A new approach for curing light activated oral biomaterials

Key Points

• A new technological approach for curing light activated oral biomaterials is presented. The new light curing unit (LCU) is based on blue light emitting diodes (LED).

• The main potential benefits of LED LCU technology are: long lifetime of LED LCU (several thousand hours), no filters or cooling fan required, virtually no decrease of light output over lifetime with resulting consistent and high quality of material curing.

• Simple depth of cure experiments of dental composites cured with LED technology show promising results.

Abstract

Objectives

To test the hypothesis that a blue light emitting diode (LED) light curing unit (LCU) can produce an equal dental composite depth of cure to a halogen LCU adjusted to give an irradiance of 300 mWcm–2 and to characterise the LCU's light outputs.

Materials and methods

Depth of cure for three popular composites was determined using a penetrometer. The Student's t test was used to analyse the depth of cure results. A power meter and a spectrometer measured the light output.

Results

The spectral distribution of the LCUs differed strongly. The irradiance for the LED and halogen LCUs were 290 mWcm–2 and 455 mWcm–2, when calculated from the scientific power meter measurements. The LED LCU cured all three dental composites to a significantly greater (P < 0.05) depth than the halogen LCU.

Conclusions

An LED LCU with an irradiance 64% of a halogen LCU achieved a significantly greater depth of cure. The LCU's spectral distribution of emitted light should be considered in addition to irradiance as a performance indicator. LED LCUs may have a potential for use in dental practice because their performance does not significantly reduce with time as do conventional halogen LCUs.

Main

Dental composite depth of cure with halogen and blue light emitting diode technology Mills R W, Jandt K D, Ashworth S H Br Dent J 1999; 186: 388–391

Comment

It is generally accepted that the properties and clinical performance of visible-light activated resin-based materials is related to their extent of cure. Research has shown that the extent of cure of dental composites is most affected by factors under the control of the clinician, such as composite thickness, duration of light exposure and light source intensity.¹ A minimal level of irradiance of blue light necessary to produce acceptable cure has been identified,² and there are many ways to achieve and exceed this minimal level. Conventional halogen bulbs, argon lasers and xenon arc lights are currently used in clinical practice. This study describes another approach employing a collection of blue light emitting diodes. The new curing light claims the following benefits over existing halogen bulb systems: significantly longer bulb life, consistent light output over time, filterless operation, and minimal heat buildup.

In this paper, a light curing unit composed of 25 blue LEDs was compared with a conventional halogen light curing unit in terms of its ability to cure three different dental composites. The irradiance of both curing units was measured accurately with a power meter, and their spectral outputs were evaluated with an imaging spectrograph. Depth of cure was evaluated using a penetrometer.

This study showed that the light emitting diode system produced slightly greater depth of cure for each composite despite having only 70% of the irradiance of the halogen source. An important distinction made in this work is that the output of these light sources differ and that this has a large effect on curing efficiency. The authors explain that the LED system is more efficient for curing composites because it has higher irradiance at the wavelengths over which the camphoroquinone initiator molecule absorbs in the visible spectrum. Previous work has shown that depth of cure and degree of conversion in composites is dependent upon total light exposure, as represented by the product of light intensity and irradiation time.³ However, as the current study clearly shows, this is only true for a given light source because it does not account for differences in spectral output.

As the authors correctly point out, there are many other factors that must be addressed to determine the clinical efficacy of this new light curing method. A few of note are the extent of cure as measured by IR spectroscopy, mechanical properties, wear, cost, and durabilty. However, the listed advantages coupled with the data presented in this study provide strong justification to continue the development of blue light emitting diode curing units for dentistry.