Efficiency of light curing units in Dental clinics in Nairobi, Kenya

Citation:
Alasow KB. Efficiency of light curing units in Dental clinics in Nairobi, Kenya.; 2010.

Abstract:

Background: To achieve adequate cure, a resin composite restoration must be
exposed for a specified duration of time to a light of sufficient intensity and the right
wavelength. However, some commonly used light curing units (LCUs) may yield
inadequately cured restorations due to their insufficient light intensity output.
Furthermore, the efficiency of light curing units in dental clinics and the extent to which
dentists practice the recommended maintenance techniques is largely unknown.
Objective: To determine the efficiency of Light Curing Units (LCUs) in dental clinics in
Nairobi, Kenya.
Study design: A laboratory-based, cross-sectional analytical study.
Study area: The study was set in private and public dental clinics in Nairobi, Kenya. A
total of 83 light curing units selected through a convenient sampling procedure were
used.
Materials and methods: The light intensity output of light curing units in dental clinics
was measured using a digital dental radiometer and the result entered in a data
collection form. Each light curing unit was then used to polymerise two cylindrical resin
composite specimens made using custom-made split brass moulds; one measuring
4mm in diameter and 6mm in thickness used to determine the depth of cure (DOC) and
the other 8mm in diameter and 3mm in thickness used to determine the surface
hardness by using a Vickers Hardness tester. Within 6-7 hours of fabrication, the depth
of cure specimens were immersed in a capsule containing 99%- acetone solvent which
was then vibrated in a mixing device. The DOC was calculated from the undissolved
length of the specimen. The surface Vickers Hardness was evaluated by making three
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surface indentations with a diamond indenter using a load of 200g and a dwell time of
15-seconds. A conversion table was used to convert measurements from the diamond
indentations into hardness numbers. The light intensity output and the depth of cure and
surface micro-hardness numbers of the resin composite specimens were then used to
assess the efficiency of each dental light curing unit. Three main components of the
maintenance history of the light curing units, as well as the age and type of the light
curing unit were also recorded.
The data was entered into a computer using SPSS version 12. The independent sample
t-test, one way analysis of variance (ANOVA) with Post Hoc test and Chi-square tests
were used for data analysis. The results were summarized in tables and figures.
Results: Of the 83 LCUs studied, 43(51.8%) were LED and 39(47.0%) were OTH and 1
(1.2%) was PAC light.
LCU type and light intensity output, DOC and hardness: Mean light intensity for OTH
and LED lights was 526.59mW/cm2 and 493.67mW/cm2 respectively (p=0.574), while
the mean DOC for OTH lights was 1.71mm and LED was 1.67mm (p=0.690). Mean
VHN for LED was 57.44 and for OTH was 44.14 (p=0.713). Light curing unit type had no
statistically significant effect on DOC, surface hardness and the intensity of the light.
Effect of age of LCU on light intensity output, hardness and DOC: Mean light intensity
for LCUs ::;5years was 596.03mW/cm2 and 363.17mW/cm2 for units> 5years old. Age
showed a significant effect on light intensity (p=O.024). The mean DOC for the two age
groups was 1.74mm and 1.57mm respectively (p=O.073). For surface micro-hardness,
the ::; 5years and > 5years age groups gave a mean VHN of 58.81 and 51.46
respectively (p=O.1)
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Efficiency of the LCUs: when intensity was used to measure efficiency, 48 (57.8%)
LCUs were efficient and 35 (42.2%) were inefficient. Only the LCU age significantly
affected efficiency by light intensity output (p=O.008). Only 24 (28.9%) LCUs gave
sufficient DOC as opposed to 59 (71.1%), which gave insufficient DOC. Of the units
tested for surface micro-hardness, 15 (25.9%) had adequate surface micro-hardness
while the rest (43 or 74.1%) had inadequate surface micro-hardness. The type of LCU
and its age did not significantly influence efficiency as measured using depth of cure
and surface micro-hardness of the resin restoration.
On the whole, 11 (19%) of the LCUs which had all the three tests of efficiency done
were satisfactory in all the 3 aspects.
Conclusions: Eleven (19%) of the light curing units used in Nairobi dental clinics were
efficient when subjected to a combined light intensity, and composite resin depth of cure
and surface hardness evaluation, and that the type and maintenance history of a LCU
had no significant influence on its efficiency. Age had a significant influence on the light
intensity of the curing units - there was a decrease in light intensity output with increase
in age of the units. There was a non-linear relationship between the light intensity output
of a LCU and the depth of cure and surface micro-hardness of the cured composite.

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