Oro-Dental-Derived Stromal Cells for Cranio-Maxillo-Facial Tissue Engineering - Past, Present and Future

Stomal/Stem Cells (SCs) can be classified as either embryonic (ESCs) or adult stem cells (ASCs), depending on origin. Embryonic stem cells (ESCs) can be derived from the inner cell mass of blastocyst stage embryos after fertilization. ESCs are potent and have un-limited self-renewal capacity, and can differentiate into cells of all three germinal layers of the organism; mesoderm, endoderm and ectoderm . While their characteristics are extraordinary and attractive for further investigation, the use of human ESCs is limited by an ethical controversy. Hence, ASCs have emerged, with no ethical debate (s) orbiting their study. ASCs can be harvested from many bodily tissues, and do fulfill all the criteria necessary to be considered as SCs, since they are long-lived, have a significant self-renewal capacity, can differentiate toward a set of various cellular types (such as chondrocytes, adipocytes, osteoblasts, among others) and have potential need/use in regenerative and reparative medicine.
Mesenchymal Stem Cells (MSCs) are one of the most controversial groups, not because ethical concerns regarding their harvesting, but for the proper utilization of the term. MSCs were first described by Arnold Caplan in 1991, taking their name from the Greek terms “meso” (middle) and “enchyme” (infusion, related to cellular tissue) making a relation with the embryonic mesoderm layer, establishing their capacity to differentiate toward skeletal tissues (cartilage, bone, marrow stroma, connective tissue, etc) as one of their principal characteristics [7]. Despite the amount of evidence of their existence, characteristics and functionality, there is controversy around them with respect to the nuances of the term MSCs, and what specific characteristics do all MSCs share.
To solve this situation, the International Society for Cellular Therapy (ISCT) stated minimum criterions to classify a potential lineage as MSCs. The first criterion is to display plastic-adherence capacity. Second, they must express certain biomarkers, such as the surface membrane protein Thy-1, usually denominated CD90 (Cluster of Differentiation 90), or the membrane gluco-protein Endoglin (also called CD105). Besides from the presence of the already mentioned CD90 and CD105, MSCs must be at least CD73+, CD14-, CD34-, CD44- and HLA-DR-. Finally, should be capable to differentiate to chondrocytes, adipocytes and osteoblasts, to be classified as MSCs.
Since the year 2000, several MSC types have been identified and isolated from oral tissues, including the teeth, dental pulp, gingival, periodontal and supporting structures (Figure 1) [10, 11, 12]. This has provoked cellular biologists and dentists to bridge and strengthen their relation, communication and collaboration even more, as a thorough understanding of the cellular mechanisms underlying these oro-dental MSCs must come along or go in parallel with the expected development of their use in different and wide range of therapies and/or therapeutic strategies.