High Demand for Composites a Driving Force for Curing Light Advancements
As advances in composite material continue to emerge, so do various types of curing lights. Curing-light units were first introduced in the mid-1970s, beginning with the Nuva Light by DENTSPLY Caulk.1 This curing system utilized ultraviolet light, which posed various safety issues and offered limited reliability, making clear the need to improve the system.2 Next, developments in technology that produced various types of polymerization sources led to the introduction of visible light-cured systems. To date, available curing-light systems now include quartz-tungsten-halogen (QTH), plasma arc (PAC), argon laser, and light-emitting diode (LED).3 An overview of each of these systems, including benefits and drawbacks unique to each, is provided below.
Known as the most common curing system, QTH units are composed of a quartz bulb with a tungsten filament in a halogen setting.4 These units illuminate both UV and white light and emit light only in the violet-blue section of the spectrum, which conforms to the photoabsorption range of comphorquinone.4 Most of this generated light is transferred to heat, leaving somewhat less than 0.5% appropriate for curing.2 The generated heat is controlled and kept at the lowest possible level during actual light-curing due to the inclusion of filters within the system. To keep this curing-light system cool, a ventilating fan is incorporated within the infrastructure to eliminate any undesirable heat from the reflector and filters.
A QTH system is relatively inexpensive—as are replacement halogen bulbs—and all composite materials can be cured within 20 to 40 seconds. The chief complaints about QTH units are that they are quite large and heavy and employ a noisy fan, and the bulbs need regular replacement.5 But perhaps the biggest drawback is that the units are corded, which limits their mobility.
In addition to conventional QTH units, a more intensified, enhanced halogen curing system has hit the market that offers better curing magnification and faster curing. However, this enhanced unit is more expensive than a conventional QTH and still exhibits some of the same shortcomings.5
Plasma Arc (PAC)
Newer to the dental market than the conventional QTH, plasma arc curing-light units offer higher intensity as well as more rapid curing, enabling clinicians to be more productive. The PAC light unit utilizes a plasma-containing fluorescent bulb in which light is formed between two tungsten electrodes under pressure. There are no filaments in this bulb, as with the QTH; instead, it has two rods that arc and create a constant spark when the unit is started.6 The PAC light emits a power density greater than 2,000 mw/cm2, but a wait time of 10 seconds is necessary after each use to allow the unit to recover.7
Despite the advantage of a curing time of approximately 3 seconds, there are reports of greater polymerization shrinkage compared to that with the QTH units.4 It has also been reported that the short curing times suggested by the manufacturers are inadequate for many composite materials.3 Other disadvantages include the expense of purchasing the unit and replacement bulbs and that it is corded as well as large and heavy.
Laser units have been available in dentistry since the 1990s. The argon laser unit, which emits blue light, has the highest intensity of all curing lights available.4 Many clinicians find the cordless lasers to be more convenient and efficient because of their rapid curing time and the small amount of heat they emit due to their limited infrared output. These units are not only filter-less, but they are most effective within a narrow field of wavelengths.4 Due to the argon laser’s small fiber size, difficult-to-access areas of the mouth are more easily reached by the curing light, contributing to a more satisfactory result for the completion of composite restorations.7
Other notable advantages of argon lasers are that they produce an increased magnitude and penetration of composite curing, and no variance in bond strength is displayed when compared to conventional QTH systems. Among their disadvantages is constricted spot size, which makes it necessary for the clinician to go beyond the normal curing cycles when the size of the restoration is greater than the curing tip.7 In addition, argon lasers are expensive, they can only be used for composite curing, and increased marginal leakage and polymerization shrinkage of composites have been reported with their use.4
Light-Emitting Diode (LED)
The LED is the newest of the curing lights available on the market today, consisting of first-, second-, and third-generation series. The light that is emitted from LEDs is produced from junctions of doped semiconductors.7 The second-generation series of LED curing lights are said to offer the highest photopolymerization productivity.7 Unlike the halogen curing system, LED curing units give off a narrow spectrum of light. This light falls within the absorption range of camphoroquinone, resulting in high-energy performance of curing light.4 This can be a problem with composites using other initiators; therefore, some manufacturers have added an additional LED wavelength to allow for the curing of all composites. Other positive attributes of LED units include: they are cordless, small in size, and lightweight; there is no generation of heat; and frequent replacement of the diodes is not necessary.5
An improved wavelength range is seen with the third-generation series, which offers the clinician a well-proportioned combination of positive characteristics.3 However, these units can be relatively expensive, the batteries need frequent recharging, and the curing time is greater than that of PAC units and some enhanced QTH devices.4 Since these units do not have a fan, some will only cure for a limited amount of time (2 to 3 minutes) before they shut off to cool down. Some of the newer LED curing lights allow for the clinician to decide whether to use different curing methods (step-cure, pulse-cure, high-intensity cure, or regular cure) for each clinical situation.
Composites are an essential dental material for most practicing clinicians. Major improvements in this highly demanded material have prompted the manufacturing of more efficient and compatible curing lights. Among the various light-curing devices in today’s market, clinicians face the challenge of selecting a unit that best suits their individual needs within their daily practices. Whatever qualities a clinician is seeking, there is a wide variety of features available: high-intensity cure, low-intensity slow cure, corded or cordless, differing curing tip sizes and focal points, smaller dimensions, and lighter in weight.
Looking ahead, curing devices will likely become even more user-friendly and efficient. In the future, it is expected that companies will focus on producing faster and less cumbersome curing lights. Emphasis will be placed on improvements to the halogen and LED devices, which are the types most used by clinicians. One key aspect that remains true regardless of what type of curing light a clinician selects is that the device must be able to adequately cure all composite material. Clinicians are advised to select curing devices of good quality and to periodically assess their units to ensure sufficient power output.7 By placing the composite material in appropriately sized increments and adhering to each manufacturer’s instructions for adequate light cure, clinicians should be able to consistently achieve a successful outcome.
1. Curing lights for composite resins. Health Mantra Web site. https://www.healthmantra.com/lightcure.shtml. Accessed March 1, 2012.
2. Roberson T. Biomaterials. In: Sturdevant’s Art and Science of Operative Dentistry. 5th ed. St. Louis, MO: Mosby; 2006:204-205.
3. Mahn E. Light polymerization. Inside Dentistry. 2011;7(2):66-73.
4. Mala K, Malhotra N. Light-curing considerations for resin-based composite materials: a review. Part 1 . Compend Contin Educ Dent. 2010;31(7):498-508.
5. Goster C. The evolution of curing lamps. https://www.articlesbase.com/business-opportunities-articles/the-evolution-of-curing-lamps-4353559.html. Accessed March 1, 2012.
6. Rueggeberg F. An expert’s buying guide for curing lights . ADA Professional Product Review. 2009;4(4):13-15.
7. Ataide I, Fernandes M, Lambor R, Singh T. Light curing devices - a clinical review. J Orofacial Res. 2011;1(1):15-19.
Related content: Learn more about curing lights at dentalaegis.com/go/cced158
About the Authors
Ashanti D. Braxton, DDS
University of Tennessee College of Dentistry
James F. Simon, DDS, MEd
Professor and Director
Division of Esthetic Dentistry
University of Tennessee College of Dentistry