Keywords
beam profile - light curing units - spectrophotometric analysis - digital cameras
Introduction
Light curing units (LCUs) are used for light activation of dental adhesives, resin-based
composites, resin cements, resin-modified glass ionomers, and many other light-curable
dental materials.[1]
[2] Frequently, manufacturers clearly state that the LCU’s irradiance (mW/cm2), and for the most part of the industry, LCUs with an average irradiance higher than
1000 mW/cm are considered decent.[3] It is important to mention that the irradiance is the power (mW) received by a determined
area (cm2) of a resin-based material, and the radiant emittance (or radiant exitance) is the
power (mW) being emitted by a determined area (cm) of the light tip of an LCU.[2]
[3] Both units (mW/cm2) are the quotient of the power (mW) of the light divided by the area (cm2), but LCUs with the same radiant emittance (mW/cm2) might not have the same irradiance (mW/cm2).
However, even if the radiant emittance of an LCU is appropriately described, it does
not fully address all significant characteristics of the LCU. Other aspects are extremally
important to evaluate the quality of the light emitted, such as the LCU light tip
size in comparison to the specimen size, the spectral power, and specially the light
beam profile homogeneity.[2]
[3]
[4] Thus, to systematically comprehend the emitted-light quality of an LCU, a complete
characterization of the light beam emitted by the LCU is essential.[2]
[3]
[5]
The light beam spectral power distribution of an LCU influences in the polymerization
homogeneity of resin-based materials.[6]
[7] For Monowave LCUs with narrowband spectral emission (within the blue wavelength
spectrum only), the use of optical apparatus such as microlenses or optical fiber
bundles can collimate the light creating a homogeneous light beam emission. Thus,
homogeneously light activating the polymerization of resin-based materials containing
only camphorquinone (CQ) as the photoinitiator system.[8] For multiwave LEDs that emit more than one wavelength spectrum (within the violet
and blue wavelength spectra), the physical location of the LED chips emitting the
different wavelengths seems to be directly correlated with the nonuniform nature of
the light beam output of these multiwave LCUs.[9]
[10]
[11] Manufacturers’ claim that the combination of multiple LEDs emitting different wavelengths
(violet and blue) and different photoinitiators, such as the diphenyl(2,4,6- trimethylbenzoyl)phosphine
oxide (TPO) and the benzoyl germanium (Ivocerin), provide better photopolymerization
for resin-based materials.[9] However, one of the main obstacles is to build an LCU by using multiple LED chips
with a homogeneous light beam emission.[10]
[11]
Therefore, the light beam profile is an important aspect that reveals valuable information
about the LCU. A light beam profile can be defined as the power intensity plot of
a light beam at a given location along with the light beam output. To characterize
the light beam profile, camera-based beam profilers are often used.[12]
[13] The camera-based beam profiler is an instrument that uses a charge-coupled device
(CCD) or complementary metal-oxide-semiconductor (CMOS) camera-based detectors to
measure the spatial distribution of light intensity in the cross-section of a light
beam according to the conversion of the light photon flux to an electrical current-voltage
signal.[14] With the use of bandpass filters, the wavelength distribution of the light beam
could also be detected. However, one of the main obstacles of this method is the cost
of the complete instrumentation for a camera-based beam profiling system.
The high cost of a beam profiling system is related to the special CCD cameras, which
includes a frame grabber card to transcript the signal, a software for controlling
the frame grabber card to display beam profiles and to make respective quantitative
calculations. Perhaps the most significant reason for this equipment high cost is
that those commercially available beam profilers are designed to characterize industrial
or medical lasers, and those lasers have an extremely high-powered light beam emission
from 10 to 100 W in areas of 1 to 5 mm2. However, for dental LCU that uses LEDs with power emission from 1 to 5 W in areas
of 5 to 10 mm2, it is not necessary to use equipment with that sophistication.
Thus, it would be great to have low cost equipment that dentists and researchers could
get a more robust report of the beam profile of the LCUs that they have been using
in their clinics or laboratories. The aim of this study was to demonstrate a method
to perform the beam profile of dental LCUs by using low budget cameras and a free
open-source software and correlate it to a gold-standard method using camera-based
beam profiling system. The research hypothesis was that there are no differences on
the beam profiling of different LCUs obtained by using mirrorless, smartphone, and
standard camera-based beam profiling systems.
Materials and Methods
Spectral Radiant Power
Three LCUs were characterized in this study: Radii Plus (SDI Ltd., Bayswater, Victoria,
Australia), Bluephase G2 (Ivoclar Vivadent, Schaan, Liechtenstein), and Valo Cordless
(Ultradent Products Inc., South Jordan, Utah, United States). [Fig. 1] shows pictures of the light tip and a schematic representation of the chipset array
of the LCUs. For each LCU, the area of light emission (cm2) was measured by using a digital caliper by the mean of five readings of the inner
diameter (d) of the light tip and calculating the area (Acircle) using the formula of the area of a circle (Acircle = (d/2)2. The spectral radiant power (mW/nm) of the LCUs was measured five times
by using a spectrophotometer with a 16-mm diameter light collection area (MARC Light
Collector, BlueLight Analytics, Halifax, Nova Scotia, Canada).[4] For each LCU, the radiant emittance (mW/cm2) was calculated by the division of the radiant power (mW/nm) by the area of light
emission (cm2), and the irradiance (mW/cm2) was calculated by the division of the radiant power (mW/nm) by a predetermined circle
area of 10 mm in diameter (A = 0.785 cm2). The irradiance values in this scenario would represent the exact amount of light
delivered in hypothetical situations of light curing a molar tooth with 10 mm of distance
mesiodistal or light curing a disk specimen with 10 mm in diameter for in vitro studies.
Fig. 1 Light tip illustration showing in proportional size the differences between the LCUs
([A] radii plus, [B] Bluephase G2, and [C] VALO Cordless) and LED chipset array distribution according to the number of LED
chips, LED chip wavelength peak of emission, and the position of the LED chips for
each LCU. The Chipset Array scheme is based on images collect from the LED chip by
using a digital optical microscope (VHX-100, Keyence, Osaka, Japan). LCU, light-curing
units
As specified by the manufacturer,[15] the Radii Plus has four LED chips in the blue wavelength range with an emission
peak at 450 nm. The Bluephase G2 has four LED chips, one in the violet wavelength
range with a spectral emission peak at 410 nm and the other three in the blue wavelength
range with an emission peak at 460 nm.[16] The VALO Cordless light, which also has four LED chips, contains one in the violet
wavelength range (spectral peak at 405 nm) and the other three in the blue wavelength
range, with one chip emitting at 440 nm and the other two at 460 nm.[17] The radiant emittance (mW/cm2) and the irradiance (mW/cm2) on the ultraviolet (<380 nm), violet (380–420 nm), royal-blue (420–450 nm), cyan-blue
(450–495 nm), green (495–540 nm), as well as, the overall wavelength range (360–540
nm) of each LCU was calculated by integrating the radiant emittance (mW/cm2) and the irradiance (mW/cm2) versus wavelength curves obtained from the spectrophotometer.
Beam Profile Image Acquisition
A schematic representation of the set up used to make the beam profile images acquisition
is showed in [Fig. 2]. Each LCU was attached to an x-y-z positioning device mounted on an optical bench
(450 × 300 mm breadboard, Edmund Optics, Barrington, New Jersey, United States) to
standardize the positioning of the light beam in contact with a diffusive surface
of a frosted diffuser glass (DG20–1500, Thorlabs, Inc.). To assess the irradiance
distribution according to different wavelength range emission and to narrow the differences
in the camera pixel absorption profile, bandpass filters (FB410–10, FB440–10 and FB-460–10,
Thorlabs, Inc.) were placed between the diffuser glass and the cameras. As the bandpass
filters used in this study has an optical density of approximately 0.2, no neutral
density filters were necessary to attenuate the LCU light to avoid pixel intensity
saturation on the images. More specific information about the bandpass filter characteristics
is provided in the ►Supplementary Material (available in the online version). For
the Radii Plus, a bandpass filter centered first at 460 ± 2 nm with a 10 ± 2 nm full
width at half maximum (FB460–10, Thorlabs, Inc.) was used to identify the LED chip
with a spectrum emission peak at 460 nm. For the Bluephase G2, a bandpass filter centered
first at 410 ± 2 nm with a 10 ± 2 nm full width at half maximum (FB410–10, Thorlabs,
Inc.) was used to identify the LED chips with a spectrum emission peak at 410 nm.
A different bandpass filter, centered at 460 ± 2 nm with a 10 ± 2 nm full width at
half maximum (FB460–10, Thorlabs, Inc.) was used to identify the LED chips generating
emission peak near 460 nm. For the VALO Cordless, the same bandpass filters described
above (FB410–10 and FB460–10) were used to identify the LED chips with spectrum emission
peaks at 405 and 460 nm. An additional bandpass filter, centered at 440 ± 2 nm with
a 10 ± 2 nm full width at half maximum (FB440–10) was used to identify the LED chip
having an emission peak near 440 nm.
Fig. 2 Representative picture of the method setup for the collection of the beam profile
data using different cameras: Each LCU (A) was positioned perpendicular to a glass diffuser (B) target and pictures were taken by using different cameras (D) with different bandpass filter (C) between the glass diffuser and the cameras’ lens; the focal distance between the
camera lens and the LCU light tip was 25 cm for the Ophir camera, 28 cm for the NEX-F3
camera, and 10 cm for the iPhone camera. LCU, light-curing units.
The resulting images were recorded by using different cameras: a standard beam profiler
CCD camera (Ophir, Model SP503U, Ophir-Spiricon, Logan, Utah, United States),[4] a mirrorless camera (NEX-F3, Sony Corporation, Tokyo, Japan) with 50 mm focal length
lens and a smartphone camera (iPhone 7 Plus, Apple Inc., Cupertino, California, United
States). The details of the three cameras used in this study (Ophir, NEX-F3 and iPhone)
are reported in [Table 1].
Table 1
Specification of the cameras used in this study
|
Camera
|
Manufacturer
|
Sensor
|
Sensor type
|
Resolution
|
Sensor Size
|
Pixel size
|
Pixel depth (raw format)
|
Subpixel layout
|
Dynamic range
|
Signal-to-noise ratio
|
Accuracya
|
|
Abbreviations: CCD, charge-coupled device; CMOS, complementary metal-oxide-semiconductor;
RGB, red, green, and blue.
aConsidering a light source with 1 W; MP (megapixels); dB (decibel). Data are from
technical datasheets of the sensors used in each camera provided by the manufacturers.
|
|
Ophir SP503U
|
Ophir-Spiricon, Logan, UT, USA
|
Ophir-Spiricon Silicon CCD
|
CCD
|
640 × 480
(0.3 MP)
|
29.61 mm2
(6.3 × 4.7 mm)
|
9.90 μm2
|
12-bit
|
Monochrome
|
64 dB
|
1600:1
|
0.6 mW
|
|
NEX-F3
|
Sony Corp., Tokyo, Japan
|
Sony Exmor APS HD - IMX 071
|
CMOS
|
4,912 × 3,264
(16 MP)
|
366.6 mm2
(23.5 × 15.6 mm)
|
4.78 μm2
|
14-bit
|
RGB
|
49 dB
|
282:1
|
3.5 mW
|
|
iPhone 7 Plus
|
Apple Inc., Cupertino, CA, USA
|
Sony Exmor RS - IMX 315
|
CMOS
|
4,032 × 3,024
(12 MP)
|
32.3 mm2
(5.2 × 6.2 mm)
|
1.22 μm2
|
14-bit
|
RGB
|
42 dB
|
125:1
|
8.0 mW
|
For the Ophir camera, the images were captured by using the BeamGage Standard software
(v.6.13.1, Ophir-Spiricon). First, the system was automatically corrected for ambient
light and pixel response. Then, the LCUs were powered on and the Ophir SP503U 50 mm
lens camera iris was adjusted to use the full dynamic range of the CCD camera without
pixel intensity saturation. For the NEX-F3, a sequence of images was captured manually
with ISO 200 an aperture of f/32 and shutters speed from 1/4,000 to 1/200. For the
iPhone, a series of images was captured manually by using the application software
Adobe Photoshop Lightroom CC (v. 3.4.0 F59BE2, Adobe, San Jose, California, United
States) to adjust the iPhone 7 Plus rear camera to an ISO 25, an aperture of f/1.8,
and a shutter speed from 1/8,000 to 1/200.
The NEX-F3 and the iPhone cameras images were captured in the RAW format with minimally
processed data from the image sensor to achieve the maximum dynamic range of both
cameras. The images with different times of exposure accordingly to the different
shutter speed settings for each camera were examined by histogram analysis of the
pixel intensity using the Fiji software to ensure that the images obtained were not
saturated (pixel intensity over 65,536 since the images were taken in 16 bit). The
images in which the pixel intensity reached the values closer 65,536 and lower than
to 65,535 were chosen to be used as the beam profile images.
Each image was individually calibrated according to the power (mW) recorded with the
MARC LC for each LCU. The spectral irradiance for violet (peak at 405 nm), royal-blue
(peak at 440 nm), and cyan-blue (peak at 460 nm) wavelength regions were recorded
and calibrated on separate images with the aid of appropriate bandpass filters. For
the Ophir camera, the average power of each LCU was entered into the Beamgage software,
and the irradiance distribution was determined by the average pixel intensity distribution
interpolated with the size of the area of the light beam. As the Beamgage software
offers limited options to customize the graphs and to manipulate the data, the 307,200
calibrated data points from the 640 × 480 matrix array were exported into a scientific
graphing and data analysis software (Origin Pro, OriginLab Co., Northampton, Massachusetts,
United States).
For the NEX-F3, the images files in the Sony Alpha Raw format (ARW) were transferred
to a personal computer, and the images files in ARW were converted into a 16-bit Tagged
Image File Format (TIF). The converted images were imported into a free open-source
image processing and data analysis software (Fiji, ImageJ, National Institute of Health,
Bethesda, Maryland, United States).[18] The same process was performed for the iPhone images. The iPhone images in the Adobe
Digital Negative Raw Image file format (DNG) were also converted to a 16-bit TIF file.
For NEX-F3 and iPhone cameras, the average power of each LCU was entered into the
Fiji software, and the irradiance distribution was determined by the average pixel
intensity distribution interpolated with the size of the area of the light beam. Similar
to the Beamgage software, the Fiji software offers limited options to customize graphs
and manipulate the data. Thus, the calibrated data points were exported into a scientific
graphing and data analysis software (Origin Pro, OriginLab Co.).
Statistical Analysis
Statistical analysis was performed by digital image correlation. Each calibrated beam
profile image was transformed into an XYZ matrix array, where the X- and Y-axis represent
the location of the pixel and Z represents the calibrated irradiance value (according
to the 16-bit grayscale pixel intensity). The data were entered into statistical analysis
software (Stata/MP 13, StataCorp, College Station, Texas, United States). For each
LCU beam profile image with different wavelength spectrum bandpass filter, the correlation
was performed between the control group camera (Ophir) and the mirrorless camera (NEX-F3)
and the smartphone camera (iPhone). A correlation analysis was performed by using
Pearson’s correlation with α = 0.05 and β = 0.2.
Results
Spectral Radiant Power
[Table 2] shows the total power output (mW), the area of light emission (cm2), radiant emittance (mW/cm2), and the irradiance (mW/cm2) over a 0.765 cm2 area according to the different wavelength ranges. [Fig. 3] illustrates the spectral power (mW) distribution according to each wavelength (nm).
The Radii Plus had total power of 607 ± 9.3 mW within area of emission of 0.442 cm2 resulting an average radiant emittance of 1,378 ± 8.2 mW/cm2 and an average irradiance of 776 ± 4.6 mW/cm2. As expected, the majority of the light emission of this monowave LCU was inside
“royal-blue” and “cyan-blue” wavelength range with a single peak at 454 nm. For the
Bluephase G2 in the high-power mode, the total power was 843 ± 7.8 mW with an area
of emission of 0.635 cm2 resulting in an average radiant emittance of 1,305 ± 9.4 mW/cm2 and an average irradiance of 1,056 ± 7.6 mW/cm2. As the Bluephase G2 is a dual peak multiwave LCU, with one violet LED chip, and
three blue LED chips, the light emission of this LCU was inside the “violet,” “royal-blue,”
and “cyan-blue” wavelength ranges with peaks at 408 nm (violet) and 458 nm (cyan-blue).
For the VALO Cordless in the standard mode, the total power was 843 ± 7.8 mW with
an area of emission of 0.635 cm2 resulting in an average radiant emittance of 1,066 ± 2.4 mW/cm2 and an average irradiance of 938 ± 2.1 mW/cm2. As the VALO Cordless is a triple peak multiwave LCU, with one violet LED chip, one
royal-blue LED chip and two blue LED chips, the light emission of this LCU was inside
the “violet,” “royal-blue,” and “cyan-blue” wavelength ranges with peaks at 403 nm
(violet), 442 nm (royal-blue), and 458 nm (cyan-blue).
Table 2
Mean ± standard deviation of the total power output (mW), active area of light emission
(cm2), radiant emittance (mW/cm2), and irradiance (mW/cm2) according to the different
spectral ranges
|
Light curing unit
|
Radii plus
|
Bluephase G2
|
VALO cordless
|
|
(High power mode)
|
(Standard mode)
|
|
Area of light emission (cm2)
|
0.442 ± 0.002
|
0.635 ± 0.001
|
0.691 ± 0.001
|
|
Total (360–540 nm)
|
Power (mW)
|
607 ± 9.3
|
843 ± 7.8
|
737 ± 9.1
|
|
Radiant Emittance (mW/cm2)
|
1,378 ± 8.2
|
1,305 ± 9.4
|
1,066 ± 2.4
|
|
Irradiance (mW/cm2)
|
776 ± 4.6
|
1,056 ± 7.6
|
938 ± 2.1
|
|
Ultra-violet (<380 nm)
|
Power (mW)
|
0.6 ± 0.1
|
1 ± 0.5
|
1 ± 0.6
|
|
Radiant Emittance (mW/cm2)
|
1 ± 0.1
|
2 ± 0.3
|
2 ± 0.2
|
|
Irradiance (mW/cm2)
|
<1
|
2 ± 0.2
|
2 ± 0.2
|
|
Violet (380–420 nm)
|
Power (mW)
|
9 ± 0.2
|
123 ± 3.9
|
144 ± 7.1
|
|
Radiant Emittance (mW/cm2)
|
81 ± 1.4
|
190 ± 4.1
|
210 ± 3.1
|
|
Irradiance (mW/cm2)
|
46 ± 0.8
|
154 ± 3.3
|
185 ± 2.7
|
|
Royal-blue (420–450 nm)
|
Power (mW)
|
365 ± 7.6
|
134 ± 5.2
|
211 ± 3.3
|
|
Radiant Emittance (mW/cm2)
|
1,072 ± 4.0
|
207 ± 3.2
|
305 ± 3.1
|
|
Irradiance (mW/cm2)
|
604 ± 2.2
|
167 ± 2.6
|
268 ± 2.7
|
|
Cyan-Blue (450–495 nm)
|
Power (mW)
|
230 ± 9.8
|
572 ± 3.1
|
369 ± 5.2
|
|
Radiant Emittance (mW/cm2)
|
219 ± 4.6
|
885 ± 4.5
|
534 ± 6.7
|
|
Irradiance (mW/cm2)
|
123 ± 2.6
|
716 ± 3.6
|
470 ± 5.9
|
|
Blue (420–495 nm) (Royal + Cyan)
|
Power (mW)
|
595 ± 6.4
|
706 ± 2.6
|
580 ± 4.2
|
|
Radiant Emittance (mW/cm2)
|
1,346 ± 4.5
|
1,112 ± 8.1
|
839 ± 3.6
|
|
Irradiance (mW/cm2)
|
778 ± 8.3
|
923 ± 8.7
|
758 ± 3.4
|
|
Green (495–540 nm)
|
Power (mW)
|
3 ± 0.4
|
13 ± 1.8
|
11 ± 2.6
|
|
Radiant Emittance (mW/cm2)
|
4 ± 0.5
|
20 ± 1.2
|
16 ± 0.9
|
|
Irradiance (mW/cm2)
|
2 ± 0.3
|
16 ± 1.0
|
14 ± 0.8
|
Fig. 3 Spectral radiant power (mW/nm) of the Radii Plus, Bluephase G2, and VALO Cordless.
Light-Curing Units Beam Profile
[Figs. 4]
[5]
[6]
[7]
[8] show the 2D and 3D beam profile images for the different LCUs using the Ophir, NEX-F3,
and iPhone cameras. All the images were calibrated accordingly to the radiant emittance
(mW/cm2) for each respective LCU. Also, the active area of emission (cm2), the radiant emittance (mW/cm2), and irradiance (mW/cm) distribution of each LCU according to the different wavelength
ranges are described in [Table 3].
Table 3
Active area of emission (cm2), radiant emittance (mW/cm2) and Irradiance (mW/cm2)
distribution of each LCU according to the different wavelength ranges
|
|
Active area of emission (cm2)
|
Average
|
Mode
|
Minimum
|
Maximum
|
Deviation
|
|
Radiant Emittance (mW/cm2)
|
Irradiance (mW/cm2)
|
Radiant Emittance (mW/cm2)
|
Irradiance (mW/cm2)
|
Radiant Emittance (mW/cm2)
|
Irradiance (mW/cm2)
|
Radiant Emittance (mW/cm2)
|
Irradiance (mW/cm2)
|
Radiant Emittance (mW/cm2)
|
Irradiance (mW/cm2)
|
|
Note: No statistical differences were found between the different beam profiling systems.
|
|
Radii Plus - Blue 460 ± 2 nm (FWHM 10 ± 2 nm)
|
Ophir
|
0.423
|
1,355
|
763
|
385
|
217
|
154
|
86
|
3,745
|
2,109
|
935
|
527
|
|
NEX-F3
|
0.425
|
1,389
|
782
|
268
|
151
|
186
|
105
|
3,466
|
1,952
|
1,035
|
583
|
|
iPhone
|
0.411
|
1,298
|
731
|
711
|
400
|
134
|
75
|
3,116
|
1,754
|
895
|
504
|
|
Bluephase G2 - Violet 410 ± 2 nm (FWHM 10 ± 2 nm)
|
Ophir
|
0.547
|
195
|
158
|
88
|
71
|
50
|
40
|
584
|
472
|
108
|
87
|
|
NEX-F3
|
0.545
|
200
|
162
|
150
|
121
|
50
|
40
|
492
|
398
|
112
|
91
|
|
iPhone
|
0.608
|
194
|
157
|
178
|
144
|
50
|
40
|
382
|
309
|
71
|
57
|
|
Bluephase G2 - Blue 460 ± 2 nm (FWHM 10 ± 2 nm)
|
Ophir
|
0.589
|
1092
|
883
|
933
|
755
|
130
|
105
|
2,977
|
2,408
|
531
|
430
|
|
NEX-F3
|
0.604
|
1,089
|
881
|
784
|
634
|
109
|
88
|
2,253
|
1,822
|
538
|
435
|
|
iPhone
|
0.603
|
1,094
|
885
|
952
|
770
|
112
|
91
|
2,350
|
1,901
|
595
|
481
|
|
VALO Cordless - Violet 410 ± 2 nm (FWHM 10 ± 2 nm)
|
Ophir
|
0.468
|
209
|
184
|
83
|
73
|
50
|
44
|
555
|
489
|
130
|
114
|
|
NEX-F3
|
0.433
|
210
|
185
|
103
|
91
|
50
|
44
|
453
|
399
|
104
|
92
|
|
iPhone
|
0.465
|
210
|
185
|
84
|
74
|
50
|
44
|
437
|
385
|
113
|
99
|
|
VALO Cordless - Royal-Blue 440 ± 2 nm (FWHM 10 ± 2 nm)
|
Ophir
|
0.523
|
515
|
453
|
242
|
213
|
106
|
93
|
1,075
|
946
|
242
|
213
|
|
NEX-F3
|
0.608
|
514
|
452
|
692
|
609
|
133
|
117
|
819
|
721
|
133
|
117
|
|
iPhone
|
0.574
|
514
|
452
|
248
|
218
|
135
|
119
|
887
|
781
|
208
|
183
|
|
VALO Cordless - Cyan-Blue 460 ± 2 nm (FWHM 10 ± 2 nm)
|
Ophir
|
0.609
|
838
|
738
|
1,040
|
915
|
117
|
103
|
2,106
|
1,854
|
430
|
379
|
|
NEX-F3
|
0.614
|
839
|
739
|
471
|
415
|
120
|
106
|
2,115
|
1,862
|
433
|
381
|
|
iPhone
|
0.613
|
839
|
739
|
372
|
327
|
50
|
44
|
2,181
|
1,920
|
476
|
419
|
Fig. 4 Using the Ophir, NEX-F3 and iPhone cameras: 2D and 3D beam profile images of the
Radii plus with the 460 ± 2 nm, full-width at half-maximum 10 ± 2 nm bandpass filter
showing the radiant emittance distribution.
Fig. 5 Using the Ophir, NEX-F3 and iPhone cameras: 2D and 3D beam profile images of the
Bluephase G2 with the 410 ± 2 nm, full-width at half-maximum 10 ± 2 nm bandpass filter
showing the radiant emittance distribution.
Fig. 6 Using the Ophir, NEX-F3 and iPhone cameras: 2D and 3D beam profile images of the
Bluephase G2 with the 460 ± 2 nm, full-width at half-maximum 10 ± 2 nm bandpass filter
showing the radiant emittance distribution.
Fig. 7 Using the Ophir, NEX-F3 and iPhone cameras: 2D and 3D beam profile images of the
VALO Cordless with the 410 ± 2 nm, full-width at half-maximum 10 ± 2 nm bandpass
filter showing the radiant emittance distribution.
Fig. 8 Using the Ophir, NEX-F3 and iPhone cameras: 2D and 3D beam profile images of the
VALO Cordless with the 440 ± 2 nm, full-width at half-maximum 10 ± 2 nm bandpass
filter showing the radiant emittance distribution.
[Fig. 4] shows the 2D and 3D beam profile images for the Radii Plus using the Ophir, NEX-F3,
and iPhone cameras. The Radii Plus had a higher light emission at the center part
of the light tip and a lower radiant emittance on the boundaries of the light tip
emission. Using the Ophir camera for the Radii Plus beam profile analysis, it was
detected an average radiant emittance of 1,355 mW/cm2, with a maximum radiant emittance of 3,745 mW/cm2 and a minimum radiant emittance of 154 mW/cm2, inside an active area of emission of 0.423 cm ([Table 3]). Using the NEX-F3 camera for the Radii Plus beam profile analysis, it was detected
an average radiant emittance of 1,389 mW/cm2, with a maximum radiant emittance of 3,466 mW/cm2 and a minimum radiant emittance of 186 mW/cm2, inside an active area of emission of 0.425 cm2. Using the iPhone camera for the Radii Plus beam profile analysis, it was detected
an average radiant emittance of 1,298 mW/cm2, with a maximum radiant emittance of 3,116 mW/cm2 and a minimum radiant emittance of 134 mW/cm2, inside an active area of emission of 0.411 cm2.
[Figs. 5] and [6] show the 2D and 3D beam profile images for the Bluephase G2 using the Ophir, NEX-F3,
and iPhone cameras within the violet spectrum and the blue spectrum, respectively.
For the Bluephase G2, an area with higher light emission was detected on the boundaries
of the light tip. However, according to the LED chips distribution, the violet and
blue spectrum were placed in different regions across the light tip. Within the violet
spectrum (410 ± 2 nm, FWHM 10 ± 2 nm), an area of higher radiant emittance was detected
on the left side of the light tip, where the violet LED chip is located inside the
body of the LCU next to an optical reflector. Using the Ophir camera for the analysis
of the Bluephase G2 inside the violet spectrum (410 ± 2 nm, FWHM 10 ± 2 nm), an average
radiant emittance of 195 mW/cm2 was detected, with a maximum radiant emittance of 584 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.547 cm ([Table 3]). When the NEX-F3 camera was used for the beam profile analysis of the Bluephase
G2 inside the violet spectrum (410 ± 2 nm, FWHM 10 ± 2 nm), an average radiant emittance
of 200 mW/cm2 was detected, with a maximum radiant emittance of 492 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.545 cm2. For the iPhone camera, the Bluephase G2 inside the violet spectrum (410 ± 2 nm,
FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of 194
mW/cm2, with a maximum radiant emittance of 382 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.608 cm2.
Considering the beam profile analysis of the Bluephase G2 within the blue spectrum
(460 ± 2 nm, FWHM 10 ± 2 nm), an area of higher radiant emittance on the top side
of the light tip was detected, where one of the LED chips emitting blue light is located
inside the body of the LCU next to an optical reflector. The Ophir camera for the
Bluephase G2 inside the blue spectrum (460 ± 2 nm, FWHM 10 ± 2 nm) beam profile analysis
detected an average radiant emittance of 1,092 mW/cm2, with a maximum radiant emittance of 2,977 mW/cm2 and a minimum radiant emittance of 130 mW/cm2, inside an active area of emission of 0.589 cm ([Table 3]). The NEX-F3 camera for the Bluephase G2 inside the blue spectrum (460 ± 2 nm, FWHM
10 ± 2 nm) beam profile analysis detected an average radiant emittance of 1089 mW/cm2, with a maximum radiant emittance of 2,253 mW/cm2 and a minimum radiant emittance of 109 mW/cm2, inside an active area of emission of 0.604 cm2. The iPhone camera for the Bluephase G2 inside the blue spectrum (460 ± 2 nm, FWHM
10 ± 2 nm) beam profile analysis detected an average radiant emittance of 1,094 mW/cm2, with a maximum radiant emittance of 2,350 mW/cm2 and a minimum radiant emittance of 112 mW/cm2, inside an active area of emission of 0.603 cm2.
[Figs. 7]
[8]
[9] show the 2D and 3D beam profile images for the VALO Cordless using the Ophir, NEX-F3,
and iPhone cameras within the violet spectrum, the royal-blue spectrum and cyan-blue
spectrum), respectively. The VALO Cordless had a higher light emission on the boundaries
of the light tip emission. However, according to the distribution of the LED chips,
the violet, the royal-blue, and the cyan-royal blue spectra were located in different
regions of the light tip.
Fig. 9 Using the Ophir, NEX-F3 and iPhone cameras: 2D and 3D beam profile images of the
VALO Cordless with the 460 ± 2 nm, full-width at half-maximum 10 ± 2 nm bandpass
filter showing the radiant emittance distribution.
Within the violet spectrum (410 ± 2 nm, FWHM 10 ± 2 nm), the VALO Cordless had an
area of higher radiant emittance on the right-bottom side of the light tip, where
the violet LED chip is located inside the head of the LCU. The Ophir camera for the
VALO Cordless inside the violet spectrum (410 ± 2 nm, FWHM 10 ± 2 nm) beam profile
analysis detected an average radiant emittance of 209 mW/cm2, with a maximum radiant emittance of 555 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.468 cm ([Table 3]). The NEX-F3 camera for the VALO Cordless inside the violet spectrum (410 ± 2 nm,
FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of 210
mW/cm2, with a maximum radiant emittance of 453 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.433 cm2. The iPhone camera for the VALO Cordless inside the violet spectrum (410 ± 2 nm,
FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of 210
mW/cm2, with a maximum radiant emittance of 437 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.465 cm2.
Inside the royal-blue spectrum (440 ± 2 nm, FWHM 10 ± 2 nm), the VALO Cordless had
an area of higher radiant emittance on the top and right side of the light tip, where
one of the royal-blue LED chip is located inside the body of the LCU. The Ophir camera
for the VALO Cordless inside the blue spectrum (440 ± 2 nm, FWHM 10 ± 2 nm) beam profile
analysis detected an average radiant emittance of 515 mW/cm2, with a maximum radiant emittance of 1,075 mW/cm2 and a minimum radiant emittance of 106 mW/cm2 inside an active area of emission of 0.523 cm2. The NEX-F3 camera for the VALO Cordless inside the royal-blue spectrum (440 ± 2
nm, FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of
514 mW/cm2, with a maximum radiant emittance of 819 mW/cm2 and a minimum radiant emittance of 133 mW/cm2, inside an active area of emission of 0.608 cm2. The iPhone camera for the VALO Cordless inside the royal-blue spectrum (440 ± 2
nm, FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of
514 mW/cm2, with a maximum radiant emittance of 887 mW/cm2 and a minimum radiant emittance of 135 mW/cm2, inside an active area of emission of 0.574 cm2.
Within the cyan-blue spectrum, the VALO Cordless had an area of higher radiant emittance
on the top-right and bottom left side of the light tip, where each of two blue LED
chips are located inside the head of the LCU. The Ophir camera for the VALO Cordless
inside the cyan-blue spectrum (460 ± 2 nm, FWHM 10 ± 2 nm) beam profile analysis detected
an average radiant emittance of 838 mW/cm2, with a maximum radiant emittance of 2,106 mW/cm2 and a minimum irradiance of 117 mW/cm2, inside an active area of emission of 0.609 cm ([Table 3]). The NEX-F3 camera for the VALO Cordless inside the cyan-blue spectrum (460 ± 2
nm, FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of
839 mW/cm2, with a maximum radiant emittance of 2,115 mW/cm2 and a minimum radiant emittance of 120 mW/cm2, inside an active area of emission of 0.614 cm2. The iPhone camera for the VALO Cordless inside the cyan-blue spectrum (460 ± 2 nm,
FWHM 10 ± 2 nm) beam profile analysis detected an average radiant emittance of 839
mW/cm2, with a maximum irradiance of 2,181 mW/cm2 and a minimum radiant emittance of 50 mW/cm2, inside an active area of emission of 0.613 cm2.
[Table 4] shows the Pearson’s correlation of the images pixel intensities according to the
x and y position using the NEX-F3 and iPhone cameras in comparison to the Ophir camera.
A strong correlation in the pixel intensity distribution was found between the Ophir
camera and the NEX-F3 camera (Pearson’s r = 0.91 ± 0.03 with 95% CI: 0.88–0.94) and
as well between the Ophir camera and the iPhone camera (Pearson’s r = 0.88 ± 0.04
with 95% CI: 0.84–0.92 for the iPhone).
Table 4
Correlation of the images using the NEX-F3 and iPhone cameras versus the Ophir camera
|
Light curing unit
|
Wavelength
|
NEX-F3
|
iPhone
|
|
Pearson’s r
|
Adjusted R-square
|
p
-Value
|
Pearson’s r
|
Adjusted R-square
|
p
-Value
|
|
Radii Plus
|
Blue
|
0.92
|
0.85
|
0.0001
|
0.89
|
0.79
|
0.0001
|
|
Bluephase G2
|
Violet
|
0.94
|
0.89
|
0.0001
|
0.88
|
0.78
|
0.0001
|
|
Blue
|
0.92
|
0.84
|
0.0001
|
0.85
|
0.72
|
0.0001
|
|
VALO Cordless
|
Violet
|
0.93
|
0.87
|
0.0001
|
0.95
|
0.89
|
0.0001
|
|
Royal-Blue
|
0.86
|
0.74
|
0.0001
|
0.84
|
0.71
|
0.0001
|
|
Cyan-Blue
|
0.89
|
0.79
|
0.0001
|
0.86
|
0.73
|
0.0001
|
Discussion
The research hypothesis that the mirrorless and smartphone cameras would have the
same performance as the camera-based beam profiling systems was accepted. As mentioned
in this study introduction, the Ophir camera-based laser beam profiling system and
other elaborated beam profile systems are considered the best quality scientific equipment
regarding the characterization of light beams of medical and industrial laser. Those
beam profiling systems are proven to be also reliable to characterize the light beam
profile of dental LCUs.[1]
[2]
[7] However, in terms of characterizing a dental LCU, the use of more accessible technologies
can provide results with similar quality but at low cost. Nevertheless, it is important
to state that there are some differences between the Ophir camera and the NEX-F3 and
the iPhone cameras used in this study. Indeed, these differences found in the NEX-F3
camera (mirrorless) and in the iPhone (Smartphone) camera might be the same differences
observed in other models of mirrorless and smartphone cameras, since these electronical
devices share similar camera technology.[19]
The first difference is that the Ophir camera uses a charge couple devices (CCD) sensor
while the NEX-F3 and the iPhone cameras use a complementary metal-oxide semiconductor
(CMOS) sensor. The CCD and CMOS sensors operate quite similar using an array of photodetectors.
Then, when a photon from the LCU reaches the photodetector, a photoelectric conversion
occurs generating electrons in each photodetector.[20]
[21]
[22] The number of electrons generated in each photodetector is proportional to the number
of photons that have reached the sensor. However, the difference between CCD and CMOS
sensors is in the conversion of the analog electron signal in each photodetector to
a digital signal in a form of image pixel.[20] Basically, for the CMOS sensor, each photodetector has its motherboard processor
located at each pixel, which converts the analog to the digital signal. On the other
hand, the motherboard processor of a CCD sensor that converts the analog to the digital
signal is located nearest to the edge of the sensor.[21] Thus, the photodetectors on the edge of the sensor transfer their electrons to the
motherboard processor. However, all other photodetectors transfer their electron charge
to the neighboring photodetector that is closer to the motherboard and the process
continues when these photodetectors transfer the electrons to the motherboard processor.[20]
[21]
[22] Once the motherboard processes the analog signal and transforms it into a digital
signal, this process continues until all electrons captured in an image are detected
and converted into digital. In this way, the electrons are removed from the sensor
one photodetector at a time.[20] The fact is that for many years, CCD sensor was the predominant sensor used in laser
beam profiling applications. Also, one of the foremost reasons behind the CCD use
was their lower noise level, which means that the images are smoother and the pixel
intensity values are more accurate.
However, recent advances in CMOS technology have steadily reduced the CMOS noise.
As shown in [Table 1], the dynamic range of the Ophir camera (64 dB) is higher than the NEX-F3 (49 dB)
and iPhone (42 dB) cameras. The dynamic range is the range that a sensor can detect
from the lowest light intensity to the higher light intensity. That means that the
Ophir camera can detect differences in a wider range than the NEX-F3 and iPhone camera.
It is known that a camera with a higher dynamic range would have a lower signal-to-noise
ratio and, as a consequence, a higher accuracy to detected differences in the power
of the light beam.[19]
[23]
[24] When considering the dynamic range of each camera in a minimum detection threshold
of 50 mW/cm2 for the characterization of a dental LCU, the Ophir camera can detect differences
without pixel saturation up to 79,244.5 mW/cm2 with an accuracy of 0.6 mW/cm2. While, the NEX-F3 can detect differences without pixel saturation up to 14,091.9
mW/cm2 with an accuracy of 3.5 mW/cm2, and the iPhone can detect differences without pixel saturation up to 6,294.6 mW/cm2, with an accuracy of 3.5 mW/cm. Indeed, the Ophir camera is by far better than the
NEX-F3 and iPhone cameras. However, a recent study[4] has shown that the maximum irradiance of the majority dental LCUs might have a range
from 1,508 to 5,950 mW/cm2, which means that both NEX-F3 and iPhone are still capable of performing the light
collection without sensor oversaturation. However, some exceptions would be expected,
such as the use of the iPhone camera for the beam profile characterization of the
S.P.E.C. 3 (Coltene/Whaledent AG, Altstätten, Switzerland) that had a maximum irradiance
of 8,325 mW/cm.[4] Thus, when choosing a low-budget camera to do a beam profile of a dental LCU, look
for a CCD or a CMOS camera that has a dynamic range higher than 41 dB.
Regarding the image resolution, the NEX-F3 and iPhone cameras have better resolution
with more megapixels and smaller pixel sizes, which means that in terms of spatial
distribution, those cameras would have better precision than the Ophir camera. However,
these results do not rule out the influence of other factors such as the subpixel
layout, as shown in [Table 1]. The subpixel layout defines if a silicon-based camera sensor can detect light signals
in grayscale or color by means of pixel intensities in different color channels (red,
green, and blue [RGB]). In general, all camera sensors are currently monochrome, the
photodiodes sensors that accept the photons and convert them into electrons, and so
forth, all of them only deliver a level of gray as the sort of quantitative pixel
intensity information.[21] However, if filters are placed in front of them, levels of gray of a blue, green,
or red channels can be detected. The mirrorless and smartphone cameras are designed
to capture images with color depths; thus, necessarily, a microfilter in a Bayer array
pattern with RGB in a 1:2:1 proportion is placed in front of the sensors.[21] Considering that the wavelength range of the dental LCUs is within the blue channel
of the Bayer array, it is almost certain that three quarters of the total pixels captured
by the sensor are lost. As an example, the images obtained with the NEX-F3 and iPhone
had higher resolution and more megapixels than the Ophir camera. However, it does
not mean that after transforming the color image (color-chrome) obtained using the
NEX-F3 and iPhone into a black and white image (monochrome), the transformed monochrome
images would have better resolution than the original monochrome images obtained using
the Ophir camera. The fact is that when the color-chrome images are transformed into
a monochrome image, the color-coded pixels (red, green, or blue) are interpolated
and reduced by four. This interpolation reduces the image resolution by estimating
the pixel intensity from surrounding pixel intensity known values. As a consequence,
making the image acquisition with larger pixels and more noise. Thus, it is suggested
that when using color-chrome mirrorless or smartphone cameras for beam profile purposes
that the camera should have at least 2,560 × 1,920 pixels (~5.0 megapixel) of resolution
to get similar results as the standard Ophir cameras.
When a photon from a dental LCU reaches the detector of a beam profile camera, its
energy is converted from an electron-volt analog signal into a digital signal, as
fully explained in many previous studies.[22] Also, as mentioned before, the dynamic range is the range that a sensor can detect
from the lowest light intensity to the highest light intensity. However, from the
lowest to the highest pixel value, there is a continuous variable that could have
an infinite number of possible values. Thus, the relation between the lowest to the
highest signal detected by the sensor, associated with the amount of data stored digitally,
defines the bit depth of the beam profile images.[23] The bit depth is the number of intervals, or steps, between the minimum and the
maximum pixel value, which is essential to differentiate the threshold between the
value of two different pixels (the pixel value, for the beam profile images represents
the irradiance (mW/cm2)). Digital cameras usually have 8-bit (28 = 256), 10-bit (210 = 1,024), 12-bit (212 = 4,096), or 16-bit (2= 65,536).[19] In terms of beam profile analysis, if a camera sensor has 8-bit, there is 256 levels
for the pixel value; this means that if a dental LCU with a maximum irradiance of
1,000 mW/cm2 is being evaluated, the camera can detect differences in irradiance of 3.9 mW/cm.
Still, it is important to mention that if images are captured in JPEG format, the
bit depth is limited to 8-bit, which gives 256 levels of gray and as consequence,
256 levels of irradiance, regardless of the bit depth of your camera sensor.[24] However, images captured in RAW/DNG format can be anywhere from 10- to 16-bit, with
the latter giving 65,536 levels of grays, meaning that it has a lot more accuracy
in detect differences between pixels and when those images are converted to a TIFF
file, there is no compression or loose of data. Thus, for the use of mirrorless or
smartphone cameras as a beam profiling analysis system, the camera RAW file should
be accessible because besides shooting the images without any digital processing,
the images have more information (bit depth) about the dental LCU analyzed.
One of the main obstacles in beam profile analysis is to calibrate the images properly.
The reason that occurs is because the absolute power fed to the camera is relative
to the total power of the light beam.[13]
[22] Therefore, it is essential to have an accurate method to collect the total power
of the dental LCU. Otherwise, the irradiance distribution of the beam profile images
would not be consistent. Several methods have been reported in the literature to collect
the power (mW) and the spectral irradiance (mW/cm/nm) of LCUs.[4]
[7]
[12]
[13] It is almost certain that the method that uses an integrated sphere coupled to a
spectrometer is the most reliable and precise of all methods.[4] However, alternatives to that are also valid, but a note of caution is due here
because each of these methods has their limitations.[25]
[26] In this study, a portable-spectrometer with a 16-mm in diameter area of the collection
was used to collect the spectral power (mW/nm) and the spectral irradiance (mW/cm/nm)
of the dental LCUs from the entire light tip. It seems possible that other methods
using a spectrometer coupled with a cosine corrector (MARC Resin Calibrator, BlueLight
Analytics) might work as well, but it is important to mention that the power collected
should be calibrated accordingly to the size of the cosine corrector (usually 3.9
mm in diameter) and not accordingly to the size of the light tip. In addition, cameras
do not have uniform wavelength absorption.[27] Therefore, they would have a different calibration factor for every wavelength of
the light source that is used, and the attempt to calibrate the camera as a function
of wavelength by using bandpass filters is the best way to get the best correlation
among cameras.[27] In this study, the intended purpose was to separate the royal- and cyan-blue spectrum,
so a bandpass filter with a FWHM 10 ± 2 nm was used. However, for more information
regarding the use of bandpass filters with FWHM of 40 nm that covers the royal- and
cyan-blue spectrum together, refer to the supporting information provided in this
article.
There is a strong correlation between the dental LCU beam profile, and the physical
and chemical properties of resin-based materials have been reported in the literature.[6]
[7]
[28]
[29] The results of the present study broadly support the work of other studies that
the beam profile of the dental LCU are notably different.[4]
[7] There are many LCUs available in the market with a considerable variation in the
number of LED chips, light tip sizes, and so many other aspects. All these variations
can affect the beam profile of dental LCU, and it is essential to measure the light
beam profile in any application if the energy distribution affects the performance
of the dental LCU for its intended purpose.
The beam profile characterization of the Radii Plus, which represents a monowave LED
LCU, showed big discrepancies between the radiant emittance at the center of the light
tip and the irradiance in areas on the boundary of the light tip, regardless the camera
used for beam profile analysis. The Radii Plus has a light tip with an external dimension
of 1.2 cm in diameter. However, the inner exit window of the microlens has only 0.75
cm in diameter, resulting in an area of emission 0.442 cm2. Thus, Radii Plus had an average radiant emittance of approximately 1,378 mW/cm2. But there were areas of higher radiant emittance at the center of the light tip
with approximately 3,700 mW/cm2, and areas of low radiant emittance at the periphery of the light tip with 160 mW/cm2. One possible reason for these findings is probably due to the Radii Plus LCU design.
The Radii Plus consist of four high-power LED chips at the center of the light tip
associated to a plastic microlens that does not have much optical capability of mixing
and collimate the light beam throughout the light tip.
The Bluephase G2 is a multiwave LED LCU with two peaks of emission. The beam profile
showed differences in the radiant emittance and in the spectral radiant emittance
regardless of the camera used for the analysis. The Bluephase G2 has a fiber optic
light tip with an incoherent bundle and an external dimension of 1.0 cm in diameter.
However, the active area of emission has 0.92 cm in diameter, resulting in an area
of emission 0.635 cm2. The Bluephase G2 had an average radiant emittance of approximately 1,305 mW/cm2. However, for the violet wavelength range, there were areas of higher radiant emittance
(~555 mW/cm2) at the left part of the light tip and areas of low radiant emittance (~50 mW/cm2) on the bottom left of the light tip. For the blue wavelength range, there were areas
of higher radiant emittance (~3,000 mW/cm2) at the top part of the light tip, and areas of low radiant emittance (~130 mW/cm2) on the bottom left of the light tip. These findings are also probably related to
the Bluephase G2 design because the Bluephase G2 has four high-power LED chips emitting
different wavelengths, three LED chips emitting blue light, and one LED chip emitting
violet light). All four LED chips are located at the center of the body of the LCU
associated with diffusive reflectors that orientate the light beam toward the boundary
of the light tip. Plus, the coherent light tip bundle from the Bluephase G2 does not
have any optical capability of mixing and collimate the light beam throughout the
light tip.
The beam profile characterization of the VALO Cordless also showed differences in
the irradiance and in the spectral irradiance regardless of the camera used for beam
profile analysis. The VALO Cordless is a multiwave LED LCU with three different peaks
of emission, two within the blue spectrum (at 440 [cyan-blue] and 460 nm [royal-blue])
and one within the violet spectrum (at 405 nm). The VALO Cordless has a quartz microlens
with an external dimension of 1.2 cm in diameter. However, the active area of emission
of the VALO Cordless has 0.96 cm in diameter, resulting in an area of emission 0.691
cm2. The VALO Cordless had an average radiant emittance of approximately 1,066 mW/cm2. However, for the violet wavelength range, there were areas of higher radiant emittance
(~210 mW/cm2) on the bottom left part of the light tip, and low radiant emittance (~50 mW/cm2) on the top left of the light tip. For the royal-blue wavelength range, there were
areas of higher radiant emittance (~1,075 mW/cm2) at the top part of the light tip, and low radiant emittance (~106 mW/cm2) on the bottom of the light tip. For the royal-blue wavelength range, there were
two areas of higher radiant emittance (~2,100 mW/cm2), one at the top right and another on the bottom left part of the light tip, and
areas of low radiant emittance (~120 mW/cm2) on the bottom right of the light tip. These findings are also probably related to
the VALO Cordless design. The VALO Cordless has four high-power LED chips emitting
different wavelengths, two LED chips emitting royal-blue light, one LED chip emitting
cyan-blue light, and one LED chip emitting violet light. All LED chips are located
at the center of the light tip associated with a quartz microlens that does mix the
light beam throughout the light tip, but not completely.
In summary, a slight difference was noted between cameras, as showed and further explored
in the histograms presented in the Supplementary Material (available in the online version). The results suggest that the mirrorless camera
(NEX-F3) had a somewhat better performance than the smartphone camera (iPhone). However,
it is important to point out that both the NEX-F3 and the iPhone cameras data showed
a strong correlation with the data obtained using the Ophir camera. Thus, different
cameras could be used in dentistry to perform the beam profile analysis of dental
LCUs, since minimal requirements for the camera are respected. In a previous study,[5] the authors attempted to use a digital single reflex camera and an iPad camera to
analyze the light beam profile of different LCUs qualitatively. However, this study
failed to address the statistical analysis of the images, and the conclusions are
made on the assumption of visual comparison without any digital image correlation
analysis. Besides that, the beam profiles images of the inactive light guide tips
do not coincide with the real intensity distribution in all cases. With the referenced
study based on imaging comparison in pseudo color, the methods reported do not provide
any data reproducibility.
The findings in the present study have significant implications for understanding
how imaging sensors’ technology and how to adapt to dental LCU analysis. The methods
reported here can contribute tremendously to further research projects and articles
that intend to report the light-curing unit spectrum, irradiance, and beam profile.
This study demonstrates and guides the reader on making a light beam profiler with
different CCD/CMOS sensors. It can provide many authors with the opportunity to report
the full characteristic of the LCUs used in their studies inexpensively and reproducibly.
As state by Price et al[2], “for improved interstudy reproducibility, reduced risk of premature failures, and
ultimately better patient care, researchers and dentists need to know how to accurately
characterize the electromagnetic radiation (light) they are delivering to the resins
they are using.” Overall, the present study strengthens the idea that it is very challenging
to publish and validate any research paper that does not report the full characteristics
of the studies’ LCUs.
Still, a note of caution is due here since the number of LCUs and camera devices evaluated
in this study is limited, and a more comprehensive study would include more groups.
Questions remain unanswered at present, but this study directs further studies to
pursue the development of camera gadgets and software, as well as the validation of
these devices according to the ISO standards. Continued efforts are needed to make
light beam profile and spectral analysis of the dental LCUs more accessible to dentists
in the clinical practice.
Conclusion
This study demonstrated that mirrorless and smartphone cameras are able to perform
beam profiling analysis of dental LCUs. The standard Ophir beam profile system presented
the most accurate distribution, but the mirrorless and smartphone cameras presented
a strong correlation in the irradiance distribution of the beam profile images. Specific
requirements for the camera devices such as type of sensor, image bit depth, and image
processing are important to achieve consistent results when using alternative methods
for dental LCUs beam profiling.
