Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites
Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites
Céline M. Desmet 0 1 2
Andrej Djurkin 0 1 2
Ana Maria Dos Santos-Goncalvez 0 1 2
Ruhong Dong 0 1 2
Maciej M. Kmiec 0 1 2
Kyo Kobayashi 0 1 2
Kevin Rychert 0 1 2
Sébastien Beun 0 1 2
Julian G. Leprince 0 1 2
Gaëtane Leloup 0 1 2
Philippe Levêque 0 1 2
Bernard Gallez 0 1 2
0 1 Biomedical Magnetic Resonance Research group, Louvain Drug Research Institute, Université catholique de Louvain , Brussels , Belgium , 2 School of Dentistry and Stomatology, Université catholique de Louvain , Brussels , Belgium , 3 Advanced Drug Delivery and Biomaterials Research Group, Louvain Drug Research Institute, Université catholique de Louvain , Brussels , Belgium , 4 EPR Center for the Study of Viable Systems, Geisel School of Medicine at Dartmouth, Hanover, NH, United States of America, 5 Center for Research and Engineering on Biomaterials CRIBIO, Université catholique de Louvain , Brussels , Belgium
1 Funding: The project was supported by The National Institutes of Health, grant number U19AI091173. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
2 Editor: Gayle E. Woloschak, Northwestern University Feinberg School of Medicine, UNITED STATES
In the aftermath of a major radiological accident, the medical management of overexposed individuals will rely on the determination of the dose of ionizing radiations absorbed by the victims. Because people in the general population do not possess conventional dosimeters, after the fact dose reconstruction methods are needed. Free radicals are induced by radiations in the tooth enamel of victims, in direct proportion to dose, and can be quantified using Electron Paramagnetic Resonance (EPR) spectrometry, a technique that was demonstrated to be very appropriate for mass triage. The presence of dimethacrylate based restorations on teeth can interfere with the dosimetric signal from the enamel, as free radicals could also be induced in the various composites used. The aim of the present study was to screen irradiated composites for a possible radiation-induced EPR signal, to characterize it, and evaluate a possible interference with the dosimetric signal of the enamel. We investigated the most common commercial composites, and experimental compositions, for a possible class effect. The effect of the dose was studied between 10 Gy and 100 Gy using high sensitivity X-band spectrometer. The influence of this radiation-induced signal from the composite on the dosimetric signal of the enamel was also investigated using a clinical LBand EPR spectrometer, specifically developed in the EPR center at Dartmouth College. In X-band, a radiation-induced signal was observed for high doses (25-100 Gy); it was rapidly decaying, and not detected after only 24h post irradiation. At 10 Gy, the signal was in most cases not measurable in the commercial composites tested, with the exception of 3 composites showing a significant intensity. In L-band study, only one irradiated commercial composite influenced significantly the dosimetric signal of the tooth, with an overestimation about 30%. In conclusion, the presence of the radiation-induced signal from dental composites should not significantly influence the dosimetry for early dose assessment.
Competing Interests: The authors have declared
that no competing interests exist.
The risk of a major radiological incident, resulting from an accident in a nuclear power plant,
such as in Fukushima, or from a terrorist device emitting radiation, has drawn increasing
attention over the last years. Among the different consequences of such incident, the determination
of the amount of the exposure and the appropriate management of overexposed individuals
will be a major parameter [1, 2]. Those scenarios are studied and handled by many different
actors, both on a national and international level, as official institutions have developed several
programs aiming at developing tools to face those situations. To cite only a few examples, the
International Atomic Energy Agency (IAEA), through its Incident and Emergency Centre ,
has published various guidelines and technical tools covering preparedness and response to
nuclear and radiological emergencies [4, 5]; NATO Science and Technology Organisation also
coordinates a task group (Ionizing Radiation Bioeffects and Countermeasures HFM-222)
promoting research on biodosimetry [6–8]; at the US level, the National Institute of Allergy and
Infectious Diseases (NIAID) coordinates a joint program “Radiation and Nuclear
Countermeasures Program” with the US Department of Health and Human Services [9–11]; the Biomedical
Advanced Research and Development Authority (BARDA) of the US-HSS is also fostering
developments in biodosimetry in case of mass casualty event [9, 10]. Networks are currently
also developing at the European level, such as the European Network of Biodosimetry RENEB
 or EURADOS [13–15].
In this context, a key parameter is the determination of the dose of ionizing radiations
absorbed by the overexposed individuals, as this will determine the appropriate medical
treatment strategy . The difficulty is that people in the general population do not possess
dosimeters such as those available for workers in controlled areas of nuclear facilities. The dose must
consequently be evaluated after the fact, using retrospective dosimetry or dose reconstruction
methods . Several approaches are available for retrospective dosimetry, namely cytogenetic
assays, changes in genes and gene products, changes in metabolites, mathematical modelling
using MonteCarlo simulation, and biophysical methods . In the hypothesis of a large scale
incident, there will be an immediate and urgent need to perform triage of a large number of
people at risk. This will rely on a first assessment of the individual dose, which should
preferably occur in the field and very quickly. Progress has been made in many biodosimetry
approaches [6, 18], and it has been suggested that Electron Paramagnetic Resonance (EPR)
biodosimetry, using tooth enamel of victims as a natural dosimeter, could help in the early
assessment of the dose for initial triage. Indeed, ionizing radiations generate very stable carbonate
free radicals within the hydroxyapatite matrix of the enamel, in a linear dose-dependent
manner, and can be readily detected with EPR . Over the last years, the Dartmouth Center for
Medical Countermeasures Against Radiation (CMCR) has developed specific low frequency
(L-band) EPR spectrometers for non invasive in vivo measurements, directly in the subject’s
mouth. Importantly, those spectrometers are in the field deployable, and particularly adapted
for mass triage. They are currently under extensive evaluation [20–24].
Apart from the issues linked to the instrumentation, factors affecting the dosimeter itself,
and consequently also potentially affecting the dosimetric signal, should be investigated in
order to fully validate the method. In a previous work, we investigated the influence of tooth
restorations on the dosimetric signal, and more specifically the influence of the signal due to
the photopolymerization process . Indeed, dimethacrylate based composites used for
restoration of teeth are photopolymerized in situ using visible light, and this polymerization process
generates stable free radicals giving a strong EPR signal [26, 27]. Free radicals created in the
organic matrix will recombine at the end of the polymerization process, but as the vitrification
progresses, the mobility of the free radicals becomes too low to allow recombination, and they
Fig 1. Typical polymerization signal recorded in a commercial composite (Filtek Supreme Ultra).
remain trapped in the polymerized matrix , giving an intense and complex 9 lines spectrum
. This signal was shown to fade more or less rapidly, depending on the storage environment
, likely due to a hydroperoxidation phenomenon . We observed that a strong
polymerization signal, the complex 9 lines spectrum, was indeed systematically present in every
composite tested (Fig 1), with the same resonance frequency as the dosimetric signal of the enamel.
This “polymerization signal” was nevertheless rapidly decaying with time so that, in L-band, it
was hardly detectable 18 days after the initiation of the polymerization, and its influence on the
dosimetric signal could be neglected . After decaying of this polymerization signal, in some
composites, a stable atypical signal, resembling to an immobilized nitroxide signal, was also
Restorations are not easily detected by untrained operators, but could be with the help of an
appropriate device such as a UV lamp. One strategy could consist in excluding restored teeth
from measurements, and consider measuring an adjacent tooth, although it is not granted that
they would not bear any restoration.
So the systematic exclusion of restored teeth would significantly impact the global efficacy
of the technique. On the contrary, a procedure designed to include the measurement of
restored teeth, including a correction of the signal if necessary, would offer a better adaptability
of the technique. In this context, in the present study, we raised the issue of another possible
EPR signal, different from the photopolymerization signal, induced in the composite when it is
exposed to ionizing radiations, a situation that would be very likely for victims of a radiological
incident, as teeth of a large part of the population do bear restorations. Dental composites
contain a large fraction of inorganic fillers (circa 50 to 80% wt), such as silica particles or barium
glasses , materials which are known to give an EPR signal when exposed to ionizing
radiations [32–34]. Free radicals are also likely to be induced in the organic matrix itself, where they
can remain stable for an undetermined period of time. The aim of the present study was to
screen irradiated composites for a possible radiation-induced EPR signal, to characterize it in
terms of intensity and stability, and evaluate the possible interference with the dosimetric signal
of the tooth enamel. We investigated the most common commercial composites available on
the market, and experimental compositions for a possible class effect.
In the first part of this study, the effect of the radiation at high dose (100 Gy) was
investigated using a X-band spectrometer, because it allowed higher sensitivity. The signal was
characterized and its stability investigated by means of kinetics study. The delivered dose was
progressively lowered to 10 Gy in order to determine the level of dose at which no
radiationinduced signal could be observed.
In a second part of the study, the influence of the radiation-induced signal from the
composite on the dosimetric signal of the enamel was also investigated using a clinical L-Band EPR
spectrometer, developed in the EPR center at the Dartmouth College and designed for in vivo
measurements in humans, and an experimental setting close to a realistic situation.
Materials and Methods
This study was divided in two parts. First, we investigated the occurrence of a
radiationinduced signal in the resins and composites using X-band EPR spectroscopy, because X-band
allowed a higher sensitivity, a better characterization of the signal, and faster measurements.
Measurements were performed on small bars of composites submitted to various doses of
radiation, first at high dose (100 Gy) in order to characterize the signal and study its stability, then
at lower doses in order to determine whether a threshold was observable.
In a second part, we checked the influence of the irradiated composite on the dosimetric
signal of the tooth, using a setting mimicking more realistic conditions. Bars of composites were
irradiated in the low dose range and inserted in a tooth, irradiated separately at the same dose.
Measurements were carried out using a L-band spectrometer, developed in Dartmouth (USA)
specifically for in the field direct measurement of teeth in the mouth of individuals.
Part I: characterization of the radiation-induced signal in restorative
material using X-band
Composites. Nineteen composites were selected among the commercial composites the
most widely used by dentists and routinely used for restoration of incisors (Table 1). These
composites were identical to those characterized in our previous work about the EPR signal of
restorative materials .
Experimental resins. Experimental resins were prepared using different proportions of
the most common monomers. Bisphenol A glycidyl dimethacrylate (Bis-GMA), triethylene
glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), ethoxylated bisphenol
A glycidyl dimethacrylate (Bis-EMA-2 and Bis-EMA-15) were all purchased from
SigmaAldrich (Belgium). Fourteen compositions of these monomers were prepared according to
Sideridou et al. (Table 2) . Each composition contained 2% (molar) camphorquinone
(Sigma-Aldrich, Belgium) as the photo-initiator and 2% (molar)
ethyl-4-dimethylaminobenzoate (Sigma-Aldrich, Belgium) as the co-initiator.
Polymerization of samples. Composites and resins were polymerized as already described
. Briefly, 30 mg of resin material was cast in a PTFE mould (7 mm x 1.4 mm x 1.4 mm) and
polymerized using a BluePhase G2 lamp (Ivoclar Vivadent, Schaan, Liechtenstein) at high
power (1200 mW/cm2) during 20 seconds. Samples were stored in dry conditions and in the
dark during all the study.
All resins were used at least six months after polymerization in order to ensure a total decay
of the photopolymerization signal.
Irradiation of samples–Occurrence of the radiation-induced signal in composites and
resins. In order to detect the occurrence of a possible radiation-induced signal, commercial
composites and experimental resins were first all irradiated at the dose of 100 Gy (dose
absorbed in water) with a 137Cs gamma irradiator (IBL637, Oris Industrie), in order to detect
and characterize a possible radiation-induced signal. Other samples were then irradiated at
lower doses (50, 25 and 10 Gy) to determine the level of dose not giving any signal. All samples
were polymerized at least six months before the external irradiation.
EPR X-band measurements. X-band measurements were carried out with a Miniscope
MS200 spectrometer (Magnettech, Berlin, Germany) operating at ~9.5 GHz. The spectrometer
was calibrated with a standard of 2,2-diphenyl-1-picrylhydrazyl (dpph) (batch # 1204D191
Bruker Biospin, Rheinstetten, Germany) before and after the measurements of samples. The
acquisition parameters were as follows: center field: 335.600 mT, sweep field: 13.000 mT,
acquisition time: 30 s, number of points: 4096, number of scans: 1, modulation frequency: 100 kHz,
G: Bis-GMA, T: TEGDMA, U: UDMA, E-15: Bis-EMA (15-ethoxy/phenol), E-2: Bis-EMA (2-ethoxy/phenol).
modulation amplitude: 0.1 mT, power: 0.5 mW, gain: 300. The signal intensity was measured
as the peak-to-peak height of the central peak of the spectrum.
As the measurements had to be carried out over several hours, and repeated on several days,
the signal intensity was normalized with the signal intensity of the dpph standard and
expressed as normalized units (n.u.). This ensured quantitative data by minimizing any drift of
the signal and intraday as well as interday variations.
Kinetics of decay of the radiation-induced signal in composites and resins. The study of
the decay kinetics of the radiation-induced signal was performed on composites and resins at
least six months after their initial polymerization, after the decay of the polymerization signal.
For this part of the study, samples still presenting an atypical residual (nitroxide-like) signal
were excluded, as a low radiation-induced signal would be masked by the residual signal and
would prevent any further measurements. The delivered dose was 100 Gy. Measurements were
carried out in X-band for sensitivity reasons, in triplicate, and were started one hour after the
end of the irradiation. The EPR signal was then measured once a day during one week, and
once a week during one month when necessary. Decay curves were fitted with a
monoexponential decay model using Prism 5 (GraphPad Software, La Jolla, CA, USA) where applicable.
Powder of dental enamel. A powder of dental enamel (164 mg) was obtained by crushing
the crown of a molar tooth after removal of the dentin. The molar was obtained from the
collection of the laboratory of anatomy at the faculty of medicine, Université catholique de
Louvain. The powder was irradiated at 5 and 10 Gy with the same 137Cs gamma irradiator. The
ratio of the mass of composite to the mass of enamel was 0.18, which is considered as
representative of a medium sized restoration.
Part II: Influence of the radiation-induced signal on the dosimetric signal
using clinical L-band
Influence of irradiated restoration on the dosimetric signal from an irradiated tooth.
A cavity of 2.1 mm was prepared in an incisor obtained from a cadaver (anatomy department,
Université catholique de Louvain). The tooth was then submitted to a dose of 15 Gy (dose to
water) using a 137Cs gamma irradiator at a dose rate of 1Gy/min (JL Shepherd and Associates,
San Fernando, CA, USA). The EPR dosimetric signal was measured using a L-band
spectrometer operating at 1.15 GHz and an associated magnetic field of 41 mT [20–24]. The parameters
of acquisition were the following: modulation amplitude 0.4 mT, modulation frequency 21780
Hz, sweep width 4.0 mT, 1024 points/scan, scan time 3.0 s, time constant 5 ms, power 6 dB (25
mW). Twenty consecutive scans were performed for each sample. Small bars (7 mm x 1.4 mm
x 1.4 mm) of commercial composites, polymerized at least six months earlier, were exposed to
the same 15 Gy dose. After irradiation, the bar was inserted in the cavity prepared in the tooth,
and the tooth was measured a second time in order to check the possible influence of the
irradiated composite on the dosimetric signal, using the same parameters. Measurements were
performed 5 hours after the irradiation. This time point was selected so that the measurements
would be carried out in a timeframe as close as possible from the initial irradiation, when the
signal was suspected to be the most intense and consequently with the strongest influence on
the dosimetric signal. Five acquisitions were performed for each composite. Means were
compared using student t-test.
Ethics statement. Human samples were obtained and used after approval of the study by
the local ethics committee “Commission d’éthique biomédicale hospitalo-facultaire” from the
university hospital “Cliniques universitaires Saint-Luc” (IRB 00001530).
Teeth were obtained from people who offered their body for medical teaching and research.
Samples were anonymized prior to analysis.
After a 100 Gy irradiation, a radiation-induced EPR signal was clearly observed in X-band in
14 composites. This radiation-induced signal is characterized by various and complex spectral
shapes (Fig 2). Normalized intensities (n.u.) ranged from 0.37 n.u. to 0.82 n.u. (Table 3), one
hour after irradiation. After a 10 Gy irradiation, the radiation-induced signal was observable in
only 3 composites (N’Durance, Herculite Ultra, Clearfil Majesty Esthetic). No signal was
observed in the 11 other commercial composites. At 10 Gy, the radiation-induced signal in
commercial composites ranged from 0.29 n.u. to 0.33 n.u. whereas the EPR dosimetric signal
measured in irradiated enamel had an intensity of 0.73 n.u. at 10 Gy and 0.42 n.u. at 5 Gy.
Above 10 Gy, the relation between the dose and the signal intensity was compatible with a
linear model in 8 of the 14 composites (r2 > 0.90), in the interval of doses tested (Fig 3 and
Table 4). Below 10 Gy, no signal was observed (S1 Fig), except noise around 0.13 n.u., so that
the value of the intercept should not be used to extrapolate the intensity of the
radiationinduced signal at lower doses, nor anticipate interference with the dosimetric signal in that
particular range of doses.
Among the five other composites, showing a residual stable nitroxide-like signal at the onset
of the irradiation, no particular additional signal was observed for GrandioSo, Clearfil AP-X &
Ceram-X, even after a 100 Gy irradiation. However, for IPS Empress Direct and Tetric
Fig 2. Illustrative examples of some radiation-induced signals recorded in commercial composites before irradiation (gray line) and irradiated at
100 Gy (black line). Filtek Supreme Ultra (A), Venus Diamond (B), N’Durance (C), Clearfil Majesty Esthetic (D).
EvoCeram a small extra contribution was noted, superimposed on the nitroxide-like signal
(Table 3 and Fig 4). This signal was not detected after irradiation at lower doses.
Radiation-induced signal in experimental resins
In the pure monomers, after a 100 Gy irradiation, no radiation-induced signal was measured in
the TEGDMA nor Bis-EMA-15 monomers. In the UDMA, Bis-GMA and Bis-EMA-2
monomers, a signal was observed with an intensity ranging from 0.57 n.u. to 1.30 n.u. (Table 5). In
Fig 3. Relationship between radiation-induced signal intensity and irradiation dose in the commercial
composite Filtek Supreme Ultra.
n.a.: not applicable, nitroxide-like signal.
some experimental compositions of monomers irradiated at 100 Gy, an intense
radiationinduced signal was detected (Table 5). A class effect was observed in experimental resins: a
radiation-induced signal was detected in the G/T, G/U and G/(T)/U/E-15 compositions. No
radiation-induced signal was detected in G/E-15 compositions.
The shape of the radiation-induced signal, a single broad line spectrum (linewidth = ~1 mT,
gvalue = 2.0039), different from the complex radiation-induced signal observed in commercial
composites, was the same for all samples with the exception of UDMA monomer showing a
more complex signal with an overall linewidth of 5 mT (Fig 5).
When present, the radiation-induced signal increased linearly with the dose (Fig 6 and
Decay kinetics of the radiation-induced signal in commercial composites
The decay kinetics study, performed over a one month period, showed that the
radiationinduced signal in commercial composites was unstable. In 7 out of the 14 composites selected
for the decay kinetics, no signal was observed after only 24 hours post irradiation (Table 7). A
slower decay was observed for the 7 other composites, compatible with a monoexponential
decay with t1/2 ranging from 15 to 91 hours (Table 7 and Fig 7). The signal completely
disappeared in one week, except for the N’Durance composite, showing a more stable signal, still
present one month after the initial irradiation.
Decay kinetics of the radiation-induced signal in experimental resin
In the experimental resins giving an EPR signal after irradiation, the decay kinetics of the
radiation-induced signal was generally fast, with a half-life below 10 hours. UDMA was an exception
with a t1/2 approaching 100 hours (Table 8).
Fig 4. Nitroxide-like signal recorded in GrandioSo (A-B), IPS Empress Direct (C-D) and Tetric EvoCeram (E-F) before (A-C-E) and after irradiation
(100 Gy) (B-D-F). Arrow shows the contribution of the radiation-induced signal.
Influence of irradiated composites on the dosimetric signal in tooth
Measurements were also performed using the clinical L-band spectrometer developed by the
Dartmouth EPR Center for in the field and in vivo measurement of teeth. It was equipped with
a resonator specifically designed and optimized for teeth . After irradiation at 15 Gy, the
mean dosimetric signal intensity from the enamel of an incisor was 0.30 ± 0.02 a.u. As a cavity
was prepared in the tooth before irradiation, it was possible to insert a small bar of commercial
composite separately irradiated at the same level of dose (15 Gy), in order to mimic a standard
restoration. A second measurement was then performed 5 hours after the irradiation of the
composite to check its influence on the dosimetric signal from the enamel. Data for each
Units are normalized to the dpph signal intensity (n.u.).
G: Bis-GMA, T: TEGDMA, U: UDMA, E-15: Bis-EMA (15-ethoxy/phenol), E-2: Bis-EMA (2-ethoxy/phenol).
n.d.: not detectable.
composite are presented in Table 9. Overall, the signal measured after inclusion of the
irradiated bar was very close to the one observed without the restoration (Table 9). A statistically
significant difference was observed for only one composite, IPS Empress (Fig 8). A possible
influence can not be completely ruled out for GC Kalore, with a p value very close to the
Retrospective dosimetry using EPR relies on the detection of stable free radicals generated by
ionizing radiations in the enamel of teeth. Parameters interfering with this dosimetric signal
can potentially affect the accuracy of the dosimetry. Among those factors, the presence of
restorations in teeth is a possible concern. In a previous work, we investigated a first aspect which
was the occurrence of an EPR signal arising from the photopolymerization of the composite
. We concluded that this polymerization signal was quite unstable, and that in most cases
only recent restorations would affect the dosimetric signal, because the polymerization signal
Fig 5. Radiation-induced signal recorded in irradiated experimental resins at 100 Gy. Bis-GMA 100% (A), UDMA 100% (B), G/T 0.3582/0.6418 (C).
Fig 6. Relationship between radiation-induced signal intensity and irradiation dose in experimental
resin Bis-EMA-2 (E-2).
was not anymore detectable 6 months after the polymerization. Nevertheless, the effect of
ionizing radiations on the composites themselves, after their polymerization, had not been
investigated, and was an important parameter to consider for further validation of this technology.
The purpose of the present study was to evaluate whether the irradiation of restorative material
(composites) would induce free radicals in the matrix, either organic or mineral part, and
consequently a detectable EPR signal, different from the photopolymerization signal, and also
possibly interfering with the dosimetric signal of the enamel.
We investigated the occurrence of an EPR signal after irradiation of polymerized
commercial composites and experimental resins, and characterized the signal in terms of shape,
intensity and decay kinetics with X-band studies. A radiation-induced signal was observed for very
high doses (25–100 Gy), and was generally rapidly decaying. Based on scenarios published by
different official authorities dealing with radiation, such as NCRP and other consensus
conferences [36–38], this range of doses is only expected in the near vicinity of the nuclear device,
n.a.: not applicable
G: Bis-GMA, T: TEGDMA, U: UDMA, E-15: Bis-EMA (15-ethoxy/phenol), E-2: Bis-EMA (2-ethoxy/phenol).
Clearfil Majesty Esthetic
t1/2 (h) (CI 95%)
Half-lifes (T1/2) expressed in hours (h) with confidence interval at 95% (CI 95%).
n.a.: not applicable, complete decay < 24h.
and a limited number of individuals would be exposed to doses above 10 Gy. Those victims
would present very rapidly severe deterministic effects (vomiting, erythema, neurological
syndrome etc.) so that dose evaluation could be based on the symptoms alone, as they would be
indicative of a fatal issue on a very short term. Only palliative care would be required in this
At the dose of 10 Gy, the signal was in most cases not measurable in the commercial
composites tested. In 3 composites however (N’Durance, Clearfil Majesty Esthetic, Herculite
Fig 7. Monoexponential fitting of the decay curves of the radiation-induced signal intensity in
composites. Filtek Supreme Ultra , N’Durance ☐, TPH3 4.
t1/2 (h) (CI 95%)
Half-lifes (t1/2) expressed in hours (h) with confidence interval at 95% (CI 95%).
G: Bis-GMA, T: TEGDMA, U: UDMA, E-15: Bis-EMA (15-ethoxy/phenol), E-2: Bis-EMA (2-ethoxy/phenol).
-: no radiation-induced signal. n.a.: not applicable, complete decay < 24h. n.d.: not determined.
Ultra), a signal with a significant intensity was observed, ranging from 0.29 to 0.33 n.u.,
compared to the dosimetric signal of enamel for the same delivered dose (0.73 n.u.). The decay of
the signal for Herculite Ultra was extremely fast, so that it was not detectable after a few hours.
No real influence of this composite is to be expected. The half-life for Clearfil Majesty Esthetic
was somewhat longer (29 h), so that a possible influence might be anticipated during the first
24 hours after irradiation. As the t1/2 of N’Durance was quite longer (91 h) an overestimation
of the dose is to be anticipated. Those results were obtained using high frequency X-band
spectrometry to ensure high sensitivity, and a geometry of cavity allowing the detection of the signal
from the whole volume of the composite. This must be considered as a worst-case situation.
Indeed, in the field, measurements will be carried out using a low frequency L-band
spectrometer equipped with a surface resonator, optimized for the detection of the surface enamel of the
tooth. The geometrical factor will then be much more favourable to the detection of the
enamel. The mass of composite susceptible to be detected by the system will be quite lower
than the 30 mg used in this study. Depending on the size and geometry of the restoration, only
a few mg will be present within the sensitive volume of the resonator.
Based on the results obtained in X-band, we extended the study using a clinical L-band
spectrometer developed by the Dartmouth EPR Center for in the field measurements, and a
resonator specifically designed for the detection of the dosimetric signal of the enamel. One tooth was
used for the whole study, in order to standardize as much as possible the setting, so that
confounding factors were reduced to the minimum. The geometry of the tooth and of the
composite tested were kept constant throughout the study. Under these conditions, only the influence
of the composite should be measured, all other parameters being controlled and unchanged.
Using this more realistic setting, only one irradiated composite (IPS Empress Direct)
showed a significant contribution to the dosimetric signal, with an overestimation about 30%.
At lower doses, this overestimation is expected to be even higher. This overestimation could
also be eliminated using an adequate fitting model. Indeed the radiation-induced and
nitroxide-like signals from composites are different from the dosimetric signal of teeth in terms of
Mean ± SD expressed in arbitrary units (a.u.). P value are significative < 0.01
shape and position (Fig 8), so that each contribution could be quantified separately after
From the operation standpoint, this overestimation should be acceptable, and should not
fundamentally alter the decision making process for the appropriate management of
overexposed individuals. More accurate dosimetry can be performed after triage, on a smaller number
of subjects, when necessary. Nevertheless, only one geometry was considered in this study, so
that the effect of the loss of enamel, due to the restoration, on the dosimetric signal was not
completely investigated. Other geometries of restoration, including a variation of both the
location of the restoration and its size, should be further investigated in order to complete the
Another aspect possibly affecting the results is the storage conditions of samples (tooth and
composites). In this study, all the samples were kept in dry conditions, but other storage
conditions could change the situation to some extent. Teeth and restored teeth are naturally placed
in a very humid atmosphere inside the mouth. This environment can affect both the kinetics of
radicals induction/recombination and their detection, as EPR uses microwaves which are
readily absorbed by water. Also, composites were polymerized out of the tooth, whereas in normal
conditions they are cured directly in the tooth. Specific radicals due to the interaction between
tooth tissue and restorative material cannot be excluded.
In conclusion, the influence of a radiation-induced EPR signal arising from the composites
used for teeth restoration is rare and of low intensity. Nevertheless, the presence of a
restoration will affect the mass of enamel detected, which is a more important parameter to take into
account. A correction of the dose based on the loss of enamel material could be envisaged,
using simple and fast imaging techniques (UV, IR or near IR) susceptible to detect and quantify
the amount of restorative material, or reciprocally the loss of enamel material.
Fig 8. L-band measurement of an irradiated tooth (15 Gy, A), irradiated composite alone (15 Gy, B),
irradiated tooth including the irradiated composite (15 Gy, C) and non irradiated tooth (D). Black line is
the median of 20 scans. Red line is the fit. Peaks at low and high field are due to the standard used
The authors wish to thank Prof. B. Lengelé, Laboratory of Anatomy, Université catholique de
Louvain for providing the teeth used in the present study, and Dr Benjamin Williams,
Associate Director, EPR Center for the Study of Viable Systems (Dartmouth), for providing the
Matlab spectral fitting routines and for his helpful advice and guidance.
Conceived and designed the experiments: CD SB JL GL PL BG. Performed the experiments:
CD AMDS SB AD MMK RD KK PL. Analyzed the data: CD JL GL MMK RD KK KR PL BG.
Contributed reagents/materials/analysis tools: CD SB AD JL MMK RD KK KR PL. Wrote the
paper: CD AMDS SB AD JL GL MMK RD KK KR PL BG.
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