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Photodiagnosis and Photodynamic Therapy 13 (2016) 114–119
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Photodiagnosis and Photodynamic Therapy
journal homepage: www.elsevier.com/locate/pdpdt
Differences in the intensity of light-induced fluorescence emitted by
resin composites
Bo-Ra Kim, Si-Mook Kang, Gyung-Min Kim, Baek-Il Kim ∗
Department of Preventive Dentistry & Public Oral Health, BK21 PLUS Project, Oral Science Research Institute, Yonsei University College of Dentistry, 50-1
Yonsei-ro, Seodaemun-Gu, Seoul 03722, Republic of Korea
a r t i c l e
i n f o
Article history:
Received 24 September 2015
Received in revised form
11 December 2015
Accepted 7 January 2016
Available online 12 January 2016
Keywords:
Detection
Fluorescence
Resin composites
Quantitative light-induced fluorescence
technology
a b s t r a c t
Background: The aims of this study were to compare the intensities of fluorescence emitted by different
resin composites as detected using quantitative light-induced fluorescence (QLF) technology, and to
compare the fluorescence intensity contrast with the color contrast between a restored composite and
the adjacent region of the tooth.
Methods: Six brands of light-cured resin composites (shade A2) were investigated. The composites were
used to prepare composite discs, and fill holes that had been prepared in extracted human teeth. Whitelight and fluorescence images of all specimens were obtained using a fluorescence camera based on QLF
technology (QLF-D) and converted into 8-bit grayscale images. The fluorescence intensity of the discs as
well as the fluorescence intensity contrast and the color contrast between the composite restoration and
adjacent tooth region were calculated as grayscale levels.
Results: The grayscale levels for the composite discs differed significantly with the brand (p < 0.001): DenFil (10.84 ± 0.35, mean ± SD), Filtek Z350 (58.28 ± 1.37), Premisa (156.94 ± 1.58), Grandio (177.20 ± 0.81),
Charisma (207.05 ± 0.77), and Gradia direct posterior (211.52 ± 1.66). The difference in grayscale levels
between a resin restoration and the adjacent tooth was significantly greater in fluorescence images for
each brand than in white-light images, except for the Filtek Z350 (p < 0.05). However, the Filtek Z350
restoration was distinguishable from the adjacent tooth in a fluorescence image.
Conclusions: The intensities of fluorescence detected from the resin composites varied. The differences
between the composite and adjacent tooth were greater for the fluorescence intensity contrast than for
the colors observed in the white-light images.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
The commercially available resin composite material used in
dentistry now have color and translucency properties that are close
to those of human teeth. The use of a layering technique using
enamel and dentin shading, and the development in dental adhesives technology have also contributed to improvements in the
esthetics of resin restorations [1]. These technical developments
mean that well-placed tooth-colored resin restorations can now
fulfill the esthetic demands of patients. However, this also means
that detecting resin restorations can be a challenging task for dental
professionals during oral examinations.
∗ Corresponding author at: Department of Preventive Dentistry & Public Oral
Health, Yonsei University College of Dentistry, 50-1 Yonsei-Ro, Seodaemun-Gu,
Seoul 03722, Republic of Korea. Fax: +82 2 392 2926.
E-mail addresses: [email protected] (B.-R. Kim), [email protected] (S.-M. Kang),
[email protected] (G.-M. Kim), [email protected] (B.-I. Kim).
http://dx.doi.org/10.1016/j.pdpdt.2016.01.005
1572-1000/© 2016 Elsevier B.V. All rights reserved.
The ability to accurately detect a tooth-colored resin restoration
can affect the repair procedure applied to a damaged restoration
and the removal of excessive materials in a clinical situation, as
well as the results of mass dental examinations such as in forensic
analysis and epidemiological studies [2–5]. It is well established
that the presence of a resin restoration can been confirmed by
visual and tactile inspections with air-drying during a general oral
examination [6]. However, since this method is influenced by subjective decisions made by the examiner, the diagnosis accuracy
can vary with the experience of the examiner. Extra radiography
investigations can be used to compensate for this limitation by supporting the detection of radiopaque resin materials and pathologic
alteration of the tooth around the restoration [7]. However, it is
still difficult to discriminate some resin materials and teeth due
to recommendations to use resin composite with similar or higher
radiopacity than the tooth tissue when evaluating small defects
or caries [8]. In addition, radiography investigations expose the
patient to the potentially detrimental effects of ionizing radiation,
B.-R. Kim et al. / Photodiagnosis and Photodynamic Therapy 13 (2016) 114–119
given that it has been reported that the risk of meningioma may be
elevated among those with frequent exposure to dental X-rays and
younger age groups [9]. Therefore, the development of an alternative method that is noninvasive and intuitive would be valuable to
clinicians for use in dental inspections.
Differences in the intensity and wavelength of the fluorescence
emitted from teeth and resin restorations illuminated by certain
wavelengths of light have recently been reported [3,5,10–12]. It is
known that such differences are attributable to the different chemical compositions of teeth and resin composites [4,13–15]. Teeth
exhibit bluish autofluorescence when illuminated by ultraviolet
(UV), and its intensity is believed to be most affected by fluorophores in organic components of dentin, whose fluorescence is
greater than that of enamel [13]. The visible fluorescence intensity
of a tooth may be affected by the layering of dentin and enamel
[14], while the visible fluorescence of a resin composite is induced
by luminescent elements, such as europium, ytterbium, or other
rare-earth elements. These additives are included in glass fillers
to improve the appearance of the resin [4,15], and their presence
results in the excitation and emissions appearing within different wavelength ranges. A method that utilizes this property could
improve visual inspections involving evaluations of the esthetic
appearance and the detection of a tooth-colored resin restoration.
Several previous studies have shown that a UV light source
is useful for discriminating teeth and resin restorations based on
fluorescence [11,12,15,16]. However, the use of UV light requires
protective gear such as a dental dam due to this radiation being
harmful to the oral tissues [3]. In addition, these studies have been
limited by the difficulty of interpreting the results since most such
studies have involved spectral analyses.
The usefulness of visible light that is safer than UV light has also
been investigated, and it was found that the absolute fluorescence
intensities detected from teeth and composites decreased when
the excitation intensity increased within the wavelength range of
400–500 nm, whereas the relative difference in intensities between
the teeth and composites increased [10]. In addition, a device based
on quantitative light induced-fluorescence (QLF) technology, consisting of a visible-light lamp (about 405 nm) and a long-pass filter
(>520 nm), has been shown to increase the validity and intraexaminer agreement over that obtained with standard white light images
when detecting resin restorations of shade B3 in a restored tooth
[17]. However, the potential of visible-light sources for identifying
various resin composite materials from tooth structures using specific fluorescence properties—and usefulness of these lights sources
in clinical situations—remain to be established.
Based on the above-mentioned considerations, this study had
two objectives: (1) to compare the intensities of the fluorescence
emitted from different resin composites as detected using a
combination of a 405-nm light source and a specific filter, and
115
(2) to compare the fluorescence intensity contrast and the color
differences detected from a resin restoration and the adjacent
region of the human tooth.
2. Materials and methods
2.1. Specimen preparation
The fluorescence intensities of the following six brands of
light-cured resin composites of shade A2 were investigated:
Charisma (Heraeus Kulzer, Hanau, Hesse, Germany), DenFil (Vericom, Anyang, Republic of Korea), Filtek Z350 (3 M ESPE, St. Paul, MN,
USA), Gradia direct posterior (GC, Tokyo, Japan), Grandio (VOCO,
Cuxhaven, Niedersachsen, Germany), and Premisa (Kerr, Orange,
CA, USA). The details of the following six products are listed in
Table 1. Two types of specimens were prepared: (1) composite discs
made of each composite product and (2) human teeth restored with
each product.
2.1.1. Resin discs
In order to prepare composite discs that were 3 mm wide and
2 mm thick, a portion from each composite product was packed
into a rubber mold in increments of 1 mm and polymerized for 40 s
with a light-emitting diode (LED) curing unit that had a luminous
power density of 1200 mW/cm2 (EliperTM S10, 3 M ESPE). To form
a flat and smooth surface, the disc in the mold was covered with a
Mylar strip and a slide glass on each side, pressed down by a 1-kg
weight for 3 min, and polymerized by light exposure. Eleven discs of
each product were constructed, one of which was used as a baseline
to take photographs of the specimens. All discs were immersed in
distilled water at 37 ◦ C for 24 h until taking photographs for use in
image analysis.
2.1.2. Human teeth specimens
Extracted human premolars and molars were collected according to the protocol approved by Institutional Review Board
(Approval No. 2-2014-0023) of Yonsei University Dental Hospital
in Republic of Korea. Calculus and debris were removed from the
teeth surfaces using a hand scaler. Seven teeth with a shade similar to that of a ready-made resin disc of each composite product
were selected by one examiner when the teeth had been wetted with distilled water. A standardized hole (1.5 mm deep and
2.0 mm in diameter) was made on the smooth surface with a round
bur attached to a low-speed handpiece (32,000 rpm). The inside of
the hole was etched with 37% phosphoric acid gel (B&E Etch-37,
B&E Korea, Gwangmyeong, Republic of Korea) for 15 s and then
washed thoroughly with water. After applying a bonding solution
(ONE-STEP® , Bisco, Schaumburg, IL, USA) in accordance with the
manufacturer’s instructions, the hole was restored by filling with a
Table 1
List of analyzed dental resin composites of shade A2.
Brand name
Composition
Filler type
Manufacturer
Charisma
Bis-GMA, barium aluminium fluoride glass, silicium
dioxide
Bis-GMA, TEGDMA, UDMA, barium aluminosilicate,
fumed silica
Bis-GMA, Bis-EMA, UDMA, TEGDMA, PEGDMA,
non-agglomerated/non-aggregated silica filler,
non-agglomerated/non-aggregated zirconia filler,
aggregated zirconia/silica cluster filler
UDMA, prepolymerized filler, silica,
fluoro-alumino-silicate glass
Bis-GMA, TEGMDA, nanohybrid filler
Microhybrid
Microhybrid
Heraeus Kulzer, Hanau, Hesse,
Germany
Vericom, Anyang, Republic of Korea
Nanofiller
3 M ESPE, St. Paul, MN, USA
Microhybrid
GC Corporation, Tokyo, Japan
Nanohybrid
Voco, Cuxhaven, Niedersachsen,
Germany
Kerr, Orange, CA, USA
DenFil
Filtek Z350
Gradia direct posterior
Grandio
Premisa
Bis-GMA, TEGDMA, prepolymerized filler, barium
glass, silica filler
Nanohybrid
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B.-R. Kim et al. / Photodiagnosis and Photodynamic Therapy 13 (2016) 114–119
portion from each resin composite product in increments of 1 mm
followed by light curing for 40 s using the LED curing unit. Finally,
the restoration surface was polished using water and a white stone
bur attached to a contra-angle handpiece. All restored human teeth
were immersed in distilled water at 37 ◦ C for 24 h until taking photographs for use in image analysis.
2.2. Assessments of fluorescence intensity
Each of the 10 dried composite disc constructed from each
product was placed on top of the baseline disc, and fluorescence
images were obtained to investigate the fluorescence of the composite product. For the restored human tooth, photographs were
obtained in a wet condition with excess moisture removed using a
dried cotton roll. All of the photographs of discs and restored teeth
were obtained using a fluorescence digital camera based on the QLF
technology (QLF-D BiluminatorTM 2+, Inspektor Research Systems,
Amsterdam, The Netherlands) to obtain both white-light and fluorescence images with the following parameters: ISO speed of 250,
shutter speed of 1/13 s, and aperture value of 14.0 for the whitelight images; and ISO speed of 1600, shutter speed of 1/15 s, and
an aperture value of 13.0 for the fluorescence images. The QLF-D
device had a customized digital single-lens reflex (DSLR) camera
equipped with 4 white LEDs and 12 blue LEDs that emit light at
405 nm, and a filter set, which means that it can obtain white-light
and fluorescence photographs in a single shot.
The intensities of the fluorescence detected in the resin composites and teeth images were calculated as grayscale levels. For
the first purpose of the study, only fluorescence images of resin
discs were used for the analysis. The fluorescence images of resin
discs of each brand were converted from RGB (red, green, and blue)
images into 8-bit grayscale images using the weighted conversion
[12] function of standard image analysis software (Image J version
1.47, National Institutes of Health, USA). The grayscale level was
calculated in a region of interest in the center of the resin disc
after conversion to a monochrome image. The grayscale level was
stored as an 8-bit value, which meant that the intensity scale ranged
from 0 (black) to 255 (white) according to the brightness. The mean
grayscale level of ten discs for each group was calculated, and then
the mean values were compared between the products.
The fluorescence image of the restored tooth was converted into
a monochrome image, and the mean grayscale level was obtained
from the adjacent region of the tooth as well as region of the
restored resin [12]. The difference between these two grayscale
levels represented the fluorescence intensity contrast between the
two substances. The white-light image of the restored tooth was
also converted into a monochrome image and the difference in the
grayscale levels was calculated in the same way to allow the second
purpose of the present study to be achieved.
2.3. Statistical analysis
All analyzes were performed using standard statistical software
(IBM® SPSS® Statistics version 20, IBM, Armonk, NY, USA), with a
probability cutoff for statistical significance of 0.05. Differences in
fluorescence intensities measured as grayscale levels among the
resin composite products were compared using one-way ANOVA,
and statistical significance was determined by the Tukey post-hoc
test. The paired t-test was used to compare differences in grayscale
levels between the restored resin and adjacent region of the tooth
obtained from the converted fluorescence and white-light images
for each product.
Fig. 1. Mean grayscale levels detected from converted fluorescence images of composite discs. Different letters above the standard deviation bars showed significant
differences in the mean grayscale levels (p < 0.001).
3. Results
Fig. 1 shows a graph of the mean grayscale levels calculated from grayscale images of composite discs constructed from
each product. The fluorescence intensities based on the grayscale
levels in ascending order were as follows: DenFil (10.84 ± 0.35,
mean ± SD), Filtek Z350 (58.28 ± 1.37), Premisa (156.94 ± 1.58),
Grandio (177.20 ± 0.81), Charisma (207.05 ± 0.77), and Gradia
direct posterior (211.52 ± 1.66). The value for DenFil indicates that
there was hardly any fluorescence, while the other values indicate
that there was also a wide diversity of fluorescence intensity values
for the other five products. All of the differences in the fluorescence
intensities among the six products were statistically significant
(p < 0.001).
Fig. 2 shows representative white-light, fluorescence, and the
corresponding converted grayscale images of restored teeth with
each resin composite product. Comparing the restored resin region
with the adjacent region of the tooth in a fluorescence image
revealed that the fluorescence levels of two of the resin composites (DenFil and Filtek Z350) were lower that for the teeth, while
the other four products were brighter than the teeth. Overall the
fluorescence of the teeth and restored resin composites appeared
bluish and black/bluish, respectively.
Table 2 lists the mean differences in grayscale levels between the
restored resin region and adjacent tooth region as obtained from
the converted grayscale white-light and fluorescent images. For the
six tested resin composites, the grayscale level contrast between
the two regions obtained from the converted white-light images
ranged from 7 to 12 depending on the resin product, while the
contrasts obtained from the converted fluorescence images ranged
from 15 to 61. This indicates that the difference in grayscale levels based on the difference in fluorescence between the restored
resin and adjacent tooth was significantly greater than those values based on the color difference between the two regions, with the
exception of the teeth specimen restored with Filtek Z350 (p < 0.05).
However, since that restored resin composite exhibited only weak
fluorescence, which meant that it could be clearly separated from
tooth material in the fluorescence images (Fig. 2).
4. Discussion
Most studies that have investigated the different fluorescence
properties of teeth and resin composites have been based on spectral analyses [5,14,18,19]. Although these various studies have
involved slight differences in absorption and excitation spectra, the
various resin materials showed difference maxima in fluorescence
B.-R. Kim et al. / Photodiagnosis and Photodynamic Therapy 13 (2016) 114–119
117
Fig. 2. Original images (A–F) and the corresponding converted grayscale images (A’–F’), and fluorescence images (a–f) and the corresponding converted grayscale images
(a’–f’) of restored teeth obtained by QLF-D. The brand names of the restored resin composites are as follows: DenFil (A, A’, a, a’), Filtek Z350 (B, B’, b, b’), Premisa (C, C’, c, c’),
Grandio (D, D’, d, d’), Charisma (E, E’, e, e’), and Gradia direct posterior (F, F’, f, f’).
intensity. This property has been found for different brands with the
same shade, for the same brand with different shades, and for resin
restorations layered by two types of the materials [5,14,18,19].
Nevertheless, this spectral information could be of limited use in
clinical situations. In general, a process is required to prepare the
specimen in order to obtain detailed and objective data, and it is
difficult to apply the analysis apparatus directly to the oral cavity.
The present study aimed to overcome these limitations by using a
custom camera that can be used to obtain photographs of the fluorescence emitted from resin materials and tooth tissue when the
materials are excited by a visible-light source. This study found that
the fluorescence intensities varied in the fluorescence images of the
tested materials. Moreover, the fluorescence could be determined
as being darker or brighter than that of tooth as well as the fluorescence intensities could be calculated as numerical values using
image analysis.
It is difficult to compare directly the results obtained in this
study with those from previous studies due to the use of light
sources of different wavelengths and different resin materials.
Although the present study did not perform spectral analysis, some
of the findings are comparable with those of previous studies. The
fluorescence emitted by the resin composites and teeth in the
present study was bluish in color, and the brightness of the individual resin composites varied. These results are consistent with those
of previous studies that have used UV light and visible light of different wavelengths [5,10,11]. The fluorescence of resin materials is
caused by the presence of fluorescent additives in fillers, and the
type and content of various components and the ratio of filler and
resin may vary between manufacturers [15], which could result in
variations in the intensity of the fluorescence emitted from various resin materials varying under the same fluorescence-inducing
condition.
The condition under which QLF technology is used for inducing and detecting fluorescence may also lead to differences in the
fluorescence intensity of resin products. The excitation wavelength
that induces the largest emission intensity varied between different
resin composites. An early study found that natural teeth emitted
a maximum fluorescence intensity at about 450 nm for excitation
by UV light at 365 nm [16]. A recent study that made direct measurements with a spectrometry demonstrated that teeth—which
are composed of enamel and dentin—absorbed wavelengths in
the range of 250–300 nm and emitted fluorescence whose intensity was highest at around 490 nm and gradually reduced as the
wavelength increased to around 700 nm [14]. The shape of the
absorption and emission spectra of resin materials were found to
be similar to those of tooth, but various resin composite products
revealed absorption peaks at 250–450 nm and emission peaks at
450–485 nm [3,5,14]. In addition, some resin restorative products
could be detected in teeth using a light source of 380 nm but not
one of 365 nm in a previous study [11]. It is therefore possible that
the blue light source (with an emission peak at 405 nm) used in
the present study is not the most suitable for inducing the high-
Table 2
Differences in grayscale levels between each resin restoration and the adjacent region of the tooth obtained from the fluorescence images, and the difference in color obtained
from the white-light images.
Brand name of resin
composite
DenFil
Filtek Z350
Premisa
Grandio
Charisma
Gradia direct posterior
Difference in grayscale levels between a resin restoration and the adjacent region of the tooth
In white-light images
In fluorescence images
9.31 (6.87)
9.97 (4.79)
11.62 (4.86)
10.41 (4.96)
8.80 (3.69)
7.44 (4.53)
22.68 (5.14)
14.68 (5.02)
30.36 (2.06)
35.96 (6.07)
61.26 (5.05)
57.77 (7.93)
p-value*
0.016
0.153
<0.001
<0.001
<0.001
<0.001
The difference in grayscale levels were obtained from converted 8-bit grayscale images of the white-light and fluorescence images, and they were presented in mean (standard
deviation).
*
p-values were obtained by paired t-test at ˛ = 0.05.
118
B.-R. Kim et al. / Photodiagnosis and Photodynamic Therapy 13 (2016) 114–119
est fluorescence intensity from some of the tested resin products.
Another possibility is that the filter set mounted on the QLF-D filtered out certain wavelengths at which some resin materials might
emit greater fluorescence. These backgrounds provide a reason for
the reduced fluorescence that was observed from DenFil and Filtek
Z350 on the fluorescence images taken by QLF-D. Nevertheless, the
results obtained in the current study indicate that the use of a fixed
QLF-D condition to induce fluorescence from resin restorations and
teeth made it possible to differentiate the fluorescence emissions
from different materials and between the two substances.
The fluorescence intensity contrast between the region restored
with Filtek Z350 and the adjacent region of the tooth, as measured in converted fluorescence images, did not differ significantly
from the color contrast between these two regions as detected in
a white-light image (Table 2). However, the restored Filtek Z350
was distinguishable as darker fluorescence relative to the adjacent
tooth in the original fluorescence image (Fig. 2). This reduced fluorescence tendency of Filtek Z350 is consistent with the findings
of a previous study that evaluated the relative fluorescence intensity contrast between the tooth material and resin composites of
the same brand (with trademarked names of Filtek Z250 and Z100)
[12]. That study also found that the fluorescence contrast between
the tooth and resin composite material was more pronounced for
the Filtek materials than for Charisma, with the fluorescence being
darker for the former. However, the Charisma materials exhibited
a higher fluorescence intensity than enamel in the present study,
which contrast with the result found in the previous study due to
a UV light source with a wavelength range of 340–400 nm and a
filter with a cutoff wavelength of 405 nm being used. In addition, in
accordance with the present study, another previous study demonstrated that the intensity of the blue–green light with a wavelength
range of 450–600 nm emitted by Filtek Z350 of shade A2 was
slightly lower than that emitted by an enamel/dentin combination
specimen [14]. These results indicate that the fluorescence-based
device used in the present study that combined a light source and a
filter set can provide reliable evaluations of the fluorescence intensity of resin materials and teeth.
The intensity of the fluorescence of various composite products
varied in grayscale level under a constant illumination condition.
In the present study, the hue, saturation, and intensity values of
the QLF-D fluorescence images of the resin discs were evaluated
using image analysis software before producing the monochrome
images; this confirmed that the colors of the fluorescence emitted were similar for the various brands of resin composites under
investigation. The hue values of five of the six tested resin composites were similar (from 116 to 124, out of a possible range from 0
to 255). However, while the fluorescence emitted by DenFil had a
different hue, its intensity was very low, appearing almost black
with a mean intensity value of 10, and so it can be considered that
there was actually little difference in the color of the fluorescence
detected for all six resin brands [20]. It was therefore determined
that grayscale levels could be used to differentiate the intensities
of fluorescence between resin composites in this study.
The present study was subject to some limitations. The first
stemmed from the device used to obtain the white-light and fluorescence photographs. This study utilized QLF technology with a
DSLR camera, which can result in different absolute fluorescence
intensities being measured depending on the camera settings.
Moreover, obtaining fluorescence images that are either too bright
or too dark will make it difficult to differentiate the color and fluorescence of the materials. Therefore, future studies should attempt
to identify the best camera settings for capturing optimal QLF-D
images. The second limitation was that resin composite products of
only one shade (A2) were used. Further research is needed to evaluate the fluorescence properties of sealant [21], combinations of
different composites [22], and changes in the fluorescence intensity
according to the thickness of the resin materials [3], while considering the clinical relevance of the QLF technology used in this study.
The technology was originally developed for the detection of early
dental caries and dental plaque by representing the loss of fluorescence and red fluorescence using a visible light source rather than
UV light [23–25]. In order to use this technique to detect toothcolored composite restoration in clinical fields, it was necessary to
determine whether the fluorescence images obtained by the technology can be used to discriminate different composite products
and improve the ability of composite restoration, ensuring that it
is more sensitive than the naked eye.
The results obtained in this study demonstrate that variations in
the intensities of the fluorescence emitted by resin composites can
be detected in images of light-induced fluorescence. The composite
restoration exhibits fluorescence that is greater or less than that of a
tooth, and the differences in the fluorescence intensity between the
composite and the adjacent tooth is greater than that in the colors
evident in white-light images. These results indicate that the lightinduced fluorescence technology provides superior capabilities for
detecting restored composites relative to simply using the naked
eye.
Conflicts of interest
The authors declare that there are no conflicts of interest related
to the present study.
Acknowledgments
This research was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education (2013R1A1A2062505).
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