific evidence for its clinical applications. Currently, adult stem cells have been harvested from bone marrow and fat, among other tissues. Bone marrow is haemat- opoietic, that is, capable of pro- ducing all the blood cells. Since the 1950s, when Nobel Prize winner Dr E Donnall Thomas demonstrated the viability of bone marrow transplants in patients with leukaemia, many lives have been saved using this approach for a variety of immunological and haemat- Stem cells in implant dentistry Dr André Antonio Pelegrine Fig. 1 A stem cell following either self-replication or a differentiation pathway. Fig. 2 Different tissues originated from mesenchymal stem cells. Fig. 3 The diversity of cell types present in the bone marrow. Fig. 4a Point of needle puncture for access to the bone marrow space in the iliac bone. Fig. 4b The needle inside the bone marrow. Fig. 5a A bone graft being harvested from the chin (mentum). Fig. 5b A bone graft being harvested from the angle of the mandible (ramus). Fig. 5c A bone graft being harvested from the angle of the skull (calvaria). Fig. 5d_A bone graft being harvested from the angle of the leg (tibia or fibula). Fig. 6 A critical bony defect created in the skull (calvaria) of a rabbit. Fig. 7 A primary culture of adult mesen- chymal stem cells from the bone marrow after 21 days of culture. Fig. 8a A CT image of a rab- bit’s skull after bone-sparing grafting without stem cells (blue arrow). Note that the bony defect remains. Fig. 8b A CT image of a rab- bit’s skull after bone-sparing grafting with stem cells. Note that the bony defect has almost been resolved. ‘Research into stem cells seeks to under- stand tissue maintenance and repair in adulthood and the derivation of the significant number of cell types from human embryos’ Fig. 9 A bone block from a mus- culoskeletal tissue bank. Fig. 10a A histological image of the site grafted with bank bone combined with bone marrow. Note the presence of considerable amounts of mineralised tissue. Fig. 10b A histological image of the site grafted with bank bone not combined with bone marrow. Note the presence of low amounts of mineralised tissue. Fig. 11a_Bone marrow. Fig. 11b_Bone marrow transfer into a conic tube in a sterile environment (lami- nar flow). Fig. 11c_Bone marrow homogenisation in a buffer solution (laminar flow). Fig. 5e_A bone graft from the pelvic bone (iliac).