Editorial Type:
Article Category: Research Article
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Online Publication Date: 09 Aug 2021

An Evaluation of the Efficacy of LED Light Curing Units in Primary and Secondary Dental Settings in the United Kingdom

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Page Range: 271 – 282
DOI: 10.2341/20-092-LIT
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SUMMARY

Objective:

This study aimed to evaluate the irradiance and the quality of LED light curing units (LCUs) in primary and secondary clinics in the UK and to assess the effect of damage, contamination, use of protective sleeves, and distance of light tips to target on the irradiance and performance of LCUs.

Methods:

The irradiance levels (mW/cm2) of 26 LED LCUs from general dental practices and 207 LED LCUs from two dental hospitals were measured using a digital radiometer (Blue Phase II, Ivoclar, Vivadent, Amherst, NY). Ten LED light guide tips (Satelec Mini, Acteon, Merignac, France) were selected to evaluate the effect of chipping, contamination (tip debris), and use of protective sleeves and tips to sensor distance on irradiance (mW/cm2) using a MARC Resin Calibrator (Blue Light Analytics, Halifax, Canada). Homogeneity of the light output was evaluated using a laser beam profiler (SP620; Ophir-Spiricon, North Longan, UT, USA). Statistical analysis was conducted using a one-way analysis of variance (ANOVA) with post hoc Tukey test (α=0.05) and linear regression with stepwise correlation tests.

Results:

Thirty-three percent of the LCUs delivered irradiance output less than 500 mW/cm2. The condition of the light curing tips was poor, with 16% contaminated with resin debris, 26% damaged, and 10% both contaminated and damaged. The irradiance output was significantly reduced in contaminated (62%) and chipped (50%) light curing tips and when using protective sleeves (24%) (p<0.05). Irradiance was also reduced when increasing the distance with 25% and 34% reduction at 7 mm and 10 mm, respectively (p<0.05).

Conclusion:

There remains a lack of awareness of the need for regular monitoring and maintenance of dental LCUs. Damaged and contaminated light curing tips, use of protective sleeves, and increasing the distance from the restoration significantly reduced the irradiance output and the performance of the LCUs.

INTRODUCTION

The introduction of light cured dental resins led to a revolution in modern dental practice. Consequently, the dental light curing unit (LCU) has become an integral piece of equipment in every dental practice. However, the lack of knowledge among dental practitioners concerning factors affecting the performance of LCUs raises a major concern, especially as the use of resin based materials has significantly increased worldwide. It was reported that approximately 800 million composite restorations were placed worldwide in 2015,1 of which 80% were posterior composite restorations, exceeding the use of amalgam restorations in several countries.2–4 This increase is expected to continue following the Minamata convention and the calls for a phase down of the use of mercury-containing products, which has placed resin composites as the most suitable alternative to amalgam as a direct restorative material.5

Current resin composite formulations exhibit enhanced mechanical and physical properties, allowing them to be used as a posterior restorative. However, the average life span of composite restorations remains just under 10 years, after which clinical intervention may be required.6 Recurrent caries and restoration fracture remain as the primary reasons for clinical failures of composite restorations.7,8 Inadequate polymerization of resin composites has a major impact on the mechanical and physical properties of the material, including reduced bond strength to the tooth, bulk fractures, increased wear, and increased amount of residual monomers within the resin.9–13 Therefore, a major contributing factor to the early failures of resin composite restorations might be related to limited polymerization and suboptimal curing of the material. While it was reported that an irradiance of 400 mW/cm2 was the minimum that must be delivered for effective polymerization of most resin based composites when appropriate curing times were used,14 most dental composite manufacturers recommend delivering a minimum of 500 mW/cm2 for a duration of 40 seconds for optimum curing and many recommend shorter curing times if irradiance is higher, eg >1000 mW/cm2 for 10 seconds. Such arbitrary values may provide some margin for error; however, if the absolute irradiance output is unknown, there would exist a greater risk of suboptimally cured materials. Additionally, there has been an increase in the popularity of bulk-fill composite materials, which are claimed to enable restoration build up in thicker increments of 4–6 mm.15 The composition of bulk-fill composites varies depending on the type and amount of filler content and the photoinitiator systems used; therefore, adequate curing is essential to achieve adequate polymerization and the desired mechanical properties of these materials.16–18

LCUs containing light emitting diodes (LED) are the most common LCU used in dental practice19 as they exhibit specific spectral output to closely match camphorquinone (CQ) absorption without the need for optical filters.20,21 LED LCUs have several advantages because they are ergonomic, lightweight, battery operated, and they present greater efficiency compared with quartz tungsten halogen (QTH) LCUs due to the non-filtered irradiation.21,22 Furthermore, LED light sources can provide much longer working life compared to QTH and plasma-arc (PAC) light sources.23 Therefore, nowadays there is a general trend toward using LED LCUs only. The first generation of LED LCUs contained arrays of multiple individual LED emitters that generated low irradiance output and required prolonged curing times.21,23 The second generation of LED lights evolved to incorporate small surface-mounted LEDs instead of discrete LED multiple arrays.22 Following this innovation, the irradiance output was significantly increased,24 resulting in less exposure time being required to adequately photocure restorations.25,26

More recently, alternative photoinitiators to CQ such as phenyl propanedione (PPD), benzil (BZ) and Norrish Type I photoinitiator systems such as mono- (Lucirin TPO) and bi-(Irgacure 819) acylphosphine oxides have been introduced27,28 These have been used in an attempt to increase the curing efficiency and the depth of polymerization in so-called bulk fill resin composites.16 Additionally, most of these photoinitiators are less pigmented and can therefore be used in bleached shades of resin composites, overcoming the yellowing effect of CQ when used solely. However, these alternative photoinitiators require shorter wavelengths of light at or below 410 nm. Consequently, the third generation of LED lights were introduced by incorporating multiple LED chips generating distinct wavelength bands (~380–500 nm, LCU dependent).22 These LCUs are considered broad-spectrum lights and sometimes they are referred to as polywave LCUs. Polywave lights are proposed to effectively photopolymerize all dental resin-based restorative materials that contain a variety of photoinitiators. Therefore, clinicians need to know if the restorative materials used contain alternative photoinitaors, which will require a polywave LCU rather than assuming that all LED LCUs are suitable.

To achieve optimal photopolymerization of resin based materials, clinicians should aim to deliver sufficient radiant exposure at the correct wavelength(s) of light according to the intrinsic characteristics of the material (thickness, shade, photosenstisters, etc). Many clinicians do not understand proper use of a dental LCU or the critical factors for optimizing the material properties of light cured resin composites.29–31 Several studies have shown that LCUs used in dental practices are poorly maintained and deliver inadequate light output.32–37 Additionally, most clinicians did not know the irradiance and wavelength of their LCU and were unaware that LCUs with low irradiance output were unable to adequately cure the resin routinely used in restorations.30,35

Evaluating the condition of the light guide is a key factor in optimizing light curing, as the regular and frequent use of LCUs in most dental practices lead to damage and resin contamination, which result in a reduced power output.38,39 Furthermore, various clinical factors have been shown to influence the irradiance of the light, such as increasing the distance from the restoration.40 It was reported that some LCUs deliver only 25% or less of the irradiance measured at the tip when the distance is increased by 8 mm.12,41,42 Further, the use of protective sleeves to minimize potential cross infection from the LCU tip is reported to reduce the irradiance by 40%.43,44 An additional clinically relevant factor to consider is the beam homogeneity of the LCUs, which can be evaluated using the beam profiling technique that is commonly used to examine lasers and other light sources.45 It was reported that many LCUs do not have a uniform light beam across the tip with hot spots of high irradiance and areas of significantly reduced irradiance across the tip.46 The impact of light guide properties and other clinical factors varies between different LCUs and is dependent upon individual design and optics of the light guide. Therefore, it is important to evaluate the effect of these factors on the performance of commonly used and newly introduced LED LCUs.

Although several studies have evaluated LCUs in various dental settings, to our knowledge no studies have been published to date evaluating the irradiance and the condition of LCUs used in United Kingdom primary and secondary dental settings. Therefore, the aims of this study were: 1) to evaluate the irradiance and the condition of LCUs in both primary and secondary dental care units in the United Kingdom; and 2) to evaluate common clinical and light guide factors that may influence the light output and the performance of contemporary LED-based LCUs.

METHODS AND MATERIALS

Two hundred thirty-three (233) light curing units were evaluated in the first part of this study, which included the following: Leeds Dental Institute (n=102) and Newcastle Dental Hospital (n=105) as secondary care units, and general dental practices in West Yorkshire (n=26) as primary care units. Various LCU brands were used with light curing tip diameters ranging from 6 mm to 12 mm; details of the lights tested are shown in Table 1.

Table 1: Summary of All LCUs Tested in this Study
Table 1:

The light output irradiance (mW/cm2) was measured for each LCU using a Blue Phase II (BPII) digital radiometer (Ivoclar Vivadent, Amherst, NY). The BPII calculates the light irradiance based on the measured power (mW) when the light tip diameter is entered into the meter software and has a minimum detection threshold of 20 mW/cm2. The BPII radiometer contains a large sensor area, which enables measurement of the radiant power up to a 13-mm diameter tip size. Higher accuracy of the BPII compared with other commercial radiometers has been reported previously, and an accuracy of ±10% compared to a laboratory-grade meter47 has been reported. For each unit tested, three separate measurements of 20 seconds duration were taken and the mean reading was recorded. The LCU type and the size of the fiber optic tip was recorded for each unit using the BPII integrated template to determine the diameter of circular light probes. The appearance of the light curing tip was also evaluated and observations of chipping and debris noted. The readings were recorded by a single investigator and recordings of light irradiance below a threshold of 500 mW/cm2 were considered unsatisfactory. The output intensity (mW/cm2) of all the examined lights were categorized into three groups: <200 mW/cm2, 200–500 mW/cm2, and >500 mW/cm2.

Based on investigator visual examination, 10 Satelec mini LED light guides (Acteon, Merignac, France) were selected to evaluate the effect of chipping, contamination, and tip-debris on the overall light output (mW/cm2) using a MARC Resin Calibrator (Blue Light Analytics, Halifax, Canada). The MARC Resin Calibrator was fixed to an optical board and a universal joint, and clamps were used to allow accurate and concentric positioning of the tip and sensor. The exposure time was set to 20 seconds and the energy level of 16 J/cm2 for all LCUs.14,48. The irradiance of the damaged and contaminated LCU curing tips were measured using the same light source (Satelec Mini LED) of known output with a clean and undamaged (control) tip. LCUs with debris on the fiber optic tip surface were selected based on residue of up to 50% over the surface of the tip, which was identified after investigator visual examination. Irradiance measurements were taken with the LCU tip placed perpendicular to the sensor surface at 0-mm distance (n=3).

To evaluate the effect of the protective sleeves on LCU output, a light protective sleeve (WRAPAROUND, UnoDent, Essex, England) was placed on the LCU (Figure 1) with a new light curing tip, and irradiance values were recorded (n=10). To evaluate the effect of distance of the light from the restoration, the LCU with a new light guide tip was mounted securely on the optical bench and placed perpendicular to the sensor surface on the MARC Resin Calibrator; three readings were taken at 1 mm intervals from 0 to 10 mm from the sensor surface, the mean reading at each individual distance was then recoded.

Figure 1.Figure 1.Figure 1.
Figure 1. Satelec Mini LED (Acteon, Merignac, France) with a light protective sleeve (WRAPAROUND, UnoDent, Essex, England) over the tip.

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

The homogeneity of the light beams was evaluated using a laser beam profiler (Ophir Spiricon, SP620, Israel) and analysed in BeamGage 6.3 (Ophir-Spiricon).46,49 The laser beam profiler has a high resolution CCD sensor (4.4 μm square pixels) that takes images of the light output and the power received within each pixel. A 50 mm CCTV lens (Ophir, Spiricon) was attached to a camera and was focused directly onto the tip of the light source. Following a linear calibration to correct pixel dimension due to the magnification by the lens, saturation of the CCD sensor was controlled using: 1) neutral density filters (OD 2 and 1, Ophir Spiricon) stacked above the lens, 2) the aperture on the 50 mm lens, and 3) the integration time within BeamGage software. Subsequently, an ambient light correction was performed using the builtin UltraCal function within BeamGage. Pixel response was then calibrated using previously determined power values measured using a photodiode power meter (PD300, Ophir Spiricon). For each LCU, the distance between the camera and the light guide tip was fixed. The beam profile images were then analysed using Ophir-Spiricon software and displayed on a computer screen as a color-coded image of the beam irradiance distribution across the emitting surface.

Three light curing devices that represented second-generation LCUs were used: single diode, one wave and emission; Satelec Mini LED (Acteon), Elipar S10 (3M Oral Care, St. Paul, MN, USA), and Woodpecker LED (Woodpecker, China) and one third-generation LED light: double diode, multi-waveband emission; BluePhase Style (Ivoclar Vivadent) were selected to evaluate the variability of the beam light homogeneity among different LCU brands. Selected LCUs with chipped and contaminated light curing guides were also evaluated using the laser beam profiler. To demonstrate the clinical implications of beam light homogeneity, scaled beam profile images were superimposed over a tooth preparation to demonstrate the radiant power received over various regions within a typical cavity preparation.

Statistical analysis was conducted using IBM SPSS version 21 (IBM Inc, NY, USA). Data were analysed for normality using Shapiro-Wilk Test, and comparisons were made using one-way analysis of variance (ANOVA) and post hoc Tukey tests (α=0.05). Linear regressions with stepwise correlation were also used to analyze the correlation between the light output and the presence of tip debris and chipping, as well as the effect of increasing the distance from the target and the effect of using protective sleeves.

RESULTS

Data showed that 33% of the tested lights showed irradiance output at or below 500 mW/cm2, which was considered unacceptable; details are shown in Table 2. The condition of the light curing guides was also poor, with only 48% identified to be in good condition (Table 3).

Table 2: The Irradiance Output (mW/cm2) of the Light Curing Units (LCUs) Tested
Table 2:
Table 3: The Condition of the Light Curing Tip Guides Tested
Table 3:

Data showed that all variables tested had a highly significant impact on the irradiance output emitted from the LED LCUs; these variables were as follows:

Light Guide Factors: Effect of Debris Build-up, Chipping, and Use of Protective Sleeve

Resin debris build-up (r2=0.95, p<0.05)

Chipping of the light curing tip (r2=0.96, p<0.05)

Use of protective sleeve (r2=0.82, p<0.05)

In this study, using a light curing tip with resin debris build-up resulted in a significant reduction in the irradiance output by an average of 62% (p<0.05). Similarly, the use of a chipped tip or using protective sleeves resulted in a reduction of the irradiance output by 50% and 24% (p<0.05), respectively. Details are shown in Table 4 and include the reported irradiance values and the impact on the light performance.

Table 4: The Mean Irradiance Values (mW/cm2) and the Performance (%) of the Satelec Mini LED when Used with New Light Guide Tips, with Debris Build up, Chipped Tips, and when Used with Protective Sleeves
Table 4:

Operator Factors: Effect of Distance

Distance from the sensor target (r2=0.98, p<0.05)

Increasing the distance of the light guide tip from the sensor target also resulted in a reduction in the irradiance output; the irradiance was reduced by 25% at 7 mm and 34% at 10 mm (p<0.05), respectively. Figures 2 and 3 show the effect of increasing the distance from the target on the overall irradiance output and the time required to reach an energy level of 16 J/cm2 required to cure resin composites. Figure 4 illustrates the clinically relevant distances; for example, the distance between the cusp tip and the base of a posterior interproximal box, which may exceed 7 mm,48,50 and its effect on the light output and performance.

Figure 2.Figure 2.Figure 2.
Figure 2. Effect of increasing the distance between the light guide tip and the sensor target on the irradiance output using Satelec Mini LED (Acteon, Merignac, France). The red line represents the manufacturer's recommended irradiance of 500 mW/cm2.

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

Figure 3.Figure 3.Figure 3.
Figure 3. The effect of increasing the distance on the time required to reach 16 J/cm2 recommended to cure resin composites using Satelec Mini LED (Acteon, Merignac, France).

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

Figure 4.Figure 4.Figure 4.
Figure 4. The effect of increasing the distance of the light tip on the irradiance output using Satelec Mini LED (Acteon, Merignac, France). The light irradiance performance is reduced to 75% at 7 mm and 66% at 10 mm.

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

Beam Light Uniformity

The light output uniformity across the emitting tip and the irradiance distribution from four representative lights tested in this study are shown in Figure 5. The beam profiles show differences in the beam diameters among different lights and inhomogeneous irradiance distribution with the presence of hot spots (indicated by the color scales on the right of each beam profile image).

Figure 5.Figure 5.Figure 5.
Figure 5. Beam profile images of four LED units showing the differences in the beam diameter and the beam heterogeneity across the tips.

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

Figure 6 shows examples of beam profile images comparing the effect of contamination and damage on the irradiance output.

Figure 6.Figure 6.Figure 6.
Figure 6. Examples Satelec Mini LED (Acteon, Merignac, France) LCU fiber optic tips and their corresponding beam profile images. (A,B) Representative control showing clean tip with unaffected beam profile distribution albeit with central hot spots of high irradiance output. (C,D) Representative images of chipped light guide tips showing compromised beam profiles where irradiance has significantly decreased in areas of chipping and damage. (E,F) Representative beam profile images of light guide tip with resin build up covering the surface resulting in significantly reduced irradiance in areas of resin build up. (G,H) Severely damaged light guide tip with large cold area in the corresponding beam profile image.

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

DISCUSSION

The dental light curing unit (LCU) is an essential piece of equipment in every dental practice. However, with most operators, proper use and maintenance of LCUs is not very well understood and often underappreciated. This study showed that 33% of the LED LCUs across primary and secondary dental settings were considered to be out of compliance with the minimum recommended light irradiance required to optimally cure resin composites using a convenient exposure time (~40 seconds). Most dental composite manufacturers recommend delivering a minimum of 500 mW/cm2 for a duration of 40 seconds for optimum curing, and many recommend shorter curing times if irradiance is higher, eg, >1000 mW/cm2 for 10 seconds. It has been previously reported that delivering 400mW/cm2 for 60 seconds is required to adequately cure a 1.5-to 2-mm thickness of resin composite.14,51 Consequently, when the irradiance is multiplied by exposure time, a sufficient radiant exposure of 16- to 24-J/cm2 is often quoted. It is possible to compensate for lower irradiance by prolonging the exposure time;1 however, this is not recommended by the manufacturers due to increased risks of overheating the pulp. The findings of this study are in agreement with other studies evaluating QTH and LED LCUs in dental practices ,which have shown that most curing lights are poorly maintained and deliver inadequate light irradiance for optimal curing process.32–37 This study also found that there was a general lack of awareness of the type and the irradiance output of the LCUs that are already in use. Practitioners were also unaware that a large number of LCUs were unable to deliver a sufficient light output to adequately cure resin composite restorations. Despite their routine use, most operators were simply using any LCU for 20 seconds without further knowledge on the wavelength and irradiance requirements. Additionally, there was a general lack of awareness of the impact of various clinical factors and the light guide factors on the efficiency and the performance of the LCUs.

This study investigated the effect of contamination of the light guide tip with debris, damage, increasing the distance, and using protective sleeves on the irradiance output and the performance of LCUs. Our data showed that all aforementioned factors have significant impact on the overall light output and performance and should be taken into consideration when the LCU is used. These results showed that presence of debris build-up and damage of the light curing tip resulted in reducing the irradiance output by 62% and 50%, respectively.

The effect of increasing the distance from the restoration was also evaluated in this study. It might be assumed that this falls under the inverse square law; however, this does not always occur. The inverse law is applicable on a point source of radiation emitting 360° in space, whereas the emission from the light curing unit does not act as a point source. The light emitted from dental LCUs varies depending on the design and the optics within the unit. The findings of this study showed significantly lower irradiance values reached by the surface when the distance of the light source from that surface increases. The total irradiance output for the Satelec Mini LED (Acteon) was reduced by 25% and 34% at 7 mm and 10 mm, respectively. Previous studies also reported that some curing lights deliver only 25% or less of the irradiance measured at the tip when the distance is increased by 8 mm.12,45,50,52 Therefore, operators should take into consideration the clinically relevant distances that may affect the irradiance output delivered to the restoration, especially in a Class II cavity box where the distance between the cusp tip and the base of the box may exceed 7 mm.52 Furthermore, it is important to ensure that the LCU is emitting sufficient light to compensate for the reduction over the distance and to consider increasing the exposure times for the initial increments.

The effect of barriers including use of protective sleeves was also evaluated. Our data showed that the use of protective sleeves reduces the overall output by 24%. It was previously reported that when some commercial barriers are used, the light output can be reduced by up to 40%.44,53,54 Therefore, it is important to emphasize that when a barrier is used, it should fit tightly over the light tip and not obstruct the light output (Figure 7) in order to minimize the refraction that occurs when light passes through different mediums and the impact on the light output. Additionally, it is recommended that the light output from the LCU should be recorded with the barrier over the tip when they are routinely used. Having a tightly fitted barrier not only will be a good infection control measure, it will also prevent debris build up on the LCU tip, which also affects the irradiance output. It was suggested that clear plastic food wrap can be an inexpensive and effective infection control barrier with minimal effect on light output.44,53

Figure 7.Figure 7.Figure 7.
Figure 7. The light protective sleeve is (A) fitted tightly over the light tip whereas (B) shows a less ideal fit, which impedes the light output.

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

Several studies have shown that the light output from many LCUs is not uniform and the irradiance homogeneity depends on the design of the curing light and optical arrangement.55–58 In this study, beam profiles were not uniform, with hot spots of high irradiance and cold spots of lower irradiance values. Therefore, using a single irradiance value does not describe the irradiance across the entire light tip. Consequently, manufacturers should provide the beam profile of their LCUs. The clinical relevance of the beam profiles is highlighted by overlaying the irradiance beam images on a cavity preparation, shown in Figure 8. This shows that some locations in the cavity may receive different amounts of light depending on effective light tip size and the homogeneity of the light output. It also shows that the size of the light curing tip may not necessarily reflect on the actual active tip emitting sufficient irradiance output. Consequently, the light received at the proximal boxes from some LCUs may be inadequate for optimal curing if used for one exposure cycle. Therefore, multiple exposure cycles may be required especially if a small tip is used to cover the entire restoration (Figure 8).

Figure 8.Figure 8.Figure 8.
Figure 8. (A–C) Images showing molar tooth preparation, Satelec Mini LED (Acteon, Merignac, France) light curing tip with 7 mm diameter and its corresponding beam profile image superimposed on the cavity preparation. This shows that the light beam does not cover the entire cavity and will require multiple exposures to cover the entire restoration, as shown in (D).

Citation: Operative Dentistry 46, 3; 10.2341/20-092-LIT

The condition of the light curing tip can degrade over time due to debris build-up or simply damage that may occur with regular use and autoclave procedures.38 Additionally, clinical barriers are often present, such as matrix bands and tooth position, which limit the access of the light curing tip to the intended restoration. It is also important to appreciate that these factors are usually combined, such as distance of the light from the restoration and the use of a protective sleeve, which would act together, resulting in a significant reduction in the overall light output. Consequently, composite restorations could be undercured and prone to early failure due to decreased bond strength, bulk fractures, and increased wear.9,10,12

Regular monitoring and maintenance protocols for LCUs should be in place in every clinic. This should include regular evaluation of the irradiance output and careful evaluation of the light curing tips for debris build-up and damage. Handheld dental radiometers are widely available and can be used to monitor the light output, even if only as a relative measurement of performance with continued use. However, several studies have reported their inaccuracy in measuring absolute irradiance.59–62 The sensor area of most commercial dental radiometers is usually smaller than the LCU tip diameter, which therefore provides inaccurate values. However, a recently introduced dental radiometer, the BluePhase II from Ivoclar Vivadent (Schaan, Liechtenstein), used in this study, was able to measure the irradiance of up to a 13-mm diameter tip due to its large sensor area. It was reported that the accuracy of the Blue Phase II is comparable to laboratory-grade spectrophotometers, providing the most accurate data compared to other commercial dental radiometers47.

It is also important to appreciate the role of education and training on the use of LCUs. It has been reported that there is up to a 10-fold difference in the ability of different operators to deliver adequate light exposure even when the same light source is used.63,64 Operator variability can be minimized and improved techniques can be employed if users are trained on how to use the curing lights using a device such as the MARC patient simulator (Blue Light Analytics). Training on this device allows operators to learn how to correctly position the light and the patient to improve access to the restoration for effective curing process. The MARC patient simulator has been shown to be effective in teaching appropriate light curing techniques by providing direct feedback to the operator on how much irradiance is delivered and highlights operator factors that result in a suboptimal curing process.65–67

On the basis of this study, in order to help improve the use of LCUs, the authors make the following recommendations:

  • Have a protocol in place for regular monitoring and maintenance of LCUs to meet the manufacturers' specifications.

  • Inspect and clean the LCU before use to ensure that it is free of defects and debris.

  • Use infection control barriers that fit tightly over the light tip without impeding the light output.

  • Follow the light exposure times and increment thickness recommended by the resin composite material manufacturer.

  • Position the light tip as close as possible (but without touching the uncured resin composite material to avoid debris) and parallel to the surface of the resin composite being cured.

  • Stabilize and maintain the tip of the LCU over the resin composite throughout the exposure.

  • Be aware that further light exposure cycles may be required when there is limited access, barriers present, curing larger restorations, and when using protective sleeves.

  • Ensure eye protection by using appropriate blue blocking filters.

Following the findings of this study, LCUs which were found to be of poor quality and with low irradiance output were immediately removed from the clinics and replaced. Furthermore, local protocols were put in place within both dental hospitals to regularly check and evaluate the LCUs in use. LCUs were then followed up to ensure sufficient output, and are now regularly monitored and audited. General dental practices were also made aware of the findings, and further measures were taken to ensure that their lights are able deliver sufficient light output. General dental practices were also given a suitable maintenance and monitoring protocol to follow.

CONCLUSIONS

This study showed that there is lack of protocols for regular monitoring and maintenance of LCUs used in primary and secondary care. Thirty-three percent of the LCUs delivered irradiance output less than 500 mW/cm2. The condition of the light curing tips was also poor, with 16% contaminated with resin debris, 26% damaged, and 10% both contaminated and damaged. Using damaged and contaminated light curing tips, protective sleeves, and increasing the distance from the restoration significantly reduce the irradiance output and the performance of the LCU.

    Conflicts of Interest The authors of this article certify that they have no proprietary, financial, or other personal interest of any nature or kind in any product, service, and/or company that is presented in this article.

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Copyright: © Operative Dentistry, 2021 2021
Figure 1.
Figure 1.

Satelec Mini LED (Acteon, Merignac, France) with a light protective sleeve (WRAPAROUND, UnoDent, Essex, England) over the tip.

Figure 2.
Figure 2.

Effect of increasing the distance between the light guide tip and the sensor target on the irradiance output using Satelec Mini LED (Acteon, Merignac, France). The red line represents the manufacturer's recommended irradiance of 500 mW/cm2.

Figure 3.
Figure 3.

The effect of increasing the distance on the time required to reach 16 J/cm2 recommended to cure resin composites using Satelec Mini LED (Acteon, Merignac, France).

Figure 4.
Figure 4.

The effect of increasing the distance of the light tip on the irradiance output using Satelec Mini LED (Acteon, Merignac, France). The light irradiance performance is reduced to 75% at 7 mm and 66% at 10 mm.

Figure 5.
Figure 5.

Beam profile images of four LED units showing the differences in the beam diameter and the beam heterogeneity across the tips.

Figure 6.
Figure 6.

Examples Satelec Mini LED (Acteon, Merignac, France) LCU fiber optic tips and their corresponding beam profile images. (A,B) Representative control showing clean tip with unaffected beam profile distribution albeit with central hot spots of high irradiance output. (C,D) Representative images of chipped light guide tips showing compromised beam profiles where irradiance has significantly decreased in areas of chipping and damage. (E,F) Representative beam profile images of light guide tip with resin build up covering the surface resulting in significantly reduced irradiance in areas of resin build up. (G,H) Severely damaged light guide tip with large cold area in the corresponding beam profile image.

Figure 7.
Figure 7.

The light protective sleeve is (A) fitted tightly over the light tip whereas (B) shows a less ideal fit, which impedes the light output.

Figure 8.
Figure 8.

(A–C) Images showing molar tooth preparation, Satelec Mini LED (Acteon, Merignac, France) light curing tip with 7 mm diameter and its corresponding beam profile image superimposed on the cavity preparation. This shows that the light beam does not cover the entire cavity and will require multiple exposures to cover the entire restoration, as shown in (D).

Contributor Notes

*Asmaa Altaie, BDS, MSc, MFDS RCS (Edin), PhD, Restorative Dentistry Department, School of Dentistry, University of Leeds, Leeds, UK

Mohammed A Hadis, BSc (Hons), PhD, Biomaterials Unit, School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK

Victoria Wilson, BDS (Merit), MFDS RCS (Edin), School of Dental Sciences, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK

Matthew J German, BEng (Hons), MSc, PhD, School of Dental Sciences, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK

Brian R Nattress, BChD, PhD, MRD RCS (Edin), FDS RCS (Edin), FFDTEd, Restorative Dentistry Department, School of Dentistry, University of Leeds, Leeds, UK

David Wood, BSc (Hons) Materials Science, PhD, Division of Oral Biology, School of Dentistry, University of Leeds, Leeds, UK

William M Palin, BMedSc, MPhil, PhD, Biomaterials Unit, School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK

*Corresponding author: Restorative Dentistry Department, School of Dentistry, Worsley Building, Clarendon Way LS2 9LU, West Yorkshire, Leeds, UK; e-mail: A.ALTAIE@LEEDS.AC.UK

Clinical Relevance

Clinicians should regularly monitor and maintain their light curing units (LCUs) to ensure an optimal light curing process. It is also essential to appreciate the factors that reduce the performance of the LCU.

Accepted: 13 Sept 2020
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