 I'm Arthur Nailor, I'm the Interim Principal here at St Mary's, and it's my very pleasant responsibility and duty to introduce Professor John Nicholson's inaugural lecture. John Nicholson is a very distinguished materials scientist whose research concerns advanced materials for the repair of teeth and bones. Since coming to St Mary's, he's actually been very much more than a great research scientist. He's leading on a new degree in applied physics with the National Physical Laboratory, and he's also the interim head of the School of Health and Applied Science, of Sport Health and Applied Science, and I must say, after a few weeks back, a very, very great asset to St Mary's. John studied chemistry at Kingston University as doctorates from London South Bank. He then joined the laboratory of the government chemist in 1983, where he eventually became head of materials research, next he moved to teach and research at the Dental Institute of King's College London, before taking up a personal chair in biomaterials chemistry at the University of Greenwich in 2002. And joined St Mary's as Professor of Applied Science in 2012. John, tonight, is going, well that's the title, Long in the Tooth, and he tells me that tooth decay is generally considered to be the most prevalent of all human diseases. Actually coming from Scotland, that's something you'd recognise, because the combined effect of sweets, cakes, and deep fried Mars bars, it means that it's quite prevalent from an early age. In fact, I was looking at the statistics, because Scotland's got a desperate record in dental decay, but it's sad, it's awful that a third of primary one children have dental decay. It used to be 50%. So this is going to be a fascinating evening for those of us who remember dentistry with absolute horror in our own time. John has published 160 scientific papers, he's written four books, and he's had 2,000 citations, and if you spare me for a horrible use of puns and words, John, you're a man of great wisdom and impact. Thank you, and after that introduction, I can't wait to hear what I've got to say. I called today's talk, Long in the Tooth, partly in recognition of my extreme personal advancing years, but I wanted to add the subtitle, The Physics of Tooth Repair, again partly because, as Arthur's mentioned, I'm here in part at St Mary's to lead the new applied research. My physics degree, and so I thought it was appropriate to mention physics in the context of this talk. I could have equally said the material science of Tooth Repair, and that's what we're going to be looking at tonight. As we go through, I will drop hints, not very subtle ones, about my personal contribution to this field, where I'm going to be talking about my research. But before we do that, I want to thank, firstly, everybody who's come. It's a very interesting collection as I look round the faces in the audience of new colleagues, former colleagues, old friends and family members, and I do appreciate the fact that all of you have spared the time tonight, and I just hope, as I say, I make it worth your while. So tonight I'm going to be looking at these aspects of the subject. We will start with some fairly dramatic discussion about the horrible topic of Tooth Decay, and then we're going to move on and look at how teeth are repaired. I'm going to take as the third point modern materials, the kind of materials I've been working on, not as my exclusive research concern, but as my main ones, for about the last 30 years, and I shall finish by saying a little bit about some of our current research activities. Current in the sense that I'm still writing some of them up, and in the sense that they represent some of the future work that we're going to be doing here, partly at some areas and also with our involvement with National Physical Laboratory. The one person who can't be here, but I would like to pay tribute to, and this is Dr Alan Wilson, who was my mentor in this field. He was my head of department when I was at the laboratory of the government chemist. He was a brilliantly inventive scientist, and he invented the particular tooth material, the glass enormous cement that I'll be spending quite a lot of time talking about. And he, although he was my boss, we ended up becoming good friends, and he came to work with me when I moved to the King's Dental Institute. He was honorary senior research fellow there for several years, and in fact we published together what turned out to be his last paper in 2004. As he told me with some regret, he didn't quite make 50 years of publishing. His first paper was published in 1955, and so I did try, but we couldn't quite squeeze any more data out to give him his 50th year. But a very engaging man, and I wanted to honour him tonight at the beginning of my lecture. So now let's think about tooth decay, this horrible subject which we all have some idea about and no doubt some personal experience of. So here is a tooth, a typical sort of tooth, and these are the kind of components of the tooth that we need to be aware of. First of all, let me just see if I can work this one. Right, here is a tooth sitting in its socket in a piece of bone. The bone sort of rises to carry the tooth in what is known as the alveola ridge, and running around the edge we have something that keeps it in place, the periodontal ligament. This may cause problems, but we're not going to be talking about those while we're concerned with teeth. I'm going to be thinking about the upper part of the tooth, and the upper part of the tooth is divided into three zones. On the outer layer we have the enamel. The enamel is a substantially mineral tissue, it's the hardest tissue in the body. It's made up of a mineral called hydroxyapatite, and about 97% of the enamel is made up of this mineral. There's a few other bits and pieces in there, a pinch of water, a tiny bit of protein, but mainly it's the mineral phase. Below it, in this sort of off-white colour, we have the dentine, and that consists of the mineral phase, about 70%, and the rest made up of water and of protein molecules, a type of collagen. There's a sort of structure here, because running through the dentine are tubules which are filled with liquid. That structure makes a difference to the way dental decay progresses. Right inside we have what is known as the pulp, which consists of a mixture of blood vessels and nerve endings. We will see both of those are significant when tooth decay takes hold. Here's what the healthy tooth consists of, the mineral phase, and something about the mineral phase which is not immediately obvious, I think to those of us not involved in dental research or in dentistry, and that is that the mineral phase is dynamic. You might think that if anything is going to be left of you in about 500 years when the 26th century version of Tony Robinson is running time team, it will be your teeth and your bones, and therefore they must be fairly innocuous, they must be sort of there. They are the bits on which you hang the flesh and the muscles and the bits that you recognise, but everything else is pretty dead. The answer is that's not true, and it's not true particularly of the teeth because the mineral phase is dynamic. It's bathed by saliva, and saliva contains, among other things, calcium and phosphate ions. What happens is that as the local concentration may rise for some reason, these calcium and phosphate ions combine as the hydroxyl appetite mineral and are deposited, and somewhere else you may have a bit of the saliva that's a little bit depleted in calcium and phosphate so the tooth dissolves. We end up with a cycle, sometimes incorrectly referred to as an equilibrium, but a cycle where we have some deposition of mineral phase known as remineralisation and some loss of mineral phase known as demineralisation, and this cyclic process is happily taking place all the time in your healthy teeth. And if you want to just prove that it's taking place, if you eat something acidic that will have an effect, for example rhubarb, you will be able to run your tongue over your teeth and feel the surface is roughened up, roughened up by the oxalic acid in the rhubarb, and that's because some of the ions have been stripped out, but an hour or two later your tooth surface will feel perfectly smooth because all those roughened parts have been smoothed out by the deposition of the calcium and the phosphate. So your teeth are dynamic, and they're happily looking after themselves bathed by this saliva and everything should be well. However, there is a problem, and the problem is twofold. Amals have got a layer on the teeth of microorganisms, a sort of colony, the main one is streptocopus mutens, but there are others in that colony, and they sit on the tooth surface or they stick on the tooth surface. They depart briefly when you brush your teeth, but when they can they are back on there, and they will metabolise sugar, and when they metabolise sugar you get acid produced. You get particularly lactic acid, and there's been some really elegant research over the years that has analysed in great detail the cocktail of acids that these microorganisms can produce and evaluate their effect. It doesn't take very much, the surface of your tooth doesn't have to be especially acidic, and the demineralisation, remineralisation balance is unbalanced, and it starts to favour the demineralisation, so your mineral phase starts to be lost. What happens then in time, if nothing is done about it, is the tooth softens and discolours. In order for that to happen the dental decay, the so-called dental caries, has to progress through the enamel into the dentine, but that is certainly an interesting staging post in the loss of structure of your teeth when they start to decay. Here's a diagram to show the effects, and I'll try to divide this into three stages. First of all we have early decay, which only affects the enamel, and it says here this damage is reversible. It's a bit like the damage you would do by eating rhubarb, that will reverse itself if you remove the source of the acid and you let the natural remineralisation activity of the saliva take place. That may not be what happens because the other possibility is that the decay goes through the dentine, and then it does something that's important, it sort of balloons out, it spreads, and it spreads because the dentine is lower in mineral phase, it's also got structure through which the acids can penetrate and through which the microorganisms can operate, and so there's a spreading out of the dental decay. And so when you are in the dentist's chair and he or she comes at you with a mirror and a probe, what they're doing is poking the tooth to see if those little openings may conceivably be the start of dental decay because it means you could well have very significant spread out of sight of the dentist going on below the layer of enamel. And then if you don't do anything about it, if you are stoic or if you're a dental phobic, whatever your motivation, the whole thing spreads and it goes into the nerve, into the blood vessels and so on, as it says here, accompanied by severe toothache, and eventually you can damage the root canals and do further damage to your body. Toothache always seems a bit of a joke, but it's actually not because of what it leads to. Now here's a decayed tooth. It's not the most in focus of the pictures, but I thought all the others were so revolting I couldn't possibly show them to a polite audience. There are some really horrendous things. So you really want to make yourself feel ill, have a look at tooth decay on Google and have a look at some of the pictures there. But you can see what's happened. There is this discoloration as this carries a spread. And you get this pain. You get a pain that occurs because the nerves in the pulp are affected. That's the first point. You have nerves inside your teeth. You may have an inflammation that starts squeezing the nerves. Whatever it is, you get a pain. And once upon a time the people who studied this considered that this was probably caused by an organism that they would have ever seen called the toothworm. It may not have seen it, but they certainly knew what it did because here is an ivory carving that shows the toothworm. And this actually fits together. So it's got all the components of toothache that we know and love and hate. Here's the worm. It's got its tail well wrapped around some poor person. But more importantly on this side we have the fires of hell which represent the pain and clearly the fires are being, the flames are being fanned to keep them going well, which I'm sure is anybody's experience who's ever had tooth decay and toothache of this sort. So that was what they thought was happening, I don't know, four or five hundred years ago. We know better now, but we've got to think about how we treat it. Now one question that we might ask is does it matter? And there are various answers to this. Clearly it does matter because the decay tooth is a sort of focus of infection and it can lead to all sorts of other unpleasant side effects or effects. For example you can get an infection that leads to the heart called endocarditis, which nobody would want. You can also get a condition called Ludwig's angina, which in its worst manifestation causes swelling to travel down the neck and the patient to suffocate. So toothache is non-trivial. Tooth decay is non-trivial and we need to remember that. Over the idea that teeth are nasty things because of the really significantly high quality dentistry we've had in this country for a long time. But if you went back about a hundred years, in order to stop these kind of things happening to you, you may, if you've been lucky, have had as your 21st birthday present a trip to the dentist to have all your teeth taken out. And that was a very common preventive measure. If you haven't got any teeth they can't decay and you can't get all these conditions. Unfortunately there are problems with that, not least that your alveolar ridge disappears. So by the time you get into your 50s and 60s you can't balance any dentures on anything so you can't eat anything except soup or drink things through a straw. So it wasn't a wise move and we must be grateful that's no longer considered a good idea, but that certainly was the sort of treatment that people had. So it does matter. The question is what do we do about it? And when I say we I'm now referring to dental profession, now we've got at least one of my dental colleagues here in the audience so I hope I'm getting it all right so far. So what do we do? Well the first thing is to remove the damaged tooth tissue. That tissue is infected, it's got microorganisms, busily metabolising, busily making this acid and causing further tooth decay so that's got to be removed. And in the conventions of dentistry for a long time all of the damaged tissue was removed and that doesn't necessarily have to happen in all cases now but pretty much you cut out the tooth tissue. And you wonder why you go to the dentist and you've got a big hole in the tooth from acid attack, why does the dentist start drilling. There are two reasons for that as we will see but one of them is to remove the damaged tissue. And then of course we replace that with artificial material and for a long time this was the material and indeed it still is. I used to have a colleague in my days taught at King's College who used to give a lecture called Amalgam the Materials of the Future and it's not just because he was old fashioned it's because he was making quite an important point and a provocative point that Amalgam still works pretty well. Now if we have as we have had not only in Scotland a reduction in the instance of tooth decay and actually with respect to our esteem principle in most places the reduction in tooth decay is a bit more impressive than the statistics he gave us. People don't want to have their first filling in their 30s and have a massive great cut out of the tooth and a working great bit of silver put in place. So these are no longer really considered by many people to be the desirable way to do dentistry but it's still very effective it works and the whole response of the result of the tooth is functional. It's another illustration I didn't mind taking pictures of Amalgam fillings they're not so bad but increasingly people are interested in tooth coloured and I will then say aesthetic materials. Now the profession will refer to these as aesthetic but I want to make it very clear what I mean because again from my days teaching at King's College in the dental school I started a lecture but I think my lecture was probably called aesthetic tooth materials and a student came up to me from a different ethnicity and said I don't understand what you're talking about because we find gold teeth quite attractive so they thought that was aesthetic. Well depends on your taste and your aesthetics but clinical dentists think that teeth are aesthetic and I'm trying to agree with them so I'm going to be talking about tooth coloured materials. And really we have two broad classes of material there are subsets there are hybrids of these but I don't want to take you too far down that path. I regret not being able to do so in a way because my absolute citation classic which has been cited 261 times is on the classification of modern dental restorative materials so I could have taken you through that and it would only been the sounds of other people in the row snoring that would have kept you going. So I don't want to do that but I want to just talk about these basic essential classes of material and let's go back a bit. Let's talk first about the composite resins which are the more successful more widely used of the tooth coloured materials. Essentially these are plastic fillings and when they were first on the market they came as two paste so it was very similar to gluing something together with araldite when you use these you had two tubes and you mixed two rather viscous paste together and that was your filling material. Now they do things a bit more subtly in terms of the chemistry you have one paste still fairly viscous it's put into position in the tooth and then it's cured with light that means it's turned from being a sticky viscous paste into being a solid plastic material. They look very good they have actually got extremely good aesthetics their problem is that they don't stick to the tooth surface none of the materials we talked about do so far and therefore they need special glues which are known as bonding agents. And it's worth having a little aside here because glues as a technology adhesives is a growing area of physical science people are increasingly impressed by the ability to glue things together so if you fly in the latest passenger jet lots of it's glued together and if you buy a very modern car lots of that's glued together and if you ask the technologist the scientist working on that they'll tell you it's alright as long as you don't get them wet which is great and they don't in the bits they've got. In a plane or a car but in the mouth you have a little bit of a problem with this requirement and the durability of these bonding agents is a live issue now it's sometimes difficult to persuade the clinicians and some of the researchers it's a live issue but it is and if you look at the durability look at what's happening in terms of how these glues are degrading there is a problem here so these things do look great they're very very successful materials but they are not without their problems. So this is what they look like now when the dentist or possible dental nurse opens the box they come in these black tubes now I said they were light cured so obviously you can't have them in a clear bottle or something because otherwise they'd set hard so you have them in a black tube to protect them from light. They normally come with a few other bottles of jollop to actually stick them in place and my picture that I inadvertently let to here is some happy man having a composite resin placed the little probe here showing the light shining on the filled tooth. And I hope everybody is having an dental treatment in this way now swallowing a what looks like a piece of rubber glove this is known as the rubber dam and is a way of isolating air and making it dry which is very important for the modern materials. And this is a kind of repair you can get with a composite this is actually the before somebody here has had some sort of trauma and I know it's the same sort of thing that happened to my niece she fell off her horse and broke a front tooth and so the tooth has now been repaired this is a repaired tooth repaired with composite resin and that is a phenomenal repair. There are several things about it that's phenomenal the first is the color is brilliant in the words of Eric Morgan you cannot see the join and the color not only has got the color right but there's a hint of translucency that you get in the tooth and as well as that the mechanical properties of the composite are going to be good enough for it to survive for quite a long time. It's particular property is that it's a tough material. It's got enough giving it that it can be used on the biting surface of the tooth and you can expect it to survive as indeed it will in fact it's a little bit tougher than the natural tooth that it replaced. And so the key property and I want to talk about this because of some of my research interests the key property of the composite resin is toughness and at this point I'd like to have a little digression into some of these concepts from material science. I want to talk a little bit about what we mean by toughness. First of all it's a material property if something's tough it's tough whether you have a big lump of it or a very small piece and it's generally considered the opposite of brittleness. So let's explore this a little more detail. Let's us consider some experimental work. We'll just do a kind of thought experiment at the moment and I'd like us to consider this particular experimental tool that we can use to investigate material properties. For the uninitiated this is called a hammer and we can with a hammer find out the sort of properties of materials and effectively essentially there are three types of material properties you can get and you will find if you investigate with a hammer. First of all we have metals. Metals have their own sort of behaviour and particularly metals have behaviour which only ever turn up in examination questions. You have to learn the words malleable and ductile when the word metal is mentioned even if you don't know what it means. So I've got a picture in here to show what it means. Malleable means that you can basically beat a piece of metal into a new shape. That's normally, I've got a picture of here, it's desirable. Of course if you drive your car into a lamppost you will discover that and it's not such a desirable effect because the metal will not just bounce back it will change its shape permanently. So we can, with the aid of a hammer or in this case a mallet we can change the shape of the metal. Ductile means metals can be drawn out into wires but we can change their shape by applying forces to them. Then we come on to another group of materials, the brittle materials represented by glasses and ceramics. So what happens if we explore the behaviour of a brittle material with the aid of our experimental tool? Well that's what happens. Nobody would try and change the shape of a bottle. Well you do change the shape of a bottle but you wouldn't try and change it in a controlled way with the aid of a hammer. So that's the behaviour of a brittle material. And finally we get on to tough. Now an example of a tough material is rubber which is probably an extreme example but what happens if you hit that with a hammer? Well you're not going to deform it. The hammer's going to bounce back. It may not actually be the safest experiment so probably a substantial risk assessment is required before you can think about doing it. But you can tell that if you hit something that's tough you're not going to fracture it. Now materials do tend to break if you load them enough but these are the broad categories of material. So our composite resin turns out to be of this general type. It's got toughness and that's going to be important for one of the things I want to go on to say when I talk about some of our future research. Now I want to go on to the second broad class of tooth coloured material, the glass ionoma cement. As I mentioned near the beginning invented by my former boss Dr Alan Wilson and fairly widely used in dentistry but not quite as widely used and not quite as satisfactory as the composite resins. They are cements and that means they're water based. They have all the appearance to the uninitiated polyfiller though they are a lot more subtle than that. They are so called self cured. That means that when you mix the components together they start to react and they turn from the paste into a solid material very quickly. So you have a powder and you mix it with a liquid. They look okay which is to say they're on the way to tooth coloured but you certainly could see the join if you tried to repair a front tooth with current glass ionoma cements and they don't have such a good translucency or quite such a good colour match. They have a very significant advantage that they adhere well to the tooth surface so they're naturally adhesive so you don't have to worry about degradation of your glues and things like that. You can get a glass ionoma into a tooth it will stay there and the disadvantage is that they are brittle. Think green wine bottles and you'll remember they break quite easily and that means that that particularly stunning repair that I show with composite resin can't be done with glass ionoma. Because the minute you bit into something hard it would fracture, it would snap into little bits and you'd have to be collecting the pieces and going back to the dentist. So they are not, they do not have the right properties for those sort of clinical applications. This is how they are presented, various ways they're presented but this is one of the ways they come in the powder. This actually contains a special reactive glass and amazingly when you make this glass if you first make it it actually looks like a piece of window glass. They have a clear sort of piece of glass but it's ground up into a very fine powder when it turns up as a white and normally we have a little bit of pigment added to that and let's say it looks tooth coloured. And we have a liquid and that liquid consists of water with normally polyacrylic acid dissolved in it and the polyacrylic acid reacts with the glass to make the cement set. And these are the ways that the cements are presented. This may not look like a precise piece of scientific equipment but this is actually a carefully metered scoop and the dentist or the dental nurse scoops out an amount of powder and then matches it with a number of drops from this bottle which has a fairly carefully engineered nozzle. And amazingly just measuring scoops and drops is sufficiently accurate, at least it's as accurate as you're going to get in a dental clinic. I always have to persuade my research students that we're not going to mix drops and scoops we're going to actually weigh everything out so that we know what we've done and we reduce at least one possible source of error. But not so bothered when it's going to go in a mouth so this is the sort of measurement technique that's used. This is a little picture to show how it's done. Our bottle of liquid held upside down, carefully metered out, counting out the drops, two drops of liquid, one scoop of powder on a mixing paper and then the whole thing is mixed. So here's some measuring out a small amount of the glass and you can see it looks like a white powder, in fact it is a white powder but it started off looking like a sheet of glass. And then this is it being mixed, I don't know how visible that is but there is a little lump in the cement being mixed with a spatula and say to all the world looks like a rather thick mix of polyfiller and that's going to go into someone's tooth. Now if you do put it in someone's tooth you can exploit the adhesion by using it for certain repairs that you can't otherwise make and these are the two glass enema repairs known in the dental professions class 5 cavities but you can see this is not a brilliant match for the tooth colour but it looks quite opaque. It will improve slightly with time because glass enemas do undergo slow maturation processes, not fully understood but there is some slow chemistry going on there that is associated with a slight change of appearance but that isn't totally atypical so you can tend to see where a glass enema has been placed. Now one of the great things about the adhesion is you can do things with it that are an asked prayer and one is you can do filling without drilling and this is the so called atraumatic restorative treatment technique. It was developed for use in the third world and in the third world the real problem as far as dentistry is concerned is you don't have a reliable source of electricity so you can't have your dental drill going. Yp I can hear you thinking. So what they have to do is different means of removing the diseased tissue so what they have developed is a series of metal scoops sort of hand held with such different shapes that enable the dentist to work out the softened tooth material. Now you can't make such a clean surface with this technique as you can with a dental drill. On the other hand I wouldn't be that bothered. I wouldn't mind seeing the end of the drill. It would be nice to be using it much more in western dentistry but it tends to have been used in third world countries so there have been a lot of clinical studies now. In places where sadly they began to get a western diet so they got McDonald's and they got Coca-Cola but somehow they haven't got toothpaste so places like Zimbabwe, parts of South America and so on have benefited from this sort of technique. If you go to an art type clinic this is a close up of a dentist working and this is a bigger clinic. You can see how they're working with this technique and there's not a drilling site so that's pretty good. So we can use glass itemers for this kind of process and that is very significant and that's been an important development in the health of developing countries. This is an art restoration so as before you can still see it. It's still not a fantastic match for the tooth but it's not bad and certainly better than amalgam would be and the fact that we can do it at all with no drilling is significant. So that's an important use of glass itemers to me. So that's a little bit about their background, how they're used, what we use them for, why we're bothering and I want to just talk a bit about some of the current research moving into future research and the two areas that are significant in my research activities are studies of their bioactivity and also improving their toughness. If we could get them from being very brittle materials to tougher materials well the dream might be that we could use them for the sort of restoration we see for the composite and we could get away from the worries about how long the composite glues are going to last. Whether we'll get there or not remains to be seen but that's certainly a theme that I'm working on. So let's think about bioactivity and I've actually talked to my wife about this slide because I said I did years of work on this iron exchange process, published four or five papers and I've got it all on one slide that we're going to brush over in 30 seconds. So I don't want to mention it to you as well just to say that we did a lot of work to show this was the case but we discover that glass itemers will release, well fluoride was known for a long time that wasn't our discovery. Although we have looked at the exchange of fluoride because in conditions of high fluoride, i.e. when you brush your teeth with a fluoride toothpaste, these cements will take up fluoride so then they go on releasing it on other occasions. But the release of these kind of irons and the conditions under which they are released, the amount that's released, the way it varies with time, the way it varies with local acidity and also the way it may change in the presence of saliva when calcium and phosphate might be taken up took up fair chunks of research time. That they are able to exchange these irons and that makes a big difference so one of the things that happens is that glass itemers that have been in saliva become much harder and if we look at their elemental composition they have obviously taken up calcium from saliva so they're dynamic in that extent. If you had been very thin layers and there's only been one study of this one report of this but it's a very important one, the whole structure develops a kind of artificial enamel. So here we have a material that could in the end not just be a totally artificial material we could end up with something that's going to be so biomimetic that in the presence of saliva is going to develop a sort of enamel. Now whether that normally happens or not I wouldn't like to say and I think probably doesn't but now that we know it's a possibility we need to look at the ability of these irons to be exchanged and to see what we can make of them. A fluoride release is very important and fluoride release in dental schools as a research topic is a cottage industry, lots of people get involved in it. We know that glass items were released fluoride for a long time and then you get this kind of study where someone's taken several different brands on the market and just plotted fluoride release. And very often the goal is to say well here's a brand this must be the best because it releases the most but they kind of rank them and do this kind of thing. I'm not overly impressed by this but there's quite a lot of this sort of thing that happens. I mean it shows what we know anyway which is that they release fluoride. Fluoride is included in the glass composition fluoride is desirable as a preventive measure for the spread of tooth decay because fluoridated tooth mineral fluoridated hydroxyl appetite is resistant to the attack of acids. So if you have some of your mineral phase lightly fluoridated then the acids can't progress at anything like the rate or indeed at all. So fluoride is desirable and the release of fluoride from a repaired cavity where there's a bit of a history of tooth decay is certainly beneficial. Some of the iron exchange may not be desirable if you put your glass item of cements into water quite early on and some of the iron is leaking out of the surface you start potentially to cause problems. I think we've only just found this in the last two or three years but the biggest thing that you can get is that the cements become weaker. We're not entirely sure why this is but Lizzie who's in the audience, my PhD student will be able to tell you in about three years time that she's finished her PhD because we're going to be looking at these iron exchange processes and ways of controlling them and trying to establish exactly what the correlation is between the extent of weakening and the change in composition that we see when these irons are released. Now we can control iron release and dentists quite like to do that. They may well coat a new newly placed glass iron with varnish and they're not trying to control iron release, they're actually trying to stop the whole thing which is water based from drying out before it sets. But controlling iron release may also ensure that you have a stronger filling and again that's something to be looked at. As I said here this is the plug for Lizzie's PhD project, we've got a new project to examine this aspect and various other aspects connected with surface properties of glass iron and this iron exchange. Now they do form their very durable bonds to teeth as a result of this iron exchange so this is definitely a good thing in the right place and if you have a filling right up against the tooth this is what you can find. This is an electron micrograph so it's a scanning electron microscope picture, very high magnification of the interface between a tooth and a cement and that cement has been in the tooth for about five years. Now that's a, and I chair the colleges ethics committee, I can say that's an unethical experiment except in the way it was done which is that after a period of time there may be need to remove teeth for example for orthodontic reasons and so you can then collect teeth that have been filled some years earlier and have a look at what's happened. And these are from, this is from some Australian researchers in the late 1990s and what they found to their surprise when they first did it was that the interface between the cement and the glass iron number develops quite a substantial structure and the other thing that was a surprise was the composition of it. This is a little piece of glass here so we know the glass iron number cement is this side, this is the tooth side. The glass iron number cement they happened to use in their study was strontium based so when they looked at this interface they discovered that the interface contains both strontium ions and calcium ions. So the strontium can only have come from the cement side and the calcium can only have come from the tooth side so there is a very slow chemical reaction that leads to a loss of distinct interface and the development of this rather thick zone and that means that these materials have extremely secure bonding they will stick in place really well. They won't leak, bacteria can't get down the signs if you've got this sort of filling and this sort of bonding. This is an important big plus for glass iron and the cement which takes us on to our big research topic. How are we going to improve the toughness of these materials because if we could do that we've got a lot of useful biological stuff that we can build into the materials and we're going to have something that really will have an enormous range of clinical uses and potentially at least popular with patients and as I say again if it coincided with the end of the dental drill that would be wonderful. So we'd like to make glass iron numbers tougher and then we will be able to extend their clinical uses and as well as extend their clinical uses we'd make them more durable because they're brittle they will suddenly break in service and they have to be replaced so both of these factors would improve if we could improve their toughness. So let's now think having seen what the experiment with a hammer would do, let's now have a look at the sort of structure that materials have that gives them their particular properties and it's clearly related somehow to their underlying atomic and molecular structure. So we'll start with metals which as we saw you can bend either round a lamp post or perhaps more satisfactorily into the shape of the trumpet and in the case of metals what we have is irons essentially floating in the sea of electrons without the electrons being bonded to any particular atom and they're free to move about in the solid that's why metals conduct electricity. It also means that if you bash one end of this piece and bend it for example into an L shape the irons over here are quite happy to move the electrons don't mind flowing round corners but freely so the whole thing will bend or be drawn out without too much difficulty. We go to something that's ceramic we now have directional bonds we have electrons that are in very tight locations and nothing there wants to move that's all held really rigidly and so when somebody comes along with a hammer well if you tap it lightly nothing happens but eventually you get to the point where a whole lot of chemical bonds break together they can't resist it anymore and they just all go so you get breaking of chemical bonds rapidly and catastrophically in a ceramic material because they are directional so why is that a problem or why is that what is the structural feature essentially that all these atoms are rigidly held in these sort of areas and they're knotty together fairly tightly and then we have rubbers well this is the best I could do for a polymer but we have rubbers where you can get some sort of flow in the case of rubbers there is some light knotting so the molecules will bounce back but tough materials in general have molecules with a fair amount of freedom that are able to flow past each other so is that what we want with glass-animas yes it probably is and it's not what we're getting at the moment so now we think about why glass-animas are brittle well we actually know why they're brittle we know that inside our setting cement we have polycrylic acid and we know that as the reaction takes place the glass leaches some ions out and these ions effectively tie the polymer chains up in knots and they have a very high density so the resulting cement is brittle and the main problem is caused by aluminium aluminium is in the glass aluminium is present and this is what aluminium likes to do when it's sitting in any sort of structure if you look at this and think what is this this is an aluminium atom and it's sitting there surrounded by six nearest neighbours and that's what aluminium really likes it wants to be in what we call six coordination and so for a long time we assumed that aluminium was coming out of the glass and it was finding atoms on the polycrylic acid chain to bond to and therefore were sitting there creating knots so we knew this from spectroscopic studies but more recently I've been involved in quite a big project using neutron beams and working at the Rutherford Appleton Laboratory and here's a little picture of the Rutherford Appleton Laboratory because it's quite impressive you can ignore this thing up here which is the diamond light source but what we have here may not be so obvious from the picture is a little mound in which there is a controlled nuclear reaction going on and that nuclear reaction is generating neutrons and neutrons are being fired out in fact they'll be fired in all directions but there's a lot of lead shielding around here but here are two massive factory sized huts and what you do is you get yourself a week or so on the beam and the neutrons will be provided for you you turn out with your sample, you go and work in the hut some technician takes off your sample and disappears and puts it in the beam and you can sit watching completely meaningless looking numbers appear on a computer screen for the remainder of the week and eventually some poor soul of the technician takes his glowing item out of the neutron beam and I don't know where they dispose of it they must be disposing of it safely because it's pretty radioactive by then but as a result of the diffraction patterns you can get from the neutrons you can start to look at really quite intimate details of the structure and so what we've been able to find well we knew for a long time that aluminium reacted quickly but what we discovered was that those initial fixed coordinate structures that I showed were not necessarily the same as the knots some of those aluminium are surrounded by water molecules not by polycrylic acid molecules but if it's surrounded by enough water it's not a knot at all it's just sitting there so what was gradually happening was that these aluminium were losing water or whatever else was surrounding them small and turning themselves into knots and the interesting thing is that if you look at this and just look at the details of the atomic structure it turns out that the glass ornaments are really quite tough up to about 10 hours and then they go on reacting and by 24 hours they're brittle and after several months they are extremely brittle so our challenge is can we stop the setting reaction can we stop the maturation reaction at 10 hours can we arrest the setting and make them tough well that is what we're trying to do there's going to be a big project we hope we can persuade the good folk of the Engineering and Physical Sciences Research Council of which I'm a member of the research team with a process of looking at how we can arrest what I'm calling this knotting process by controlling how aluminium is able to react inside these cements if we get that then we should have a tough tooth-coloured adhesive bioactive material so that's a very substantial goal that brings me now to the end of my lecture and just very quickly I'd like to summarise glass ornaments, the materials I've been working on are widely used in modern dentistry and we've seen why, we've seen the need to repair teeth we've seen what they do and why this is desirable clearly there is scope to improve them we'd always say that as researchers but here there really is scope and there's something particularly significant because we could conceivably make very important improvements that would change the whole public perception of the visit to the dentist so what I'd say is we are trying thank you