Everyday Dentistry | Curing Lights
Know your options
There are plenty of curing light options available. Knowing the difference between them will help ensure curing success.
By Sebastiano Andreana, DDS, MS, Professor, Department of Periodontics, Loma Linda University School of Dentistry
Curing lights have become a common tool in the dental office, so much so that a recently published review found that almost 94% of dentists surveyed use or have a visible light-curing unit in their office. Dentists who use curing lights to cure composites primarily own one of four types: light-emitting diode (LED), halogen, laser, and plasma arc (PAC). The LED and halogen lights are the two most commonly used today.
Darker shades require longer curing times than a thin layer or a very light shade of composite.
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Despite their increasing prevalence in the dental office and the fact that they all are indicated for light-curing resin-based materials such as composites and bonding agents, the curing lights demonstrate different curing capabilities based on their inherent characteristics. It behooves dentists to understand these characteristics and how they may affect the complete curing of their restorations and, ultimately, the success of the dental treatments they provide their patients.
The major difference among curing lights is the emitting light source, which subsequently dictates the wavelength of light emitted and what materials the light can cure. The emitting source for the different curing lights are:
- Halogen lights: Quartz-tungsten-halogen bulb
- LED curing lights: Diode
- PAC lights: Xenon plasma arc bulb
- Laser curing units: Argon
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Fig. 1 When the light from the curing unit reaches the composite, bonding agent, or sealant, the photo-initiators in those materials trigger the curing process. Those photo-initiators are sensitive to specific wavelengths of light.
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Fig. 2 Using a cordless curing unit—one that can be operated using finger or thumb controls to quickly and efficiently change settings—facilitates user-friendly operation.
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Consistent light output is critical to restorative success. If a clinician is curing a composite and knows that the curing time—as per the manufacturer’s instructions—is 10 seconds, then the given composite should harden or cure in 10 seconds when it’s light-cured at the specified output. However, the cure will be incomplete if there is a drop in output because the curing light’s energy will not reach the bottom layers of composite.
The halogen curing light’s emitting light source is a bulb, so its light output is diminished with each use. If dentists measured the halogen light output when the curing light was brand new and then again after using the light year-round, they would likely observe a drop in the light output.
This phenomenon does not occur with an LED curing light because its emitting light source—the diode—is more constant and consistent over time, which is one of the biggest advantages to using an LED curing light.
It is important for clinicians to know that there may be discrepancies between the advertised output and the actual output of some LED curing lights. Although sometimes insignificant, a claimed output of 1,000mW/cm² might actually be 500 mW/cm². This may happen as a result of the manufacturing tolerances of LEDs.
When dentists know for sure that they have constant and consistent output, they can feel confident that they are achieving a completely cured restoration. They do not have to overcome a loss of light output by increasing their curing time. Because they don’t actually know how much longer they would need to cure their restorations, any additional time would be a guess.
Wavelengths and intensity
An important characteristic of any curing light is the wavelength of light produced. When the light, regardless of its source, reaches the composite, bonding agent, or sealant, the photo-initiators in those materials trigger the curing process. Those photo-initiators are sensitive to specific light wavelengths, some of which may not fall within the capabilities of some curing lights.
Some halogen curing light bulbs only emit light within certain wavelengths. The LED curing lights have a narrow spectrum of light that falls closely within the absorption range of most of the photo-initiators that are used in the available products on the market today. The peak of the photo-initiators is around 470 nm, which is in the 400 to 500 nm LED curing light range.
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