Gum Stem Cells (Lay)
A Scientific Review

Introduction:

The periodontium is the area of specialized tissue surrounding the tooth and anchoring it to the underlying alveolar bone.  It is composed of four regions; the cementum, periodontal ligament (PDL), gingival (gums), and the alveolar bone.  Periodontal disease is a bacterial infection that leads to tissue damage of the periodontium and is the major cause of tooth loss.  The PDL goes through limited regeneration and repair if there is no therapeutic involvement (Ivanovski et al, 2006).  The current therapeutic methods are also somewhat ineffective in that they have variable efficacy as well as safety issues among other things. 

Figure 1:  Cross Section of a Molar and the Surrounding Tissue.

Background:

The term stem cell refers to any number of cells that are able to self renew and are not committed to being any one specific cell type.  Mesenchymal stem cells (MSC) can differentiate into different types of connective tissue such as muscle, endothelial cells, fibroblasts, osteoblasts, adipocytes and chondroblasts.  Since the periodontium is composed of these types of cells, it is believed that the PDLSC cells are derived from MSC (Ivanovski et al, 2006).  The PDLSC differentiate into three different cells in order to make up the tissues of the cementum, PDL, gingival and alveolar bone. (See Fig. 2)

Fig 2: Differentiation of adult mesenchymal stem cells and progenitor cells into PDL
            Cells.

                       
Markers of PDLSC:

PDLSC are specialized mesenchymal stem cells (MSC) that express markers that are similar to those used to identify MSCs.  A specific antigen marker does not exist for MSC’s or PDLSC’s.  Therefore, a combination of markers that are found on MSC’s must be used in order to identify the cells (Seo et al, 2004).

Potential Clinical Application

A long term goal for dentist would be to use PDLSC to regenerate damaged areas within the oral cavity in order to restore the function of PDL tissue.  With future research it may be possible to take PDLSC from a healthy donor, cause proliferation of the sample tissue and transplant it into a recipient that has periodontal disease to regenerate the PDL tissue (Ivanovski et al, 2006; Seo et al, 2004; Shi et al, 2005).  Present research is also looking at the possibility of storing cryopreserve PDL tissue for future use (See Fig.3) (Seo et al, 2005).

Figure 3: Potential Therapeutic Methods for Periodontium Regeneration using PDL Tissues.

Future Studies:

            Many issues still remain to be discovered about PDLSC.  Future experiments are still needed to determine the exact number of PDLSC, location of the PDLSC within the tissue and determining the specific markers for PDLSC.  Also, the maximum amount of time that PDLSC can be cryopreserved and are still able to retain their ability to differentiate needs to be determined.  Knowing all of this information would be necessary for the advancement of these stem cells into one day having a clinical role.

References:

1. Ivanovski S, Gronthos S, Shi S and Bartold PM. “Stem cells in the periodontal ligament.” Oral Disease. 12: 358-363, 2006.
2. Seo BM, Miura M, Gronthos S, Bartold PM, Batouoli S, Brahim J, Young M, Robey PG, Wang CY and Shi S.  “Investigation of multipotent postnatal stem cells from human periodontal ligament.”  Lancet. 364: 149-155, 2004.
3. Seo BM, Miura M, Sonoyama W, Coppe C, Stanyon R, Shi S.  “Recovery of stem cells from cryopreserved periodontal ligament.”  Dent Res.  84(10): 907-912, 2005.
4. Shi S, Bartold PM, Miura M, Seo BM, Robey PG, Gronthos S. “The efficacy of mesenchymal stem cells to regenerate and repair dental structures.”  Orthod Craniofacial Res. 8: 191-199, 2005.

Acknowledgements
This review was prepared by the following graduate students in the Stem Cell Biology Class, Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey: Mary Dovlatyan, Jorge Lau, Ruchika Mohla (in alphabetical order).

Teaching Assistant:  Michael Riccardo