From their introduction 50 years ago, curing lights have become an indispensable part of everyday dentistry, driven by the ongoing evolution of resin-based composite materials for faster, more esthetic, durable results. Whether you’re placing bulk fill or a sealant, you eventually reach for a curing light. But which one? As the variety of restorative materials expands and light technology continues to develop, the answer becomes more complex.
How dental curing lights work
Light curing, or photopolymerization, depends on converting individual resin monomer units into connected polymer chains, thereby decreasing the viscosity of the resin material until it becomes solid. This process is initiated by molecules called photoinitiators, which generate free radicals when they absorb light of a specific wavelength. The free radicals interact with the resin monomers to change their chemical bonds so that they can link to each other, releasing more free radicals in the process to help the conversion continue throughout the material. The higher the degree of conversion, the more durable the resulting restoration. However, because the process also leads to a degree of material shrinkage, care must be taken to avoid stress at the tooth-composite interface, which can lead to secondary caries.
The degree of conversion is affected by several factors, such as the intensity of the light; the shade, composition, and depth of the restorative material; the distance and angle of the light to the composite; and the time of exposure. In addition, different photoinitiators respond to different wavelengths of light, making the need to choose the right light for the right material critical to success.
From UV to laser light
The first light-cured restorative materials used photoinitiators that were activated by ultraviolet (UV) light. However, issues of color stability, depth of cure, and tissue damage – notably cataracts – associated with UV light exposure made them less than ideal for clinical use. Photoinitiators activated by visible-light wavelengths were quickly adopted, the most common of which are still in use today.
The original visible-light curing lights used a quartz-tungsten-halogen bulb that had the advantage of emitting a wide spectrum of wavelengths and therefore being able to cure any material. On the other hand, these lights were corded and bulky, required active internal cooling, and lost power over time, requiring regular bulb replacement.
Today’s lights are mostly LED-based, making them cooler, longer lasting, and more energy efficient and ergonomic. Since the late 1990s, they have evolved from units emitting only blue light to those containing multiple LEDs of different colors to cover a wider selection of photoinitiators. The lights also have increased in power to shorten curing time even in bulk fill applications. There is even a laser model now on the market.
The most commonly used photoinitiator – camphorquinone (CQ) – is triggered by blue light with a wavelength of 420 to 540 nm. The blue LED curing lights currently on the market emit wavelengths in a range between 430 and 480 nm for effective curing with CQ. However, because CQ is yellow, clear materials, such as sealants, use a different photoinitiator that requires a different light wavelength. Here are the common photoinitiators and necessary wavelengths:
- Camphorquinone (420 to 540 nm)
- Lucirin TPO (380 to 425 nm)
- Phenylpropanedione (350 to 490 nm)
Making the perfect match
Advances in composites and curing lights continue to bring great improvements to restorative dentistry, including shorter chair times, better esthetics and ergonomics, and less invasive preparations, benefiting patients and dentists alike. Ensuring compatibility between the material being cured and the light doing the curing helps keep restorations predictable, successful, and durable. Here are some factors to consider in choosing a curing light:
- Type of light source
- Light intensity
- Ability to achieve consistent, desired cure throughout restoration without excessive heat
- Beam uniformity
- No “hot spots”
- Tip diameter
- Wavelength compatibility with preferred light-cured materials
- Cordless vs. corded
- Ability to access all areas in the oral cavity
- Calibration method and ease
- Cure modes
From blue and multicolored LEDs to laser technology, the number of dental curing tools available on the market can be overwhelming. Speak with your Patterson representative for guidance on choosing the best curing units for the needs of your practice.
Dental curing light safety tips
Although curing lights are used only for a few seconds at a time, they still need to be handled with respect for their potential to cause tissue damage – to dental professionals as well as patients.
Dental staff safety
For dental staff, the eyes are particularly at risk. Exposure to high levels of blue light can immediately burn the retina, while prolonged absorption of low levels of blue light can contribute to macular degeneration. As curing lights increase in intensity, ocular tissues can become overexposed in less than 10 curing cycles. Safety glasses appropriate for the type of light – LED or laser – should be worn whenever curing lights are used. Safety glasses that meet the ISO standard for eyewear used against intense light in cosmetic and medical settings are preferable for use with LED lights.
From the patient perspective, the main concern is potential overheating of pulpal tissue while the composite is being cured. Many curing lights can generate a temperature increase of 40 to 50°F in the restorative material, causing patient discomfort and pulp damage. Cooling with continuous airflow while curing, waiting several seconds between curing cycles, and spraying with water afterward can help reduce this risk.
Basic protocol for curing-light use:
- Prepare light for use
- Place barrier
- Confirm correct settings for intended use
- Wear eye protection
- Position light for optimum cure and minimum tissue damage
- Maintain position while curing
- Use cooling techniques while curing
- Cure for recommended time
- Follow material manufacturer instructions
- Clean and disinfect light
- Follow light manufacturer instructions
- Measure intensity of emitted light periodically
As with all instruments that enter the oral cavity, curing lights must have an infection control protocol. Many units on the market are autoclavable; barrier sleeves also can be used. Cleaning should always follow manufacturer instructions to avoid damaging the light.
References and additional resources:
American Dental Association. Dental curing lights. May 5, 2021.
Brucia JJ. Light curing in restorative dentistry: The devil is in the details. Dentistry Today. February 1, 2020.
DeWood G. The evolution of composites and light-curing. Spear. December 17, 2018.
Goff S. Don’t overlook the impact of choosing, using the right curing light. Dental Products Report. October 2, 2020.
Hasanain FA, Nassar HM. Utilizing light cure units: A concise narrative review. Polymers. 2021;13(10):1596.
Mangat P, Dhingra A, Bhardwaj G. Curing lights and the science behind them – An overview. IOSR J Dent Med Sci. 2014;13(12):35-39.
Strassler H, Oxman J, Rueggeberg F. What should you look for in a curing light? Intl Dentistry Afr Ed. 2018;7(6):36-40.
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