Ability of four dental radiometers to measure the light output from nine curing lights

Abstract

Objectives

To evaluate the accuracy of four dental radiometers when measuring the output from nine light curing units (LCUs).

Methods

The light output from nine light-emitting diode LCUs was measured with a laboratory-grade power meter (PowerMax-Pro 150 HD) and four dental radiometers (Bluephase Meter II, SDI LED Radiometer, Kerr LED Radiometer, and LEDEX CM4000). Ten measurements were made of each LCU with each radiometer. Analysis of variance (ANOVA) followed by Tukey tests (α = 0.05) were used to determine if there was a difference between the calculated irradiance values from the power meter and those from the radiometers. Where applicable, the LCUs were ranked according to their power and irradiance values. The emission spectra from the LCUs was measured using an integrating sphere attached to a fiber-optic spectrometer (N = 10). The beam profile of the LCUs was measured with a beam profiler camera.

Results

Of the dental radiometers, only the Bluephase Meter II could measure power. ANOVA showed no significant difference between power values measured with the laboratory-grade meter and the Bluephase Meter II (p = 0.527). The difference between the mean irradiance reported by the various radiometers for the same LCU was up to 479 mW/cm 2 . The ranking of the power values obtained using the laboratory-grade meter was the same for the Bluephase Meter II.

Conclusion

When compared to the calculated irradiance values from the laboratory-grade power meter, the Bluephase Meter II provided the most accurate data.

Clinical significance

Considering the great variation between the irradiance values provided by radiometers and their overall inaccuracy when compared to a laboratory-grade meter, dentists should not place too much faith in the absolute irradiance value. However, hand-held radiometers can be used to monitor changes in the light output of LCUs over time.

Introduction

Both direct and indirect tooth colored restorations depend on successful photoactivation of light cured resins by light curing units (LCUs). Inadequate photocuring of resin-based materials leads to lower degrees of conversion . Since this is directly correlated to inferior mechanical properties of the resin and lower bond strength to the tooth , the success of the final restoration may be compromised. Thus, LCUs should deliver sufficient radiant exposure (J/cm 2 ) to the resin-based material. However, the radiant power that the LCU emits can be negatively affected by degradation of the components within the LCU, by restorative materials that are adhered to the light tip, or by sterilization of the light guide .

The ISO 10650 standard for measuring the output from LCUs uses a laboratory-grade power meter to measure the radiant power output . Such equipment is not commonly available in dental offices. Instead, dentists, and some researchers, use hand-held dental radiometers to monitor the output from their LCUs. However, previous studies have reported that such devices are unable to reliably make accurate measurements of the light output from LCUs . Also, until now these dental radiometers could not record the radiant power emitted from the LCU. Since the irradiance of an LCU is defined by the quotient of the emitted power and the emitting tip area, even small differences in the tip diameters can result in large differences in the irradiance values. In addition, it is now known that light is not always uniformly emitted across the entire light tip and since some dental radiometers (Supplementary Fig. 1) only have narrow apertures into the detector , different regions of high or low irradiance values may be measured depending on the position of the light tip over this aperture into the radiometer. Thus, it is not surprising that previous studies have reported that there is often a discrepancy between the irradiance values provided by the LCU manufacturer, those derived from a laboratory-grade power meter, and those obtained from dental radiometers .

The recently introduced Bluephase Meter II (Ivoclar Vivadent, Amherst, NY, USA) is a new type of dental radiometer that measures both the radiant power in mWatts and, when the light tip diameter is entered into the meter software, it will also calculate the irradiance. The manufacturer claims that this new meter can measure the radiant power output from 380 to 550 nm with an accuracy of ±10% compared to a laboratory-grade meter .

To date, the emission spectrum is not assessed by dental radiometers that the dentist can use in their office. Knowing the emission spectrum is important now that multi-peak light-emitting diode (LED) LCUs have been introduced . Some single-peak LED units deliver either no or very little light at the required wavelengths to activate some photoinitiators and yet they may deliver a high irradiance. Since some dental radiometers are designed to detect light only within a narrow range of wavelengths, this can also lead to inaccurate measurements of the light output and unexpected resin properties .

In view of the need for an accurate dental radiometer that the dentist can use in their office, this study evaluated the accuracy of hand-held dental radiometers when measuring the light output from different LCUs and compared to values to a fast response laboratory-grade power meter. This meter (PowerMax-Pro, Coherent Inc., Santa Clara, CA, USA) is constructed and configured differently than a thermopile. Specifically, the sensor contains a stack of thin films. Incident light in the range of 355 to 1100 nm and from 100 mW to 17W is absorbed and generates heat that flows vertically through these thin films. The electrical field produced moves perpendicular to the heat flow to the edges of the sensor where it is measured . In contrast to thermopile power sensors that take several seconds to respond, the PowerMax-Pro sensor is very fast and can provide a power reading within microseconds.

The null hypotheses of this study are:

  • 1.

    There will be no difference between radiant power values measured with the Bluephase Meter II radiometer and the laboratory-grade power meter;

  • 2.

    There will be no difference between the irradiance values reported using the different radiometers and the values calculated from the laboratory-grade power meter;

  • 3.

    There will be no difference in the rank order of the irradiance values from LCUs when measured with the different radiometers and using the laboratory-grade power meter.

Materials and methods

The light output from nine dental LCUs was evaluated in this study ( Table 1 ). Measurements were made with a laboratory-grade power meter and using four different dental radiometers ( Table 2 ). Supplementary Fig. 1 shows the entrance apertures into two of the radiometers and Supplementary Fig. 2 shows the external appearance of the four radiometers.

Table 1
Light curing units (LCUs), manufacturers, tip diameter and irradiance information provided by the manufacturers.
LCU Manufacturer Tip diameter provider by the manufacturer (mm) Irradiance provided by the manufacturer (mW/cm 2 )
Bluephase G2 Ivoclar Vivadent, Amherst, NY, USA 10 1200 ± 10%
Bluephase Style Ivoclar Vivadent, Amherst, NY, USA 10 >1400
Valo Ultradent, South Jordan, UT, USA 9.6 1000
Elipar Deep Cure-S 3M Oral Care, St. Paul, MN, USA 10 1470 ± 20%
Elipar S10 3M Oral Care, St. Paul, MN, USA 10 1200–10/ + 20%
Paradigm 3M Oral Care, St. Paul, MN, USA 10 1200–10/ + 20%
SmartLite FOCUS Dentsply, Milford, DE, USA 7.5 1000
Optilight Prime Gnatus, Ribeirão Preto, SP, Brazil 8 1200 ± 200
Slim Blast First Medica, Greensboro, NC, USA 8 1000–1200

Table 2
Dental radiometers, manufacturers, irradiance and wavelength ranges.
Radiometer Manufacturer Irradiance range (mW/cm 2 ) Wavelength range (nm)
Bluephase Meter II Ivoclar Vivadent, Amherst, NY, USA 300–12000 380–550
SDI LED Radiometer SDI, Bayswater, Australia <2000 400–525
Kerr LED Radiometer Kerr, Orange, CA, USA <2000 400–500
LEDEX CM4000 DENTMATE, New Taipei City, Taiwan 200–4000 390–500

Light output

The total radiant power emitted by the nine different LCUs was measured with the laboratory-grade power meter, PowerMax-Pro 150 HD (Coherent Inc.), and the Bluephase Meter II. The irradiance from these LCUs was also measured with the four brands of hand-held radiometers and the irradiance was calculated from the power values measured using the laboratory-grade power meter.

Laboratory-grade power meter

The emitted radiant output from each LCU was measured with the tip of the LCUs fixed within 0.5 mm of the PowerMax-Pro 150 HD detector, but without touching it. Ten measurements were made with the tip repositioned at each measurement. To allow the light output to stabilize, the radiant power emitted from the LCUs was averaged from the last 10 s of light exposure. The power values were compared using ANOVA and Tukey separately from the irradiance values. The internal diameter of the effective tip ( Fig. 1 ) was measured with a digital micrometer (Mitutoyo Canada Inc., Mississauga, ON, Canada), and the irradiance values from each LCU were calculated using the quotient of radiant power measured using the laboratory-grade power meter and the emitting light tip area.

Fig. 1
Tip diameter measurement. Only the tip diameter that emits light was considered as the effective tip diameter. Top figure- SmartLite Focus tip measurement and beam profile, with effective tip diameter of 8.0 mm and external tip diameter of 12.0 mm. Bottom figure- Bluephase Style tip measurement and beam profile, with effective tip diameter of 9.0 mm and external tip diameter of 9.8 mm.

Dental radiometers

Bluephase Meter II, SDI LED radiometer, Kerr LED radiometer and LEDEX CM4000

Ten measurements were made using each radiometer in a random order of radiometers and LCUs. The LCU tips were positioned as directed by the manufacturer’s instructions in contact with the meter. They were activated for 20 s, and the radiometer readings were recorded. The Kerr LED Radiometer was read in increments of 20 mW/cm 2 , whereas the digital radiometers were measured in increments of 1 mW/cm 2 . The tip diameters (mm) reported by LEDEX CM4000 radiometer were also recorded.

Bluephase meter II

The ability of four examples of the Bluephase Meter II (serial #0024, 1646, 1653, 1702) to measure the Deep Cure, Bluephase Style and SmartLite Focus LCUs were tested in a pilot study. In random order of LCUs, 15 repeat measurements were made over a three-day period. All four examples of the Bluephase Meter II reported mean power values from these three LCUs that were within 22 mW of each other. This represented at most a 4% difference between the four examples of this meter. One meter (serial #0024) was chosen for this study.

On the back of the Bluephase Meter II, there is a measurement scale ( Fig. 2 ) that allows the user to measure the external tip diameter of the LCU. This value is then entered into the meter software so that it can calculate an irradiance value (mW/cm 2 ). After the ten radiant power measurements (mW) had been made, the LCU tip diameters were measured using this scale on the back of the radiometer. The measured diameter was entered into the Bluephase Meter II and ten irradiance measurements were then made from each LCU. For each measurement, a LCU was randomly selected and positioned with the tip in contact with the radiometer and activated for 20 s.

Fig. 2
Bluephase Meter II measurement. a – Scale for tip measurement on the back of the radiometer; b – Measured tip diameter; c – Tip diameter value entered into the radiometer; d – Irradiance reported from a LCU.

To determine if there was difference between irradiance values measured by laboratory-grade power meter and the four dental radiometers, the irradiance results were subjected to analysis of variance (ANOVA) statistical tests followed by Tukey post-hoc multiple comparison tests (α = 0.05) for each LCU. To detect if there were differences between the ranked irradiance and the ranked power values, an ANOVA test followed by Tukey tests (α = 0.05) were also applied to each radiometer. The mean irradiance values were used to calculate the percentage error for each radiometer, when compared to the irradiance values that were calculated from the laboratory-grade power meter. Pearson correlation tests were applied to the radiometers results to verify if there was any correlation between their irradiance values and the power meter irradiance values (α = 0.05).

Emission spectrum

To determine if the entire spectral output from the LCUs could be measured by the dental radiometers, the LCUs were attached to an optical rail in front of the entrance to a 6” integrating sphere (Labsphere, North Sutton, NH, USA) that was connected to a fiber-optic spectrometer (the USB 4000, Ocean Optics, Dunedin, FL, USA). Ten readings were made of the spectral radiant power emitted between 350 nm and 550 nm for each LCU. An internal reference light source (Labsphere) was used to calibrate the system before starting the measurements.

Light beam profile

As previously described , a laser beam profiler that used a CCD camera with a 50-mm focal length lens (USB-L070, Ophir-Spiricon, Logan, UT, USA) was placed at a fixed distance from the diffusing surface of a translucent ground-glass target (DG2X2-1500, Thor Laboratories, Newton, NJ, USA). A custom made blue filter (International Light Technologies, Peabody, MA, USA) was used to flatten the spectral response of the CCD camera. BeamGage v6.6 software (Ophir-Spiricon) was used to calibrate the photonic count received by each camera pixel. The effective tip diameter of each LCU was measured using a digital micrometer (Mitutoyo Canada Inc.), and used to scale the image in the BeamGage software.

Before each image was collected, the UltraCal feature in the BeamGage software was used to normalize all pixels to a similar baseline value, thus eliminating the effects of ambient light. Five seconds after the LCU had been activated; the image received by the camera was captured using the BeamGage software. The mean values of emitted radiant power that had been collected with the laboratory-grade power meter were inserted into the BeamGage software to produce color-coded and calibrated images for each LCU. To illustrate what a radiometer sensor receives, beam profiles of the Bluephase Style, scaled to their maximum values, were also made through the 4.3 mm entrance aperture of the SDI LED Radiometer ( Fig. 3 ).

Fig. 3
Top images- Light tip, 2D and 3D beam profiles of the Bluephase Style, scaled to their maximum values. Bottom images- Light from LCU coming through the diffusor on the SDI LED Radiometer, 2D and 3D beam profiles made through the aperture and the light diffusor of the SDI LED Radiometer, scaled to their maximum values.

Materials and methods

The light output from nine dental LCUs was evaluated in this study ( Table 1 ). Measurements were made with a laboratory-grade power meter and using four different dental radiometers ( Table 2 ). Supplementary Fig. 1 shows the entrance apertures into two of the radiometers and Supplementary Fig. 2 shows the external appearance of the four radiometers.

Table 1
Light curing units (LCUs), manufacturers, tip diameter and irradiance information provided by the manufacturers.
LCU Manufacturer Tip diameter provider by the manufacturer (mm) Irradiance provided by the manufacturer (mW/cm 2 )
Bluephase G2 Ivoclar Vivadent, Amherst, NY, USA 10 1200 ± 10%
Bluephase Style Ivoclar Vivadent, Amherst, NY, USA 10 >1400
Valo Ultradent, South Jordan, UT, USA 9.6 1000
Elipar Deep Cure-S 3M Oral Care, St. Paul, MN, USA 10 1470 ± 20%
Elipar S10 3M Oral Care, St. Paul, MN, USA 10 1200–10/ + 20%
Paradigm 3M Oral Care, St. Paul, MN, USA 10 1200–10/ + 20%
SmartLite FOCUS Dentsply, Milford, DE, USA 7.5 1000
Optilight Prime Gnatus, Ribeirão Preto, SP, Brazil 8 1200 ± 200
Slim Blast First Medica, Greensboro, NC, USA 8 1000–1200

Table 2
Dental radiometers, manufacturers, irradiance and wavelength ranges.
Radiometer Manufacturer Irradiance range (mW/cm 2 ) Wavelength range (nm)
Bluephase Meter II Ivoclar Vivadent, Amherst, NY, USA 300–12000 380–550
SDI LED Radiometer SDI, Bayswater, Australia <2000 400–525
Kerr LED Radiometer Kerr, Orange, CA, USA <2000 400–500
LEDEX CM4000 DENTMATE, New Taipei City, Taiwan 200–4000 390–500

Light output

The total radiant power emitted by the nine different LCUs was measured with the laboratory-grade power meter, PowerMax-Pro 150 HD (Coherent Inc.), and the Bluephase Meter II. The irradiance from these LCUs was also measured with the four brands of hand-held radiometers and the irradiance was calculated from the power values measured using the laboratory-grade power meter.

Laboratory-grade power meter

The emitted radiant output from each LCU was measured with the tip of the LCUs fixed within 0.5 mm of the PowerMax-Pro 150 HD detector, but without touching it. Ten measurements were made with the tip repositioned at each measurement. To allow the light output to stabilize, the radiant power emitted from the LCUs was averaged from the last 10 s of light exposure. The power values were compared using ANOVA and Tukey separately from the irradiance values. The internal diameter of the effective tip ( Fig. 1 ) was measured with a digital micrometer (Mitutoyo Canada Inc., Mississauga, ON, Canada), and the irradiance values from each LCU were calculated using the quotient of radiant power measured using the laboratory-grade power meter and the emitting light tip area.

Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Ability of four dental radiometers to measure the light output from nine curing lights
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