Rapport de stage 3ième année Eliott Guérin

Eliott GUERIN
Material engineering - POLYTECH GRENOBLE
Internship report (third year).

Investigating the development of porosity during settlement of dental cement
pastes with SAS sensitive novel neutron imaging technique

Main Volume

College year 2015-2016
Period June-August 2016

Eliott Guérin – MAT 3 Internship report – 1A
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Table of Contents
I – Introduction ............................................................................................................................ 3
II – Tooth and dental cements ...................................................................................................... 3
A- Composition of the human tooth ......................................................................................................... 3
B- Apparition of dental caries ................................................................................................................... 3
C- Treatment of dental caries ................................................................................................................... 4
D- The glass ionomer cement alternative ................................................................................................. 4
III – Neutron imaging .................................................................................................................... 5
A- Neutrons VS X-rays ............................................................................................................................... 5
B- The ICON beam line and the imaging technique .................................................................................. 6
IV – Experimentation and results .................................................................................................. 8
A- Safety rules ........................................................................................................................................... 8
B- Advance preparation ............................................................................................................................ 8
C- Instrument calibration and tests .......................................................................................................... 9
D- Regular time measurement .................................................................................................................. 9
E- Wavelength scan measurement ......................................................................................................... 10
F- Results and comments ....................................................................................................................... 11
V – Conclusion ........................................................................................................................... 13
VI – Acknowledgements ............................................................................................................. 13
VII – Bibliography & Table of Figures ........................................................................................... 14
Back of the report ...................................................................................................................... 15

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I – Introduction
Dental caries is a worldwide-spread disease which affect around 36% of the world population and
the placement of fillings is one of the most frequent type of dental treatment.
Glass ionomer cements are water- and acid-based cements used in dentistry (dental fillings for
example). Those materials are very interesting for medical use because of their good biocompatibility.
However, dental cements have a poor mechanical resistance which leads to a short life expectancy in the
hostile oral environment (humidity, mechanical constraint…). Every time a tooth filling is performed, it is
like a small chirurgical intervention: anaesthesia, needles and various tools. Furthermore, each time, you lose
another part of your tooth and it’s very expensive. That’s why, researchers from the Niels Bohr Institute
(Copenhagen) are working on having a better comprehension of the cement settlement process, and how its
structure evolves during time. This has the potential to lead to improvements and further development.
The Niels Bohr Institute (NBI) covers a broad range of physical researches, from astronomy and
geophysics to particles physics and quantum mechanics. The institute employs 145 academic staff, 95
technical staff and 85 PhD-students. It is also important to notice that each year, the institute hosts
approximately 130 foreign researchers.
At the head of the research on dental cements are Ana R. Benneti (Copenhagen University), Heloisa
N. Bordallo (Niels Bohr Institute – Copenhagen University) and Markus Strobl (European Spallation Source,
Sweden – Niels Bohr Institute). Ana Benneti is a dentist, while Heloisa Bordallo is an X-Ray and neutron
scientist and Markus Strobl is a neutron imaging instrument scientist. I had the opportunity to join their
group for an internship from the 24th
of May to the 19th
of August.
This report, in a first time, presents the two topics of my internship: the dental cement and the
neutron scattering imaging technique. After that it relates how this imaging technique has been applied on
dental cement, at the ICON beam-line at the Paul Scherrer Institute in Switzerland and what are the results
obtained.
Key words: Dental caries, Glass ionomer cement (GIC), tooth filling, Niels Bohr Institute, Settlement
process, Neutron scattering imaging.
II – Tooth and dental cements
A- Composition of the human tooth
Teeth are made from many materials, as it can be
observed on the illustration beside. First there is the enamel,
which is the external layer of the tooth. Then come the dentin
and the pulp, which encloses nerves and blood vessels.
Around the roots of the tooth, there is a bone part, called the
cementum. Finally, the all tooth is covered by a biofilm of
bacteria.
B- Apparition of dental caries
Hard tissues, like enamel, dentin or cementum are
constantly undergoing a mineralization and demineralization Figure 1: Section of a human molar

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process. Sometimes a change can occur in the dental biofilm (because
of micro-organism in the dental plaque, a sensitive tooth surface…)
which leads the demineralization rate to be higher than the
mineralization rate. This shift in the mineralization balance causes a net
material loss in the tooth, which results in cavities (represented in black
in the illustration beside).
C- Treatment of dental caries
The treatment indicated in case of dental cavities, is most
generally a filling. Firstly, all the decay material need to be excavated,
so it won’t keep growing under the filling. After this step, the cavity
can be filled, with several materials. The most famous and most used nowadays is the amalgam, which is a
metallic filling material. But, because of the presence of mercury (from 43% to 54% in the amalgam
composition), it is a controversial solution. Therefore, there is today a big challenge about developing the
ideal restorative material. Proprieties of the ideal filling material are numerus:
Ø Physical proprieties:
o Low thermal conductivity and
expansion
o Good mechanical strength
o Resistance to chemical erosion
o Good bonding strength to the
tooth
And also:
Ø Excellent biocompatibility
Ø Match with tooth aspect
Ø Easy to manipulate
D- The glass ionomer cement alternative
Glass ionomer cements (GIC) are porous materials made through the reaction between a silicate
glass powder and a polyalkenoic acid solution.
The powder is made of three main components: alumina, silica and calcium fluoride. So the powder
has a chemical composition such as: Al2O3-SiO2-CaF2. This powder is obtained by heating the alumina and
the silica with a flow of calcium fluoride, sodium, aluminum and phosphate up to 1050°C-1350°C. After
this, the compound is brutally cooled and crushed in order to obtain particles in a range from 30 to 40 µm in
size.
The liquid, as said earlier, is a polyalkenoic acid solution, with a molecular weight between 10000
and 30000 g.mol-1
. The solution is a polyalkenoic acid, therefore it containes a lot of COOH and COO-
functions (depending on the pH). You can also find in this liquid some tartaric acid, which has the role to
decrease the viscosity, increase the manipulation and accelerate the curing.
Sometimes, the liquid can simply be deionized water. In this case, the acid solution is dehydrated and
incorporated to the silicate glass powder.
For this study, we will be looking in 4 industrial GIC which will be called:
Ø Poly (Ionofil Molar AC, Voco GmbH, Germany)
Ø Aqua (Aqua Ionofil Plus, Voco GmbH, Germany)
Ø Equia (GC equia, GC corporation, Germany)
Ø Fuji (GC Fuji Filling LC, GC corporation, Germany)
It is important to notice that they are industrial products, and therefore their compositions, protected
by industrial secrets, aren’t exactly known. For these products, there are two kinds of packaging. It can be
else a capsule (Poly, Equia, Fuji), with an activator to press in order to release the liquid into the powder
chamber. Otherwise, the liquid and the powder can be packaged separately (Aqua) and hand mixed using a
Figure 2: Progression of pit and fissure carries

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spatula. The powder to liquid ration in capsules is around 3:1.
GIC, after mixing the powder and the liquid, sets in two identified diffusion-controlled steps. Firstly,
the acid from the liquid solution partially dissolves the glass particles which releases metal ions, such as
aluminum and calcium. These metal ions then interact with carboxylic ions from the polymer triggering the
formation of carboxylate salts. In the first minutes after the mixture, Calcium carboxylates are formed.
Subsequently, from ten minutes to a day after the mixing, carboxylates salts are formed.
The presence of these carboxylic functions is not only very important into the mixing reaction of the
dental cement, but also in its linking process to the actual tooth material. A strong bond is created between
the GIC and the tooth when the carboxylic functions crosslinks with the calcium located at the tooth’s
surface. As said earlier, this is a key propriety for a restorative material. GICs have other interesting
proprieties, such as its excellent biocompatibility with the oral environment, its low thermal conduction and
expansion. Furthermore, it matches very well with the tooth aspect and it is quite easy to manipulate, in the
three first minutes after the mixing.
The only major drawback came from the fact that those materials have a short life expectancy, which
leads practitioners to spend most of their time replacing failed restorations. This is due to a low mechanical
strength which may probably come pores and hydrogen mobility within the material.
III – Neutron imaging
A- Neutrons VS X-rays
When it comes to details smaller than a micro meter, visible light isn’t enough. Among the
alternative imaging techniques, the most known is X-rays. In fact, in most cases, it works very well. The
problem is that X-rays, are sensitive to electrons, and therefore, they are not very sensitives to light elements,
such as hydrogen. However, neutrons, as they are chargeless, they are sensitive to atom’s nucleus, as showed
in the illustration below (figure 3 and 4).
As neutrons are chargeless, they interact with nuclear charges instead of electric charges, which have
a shorter range (around a femtometer). Because of this shorter interaction range, neutrons are able to travel
further into matter. For this reason, they are suitable for the study of bulk materials.
The interaction between neutrons and nucleus follows a law which hasn’t been discovered yet. But,
by experimenting known samples, we can plot the diagram below. This diagram also represents the
interaction between X-rays and atoms, which is fairly linear.
Figure 3: X-ray interaction with matter Figure 4: Neutron interaction with matter

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Finally, we can notice that, as the relation between atomic number and mass attenuation coefficient isn’t
linear with neutron, they are very suitable to differentiate closed atoms. With, neutrons, it is possible to
identify two neighbors’ atoms and even two isotopes, such as hydrogen and deuterium. It is impossible to
obtain the same precision with X-ray imaging, as it is shown in the following image.
B- The ICON beam line and the imaging technique
In order to perform our experiments, we had the chance to obtain a “beam-line time” of 5 days on the
instrument named ICON, at the Paul Scherrer Institute, near Zurich, in Switzerland. The ICON instrument in
a grating interferometer, which uses cold neutrons. The neutrons are coming from the Swiss Spallation
Neutron Source (SINQ), which is a continuous source. The reactor emits protons which are then shot on a
tungsten target. The target absorbs the protons and emits thermal neutrons. For some instruments such as
ICON, those thermal neutrons (high energy) are cooled down using deuterium at the very low temperature of
25 Kelvin. When it arrives to the sample position at ICON, the neutron flux is approximately 1,3.107
cm2
/sec/mA.
The instrument is composed of a source grating, an energy selector and a set of interferometer gratings. The
energy selector is placed upstream the beam line. It select an energy, directly related to a wavelength by the
relation: 𝑬 =
𝒉.𝒄
𝝀
.
Figure 6: Contrast in neutron (left) and X-ray imaging (centre and right)
Figure 5: Contrast in neutron and X-ray imaging

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Once the wavelength has been selected, the beam is directed into two gratings, which convert the
incoherent beam in a coherent beam. After this second grating there is a third, an absorbing one. Finally,
comes the detector, which first converts the incoming neutrons in visible light, before they hit the camera.
Multiples values can be extracted from the sinusoidal signal detected in each pixel of the detector. In
the one hand, you can look at the mean value of this signal. This value can give you the transmission rate of
the neutron beam.
On the other hand, you can also look at the amplitude of the signal. This is why the absorbing grating
is used for. By moving this grating up and down, you can isolate the maxima and the minima of the
sinusoidal signal detected in each pixel. The absorbing grating is moved step by step. You can set how many
steps you want to do and the exposure time for each step. The more step there is, the more precise the
measurement will be. Finally, the images taken in each step are combined (this step is called the
reconstruction) in one image using a dedicated software (NGITool). The resulting image is known as the
dark field image.
The principle of the imaging technique is fairly simple. Firstly, an “open beam” measurement is
realized. For this measurement, the sample isn’t in the beam trajectory. This is made in order to have a
reference. Then a second measurement, with the sample in the beam trajectory is made. Atoms inside the
sample interact with the incoming neutrons, by absorption or scattering. When they don’t interact, neutrons
are simply transmitted. The signal recorded in each pixel is analyzed using the absorbing interferometer
(looking for the mean value or the amplitude). Using a software (NGITool), the “open beam” measurement
and the measurement with the sample are compared and combined in one final image for each type of
measurement (transmission or dark field).
All images are showed in shades of grey. Looking to the dark field image, the darker a pixel is, the
more important the absorption or the scattering of neutron have been. Meanwhile, the brighter a pixel is, the
less the neutrons have interacted with the sample. In the transmission image, the brighter a pixel is, the more
the neutrons have been transmitted.
Finally, the images can be analyzed using a photography software called FIJI. With this software,
you can plot the average brightness of an area of the image (the middle of the sample or the entire sample in
our case). Underneath is an example of an image obtained by dark field neutron imaging. We can observe
that there is more contrast on the image taken using neutrons than on the image taken using X-ray.
Figure 7: Sketch of the beam travel
Figure 8: Radiography of a camera with neutron (left) and with X-ray (right)

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IV – Experimentation and results
A- Safety rules
As said earlier, experimentations on dental cement were made at the Paul Scherrer Institute (PSI)
near Zurich in Switzerland. As the institute is the home of a nuclear reactor and a lot of neutron’s
instruments, there are many rules in order to avoid exposition to radioactive particles.
Before entering the institute, you must fulfil a formation about the safety rules and procedure. Once
you have completed a small evaluation, you get a dosimeter (figure 8) and an identification badge. Those to
items must be worn all the time. The entire complex is divide in zones, related to the contamination risk. The
ICON instrument we have been working on is situated in zone 2. Boundaries of controlled zone are delimited
by warning signs and a barrier. Inside zone 2 (and in all other controlled zones) eating and drinking are
forbidden. Before leaving a controlled, you must go through a contamination monitor (figure 9) which check
for any possible contamination.
B- Advance preparation
In order to prepare the trip to PSI, I had a few meetings with Ana Benneti, Heloisa Bordallo and
Markus Strobl. As said earlier, we were granted of a five-day beam line time. The aim of the experiment we
were about to perform was to observe the settlement of the dental cement. We choose to observe a sample
just after its mixing and for approximately twelve hours. We also plan to take final images of the samples
just before leaving, so we would have an idea of the evolution of the material structure after a few days. We
decided to test four different dental cements, the ones which I introduced earlier. In order to be able to ensure
the reproducibility of our measurement, three samples of each dental would be prepared and tested.
Before leaving for PSI, Ana Benneti trained myself to the sample preparation. I had to be able to
prepare a sample and put it in the sample holder before it hardens (roughly 2 minutes). I had to get used to
the two types of packaging, else the predosed
capsules or the hand mix. The only hand mix
dental cement I had to work with was the Aqua.
To prepare it, you have to respect a powder to
liquid (which in this case is deionized water)
ratio such as 5,4 – 6,3g: 1. To mix it, you use a
spatula and a special mixing pad, which are non-
adhesive to the dental cement. Once the cement
had reach a good consistency, you just have to
put it and spread it in the chosen sample holder.
The preparation of the encapsulated dental
cements isn’t easier. They are packed in capsule
such as illustrated beside.
Figure 11: Sketch of a predosed capsule
Figure 9: Picture of a dosimeter Figure 10: Picture of two contamination monitors

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First, you have to activate the capsule. It means that you release the liquid, which is contained in a
sachet under the clamp, in the chamber with the predosed powder. Then you need to mix the powder and the
liquid together. To do so, you need to put the capsule in a capsule mixer (4000 – 4500 oscillations per
seconds) for 10 seconds. After this stage, you can applicate the cement using a specific tool.
C- Instrument calibration and tests
Firstly, before making any
measurement I had to get use to the
sample holders and see if I could fill
them fast enough. They were composed
of aluminium, because this metal has a
very low interaction with neutrons, and
so appears almost transparent in
neutrons’ imaging. They were made of
two round parts which were closing one
on the other with screws. The space
inside for the sample was up to two millimetres in height and fourteen millimetres in diameter.
After running some imaging test, we saw that amount of material (in beige on the illustration beside)
in the sample holder was too big to get a good image and so we had to reduce the space inside the sample
holder with aluminium layers (in grey on the illustration). We reduced it down to 0,5 mm.
But, even after reducing the amount of material in the sample holder, the images were still too dark
(too much interaction). We deduced that it came from the water inside the material (which as a very high
interaction rate) and so we decided to replace it with deuterium. For the Aqua it was easy, because the liquid
in the preparation was only deionized water and so very easy to replace. For the encapsulated samples, it was
harder because the liquid was a polyalkenoic acid solution. We first had to order a bottle of the solution, then
we had to dry it very slowly (at 70°C) for a day. I weighed the water loss with a very accurate scale in order
to be able to replace the water with the exact same amount of deuterium. We managed to evaporate 4,1758 g
of water and I inserted 4,1417 g of deuterium (99,18 %). Then, I had to remove the sachet containing the
liquid under the clamp of the capsules and insert the right amount of liquid instead. I knew that the powder to
liquid ratio must be around 3:1, so I opened a couple of capsules from each brand in order to weight the
powder inside. Using an accurate pipette, I insert the right amount of liquid directly
inside the powder chamber (triggering the reaction).
A last test confirm that the deuterium was the solution to our problem and
that we were able to collect good data with it. We decided to set the instrument on
13 steps per image and an exposure time of 30 seconds in order to have a good
quality. The incoming wavelength was set on 4,1 angstroms which is the point
where the machine is the more accurate.
Then I just had to build a set up able to hold four sample holder at a time,
so we could analyse four sample at a time. I used a plate of aluminium on which I
build four snicks (using aluminium tape) where I can insert the sample holders
(picture beside, figure 13).
D- Regular time measurement
We started with a measurement of three Aqua samples (in order to have time to evaporate the
polyalkenoic solution). I prepared the samples one by one and inserted them directly in the instrument. While
I was preparing the second and the third sample, we were taking an image of the previous one. You can see
Figure 12: Sketch of the sample holder
Figure 13: Picture of the
sample holder holder.

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on the illustration below (figure 14) the positions of the samples. We kept a sample holder empty in order to
have an element of comparison. In the illustration, “E” stands for empty sample holder and the numbers for
the samples (in their preparation order). The characters in black are for the real positions and the red ones are
for the position on the image beside (the reconstruction software flip the images).
We ran this experiment for 8 hours. After that, we went on with the three encapsulated brands, Poly,
Equia and Fuji. I prepared one on each by replacing the water-based solution by the deuterium based
solution. By measuring the amount of powder inside each capsule, I deduced the average appropriate amount
of liquid to put in.
Brand Poly Equia Fuji
Liquid amount (g) 0,1065 0,1184 0,1107
Table 1: Measured amount of liquid per capsule
The Poly’s sample was placed in position number one, the Equia’s sample in position number two
and the Fuji’s sample in position number three on the illustration above. The same experiment was
reproduced three times and each time, I listed the exacted amount of liquid inserted. The amounts of liquid
inserted and the percentages by comparison the expected liquid’s amount are in the table below.
Brand Poly Ratio (%) Equia Ratio (%) Fuji Ratio (%)
First run 0,1094 g 102,7 0,1180 g 99,66 0,1126 g 101,7
Second run 0,1047 g 98,31 0,1215 g 102,6 0,1133 g 102,3
Third run 0,1027 g 96,43 0,1138 g 96,11 0,1058 g 95,57
Table 2: Amount of liquid used in the samples preparation
The first run lasted for approximately 10 hours and 50 minutes while the second run lasted
approximately 3 hours and 43 minutes and the third run lasted approximately 8 hours and 38 minutes. The
second run is very short because we launched it quite late in the morning and we stopped it in the middle of
the afternoon, so we had time to launch the last run (the third one) before leaving.
Before the end of our time on the beam line, we took images on the sample (after 64 hours for the
Aqua, 17 hours, 24 hours and 40 hours for the Poly, the Equia and the Fuji).
E- Wavelength scan measurement
We also performed what we called a wavelength scan measurement. The principle is the same but
instead of taking the images with only one wavelength (4,1 angstroms), we used several wavelengths (from 3
to 5 angstroms). This technique is currently under development by Markus Strobl and Ralph Harti, so the
experiment we did was very experimental. We looked at one sample of each brand for approximately 17
hours. The main advantage of this technique is that it should provide us information on the evolution of the
pores sizes. Actually, with the regular time measurement, we can only know if the amount of pores
responding to one wavelength (4,1 A) is changing, but we can’t know if the pores are expending or
shrinking.
Figure 14: Sample's positions Figure 15: Example of a reconstruct image

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F- Results and comments
As explained earlier, the images can be analyzed using a software called FIJI. For the regular time
measurement, I plotted the scattering contribution in the dark field’s images (DFI) as a function of the time. I
did the manipulation twice for each samples: one on a large area (almost the entire sample) and one only on
the center of the sample. I normalized the data with the measurement of an area without any sample. On this
area, the scattering contribution should be equal to one, which means that there is no interaction. I calculated
the difference between the measurement value on the empty area and one. I added this difference to the
measurements on the samples.
Firstly, I displayed my data sort by samples, in order to check if the several runs were coherent.
Below is an example with the poly’s samples. “Small” stands for the small area and “big” for the larger area.
It is hard to analyze the second run (in red) because it was very short. But, between the first and the
third run, the general aspect is the same, with an increase on the first 100 minutes and then a plateau. We can
also see the measurement on a small area and on a bigger one are almost identic. This confirms that the
material is quite homogenous and that I managed to spread quite well the cement in the sample holder. The
shift in the scattering contribution between the sample may come from variation in the beam intensity
between the several measurements.
The same behavior can be found with the other dental cements brands. If you want to see them,
please don’t hesitate to ask me.
I also compared the different brands of dental cement, as shown on the next page (figure 17). This
graph is related to the first run of regular time measurement. The gaps between the curves certainly come
from the fact that the flux of neutrons is not as strong on the entire sample holder. We observed this variation
of the flux by looking at images without any sample. This image shows a weaker flow of neutrons on the
right side of the sample holder.
From this chart (figure 17), we can clearly see that the encapsulated cements (Poly, Equia, Fuji), don’t have
the same behavior that the hand-mixed cement (Aqua). This difference has also been showed in Ana
Benneti’s and Heloisa Bordallo’s paper. With, the encapsulated cements, the scattering contribution is
increasing up to one, which means that there is less interaction between the neutrons and the cements over
time. The hand-mixed cement has the opposite behavior. During time, the scattering contribution is
decreasing, which means that the material interacts more with the neutrons.
But, it seems that all the curves tend to plateau after almost 3 hours. So we can argue that the biggest
changes in the material structures occur before 3 hours. The exact same behavior is observed with the other
runs, which won’t be presented in this report.
0,67
0,72
0,77
0,82
0,87
0,00 100,00 200,00 300,00 400,00 500,00 600,00 700,00
scattering contribution
Time (minutes)
Poly DFI Nrm
Poly_1_small_DFI_Nrm
Poly_1_big_DFI_Nrm
Poly_2_big_DFI_Nrm
Poly_3_big_DFI_Nrm
Figure 16: Scattering contribution on Poly's sample as a function of time

12
The interpretation of the wavelength scan measurements is slightly different. As I did for the regular
time measurements, I started by using the software called FIJI to plot the scattering contribution on each
image. But then, instead of plotting the scattering contribution as a function of the time, I plotted it as a
function of the wavelength for each wavelength scan. From this graph, I added the trendlines for each
wavelength scan. You can observe an example realized with the Poly’s sample right below (figure 18). The
last step was to pick up the slope of each
trendline and plot them as a function of
the number of the wavelength scan (or
the time, each scan took approximately 2
hours). The result is the following graph
(figure 19):
On this graph we can clearly see an
increase in the slope (which is negative).
This means that the difference between
the scattering contribution obtained with
different wavelength is increasing.
Unfortunately, I didn’t had time to go much further with the wavelength scans during my internship. There is
still a lot of problems to solve in order to obtain good results from a material point of view. The principal one
is that the instrument is not very adapted to longer wavelength, such as 5 angstroms. At this wavelength, we
can see a lot of disturbance on the images, which may be the cause of wrong results. But this is a very
interesting and promising imaging technique and I’m convinced that in a near future it will be very useful.
0,63
0,68
0,73
0,78
0,83
0,88
0,93
0 100 200 300 400 500 600
Time (minutes)
Comparaison run 1 DFI (big)
Aqua_1_big_DFI
Equia_1_big_DFI
Fuji_1_big_DFI
Poly_1_big_DFI
Figure 17: Comparaison between samples (run 1)
0,45
0,5
0,55
0,6
0,65
0,7
0,75
0,8
0,85
3 3,5 4 4,5 5
wavelength (Ä)
Wavelength scan - Poly (big)
Wavelength scan 1
Wavelength scan 2
Wavelength scan 3
Wavelength scan 4
Wavelength scan 5
Wavelength scan 6
Wavelength scan 7
Wavelength scan 8
Wavelength scan 9
Wavelength scan 10
Wavelength scan 11
Figure 18: Scattering contribution as a function of the wavelength
0 5 10
Slope
Wavelength scan number
Slope - Poly (big)
Figure 19: Slope of the wavelength scan
trendline as a function of the number of the
wavelength scan

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V – Conclusion
The race to the best filling material is today far from being over. Materials such as resin are also
studied by researchers. Yet, dental cements are really a promising alternative. It was very interesting to be
part of this study. Trying to understand the reasons of defaults in a material is the first step in the creation of
a new material, more performant. During my internship, we managed to identified that the changes in dental
cements’ structures occurs in the first hours. We also found that the hand-mixed cement doesn’t have the
same behavior that the encapsulated ones. I was very happy to be able to bring my contribution to the
research. I had the opportunity to think of solutions by myself and to realize them.
There is still a lot of work to do with the data we collected at PSI during our experiment, especially
with the wavelength scans. The analyzation of the data was complicated because the imaging technique is
really new. It was very interesting to follow the creation of this novel imaging technique. In fact, I wasn’t
used to think about how the instruments we used to characterize our materials are developed and built. I
realized that behind those instruments was an amazing piece of engineering work. This was to my mind the
most unexpected thing I learned during my internship. I had the chance to visit great facilities, such as PSI in
Switzerland, Max IV and the construction site of the ESS in Sweden. This experience opened my mind, and
made me think to potential professional projects.
During this internship, I also had to read a lot of scientific publications, in order to be able to acquire
knowledge in new fields such as neutrons imaging. I have to admit that I wasn’t used to read a lot of
scientific publications, but I really found it interesting. This internship also pushed me to be very
autonomous. I met with my supervisor approximately once a week. Between each meeting, I was able to
manage my time as I wanted. This internship also teaches me to be able to cope with a lot of data, and to
organize my work in consequence.
The experience of leaving in a foreign country was very rewarding. I discovered a very rich country,
regarding to its culture and its landscape. Also, this internship was for me a way to test my English. This is
the reason why I choose to write this report in English, which wasn’t an obligation. This experience gave me
confidence in myself and now I know that I will try to work abroad during my carrier.
To conclude, I think that I learned a lot. I discovered advanced research, which was an all-new world
for me. I think this experience definitely changed my perception of science, which was maybe too limited to
an industrial vision. This internship really enthused myself and I will try to keep up with the research on this
subject. I will for sure try to be closer to the research in the future.
VI – Acknowledgements
I really would like to acknowledge my three supervisors, Ana R.Benneti, Heloisa N. Bordallo and
Markus Strobl. They gave me this internship, which I really liked. I would like to thanks them for their time,
patience and pedagogy. I learned a lot during those three months thanks to them.
I also would like to address a big thank to Ralp Harti at PSI, who helped me so much with the
experiment and after that with data treatment.
I also would like to acknowledge my co-workers at NBI: Everton, Marcella, José, Rosanna, Martin
and Murillo. They welcomed me in the office. It was a pleasure working with them and their good moods!
Finally, I would like to thanks the Danscatt institution and the Erasmus + program, without whom, I
wouldn’t have been able to do this internship.

14
VII – Bibliography & Table of Figures
Bibliography:
• Mirza Shahzad Baig, Garry J.P. Fleming. Conventional glass-ionomer materials: A review of the developments
in glass powder, polyacid liquid and the strategies of reinforcement. Dublin. Journal of Dentistry, Elsevier,
2015.
• M. Strobl, A. Hilger, N. Kardjilov, O. Ebrahimi, S. Keil, I. Manke. Differential phase contrast and dark field
neutron imaging. Nuclear Instruments and Methods in Physics Research, Elsevier, 2015.
• A. Hilger, N. Kardjilov, T. Kandemir, I. Manke, J. Banhart, D. Penumadu, A. Manescu, M. Strobl.
Revealing microstructural inhomogeneities with dark-field neutron imaging. Journal of applied physics, 2010.
• A. R. Benetti, J. Jacobsen, B. Lehnhoff, N. C. R. Momsen, D. V. Okhrimenko, M. T. F. Telling, N. Kardjilov,
M. Strobl, T. Seydel, I. Manke, H. N. Bordallo. How mobile are protons in the structure of dental glass
ionomer cements? Scientific Report, 2015.
• N. Kardjilov, I. Manke, A. Hilger, M. Strobl, J. Banhart. Neutron imaging in materials science. Materials
today, 2011.
• R. Pynn. Neutron scattering a primer. LANSCE, 1990.
• M. Strobl, C. Grünzweig, A. Hilger, I. Manke, N. Kardjilov, C. David, F. Pfeiffer. Neutron Dark-Field
Tomography. Physical Review Letters, 2008.
• M. Strobl, I. Manke, N. Kardjilov, A. Hilger, M. Dawson, J. Banhart. Advances in neutron radiography and
tomography. Journal of Physics D: Applied Physics, 2009
• M. Strobl. General solution for quantitative dark-field contrast imaging with grating interferometers. Scientific
Reports, 2014.
• Institut Paul Scherrer (PSI). Paul Scherrer Institut (PSI) [on line]. Available at: <https://www.psi.ch>
(02/08/2016).
• Wikipedia, the free encyclopedia, Dental Cement [on line]. (Last modified on 16 June 2016, at 15:27)
Available at: <https://en.wikipedia.org/wiki/Dental_cement> (27/07/2016).
• Neils Bohr Institute. The Institute [on line]. Available at: <http://www.nbi.ku.dk/english/about/> (06/06/2016)
Table of Figures:
All figures are exctracted from the list above.
Figure 1: Section of a human molar__________________________________________________________________ 3
Figure 2: Progression of pit and fissure carries ________________________________________________________ 4
Figure 3: X-ray interaction with matter _______________________________________________________________ 5
Figure 4: Neutron interaction with matter _____________________________________________________________ 5
Figure 5: Contrast in neutron and X-ray imaging _______________________________________________________ 6
Figure 6: Contrast in neutron (left) and X-ray imaging (centre and right) ____________________________________ 6
Figure 7: Sketch of the beam travel __________________________________________________________________ 7
Figure 8: Radiography of a camera with neutron (left) and with X-ray (right)_________________________________ 7
Figure 9: Picture of a dosimeter_____________________________________________________________________ 8
Figure 10: Picture of two contamination monitors ______________________________________________________ 8
Figure 11: Sketch of a predosed capsule ______________________________________________________________ 8
Figure 12: Sketch of the sample holder _______________________________________________________________ 9
Figure 13: Picture of the sample holder holder. ________________________________________________________ 9
Figure 14: Sample's positions______________________________________________________________________ 10
Figure 15: Example of a reconstruct image ___________________________________________________________ 10
Figure 16: Scattering contribution on Poly's sample as a function of time ___________________________________ 11
Figure 17: Comparaison between samples (run 1) _____________________________________________________ 12
Figure 18: Scattering contribution as a function of the wavelength ________________________________________ 12
Figure 19: Slope of the wavelength scan trendline as a function of the number of the wavelength scan ____________ 12
Table 1: Measured amount of liquid per capsule _______________________________________________________ 10
Table 2: Amount of liquid used in the samples preparation_______________________________________________ 10

15
Back of the report
Etudiant : Eliott GUERIN
Entreprise :
Adresse complète :
Téléphone :
Responsable administratif :
Téléphone :
Courriel :
Tuteur de stage :
Téléphone
Courriel :
Enseignant-référent :
Téléphone :
Courriel :
Année d’étude dans la spécialité : 1A
Niels Bohr Institute
University of Copenhagen
Blegdamsvej 17
2100 Copenhagen
+45 35 32 26 26
Heloisa Nunes Bordallo
+45 21 30 88 29
bordallo@nbi.ku.dk
Heloisa Nunes Bordallo
+45 21 30 88 29
bordallo@nbi.ku.dk
Alain Sylvestre
+334 76 82 79 05
alain.sylvestre@g2elab.grenoble-inp.fr
Title:
Investigating the development of porosity during settlement of dental cement pastes with SAS sensitive
novel neutron imaging technique
Summary:
Glass ionomer cements are water- and acid-based cements used in dentistry (dental fillings for
example). They are made through the reaction between a silicate glass powder and a polyalkenoic acid
solution. Those materials are very interesting for medical use because of their good biocompatibility.
However, dental cements have a poor mechanical resistance which leads to a short life expectancy in the
hostile oral environment (humidity, mechanical constraint…). That’s why, having a better comprehension of
the cement settlement process, and how its structure evolves during time has the potential to lead to
improvements and further development. This report relates my internship at the Niels Bohr Institute in
Copenhagen. In a first time, I present what is a dental cement and what is the novel imaging technique we
used. After that I relate how this technique has been applied on dental cement, at the ICON beam-line at the
Paul Scherrer Institute (PSI) in Switzerland. Finally, I explain how I treated the data obtained at PSI what are
the results I managed to get.
Résumé:
Les ciments verres ionomères (ici ciments dentaires) sont des matériaux utilisés notamment en
dentisterie (par exemple pour obturer des cavités dentaires à la suite de caries). Ils sont préparés en faisant
réagir une poudre (verre ionomère) et une solution d’acide polyacrylique. Ce matériau est très intéressant
pour des applications médicales du fait de son excellente biocompatibilité. En revanche, les ciments
dentaires présentes une résistance limité ce qui entraine une faible durée de vie dans l’environnement buccal
(humidité, contrainte mécanique…). C’est pour cela qu’avoir une meilleure compréhension du processus de
prise ainsi que de l’évolution de la structure du ciment au cour du temps pourrait permettre des améliorations
notables des propriétés du matériau. Ce rapport relate mon stage au sein de l’institut Niels Bohr à
Copenhague. Je présente dans un premier temps ce que sont les ciments dentaires et la technique d’imagerie
que nous avons utilisé. Puis, j’explique de quelle manière cette nouvelle technique d’imagerie a été appliquée
à l’étude du ciment dentaire à l’institut Paul Scherrer (PSI) en Suisse. Enfin, j’explique comment j’ai traité
les données collectées et les résultats que j’ai réussi à obtenir.

Rapport de stage 3ième année Eliott Guérin

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