THE USE OF DENTAL PULP STEM CELLS IN MEDICINE AND DENTISTRY

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Phebe Harris
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1 THE USE OF DENTAL PULP STEM CELLS IN MEDICINE AND DENTISTRY BY GLESNI HAF GUEST-ROWLANDS Pass with Merit RESEARCH PAPER BASED ON PATHOLOGY DAY LECTURES AT MEDLINK

2 ABSTRACT Stem cell research is an area of medicine that is relatively new, but it certainly raced in front of most other area of medicine. The area is rapidly growing, with new advances being made every day. My interests in oral medicine prompted me to look for any research done in the dental/oral field with stem cells, which is what this paper is about. There are many possibilities for treatment with the discovery of Dental Pulp Stem Cells. These stem cells are easily accessible, and they do not raise any ethical issues, since they are the patient s own. I concluded that stem cells have amazing potential, as long as their use is not exploited. INTRODUCTION Stem cells- they are something that is often discussed everyday in the possibilities of new and regenerative medicine, especially now, with Britain s ageing population, with the ever-growing need of self preservation. In England alone, there are 570,000 people living with dementia, a number that is likely to double in the next 30 years. These figures have prompted scientists to search for new avenues for treatment of diseases, more importantly, the prevention. A prominent source for this kind of treatment is stem cells. These cells have, in theory, the key to treating all kinds of diseases. What is a stem cell? Cells have an average lifetime of 10 years. Some cells such live a very short life; such as white blood cells, which live only for a day, or cells that line the gut, which live for a week. Other cells can live a lifetime, from when they re formed in the embryo, until death, such as cells in the eyes, heart muscle cells and brain neurons. New cells are formed through cell division, or mitosis. All cells, though, are originally formed from stem cells in the embryo. A stem cell is an undifferentiated cell that is capable of differentiating into a specialised cell. This is an exciting new concept for scientists, as a world of opportunities arises from these cells. Stem cells are capable of continuous cell division, producing stem cells, and differentiated cells. Stem cells are found in three main sources: 1. Adult Bone Marrow Many adult tissues contain stem cells that are able to replace damaged or dead tissue after an injury; this means that they are found in tissues, and generate cells for that tissue. These tissues include skin, muscle, the brain, intestine and bone marrow. Another type of adult stem cell is the mesenchymal stem cell that is found in many tissues, including bone marrow, and is able to produce bone, cartilage and fat. It is also possible that these cells can aid the regeneration of tissues, which could be used to treat arthritis and non-healing bone fractures. There are a few treatments that use adult, tissue-specific stem cells, which 2

3 include diseases of the blood, after treatment for cancers, skin cell therapies for burn victims, and corneal replacements using limbal cells. Most adult stem cells are multipotent, which means that they can differentiate into a few different cells, e.g. bone marrow can make red or white blood cells. 2. Cord Blood Stem Cells Umbilical cords are filled with blood-forming stem cells, and are able to be harvested after the baby is born, which are usually discarded after birth. These types of stem cells are similar to adult stem cells, in that they re tissue specific, and are used for the same treatment. A baby s cord blood can also be kept in a blood bank, so that if the baby ever needed stem cell treatment, it would be possible to use the baby s own stem cells, or to treat the baby s relatives. The ethical issue with this is that in countries where healthcare is not provided for free, e.g. the USA, companies are responsible for keeping the cord blood for a fee. This means that companies could exploit the price, and it would mean that only the rich would be able to have the cord blood stored. Another issue is that some disorders that affect the baby also might affect the stem cells, so they would be ineffective when treating the baby. In the future these cells could also be used to treat strokes, heart disease, diabetes and Parkinson s. Currently, there is no technology to use these cells. 3. Embryonic Stem Cells Embryonic stem cells are found in very early embryos, usually five days after fertilisation, and in theory, can specialise into any kind of cell in the body. However, getting the cells to differentiate in a lab is not an easy task, and the transplanted stem cells could transform into cancerous cells. Therefore, to use the cells, they would be needed to mature to be effective and to minimise the risk of cancer. While these cells have enormous possibilities there is strong opposition to using embryos in this way. Ethical issues play a big part in this since many opposing parties say that using embryos, then destroying them is murder since life begins at conception. Currently there are no treatments using embryonic stem cells being used. Newly fertilised eggs are totipotent; these are usually eight cells that can differentiate into any cell in the body, including the placenta, so a new organism can be formed. At three to five days after conception, the cells have split up further, creating a ball of cells called a blastocyst, which contains about 100 stem cells, which are pluripotent, see figure 1. This means that the embryonic stem cells can specialise into any type of cell, but cannot form a new organism. Figure 1. Diagram showing the stages of differentiation of embryonic stem cells. 3

4 What scientists are now researching is if there is a possibility to treat, what was previously thought of as un-curable diseases. If cells are able to be programmed into a totipotent state, it means that they can be specialised into any kind of cell in the body, by using tissue cultures. This, in turn can mean that degenerative diseases such as muscular dystrophy, Parkinson s, and Alzheimer s could possibly be cured. A big avenue that scientists are considering is transplanting organs into patients, grown from their own stem cells, through regenerative medicine. Human organs have been transplanted into patients since 1954; with the first organ to be transplanted was the kidney, in Harvard medical school. The idea of transplanting organs had been born long before this time; the problem was how to overcome the problem of rejection. Rejection is the body s natural defence mechanism, where it identifies the donated organ as a foreign body, and attacks it, under the impression that the organ will cause harm to the body. The immune system is in place to recognise antigens (which are proteins found on the surface of a harmful substances) of bacteria and viruses, which are different from the antigens found in the patient s body, so that it can attack the invaders, by using white blood cells, through process such as phagocytosis ECT. Organs which can be transplanted are the heart and heart valves, kidneys, liver, pancreas, lungs, thymus, bowel, and the tissues are femoral and saphenous veins, corneas, tendons, ligaments, bones, and skin. In the US alone, there are 113,200 people waiting for an organ, 18 people die every day waiting on the list. Using stem cells to grow organs for patients is an amazing idea, which is what many scientists hope is the future for organ transplantation. Using a patient s own cells to grow a new organ would mean that the patient wouldn t reject the organ, since the organ is made up of the patient s own cells, instead of using a donated organ. This would mean that patients would not need to be treated with immunosuppressant s, which would mean that they are less susceptible to infections, since their immune system is able to work to its full potential, and there would be no increased risk of cancer from taking the drugs. There has been some development in regenerative medicine, with the discovery of the importance of the structural element, the extra-cellular matrix (ECM). Normally, when the body is injured, cell death occurs at the damage site, where white blood cells are sent, and scar tissue heals the wound: these scar tissues prevent any further cell growth in the affected area. ECM is made up of polysaccharides, and is the structure that cells are held to inside the body. It has been observed that the ECM does more than give the cells a structure to bind to, but it also influences which cell a stem cell will specialise into, determining its function. 4

5 DISSCUSION Dental Pulp Stem Cells (DPSC s) Teeth are an essential part of the digestive tract. They re the first point, at which food is digested, by physical digestion, breaking large pieces of food into smaller and more compact pieces, making it easier to swallow the food, and aiding in chemical digestion. Teeth are not nonreactive objects: they are living structures that treat and feel food while it is chewed. Every tooth has its own supply of nerves and blood vessels that gives it its sensitivity, and keeps the teeth alive. Humans have two sets of teeth during their lives; primary and permanent teeth. There are usually 20 primary teeth, which are replaced by around 32 permanent teeth. Tooth replacement usually happens at the age of 5, and takes several years to complete. Permanent teeth are grown from teeth buds below the primary teeth in the jaw. The buds contain an enamel organ in which ameloblast cells produce enamel. Inside the enamel organ odontoblast cells produce dentine, and sockets of bone grow around the roots of the teeth. The root of the teeth is held by the cementum in the periodontal membrane in the jaw bone. The tooth consists of many three main layers: the crown, the neck and the root, see figure 2. The crown of each tooth is coated with enamel, the hardest material in the body, which protects the underlying dentine. Enamel gains it s hardness from tightly packed rows of phosphorous and calcium crystals which are found within a protein matrix. Mature enamel is not considered to be living, and after its formation during tooth development, very little new enamel is produced. The layer beneath the enamel is the dentine, 5 Figure 2. Diagram showing the structure of a tooth. which is a major component inside the tooth. Dentine is slightly softer than enamel, is more similar to bone, and is elastic and compressible, unlike enamel, which is brittle. Dentine is considered as live tissue since it contains tiny tubes that connect with the nerves in the pulp, that make this part of the tooth sensitive to hot and cold. Below the gum line, the dentine of the root is covered by a thin layer of cementum, which is a hard structure, similar to bone, to which the periodontal membrane attaches itself to. The periodontal membrane holds the root of the tooth to the bone of the jaw. The membrane contains elastic fibres

6 to allow some movement, acting as a shock absorber during chewing. The pulp forms the central part of the tooth. The dental pulp is made of soft tissue, contains blood vessels to supply nutrients to the teeth and nerves, so that the tooth can sense heat and cold. The pulp also contains lymph vessels that carry white blood cells to the tooth, to help fight against bacteria. The root canal is an extension of the pulp, and connects with the surrounding tissue through the opening at the tip of the root. This opening is in the cementum, in which the tooth s blood and nerve supply enter the pulp. Stem cells are found in most tissues in the body, but some are easier to recover than others. Stem cells in tissues usually look the same as the surrounding cells; their numbers are low, about one stem cell for every 100,000 adult cells, and are buried deep within the tissue. The recent discovery of Dental Pulp Stem Cells (DPSC s) have opened a new window into stem cells research, as the cells are easily recoverable and are readily available. The stem cells are found in abundance in baby teeth, wisdom teeth and permanent teeth. The stem cells are a part of the group of dental cells called odontoblasts. Originally, it was thought that DPSC s were able to differentiate into odontoblasts, and similar tissues, such as dentine, but it has been found that the cells are much more potent. It has been discovered that DPCS s can also differentiate into dental pulp, neural cells, adipocytes (fat cells), osteoblasts (essential in bone formation), chondrocytes (cartilage), and striated muscle tissue ( found in cardiac muscles). The stem cells are mesenchymal stem cells, and are multipotent, which means that they can differentiate into a few different types of cells that are closely related. For example, a multipotent haematological stem cell would be able to differentiate into different types of blood cells, but not a heart or brain cell. Teeth extracted for orthodontic purposes, which are perfectly healthy, are great candidates for stem cell extraction, instead of being discarded. This could mean that patients could keep the stem cells and have a supply of personal stem cells available if they ever needed treatment. This would also be beneficial to the patient, as there would be no need to extract stem cells when the patient would be ill, or receive donated stem cells, there would be no need for anti-rejection drugs since the transplanted cells would be their own. There have been some recent breakthroughs in the area of regenerative medicine, with the most exciting, the development of a dental scaffolding. Currently, dental implants are used to replace teeth, or a single tooth, if the loss of tooth/teeth has caused the mouth to shrink, so that the patient is unable to wear dentures. Implants are fitted by drilling titanium screws in to the jaw bone to support a crown, denture or bridge. Implants take time to carry out, and are expensive, so is not a very practical solution for many patients. 6

7 At Columbia University Medical Centre, Dr. Jeremy Mao has developed an alternative to dental implants. In 2010, he unveiled a three-dimensional scaffold made of natural materials that has the potential to regenerate an anatomically correct tooth in nine weeks. A procedure has been developed at the university s Tissue Engineering and Regenerative Medicine Laboratory, so that a patient s own stem cells can be directed towards the implanted scaffold, where the cells will colonize the scaffold, so a tooth can grow in the socket and merge with the surrounding tissue. This technique means that the tooth doesn t need to be grown in a Petri dish, is a completely natural process of growth, and it has a faster recovery time. The technique is not yet available for patients, but holds massive potential, and if used, will revolutionise dental practice. Another breakthrough in the dental field has been the bioengineered tooth unit. Takashi Tsuji at Tokyo University of Science has used stem cells from mice to grow replacement teeth at can be implanted into the mouth, and become fully functional. To grow the teeth, the research team led by Takashi Tsuji extracted DPSC s from the molar teeth in the mice. These where then cultured in a lab and put into a mould that would give the correct size and shape to the tooth. When the cells had fully matured into complete teeth, they were transplanted into the jaws of one-month-old mice. The transplanted teeth fused with the jaw bones of the mice within about 40 days. The researchers also found that nerves had started to grow in the transplanted teeth. This research has shed light on the process of growing stem cells outside the body, and how they can develop inside the body as well. The only problem with the research is that the cells that were used where all ready differentiated, meaning that they were all ready programmed to grow into the different parts of teeth. This research is another solution for patients who have lost their teeth, meaning that they would not need to wear dentures, or have a gap inside their mouths where the tooth used to be. This research has been evolved, with a further development form Takashi Tsuji and his team. The latest method has been shown to save 10 days in growing new teeth. The research has been carried out on mice, and at the moment is unsuitable for humans. The team developed what they called a seed, combining the necessary cells to form the tooth, which later started to grow into tissue to create the tooth. The seed was then wrapped in a piece of plastic and implanted in to the mouse s kidney, where it formed into a tooth. After the tooth had developed enough, it was transplanted into the mouse s jaw, where it connected to the nerves and blood vessels, the same as in the previous study. This study is one that raises more ethical issues than previous studies, with the need to grow the tooth in the kidney, which raises the question is it a viable option, since the only benefits are that it saves 10 days in the development of the tooth? Research shows that DPSC s are among the most powerful stem cells in the body, since they replicate at a faster rate and for a longer period than other types of stem cells in the body. 7

8 A study published in IOP s Journal of Breath Research in February, showed that DPSC s were able to differentiate into hepatic cells, and this ability was increased by hydrogen sulphide. Hydrogen sulphide is produced naturally in human tissue, and is known worldwide for being the cause of bad breath, but its role in encouraging the differentiation of cells into hepatic cells is currently unknown. The DPSC s have been seen to produce a higher number of hepatic cells, and a higher purity in the cells. The fact that the cells were purer also reduces the chances of a patient developing cancer after receiving a transplant to almost negligible, compared to those patients who received bone marrow transplants. Two batches of cells where prepared, one in hydrogen sulphide, while the other was used as a control, incubated for 3, 6 and 9 days, harvested and examined, to see if they had successfully differentiated into hepatic cells. The researchers tested the cell s ability to store glycogen, and its ability to produce urea to see how successful the differentiation had been. Traditionally, hepatic cells have been obtained from fetal bovine serum, but this method would produce a higher yield and would be safer, on top of the benefits from using a patient s own cells, discussed earlier. Of course, the key issues in modern society are how to live longer, and how to make the most money. These two issues have been walking hand-in-hand when it comes to stem cells. A new avenue that entrepreneurs and biologists have been looking into is saving stem cells. Many businesses have been set-up so that patients can store a personal supply of stem cells, in case of the need during a patient s life of stem cell treatment. These businesses are very good, in the sense that they aren t too expensive, that only the hugely-wealthy can afford, and are open to the general public. The flipside to this is that people who are unable fund these kinds of projects, are yet again left out of medical care. This problem might not be that relevant in countries like the UK, where medical care is primarily funded by the government, but in countries like the USA, this is another way of widening the divide between the rich and the poor. CONCLUSION Stem cells hold the key to future medicine. The ideal case would be that scientists could reverse cell differentiation, so that the cells are reversed into a pluripotent, or even totipotent state. If cells where able to be induced into a totipotent state, it would mean that it would be possible to grow a foetus, which might bring about the development of designer babies, where people might choose the characteristics for their children. This raises a whole truck-load of ethical issues, with one being how far can we go, in tampering with life? Another problem with stem cell treatment is that we do not fully understand the longterm effects, since the research has only been around for a few decades. It might also cause the shut-down of services such as donating blood, since all patients might have a personal store of stem cells. What would happen if a patient had a disease that also affected their stored stem cells? It also is worth thinking about 8

9 how far we are willing to go to self preserve? The net birth rate in the world is increasing, with world hunger already being a problem. If less people are going to die, because they are saved by stem cell treatment, overcrowding and world hunger is going to become an ever growing issue. At the moment though, stem cells are one of the most important factors for medicine, and one that will be for a long time. What needs to be done is monitoring of research, making sure that research is being carried out for the right reasons: that is, to save lives, which is definitely what will happen. What Are Stem Cells?: Types Of Stem Cells: Overview of Stem Cells: Stem Cells, general information: The tooth is nature's 'safe' for your family's unique stem cells: Transplant Rejection: What are stem cells, and why are they so important?: How stem cells work: Creating organs from our own stem cells: Dental Pulp Stem Cells Transformed by 'Bad Breath Chemical Tooth anatomy: Dental Pulp Stem Cells: Noninvasively Obtained Stem Cells: Dental treatments: Stem Cell Dental Implants Grow New Teeth Right In Your Mouth: Japan researchers grow tooth in mouse kidney: 9

10 Books: Kent, Michael. (2000) Bioleg Uwch(Welsh Version) (Advanced Biology), OUP publishing. Page 164. Simpkins, J. And Williams, J.I, Collins Educational; Third edition edition (19 Dec 1997) Page 282 Picture References Figure 1 iw=1366&bih=625&tbm=isch&tbnid=czmj6odhtnjqrm:&imgrefurl= w.csa.com/discoveryguides/stemcell/overview.php&docid=jbkb4xc0y3gqtm&img url= 3&ei=OLFkT5TWCajX0QXIiqGyCA&zoom=1&iact=hc&vpx=447&vpy=161&dur =1455&hovh=235&hovw=214&tx=110&ty=134&sig= &p age=1&tbnh=127&tbnw=118&start=0&ndsp=24&ved=1t:429,r:3,s:0 Figure &bih=625&tbm=isch&tbnid=QJ5S9- u5rek9mm:&imgrefurl= inveneers/&docid=bbjaeoqxrhiezm&imgurl= iners.com/wpcontent/uploads/2011/06/tooth5.gif&w=300&h=342&ei=gsfkt_vplmmp0aw1u 7CuCA&zoom=1&iact=rc&dur=155&sig= &page=1&tbn h=135&tbnw=118&start=0&ndsp=23&ved=1t:429,r:3,s:0&tx=42&ty=3 10

PREMATURE PRIMARY TOOTH LOSS

Disclaimer This movie is an educational resource only and should not be used to manage your dental health. All decisions about the management of premature primary tooth loss must be made in conjunction