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Year : 2016  |  Volume : 7  |  Issue : 2  |  Page : 64-68

A clinical survey of the output intensity of light curing units in dental offices across Nellore urban area

Department of Conservative Dentistry and Endodontics, Narayana Dental College and Hospital, Nellore, Andhra Pradesh, India

Date of Web Publication19-May-2016

Correspondence Address:
Tavva Venkata Swathi
Department of Conservative Dentistry and Endodontics, Narayana Dental College and Hospital, Nellore, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0976-433X.182657

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Aim: The aim of the survey was to examine the output intensity of curing units and other related factors in private dental offices across Nellore urban area. Materials and Methods: A questionnaire was prepared about the type of curing unit, number of restorations performed in a week, maintenance of curing unit, frequency of changing bulb, measurement of output intensity, presence, or absence of composite build--ups on curing tips. The questionnaire was submitted to 100 private dental offices located in Nellore urban area. Each variable in the questionnaire had an impact on quality of the composite restoration. Each curing unit light tip was also observed for the presence or absence of composite build--up. The output intensity of the curing light was measured using a digital radiometer (Ivoclar). The average of the three readings of the output intensity was obtained for each curing light. The average output intensity was divided into three categories (<400 mW/cm2, 400–850 mW/cm2, and 850–1000 mW/cm2). Statistical Analysis: The results were statistically analyzed using linear regression analysis. Results: Among the 100 curing units examined, 84 were light emitting diode (LED) units, and 16 were quartz tungsten halogen (QTH) units. Only 22% LED machines and 3% QTH curing units had adequate intensities (>850 mW/cm2). A significant reduction in output intensity is seen with both types of older light curing units. Nearly 50% of practitioners had never checked the light output of their unit. Conclusion: It was concluded that there is a general lack of awareness among dentists of the need for maintenance of these units.

Keywords: Curing light, output intensity, radiometer, survey

How to cite this article:
Madhusudhana K, Swathi TV, Suneelkumar C, Lavanya A. A clinical survey of the output intensity of light curing units in dental offices across Nellore urban area. SRM J Res Dent Sci 2016;7:64-8

How to cite this URL:
Madhusudhana K, Swathi TV, Suneelkumar C, Lavanya A. A clinical survey of the output intensity of light curing units in dental offices across Nellore urban area. SRM J Res Dent Sci [serial online] 2016 [cited 2022 May 23];7:64-8. Available from:

  Introduction Top

Composite resins were introduced into restorative and adhesive dentistry more than three decades ago. Many improvements and changes in their composition and technique had enhanced their physical properties and led to their use in various clinical procedures.[1],[2],[3] For any failure of a restoration, practitioners usually blame the material used rather than technique or method of placement.[4] Many factors influence the clinical performance of composites, of which the utmost important is the functioning of the light curing unit (LCU).[5],[6]

Light activation units are the standard items of equipment in dental practice. This necessitates every practitioner to understand various factors relating to maintenance of a LCU and their effect on clinical performance and longevity of a restoration. Three essential components are required for adequate polymerization, namely, sufficient radiant intensity, correct wavelength of the light, and ample curing time.[7],[8],[9]

Increasing demand for esthetic restorative dentistry over recent years relatively demands a need for LCU with adequate irradiance, which can be effectively used for various procedures over many years in dental office.[10],[11]

As the curing light ages, the light output diminishes due to deterioration of the components, which can result in restorations which are incompletely polymerized.[1],[3],[4],[10],[11],[12],[13] This causes a reduction in the mechanical properties which can be responsible for secondary caries, pulpal irritation, and decreased the longevity of the restoration.[8]

The aim of this survey was to determine the output intensity, pattern of usage, and maintenance of LCUs in dental practices across Nellore urban area.

  Materials and Methods Top

A questionnaire was prepared about the type of curing unit, number of restorations performed in a week, maintenance of curing unit, frequency of changing bulb, frequency of measurement of output intensity, presence, or absence of composite build-ups on curing tips. The questionnaire was submitted to 100 private dental offices located in Nellore urban area. Collection of related information and measurement of the intensity was performed by a single operator. Consent of the dentist was obtained to examine the LCU in the operatory.

The curing units were divided into two categories: Quartz tungsten halogen (QTH) and light emitting diode (LED). The number of years in use was asked and recorded for each curing light. Each curing unit light tip was also observed for the presence or absence of composite build-up.

The output intensity of the curing light was measured using a digital radiometer (Bluephase Meter, Ivoclar Vivadent, AG, FL-9494 Schaan/Liechtenstein, Austria). The light probe is positioned exactly on the line sensor using the centering gauge, and the curing light is switched on. The intensity is shown on the digital display. Before measuring the irradiance of the curing intensity, the duration of curing time was set as 20 s irrespective of the type of curing unit used.

When a QTH unit was examined for the output intensity, the unit was activated for three consecutive 20 s intervals interrupted by 1 s of off time to reduce the cool bulb variable. When an LED unit was examined, three readings were taken, and the average values were obtained.

The output intensity (mW/cm 2) of all the examined lights were categorized as three groups: 400 mW/cm 2 and below (inadequate intensity), 400–850 mW/cm 2 (marginal intensity; where additional curing time would be required), and 850–1000 mW/cm 2 (adequate intensity).

The completed forms were returned to the author for statistical evaluation. The information was processed using linear regression analysis.[14]

  Results Top

We examined a total of 100 LCUs from 100 clinics representing 100% of private dental offices across Nellore urban area. Eighty-four of the LCUs (84%) were LED units, and 16 of the LCUs (16%) were QTH units.

The age of the curing units examined ranged from 3 months to 11 years, and all the units were categorized into three groups: 1 year and less; 1–5 years; >5 years. The age distribution of the curing lights is illustrated in [Table 1], indicating that majority of the units purchased in the last 5 years were LED units.
Table 1: Age of the unit versus type of curing unit

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The light intensity readings ranged from 200 mW/cm 2 to 1000 mW/cm 2 and the distribution of the light intensity recordings is illustrated in [Table 2]. Of the 25 units which deliver adequate intensity, 22 were LED units, and only 3 were QTH units. When expressed as a percentage, 19% of the QTH units and 26% of the LED units were delivering output intensity with adequate range.
Table 2: Output intensity versus type of curing unit

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The distribution of the age of the LCUs by light intensity [Table 3] indicates a reduction in adequate intensity with increasing age of the unit. Linear regression analysis confirmed a negative correlation between the age of the units and intensity (r = −0.433, P < 0.001).
Table 3: Output intensity versus age of the units

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With respect to maintenance of the LCUs, the data indicated that 49% of the practitioners were performing <10 composite restorations in a week, 70% of them had never checked the intensity of their units, 75% of them were changing the bulb whenever it goes off, 67% of them were using the unit without sterilization sleeves, only 31% of them were cleaning the whole unit after use, 76% of the units were evident with composite resin build-up [Table 4].
Table 4: Different variables regarding maintenance of curing unit

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  Discussion Top

The aim of this survey is to examine the output intensity of the LCUs in dental offices across Nellore urban area. Over a period, the intensity of LCUs will get reduced 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.[2],[6],[8]

It is impossible to visually determine the adequacy of the light intensity emitted by a curing unit. Other ways such as measuring the depth of cure, hardness and surface scraping are required. In general practice, assessment of the effectiveness of a curing unit is presumably based on whether the surface of a light cured resin is hard. The surface hardness of resin is not a reliable index because even an inferior curing unit was able to polymerize the surface as well as an effective unit.

The best method to determine the output intensity of LCU is to measure the percentage of carbon double bond conversion during polymerization using Knoop's hardness test and infrared spectroscopy. As these tests are expensive and difficult for the practitioner to perform regularly in the dental office, use of radiometers has been suggested as a more efficacious method.[15],[16],[17],[18] Various authors have reported the usefulness of the radiometer as a tool for measuring light output from visible LCUs. Hansen and Asmussen examined three different dental radiometers to assess their suitability in general practice. They found discrepancies between the actual depth of cure and radiometer readings. Hence, it is important that readings of dental radiometers should be used solely as reference that can be compared to the maximum intensity of the curing unit.[18],[19],[20],[21]

Dental radiometers are the devices intended to measure the amount of output intensity of curing lights. These are simplified, less accurate, chair-side versions of sophisticated laboratory equipment used to measure the output intensity of curing lights. New digital LED radiometers (Bluephase Meter, Ivoclar Vivadent, USA) have also been introduced for measuring the output intensity of LED lights. In contrast to conventional radiometers, the intelligent line sensor of the instrument takes the radiating surface into account. Therefore, it is possible to accurately determine the actually available light intensity for the 1st time.[22]

Many surveys have been undertaken and published in various articles regarding the output intensity of LCUs in various areas. In the last decade, only two surveys have been undertaken, of which one was conducted in Pune and the other was in Jordan. The intention of the present survey was not only to assess the output intensity of LCUs but also to provide awareness among all dental practitioners residing in Nellore urban area toward the maintenance of curing lights. The details are tabulated in [Table 5].
Table 5: Summary of various surveys conducted by various authors at different areas

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In the present survey 100 LCUs were covered from 100 different dental offices in Nellore urban area. Of the 100 LCUs observed, 84 units were LED, and 16 units were QTH. This may probably due to the improved performance of LED units for thousands of hours when compared to the performance of QTH bulbs.[22] In addition, the heat emitted from the QTH bulbs was more than that of LED units, which also accounts for the earlier deterioration of QTH units.[23],[24]

Out of 16 QTH units in the present survey, 7 units (44%) have inadequate intensity (<400 mW/cm 2), 6 units (38%) have marginal intensity (400–850 mW/cm 2), and the remaining 3 units (18%) have adequate intensity (850–1000 mW/cm 2), whereas out of 84 LED units, 11 units (13%) have inadequate intensity, 51 units (61%) have marginal intensity (400–850 mW/cm 2), and 22 units (26%) have adequate intensity (850–1000 mW/cm 2). Many previous surveys performed by various researchers have reported that an irradiance of 400 mW/cm 2 is the minimum output intensity that is needed for the effective polymerization of 2 mm increment of resin composite. Eighteen percentage of the curing lights delivering inadequate output intensities should be discarded; they emit output intensity in a level that they could not recommend for clinical use.[1],[3],[23],[24]

Manufacturers, recommendations vary from 20 to 40 s, with the provision that darker shades should be cured for longer periods. According to the survey conducted by Martin et al. and Barghi et al., many practitioners usually follow 20 s curing time for a 2 mm thick increment of composite resin.[1],[3] Therefore, various researchers had suggested a standard principle: With half the light intensity provided by the manufacturer, the curing time has to be doubled. This is accepted only when the irradiance values are in the marginal range.[25],[26]

Fifty-seven percentage of the units in this study recorded levels of the output intensity of light in the marginal range (400–850 mW/cm 2). The intensity of these units might be regarded as acceptable but only with additional curing time.

As age advances, the output intensity of these curing lights gradually diminishes.[26] The present survey also showed a significant reduction in light intensity with older units.

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 irradiance because the resin-based composite material partially blocks the light output.[4],[5],[10],[27] In this survey, 31% of the practitioners are following the protocol of cleaning the whole unit, and 59% are cleaning only the tip surface after use. It is likely that irradiance from the LCU can be improved by removing any resin contamination on the tip.[4],[10] The influence of the amount 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.

With regard to the monitoring of output intensity of curing units, nearly three-fourths of the practitioners in the survey had never checked the output intensity of their curing lights [Table 4]. Illustrates the various parameters related to curing units that may have an effect on the output intensity of curing lights. The present survey revealed that there is a general lack of awareness among the dentists practicing in Nellore urban area regarding the maintenance of LCUs which may have an immense effect on the clinical performance of their composite resin restorations.

It has been recommended that new or repaired units are to be tested to ensure adequate light intensity. The LCUs should then be monitored regularly at the end of week, with the initial reading providing a useful baseline for detecting changes in light intensity that occur with aging. Parts of curing light that mainly influence its output intensity are condition of lamp, filter, and fiber optic light guide. A study conducted by Miyazaki et al. revealed that when all 3 parts (lamp, filters, and fiber optic light guides) were replaced at the same time, light intensity increased by 208% and 323%. It has also been suggested by Friedman that the lamps of light polymerization units be replaced every 6 months to maintain adequate intensity. Hence, it is important to routinely replace other components, including filter and light guide along with weekly monitoring of output intensity.[5],[11],[26]

  Conclusion Top

A survey of the efficiency of light output from 100 LCUs in Nellore dental practices revealed that:

  • Approximately 18% had a light output of 400 mW/cm 2 or less, an intensity that has been reported as inadequate to cure a 2-mm thick increment of composite resin
  • An additional 57% of the LCUs registered an output of between 400 and 850 mW/cm 2. This intensity might be considered acceptable with additional curing time of 20 s
  • As units age, they lose intensity and should be checked regularly
  • There is a general lack of awareness among dentists of the need for maintenance of these units
  • As a part of the survey, we educated all the practitioners about the frequency of changing bulb for every 6 months, weekly monitoring of output intensity of LCUs, and routine replacement of other parts.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Hegde V, Jadhav S, Aher GB. A clinical survey of the output intensity of 200 light curing units in dental offices across Maharashtra. J Conserv Dent 2009;12:105-8.  Back to cited text no. 4
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Maghaireh GA, Alzraikat H, Taha NA. Assessing the irradiance delivered from light-curing units in private dental offices in Jordan. J Am Dent Assoc 2013;144:922-7.  Back to cited text no. 10
Miyazaki M, Hattori T, Ichiishi Y, Kondo M, Onose H, Moore BK. Evaluation of curing units used in private dental offices. Oper Dent 1998;23:50-4.  Back to cited text no. 11
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Moore DS, McCabe GP. Producing data. In: Freeman WH, editor. Introduction to the Practice of Statistics. 2nd ed. New York: W.H. Freeman;1993.  Back to cited text no. 14
DeWald JP, Ferracane JL. A comparison of four modes of evaluating depth of cure of light-activated composites. J Dent Res 1987;66:727-30.  Back to cited text no. 15
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Hansen EK, Asmussen E. Reliability of three dental radiometers. Scand J Dent Res 1993;101:115-9.  Back to cited text no. 20
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]

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