Article_5_2_1
DENTAL MATERIALS
BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT USING A
Original Article
SPECTROMETER-BASED METHOD
Jean-François Roulet1a*, Mateus Garcia Rocha2b, Chiayi Shen1c, Marwah Majid Khudhair1d,
Dayane Carvalho Ramos Salles de Oliveira2e
1
Department for Restorative Dental Sciences, Center for Dental Biomaterials, College of Dentistry, University of Florida, 1395 Center Drive
Gainesville, FL-32610, USA
2
Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Areiao 13419-110, Piracicaba SP, Brazil
a
Dr med dent, Dr hc, Professor, Director of Center for Dental Biomaterials
b
DDS, MSC, PhD, Researcher
c
PhD, Professor
d
DDS, Preceptor
e
DDS, MSC, PhD, Post-Doctoral Researcher
ABSTRACT DOI: 10.25241/stomaeduj.2018.5(2).art.1
Aim: The study aimed to characterize a broad spectrum light curing unit (LCU) by OPEN ACCESS This is an Open Ac-
cess article under the CC BY-NC 4.0 license.
measuring the light beam profile output of the LCU using a spectrometer-based Peer-Reviewed Article
method and correlate it with a standard camera-based beam profile method.
Materials and Methods: A broad spectrum LED LCU (Ascent OL5, CAO Group) was Citation: Roulet J-F, Rocha MG, Shen C,
Khudhair MM, de Oliveira DCRS. Beam profile
mounted above a spectrometer (MARC® Resin Calibrator, BlueLight Analytics) at characterization of a dental light curing unit using
a spectrometer-based method. Stoma Edu J.
exposure distances of 1.0, 1.5 or 2.5 mm. The position of the center of the LCU was aligned 2018;5(2):84-91.
with the spectrometer’s cosine corrector sensor, and then moved in 1-mm increments in
Academic Editor: Nicoleta Ilie, Dipl. Eng,
the x-y plane, while concomitantly recording the irradiance. The recorded irradiance was PhD, Professor, University Hospital, Ludwig-
systematically organized and reported in function of the distance from the center of the Maximilians-Universität München, Munich, Germany
LCU exiting window. Using a standard camera-based beam profiler, a beam profile of the Received: May 17, 2018
LCU was obtained and the above approach was emulated to the beam profile. For both Revised: May 24, 2018
Acccepted: June 11, 2018
methods, the irradiance decreases related to the value measured at the center position Published: June 12, 2018
was analyzed by calculating the slope, using a linear correlation. *Corresponding author: Jean-François Roulet,
Results: Both methods showed that moving away from the center showed decreased DMD, PhD, Dr hc, Center for Dental Biomaterials,
College of Dentistry, University of Florida 1395
irradiation. The beam profile of the LCU is asymmetric. The inhomogeneity of the Center Drive, Room D9-26, Gainesville, FL 32608
beam was slightly lower with farther distance from the LCU’s light exciting window. Gainesville, FL 32608, USA
Tel: +1 352 273 5850; Fax: +1 352 846 1643,
Conclusion: The spectrometer-based method was able to characterize the beam e-mail: jroulet@dental.ufl.edu
profile of the LCU and can be used in the evaluation of LCUs. Copyright: © 2018 the Editorial Council for the
Keywords: light curing units, beam profile, spectrometric analysis. Stomatology Edu Journal.
1. Introduction the irradiance of an LCU diminishes as the distance
Light curing has revolutionized the placing of increases from the light output window [6] and,
composite restorations [1]. Furthermore, light curing is besides that, the cleanliness aspect of the LCU light tip
used for multiple other applications such as cementing is fundamental, because any residual RBC stuck onto
dental fixed prostheses, including indirect restorations the light exiting window may also reduce the light
made from ceramics or composites, sealing fissures, irradiance, which is a huge problem that affects the
and bonding orthodontic brackets. Nowadays, market geometry of the light tip which may create shadows
available light curing units (LCUs) are very well build [7,8], and thus the depth of the cure may be reduced.
and really intuitive which make dentists assume that Furthermore, depending on their composition (filler,
light curing is a simple procedure, however it is not. resin mix, pigments and opacifiers), RBCs absorb more
First, to be cured properly, a resin-based composite or less light [9], which reduces the depth of the cure as
(RBC) must be exposed to a visible light energy at the well. Based on this knowledge, recommendations for
proper wavelength range (blue or blue and violet) and dentists about how to light cure were formulated by a
a radiant exposure ranging from 8-16 J/cm2 [2], which group of researchers, industry representatives, editors
means that, depending on the irradiance the RBC is and dentists [10-12]. This group is very active and
receiving, exposure times up to 60 s are required [3]. has published recommendations in dental journals,
The key problem is that dentists believe that a single newsletters and websites of associations worldwide.
irradiance value of LCU reported and stated by the Multiple studies have shown that the LCUs as used
LCUs’ manufacturer homogeneously reaches the entire in practices do not yield the light intensity output
RBC surface, which is not the case [4]. stated by the manufacturers [13-16]. The outcome of
It starts with the correct positioning of the LCU on top light curing can be influenced as well by factors which
of the RBC, controlled by the dentist only. Very large are governed by the design of the LCU and of course
differences have been documented when comparing by the RBCs themselves [9,17]. The characteristics
the light curing of untrained vs trained dentists of the LCUs have a strong influence on the incident
[5]. Furthermore, the dentist should be aware that irradiance received by a material due to a multitude of
84 Stoma Edu J. 2018;5(2): 84-91. http://www.stomaeduj.com
BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT
USING A SPECTROMETER-BASED METHOD
factors. This was observed for the first LCUs operating A light beam profile is the 2D irradiance intensity plot
Original Article
in the visible light range, based on Quartz-tungsten for a camera-based beam profiling system, requires
halogen bulbs which had been developed for other a thermopile (power meter), a spectrometer, a CCD
purposes than dentistry [18]. These light curing or CMOS camera, a modern computer with a frame
units had the advantage of a broad light spectrum grabber card to digitize the signal, and software
[19]. However, since only the blue light was usable for controlling the frame grabber card, displaying
to cure RBCs, infrared-blocking blue bandpass filters beam profiles and making respective quantitative
(at 510 nm) were built in the LCUs. These filters calculations. Also, an optomechanics apparatus,
would deteriorate over time, diminishing the light such as diffusive glasses and band pass filters, is
emission properties of the LCUs [20]. There were more almost always needed to attenuate and/or filter the
characteristics that basically made them problematic light beam before going into the camera [27,28]. In
[21], such as instability of the output, spectral general, it cannot be bought together, and requires
distribution and unreliable timers. Some LCUs had a knowledge to buy the complete and right equipment.
quite homogeneous beam profile, which means that Moreover, the operator needs to know how to use all
the surface of the irradiated composite gets the same these parts together.
energy density on every area. This is possible because Thus, the objective of the present study was to
in a halogen light the hot wire creating the light is characterize a broad spectrum LED LCU with a known
almost a point light source, which can be captured inhomogeneous beam profile using a spectrometer-
with a reflector and guided into a beam. However based method and correlate it with a standard
already in 1986 it was shown that some LCUs had an camera-based beam profile method. The following
inhomogeneous light beam [21]. This was confirmed null hypotheses were tested: 1) The irradiation is
using an acrylic optical fiber with a 1 mm diameter at the same level all over the irradiated surface. 2)
moved at 1mm steps in x-y direction in front of the The irradiation as captured with the spectrometer-
light emitting tip of the LCU. With this method the based method is similar to the irradiation shown by a
local light intensity of three QTH lights, a plasma arc standard camera-based beam profiler.
light and a LED light was measured [22].
For many reasons LED LCUs were a big improvement.
LEDs are not considered a point light source, since 2. Materials and Methods
they have the shape of a flat surface emitting the For this method-validation study a broad-spectrum
light. Early LEDs had very little power (1.2 mW) and LED LCU (Ascent OL5, CAO Group South Jordan, UT,
thus were not usable for light curing devices [20]. But, USA) was used. Its design leads to the assumption
over the years they became much more powerful that it will generate an inhomogeneous beam profile,
(e.g. 123 mW), thus multiple LEDs were used as a light since it has one LED emitting blue light mounted in the
source which made it difficult to bundle the emitting center and 4 small LEDs emitting violet light mounted
light [20]. Modern LED LCUs use 1-8 LEDs in an array at the periphery (Fig. 1). The LCU was attached to an
which is flat [23], which makes bundling the light x-y-z positioning device mounted on an optical bench
more difficult and may result in an inhomogeneous in order to standardize the positioning of the light
beam profile, despite being a mono-wavelength unit beam centered above the cosine corrector light signal
(peak at around 450-470 nm). Finally, the last step in collector of a spectrometer (MARC® Resin Calibrator,
development is the broad spectrum LED LCU, which BlueLight Analytics, Halifax, Canada) with the handle
uses different types of LEDs, emitting light with towards the right side (“EAST”, Fig. 2) at an exposure
different wavelengths (violet light (380 – 420 nm) distance of 1.0, 1.5 or 2.5 mm. The diameter of the
and blue light (420 – 495 nm) [8,20]. Therefore they cosine corrector was 3.9 mm. Using the translation
are able to activate different types of photoinitiators stage, the position of the geometrical center of the
[24]. However, these LED LCUs show more or less LCU was first aligned with that of the cosine corrector
pronounced inhomogeneity of the beam profiles [25- and then moved in 1-mm steps in the x-y plane
28]. This means that not every point on an irradiated (“EAST” – “WEST” and “NORTH” – “SOUTH”) (Fig. 2).
surface gets exposed to the same level of irradiation The irradiance was assessed at each above described
from the different wavelengths, especially in depth condition. The irradiance loss was visualized using bar
[29-31]. Thus, if the dentist aims for a short exposure graphs for the East-West (long axis of the LCU) and the
time, some areas of the irradiated RBC may not obtain North – South direction. The slopes of the irradiation
the minimally required light radiant exposure for decrease were calculated and compared.
optimal monomer conversion [24]. To obtain standard camera-based beam profile
The power of the light source determines the energy images, the same LCU was attached to an x-y-z
it can emit; the design of the optical system to capture positioning device mounted on an optical bench
and bundle the light emitted from the light source in order to standardize the positioning of the light
determines the degree of spread of the light after it beam in contact with a diffusive surface of a frosted
exits the light curing fiber bundle or lens. Turbo tips, diffuser target (DG20-1500, Thorlabs, Inc., Newton, NJ,
which concentrate the light on a smaller surface to USA) while the resulting image was recorded using a
increase the irradiation usually have a larger spread camera (NEX-F3, Sony Corporation, Tokyo, Japan) with
than conventional tips [24]. Usually, the spread is a 50 mm focal length lens. To assess the irradiance
considerable, yielding to less irradiation the farther distribution of the different LED emission wavelengths
away the target RBC is from the light exciting window from the broad spectrum LED, the beam profiler was
[25,26]. used with the addition of bandpass filters (Thorlabs,
Stomatology Edu Journal 85
BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT
USING A SPECTROMETER-BASED METHOD
optical density to calibrate each image. The scaled
Original Article numerical data associated with each image were
exported into a computer graphic software (Origin
Pro, OriginLab Co., Northampton, MA, USA).
The beam profiles were captured at 1, 1.5 and 2.5
mm from the light exciting window of the LCU and
further analysis of the local intensities was performed
the identical way as done with the MARC® resin
calibrator. A virtual aperture of 3.9 mm was created
using the computer graphic software and the average
irradiation on this surface was measured by first
placing this aperture in the geometrical center of the
beam profile and then moving it into 1 mm steps in
the “EAST – WEST” and “NORTH – SOUTH” direction.
Bar graphs comparable to the ones created with
the spectrometer-based method were generated.
In a second step, to calculate the magnitude of the
decrease in the light irradiance according to the
distance from the center of the LCU, a linear correlation
fit was made to compare the slopes produced by
the spectrometer-based method with the slopes
generated from the camera-based method.
3. Results
At 1 mm distance from the light exciting window, the
Figure 1. LED positions in the Ascent OL5 LCU. broad-spectrum LED had a total irradiance of 1159
mW/cm2, however, 1088 mW/cm2 was within the blue
wavelength range (420 - 495 nm) and only 71 mW/
cm2 was within the violet wavelength range (380 –
420 nm). As shown in Fig. 3, it is clear that the majority
of the power emitted (mW) by the broad-spectrum
was within the blue wavelength range and the violet
emission from this LED is considered insignificant.
The results of the irradiance measurements at 1, 1.5
and 2.5 mm distance from the light exciting window
are shown in Fig. 4. As expected, there is a decrease in
irradiance the farther away the measuring area is from
the center. To allow better direct comparisons, the
slopes of these decreases were calculated as shown
in Table 1. Higher absolute value means greater rate
of reduction in irradiance with distance from the
Figure 2. Measuring points as related to the position within the light exit geometric center of the LCU. Note that the farther
window. Blue cross = geometrical center of the light exiting window. away the light source is from the sensor, the flatter the
Orange circles =“WEST”, Light blue circles =“EAST”, Purple circles =“North” slope, which means that the inhomogeneity of the
and green circles =“SOUTH”. beam profile decreases.
Fig. 5 shows the beam profiles obtained at 1, 1.5
Inc., Newton, NJ, USA) placed in front of the camera and 2.5 mm distance from the light exciting window
lens. A bandpass filter centered first at 400 nm with of the LCU. Note the spread of the beam and the
a 40 nm full width at half maximum (FB400-40) was inhomogeneity of the irradiation. Fig. 4c, Fig. 4d and
used to identify the LED chips with spectrum emission Table 1 show the data as extracted from the beam
peaks at 400 nm (violet light). A different bandpass profiles. Note the similarity of the pattern.
filter, centered at 450 nm with a 40 nm full width at
half maximum (FB450-40) was used to identify the
LED chips generating emission peaks near 450 nm 4. Discussion
(blue light). To produce calibrated images and data The LCU used in this study was selected because based
showing the irradiance patterns across the surface on its design an inhomogeneous beam profile was to
of the broad spectrum LED, the mean power values, be expected. The objective of the study was to use a
obtained using the MARCⓇ resin calibrator were spectrometer-based method to detect inhomogeneity
entered into an open source optical analysis software in the light beam profile output of a LCU. Therefore, it
(Fiji, ImageJ, National Institute of Health, Bethesda, makes sense to use a LCU, where this characteristic is to
MD, USA) [32] to process the camera-based method be expected.
beam profile images. The total spectral power output The Ascent OL5 broad spectrum LCU had a significant
was integrated with each bandpass filter spectral higher amount of blue light being emitted than violet
86 Stoma Edu J. 2018;5(2): 84-91. http://www.stomaeduj.com
BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT
USING A SPECTROMETER-BASED METHOD
Original Article
Figure 3. Spectral radiant power (mW/nm) of the broad spectrum LED at 1 mm distance according to the CENTER and 4 mm distant from the CENTER
in the NORTH-SOUTH and WEST-EAST directions.
Figure 4. Irradiation measured at 1, 1.5, 2.5 mm distance from the light exiting window as a function of the offset in mm from the center position in the
East-West and North-South direction using the spectrometer-based and the camera-based methods.
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Original Article
Figure 5. Beam profile images using the camera-based beam profiler method for the blue and violet wavelength ranges at 1, 1.5, 2.5 mm distance
from the light tip.
Table 1. Slope of the decrease in irradiance in mW/cm2/mm with respect to the vertical distance of the geometric center of LCU and the NORTH,
SOUTH, WEST and EAST directions using the spectrometer-based method or the camera-based method.
1 mm 1.5 mm 2 mm
Spectrometer- Camera-based Spectrometer- Camera-based Spectrometer- Camera-based
based method method based method method based method method
NORTH -232 -231 -195 -183 -169 -171
SOUTH -244 -180 -201 -176 -142 -141
WEST -173 -167 -171 -148 -100 -142
EAST -197 -156 -181 -146 -127 -132
light as shown in Fig. 3. In Figure 1 the position of the more efficiently than CQ at their peak wavelength
LEDs in the head of the light is clearly visible. Using the absorptions. Moreover, these photoinitiators form
beam profiler and different filters the center LED was more free radicals (two or more) that have higher
identified to emit light blue light (420 – 495 nm) with nucleophilicity and electron resonance than the one
a peak emission at 450 nm with a high intensity (1579 amino radical formed by the CQ-amine electron donor/
mW/cm2) and the four LEDs in the “corners” emitting hydrogen abstraction reaction. Thus, despite the less
violet light (380 – 420 nm) with a peak emission at 390 amount of violet light being emitted by broad spectrum
nm, confirming measurements on other LCUs [23,27]. LCUs, the initiation of the polymerization is effective
Furthermore it was noticed that the irradiance from the enough to keep the physical and chemical properties of
violet LEDs was quite low (102 mW/cm2) and localized RBC containing “alternative” photoinitiators. However,
to the corners only. This discrepancy in the blue and it is important to bear in mind that broad spectrum
violet light emission could be attributed to the type of LCUs typically have a ratio of 66 to 86 % of blue light
the LED chip used to build the LCU. Despite the fact emission and 14 to 34 % of violet light emission from
that the majority of LED chips are violet, they appear the total spectral radiant power emitted [33] by the
to be a dual in-line package (DIP) LED type, which have LCU. However, the LCU used in this study had 94% of
much lower energy efficiency than the blue light chip blue light emission and 6% of violet light emission and
that appears to be a chip on-board (COB) LED type, further investigation should be performed to check if
which is considered a high-powered LED chip and the the LCU used in this study would efficiently cure RBC
most recent development in LED LCUs. But, the fact is containing “alternative” photoinitiators. Therefore, it
that “alternative” photoinitiators such as TPO or Ivocerin was decided that the impact on polymerization of
that have been used in commercial formulations are these violet emitting LEDs was low and for further
known as high reactive photoinitiators because they considerations we concentrated on the blue light.
usually have higher molar extinction coefficient than In the present study, the LCU was laterally moved in a
CQ. This means that these photoinitiators absorb light controlled way in the x- and y-direction of a coordinated
88 Stoma Edu J. 2018;5(2): 84-91 http://www.stomaeduj.com
BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT
USING A SPECTROMETER-BASED METHOD
system. This was to simulate in a reproducible way tip, which is not the case for camera-based methods.
Original Article
operator errors in light curing, which have a deleterious Camera-based beam profilers are rarely able to give a
effect on the light energy administered to a restoration direct measurement of the total irradiance of an LCU
[33]. With a homogeneous beam profile, as long light beam. First, the LCU light beam passes through
as a restoration is smaller than the diameter of the a long chain of attenuation so that the camera-sensor
light exciting window of the LCU slight positioning does not see the total power of the beam directly. Since
errors may result only in minimal decrease of exciting this attenuation is put in place so as to get the energy
irradiation if any at all. However, with an LCU that has down to the level of the camera sensor, it is not practical
a centered beam profile as the one of the Ascent OL5 to calibrate each element of attenuation. Thus, the
used in the present study, the positioning even within irradiance values that get into the camera are relative
the confines of the light exiting window has significant to the total power of the LCU light beam. Secondly,
effects on the exciting irradiation, as can be seen in Fig. cameras do not have uniform wavelength absorption
4, where a marked decrease in irradiation is noticed [36]. Therefore, they would have a different calibration
when the LCU is moved in the X-Y direction. factor for every wavelength of the LCU that is used. It
The first null hypothesis that the irradiation would be would be impractical to attempt to calibrate the camera
at the same level all over the irradiated surface was as a function of wavelength. So, after correcting for
rejected, since with both methods to characterize the the power loss, the total irradiance energy measured
LCU significant differences in local irradiance were by the spectrometer can then be entered into the
found. In this study beam inhomogeneity could be software of the beam analysis instruments. From then
shown as other researchers have done with different on, the camera can give a readout of the total power
methods [25-28]. The second null hypothesis could be or energy across the entire two-dimensional light beam
accepted, since the slopes of the decrease (in absolute distribution.
numbers) were quite similar (Table 1). It is known that For the clinical application, the findings of the present
the irradiance a target surface received is a function study mean that even with a properly positioned LCU,
of the exposure distance [25,26]. This is also visible in peripheral areas would get much less irradiation. Even
Figs. 3 and 5 confirming the results of others [25,26]. small positioning deviations would aggravate this
Furthermore, in Figs. 3 and 5 the irradiance dropped fact, e.g. looking at Fig. 4 one can see that a 1.5 mm
significantly from the center to the periphery in all positioning deviation in the “WEST” direction would
measured directions (“East”-“West” and “North”- yield approximately 50% of the maximal possible
“South”). Looking at the absolute numbers of the irradiation. At a distance of 2.5 mm this effect is slightly
slopes, the farther away from the LCU light exciting less pronounced. As a clinical relevance of this study, it
windows the smaller the numbers are, which means is important for the clinicians to understand that there
that the inhomogeneity decreases. are a lot of broad spectrum LCUs on the market, but not
With controlled lateral movements, the inhomogeneity all of them might be really effective. And, it is important
of the beam could be roughly reproduced with the to be aware of the implications of bad quality broad
spectrometer. The same could be shown with the beam spectrum LCUs on the quality of RBCs and thus on
profiler emulating a cosine corrector light collector with dental practice.
a diameter of 3.9 mm, which limits the precision. It is
suggested to use a smaller cosine corrector diameter
for future measurements. With the methods used, area 5. Conclusions
specific mean irradiations could be shown. Therefore, The analyzed LCU has an inhomogeneous beam
one has to rely on the known minimal irradiance needed profile, being the most intensive in the center and
to cure a specific resin-based material in order to assess diminishing substantially towards the periphery.
the performance of a given LCU/RBC combination. The spectrometer-based method used was able to
The differences between the spectrometer-based vs characterize an LCU which may be helpful among
camera-based beam profile methods are basically other parameters to make a selection for a specific
related to the resolution and accuracy of irradiance LCU for clinical use.
detection. Michaud et al. [29] used a laboratory grade
integrating sphere spectrometer system to measure
the irradiation and emission spectra of LCUs. Combined Author contributions
with a beam profiler camera they recorded the localized JFR: Idea, experimental design, wrote the manuscript.
irradiance across the face of the light tip. The irradiation MGR: Performed standard camera-based beam profiles,
calibrated beam profile was then divided into 45 contributed extensively to introduction and discussion.
squares of 1 mm2 each, thus being able to give more CS: Performed data analysis, proofread the manuscript.
detailed beam analysis than it was possible with the MMK: Performed spectrometer experiment. DCRSdeO:
method in the present paper. The beam inhomogeneity Contributed extensively to introduction and discussion.
was additionally confirmed by micro hardness analysis
[35].
Although the camera-based method can show Acknowledgments
higher resolution in mm2 than the spectrometer- DO is a Post-Doctoral Researcher at São Paulo
based method, the quantitative measurement of the Research Foundation - FAPESP (grant #2016/05823-
irradiance using the spectrometer-based method seems 3 and #2017/22161-7) and MR is a PhD Researcher
to be more accurate, because the spectrometer-based at São Paulo Research Foundation - FAPESP (grant
method captures light directly from the light output #2016/06019-3 and #2017/22195-9).
Stomatology Edu Journal 89
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USING A SPECTROMETER-BASED METHOD
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90 Stoma Edu J. 2018;5(2):84-91. http://www.stomaeduj.com
BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT
USING A SPECTROMETER-BASED METHOD
Original Article
Jean-François ROULET
DDS, DMD, PhD, Dr hc, Prof hc, Professor, Chair
Department of Restorative Dental Sciences
College of Dentistry, University of Florida
Gainesville, FL, USA
CV
Jean-François Roulet, DDS, Dr med dent, Dr hc, PhD, is the former chair and current professor of the Department of Restorative
Dental Sciences at the University of Florida. Professor Roulet is author/coauthor of more than 180 papers, edited/contributed
to 27 textbooks and mentored more than 150 theses. He is a renowned international lecturer with over 800 appearances to
date. Dr. Roulet is a member of many professional organizations, has won numerous awards, and holds four patents. He is
editor of the Prophylaxe Impuls and Stomatology Edu Journal. His areas of interest include minimally invasive dentistry, dental
materials (ie, composites and ceramics), adhesive dentistry, esthetic dentistry, and application concepts in preventive dentistry.
Questions
1. A beam profile is:
qa. The change if irradiance as a function of the distance from the light curing unit light outputting window;
qb. The 2D irradiance intensity plot of a light beam at a given location along the light beam output window;
qc. Identical for all light curing units;
qd. More homogeneous for broad band light curing units.
2. Which factor highly influencing the quality of a light cured resin composite is
controlled by the dentist only?
qa. The composition of the resin based composite;
qb. Resin composite residues stuck to the light curing units light output window;
qc. The geometry of the fiber bundle rod or the lens;
qd. The correct positioning of the LCU on top of the RBC.
3. The study used the following method to characterize the light curing unit:
qa. An Ulbricht sphere;
qb. Micro hardness;
qc. A spectrometer and a camera based beam profile method;
qd. Degree of conversion of the resin based composite.
4. Which was the main outcome of the study?
qa. No inhomogeneity of the beam profile could be found;
qb. Both methods showed very similar inhomogeneities of the beam profile;
qc. The beam profile inhomogeneity was the same regardless of the measuring distance;
qd. The irradiance was higher at the periphery of the beam profile.
https://orthodontics.conferenceseries.com/
Stomatology Edu Journal 91