Curing Lights 360°: Less power, more cure

July 24, 2012

Photo-polymerization, i.e. light-initiated polymerization, has become an integral part of modern dentistry.

Photo-polymerization, i.e. light-initiated polymerization, has become an integral part of modern dentistry.

In the early 1960s, the first light-cuing dental composites were introduced in the market, which also led to the development of curing lights. In modern dentistry, dental composite resins, composite-based luting materials, adhesives and provisional restorative materials are all cured with the help of curing lights, which makes them one of the most-used products in the dental practice.

Not surprisingly, many of their attributes-like high power intensity, wide light wavelength spectrum, depth of cure and exposure time-are important for adequate polymerization of dental restorative materials.

Most visible light-curing restorative materials use a diketone photoinitiator such as camphorquinone to create free radicals that initiate photopolymerization.1 These free radicals polymerize composite resin by converting monomers or short-chain carbon groups to long-chain polymers that are stable, strong and chemically resistant. The effective wavelength range to activate camphorquinone has been reported to be between 450 nm – 500 nm, with peak wavelength of 470 nm.2

The “Total Energy” concept states that the process of light-induced polymerization is energy dependent and basically a product of light intensity and time. It’s estimated that a dose between 4,000 mWs/cm2 – 16,000 mWs/cm2 is recommended to sufficiently cure a composite increment of 2 mm (depending on the shade and translucency). Curing light units with inadequate power intensity should require a longer curing period to adequately cure the same composite resin.

The first dental curing light was developed in the 1970s. These curing lights used ultraviolet light for curing restorative materials. However, the use of these curing lights was discontinued because of the use of UV light with shorter wavelength (10 nm – 380 nm) that limited depth of cure of restorative materials.3,4

Quartz-Tungsten halogen (QTH) curing lights were introduced in the late 1970s. Despite some inherent limitations, these curing light units had been the mainstay in the dental profession for more than two decades. Halogen bulbs used in these units produce energy in the visible light spectrum. The light energy passes through a series of filters that narrows the light spectrum to a usable energy of approximately 400 nm – 500 nm.5,6 However, aging of the lamp, defective filters and damaged light guides affected the power output of halogen curing lights. 

Plasma Arc curing lights were introduced in the late 1990s. The emission of light occurs through glowing plasma, which is composed of gaseous mixtures of ionized molecules such as xenon molecules and electrons. Spectral emission range of PAC curing lights are comparable with QTH curing lights and produce high power intensity, but generate high heat and are expensive and bulky. 

Argon-ion laser technology also has been used to light cure restorative materials. These units emit blue-green light of activated argon ions in selected wavelengths (between 450 nm and 500 nm). When compared to QTH lights, argon lasers show improved conversion rates and polymerization depths. Although these showed improved physical properties compared to conventional QTH systems, heat generation during polymerization combined with considerably high initial shrinkage stresses have been reported to be problematic.

Today’s LED curing lights

Light-emitting diode (LED) technology has been introduced as an alternative energy source to polymerize dental restorative materials. LED curing lights use gallium nitride as a semiconductor and produce light with a wavelength range of 450 nm – 490 nm with a peak of 460 nm. Compared to traditional halogen curing lights, LED curing lights require less power to operate and have potential to be powered with rechargeable batteries, which makes these units cordless, portable and relatively lightweight.

Unlike halogen curing lights, these units produce less heat. LEDs don’t degrade over time and last for thousands of hours, producing nearly constant intensity. The energy range of LED curing lights is nearly ideal for the photoactivation of restorative materials containing camphorquinone as the photo-initiator. However, restorative materials that don’t exclusively contain CPQ as their photo-initiator might be problematic.

The peak sensitivity of camphorquinone is near 470 nm in the blue wavelength range. As camphorquinone has an intense yellow color because of its absorption properties, other initiators like PPD (phenylpropanedione) and Lucirin TPO have been employed in the formulation of dental composites in bleach shades and colorless protective varnishes. PPD has an absorption spectrum with a maximum wavelength of approximately 410 nm, while Lucirin TPO has an absorption spectrum ranging from 375 nm – 410 nm.7 Hence, an excellent polymerization condition cannot be obtained when using the conventional LED curing light units to photoactivate materials containing photoinitiators other than camphorquinone. These materials require an LED curing light with multiple wavelength technology.

The Bluephase Style LED Curing Light

Ivoclar Vivadent’s Bluephase Style LED Curing Light (Fig. 1) provides dentists and dental assistants who routinely use curing light equipment with vast hidden potential to improve the efficiency, ease, comfort and predictability of their direct composite restoration procedures. The easy-to-program curing light features two-button operation (Fig. 2), allowing users to choose among 10-, 15-, 20- and 30-second cure times. Instructions are included to guide the operator through appropriate polymerization.

Efficient curing

Most restorative materials, indirect restorations, adhesives and temporary materials are cured using the 10-second timing. The curing recommendations for composite materials apply to all shades, and if not otherwise indicated in the instructions for use, to a maximum layer thickness of 2 mm (Fig. 3). These recommendations generally apply to situations where the light probe emission window is placed directly over the material being polymerized. Increasing the distance between the light source and material requires extending the curing time accordingly. 

Cures all materials

Most LED lights available today have a narrow broadband range, which limits their use to composites containing only specific photo-initiators. However, the Bluephase Style features Polywave™ technology and boasts the broadest spectrum of any LED on the market (385 nm – 515 nm). Therefore, the Bluephase Style can cure all dental materials on the market to date. Figure 4 shows the light curing gingival barrier and Figure 5 shows curing bonding resin.

Improved posterior access

The most efficient way to deliver energy from a curing light is via the light probe (Fig. 6). Until now, however, gaining easy access to the posterior region meant using an LED that doesn’t use a light probe, thereby affecting the light’s efficiency. The Bluephase Style’s light probe design provides optimal energy efficiency while enabling convenient access to posterior teeth.

Continuous curing

Because of energy efficient LED technology, the Bluephase Style LED Curing Light reduces the amount of heat generated internally to provide continuous curing for more than 10 minutes. This allows operators to avoid unpleasant breaks because of a shut off caused by overheating. The Bluephase Style can be used for extensive cementation procedures (Fig. 7) involving multi-unit restorations, including consecutive placement of up to 10 veneers.

Contact-free battery…with a backup

Battery issues can be an operator’s worst nightmare, because they can sometimes be unreliable and cumbersome to clean and maintain. The Bluephase Style successfully addresses both issues. Its inductive charging system removes battery contacts completely, making maintaining the battery and charging base a non-issue. In the event the battery becomes exhausted, the Click & Cure backup option enables dentists and dental assistants to use the power cord in the charging base to convert the light from cordless to corded operation in one click.

Maintenance and cleaning

Maintenance and cleaning are incredibly easy with this hygienically sealed unit. The Bluephase Style comes with disposable protective sleeves. However, if these aren’t used, the handpiece can be disinfected with wipes, and the probe is autoclavable. Because the battery is contact-free, there is no need to clean the battery contacts.

Fits small hands

Many dental assistants, hygienists, female dentists and others with small hands experience fatigue when operating curing lights that are too heavy. Retracting the tongue for visibility and steadying a light while curing can be difficult. The sleek, smaller, and lighter design of the Bluephase Style reduces the strain placed on the hand and provides easier control and stability.

Summing it up

The Bluephase Style LED Curing Light provides the size, shape, control, handling, curing time and simple operation the dentists and dental assistants need to realize the hidden potential this invaluable equipment can afford the practice.

Its futuristic and innovative design surpasses other curing lights. The lightweight and balanced handpiece allows for a good grip, and the cordless operation offers maximum freedom of movement. The battery reliability, along with a heat management system, ensure overall continuous operation of the curing light, and its ability to cure all dental materials eliminates guesswork. It’s just what the dental team ordered.

About the author

Shannon Pace Brinker, CDA, is  a national and international speaker and published author. Shannon, Editor In Chief,  and her husband Erik, own  Contemporary Product Solutions, which provides product reviews for the whole team. She is a past faculty member at the Dawson Academy and Spear Education, instructing through lectures and hands-on programs. She is an E4D Clinical Operations Operators (ECO) group member and had extensive input for the Certified Dental Designer (CDD) certification. Shannon was selected as one of Dentistry Today’s Top 100 Clinicians of 2009, 2010 and 2011; one of Dental Products Report’s 25 most influential women in dentistry; and Dr. Bicuspid’s 2012 Dental Assistant Educator of the Year. She is a consultant for many dental manufacturers. For information on dental assistant programs, call her at 757-285-9477 or email