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33
Cite this article as: Mahmood MA, Faraj BM. Evaluation of Light Curing Units and Dentists’ Knowledge About
Photo Polymerization Techniques in Sulaimani Governmental Dental Clinics. Sulaimani Dent J. 2019;6(1):33-39.
Mohammed A. Mahmood1, Bestoon M. Faraj2
Abstract
Objective: To measure the output intensity of light curing units (LCU) in governmental dental clinics of the Sulaimani governorate.
To evaluate practitioners’ knowledge on light cure application.
Methods: Ninety-four dental units and eighty-eight dentists in the Sulaimani governorate were included in this research. Output
intensity and diameter of tips of the dental LCU devices were measured. Two survey questionnaires were filled, one for the LCU and
its maintenance, the other for evaluating the knowledge, attitude, and practice of the dentists.
Results: Output power intensity results ranged from 50-2000W, with an average of 993W. The output intensity of 78% of the tested
devices was found to be acceptable regarding the manufacturer instruction of the radiometers used (every intensity below the given
range that given in the Result section is regarded as unusable or non-acceptable). The range of age in service of the devices was 1-12
years with a mean of 4.7 years. The average restorations performed in a week by a device was 17.8. Dentists had poor knowledge,
attitude, and practice towards the maintenance of the LCU devices. 51% of the dentists were quite satisfied with the devices. 48.9%
of the dentists reported that they don’t have an idea of LCU intensity.
Conclusions: Devices should be checked regularly for output intensity, light bulb efficiency, and composite build up. Dentists
express poor knowledge, maintenance, and attitude toward LCUs. Educational programs are advisable and recommended.
Keywords: Light-cure intensity, Dentists knowledge.
Submitted: March 17, 2019, Accepted: May 30, 2019, Published: June 1, 2019
DOI: https://doi.org/10.17656/sdj.10088
1. Kurdistan Board for Medical Specialties, Iraq.
2. Kurdistan Board for Medical Specialties and Department of Conservative Dentistry, College of Dentistry, University of
Sulaimani, Sulaimani, Iraq.
* Corresponding author: mhamadabm@gmail.com.
Published by College of Dentistry, University of Sulaimani
Evaluation of Light Curing Units and Dentists’
Knowledge About Photo Polymerization
Techniques in Sulaimani Governmental Dental
Clinics
Research Article
Light curing intensity and dentists’ knowledge Sulaimani Dent J. June 2019
34
Introduction
The development of the light-curing device came with
the development of light-activated composite materials
in the 1970s heralded a period of rapid progress in the
field of tooth-colored restorations. There is an
increasing demand for aesthetic restorative dentistry,
using primarily direct or indirect composites, or
composite bonded porcelain veneers(14).
Adequate depth of cure of a light-activated composite
depends on the intensity of the light source and the
exposure time, as well as on the material and other
factors(1). Many factors influence the clinical
performance of composites, of which the utmost
importance is the functioning of the light curing unit
(LCU), Duration of application is relatively easy to
control, but the intensity is not so readily monitored(2,
3). Three essential components are required for
adequate polymerization, namely, sufficient radiant
intensity, the correct wavelength of the light, and
ample curing time(4,5).
Visible light photo-activating LCU usually emit
wavelength spectra from 400 and 515 nm. Some units
may have small to moderate amounts of radiation
outside this range. Even though the dentist may
increase the irradiation time, there is a law of
diminishing returns, and the dentist must possess an
effective light source(6).
According to the results of a recent survey by Berry et
al., many current light activating units do not produce
adequate energy and increased irradiation time may not
compensate for this(7).
Light activation units are the standard items of
equipment in dental practice. This necessitates every
practitioner to understand various factors relating to the
maintenance of an LCU and their effect on clinical
performance and longevity of a restoration. For any
failure of a restoration, practitioners usually blame the
material used rather than technique or method of
placement(4,8).
Several studies have been conducted about the
measurement of output intensity and evaluation of
dentists’ knowledge on the type of light cure, exposure
time, maintenance of the device, and mode of
polymerization. Measured output intensity differs
among various researches, for example, acceptable
output intensity (every intensity below the given range
that given in the Result section is regarded as unusable
or non-acceptable) was found to be 68% in Malaysia(9)
and %45 in Israel(10), 25% in India(4). Researches from
England(11), Saudi Arabia(12) and Turkey(13) agree on
the necessity of further education, training, and
guidance of dentists about using light curing units(12).
This study has two aims: 1. to measure the output
intensity of light curing units in governmental dental
clinics of the Sulaimani governorate. 2. To evaluate
practitioners’ knowledge on light cure application.
Patients and methods
Ethical approval was taken from the Kurdistan Board
of Medical Specialties in Erbil. All of the
governmental dental clinics of Sulaimani Governorate
were selected. Two survey questionnaires were
prepared and validated by using the literature review
and previous researches with slight modification. One
of the surveys targeted light cure evaluation and
covered the following items: type of curing unit,
measurement of output intensity, manufacturer brand
or company name, age of curing unit, number of
restorations per week, maintenance of curing unit for
intensity, frequency of changing the bulb, diameter of
the light tip guides and presence or absence of
composite build-ups on the curing tips. The second
survey covered different aspects of light cure
application aiming evaluation of the dentists’
knowledge, such as knowledge of the light cure type,
used the mode of curing, type of restoration material,
application time, and regular maintenance of the device
and level of satisfaction.
The output intensity of the light cure devices was
measured by two manual radiometers (COXO) (Serial
No: P07237, CO04026) from China (Figure.1). Each
LCU was tested twice by two different radiometers for
the measurement of output intensity. The diameter of
the LCU tips was measured by a metal gauge and
checked for the presence or absence of composite build
up.
The first questionnaire was filled out by the author.
The second questionnaire was filled by the participants
(dentists) themselves in a one-to-one meeting.
Participants had the chance of asking about any part of
the survey that not understood enough. Participants
were the users of the LCUs measured in this research.
Vol 6(1) Mohammed and Faraj
35
Table 1: Dentists’ knowledge on photopolymerization techniques.
Results
Light-cure units
Ninety-four dental units were included in the research.
The majority of LCUs were Light Emission Diode
(LED) (91.5%), while the rest were Quartz Tungsten
Halogen (QTH) (8.5%). Regarding the output intensity,
the results ranged from 50-2000W with an average of
993W. According to the manufacturer of the used
radiometer, two independent criteria were used: 500-
800 mW/cm2 (recommended) and 300-500 mWcm2
(the composite should be tested to be sure).
Percentages of the unusable LCUs were 28.7% and
11.7% respectively. The majority (71.27%) of the
tested LCUs were above 500 mW/cm2. (every intensity
below the given range that given in the previous
sentence is regarded as unusable or non-acceptable).
Most of the units enrolled were of Satelec® device
made by action company from France (45.7%,
n=43)29.8% of the devices were of the unknown made
since they were without labels. The rest of the light-
cures were mostly Chinese (OSAKA, KASO,
Woodpecker, DTE, YDL-Hangzhou, Quayle, LY-
CZ40 China). The range of age in service of the
devices was 1-12 years with a mean of 4.7 years
(Figure 2). Besides, the tiredness of the devices was
measured by the number of restorations per week, with
an average of 17.8 restorations per week per each LCU
(Figure 3). All of the dental LCU lacked light intensity
maintenance, and none of them had given the chance of
bulb changing.
Variables No. %
Type of your light cure:
1. QTH.
2. LED.
3.Other
4. Not sure.
3
74
2
9
3.4
84.1
2.3
10.2
Mode of curing:
1. Soft Start
2. Continuous
3. Ramping
4. Not sure
21
62
3
2
23.9
70.5
3.4
2.3
For which restorations do you use the light cure?
1. Composite.
2. Glass Ionomer.
3. Composite + Calcium Hydroxide.
4. All.
42
2
30
14
47.7
2.3
34.1
15.9
Difference between the types regarding the efficiency of curing:
1. Yes
2. No
3. Not sure
55
9
24
62.5
10.2
27.3
How many seconds do you perform curing for composite restoration?
1. 10-15 sec.
2. 20-30 sec.
3. 30-60 sec.
9
61
18
10.2
69.3
20.5
Did you have any idea about light cure intensity previously?
1. Yes
2. No
45
43
51.1
48.9
Do you check your light cure regularly for maintenance?
Yes
N
o
25
63
28.4
71.6
Level of satisfaction with your light cure.
1. Very satisfied.
2. Quite satisfied.
3. Neither.
4. Quite dissatisfied.
5. Very dissatisfied.
27
45
8
2
6
30.7
51.1
9.1
2.3
6.8
Light curing intensity and dentists’ knowledge Sulaimani Dent J. June 2019
36
Figure 2: Linear correlation between output intensity and age of the device.
Figure 3: linear correlation between output intensity and number of
restorations/weeks.
Figure 1: Front and back side of the used radiometers.
Vol 6(1) Mohammed and Faraj
37
The diameter of the tip of the device, 52 of them (55%)
were 8 mm, followed by 7.5 mm in 36% of the devices.
As for the presence of the composite build up on the
device, most of them had composite buildups on their
tip of the light guide (75%). Sixty-seven percent of
67% of the devices were wired, while 33% were
portable. Summary of the results is shown in Table 1.
Dentists’ knowledge and the attitude most of the
participants correctly predicted the type of LCU (90%).
Regarding the common type of curing mode preferred
by the dentists, the majority (70%) used continuous
mode, followed by 23.9% for the soft start mode.
Composite was the main filling material for which
light-cure was used for; as 47.7% of the respondents
used light only for the composite, while 34% used in
combination with resin-modified glass ionomer
cement. 16% used light curing for all types of
materials. 62.5% of the participants believed that the
type of polymerization technique affects the efficiency
of the curing and the subsequent quality of the filling.
However, 10% said that there is no link between the
two, and, 27% were not sure. Most of the participating
dentists (69%) preferred 20-30 seconds for the curing,
while 10% selected 10-15 seconds and 20% selected
30-60 seconds. Nearly half of the respondents (48.9%)
reported that they don’t have an idea of light-cure
intensity. Besides, 71.6% they don’t check the device
for regular maintenance. Finally, the dentists asked
about the level of satisfaction with the light-cure they
used and, only 51% were quite satisfied.
Discussion
Light curing unit
Over a period, the intensity of LCUs will reduce due to
many factors, like composite resin build‑up on the
curing tip, condition of the bulb in units, orientation
position of the curing tip to the radiometer, voltage
regulation, and handling of the LCU(4,14).
The output of dental light-curing units is usually
evaluated indirectly by subjective tactile examination
of the upper surface of restorations. However, it has
been shown that it is not possible to completely
differentiate between adequately cured and under-cured
composite and because even an inferior curing unit can
polymerize the surface as well as an effective unit(15).
The recently marketed hand-held radiometers should
serve as a means to objectively measure the
performance of these units, instead of depending on
unreliable subjective parameters. These are simplified,
less accurate, chair‑side versions of sophisticated
laboratory equipment used to measure the output
intensity of curing lights(10).
According to the manufacturer of the radiometer used
in this research, two independent criteria were
conducted: 500-800 mWcm2 (recommended) and 300-
500 mWcm2 (the composite should be tested to be
sure) below 300mW considered as unusable.
Percentages of the unusable lighting cures (less than
300mW) were 28.7% and 11.7% respectively
(according to the two independent criteria mentioned
respectively in the previous sentence) with the average
of (20.2%). This finding is by Yogesh et al.(16) in which
unusable LCUs were estimated to be 22%.
As the age advances, the output intensity of these LCU
gradually diminishes(2). The present survey also
showed a significant reduction in light intensity with
older units. As the measured devices relatively old with
an average of 4.7 years. This agrees with the result of
similar researches(4).
Resin‑based composite build‑up on the light curing tip
was evident on 76% of 100 LCUs. This build‑up may
have a significant negative effect on intensity because
the resin‑based composite material partially blocks the
light output(8,17) since it is likely that intensity from the
LCU can be improved by removing any resin
contamination on the tip(17). The influence of the
number of composite build‑ups on the intensity of
curing light was not measured in the present survey;
hence, the effect of the cleaning of curing tips on the
outcome of this study is unknown.
About the monitoring of output intensity of curing
units, the majority of the participants reported that they
never checked the output intensity of their curing
lights. Findings from the neighbor country, Saudi
Arabia reflect the same problem(12). (the problem is
lack of maintenance).
A number of the restorations conducted with a device
in a given period could give a clue on the tiredness of
the device(17). In this study, the average number of
restorations per week per each light-cure unit is 17.8.
This result agrees with the findings of an Indian article
in which 49% of the tested LCU devices were
performing <10 restorations in a week(4).
Dentists’ knowledge
Adequate polymerization is a crucial factor in
obtaining optimal physical properties and satisfactory
Light curing intensity and dentists’ knowledge Sulaimani Dent J. June 2019
38
clinical performance of composite materials.
Inadequate polymerization reduces the strength,
hardness, water sorption, and color stability of
composites(18,19). Several factors affect resin
polymerization, including a selection of the appropriate
LCU; light intensity, wavelength and exposure time;
and size, location, and orientation of the LCU tip(20,21).
In addition to the type of LCU used, the clinician’s
knowledge and skill regarding the use of LCUs plays
an important role in the outcome of polymerization and
thus the outcome of resin-based restorations(13). The
findings of this study indicated that dental clinicians
had low levels of knowledge regarding LCUs and
materials science.
Knowledge and understanding of the LCU output
intensity are important to ensure sufficient curing of
the resin and to prevent any damage or harm(12). Most
of the respondents did not know the output intensity of
the LCU they were using, which increases their
chances of having insufficient curing and
polymerization by the LCU. This agrees with the
results of Alsuliman et al.(12) (In which 88.7% of the
participants were unaware of the intensity value of
their LCUs).
Conclusions
Based on the study results, it’s concluded that about
78% of the tested LCUs were found to be acceptable
(more than 300mW). Dentists express poor knowledge,
maintenance, and attitude toward LCUs. Educational
programs are advisable and recommended.
Acknowledgment
The authors are giving their thanks and showing their
appreciation to all effective Members of Kurdistan
Board for Medical Specialties, Restorative Dentistry.
Very special thanks to Professor Ali Al-Zubaidi for his
great help and support during the years of our study in
Kurdistan Board.
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