Recently, the governing body for dentists in Singapore sent out a circular reminding dental practitioners that they are not allowed to carry out any activity relating to the harvesting of dental pulp tissues and DPSCs (dental pulp stem cells).
The reason behind this prohibition is that “dental pulp tissue and dental pulp stem cells currently (bolding mine) lack clinical evidence for therapeutic use and have not been accepted as a form of evidence based therapy for regenerative medicine nor dentistry by the local medical and dental professions.”
Before I go further, I must declare that I have absolutely no interest whatsoever in harvesting dental pulp tissue and neither do I encourage patients to spend money paying for a service which is unlikely to be put to good use in the near future. Sounds a bit like insurance? Well, that’s almost exactly what it is. So if there is currently no evidence that you’re having cancer or kidney failure, why buy a crisis cover? The majority of people who buy insurance will not gain from it, but they buy a policy in case of untoward circumstances because having no evidence of cancer of kidney failure currently does not mean that you won’t get any evidence of cancer or kidney failure in future.
Now let’s take a look at dental stem cells. What are they?
Dental pulp stem cells (DPSCs) are stem cells present in the dental pulp, the soft living tissue within teeth. They are multipotent, so they have the potential to differentiate into a variety of cell types. Other sources of dental stem cells are the dental follicle and the developed periodontal ligament.
Why are stem cells such cool stuff? They are like promising recruits in the army. When a battalion of commandos gets wiped out, you can train them to replace the commandos. When an artillery battery gets wiped out, you can train them to be artillery men. These cells give hope for patients who need organ transplants because theoretically (and sometimes in the laboratory), stem cells can be cultivated to produce various kinds of living tissues. However, not all stem cells have the same potential.
When we talk about stem cell potency, there are several levels to consider. A unipotent stem cell refers to a cell that can differentiate along only one lineage. Of all the stem cells, a unipotent stem cell has the lowest differentiation potential. This means that the cell has the capacity to differentiate into only one type of cell or tissue. Unipotent cells are found in the skin. You can technically grow new skin using these stem cells. However, patients who need skin grafts often need them urgently and there is currently no technique that yields quick and consistent results.
Stem cells can also be pluripotent. As far as embryonic origins go, there are only 3 categories of tissues in our body. Depending on its origin, a pluripotent stem cell can differentiate into one of 3 tissue categories. An ectodermal stem cell can grow into ectodermal tissue (skin, nerves). An endodermal stem cell can grow into endodermal tissue (lung, gut lining) and a mesodermal stem cell can grow into mesodermal tissue (muscle, bone, blood, urogenital).
Dental stem cells are multipotent and there is already quite a bit of literature on it. Multipotency describes progenitor cells which have the gene activation potential to differentiate into discrete cell types. They can theoretically be induced to grow into different types of cells (independent of embryonic origin) as in blood, brain and bone. Multipotent cells have been found in cord blood, adipose (fat) tissue, cardiac (heart) cells, bone marrow, and the mesenchymal stem cells (MSCs) which are found in our wisdom teeth. Seeing the huge potential of an insurance concept, businesses have pounced on the opportunity to sell pricey storage facilities for cord blood and even extracted wisdom teeth as they are the most readily available sources of multipotent stem cells.
Right there at the top of cell potency, totipotency represents the cell with the greatest differentiation potential, being able to differentiate into any type of tissue. Totipotent stem cells are only found in an embryo that is a few hours old – before it grows 3 layers. You can theoretically grow an entire organism or organ with a totipotent stem cell, but obviously, you would need to sacrifice a living organism in the process. Ethical issues get in the way, but it gets more interesting.
Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a “forced” expression of certain genes and transcription factors. By 2007 scientists have successfully produced human iPSCs derived from human dermal fibroblasts which are not even stem cells. The feat earned Shinya Yamanaka and John Gurdon the Nobel Prize in Physiology or Medicine 2012. This discovery raised a question. Why do we need to store or harvest stem cells at all if they could be made from an ordinary cell?
But let’s not get carried away and drift into the realm of science fiction. Stem cell technology is still in its infancy and the American FDA does not approve any of the stem cell therapies out there. Some are even considered dangerous. Nevertheless, clinics there are already using stem cells to treat problems ranging from arthritis and torn tendons to paralysis and stroke. These patients are willing to take the risk even though researchers say that there’s (currently) no evidence that the treatments work or are even safe.
What do we do to such experimental therapies? We certainly should not encourage them, but the practically harmless process of harvesting cord blood or dental stem cells should both count only as insurance policies. In the case of cord blood, there is only one chance at birth. For teeth, there are more opportunities, though the process is a little more invasive. What will the outcome be? Will we be able to grow new livers and kidneys from teeth? Will induced pluripotency render cord blood and dental tissue banking obsolete? Or will all this research finally lead us to a dead end?
Hundreds of healthy teeth are extracted in Singapore every day to make way for tooth movements and alignment. What’s wrong with banking these teeth? Those who opt for the service are merely placing their bets on the future. Why should they be dictated by the “lack of clinical evidence for therapeutic use and have not been accepted as a form of evidence based therapy for regenerative medicine nor dentistry by the local medical and dental professions”? Pessimistic and cynical as I am, I believe that the final outcome of a dead end to all this research is most unlikely.
Dental Phobia by Chan Joon Yee