It’s slowly becoming apparent that stem cells reside just about everywhere inside the human body. Even in the seemingly unlikely places, such as teeth.
Because children lose their baby teeth as they grow up, the stem cells in teeth are one of few types of stem cells that are naturally molted, or exfoliated. Consequently, because these stem cells can be harvested noninvasively, without harming the patient, they are quite appealing for medical applications. These stem cells reside in the dental pulp of the tooth, which is the living tissue at the center of the tooth, and so were aptly named dental pulp stem cells (DPSCs) by their discoverers in 2000. In addition to being easy to come by, DPSCs also have the potential to become many different types of cells.
As you might guess, DPSCs can produce some of the primary components of teeth: pulp and dentin. However, they cannot grow entire new teeth. In fact, it’s unclear whether they can even create the other two major components in teeth, enamel and cementium. But, even if they cannot create whole teeth by themselves, DPSCs are still quite useful because they can turn into a wide range of cell types, which has to do with the stem cell category they belong to.
Dental pulp stem cells belong to the large umbrella family of stem cells called mesenchymal stem cells (MSC). The term “mesenchymal” may sound daunting, but it just refers to a part of the developing embryo. The early embryo is made up of three cell layers: endoderm, mesoderm, and ectoderm. Each of these layers becomes different tissues and organs of the adult animal’s body, together making a whole. The mesoderm layer becomes support structures throughout the body, such as bone, cartilage, connective tissue, smooth muscle, adipose tissue, lymph nodes, and blood cells. MSCs are mostly derived from mesenchymal tissues, which largely originate from this mesoderm layer.
In addition to teeth, MSCs have also been harvested from many different tissues in the human body (bone, cartilage, muscle, umbilical cords, blood, amniotic fluids, and some fetal tissues). Since the 1960s and 1970s it’s been known that there are MSCs in bone marrow. (However, because other stem cells were already discovered in bone marrow, specifically hematopoietic stem cells, MSCs were not widely accepted as a stem cell type until the late 1990s.) To date, MSCs from bone marrow and adipose tissue have been the most studied, as they are relatively easy to harvest in large numbers.
Since their relatively recent discovery and addition to the MSC family, dental pulp stem cells have been greatly characterized and found to literally have great potential. To understand what cell types DPSCs can become, it’s important to know what cell types MSCs in general can turn into. Although MSCs have the potential to become multiple different types of cells (they’re “multipotent”), the three key cell types all MSCs can become are osteocytes (bone cells), chondrocytes (cartilage cells), and adipocytes (fat cells). Since they are MSCs, DPSCs can become these three cell types. However, different MSCs can turn into different, additional cell types depending on the tissue they were harvested from. For example, some MSCs, including DPSCs, can also become muscle cells.
Interestingly, DPSCs actually display some properties of another group of stem cells as well. Most researchers classify them as MSCs, but DPSCs are also similar to neural crest stem cells (NCSCs) (the term “neural crest” again applies to a specific part of the developing embryo). For example, DPSCs can become melanocytes, which are not a mesenchymal cell type. Clearly, further characterization of DPSCs is desirable as even their basic classification remains unclear.
Because they can be obtained in a completely noninvasive manner and have relatively broad differentiation capabilities, dental pulp stem cells have great potential to be used in medical applications, such as healing wounds and regenerating tissues. MSCs in general have been significantly pursued for these applications, especially since MSCs have been found to inhibit inflammation and immune responses. A major barrier, which has prevented more widespread use of MSCs (including DPSCs) in the medical field, has been how they are harvested. The groups of cells can be rather heterogeneous, containing the desired stem cells but also many other cell types. Also, the cells can vary from donor to donor. However, great efforts are being made to standardize isolation procedures to bring experiments from the laboratory to clinical utility.
In the last few months, dental pulp stem cells were reported to have been successfully used in their first human clinical trials. Specifically, studies reported that DPSCs could be used to repair bone tissue, suggesting that DPSCs could also be used to safely repair or regenerate other tissues and organs. In rats, DPSCs have also been shown to reduce myocardial infarctions (heart attacks). Clearly DPSCs hold much potential, and biotechnology companies such as the National Dental Pulp Laboratory in Massachusetts have already jumped at the opportunity. They already offer to cryogenically freeze the DPSCs from baby teeth so that the DPSCs can potentially be used later in life if they’re needed (just as many companies offer to do for umbilical cords, which contain mesenchymal and hematopoietic stem cells). In other words, the tooth fairy may have just found a way to make a tidy profit from all those baby teeth.
For more on Dental Pulp Stem Cells, see Teisha Rowland’s “All Things Stem Cell post on Dental Pulp Stem Cells: Noninvasively Obtained Stem Cells” or her “All Things Stem Cell post on Mesenchymal Stem Cells: A Diverse Family, Large and Still Growing,” The National Institute of Health’s Stem Cell FAQs, a recent clinical study using DPSCs for bone repair, a study
using DPSCs to improve myocardial infarctions in rats, the Web site for the National Dental Pulp Laboratory, or, for a visual explanation of terms used, see All Things Stem Cell’s Visual Stem Cell Glossary
Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at firstname.lastname@example.org.