Here are some FAQ (Frequently Asked Questions)
about Tooth Dosimetry using EPR
1. What is “tooth dosimetry using EPR”?
• Dosimetry refers to a method to measure radiation dose.
• The dose of radiation a person receives makes a difference as to whether they are likely to experience any
health problems from radiation and, if any, how much and what kinds of damage to health are likely.
• Radiation therapy can use these effects deliberately to cause ‘harm’ to cancer cells. Doctors in these cases
have studied how much radiation to give in treating cancer and how to direct it to impact cancer while
minimizing any problems to normal cells. Doctors in this case know exactly how much dose a person is getting
and so it is not necessary to measure it after-the-fact.
• We are interested in helping in situations where people may have been accidentally exposed to doses of high
levels of radiation and don’t know what dose they received. This can happen in accidents as recently happened
to the nuclear power reactors in Japan or in terrorist attacks involving the release of radiation via explosions.
The dose received in these situations is unknown and may damage healthy cells, unless treated.
• We want to develop a fast and easy way to do dosimetry in these situations, so that doctors can use our results
to decide who would benefit from being treated for exposure and who doesn’t need to be treated.
• Tooth enamel naturally reacts to the presence of radiation in a way that itself is harmless to the person and to
his or her teeth. This natural reaction happens almost ‘instantly’, at the time of exposure, and changes the
crystalline structure of enamel to create a new feature in the crystal (called a ‘stable free radical’) that can be
detected immediately or, if necessary, even for a very long time after the radiation exposure occurred.
• EPR (electron paramagnetic resonance) measures the amount of stable free radicals in the tooth. The
amount of these free radicals indicates how much total radiation the tooth was exposed to.
• You may not have heard of EPR before. It is used in clinical research. However, it is a technique similar to
MRI (magnetic resonance imaging) that is used widely in clinical care.
Putting it all together:
• Because EPR can estimate the dose of radiation that a tooth (and more importantly, the whole person)
received, this technique is called ‘tooth dosimetry using EPR’. It is especially useful when doctors are not sure
what dose a person has received but knowing that information would help decide how best to treat the person.
2. But why measure my teeth? I haven’t been ‘accidentally exposed to
high radiation’!
• We need to test our system using “normal teeth” (i.e., without exposure to high levels of radiation), so that we
understand what the signals look like for all types of normal teeth. There are normal ‘background’ signals in
teeth and the mouth that we need to understand so we can eliminate their effects and concentrate only on the
effect of radiation. These measurements need to be done using normal (non-irradiated) teeth in volunteers.
• We also need to test our system using teeth with “known exposures to high radiation”. Teeth used in this case
have all been exposed to high radiation as part of the volunteer’s standard radiation therapy to treat cancer.
These measurements are typically made in volunteers who have had radiation therapy for head and neck cancer
or who have had whole body irradiation (usually for lymphoma or leukemia). These cancer patient volunteers
help us understand how accurate our measurements are since we know the therapeutic dose they were given.
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3. What does the EPR machine look like?
Here is a volunteer being measured. See FAQ # 5 for
more about the process.
The volunteer is sitting on an office chair adjusted to
a comfortable height for him.
His hands and arms are resting on a ‘stand’ below the
table that helps him rest comfortably and keep still
during the measurement.
His forehead is resting against a padded bar. This is
similar to the positioning commonly used in eye
exams.
His head is between the two halves (poles) of a
magnet. The strength of this magnet is about the
same as a refrigerator magnet. (See FAQ #7 for more
information.)
He is resting his open mouth on a ‘bite plate’. The
plate gently holds up his upper lip so that his upper
front tooth can be measured. (See FAQ 5.)
A Velcro strap is positioned against the back of his
head to help position him in the magnet and gently
hold his head during the measurement.
If he needs to, he can easily undo this Velcro, pull his
head back, and move the chair away. It is important
to try to stay in place, so we try to make him as
comfortable and gently supported as we can.
The operator needs to place a small loop on his upper
front tooth to make the measurement.
Each measurement lasts about 80 seconds, with 5
different measurements in total. He may be sitting at
the magnet for about 15 minutes total.
A Volunteer Being Measured
4. What does it feel like to be measured?
•The machine is very quiet during operation but you may hear a soft ticking noise when the actual
measurements occur.
•You can see through the opening at all times; you will see the operator and detector apparatus.
•You can talk to the operator before and after measurements but please try not to talk when your teeth
are being measured. It will seriously harm the quality of the EPR measurement if you move.
•There is no smell.
•You should not feel anything from the measurements.
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5. What is happening during the measurement?
A Volunteer Being Measured.
To better show the detector loop and how retractors
gently hold the upper lip, we do not show the small
plastic bag that will be used.
The person bites gently on the block (light green area in
the picture below). The two dark green plastic retractors
(we call them ‘antenna’) fit inside the upper lip—as
shown above using white ‘antenna’.
Before you use the bite block, we will cover it with a
plastic bag. Each person uses a different bag and bite
block.
A Disposable ‘Bite Block’
1. Before putting your head in the magnet, the
operator will help you place cotton balls in your
cheeks and lips to collect any saliva.
2. The operator will help you place the two white
plastic retractors on your upper lip to hold it
away from your upper front teeth.
3. The operator will then use a cotton swab to dry
the front of the tooth to be measured.
4. A detector loop is then placed very close to the
surface of the front tooth to be measured.
5. You may feel pressure from the loop but it
should not be uncomfortable. Tell the operator if
you are uncomfortable so it can be repositioned.
6. At this point the operator will spend some time
‘tuning’ the instrument, including turning a
small knob at the far end of the detector (that
you can see), and will communicate back and
forth with the computer operator.
7. You will be asked to stay very still during the
actual measurement. Each measurement takes
about 80 seconds.
8. You will be told when the measuring process is
starting and asked to stay still.
9. You will hear a very soft ticking sound; this
indicates that the measurement is in progress.
10. You will be told when the measuring process is
half way completed (i.e., ~40 seconds later).
11. You will be told when the measuring process is
done (i.e., after about 80 seconds). You may
relax then but please remain in position, keeping
your head in the magnet and your mouth open.
12. Do not respond to any of the operator’s
announcements during measurements since any
movement or talking will impair the quality of
the measurement.
13. During the time you are in the magnet, five
measurements will be taken on the same tooth.
14. Prior to each measurement, the detector loop
will be repositioned on your tooth and the
operator will check for saliva and give you new
cotton balls if needed.
15. You will be informed when every set of
measurements starts so you can try to hold still
during the measuring period.
16. The total time inside of the magnet will be
approximately 10 to 15 minutes.
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6. What happens after the measurement is completed?
• Once the measurement is over, the detector loop will be moved away from your tooth and the strap released.
• You will be asked to release your bite, and to slowly move your head backward and out of the magnet.
• The operator will remove the cotton balls from your mouth and dispose of them.
• You will be told you are ready to leave the measurement area.
• If this is your first measurement session, you will be invited to fill out a questionnaire about your
experience. This is very helpful for us to make improvements in our system and to make the experience as
pleasant and comfortable as we can, based on feedback from people like you. You are also invited to tell us
anything that will help us understand your experience in being measured at any time. That will really help!
7. How strong is the EPR magnet?
• ‘Tesla’ is a unit used to measure the strength of a magnetic field.
• The strength of the magnet system used in EPR dosimetry is .04 tesla.
• For comparison, a typical magnet that people put on the refrigerator door is usually in the range of .01tesla
to .05 tesla, i.e., one refrigerator magnet has about the same strength as our EPR magnet system.
• In contrast, modern MRI magnets used in patient care are 3 tesla each, i.e., they are 75 times more powerful
than our magnet. In other words, the strength of an EPR magnet is about 4% that of a clinical MRI.
8. Has anything ever happened that subjects didn’t like?
After being measured, we ask people to help us understand how they felt during measurement. Almost all
people are satisfied with the process and report no problems.
However, a few have reported some things they didn’t like:
• Some people bite hard on the bite block or otherwise feel tense and have sore muscles at the end of the
session in the magnet. A solution: Relax as much as you can; it isn’t necessary to bite hard or stay very still
between each actual measurement.
• A few people ‘drool’ a bit and find it embarrassing. A solution: We place cotton balls in your mouth to try to
minimize this possibility. We will give you new cotton balls between measurements if they are very wet and you
can have a tissue to catch any drips. We also now measure the incisor (front) tooth and people are much less
likely to experience drooling compared to when we measured the back molars.
• Only one person has reported feeling uncomfortably ‘closed in’ inside the magnet. A solution: we’ve
changed our design since then to have a larger opening and made it easier to see while inside. But if you panic,
just slowly move your head out. You may ask to stop being measured at any time.
• Some people feel like it’s stuffy in the magnet. A solution: We can position fans to help the air circulate.
• Some people worry about cleanliness of the bite block and loop. A solution: We carefully clean surfaces
using the same hygiene practices that dental offices use. We use disposable plastic over the retractors, and the
operator changes disposable gloves for each person measured. Each person uses a different bite block too. Our
procedures follow what your institution has approved. We all want to be sure it is clean for you.
9. What are the risks to my health?
The risk of measurement by EPR is ‘minimal’. In particular, there is no known adverse health consequence
from animal studies or studies in humans. Nonetheless, during informed consent, you will be asked to confirm
that you do not have a pacemaker or and that you do not have any embedded magnetic fragments (such as a
welder might experience from an accident). Other potentially magnetic implanted devices (such as cardioverter
defibrillators, neurostimulators, cochlear implants, and implanted infusion devices) may interact with the
magnet field even though it is very low. We will ask about whether you have any of these devices and, if so,
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will investigate whether your doctors have any concerns about our measuring you before we do any
measurements. Risks for these people are likely to be minimal, but we want to avoid exposing these people to
our magnets, either by coming too close to the magnetic field or by being measured inside our magnet. We also
want subjects to be 18 years or older so that they can easily understand our informed consent material and to
truly give ‘informed consent’ to participate in this research study.
10. Can I wear my glasses in the magnet?
Yes. Glasses can be worn in the magnet safely. However, if they are very big, it may be more comfortable to
take them off.
11. Can I wear my jewelry in the magnet?
Yes, but you may wish to remove them. Jewelry can be safely worn in the magnet, regardless of the metal.
You may take them off if you prefer, but jewelry won’t interfere with the measurement, and nothing will
happen to your jewelry if you leave it on. You might experience a slight tug if your jewelry is attracted and so
we generally recommend taking earrings, nose piercings and necklaces off if you have any concerns.
12. Is it okay to have fillings or crowns on some of my teeth or have
removable bridges?
Yes. Our instruments are measuring the enamel specific to the tooth being measured. It does not matter if other
teeth have fillings of any type, including porcelain, resin, amalgam (the old fashioned kind) or gold. Crowns
and removable bridges are also okay.
If the tooth we measure (i.e., one of your two upper front teeth) has a filling, please let the operator know when
you are getting measured and tell us that in your questionnaire. Your tooth will not be harmed by our
measurement, but the filling may make our measurement look ‘odd’ so we’d like to know that may be the
reason why.
13. Can I be measured if all my teeth are false?
No. False teeth do not have enamel, which is the basis of our measurement.
14. Is it okay if I have implants or veneers on my teeth?
Yes. However, please tell us about this when the clinical coordinator asks you.
15. Is it okay if I use whitening on my teeth?
Yes. However, please tell us about this when the clinical coordinator asks you.
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16. What if I have had radiation therapy?
We would still like to measure you. Please tell us about this when the clinical coordinator asks you.
If you had radiation therapy to any part of your body below the neck, we should not be able to detect it. That is
because our measurements are specific to the tooth.
However, if you have had radiation therapy involving the head (such as for head and neck cancer) or total body
irradiation (such as for leukemia or lymphoma), our measurements should be able to detect radiation in your
teeth—even if your therapy happened many years ago.
17. Will you tell me what my dose is after your measurement is done?
No.
If you are receiving radiation treatment, your doctor will explain what dose you are getting. Our instrument is a
part of our research and is being tested to see how well we can detect the radiation you have received, but it is
not the best source for that information; your doctor is.
If you have not been irradiated previously, our measurement will simply measure background signal of the
enamel.
18. Why am I being filmed?
Our photos will NOT include your face and will not allow anyone to recognize you.
Still photos: We are taking a digital photo of your front tooth. One reason is determine how well we placed the
resonator; that may help explain what we did wrong if we get some unexpected readings. Another reason is to
look at the enamel of your tooth. Finally, we are studying how to use light to automatically choose a good tooth
to measure.
Video [if used]: We are filming your head and neck placement and how comfortably you appear to be sitting
when you are being measured. We want to improve the comfort of our instrument and make it as easy and quick
for the person getting measured as we can.
19. What if I am or might be pregnant?
Our instrument will not harm you or your fetus.
20. What else can I do?
If you have some suggestions about what would help you or others be measured more comfortably or simply
have some ideas about what you didn’t like about the experience, please let us know. Your experience and
suggestions are extremely valuable for us to know. We have provided questionnaires for you to add this
information, but please feel free to talk to any of our staff at any time. Your ideas are always welcome.
We are all very grateful for your help and appreciate your willingness to help us in our research!
Harold M. Swartz, M.D., Ph.D., Principal Investigator and the Entire Team at the Dartmouth EPR Center
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