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37Dental Tribune Middle East & Africa Edition | May - June 2014 implant tribune > Page 38 Stem cells in implant dentistry By Dr. André Antonio Pelegrine, Brazil T he human body con- tains over 200 dif- ferent types of cells, which are organised into tissues and organs that perform all the tasks required to maintain the viability of the system, including reproduc- tion. In healthy adult tissues, 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 re- pair the damage. In order to achieve this, quiescent cells (dormant cells) in the tissue become proliferative, or stem cells are activated and differ- entiate 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 deriva- tion of the significant number of cell types from human em- bryos. 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 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 abil- ity to generate daughter cells with the capacity of differen- tiation. 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 pro- duce 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 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 rea- sons, most scientific studies fo- cus on the applications of adult stem cells. Adult stem cells Fig. 1: A stem cell following either self- replication or a differentiation pathway. (All images are from: A. A. Pelegrine, A. C. Aloise & C. E. Sorgi da Costa, Células Tronco em Implantodontia; São Paulo: Napoleão, 2013). 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 mar- row.