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Dental Tribune Pakistan Edition

Pakistan Edition May 20146 DENTAL TRIBUNE The human body contains over 200 different types of cells, which are organised into tissues and organs that perform all the tasks required to maintain the viability of the system, including reproduction. In healthy adult tissues, the cell population size is the result of a fine balance between cell proliferation, differentiation, and death. Following tissue injury, cell proliferation begins to repair the damage. In order to achieve this, quiescent cells (dormant cells) in the tissue become proliferative, or stem cells are activated and differentiate 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 differentiated cells possess a short half-life and are incapable of renewing 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 undifferentiated 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 differentiation 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 regenerative medicine. It has made it possible to consider the regeneration of damaged tissue or an organ that would otherwise be lost. Because the use of embryo stem cells raises ethical issues for obvious reasons, most scientific studies focus on the applications of adult stem cells. Adult stem cells are not considered as versatile as embryo stem cells because they are widely regarded as multipotent, that is, capable of giving rise to certain types of specific cells/tissues only, whereas the embryo stem cells can differentiate 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 primary teeth has been thoroughly investigated as a potential source of stem cells with promising results. However, the regeneration of an entire tooth, known as third dentition, is a highly complex process, which despite some promising results with animals remains very far from clinical applicability. The opposite has been observed in the area of jawbone regeneration, where there is a higher 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 haematopoietic, that is, capable of producing 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 haematopoietic illnesses. However, the bone marrow contains more than just haematopoietic stem cells (which give rise to red and white blood cells, as well as platelets, for example); it is also home to mesenchymal stem cells (which will become bone, muscle and fat tissues, for instance; Fig. 3). Bone marrow harvesting is carried out under local anaesthesia using an aspiration needle through the iliac (pelvic) bone. Other than requiring a competent doctor to perform such a task, it is not regarded as an excessively invasive or complex procedure. It is also not associated with high levels of discomfort either intra or post- operatively (Figs. 4a & b). Bone reconstruction is a challenge in dentistry (also in orthopaedics and oncology) because rebuilding bony defects caused by trauma, infections, tumours or dental extractions requires bone grafting. The lack of bone in the jaws may impede the placement of dental implants, thus adversely affecting patients’ quality of life. In order to remedy bone scarcity, a bone graft is conventionally harvested from the chin region or the angle of the mandible. If the amount required is too large, bone from the skull, legs or pelvis may be used. Unlike the process for harvesting bone marrow, the process involved in obtaining larger bone grafts is often associated with high levels of discomfort and, occasionally, inevitable post-operative sequelae (Figs. 5a–e). The problems related to bone grafting have encouraged the use of bone substitutes (synthetic materials and bone from human or bovine donors, for example). However, such materials show inferior results compared with autologous bone grafts (from the patient himself/herself), since they lack autologous proteins. Therefore, in critical bony defects, that is, those requiring specific therapy to recover their original contour, a novel concept to avoid autologous grafting, involving the use of bone-sparing material combined with stem cells from the same patient, has been gaining ground as a more modern philosophy of treatment. Consequently, to the detriment of traditional bone grafting (with all its inherent problems), this novel method of combining stem cells with mineralized materials uses a viable graft with cells from the patient himself/herself without the need for Continued on page 11 Stem Cells in Implant Dentistry Author: Dr. André Antonio Pelegrine, Brazil Fig.1 Fig.2 Fig.3 Fig.4a Fig.4b Fig.5e Fig.5d Fig.5c Fig.5b Fig.9Fig.6 Fig.7 Fig.8a Fig.11d Fig.11cFig.11bFig.11a Fig.11g Fig.11hFig.11fFig.11e Fig.10a Fig.10b Fig.8b Fig.5a 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.5e A bone graft from the pelvic bone (iliac). Fig. 6 A critical bony defect created in the skull (calvaria) of a rabbit. Fig. 7 A primary culture of adult mesenchymal stem cells from the bone marrow after 21 days of culture. Fig. 8a A CT image of a rabbit’s skull after bone-sparing grafting without stem cells (blue arrow). Note that the bony defect remains. Fig. 8b A CT image of a rabbit’s skull after bone-sparing grafting with stem cells. Note that the bony defect has almost been resolved. Fig. 9 Abone block from a musculoskeletal tissue bank combined with a bone marrow concentrate. 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 (laminar flow). Fig. 11c Bone marrow homogenisation in a buffer solution (laminar flow). Fig. 11d Bone marrow combined with Ficoll (to aid cell separation). Fig. 11e Pipette collection of the interface containing the mononuclear cells (where the stem cells are present). Fig. 11f Second centrifuge spin. Fig. 11g The pellet containing the bone marrow mononuclear cells after the second centrifuge spin. Fig. 11h A bovine bone graft combined with a bone marrow stem cell concentrate. All images courtesy of Células Tronco em Implantodontia.2 Implant Dentistry

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