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The performance of light emitting diode (LED) light curing units and dental radiometers

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The performance of light emitting diode (LED) light curing units and dental radiometers

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The Performance of Light Emitting Diode (LED) Light Curing
Units and Dental Radiometers
Part I: The Performance of Light Emitting Diode (LED) Light Curing Units Over Time
Part II: Comparison of Radiant Emittance of Light Emitting Diode (LED) Light Curing Units
Using Two Different Dental Radiometers

By: Reham M. Alsamman, BDS
Advisor: Dr. Jin-Ho Phark

In Partial Fulfillment of the Requirements
for the Degree of Master of Science in Craniofacial Biology
University of Southern California
August 2017
2
Table of Contents
Dedication ................................................................................................................................ 3
Acknowledgment ..................................................................................................................... 4
List of Figures and Tables ....................................................................................................... 5
Abbreviations ........................................................................................................................... 6
Chapter I: The Performance of Light Emitting Diode (LED) Light Curing Units Over Time 7
Abstract .................................................................................................................................... 8
1.1 Introduction ..................................................................................................... 10
1.2 Objective of the Study .................................................................................... 17
1.3 Material and Methods ..................................................................................... 18
1.4 Statistical Analysis .......................................................................................... 22
1.5 Results ............................................................................................................. 23
1.6 Discussion ....................................................................................................... 29
1.7 Conclusions ..................................................................................................... 32
Chapter II: Comparison of Radiant Emittance of Light Emitting Diode (LED) Light Curing
Units Using Two Different Dental Radiometers ................................................................... 33
Abstract .................................................................................................................................. 34
2.1 Introduction ..................................................................................................... 36
2.2 Objective of the Study .................................................................................... 40
2.3 Material and Methods ..................................................................................... 41
2.4 Statistical Analysis .......................................................................................... 46
2.5 Results ............................................................................................................. 47
2.6 Discussion ....................................................................................................... 49
2.7 Conclusion ...................................................................................................... 53
References .............................................................................................................................. 54
3
Dedication
I would like to dedicate this thesis to my family and friends, who have supported me throughout
this process.
To my parents, Sahar A. Brollos and Mohammed N. Alsamman, for their unconditional love and
countless sacrifices.
To my husband, Ali N. Nusair, for his unfailing support and words of encouragement. I could
never have accomplished this without you.
To my daughter, Jude A. Nusair, for bringing joy into my life.
To my sibling, Roaa, Rawabi and Nasser, for being there for me.
To my aunt, Mariam A. Brollos, and my mother-in-law, Najat Suliman, for helping me when I
needed them the most.

4
Acknowledgment
I would like to express my gratitude to my advisor Dr. Jin-Ho Phark for his guidance and support
through the learning process of this master thesis. He consistently provided me with useful
comments and guided me to the right the direction whenever he thought I needed it. Without his
valuable assistance this work would not been completed.

Beside my advisor, I would like to express my appreciation to my committee members: Dr. Sillas
Duarte, Dr. Michael Paine and Dr. Neimar Sartori for their insightful comments, encouragement,
and questions that incented me to widen my research from various perspectives.

I would like to acknowledge Colleen Azen for her hard work and valuable contributions in the
statistical analysis, and SC CTSI Biostatistics Resources for their cooperation and support.

Finally, I would also like to acknowledge the staff, faculty and co-resident in the Advanced
Operative Program of the Herman Ostrow School of Dentistry of the University of Southern
California for providing assistance and support whenever I needed it.

5
List of Figures and Tables
Figures
Figure 1.1: Absorption spectra of photoinitiators and spectral emission of LCUs ....................... 15
Figure 1.2: (A) dental radiometer (BM-I), (B) LCU positioning during the measurement (parallel
to the radiometer sensor surface) .......................................................................................... 21
Figure 1.3: The radiant emittance values of LED LCUs in relation to the age of LCUs (years of
operation) .............................................................................................................................. 25
Figure 1.4: The mean values of radiant emittance of LCUs in relation to light tip contamination
............................................................................................................................................... 26
Figure 1.5: The frequency of light tip contamination (%) of LCUs in relation to years of
operation ............................................................................................................................... 28
Figure 2.1: Handheld dental radiometers. (A) Bluephase Meter (BM-I), (B) Bluephase Meter II
(BM-II) .................................................................................................................................. 42
Figure 2.2: (A) BM-II radiometer, (B) measurement scale on the back of BM-II, (C) measuring
the light tip diameter, (D) diameter value entered into BM-II as 9mm ................................ 45
Figure 2.3: The mean radiant emittance values of BM-I and BM-II ............................................ 47
Figure 2.4: The tested LCU (VALO, Ultradent, South Jordan, UT, USA). (A) convex lens
configuration, (B) red line is the external tip diameter (13 mm), blue line is the lens
diameter (9.6 mm) ................................................................................................................. 50

Tables
Table 1.1: Terminology used to report light output measurements (4) ........................................ 11
Table 1.2: Display of four measuring cycles (from year 2013 to year 2016), the participating
classes and the age of LCUs (in years) within each cycle .................................................... 19
Table 1.3: Specifications of the dental radiometer (BM-I) as provided by the manufacturer (40)
............................................................................................................................................... 20
Table 1.4: LCUs type, manufacturer and mode in the original sample (N=1,202) ...................... 23
Table 1.5: The number of LCUs in each measuring pattern. (+) measured at that age, (-) not
measured at that age .............................................................................................................. 24
Table 1.6: The means and standard deviations of radiant emittance (mW/cm
2
) of LED LCUs
categorized by age and contamination of the tip (P-values stand for comparisons between
contaminated and contamination-free tips within each age category) .................................. 27
Table 2.1: Specifications of the dental radiometers (BM-I and BM-II) as provided by the
manufacturer (40, 67) ............................................................................................................ 43
Table 2.2: Specifications of the tested LCU as provided by the manufacturer (68) ..................... 44
Table 2.3: The means and standard deviations of radiant emittance (mW/cm
2
) of the LED LCUs
categorized device (BM-I and BM-II). (M1) measuring cycle 1, (M2) measuring cycle 2,
(M3) measuring cycle 3, (Avg1) average value of the three radiant emittance measurements
performed by BM-I, (Avg2) average value of the three radiant emittance measurements
performed by BM-II .............................................................................................................. 48

6
Abbreviations
RBC: resin based composites
CQ: camphoroquinone
PPD: phenylpropanedion
UV: ultraviolet
VLC: visible light curing
LCU: light curing unit
QTH: quartz tungsten halogen
PAC: plasma-arc light
LED: light emitting diode
BM-I: Bluephase Meter
BM-II: Bluephase Meter II
SD: standard deviation
SE: standard error
LS-Means: least squares means

7

Chapter I: The Performance of Light Emitting Diode (LED) Light
Curing Units Over Time

8
Abstract
Objectives: It is well established that conventional light curing units (LCUs) degrade over time.
However, minimal data is available on the long-term performance and degradation of modern light
emitting diode (LED) LCUs. Therefore, the aim of this study was (1) to evaluate the long-term
performance of LED LCUs used in pre-clinical and clinical settings of a dental educational
institution and (2) to evaluate the effect of contamination of the light tip of these units on the
measured radiant emittance.

Material and methods: The study was conducted at the Herman Ostrow School of Dentistry of
the University of Southern California as a part of an ongoing quality control program, which
checks the performance of LCUs that are being used in the pre-clinical and clinical courses to
ensure an optimal standard for all light cured restorations. In this study, data from year 2013 to
year 2016 were collected which represents four measuring cycles. The radiant emittance of LCUs
was measured with a handheld dental radiometer (Bluephase Meter [BM-I], Serial No. 007249,
Ivoclar Vivadent, Schaan, Liechtenstein) according to manufacturer instructions. Each LCU was
measured three times and the average value was calculated. Information about unit type (cordless
or corded), manufacturer, model, and age (in years) were recorded. Furthermore, the measurements
were repeated annually, and at each visit visual inspection was performed to evaluate light guide
tip for damage or contamination by adherent material. A total of 780 LED LCUs were included in
the statistical analysis that was performed using a repeated measures mixed model at a significance
level of α=0.05.

9
Results: A statistical difference in the radiant emittance values of the evaluated LED LCUs was
observed over time (p<0.0001). The radiant emittance measurements were significantly reduced
in year 1 compared to year 0 (p<0.0001). However, values in years 0, 2, and 3 were not
significantly different from each other (p>0.05). Contamination of the light tip significantly
decreased the radiant emittance values (p<0.0001).

Conclusion: Within the limitation of our study, the radiant emittance of LED LCUs measured by
a dental radiometer (BM-I) varied over time. However, no long-term degradation was observed
within the period of our study. The contamination of the light tip attributed to the decrease in the
radiant emittance. Therefore, it is essential to establish a periodic evaluation of LED LCU
performance as well as checking the light tip for contamination or damage.

10
1.1 Introduction
Resin based composites (RBCs) restorations have been widely used worldwide. They are
composed of three main components: a highly cross-linked polymeric resin matrix, reinforcing
filler particles, and a silane coupling agent that bonds the fillers to the matrix (1). In addition, other
components such as initiators, inhibitors and pigments are incorporated into the composite to serve
different functions (1). The early composites were chemically cured; supplied as two pastes, one
contained benzoyl peroxide as an initiator and the other an aromatic tertiary amine serving as an
activator (1, 2). When the two pastes are mixed, free radicals are formed by the reaction between
the amine and the benzoyl peroxide (1). These free radicals attack the double bonds in the resin
monomer to form a single bond cross-linked polymer network in a process called polymerization
(1). The disadvantages of the chemical cured composite were air entrapment during mixing, color
instability due to the presence of tertiary amines, and lack of control over the working time (1).
Light-activated composites were introduced to the market in 1970s to overcome the
drawbacks of chemically cured composites (2). The polymerization of this material depends on a
photosensitive initiator and a light source for activation (1). The photoinitiator becomes excited
when exposed to a light with specific wavelength, which then interacts with the amine to form free
radicals (1). When a critical concentration of free radicals is reached, polymerization reaction
occurs (1). An efficient light curing unit (LCU) is an important tool for an optimal curing process.
The performance of LCUs is usually described in terms of light intensity or power density which
is an inaccurate description (3). Additionally, there is inconsistency in the terms used by the
manufacturers and researchers when reporting the light output from LCUs (3). This led to
confusion and misunderstanding in regards to the photo-curing kinetics and requirements of light
11
cured materials (3). Table 1.1 illustrates the appropriate terminology for reporting the light output
measurements (4).
Terms Units Description
Radiant energy J Energy of electromagnetic waves
Radiant exposure J/ cm
2
Radiant energy received by a surface per unit area
(also, power density).
Radiant energy density J/ cm
3
Radiant energy per unit volume.
Radiant Power/ flux W or J/s Radiant energy per unit of time.
Irradiance mW/ cm
2
Radiant power per unit area (at some distance
away).
Radiant emittance/
exitance
mW/ cm
2
Radiant power per unit area (at zero distance).
Spectral radiant power mW/ nm Radiant power per wavelength.
Spectral irradiance mW/ cm
2
/nm Irradiance of a surface per wavelength.
Table 1.1: Terminology used to report light output measurements (4)
Characterization of the light output should consider different aspects: the exposure time,
the surface area, the distance from the emitting surface and the wavelength (3, 4). Light consists
of electromagnetic waves which transfer energy measured as “radiant energy”. When this radiant
12
energy is received by a certain surface area, it is described as “radiant exposure”. The volumetric
energy deposition is described as “radiant energy density”. Additionally, the light energy can be
measured in relation to time as “radiant power”. When radiant power is received by a surface area
at zero distance, it is described as “radiant emittance”. If there is some distance between the light
source and the irradiated surface area, it is described as “irradiance”. Furthermore, the irradiance
of a surface in relation to the wavelength is described as “spectral irradiance”. And, the radiant
power per the wavelength is known as “spectral radiant power” (3, 4).
For understanding of the polymerization process of resin based composite in-depth, one
must know the different aspects that might relate to the complete process. Besides, the efficiency
of LCUs, many other factors have an effect on the polymerization of RBC such as the resin
monomer type (5), the filler size and distribution (6), the shade of the composite, and its
translucency (6). Additionally, the polymerization of RBC is influenced by the thickness of the
cured increment (7, 8), the distance between the light tip and the restoration (9, 10), the curing
time (10), the light output, and the wavelength (7).
The activation of the photoinitiator in RBCs occurs at specific a wavelength that should
match the absorption spectrum of the material (11). Many types of photoinitiators are used in RBCs
such as camphoroquinone (CQ), lucirin TPO, phenylpropanedion (PPD) and ivocerin (7, 12). The
most common photoinitiator in light-activated composites is CQ (13) which has an absorption
curve lies between 410- 500 nm (14). Due to the yellowish color of CQ, other photoinitiators such
as Lucirin TPO and phenylpropanedion (PPD) were incorporated into RBCs (7, 15). These
initiators have absorption spectra between 350-430 nm and 360-480 nm respectively (14). A light
source with a narrow emission spectrum will activate the camphorquinone (CQ), but not the other
photoinitiators which require a light source with a broader spectral emission (16).
13
Evolution in restorative dentistry requires constant improvement in the materials as well as
the techniques and technology. The first light source used for curing resin materials was ultraviolet
(UV) light (17). This light utilized a wavelength of 365 nm with limited penetration depth into the
restoration causing shallow polymerization (18). UV light has a potential harm on the eye and soft
tissues (19). Therefore, it was discontinued and replaced by the visible light curing (VLC) units.
The main commercially available light curing unit (LCU) types are: quartz tungsten halogen
(QTH), plasma-arc light (PAC), argon ion laser, and light emitting diode (LED) (18).
In late 1970s, quartz tungsten halogen (QTH) light was introduced. It uses incandescent
tungsten filament and halogen gas (7). The presence of halogen gas causes the evaporated tungsten
to redeposit to the filament maintaining the light output (7). QTH light emits UV and white light
which must be filtered to irradiate light in the violet-blue range (400 to 500 nm) (20). This broad
spectral emission is able to activate all types of photoinitiators that are present in current RBCs
(16, 18, 21). The main drawbacks of QTH are heat generation, the need for filters, and a ventilating
fan that make the device heavy and less energy efficient (22).
Plasma-arc (PAC) light uses a fluorescent bulb containing xenon gas that ionizes and
produces plasma (18). It emits white light, which is filtered to emit only blue light ranging between
400 to 500 nm in wavelength (18, 21). The disadvantages of this unit are similar to those of QTH:
heat, the need for filters and fan, and the low energy performance (16). Another type of light curing
unit is powered by argon laser. It is based on the stimulation of excited atoms (argon gas), which
tend to release energy in the form of electromagnetic radiation (18). These intense units emit light
in the blue range and do not require filters (16). However, they are very expensive.
Light emitting diode (LED) units are based on the electroluminescence of light by the use
of gallium nitride semiconductor material that generates blue light without the need of filters (18)
14
LED units have a longer life span, more consistent output, less power consumption, and produce
less heat than QTH curing units (23). The reduced heat generation eliminated the need of the
cooling fan which resulted in the development of battery powered cordless LCUs (7). In 2000, the
first generation of LED LCUs was made commercially available. It generates light in the blue
range using multiple LED chips (21). However, it was lower powered compared to the
conventional QTH (21). Thus, in the second generation of LED LCUs, the multiple discrete LED
chips were replaced with a more powerful single LED (21). Both, first and second generations of
LED LCUs (conventional LED LCUs) have a narrow emission spectrum that coincides with the
absorption of camphorquinone (CQ) only, but not with that of other photoinitiators (18, 21).
Therefore, in a third generation of LED LCUs an additional LED chip that emits light in the violet
range in addition to the blue range was added. Such lights are also referred to as “polywave” lights
(21). The broader spectral emission of light (380-500 nm) makes these LCUs compatible with all
photoinitiators in RBCs (18, 21). Figure 1.1 shows the spectral emission of different LCUs and the
absorption spectra of different photoinitiators.

15

Figure 1.1: Absorption spectra of photoinitiators and spectral emission of LCUs
In addition to the different spectral emission of light, LCUs have different curing modes
with different radiant emittance that influence the polymerization process (24). Manufacturers
introduced various names for the light curing modes, but generally they can be classified into
continuous or discontinuous light curing techniques (25). The dentist should set the LCU to the
appropriate curing mode with sufficient radiant emittance and the correct wavelength to cure the
RBCs properly (25). For sufficient polymerization of RBCs, some studies (26, 27) reported a
minimum radiant emittance of 400 mW/cm
2
, while others recommended a minimum of 600
mW/cm
2
(28).
The radiant emittance of LCUs can be affected by resin contamination of the light tip (29),
sterilization of the light guide (30, 31), and degradation of LCU’s components (29). It is well
established that the performance of QTH lights reduce over time which can be a result of
degradation of the bulb, the reflector, or the filters (32, 33). Additionally, voltage fluctuations or
16
disruption of the fiber optic bundle can be considerable causes (33, 34). Most of halogen bulbs are
expected to last between 40 to100 hours of constant use (23, 35). On the other hand, LED lights
can last longer, up to 100,000 hours without significant reduction of the light output (23, 35).
The degradation mechanism of LED lights is different than that of other conventional light
sources (36). QTH lights fail instantly as a result of the tungsten filament becoming thinner and
stiffer over time until they reach a point of breakage (32). On the other hand, LED lights fail
gradually until they reach a point where they emit only 70% of their initial output (37). So, it is
still producing light, but at a lower level. The causes of failure in the LED LCUs can be either
structural defects, thermal stresses, or electrical stresses on the LED chip (37, 38). High voltage
and elevated temperature accelerate the LED chip degradation causing reduction in the light output
(37). Although LED units are designed to have reliable and consistent performance, routine
evaluation of their performance is still needed (39).

17
1.2 Objective of the Study
As any light source, LED LCUs can degrade over time. However, no data is available
regarding the long-term performance of these LCUs. Therefore, the aim of this study was (1) to
evaluate the long-term performance of LED LCUs used in pre-clinical and clinical settings of a
dental educational institution and additionally (2) to evaluate the effect of contamination of the
light tip of these units on the measured radiant emittance.

The null-hypotheses of this investigation were:
(1) There is no significant difference in the radiant emittance values of LED LCUs over time.
(2) There is no significant difference in the radiant emittance values of LED LCUs regardless of
contamination of the light tip.

18
1.3 Material and Methods
The study was conducted at the Herman Ostrow School of Dentistry of the University of
Southern California as a part of an ongoing quality control program, which checks the performance
of light curing units (LCUs) that are being used in the pre-clinical and clinical courses to ensure
an optimal standard for all light cured restorations. Usually, each dental student receives a brand
new LED LCU at the beginning of the first academic year and continues to use the same LCU
throughout the next four years of dental education. Therefore, the program is conducted annually
in the fall trimester shortly after the begin of the new academic year. For this purpose, a complete
list of all current dental students of each academic year is obtained. The students are then contacted
via email explaining the purpose of the project as well as the designated time and location for the
measurements. Each LCU is then identified by the corresponding student’s identification number.
For standardization of the measurements, the investigators are retrained and recalibrated annually
before each measuring cycle.
In this study, data from year 2013 to year 2016 were collected, which represents four
measuring cycles. Each measuring cycles included four classes of current students representing
the four academic years. Due to the nature of the academic institution with the senior class
graduating and a new freshmen class entering each year, only one class had completed the four
measuring cycles (Class of 2017) in this data set. Two classes participated in three measuring
cycles (class of 2016, and class of 2018), two classes participated in two cycles (class of 2015 and
class of 2019) and two classes had only one measuring cycle (class of 2014 and class of 2020).
Table 1.2 displays the four measuring cycles with the different academic years that were measured
throughout this time frame. Once the students graduate, their LCUs are not monitored through this
program anymore.
19

Participating
Classes
Cycle 1
(Year 2013)
Cycle 2
(Year 2014)
Cycle 3
(Year 2015)
Cycle 4
(Year 2016)
Total #
of Cycles
Class of 2014 (age 3) 1
Class of 2015 (age 2) (age 3) 2
Class of 2016 (age 1) (age 2) (age 3) 3
Class of 2017 (age 0) (age 1) (age 2) (age 3) 4
Class of 2018 (age 0) (age 1) (age 2) 3
Class of 2019 (age 0) (age 1) 2
Class of 2020 (age 0) 1
Table 1.2: Display of four measuring cycles (from year 2013 to year 2016), the participating
classes and the age of LCUs (in years) within each cycle
During the period of the study, a total of 1,202 LCUs were measured. All evaluated LCUs
were LED powered. Information about each LED LCU was recorded, including the unit type
(corded or cordless), manufacturer, model, and age (in years). Additionally, a visual inspection of
the light tip was performed to assess damage or contamination by adherent materials or debris.
Presence of contamination was recorded either as “Yes” or “No”. Degree and type of
20
contamination were not recorded. Battery-operated LCUs had to be fully charged before being
tested. Also, all LCUs were set to a standard power mode for the testing.
A handheld dental radiometer (Bluephase Meter [BM-I], Serial No. 007249, Ivoclar
Vivadent, Schaan, Liechtenstein) was used to measure the radiant emittance (mW/cm²) of each
curing light unit (Table 1.3). The radiometer that was used in this study measures the radiant
emittance in a range from 300 to 2,500 mW/cm² within a wavelength range from 385 to 515 nm
(40). The device automatically switches on at a radiant emittance of at least 300 mW/cm². A
measurement lower than that will be indicated with "----" on the display (40). BM-I measures both,
QTH and LED LCUs (40). However, it can only measure LCUs with circular emission that have
tip diameter of 7-13 mm (40).
Bluephase Meter (BM-I)
Manufacturer Ivoclar Vivadent, Schaan, Liechtentstein
Wavelength range 385-515 nm
Radiant emittance range 300-2,500 mW/cm
2

Aperture size ∅ 7-13 mm
Compatible LCUs QTH and LED
Accuracy ±20%
Table 1.3: Specifications of the dental radiometer (BM-I) as provided by the manufacturer
(40)
21
Measurements were performed according to the manufacturer’s instructions (40): The light
tip was placed in contact with and parallel to the radiometer sensor surface (Figure 1.2). Then, the
LCU was switched on until a static reading was displayed. Each LCU was measured three times
and the average value was calculated. For the quality control program, a minimum of 600 mW/cm
2
was considered acceptable (28). Each LCU with radiant emittance ≥600 mW/cm
2
was certified
with numbered sticker. Students with LCUs of radiant emittance <600 mW/cm
2
were asked to
get their units repaired or replaced until they met the standard required by the program. The same
measurement procedure was repeated annually at the fall trimester for 4 years.

Figure 1.2: (A) dental radiometer (BM-I), (B) LCU positioning during the measurement
(parallel to the radiometer sensor surface)

22
1.4 Statistical Analysis
For statistical analysis, not all data could be included. While the original sample size was
1,202 LED LCUs, some data sets were not included in the analysis. The exclusion process was in
the following order and for the following reasons:
(1) Data entry errors (n=4)
(2) LCUs that only participated in one measuring cycle (n=255).
(3) LCUs that only have two consecutive measurements with no initial (year 0)
measurement (n=150).
(4) From the remaining samples, all cordless LED LCUs (originally 44 cordless
LED LCUs were measured, but after applying exclusion rules (1), (2), and (3),
only 1.4% (n=13) remained at the end.).
Therefore, the statistical analysis included only 780 LED LCUs. Repeated measures
ANOVA could not be used due to the presence of some missing measurements. A repeated
measures mixed model and least squares means (LS-means) were used in the analysis as they can
deal with missing data.
Individual measurements of radiant emittance and the average of the triplicate measures
were summarized with standard statistics (mean, standard deviation [SD], standard error [SE],
median, minimum and maximum), at each age (year 0, year 1, year 2, and year 3) and by
contamination (yes and no). Statistical analyses were performed with SAS/STAT v9.2 software
(SAS Institute Inc, Cary, NC, USA) at significance level of α= 0.05. The effect of the LCU’s age
and tip contamination on the radiant emittance were analyzed by a repeated measures mixed model
with age and contamination as fixed effects, LCUs as a random effect, and the average of triplicate
measurements at each age as the dependent variable.
23
1.5 Results
The original sample size consisted of 1,202 LCUs. The majority were corded VALO LCUs
(Ultradent, Jordan, UT, USA), but other different models were also present in the original sample
as described in Table 1.4. Most of the students owned corded LED LCUs (n=1,157), while a few
owned cordless LED LCUs (n=44). For the purpose of making the data statistically manageable,
some data sets were excluded as described in the previous section resulting in only 780 LED LCUs
of the same model (VALO, Ultradent, Jordan, UT, USA) to be included in the statistical analysis.
Model Manufacturer Type of LCU Number
VALO Ultradent, Jordan, UT, USA LED Corded 1,157
VALO Cordless Ultradent, Jordan, UT, USA LED Cordless 1
Radii Plus SDI, Bayswater, VIC, Australia LED Cordless 9
G-Light GC America, Tokyo, Japan LED Cordless 1
Elipar FreeLight 2 3M ESPE, St. Paul, MN, USA LED Cordless 1
Bluephase 20i Ivoclar Vivadent, Schaan,Liechtenstein LED Cordless 1
Allegro Dent-Mat, Santa Maria, CA, USA LED Cordless 4
Unknown Unknown LED Cordless 28
Table 1.4: LCUs type, manufacturer and mode in the original sample (N=1,202)
24
This study included four measuring cycles that were designed to measure the radiant
emittance of LCUs of different ages (year 0, year 1, year 2 and year 3). Only 16.2 % (n=126) of
the sample were measured from year 0 to year 3. 16.8 % (n=131) of LCUs were measured from
year 0 to year 2, and 36.5 % (n=285) from year 0 to year 1. Furthermore, 30.5 % of the sample
(n=238) were not measured at year 0 of age, and were measured from year 1 to year 3. These
measuring patterns are displayed in Table 1.5.
Measuring patterns Number of LCUs Percentage (%)
+ + + + 126 16.2
+ + + − 131 16.8
+ + − − 285 36.5
− + + + 238 30.5
Total 780 100
Table 1.5: The number of LCUs in each measuring pattern. (+) measured at that age, (-) not
measured at that age
The effect of age of LED LCUs on the radiant emittance:
As shown in Figure 1.3, the radiant emittance values differ over time (p<0.0001). The
radiant emittance of LCUs was significantly higher in year 0 than year 1 (p<0.0001), but not
significantly different than in year 2 and year 3 (p>0.05). Moreover, the radiant emittance values
25
in year 1 were statistically lower than those in year 2 and year 3 (p<0.0001). There was no
statistical difference between measurements in year 2 and year 3 (p>0.05).

Figure 1.3: The radiant emittance values of LED LCUs in relation to the age of LCUs (years
of operation)
The effect of light tip contamination on the radiant emittance:
The statistical analysis reported a significant influence of the contamination of the light tip
on the measured radiant emittance values (p<0.0001). The radiant emittance of LCU decreased in
the presence of resin contamination, regardless of the degree of contamination, in all years (Figure
1.4).

26

Figure 1.4: The mean values of radiant emittance of LCUs in relation to light tip
contamination
The mean radiant emittance values and standard deviation (SD) are displayed in Table 1.6.
For LCUs with tip contamination, the mean values were 807.8 ± 98.6 at age 0, 786.9 ± 97.1 at age
1, 804.1 ± 85.6 at age 2, and 808.2 ± 82.8 at age 3. LCUs with no contamination presented mean
values of 872.3 ± 94.6 at age 0, 810.5 ± 92.5 at age 1, 865 ± 100.3 at age 2 and 866.2 ± 87 at age
3.

27
Table 1.6: The means and standard deviations of radiant emittance (mW/cm
2
) of LED LCUs
categorized by age and contamination of the tip (P-values stand for comparisons between
contaminated and contamination-free tips within each age category)
Furthermore, 71.9 % (n=561) of the tested LCUs reported as contaminated at least one time
during the study period. The least number of contaminated LCUs was at year 0 (11.8 %), the
number increased to 54.7 % in year 1, and 50% in year 2 and year 3 (Figure 1.5).
Age Contamination N Mean SE Med Min Max LS-Mean SE P-value
Year
0
Yes 64 807.8 ± 98.6 12.3 800 613.3 1016.7 801.86 10.3648
<0.0001
No 478 872.3 ± 94.6 4.3 856.7 663.3 1143.3 869.34 4.0292
Year
1
Yes 427 786.9 ± 97.1 4.7 793.3 603.3 1153.3 780.31 4.2305
<0.0001
No 353 810.5 ± 92.5 4.9 796.7 620 1060 818.42 4.5838
Year
2
Yes 246 804.1 ± 85.6 5.5 806.7 610 1076.7 802.6 5.3407
<0.0001
No 249 865 ± 100.3 6.4 866.7 586.7 1096.7 837.58 5.2595
Year
3
Yes 182 808.2 ± 82.8 6.1 803.3 613.3 1016.7 801.67 6.0807
<0.0001
No 182 866.2 ± 87 6.4 863.3 646.7 1043.3 839.14 6.0441
28

Figure 1.5: The frequency of light tip contamination (%) of LCUs in relation to years of
operation
29
1.6 Discussion
This study was conducted to evaluate the long-term performance of light emitting diode
(LED) light curing units (LCU), and to demonstrate the effect of the light tip contamination on the
radiant emittance values. The first null hypothesis proposed that the age of LCU does not have a
significant effect on its radiant emittance value. This null hypothesis was partially rejected as the
results showed a statistical difference in the radiant emittance values measured over time. A
significant reduction in the radiant emittance measurements was observed at year 1 of age.
However, the radiant emittance values were similar at year 0, year 2, and year 3 of age (Figure
1.3).
It is well established that the performance of halogen (QTH) and plasma arc (PAC) lights
decrease over time (32, 33). This reduction in output is a result of degradation of the unit’s internal
components as the reflector, the bulb and the filters (32, 33). Other reasons for lowering the light
output may include contamination of the light tip with debris or restorative materials (29),
autoclaving of the light guide (30) or using certain disinfectants (31). On the other hand, LED
LCUs differ in the mechanism of degradation, which is mainly caused by heat (41). The new LED
units operate at a lower temperature to prevent LED chips degradation over time (42). For example,
the tested LCU (VALO, Ultradent, South Jordan, UT, USA) is designed to be more efficient and
degrade less over its life expectancy (42). It has a ceramic heat transfer device and delivers one-
third to one-half of its ability to avoid overheating (42). In addition, it uses a rhodium plated
reflector as rhodium will not degrade with time (42). All of these features are added to improve
the long-term performance of the LED LCUs.
LED lights are expected to last longer time compared to other types of lamps (43, 44).
Several studies have reported that QTH units present inadequate light output after three years of
30
operation (44, 45). compared to six years of operation for LED units (44). Our study tested LED
LCUs at a time frame that did not exceed the three years of operation. This explains the statistically
similar values of radiant emittance at years 0, 2, and 3. The drop in radiant emittance at year 1
could be associated with the high percentage of tip contamination at this time, compared to the rest
of the years (Figure 1.5). It is possible that the reduced radiant emittance would improve by
eliminating the tip contamination that blocks the light. However, the present study did not quantify
the amount of contamination on the light tip and did not record the effect of cleaning the light tip
on the measured radiant emittance.
The second null hypothesis stated that light tip contamination does not have a significant
impact on the radiant emittance measurements of LED LCUs. This hypothesis was rejected as our
results confirmed that the tip contamination with adherent materials will lower the radiant
emittance of the tested LED LCUs. This result is in agreement with other studies that reported that
the light output is significantly affected by resin contamination of the light tip as well as damage
or chipping of the light tip (43, 46). In addition, our results show that 72% of the tested LCUs had
tip contamination at least one time during the study period. This high percentage raises a concern
as this tip contamination will affect the photo-curing process and the quality of the delivered
restorations. Thus, checking the light tip condition for contamination or damage is recommended
to be part of the quality control program in addition to monitoring the light output. Furthermore,
disposable, translucent barrier materials should be used to avoid contamination of the light tip.
A laboratory-grade meter is the gold standard for testing the light output of LCUs (47).
However, it is impractical for use in dental offices. Instead, a dental radiometer can be used in a
clinical setting to evaluate the performance of LCUs over time (41, 48, 49). It has a limited
accuracy but it can provide relative information regarding the radiant emittance of LCUs (41, 48,
31
49). To limit the variability and inaccuracy of dental radiometers, the current study used the same
dental radiometer (Bluephase Meter [BM-I], Serial No. 007249, Ivoclar Vivadent, Schaan,
Liechtenstein) to measure the radiant emittance of all LCUs throughout the study period.

32
1.7 Conclusions
Within the limitation of our study, the radiant emittance of LED LCUs measured by a
dental radiometer (BM-I) varied over time. However, no long-term degradation was observed
within the period of our study. The reduced radiant emittance was mostly attributed to the
contamination of the light tip. Therefore, it is essential to establish a periodic evaluation of LED
LCU performance as well as checking the light tip for contamination or damage.

33

Chapter II: Comparison of Radiant Emittance of Light Emitting
Diode (LED) Light Curing Units Using Two Different Dental
Radiometers

34
Abstract
Objective: Dental radiometers are not regarded as the gold standard in measuring the light output
of light curing units (LCUs). However, a recently introduced dental radiometer (Bluephase Meter
II [BM-II], Ivoclar Vivadent, Schaan, Liechtenstein) has improved features that are supposed to
overcome the deficiencies of conventional dental radiometers. Therefore, the aim of this study was
to compare the performance of a dental radiometer (Bluephase Meter [BM-I], Ivoclar Vivadent,
Schaan, Liechtenstein) with its upgraded version (BM-II) when measuring the radiant emittance
of light emitting diode (LED) light curing units (LCUs).

Material and methods: The study was conducted at the Herman Ostrow School of Dentistry of
the University of Southern California as a part of an ongoing quality control program. The radiant
emittance of 142 brand new LED LCUs (VALO, Ultradent, South Jordan, UT, USA) was
measured with two different dental radiometers (Bluephase Meter [BM-I], Serial No. 007249 and
Bluephase Meter II [BM-II], Serial No. 1300000032, Ivoclar Vivadent, Schaan, Liechtenstein)
according to manufacturer instructions. Each LCU was measured three times using both dental
radiometers, followed by calculating the average values. Statistical analysis using a repeated
measures mixed model was performed to compare the measured radiant emittance values from the
two dental radiometers at a significance level of α=0.05.

Results: A significant difference was found between the radiant emittance values measured by
BM-I and BM-II (p<0.0001). Measurements of both devices presented a large variation of up to
500 mW/cm
2
with no overlap. Overall, the radiant emittance values measured with the BM-II were
higher than those measured with the BM-I.
35

Conclusion: Within the limitations of the present study, it was determined that the two dental
radiometers (BM- and BM-II) significantly differ in the measurement of LED LCUs. Dental
radiometers still do have limitations, so they are only recommended for tracking the performance
of the same LCU over time. A laboratory grade meter is still the gold standard for light output
measurement.

36
2.1 Introduction
The advances in adhesive and esthetic dentistry increased the demands for efficient and
reliable light curing units (LCUs) which are used to polymerize the light activated restorative
materials. A suboptimal polymerization can result in inferior mechanical properties of the
restoration (50, 51), lower bond strength (51, 52) and early failure of the delivered restoration (14,
26). Many factors that influence the polymerization of the materials are related to the photo-curing
process including: the curing mode, curing time, light output, wavelength, and the distance of the
light tip from the restoration (53, 54). Several studies tested the performance of LCUs worldwide
and determined insufficient light output in many dental offices which might affect the quality of
the delivered restorations (43, 44, 55). The majority of dentists never checked the performance of
their light curing units (44, 56). Even though multiple devices are available for measuring the light
output, e.g., integrating spheres, thermopiles, spectrometers, and radiometers; all can be used in
laboratory and/or clinical settings (57).
The integrating sphere is an optical device used to determine the absolute radiant power. It
consists of a hollow sphere with an internal reflective coating and small apertures for entrance and
exit ports (18). It measures the radiant power in Watt independent of the diameter of the LCU tip
with an accuracy of ±5% (18). Another instrument that measures the radiant power is thermopile.
It is a device that converts thermal energy into electrical energy. It is composed of connected
thermocouples that response to absorption of radiant energy in a linear matter (18). Both devices
only determine the radiant power (mW) irrespective of the area of the light tip (18). To take
different sizes of light tips into consideration, the radiant emittance (mW/cm
2
) can be calculated,
after measuring the light tip diameter, by dividing the radiant power per surface area of the light
tip.
37
Besides the surface area of the light tip, the spectrum of the emitted light is also of
importance for the characterization of the overall light output (3). Certain devices, such as
spectrometers, consider the spectral emission when measuring radiant power. They do report the
spectral radiant power (mW/nm) of light as the light is focused on its entrance slit, dispersed and
registered at different wavelengths. Spectrometers measure which wavelengths a material absorbs
and which wavelengths it reflects (57). Another device is a spectroradiometer that measures the
spectral power distribution expressed as spectral irradiance (mW/ cm2/nm) and spectral radiant
power (mW/nm) (18).
The integrating sphere connected to spectroradiometer is considered as the gold standard
for testing LCUs, since it can measure the radiant power (mW) and the spectral radiant power
(mW/nm) (47). An alternative method is to use a laboratory grade thermopile that measures the
radiant power (mW) (47). These laboratory grade power meters are expensive and impractical for
use in dental offices. Instead, dental radiometers can be used to regularly monitor the output of
light curing units in clinical settings (41, 48, 49, 58).
A dental radiometer is a device that contains silicon or selenium photodiodes. It converts
incoming light into an electric current, which is then displayed by an analogue or digital meter to
report the radiant emittance of the curing light (48). Typically, the main components in a dental
radiometer are the port, diffusers, filters, a detector (photodiodes) and a display (42). It is
commercially available in two forms; handheld radiometers and integrated in LCUs. Although, it
is relatively inexpensive and easy to use, only less than 30% of dentists reported using a radiometer
in their dental offices (56).
Dental radiometers differ in the measured wavelength range, the power output range, and
the aperture diameter range. Furthermore, radiometers can be divided into two categories based on
38
the light source: halogen-based and LED-based radiometers. Both types of radiometers have
bandpass filters that limit the measurement to wavelengths of approximately 400 to 500 nm (49).
While LED-based radiometers are calibrated to a narrow-band LED light source, halogen-based
radiometers are calibrated to a wider-range halogen light source (49). Therefore, only the
appropriate type of radiometer should be used depending on the measured light source.
Dental radiometers are widely used for regular check-ups of LCUs, as it provides relative
information on the decrease in light output over time (41, 48, 49, 58). However, several studies
reported that the accuracy of dental radiometers remains questionable (34, 41, 48, 49, 58). This
inaccuracy could be attributed to several factors related to the radiometer itself, but also the
measured LCU. Variability in the original calibration of the radiometer and the device degradation
over time have an effect on the accuracy (48). The differences in the type, size and aperture of the
sensor between different radiometers also influence the recorded results (49). Furthermore, the
light tip diameter (59) and the light spectral emissions (49) affect the radiometer readings.
Dental radiometers have some limitations as they do not record the radiant power or the
emission spectrum that is emitted from the LCU (18, 60). These devices only provide an indication
of radiant emittance measured at zero distance, which is not an indicator of light performance when
held at a distance from the restoration (18, 61, 62). Since the intensity of light is inversely
proportional to the square of the distance from the light source (inverse-square law) (63). Also,
inhomogeneous light distribution in some LCUs (64-66) accompanied with the narrow aperture
into the detector of certain radiometers (48) results in different values depending on the position
of the light tip over the radiometer (60). In addition, dental radiometers calculate the radiant
emittance based on the area of their fixed apertures, neglecting the effect of light tip diameter (49).
39
In an attempt to overcome the aforementioned limitations of commercially available
radiometers, the company Ivoclar Vivadent introduced modified radiometers. The first version of
this device (Bluephase Meter [BM-I], Ivoclar Vivadent, Schaan, Liechtenstein) can accommodate
different light tip diameters ranging between 7 to 13 mm (40). Its wider wavelength range (385-
515 nm) enables it to measure QTH and LED LCUs with a radiant emittance ranging from 300 to
2,500 mW/cm² (40). The BM-I uses linear sensors to determine the diameter of the radiating
surface. Based on this data, an integrated micro-processor calculates the radiant emittance
(mW/cm²) with an accuracy of ±20% compared to laboratory grade power meters (40, 48).
The second version (Bluephase Meter II [BM-II], Ivoclar Vivadent, Schaan, Liechtenstein)
can measure both, the radiant power in mW and the radiant emittance in mW/cm² (67). It has a
measurement scale on the back of the device for measuring the light tip diameter which is entered
into the meter software to calculate the radiant emittance. The manufacturer claims that this
radiometer can measure the light with wavelengths from 380 to 550 nm and radiant emittance from
300 to 12,000 mW/cm² (67). It is compatible with all types of curing lights, including LED, QTH,
PAC, and laser LCUs, with tip diameters between 5-13 mm (67). The BM-II reported to be the
most accurate radiometer with an accuracy of ±10% compared to a laboratory grade meter (60, 67)
40
2.2 Objective of the Study
The recently introduced dental radiometer (BM-II) has improved features to overcome the
limitations of the conventional dental radiometers. However, only limited data is available
regarding its performance. Therefore, this study was conducted to compare two different
radiometers (BM-I and BM-II) by measuring the radiant emittance values of LED LCUs.

The null-hypothesis of this study was:
There is no significant difference between the radiant emittance values measured by
Bluephase Meter and those of Bluephase Meter II.

41
2.3 Material and Methods
The study was conducted at the Herman Ostrow School of Dentistry of the University of
Southern California as a part of an ongoing quality control program, which checks the performance
of light curing units (LCUs) that are being used in the pre-clinical and clinical courses to ensure
an optimal standard for all light cured restorations as described in chapter I. In this study, only
students in the first academic year (class of 2020) were included. For this reason, all students were
contacted via email explaining the purpose of the project, the designated time and location where
the measurements will take place. Each LCU was identified by the corresponding student’s
identification number. The investigator was trained and calibrated to ensure standardization of the
measurements.
In contrast to the measurements of LED LCUs in chapter I, LCUs of students in this study
were evaluated with two handheld dental radiometers (Figure 2.1) to measure the radiant emittance
in mW/cm²; (Bluephase Meter [BM-I], Serial No. 007249 and Bluephase Meter II [BM-II], Serial
No. 1300000032, Ivoclar Vivadent, Schaan, Liechtenstein).The BM-I measures radiant emittance
ranging from 300 to 2500 mW/cm² and within a wavelength of 380 to 515 nm (40). The device
automatically switches on at a radiant emittance of at least 300 mW/cm² (40). A lower
measurement will not be recorded. It measures both, QTH and LED LCUs (40). However, it can
only measure circular emission with a diameter up to 13 mm (40).
42

Figure 2.1: Handheld dental radiometers. (A) Bluephase Meter (BM-I), (B) Bluephase
Meter II (BM-II)
The BM-II represents the latest version of dental radiometers manufactured by Ivoclar
Vivadent. It can measure the radiant power in mW and the radiant emittance between 300 and
12,000 mW/cm² of all types of curing units (LED, QTH, PAC, and laser) (67). It has a slightly
wider measuring range regarding the wavelength (380-550 nm) and can accommodate circular
light tips with a diameter of up to 13 mm (67). The details of both dental radiometers are
summarized in Table 2.1.

43
Bluephase Meter (BM-I) Bluephase Meter II (BM-II)
Manufacturer
Ivoclar Vivadent, Schaan
Liechtenstein
Ivoclar Vivadent, Schaan
Liechtenstein
Wavelength range 385-515 nm 380-550 nm
Radiant emittance
range
300-2,500 mW/cm
2
300-12,000 mW/cm
2

Aperture size ∅ 7-13 mm ∅ 5-13 mm
Compatible LCUs QTH and LED QTH, LED, PAC, laser
Accuracy ±20% ±10%
Measurement Radiant emittance
Radiant emittance
Radiant power
Table 2.1: Specifications of the dental radiometers (BM-I and BM-II) as provided by the
manufacturer (40, 67)
Both dental radiometers were used to measure the radiant emittance of a total of 142 LED
LCUs, which were of the same type and model (VALO, Ultradent, South Jordan, UT, USA) (Table
2.2). Besides being new with no record of use they also showed no contamination or damage of
the light tip. Before measurement, all LCUs were set to the standard power mode. All
measurements were performed using the two different radiometers according to the manufacturer’s
instructions as outlined below.
44
VALO LED LCU
Manufacturer Ultradent, South Jordan, UT, USA
Type of LCU
Polywave LED (Corded)
Wavelength range 395–480 nm
Light output range
Standard power 1,000 mW/cm
2

High power 1,400 mW/cm
2

Xtra power 3,200 mW/cm
2

Timing program Adjustable (3 to 20 s)
Lens diameter 9.6 mm
Table 2.2: Specifications of the tested LCU as provided by the manufacturer (68)
First, the LCUs were measured with the BM-I, the LCU tip was placed in contact with and
parallel to the radiometer sensor surface. Then, the LCU was switched on until a static reading was
displayed. And, the radiant emittance was recorded. Each LCU was measured three times and the
average was calculated. For the quality control program, a minimum of 600 mW/cm² was
considered acceptable (28). Each LCU with radiant emittance ≥600 mW/cm² was certified with
numbered sticker. Students with LCUs of radiant emittance <600 mW/cm² were asked to get
their devices repaired or replaced until they met the standard required by the program.
After measuring the LCU with the BM-I, the LCU was cooled off for 10 seconds before
being measured with the BM-II in the same way as with the BM-I. The only difference was that
45
the diameter of the LCU tip was measured using a scale on the back of the radiometer, and was
entered as 9 mm into the BM-II before starting the radiant emittance measurements (Figure 2.2).
Again, each LCU was measured three times and the average value was calculated.

Figure 2.2: (A) BM-II radiometer, (B) measurement scale on the back of BM-II, (C)
measuring the light tip diameter, (D) diameter value entered into BM-II as 9mm
46
2.4 Statistical Analysis
A total 142 LED LCUs of the same type and model were included in the statistical analyses
that were performed with SAS/STAT v9.2 software (SAS Institute Inc, Cary, NC, USA) at a
significance level of α= 0.05. Individual measurements of radiant emittance and the average of
triplicate measures were summarized with standard statistics (mean, standard deviation [SD],
standard error [SE], median, minimum and maximum) by device (dental radiometer).
The comparison between the two dental radiometers (BM-I and BM-II) used a repeated
measures mixed model with radiant emittance measurements (3 measurements per radiometer for
each light curing unit) as the dependent variable, the radiometer device as a fixed effect and light
curing unit as a random effect.
47
2.5 Results
The mean values of radiant emittance were 847 ± 58.1 mW/cm
2
for BM-I and 1348 ± 44.0
mW/cm
2
for BM-II (Figure 2.3). When comparing the radiant emittance results obtained by BM-I
and BM-II, there was a large difference between the two devices of up to 500 mW/cm
2
with no
overlap in the readings of both devices. Overall, the radiant emittance values from BM-II were
higher than those of BM-I. Statistical analysis using a repeated measures mixed model found a
significant difference (p<0.0001) between the radiant emittance values measured by BM-I and
BM-II. The data obtained are presented in Table 2.3.

Figure 2.3: The mean radiant emittance values of BM-I and BM-II

48
Variable Mean SE Med Min Max LS-Mean SE
BM-I
M1 845.9 ± 58.1 4.9 850.0 640.0 960.0
M2 848.1 ± 59.9 5.0 850.0 650.0 960.0
M3 848.7 ± 61.2 5.1 860.0 650.0 960.0
Avg1 847.6 ± 58.1 4.9 853.3 646.7 960.0 847.56 3.7
BM-II
M1 1350.4 ± 43.7 3.7 1345.0 1240.0 1510.0
M2 1347.1 ± 44.9 3.8 1340.0 1240.0 1500.0
M3 1347.5 ± 44.8 3.8 1340.0 1250.0 1490.0
Avg2 1348.3 ± 44.0 3.7 1343.3 1243.3 1493.3 1348.3 3.7
Table 2.3: The means and standard deviations of radiant emittance (mW/cm
2
) of the LED
LCUs categorized device (BM-I and BM-II). (M1) measuring cycle 1, (M2) measuring cycle
2, (M3) measuring cycle 3, (Avg1) average value of the three radiant emittance
measurements performed by BM-I, (Avg2) average value of the three radiant emittance
measurements performed by BM-II
49
2.6 Discussion
This study was conducted to compare the performance of two dental radiometers, the
Bluephase Meter (BM-I) and the Bluephase Meter II (BM-II). The null hypothesis was rejected as
the results of our study presented a significant difference between the radiant emittance
measurements obtained by BM-I and BM-II. The radiant emittance readings from both dental
radiometers did not overlap. Overall, the measurements obtained by BM-II were higher than those
of BM-I.
The origin of inaccuracy of dental radiometers has not been completely understood.
However, it is well established that the LCU tip diameter has an impact on the measured radiant
emittance (59). Shimokawa et al. reported that Bluephase Meter II and LEDEX CM4000 are the
only radiometers that consider the tip diameter when calculating the radiant emittance (60).
However, the measured tip diameter varies according to the measurement method used. While
some radiometers have fixed diameters to calculate the radiant emittance (49), both versions of the
Bluephase Meter rely on different methods for measuring the tip diameter (40, 67). The first
version (BM-I) determines the tip diameter by intelligent line sensors. The distance between the
first and last irradiated sensor is used as the diameter of the tip (40). For the second version, the
user must enter the diameter of the tip value after measuring it using a scale on the back of the
device (67). However, this scale only measures the external tip diameter, not the actual effective
tip diameter (the tip diameter that emits light) (60). Such difference between external tip and
effective tip diameters can be a source of error (60).
The tested LCUs (VALO, Ultradent, South Jordan, UT, USA) have an external diameter
of the housing of 13 mm. Mounted in the center of the housing is a convex circular lens which is
held in place by a surrounding metal ring (Figure 2.4). The lens diameter is 9.6 mm as reported by
50
the manufacturer (68). Furthermore, the measuring scale on the back of the BM-II allows only an
approximate measurement of the tip diameter in whole numbers. Additionally, BM- II requires the
entry of the measured tip diameter as a whole number to calculate the radiant emittance (67). Due
to these limitations, the tip diameter of the tested LCUs had to be entered as 9 mm in the present
study. Another study used BM-II to test the same LCUs (VALO, Ultradent, South Jordan, UT,
USA) and entered a tip diameter of 11 mm based on personal communication with the
manufacturer of the radiometer (60). These changes in tip diameter result in a noticeable difference
in the calculated radiant emittance as it is the quotient of the radiant power and the area of the tip.
For further improvement of the radiometer we would like to recommend that the entry of the tip
diameter allows at least one decimal.

Figure 2.4: The tested LCU (VALO, Ultradent, South Jordan, UT, USA). (A) convex lens
configuration, (B) red line is the external tip diameter (13 mm), blue line is the lens
diameter (9.6 mm)
BM- II is designed to record both the radiant power and radiant emittance (67). In this
study however, we only recorded the radiant emittance in order to be able to compare it to the
51
radiant emittance measured with the BM-I. The BM-I is not able to measure radiant power.
Furthermore, comparing radiant power would have required the use of an integrating sphere, which
was not available for this study. When comparing measurements obtained by an integrating sphere
with measurements obtained by the two radiometers used in our study, it was reported that the
BM-I overestimates and the BM-II underestimates the output of LCUs (69).
The tested LCUs in this study have an external diameter of 13 mm, and emit light within a
range of 395 to 480 nm (68). Both versions of Bluephase Meter can measure circular light tip with
a diameter up to 13 mm and wide wavelength range between 380 to 550 nm (40, 67). Therefore,
the emitted light across the entire light tip was captured during radiant emittance measurements.
This is in contrast to other commercial radiometers which have narrower apertures, resulting in
different readings for the light passing though the aperture depending on the position of the light
tip over the aperture (60).
Additionally, the tested LCUs have a non-standard light source exit window (convex lens).
It is well established that the configuration of the light tip influences the measured output (49, 60).
Moreover, the convexity of the surface prevents the light tip to be completely in contact with the
radiometer surface during testing as the manufacturer recommended. Also, the convexity might
affect the stability of the LCU (rocking motion) and change the orientation of the device during
measurement. Therefore, the investigator was trained and calibrated in the positioning of the LCUs
during measurement to avoid variability.
In this study only one unit of each radiometer was used. However, a previous study reported
significant variations in radiant emittance readings measured by different radiometers of the same
brand (48). These intra-brand differences could be explained by the different time points when
each sample was manufactured, which might have led to variability in the device’s construction
52
and its original calibration (48). However, another study reported that four units of the BM-II
presented mean values within 4% of each other and that this small difference is clinically irrelevant
(60). Even though there might be differences between different devices of the same brand, in this
study the same devices were used to measure the whole sample of LCUs, which attributed to less
variability within the study.
A previous study reported the need to develop an accurate handheld dental radiometer to
be used in the dental office that could measure any type of LCUs (70). BM-II can measure all type
of light sources and reported to be the most accurate dental radiometer (60). Despite its
improvement, the BM-II is by some researchers still not regarded as up to par with the “gold-
standard” equipment (60). Thus, researchers should use laboratory grade meters as recommended
in ISO 10650 to provide accurate radiant power measurements and calculate the radiant emittance
based on the measured effective tip size (47). However, the BM-II can still be used to monitor the
performance of LCUs in dental offices over time. The measurements should be recorded with the
same tip diameter value using the same radiometer device to limit the variability.

53
2.7 Conclusion
Within the limitations of the present study, it was determined that the two evaluated
radiometers significantly differ in the measurement of LED LCUs due to their difference in
technology. This should be considered when monitoring the light output of LCUs over time in a
dental office setting, especially when changing or upgrading the monitoring device while
maintaining the same LCU. The current monitoring devices still need to improve and cannot be
used as replacement for laboratory grade power meters.

54
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Abstract (if available)

Abstract Part I ❧ Objectives: It is well established that conventional light curing units (LCUs) degrade over time. However, minimal data is available on the long-term performance and degradation of modern light emitting diode (LED) LCUs. Therefore, the aim of this study was (1) to evaluate the long-term performance of LED LCUs used in pre-clinical and clinical settings of a dental educational institution and (2) to evaluate the effect of contamination of the light tip of these units on the measured radiant emittance. ❧ Material and methods: The study was conducted at the Herman Ostrow School of Dentistry of the University of Southern California as a part of an ongoing quality control program, which checks the performance of LCUs that are being used in the pre-clinical and clinical courses to ensure an optimal standard for all light cured restorations. In this study, data from year 2013 to year 2016 were collected which represents four measuring cycles. The radiant emittance of LCUs was measured with a handheld dental radiometer (Bluephase Meter [BM-I], Serial No. 007249, Ivoclar Vivadent, Schaan, Liechtenstein) according to manufacturer instructions. Each LCU was measured three times and the average value was calculated. Information about unit type (cordless or corded), manufacturer, model, and age (in years) were recorded. Furthermore, the measurements were repeated annually, and at each visit visual inspection was performed to evaluate light guide tip for damage or contamination by adherent material. A total of 780 LED LCUs were included in the statistical analysis that was performed using a repeated measures mixed model at a significance level of α=0.05. ❧ Results: A statistical difference in the radiant emittance values of the evaluated LED LCUs was observed over time (p<0.0001). The radiant emittance measurements were significantly reduced in year 1 compared to year 0 (p<0.0001). However, values in years 0, 2, and 3 were not significantly different from each other (p>0.05). Contamination of the light tip significantly decreased the radiant emittance values (p<0.0001). ❧ Conclusion: Within the limitation of our study, the radiant emittance of LED LCUs measured by a dental radiometer (BM-I) varied over time. However, no long-term degradation was observed within the period of our study. The contamination of the light tip attributed to the decrease in the radiant emittance. Therefore, it is essential to establish a periodic evaluation of LED LCU performance as well as checking the light tip for contamination or damage. ❧ Part II ❧ Objective: Dental radiometers are not regarded as the gold standard in measuring the light output of light curing units (LCUs). However, a recently introduced dental radiometer (Bluephase Meter II [BM-II], Ivoclar Vivadent, Schaan, Liechtenstein) has improved features that are supposed to overcome the deficiencies of conventional dental radiometers. Therefore, the aim of this study was to compare the performance of a dental radiometer (Bluephase Meter [BM-I], Ivoclar Vivadent, Schaan, Liechtenstein) with its upgraded version (BM-II) when measuring the radiant emittance of light emitting diode (LED) light curing units (LCUs). ❧ Material and methods: The study was conducted at the Herman Ostrow School of Dentistry of the University of Southern California as a part of an ongoing quality control program. The radiant emittance of 142 brand new LED LCUs (VALO, Ultradent, South Jordan, UT, USA) was measured with two different dental radiometers (Bluephase Meter [BM-I], Serial No. 007249 and Bluephase Meter II [BM-II], Serial No. 1300000032, Ivoclar Vivadent, Schaan, Liechtenstein) according to manufacturer instructions. Each LCU was measured three times using both dental radiometers, followed by calculating the average values. Statistical analysis using a repeated measures mixed model was performed to compare the measured radiant emittance values from the two dental radiometers at a significance level of α=0.05. ❧ Results: A significant difference was found between the radiant emittance values measured by BM-I and BM-II (p<0.0001). Measurements of both devices presented a large variation of up to 500 mW/cm² with no overlap. Overall, the radiant emittance values measured with the BM-II were higher than those measured with the BM-I. ❧ Conclusion: Within the limitations of the present study, it was determined that the two dental radiometers (BM- and BM-II) significantly differ in the measurement of LED LCUs. Dental radiometers still do have limitations, so they are only recommended for tracking the performance of the same LCU over time. A laboratory grade meter is still the gold standard for light output measurement.

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Creator Alsamman, Reham Mohammed (author)

Core Title The performance of light emitting diode (LED) light curing units and dental radiometers

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 07/21/2017

Defense Date 06/20/2017

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag LED,light curing unit,light emitting diode,OAI-PMH Harvest,radiometer

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Phark, Jin-Ho (committee chair), Duarte, Sillas (committee member), Paine, Michael (committee member), Sartori, Neimar (committee member)

Creator Email alsamman@usc.edu,Dr.reham.alsamman@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c40-407675

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