Stem Cell Research for Dentistry - Literature review Example

Stem cell research and its connection to the dental field Introduction Stem cell research is one of the most exciting and fast moving but at the same time triggering several controversial ethical issues in medical science today. These are the subjects that continuously make headlines with new developments. Though there are several controversies around stem cell research this has helped to develop hope in those people who are suffering form various aliments. Before we get into the details of stem cell research, it is important to understand to basics of stem cells and why there are controversies in this field. The basic unit of stem cell research is the cell itself. A stem cell is a kind of cell that has the potential to divide or multiply indefinitely in culture. In fact these cells are destined to become any one of more than 200 different types of tissue cells in the body, such as muscle cells, blood cells, nerve cells and even new teeth. Science and technology has developed so much that in the recent years scientists hope to use these cells to develop new tissues, treatments and potentially even organs for transplanting into a patient. First and foremost argument made by the scientific community is that human stem cell research is said to promise new life changing treatments and possible cures for many devastating diseases and injuries, such as Parkinson’s disease, diabetes, heart disease, multiple sclerosis, burns and spinal cord injuries (Young 2-16). There are a number of sources for obtaining human stem cells. The first is IVF (In Vitro Fertilization) treatment, where surplus embryos (and unfertilized eggs for creating embryos) are donated for research with the consent of the donor rather than being destroyed following treatment. The second source is aborted tissues, which are used as stem cells taken from the aborted fetus. Another is umbilical cord blood, rich in stem cells. These cells are harvested following the baby’s birth. The most controversial is perhaps therapeutic cloning, where cells are created for research that is genetically identical to the donor (patient). This is done by removing the nucleus of an egg and fusing this egg with any enucleated cell from the donor. This will create an embryo genetically identical to the donor. Cells can then be harvested from this embryo for treatment. Being an exact replica, there is potentially less chance of rejection following transplantation. The US President’s Council on Bioethics recently published a whole white paper on Alternate Sources of Human Pluripotent Stem Cells (www.bioethics.gov). Sometimes these cells could be taken from the recipient patients themselves, avoiding any immune-rejection difficulties. At other times they are taken from donors. There are even proposals to create new non-embryonic organisms which can produce human stem-cells. What all these ‘adult’ stem-cells have in common is that they are derived from people without harming anyone. Umbilical cord blood, the placenta and even the amniotic fluid have in fact been found to be rich in stem-cells (McGuckin et al 245-255). Stem-cells have also been found in all the tissues found in our bodies such as the brain, pancreas, liver, skin, fat, muscle, blood, bone marrow, lungs, nose and tooth pulp. This paper discusses the importance of stem cell research in the dental field. At this point of time it is important to understand the how the tooth is formed and what are the fundamental cells involved in this process. The process of tooth formation begins with the interactions between epithelial and dental papilla cells. This interaction promotes tooth morphogenesis by stimulating a subpopulation of mesenchymal cells to differentiate into odontoblasts. These odontoblasts are finally destined to form the primary dentin. If we look into the morphology of odontoblasts, these are columnar polarized cells with eccentric nuclei and long cellular processes aligned at the outer edges of dentin (Smith et al. 273–280). Once the tooth erupts, reparative dentin is formed by odontoblasts as a result of common mechanical erosion, and through dentinal degradation which is generally caused by bacteria (Kitamura et al. 673–680). In fact, it is predicted that the odontoblasts arise from the proliferation and differentiation of a precursor population, probably within the pulp tissue (Ruch 923–938). Even though with the advancement in dentistry we have developed extensive knowledge of tooth development, and of the various specialized tooth-associated cell types, there is a lack of complete knowledge about the characteristics and properties of their respective precursor cell populations in the postnatal organism. It is not surprising to note that even till today, the identification and isolation of an odontogenic progenitor population from adult dental pulp tissue has never been done. Studies have shown that cultures of pulp cells resulting from early developing dental root tissue and pulp tissue can develop an odontoblast-like appearance with the capacity to form mineralized nodules in vitro (Couble et al. 129-138). This is a common trait that is normally attributed to cultures of bone or bone marrow cells (Gronthos et al. 4164–4173). Recent developments in stem cell research and tissue culture are leading to the development of revolutionary approaches to dentistry both in the repair and replacement of teeth. As the age passes by, most of us are worried about problems in the tooth, gum problems etc. However, these new researches are a hope for all of us as it can offer great dental solutions. It is nothing but the basic understanding of the genetic control of the key processes that form teeth in the embryo, has been a source of tremendous potential for further research. In fact, this understanding has led to the development of a tooth that could be recreated in the mouth of an adult. Studies conducted on mice populations show that tooth rudiments can be formed from in vitro cultures of non-dental stem cell populations. Additionally, the complete teeth and associated bone can also be obtained when these rudiments are transferred to adults. In general, it is seen that the periodontal diseases can slowly destroy the periodontal ligament (PDL), bone, and cementum which help to hold teeth in the jawbone. Most of the people are concern as destruction of this tissue is a major cause of tooth loss. Recent research has opened a new ray of hope in these people as through the stem cells within the PDL of third molars or the wisdom teeth it is now possible to generate cementum and new PDL (Seo et al. 149-155). Studies have demonstrated that the transplantation of these newly discovered stem cells holds great promise for restoring tissues destroyed by periodontal diseases among the large number of populations around the world. It is important that these studies should be conducted extensively on laboratory animals followed by clinical research. It is only through such studies that, we will be able to come to an era in which stem cells could be preserved when third molars are removed and “banked” against a probable need for biology-based regenerative treatment later in once life 1. In such cases no controversies of today that surround the stem cell research will arise and such an approach would conquer potential problems associated with rejection, since the person's own cells would be used in the treatment. In another set of research it was said that stem cells have been identified in the pulp of human primary (baby) teeth which are designated as SHED (Stem cells from Human Exfoliated Deciduous teeth). In fact studies show that SHED have an immense potential to divide continuously and differentiate into a variety of cell types, such as nerve, fat, and tooth generating cells. In animal studies using SHED, it was found that in mice when SHED cells are transplanted, they can differentiate into bone and dentin. It has been proven beyond doubt that deciduous teeth may be an ideal source of stem cells to repair damaged tooth structure, to regenerate bone, and perhaps even to treat nerve damage. It is important to understand that stem cells from deciduous teeth differ immensely from those found in permanent teeth. The reason behind this is because they divide more quickly and can generate bone, on the other hand cells from adult human dental pulp can only form a tooth-like complex of dentin and pulp (Miura et al. 5807-5812). Studies conducted by scientists in United States and Australia have found that deciduous teeth have healthy stem cells in their dental pulp. And such teeth may serve as an easily obtainable alternative to embryonic stem cells, the use of which is controversial. In some of the studies it was shown that when stem cells would be programmed to develop into teeth and then transplanted into the patient's jaw where the gap, it is thought it would then take roughly about two months for the tooth to fully develop. However this kind of research is only in its initial stages and it could be many more years before the technology is widely available to the general public. On average it is estimated that Britons aged over 50 lose around 12 teeth out of 32. according to Professor Paul Sharpe who is the genetic research scientist behind the technique and head of division of Craniofacial Biology and Biomaterials at the Dental Institute at King's College, "A key advantage of our technology is that a living tooth can preserve the health of the surrounding tissues much better than artificial prosthesis…. Teeth are living, and they are able to respond to a person's bite…. They move and in doing so they maintain the health of the surrounding gums and teeth." (BBC News 2004). Dr Songtao Shi, who is a paediatric dentist from the National Institute of Dental and Craniofacial Research, Bethesda, Maryland, isolated stem cells from the baby teeth of children aged seven or eight years. Dr Shi had earlier successfully isolated stem cells from adult dental pulp and thought that deciduous teeth might be a better source than the carious teeth of adults (Proceedings of the National Academy of Science of the United States of Americas 2000;97:13625). This study predicts that SHED cells may one day be used to regenerate native teeth or to secrete dentin, obviating the need for composite bone or metal implants. Besides since deciduous teeth are present though much of childhood they may serve as an easy and readily accessible and bankable source of autologous progenitor cells (Josefson 950). There are several factors including the dietary patterns that determine the dental health. Periodontal diseases are very common all over the world and the main signs are bone tissue destruction and subsequent tooth loss. Today’s research focuses mainly on regenerating the periodontium and is given high priority in craniofacial regenerative biology. Due to the complex structure of the periodontium consisting of both hard and soft tissues such as cementum, bone, periodontal ligament, and gingiva, its complete regeneration would require a multipotent cell population (Bartold et al, 169-189; Grezesik and Narayanan 474-484). According to Kawaguchi et al. (1281-1287) transplantations of ex vivo expanded autologous Mesenchymal Stem Cells (MSC) can regenerate new cementum, alveolar bone, and periodontal ligament in class III periodontal defects in dogs. Morphometric analysis revealed a 20% increase in new cementum length and bone area in animals treated with MSC. Additionally in subsequent study they reported a similar approach in humans when they transplanted 2 × 107 cells ml1 autologous expanded bone marrow-derived MSC mixed with Atelocollagen into periodontal osseous defects (Kawaguchi et al, 1197-1202). And all the patients showed significant improvement. In yet another study conducted by Ohazama et al (518–522) significant progress was reported toward the creation of tissue-engineered embryonic tooth primordia (tooth buds) using cultured cells. Using a mouse model, they tested different combinations of non-dental-derived mesenchymal cells such as embryonic stem cells, neural stem cells, and adult bone marrow cells with embryonic oral epithelium cells. For this purpose, the mesenchymal–epithelial mixtures were transplanted into the renal capsules of adult mice. The results showed that all mixtures resulted in the development of a tooth structure and bone. Additionally they also observed that the host tissues make no contribution to the donor tissue. It was also demonstrated that transfer of embryonic tooth primordia into the adult jaw resulted in the development of tooth structures meaning that an embryonic primordium can develop in its adult environment. These experiments conducted by Ohazama and others concluded that bone marrow-derived cells can form all mesenchymal-derived cells in a tooth structure. In conclusion, it can be said that stem cell research has a potential to find remedies for various diseases. Hence it is the need of the hour to promote this research. Above all since the adult stem cell has been proven to be as good as embryonic stem cells, research using adult stem cells need to be encouraged. There is a need to promote this research as it promises new treatments and possible cures for many devastating diseases and injuries and will allow scientists to explore the potential of this research to benefit the lives of millions of people who suffer from life destroying diseases. Progress in stem cell research and tissue engineering promises novel prospects for tissue regeneration in dental practice in the future. Hence it holds a great importance in the field of dentistry. Though embryonic stem cell research is under controversies, stem cells have been discovered in many adult tissues, including teeth that have the potential to form all adult tissues including the nerve and fate tissues. This branch of science have advanced so much that today it is possible that embryonic stem cells can be cultured and even produced from adult cells by the nuclear transfer method. Further, in future it may also be possible to perhaps grow new enamel, dentine, periodontal ligament, bone, or even whole new teeth using the stem cells for patients. This research is only in the initial stages and it is important to promote the research so that when tooth decay occurs, and the doctors would suggest for root canal treatments or replacing the complete set of original teeth with artificial once, this research would be considered as an alternative. 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