BEAM PROFILE CHARACTERIZATION OF A DENTAL LIGHT CURING UNIT
USING A SPECTROMETER-BASED METHOD
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/cm 2 /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
Spectrometer-
based method Camera-based
method Spectrometer-
based method Camera-based
method Spectrometer-
based method Camera-based
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
LEDs in the head of the light is clearly visible. Using the
beam profiler and different filters the center LED was
identified to emit light blue light (420 – 495 nm) with
a peak emission at 450 nm with a high intensity (1579
mW/cm 2 ) and the four LEDs in the “corners” emitting
violet light (380 – 420 nm) with a peak emission at 390
nm, confirming measurements on other LCUs [23,27].
Furthermore it was noticed that the irradiance from the
violet LEDs was quite low (102 mW/cm 2 ) and localized
to the corners only. This discrepancy in the blue and
violet light emission could be attributed to the type of
the LED chip used to build the LCU. Despite the fact
that the majority of LED chips are violet, they appear
to be a dual in-line package (DIP) LED type, which have
much lower energy efficiency than the blue light chip
that appears to be a chip on-board (COB) LED type,
which is considered a high-powered LED chip and the
most recent development in LED LCUs. But, the fact is
that “alternative” photoinitiators such as TPO or Ivocerin
that have been used in commercial formulations are
known as high reactive photoinitiators because they
usually have higher molar extinction coefficient than
CQ. This means that these photoinitiators absorb light
88
2 mm
more efficiently than CQ at their peak wavelength
absorptions. Moreover, these photoinitiators form
more free radicals (two or more) that have higher
nucleophilicity and electron resonance than the one
amino radical formed by the CQ-amine electron donor/
hydrogen abstraction reaction. Thus, despite the less
amount of violet light being emitted by broad spectrum
LCUs, the initiation of the polymerization is effective
enough to keep the physical and chemical properties of
RBC containing “alternative” photoinitiators. However,
it is important to bear in mind that broad spectrum
LCUs typically have a ratio of 66 to 86 % of blue light
emission and 14 to 34 % of violet light emission from
the total spectral radiant power emitted [33] by the
LCU. However, the LCU used in this study had 94% of
blue light emission and 6% of violet light emission and
further investigation should be performed to check if
the LCU used in this study would efficiently cure RBC
containing “alternative” photoinitiators. Therefore, it
was decided that the impact on polymerization of
these violet emitting LEDs was low and for further
considerations we concentrated on the blue light.
In the present study, the LCU was laterally moved in a
controlled way in the x- and y-direction of a coordinated
Stoma Edu J. 2018;5(2): 84-91
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