Written by Jeffrey M. Rosenberg, DDS Wednesday, 31 October 2007 19:00
Light energy is now a part of the equation in figuring how to optimize adhesion, reinforce material to dental structures, protect tissues, speed up the dental procedure itself, and further a host of other situations. Light-activated dental materials have expanded tremendously over the past 2 decades,1 and a diverse, multifunctional curing light has many benefits. This article describes my experience with a versatile, new-generation LED curing light, J. Morita USA’s Jetlite 5000.
WHY LED LIGHTS
Modern curing lights evolved to feature quartz-tungsten halogen bulbs as their light source.2 Research proved that an acceptable light intensity level was near 1,000 mW/cm2. As materials began using more and more light-curing initiation, the appearance of newer and more diverse curing lights appeared. The LED and plasma arc curing (PAC) lights were developed.
Halogen lights produced heat that affected the lifespan of the halogen lamp and could affect the dental tissues as well. Initially, concerns over heat buildup in the dental tissues and longer curing times were also obstacles to newer, LED technology.
Plasma arc lights became known to cure fast, but the heat buildup was much higher than LED and halogen lights and often uncomfortable to unanesthetized teeth.
There has been a trend in moving away from the traditional halogen and xenon plasma arc curing lights to smaller, more efficient, portable LED curing sources. This trend is probably due to the rugged nature of the LED and its ability to convert electrical energy to light efficiently and economically.2 Instead of a heat-producing filament, as used in traditional sources, LED curing lights use light-emitting diodes and a semi-conductor. Voltage is applied to the semi-conductor module, and electromagnetic energy is emitted in the form of a photon of light.
The light energy produced by the Jetlite 5000 is a visible blue light with a spectrum of 450 to 490 nm. Most of the newest generations of LEDs produce a wavelength of blue light that is in the absorption spectrum of the two most common photoinitiators: camphoroquinone (CQ) and phenylpropanedione (PPD). The CQ is initiated at approximately 468 nm,2 while the PPD is activated in the 430-nm range.3,4 CQ is the most common photoinitiator for most dental composites, bonding agents, and cements. The Jetlite 5000 cures most popular materials. The clinician should verify light-curing compatibility of materials by curing a small amount outside the mouth before clinical use.
PERFORMANCE FEATURES OF CURING LIGHTS
Power and reliability are the first features that are absolute necessities. There are “moments of truth” during the adhesion processes when you do not want your light to shut down. The Jetlite 5000 is a portable, gun-style handpiece with a convenient recharging holder base. The device can operate in a cordless mode producing 300 to 400 activations of 10 seconds before recharging. The device can also operate in a corded mode in case the battery charge is low.
The Jetlite 5000 has an intensity of up to 1,500 mW/cm2 with a unique heat sink technology to keep the curing temperature low. This high intensity allows for a fast, deep cure. The charger base has a bar graph indicator that serves as a battery status meter, charging indicator, and light intensity meter. It also has a power indicator light, a sound buzzer, and a light intensity sensor. These features make it easy to know when your light is ready to work and perform at the highest level. Maintenance of curing light optics is a neglected task that may result in ineffective curing. A built-in light meter serves as a perpetual reminder to keep your light maintenance up to par. The battery is a lithium ion type that allows for faster recharging over the older metal halide batteries. Full charging takes about 2 hours.
The digital display on the light’s handpiece has a battery use/indication icon that is useful. This way you or your staff can know when to recharge without emptying the battery. This light can also be used with a cord, which can get you out of a jam if you need it right away or for extended periods of curing such as full resin bonding cases or bleaching.
The handpiece has very convenient operation. One button allows selection of one of 3 intensity modes: fast, standard, and ramp. Another button allows selection of a curing time of 5, 10, 15, 20, or 40 seconds. The trigger button starts the curing exposure.
The fast mode produces an intensity of 1,500 mW/cm2 at durations of 5, 10, 15, or 20 seconds. This mode is ideal for dual-cure materials when a large energy application will initiate the cure and there is no concern for polymerization shrinkage. The standard mode is a pulsed mode. Light intensity of 1,200 mW/cm2 will cure large composite resin restorations with less polymerization shrinkage.5 The ramp mode increases light output gradually over one quarter of the selected duration and remains at maximum intensity for the rest of the duration. The mode has a 20- or 40-second duration.
UNIQUE USES OF LIGHT CURING
Although curing lights are predominantly used for the application of resin in dentistry, the evolution of photoinitiation in more materials allows the clinician to be creative.
Case 1: Minimizing White Lines
Figure 1. Conservative class II resin preparation.
Figure 2. Resin restored with ramp cure on buccal, fast cure on the palatal.
Many believe the white lines seen around class I and II restorations are due to resin shrinkage stress. The amount of resin material relative to the cavity preparation sets up a “tug-of-war” between the resin shrinking and cracking of the enamel prisms just outside the margin. The microcracks show up as a white line through the resin.
The preparation design should maximize enamel rod exposure; yet control of the cure has been a challenge until the use of ramp curing.
Figure 1 shows a class II resin preparation. Figure 2 shows the margins cured with a ramp cure on the buccal and a standard cure on the palatal. The use of a ramp cure slows down the composite’s plastic phase, allowing it to pull toward the bonded tooth surface and reducing microcracking.
Case 2. Modification of Orthodontic Aligners
Figure 3. Orthodontic tray aligner.
Figure 4. Curing of resin to accelerate tooth movement in aligner system.
The field of aligner orthodontics is growing rapidly, and the modification of aligners allows more creative and effective movements to occur within the confines of the aligner. Figures 3 and 4 show the placement of light-cured resin to a cut-out portion of an Invisalign (Align Technology) aligner to facilitate a more rapid movement of a tooth out of cross-bite.
Case 3. Use of Light-Cured Acrylic Provisionals
Figure 5. Light-cured acrylic (GC America) mixing.
Figure 6. Light-activated resin in dough state in preoperative impression.
Figure 7. Cured acrylic before trimming.
Figure 8. Final cure in the mouth.
Figure 9. Final gold restoration fit precisely in temporized space.
Case 4. Quick Replacement of Fractured Tooth Pieces
Figure 10. Fractured buccal cusp tip.
Figure 11. Reattached tooth structure with direct dual-cure cement.
Many times a bicuspid will lose the buccal or lingual cusp due to expansion of an occlusal amalgam combined with occlusal forces (Figure 10). The use of dual-curing cement applied to both parts of the tooth structure and properly cured can serve as a lasting repair for many years of service. The lighter color of the cusp is due to dehydration. This portion will partially rehydrate within the next 48 hours (Figure 11).
LED technology has caught up and even surpassed halogen technology. Clinicians should learn what they can about the available lights on the market relative to the materials and applications that they will be using them for. This article has described the Jetlite 5000 light, which is versatile, cordless, high powered, quiet, and fast. Creative uses for the LED curing light have also been described.
- Yeh CL, Miyagawa Y, Powers JM. Optical properties of composites of selected shades. J Dent Res. 1982;61:797-801.
- Resin curing lights state of the art 2006. CRA Newsletter. Feb 2006;30:2.
- Nomoto R. Effect of light wavelength on polymerization of light-cured resins. Dent Mater J. 1997:16:60-73.
- Jandt KD, Mills RW, Blackwell GB, et al. Depth of cure and compressive strength of dental composites cured with blue light emitting diodes (LEDs). Dent Mater. 2000;16:41-47.
- Nomoto R, Uchida K, Hirasawa T. Effect of light intensity on polymerization of light-cured composite resins. Dent Mater J. 1994;13:198-205.
Dr. Rosenberg maintains a private practice in Philadelphia emphasizing restorative and aesthetic dentistry. He is a fellow of the AGD and holds associations with various restorative, aesthetic, and orthodontic organizations. He publishes in this field to increase awareness of high-tech materials and procedures and performing dentistry more efficiently and with higher quality. He places hundreds of bonded restorations monthly and has a patent pending in the area of nonmetal dental restorations. He is also the head of The Dental Healthcare Group, which provides high-quality continuing education in the Philadelphia area. He can be reached at (215) 592-4747.
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