This study investigated the accuracy of sixteen models of commercial dental radiometers (DR) in measuring the output of thirty-eight LED light curing units (LCUs) compared with a 'gold standard' laboratory-grade spectrometer integrating-sphere (IS) assembly. Nineteen Type I (fiber-bundle light guide) and nineteen Type II (light source in head) LED LCUs were tested, some using different output modes and light guides, resulting in 61 test subsets per radiometer. Gold standard (GS) output measurements (n = 3) were taken using the IS and confirmed with two types of laboratory-grade power meter (PowerMax-Pro 150 HD and PM10-19C; Coherent). One DR (Bluephase Meter II, Ivoclar; BM II) allowed power (mW) as well as irradiance (mW/cm2) recordings. Irradiance readings (n = 3) for each DR/LCU were compared with the IS derived irradiance. Individual LCU irradiance values were normalized against IS data. The GS method yielded reproducible data with a 0.4% pooled coefficient of variation for the LCUs. Mean power values ranged from 0.19 W to 2.40 W. Overall power values for the laboratory-grade power meters were within 5% of GS values. Individual LCU/DR normalized irradiance values ranged from 7% to 535% of the GS; an order of magnitude greater than previous reports. BM II was the only radiometer to average within 20% of normalized pooled GS irradiance values, whereas other radiometers differed by up to 85%. Ten radiometers failed to provide any reading for 1 LCU. When tested with the PowerMax-Pro in high speed (20 kHz) mode, eight LCUs demonstrated pulsing outputs undetectable at the standard (10 Hz) data acquisition rate. Sufficient light exposure is critical for the successful curing of dental resin-based materials. Substantial discrepancies may occur between actual and estimated radiometric data using current DRs. More accurate DRs need to be developed. Manufacturers' accuracy claims for DRs should specify compatible LCUs and testing parameters.
The dental light-curing unit (LCU) is an essential item of equipment in contemporary dental practice, and since the development of light-activated resin-based composites in the 1970s, over 1000 different types, makes, and models of LCUs have been marketed [[
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Table 1 Type I LCU optical properties and dimensions.
Light curing unit Manufacturer/ Distributor Serial Number Modes tested External tip diameter Active diameter Active area Wavelength Range (nm) Violet/ Blue Chip Peak Irradiance Bluephase 20i Ivoclar 500339 Low, High, Turbo 8 10 7.4 9.0 43.0 63.6 385–515 V/B 650, 1200 & 2000 Bluephase Style Ivoclar 1100001962 Standard 10 9.0 63.6 385–515 V/B 1100 Bluephase Style M8 Ivoclar 1130000241 Standard 10 9.0 63.6 430–490 B 800 TransLux2Wave Kulzer 312SF024 Standard 8 7.5 44.2 385–510 V/B >1400 (Cure Rite) Scanwave Prototype Acteon PRT06 tP, PP & CQ 7.5 (Multifiber) 7.5 (Monofiber) 6.9 7.4 37.4 43.0 390–510 V/B N/A S10 3M 9.3912300E+11 Standard 10 9.6 63.6 430–480 B 1200 Deep Cure 3M 9.3312300E+11 Standard 10 9.6 63.6 430–480 B 1470 Bluephase 16i Ivoclar 1674493 Standard 8 13 7.4 11.8 43.0 109.4 430–490 B 1600 Supercharged Mini LED Acteon 302320–025 High 7.5 7.0 38.5 420–480 B 2000 SK-L036 Spark N/A Standard 8 7.5 44.2 420–480 B 2200 Cybird XD Dentazon CXD-13142425 High & PE 8 7.2 40.7 430–490 B 1500 & 2700 S.P.E.C 3 Coltene 130630030 High & 3K 8 11 7.4 10.0 43.0 78.5 430–490 B 1600 & 3000–3500 BA Ultimate 1400 BA International BA110507 Standard 8 7.0 38.5 400–480 V/B 1400 Xlite 3 3H Dental 114000089 Standard 8 6.5 33.2 385–515 V/B 1100 BLAST lite First Medica BL0446 Standard 8 7.2 40.7 not available B 2200 Omega LED O'Ryan L-LS6:0 08080520 Standard 8 7.6 45.4 not available B 450 Bluephase C8 Ivoclar N/A Standard 8 7.4 43.0 420–480 B 800 JAS-2001 B Online N/A Standard 8 6.6 34.2 400–490 B >2700 Demetron A2 Kerr 95 430 Standard 4 8 11 13 3.7 7.4 9.9 12.5 10.8, 43.0, 77.0, 122.7 450–470 B 1100
1 *Manufacturers stated.
2 **Measured light-emitting diameter and calculated area
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Table 2 Type II LCU optical properties and dimensions.
Light curing unit Manufacturer Serial Number Modes tested Active diameter Active area Wavelength Range (nm) Violet/ Blue Chip Peak Irradiance Xlite 2 3H Dental 6700001695 Standard 7.8 47.8 380–515 V/B 1600 Smartlite Focus Dentsply SLAB01489 Standard 7.5 44.2 430–490 B 1000 Demi Ultra Kerr 786000330 PLS 7.9 49.0 438–485 B 1100–1330 SiriusMax ND MC-132699 Normal/Xtra 9.1 65.0 430–490 B 1200 & 3000 Pencure VL-7 Morita YD3024 Standard 8.8 60.8 420–480 B 1000 Pencure VL-10 Morita CG5004 M2 8.8 60.8 420–480 B 1000 Fusion 3.0 Blue Dentlight 1AF50505 High 9.6 72.4 420–490 B 2700 Fusion 3.0 Violet Dentlight 9AE42226 High 9.6 72.4 390–430 V 2700 Fusion 5.0 Blue Dentlight LH80306 SF80306 Standard / Plasma 9.6 72.4 415–490 B 4000 (Plasma) Fusion 5.0 Violet Dentlight VH10640 SF80306 Standard / Plasma 9.6 72.4 390–430 V 2700 (Plasma) Valo Ultradent V02539 Standard 9.6 72.4 395–480 V/B 1000 Valo Grand Ultradent S00906 Standard/High/Xtra 11.7 107.5 395–480 V/B 3200 (Xtra) Radii Plus SDI 31950 Standard 7.0 38.5 440–480 B 1500 Coltolux Coltene 9224025 Standard 7.8 47.8 450–470 B NA FLASH lite Magna Den-Mat 9338018 Standard 11.0 95.0 440–490 B > 1100 i LED Woodpecker L1731737i P1 & P2 7.8 47.8 420–480 B 2300 (P1) DTE LUX-1 Woodpecker L176_7X1 Standard 6.4 32.2 420–480 B 850–1000 Xlite 4 3H Dental C000120B4 Standard 7.0 38.5 385–515 V/B 2000 Radii Xpert SDI 15010 Standard 7.5 44.2 440–480 B 1500
- 3 *Manufacturers stated values.
- 4 **Measured light-emitting diameter and calculated area. For Type II LCUs the external head diameter is neither relevant nor reported by the manufacturers.
Effective photopolymerization is a significant contributing factor for the quality and long-term clinical success of light-activated resin-based composite restorations. Many factors influence polymerization efficiency, and the LCU is a key extrinsic variable in the final material properties of the photocured resin [[
Light meters or dental radiometers (DRs) have been proposed as a better way of monitoring LCU performance compared with simple tactile surface hardness 'tests,' and different conclusions are reported in the literature [[
While manufacturers of DRs claim accuracy of their units between ~5–20%, comparisons against GS test instruments (mentioned above) typically reveal differences of ~20–50%. Reported inaccuracies include physical [[
Consequently, the aims of the current work were to:
- Test the ability of a range of commercial dental radiometers to measure a representative selection of 19 Type I and 19 Type II LED LCUs relative to the "gold standard" laboratory-grade integrating sphere, and fiber-optic coupled spectrometer derived irradiance values.
- Measure the "snapshot" power output of the LED-LCUs with three examples of a BM II DR and to compare the data with power outputs recorded with a traditional laboratory thermopile sensor instrument (PM10-19C; Coherent) and the fast response power meter (PowerMax-Pro 150 HD; Coherent).
- Measure the spectral radiant power outputs of the Type I and Type II LCUs over the entire exposure period with a benchtop fiber-coupled spectrometer instrument (MARC-LC, BlueLight Analytics) and to compare this method with the "GS" radiometric test.
- Determine whether the dental DRs are less accurate in recording irradiance for broad-spectrum LED-LCUs, given that the spectral response of silicon photodiode sensors varies between violet, violet-blue and blue wavelength bands.
The null hypotheses of this study were:
- There will be no significant difference (P>0.05) between the mean pooled radiant power values measured with the integrating sphere and fiber-coupled spectrometer "GS" test method and a radiometer with wide spectral sensitivity (~380–550 nm; BM II, Ivoclar-Vivadent), for either Type I or Type II LED-LCUs.
- There will be no significant difference (P>0.05) between radiant power values measured with a laboratory-grade thermopile sensor (PM10-19C, Coherent) and a fast response thin-film detector (PowerMax-Pro 150 HD).
- There will be no significant difference (P>0.05) between radiant power values measured with the "GS" test method and the mean of the power values recorded over the entire exposure duration as recorded with a benchtop calibrated instrument (MARC-LC, BlueLight Analytics).
- No tested commercial DR will be within ±20% of the mean irradiance value derived using the "GS" test method.
- All tested commercial DRs will give significantly lower (P<0.05) normalized irradiance values for LCUs where the majority (>60%) of spectral power is <450 nm in comparison with those lights where most (>65%) of the spectral radiant output is >450 nm.
The commercial DR models under investigation are described in Tables 1 and 2 according to the manufacturer, model, serial number, display type, sensor window aperture diameter, irradiance recording, and spectral sensitivity ranges. The Bluephase Meter I (BM I) and the Ledex CM 4000 are the only radiometers which use linear sensors.
The light output of nineteen Type I (Table 1) and nineteen Type II LCUs (Table 2) was evaluated. A number of the units were tested in different power and/or spectral radiant power combinations. Five Type I units were also tested with light guides of different exit diameters or configuration, resulting in 61 test groups. The Type I 'Scanwave' (Satelec, Acteon, France) was a prototype unit that, unlike the commercially marketed variant (Mini-LED Scanwave), allowed continuous light output in three different spectral ranges depending on which pair of the four different wavelength chips were activated. This unit was tested both with a standard multifilament tip as well as a solid (single filament) glass tip, which distributed the light output more uniformly across the tip exit face. Six of the Type I and Type II LCUs incorporated some or all of their light output in the violet range (Tables 1 and 2).
Two spectrometer systems were compared, namely:
A 15 cm diameter laboratory-grade integrating sphere (Labsphere, North Sutton, NH USA) with a custom 16 mm entrance port linked to a calibrated fiber-optic coupled spectrometer (USB 2000+, Ocean Optics) was used to record total power in a "snapshot" fashion, ~1 s after the light was activated, within the 380–540 nm range, and spectra for each LED-LCU (n = 3). An internal reference light source (Labsphere) was used to calibrate the system before the measurements. The percentage of the power output for each LCU in the 380–450 nm range and the 450–520 nm range was also determined. The current international standard for testing dental powered polymerization activators (ISO 10650–2018) has added a method for measuring radiant exitance (section 7.4.1) using a spectrometer and compatible Integrating Sphere assembly to the previous method (section 7.4.2) which used bandpass filters in conjunction with a flat response power meter.
The MARC LC
Two laboratory-grade power meters, a traditional thermopile sensor (PM10-19C; Coherent, Ely, UK), and a fast response thin-film detector (PowerMax-Pro 150 HD; Coherent) were used to record power outputs for the LCUs (n = 3) at 10 Hz. The emitted radiant power of each LCU was measured with the LCU light source exit tip or window fixed ~0.5 mm from, but without touching, the detector surface. Power output was recorded continuously, and the peak power output was registered. For the PowerMax-Pro, LCU power was also measured with the 20 kHz (high-speed) acquisition rate to resolve any temporal pulse output pattern for each LCU and to eliminate the effect of aliasing on average power readings with LCUs that exhibited a high pulse repetition rate.
The internal diameters corresponding to the "effective" or optically active light-emitting exit window diameters of the Type I and Type II LCUs were measured to the nearest 0.1 mm with a digital micrometer (Mitutoyo Inc., Japan) and confirmed with a digital microscope (Veho, Dayton, OH, USA). Irradiance values for each LCU were then derived from the radiant power measurements using the quotient of the radiant power and the calculated light source emission area.
Three examples of the BM II (Table 3) were used to record power measurements for each LCU (n = 3 per LCU). Light guide or light exit window surfaces were positioned as directed by the manufacturer's instructions, i.e., in contact with the meter surface.
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Table 3 The radiometer models tested are listed according to the manufacturer, model, sensor aperture diameter, irradiance, and spectral sensitivity range.
Manufacturer Model Serial Number Analog / Digital Sensor Window Aperture (mm) Irradiance Range (mW/cm2) Wavelength (nm) Demetron L.E.D. 79309372 Analog 7 < 2000 400–500 S.D.I LED 2–22481 Digital 12 < 2000 400–525 Ivoclar Bluephase Meter I (BMI) 5667 Digital 3 300–2500 385–515 Ivoclar Bluephase Meter II (BMII) 1300000003; 1300001134; 1300001150 Digital 15 300–12000 380–550 Tpcdental TPC LM-300 LED & QTH L143000296 Digital 7.25 0–2500 400–500 Efos Cure Rite 8000 3594 Digital 10 0–2000 400–525 Dentsply Cure Rite 644726 7886 Digital 6.5 0–2000 400–525 Coltene Coltolux C7900 95101064 Digital 8.5 0–2000 400–525 Mega-Physik Cromatest 7041 70410366 Digital 9 100–1999 400–525 Dentmate Ledex CM 4000 CB0520 Digital 2 200–4000 390–500 Rolence Meter 200 1317/2009 Digital 6 0–5000 400–520 CMS CQ LIT 2013 Analog 6 0–6000 N/A 3H LED N/A Digital 8.5 0–2000 350–550 Holz LED C00000CC2 Digital 8 50–3600 350–550 Woodpecker LM-1 541004 Digital 8 0–3500 400–500 FVE BTM-2000 FVB001415 Digital 10 0–999 400–540
5 Irradiance and wavelength ranges are drawn from manufacturers' literature. The two underlined meters BM I and Ledex CM 4000 are the only ones that use linear sensors. Of the tested models, the BM II (n = 3) (Ivoclar-Vivadent, Liechtenstein) is the only radiometer that can measure power. It can also calculate the irradiance if the light probe has a 6 to 12 mm circular diameter.
Three readings were taken for each of the LCUs in each test condition, i.e., 'modes tested' and 'tip type and diameter' (Tables 1 and 2) using the hand-held DRs listed in Table 3. Two of the DRs (Ledex CM 4000 and BM I) incorporate linear strip sensors, 2 mm and 3 mm in width, respectively, that are designed to estimate light output tip diameter to calculate LCU irradiance. For the BM II, the scale on the underside of the instrument allowed the round exit tip external diameters from 6 to 12 mm of the Type I LCUs to be estimated to the nearest 1 mm for irradiance measurement. GS irradiance of the Type II LCUs was calculated from power measurements using the 'active light-emitting areas' (Table 2). All the irradiance values for each LCU and radiometer combination were normalized relative to the mean irradiance determined for the LCU from the "GS" test method (Section 2.1.1), which allowed differences to be determined for each light source, mode and tip combination. Fitted line regression plots with 95% confidence and prediction intervals were generated to assess the power meter and DR results using the GS as the predictor variable.
A light source (AURA, Lumencor, USA; optically active (light-emitting) diameter = 5 mm) with three spectral band outputs (λ
Beam profile images were recorded for the LCUs using a CCD array laser beam profiler camera placed at a fixed distance from the diffusing surface of a translucent frosted glass screen target (DG2X2-1500, Thor Laboratories, Newark, NJ, USA). The light tip or exit window was placed against the target diffusing surface to record the images. Details of the method have been described previously [[
Linear regression analysis (Minitab v18 software) was used to investigate the relationship between the power data determined by the BM II radiometer, the laboratory-grade power meters, and the GS integrating sphere assembly test method. Similar analyses were performed for irradiance data derived from the power measurements using the GS test method and the tested commercial DRs. Parametric analysis of variance methods (balanced and general linear model methods) were used to compare raw data at P = 0.05 significance level. Distribution free Mann-Whitney U tests were employed to compare the spectral responsivity of the commercial radiometer models to the GS test method using the normalized irradiance data generated by two subsets of LCUs where the majority of the spectral output was either above (>65%) or below (>60%) 450 nm.
Individual power values recorded using GS integrating Sphere system ranged from a low of 0.19W for the Omega LED-LCU to a high of 2.40W for the Xtra Power mode of the Valo Grand. Excellent agreement (R
Graph: Fig 1 Regression analyses and fitted line plots with 95% confidence and prediction intervals for mean power recordings of the Type I and Type II LED-LCUs using (a) the PM10-19C thermopile, (b) the LabMax Pro, (c) the MARC LC and, (d) the BMII (sn: 1300001150). For each analysis, the integrating sphere gold standard power (W) data was used as the predictor variable. Several high outlier results were noted in Fig 1 (d) for Type II LED-LCUs (I LED in standard and high output modes, Pencure VII and Fusion 5 (Blue Head) in Plasma mode). As the BM II is only designed to generate irradiance data for light guide tip diameters between 6 and 12 mm, the values generated for the 4 mm and 13 mm tips of the Demetron A2 LED LCU were based on programming the nearest tip diameter value (6 mm and 12 mm, respectively) to obtain the readings which were then corrected for area differences.
No statistically significant difference (P>0.05) in the power values from the LCUs were recorded for the three examples of the BM II. The mean pooled difference between individual LCUs compared by any two of these three meters was < 2% showing excellent intra-meter power reading reproducibility. For the three BM II instruments, overall power values for Type I LED-LCUs were 6.9% lower than the GS. However, the mean pooled normalized results for Type II LCUs tested with the BM II instruments ranged from 6.7 to 8.3% greater than the GS values (Fig 2), and the difference was statistically significant (P < 0.001; DF = 24). Power data for Type II LCUs recorded with the PM10-19C and PowerMax-Pro were 4.1% and 3.8% lower than the GS value, respectively; a pattern similar to the results for the Type I LCUs. Individual Type II LCUs (Smartlite Focus, Pencure VII, Fusion 5.0, and i LED) generated power readings >10% above the corresponding GS test method data for all three tested examples of the BM II. For three LCUs (Pencure VII, Fusion 5.0, and i LED) the mean readings were >25% above the GS. Power readings taken with the MARC LC yielded results closest to the GS test method with normalized pooled values that were 1.2% and 0.5% lower for Type I and Type II LCUs, respectively.
Graph: Fig 2 Pooled normalized mean power readings for all LED-LCUs relative to the integrating sphere gold standard data 100% values.Note the difference between the Type I and Type II LED-LCU data distributions for the BM II units (average of the three tested units shown) compared with the two laboratory-grade power meter instruments and the MARC LC integrating sphere / spectrometer apparatus.
Agreement (R
Graph: Fig 3 Regression analysis fitted line plots comparing irradiance data for the (a) BMII (sn:1300001150) and (b) the CQ LIT radiometer with the corresponding Integrating Sphere derived irradiance data sets as the independent variable.
Graph: Fig 4 Normalized pooled mean irradiance for all LCUs; (a) Type I and (b) Type II tested with the sixteen models of dental radiometers—the 3 examples of the BM II are denoted by the last 4 digits of their respective serial numbers ...0003, ...1134, ...1150 and the MARC LC instrument (calculated from mean power data) relative to the gold standard Integrating Sphere method. Note the extremely wide data spread for many radiometers.
Based on the results, the:
- The first null hypothesis was accepted as there was no significant difference between the pooled mean power value recorded for the GS ((Type I LCUs pooled mean 0.6988 W (95% C.I. 0.6422–0.7554) and Type II LCUs pooled mean 0.8251 W (95% C.I. 0.3404–2.4068)) and the BM II (Type I LCUs pooled mean 0.6487 W (95% C.I. 0.5921–0.705) and Type II LCUs pooled mean 0.8896 W (95% C.I. 0.3743–2.508)) for either type I (P = 0.219) or type II (P = 0.423) LCUs. When individual LCU mean power values were compared however, significantly greater mean power values (P<0.05) were recorded for GS versus BM II for all but one type I LCU (JAS-2001 B) which showed no significant difference (P>0.05) between GS and BM II. In contrast, when individual LCU comparisons were made for type II LCUs fifteen units registered significantly greater mean power (P < 0.05) when tested by GS in comparison to BM II and only four LCUs (Demi Ultra, Valo, Coltolux and Radii Expert) the opposite. As a consequence, the pooled mean power values for the BM II normalized to the GS test method were significantly higher for Type II versus Type I LCUs (P<0.05; Fig 2). Further, there was no significant difference (P>0.05) between the response of Type I and Type II LCUs for either of the two laboratory-grade power meters or the MARC LC instrument (Fig 2).
- The second null hypothesis was accepted as there was no significant difference (P = 0.856) between mean power readings recorded with the PM10-19C thermopile instrument and the fast response PowerMax-Pro sensor (Fig 2).
- The mean power for all LCU tests recorded using the MARC LC was 0.743 W (95% CI: 0.686–0.800), and for the GS test method, it was 0.753 W (95% CI: 0.696–0.810). There was no significant difference between the means (P = 0.807), and therefore, the null the third null hypothesis was accepted.
- All three examples of the BM II produced an average irradiance deviation from the GS test method of between 16.4–17.4%. Therefore, the fourth null hypothesis was rejected in part. However, the remaining radiometers produced greater mean deviations from the GS, ranging from 23.2% (BM I) to 84.5% (CQ LIT radiometer; Fig 3). Fig 4 highlights the substantial deviation in irradiance data for the sixteen models of radiometer relative to the IS control and the MARC LC instrument. Ten of the radiometers failed to give any reading with one or more LCU. The CQ LIT instrument was unable to provide any reading in one or more test conditions, with 20 of the 38 tested LCUs. Individual LCU and radiometer combinations produced mean irradiance values ranging from 7% (Fusion 5.0, "Plasma" output mode tested with the SDI radiometer) to 535% (Smartlite Focus tested with the CQ LIT radiometer) of the GS normalized value.
- Fig 5A and 5B highlight the spectra for those LCUs and operation modes having >60% of their output below or >65% above 450 nm, respectively (S1 Fig provides the radiant power exitance for all the tested LED LCUs). Eight LCUs in one or more modes had >60% of their output below 450 nm, and eleven had >65% of their output above 450 nm. Normalized data for these two subsets of lights were compared with Mann Whitney U-tests. LCUs with a majority of violet output had significantly lower (P<0.05) normalized median responses (relative to the GS) compared with the LCUs with a majority of blue light output for most radiometers. Consequently, the fifth null hypothesis was accepted in part. However, the BM I and the three tested examples of the BM II exhibited no significant difference (P>0.05) between medians; thus, these four radiometers behaved differently from the other dental radiometers.
Graph: Fig 5 Radiant power of the LCUs, that delivered a) greater than 60% of their power output below 450 nm and b) greater than 65% of output above 450 nm.
A further series of tests were performed with a calibrated light source (AURA, Lumencor) with three waveband outputs (λ
Graph
Table 4 Mean irradiance readings (n = 3) for the radiometers generated using the Lumencor Light Engine (LE) with irradiance set at 1049 ± 146 mW/cm2 for the separate violet (λmax = 405nm), blue (λmax = 470nm) and green light (λmax = 550nm) outputs three wavebands.
Light Meter LE 405 nm LE 470 nm LE 550 nm Kerr LED 100.0 (0) 376.7 (5.8) 0.0 (0) S.D.I. LED 0.0 (0) 413.3 (5.8) 0.0 (0) Bluephase Meter I 830.0 (0) 723.3 (5.8) 850.0 (0) Bluephase Meter II 521.1 (16.2) 482.2 (4.4) 896.7 (10) TPC LM-300 420.0 (0) 510.0 (0) 670.0 (0) Efos Cure Rite 115.7 (1.2) 431.3 (2.5) 60.7 (4.7) Caulk Cure Rite 39.7 (0.6) 389.7 (0.6) 19.7 (0.6) Coltolux 226.7 (0.6) 520.0 (0) 250.0 (0) Cromatest 83.0 (0) 463.3 (0.6) 202.0 (0) Ledex CM 4000 460.0 (0) 776.7 (2.9) 2633.3 (7.6) Rolence meter 200 79.3 (1.5) 406.0 (2.6) 0.0 (0) CQ LIT 0.0 (0) 0.0 (0) 6000 (0) 3H LED 317.7 (2.3) 1291.7 (2.3) 1868.7 (2.3) FVE BTM-2000 0.0 (0) 274.7 (0.6) 0.0 (0) Woodpecker LM-1 175.0 (0) 550.0 (0) 1225.0 (0) Holz LED 0.0 (0) 317.3 (1.5) 0.0 (0)
6 The BM II readings are based on the average of the three tested examples of this radiometer. The discrepancy between the programmed irradiance for the LE and the values here is attributable to the fact that the light engine liquid-filled light guide's external diameter is 2 mm greater than the active light-emitting diameter. When the irradiance is calculated based on the smaller output area the BM II values for the violet and blue wavebands approximated the programmed 1,000 mW/cm
A supplementary investigation was conducted on a retrieved mirror attenuator from one of the BM II instruments (sn: 1300001134). Light transmission was measured through the attenuator and without it using the λ
The minimum and maximum power values recorded with the GS Integrating Sphere test setup were 0.19 W for the Omega LED-LCU and 2.40 W for the Valo Grand in Plasma output mode. The BM II mean power values for the SmartLite Focus Type II LCU were 12 to 13% higher than the mean integrating sphere control value and 20 to 21% higher than the PowerMax-Pro value.
The optics of the disassembled BM II mirror attenuator (Fig 6A) and Demetron L.E.D. radiometer (Fig 6B) were used to image the beam profiles of selected LCUs (Fig 6C). Beam profiles demonstrated that the light was diffused by the Demetron L.E.D. radiometer optics. In contrast, the light pattern was essentially unaltered as imaged through the BM II mirror attenuator for the two monowave LCUs. The output from the violet chip of the Bluephase Style "polywave" LCU was increased relative to the corresponding blue light output when imaged through the BM II mirror, in contrast, to directly imaging the light tip exit face (Fig 6C). In this study, all power and irradiance data for the Bluephase Style was recorded using the unit with the current beam homogenizing tip. The original non-homogenizing tip was only used for the beam profile work in Fig 6 to show the effect of the BM II mirror on the violet and blue chips output separately.
Graph: Fig 6 (a) The front surface mirror attenuator from the disassembled BM II (sn:1300001134) and the large area photovoltaic cell array light sensor which lay directly beneath it; and (b) the "optics" components (diffusers, heat and bandpass filters) from a disassembled Demetron L.E.D. radiometer and the small area photodiode sensor typical of other dental radiometers for comparison. The BM II meter incorporates a light tip diameter guide, allowing the operator to measure the light guide tip diameter for programming the instrument in "irradiance reporting" mode. (c) Beam profile images of 2 single spectral peak Type I LED LCUs (S10 and S.P.E.C.3) and one LED LCU with 2 wavelength band outputs (Bluephase Style with the original non-homogenizing light guide to show the two blue and one violet LED chips separately). From left to right the profiles were recorded by imaging: 1, directly onto the light guide exit face (left column); 2, through the mirror attenuator of the BM II (middle column) which was disassembled after the remainder of the project was completed (Fig 6A; sn: 1300001134); and, 3, through the reassembled optics (Fig 6B) of the Demetron L.E.D. radiometer (right column). Note the relative increase in output for the violet chip (~7 o' clock position on the image) versus the two blue chips of the Bluephase Style when imaged through the BM II mirror attenuator (middle column–bottom image) compared to imaged directly onto the light guide exit face (left column).
Using the MARC LC device, the irradiance from the central 4 mm diameter of the light guides of two LCUs (Elipar S10 and Elipar Deep Cure) was measured and compared with the mean irradiance over the full optically active area of the 10 mm diameter light guide. Hence, overall irradiance was greater for the Deep Cure unit (1303 mW/cm
Graph: Fig 7 Beam profiles of the (a) Elipar Deep Cure and (b) Elipar S10 units. The beam widths in both the horizontal and vertical directions (x and y, respectively) are given by D4σ which is 4 times σ, where σ is the standard deviation of the horizontal or vertical marginal distribution respectively. Note the more uniform color-coded irradiance distribution across the exit window face of the Deep Cure light guide compared to the central "high spot" peak irradiance region for the S10. The dotted lines represent the beam area that faced the 4 mm cosine corrector of the MARC LC lower sensor. The images explain why the irradiance ranking for these two LCUs reverses when the irradiance is measured over the central 4 mm diameter region of the beam in comparison with irradiance calculated from the total power output related to the optically active area of the light guide (9 mm diameter). Fig (c) and (d) show the local irradiance distributions for the Satelec Supercharged and Spark SK-L036A units, respectively. Readers should note that these images use different irradiance scales.
Graph: Fig 8 Fitted line plot of irradiance recorded with the BM I linear sensor radiometer versus integrating sphere derived irradiance for Type I and Type II LED-LCUs.High outliers (circled from left to right of the graph) were noted for the Spark SK-L036A, Satelec Supercharged, and Blast Mini LED-LCUs. A similar pattern was noted with the Ledex CM 4000 sensor. These two radiometers were the only ones with relatively narrow linear sensors. When beam profiles for these three units were inspected, it was noteworthy that all three units exhibited centrally located "hot spots" with low areas of light output on the outer regions of the light guide exit faces. Fig 7C and 7D show representative beam profiles for two of these three LCUs.
For the Demetron A2 LCU (4 mm tip), every DR underestimated the irradiance by 18 to 39% compared to the GS. Irradiance was determined with the BM II meters first by using the lowest programmable light guide diameter (6 mm) and then re-estimated according to a 2.25 times greater area correcting for tip diameter (Fig 9). When the S.P.E.C.3 LCU was tested in standard output mode, three radiometers gave significantly greater (P<0.05) irradiance readings with the 11 mm diameter tip while five gave significantly (P<0.05) greater readings with the 8 mm tip.
Graph: Fig 9 (a) Irradiance values calculated for the four tested guide diameters (D: 4, 8, 11, 13 mm) of the Demetron A2 LED LCU based on power (mW) readings recorded (
Recording power output over the full exposure cycle time of each LCU with the MARC LC spectrometer-based instrument revealed additional information compared with the momentary or snapshot recordings of power captured by the BM II instruments, or in the way that the laboratory-grade power meters, and the GS integrating sphere were initially configured (Fig 10A). Power recorded with the high speed (20 kHz) acquisition mode of the PowerMax-Pro sensor revealed that eight of the LCUs under investigation (see Fig 10B for details of the names of the eight LCUs) had a high frequency pulsing power output in one or more modes which is not apparent at the normal 10 Hz acquisition rates commonly used with laboratory-grade power meters.
Graph: Fig 10 (a) Stable power output over time for the Elipar Deep Cure-S LED-LCU compared with other LCUs (BA Ultimate 1400, Bluephase 16i HIP mode, Fusion 5 Plasma power), recorded using the MARC LC spectrometer-based instrument acquiring data at 30 frames per second. A relatively slower rise in power output versus time is seen for the Bluephase 16i in "High Power" output mode while the output from the Fusion 5.0 declines slightly over the 3 s Plasma output mode run time. Note pulsing nature of light output for the BA Ultimate 1400 seen at the 30 Hz rate, (black) At ~5 s, the BA Ultimate 1400 LCU switches off briefly and immediately restarts. The pulsing output was found to relate to changes in the violet component of the light output over time. (b) Four of the eight LCUs from the 38 tested exhibiting pulsing output patterns in high speed (20 kHz) data acquisition mode with the PowerMax-Pro fast response power meter (S.P.E.C.3, Omega, I LED and Xlite 2 not shown). Fig 10Bi shows Power output (W) for the S.P.E.C.3 in standard and 3K modes. Ten pulses over 0.005s equalling a rate of 20 kHz for this LCU. Note similar peak power output in both modes with lower average power output for the standard mode due to longer off duty times between pulses. The manufacturers claimed irradiance values for these modes (1600 and 3000–3500 mW/cm2) corresponded closely with GS irradiance data recorded using the I.S./spectrometer test method (~1900 and ~3400 mW/cm2). Fig 10ii to iv show the outputs for the BA Ultimate 1400, Radii Xpert, in their standard operating modes. The Cybird XD LCU in High and Plasma power output modes and the Sirius Max in Xtra power mode. The standard output mode for the Sirius Max showed steady output with no pulsing behaviour. Fig 10ii to 10iii are the same apart from the different x-axis time scales. (c) (i) shows power output for the S.P.E.C.3 in standard and 3k modes. Ten pulses over 0.005s equalling a rate of 20 kHz for this LCU. Note similar peak power output in both modes with lower average power output for the standard mode due to longer off 'duty' times between pulses. Depending on tip diameter (8 or 11 mm), averaged power values recorded with GS method were ~1.45–1.55 W for 3K mode and 0.85–0.9 W for standard mode and ~0.1 W less as recorded with the LabMax-Pro as displayed here. The manufacturers claimed irradiance values for these modes (1600 and 3000–3500 mW/cm2) corresponded closely with GS irradiance data recorded using the I.S./spectrometer test method (~1900 and ~3400 mW/cm2). (ii) shows the standard output mode for the S.P.E.C.3 recorded this time with the LabMax-Pro operating in Snapshot mode at 625 kHz. Note changes in pulse shape between (i) and (ii) due to ~30-fold increase in acquisition rate.
Challenges exist when measuring the irradiance delivered by dental LED-LCUs [[
Frequently, DRs incorporate bandpass filters to limit light transmission to specific wavelength ranges. This may cause the spectral response of different meters to vary even though they share silicon photodiodes in common. Furthermore, the vast majority of radiometers have smaller sensor areas than the tested areas of the light source exit windows, and therefore may not yield irradiance data in line with light source radiant exitance [[
The supplementary investigation on a retrieved mirror attenuator of one of the BM II meters outlined in the second paragraph of section 3.2 of the results, the BM II manufacturer likely uses an attenuator that exhibits higher violet wavelength transparency to compensate for the longer wavelength sensitivity of the photovoltaic cell array used in this DR (S3 Fig). Based on their findings, Kakeyama et al. [[
The fact that the mean power readings for the Smartlite Focus tested with the BM II meters were 20% to 21% greater than for the corresponding Powermax-Pro power value accords with the findings of the study by Shimokawa et al. [[
Two DRs (Ledex CM 4000 and BM I) incorporate line sensors which are designed to measure effective light output diameter in order to be able to calculate irradiance. Shimokawa et al. [[
Modern dental LED-LCUs have very diverse design and output characteristics. Multi-spectral peak or so-called "polywave" units have been marketed to activate alternative photoinitiators that respond to violet light wavelengths (either for cosmetic purposes since camphorquinone may cause yellowing, or to increase polymerization rate since molar absorptivity of such alternatives is usually higher). Some LCUs vary their spectral output throughout the radiation cycle (BA Ultimate 1400, Bluephase G2 and 20i in soft start mode) and the Scanwave LCU [[
Since modern LCUs are now used for a much broader range of clinical applications, many manufacturers have introduced additional light guide tips of various diameters and shapes for Type I LCUs. Previous studies have reported that commercial radiometers overestimate actual irradiance with larger diameter (10.5 to 12.5 mm) tips but underestimate irradiance values with smaller diameter (≤8.0 mm) guides [[
Using the BM II light tip diameter guide (Fig 6A) to measure the external diameter of light guides in 1 mm increments can impose a significant inaccuracy for Type I LCUs. For example, a difference of only 0.5 mm between the external 8.5 mm tip diameter (56.74mm
Power measurements taken with traditional thermopiles typically acquire data at 10 Hz and have a relatively slow response time [[
DR measurements only provide an estimate of momentary light output and do not indicate the appropriate radiation time for a given material/LCU combination. Previous work has focussed on developing a practical test method to predict the setting time of any light-activated restorative material irrespective of light source or material formulation variables [[
A limitation of the current work is that in most cases only one example of each make and model of dental radiometer was tested. Current DRs cannot reliably estimate power or irradiance for a wide range of dental LED-LCUs. However, their value is that they may be used to periodically monitor the output of a LCU from new provided the test conditions are standardized (same DR, LCU operating mode and tip and etc.,) to guard against significant output decline. Manufacturers face major challenges in making an affordable and easy-to-use hand-held DR, which can accurately measure the power and/or irradiance of dental LCUs. Dentists will not be interested in purchasing laboratory-grade test instruments, which can prove to be very costly and more challenging to use. Even they have limitations such as the inability of most of them to register peak power of all LCUs unless operated at very high (20 KHz) data acquisition rates. It is believed that by addressing the issues with current DRs reported and discussed in the current investigation that dental manufacturers may be able to manufacture more reliable DRs based on innovative design features and sensor materials. Sensors which are larger than the light-emitting source area and have faster acquisition rates than current sensors, filters or attenuators which flatten the sensor spectral response, automated ways of measuring light source area and programs which allow power, as well as irradiance to be estimated, will be among the design features of new and improved DRs. New sensor materials, reductions in the cost of components, miniaturization of electronic components, and linking DR software to manufacturers' databases will all contribute to improvements in DR performance.
This study offers new insights into the possible reasons for DR inaccuracy and how they may possibly be addressed. Profound differences between actual and estimated irradiance were reported ranging from 7% to 535% of GS method for individual LCU/DR combinations–an order of magnitude greater than previously reported. Consequently, there is a need to use more reliable DRs for greater light measurement accuracy in a clinical setting. Despite this, the major value of currently available DRs lies in the fact that they may be used to periodically monitor the output of a LCU from new to guard against significant output decline in service.
Manufacturers should provide more accurate information on the output of their LCUs, including spectral emission characteristics and radiant power outputs of different modes over the full exposure period. Single irradiance values are of limited value and are often less reliable than the power measurements from which they are derived.
When researchers or manufacturers report irradiance values recorded using laboratory-grade test instruments, the light emitting diameter and area of the source, and test instrument sensor measurement diameter or area should always be stated along with the power.
Researchers who study resin photopolymerization should not rely on radiometers to assess the LCU output but rather report spectral radiant power output ideally over the full exposure cycle and emission spectrum characteristics. Current dental radiometers are not able to estimate these parameters.
S1 Fig.
Radiant power for all tested Type I (a) and Type II (b) LCUs.
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S2 Fig.
The calibration data of the AURA, Lumencor light source (light engine) with three spectral band outputs at λ
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S3 Fig.
A supplementary investigation was conducted on a retrieved mirror attenuator from one of the BM II instruments (sn: 1300001134)' light transmission was measured directly through a cosine corrector (top) and then with BM II mirrored attenuator interposed (bottom) using the 405 nm and 470 nm wavelengths of the Lumencor AURA Light Engine (set at ~1049 ± 146 mW/cm
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S4 Fig.
(a) Specular reflection for the BM II mirrored attenuator and the light entrance diffuser of the Demetron LED radiometer or "Kerr Optics". (b) Diffuse reflection (specular excluded) for the BM II and the Demetron "Kerr Optics" diffuser. Reflectance from the BM II is specular whereas it is diffuse from the "Kerr Optics" which is typical of the diffusers incorporated in nearly all dental radiometers. Note the reduced specular reflectance of the integrating sphere light for the BM II at shorter wavelengths consistent with the fact that this attenuator transmits a higher percentage of violet compared to blue compared to violet wavelengths. Spectra obtained using an Ocean Optics ISP-REF integrating sphere / spectrometer assembly. Reflectance waveband shown (380–550 nm) is the stated light sensing range for the BM II radiometer.
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By Adrian C. Shortall; Mohammed A. Hadis and William M. Palin
Reported by Author; Author; Author