Proper Light Curing for Composite Resin Restorations
DENTSPLY Caulk’s new SmartLite® Focus helps maximize curing efficiency and access
Polymerization of composites is the process by which the material “sets” and the physical properties and functionality of the composite are established. The energy from the light-curing unit interacts with photoinitiators in the material to initiate the process of monomers joining together to form polymers. The more energy delivered to the restoration by the light-curing unit, the more monomers will convert into polymers, and the more effective the material will be.
Despite the importance of ensuring a high degree of polymerization, the lack of attention paid to this step in the procedure may help to explain research findings reporting that more than 37% of composite restorations are being insufficiently cured.1 An insufficient cure can lead to adverse effects on physical properties, reduced bond strengths, breakdown at the margins, decreased biocompatibility, increased potential for microleakage, and ultimately secondary caries and failure.2 These risks can be mitigated by following guidelines to ensure adequate light curing and maximum photopolymerization of the restoration. To help clinically, practitioners should remember the acronym CORE (Curing light, Operator technique, Restoration characteristics, and Energy requirement) to ensure best performance and outcomes when using a light-curing unit.3,4
One of the most often advertised characteristics of a light-curing unit is the output or irradiance, measured in mW/cm2. Just because a light-curing unit has an advertised irradiance of 1400 mW/cm2 does not mean that is how much energy is making it into the composite to cure it. All curing lights experience an energy drop-off that decreases the amount of energy delivered to the restoration over distance, and the amount of energy lost varies among curing lights.5 In one study, a 50% reduction of irradiance was reported at a 6 mm distance from the light guide.6 If the average clinical crown height of posterior teeth is 6 mm, clinicians may be faced with curing composite resins in deep preparations a significant distance from the light-curing unit tip.7 Remembering the acronym CORE, deep composite resin restorations demand a high-quality light-curing unit, good operator technique, the ability to direct the light into the preparation, and sufficient curing time for the individual type and shade of material. To provide clinicians with a light-curing unit that can perform at clinically relevant distances and help maximize curing efficiency, DENTSPLY Caulk (www.caulk.com) has introduced the SmartLite® Focus (Figure 1).
The SmartLite Focus is an ergonomic, powerful, cordless, pen-style LED curing light for both direct and indirect restorative applications. SmartLite Focus is designed to enhance intraoral access and curing efficiency, and provide reliable curing power over clinically relevant distances. Some important features of this new light-curing unit include:
Improved access. The newly designed light probe maximizes intraoral access by providing a low head profile and long rotatable tip that can swivel 330° to achieve proper position anywhere in the mouth.
Maximized curing power and efficiency. The unit features a homogenous beam profile for uniform performance in the curing area. The SmartLite Focus optics reduces divergence and ensures enhanced energy transmission through a collimated beam; this allows efficient curing of surfaces up to 8 mm from the tip. The SmartLite Focus has an average output of 1,000 mW/cm2, and maintains that output over clinically relevant distances.
Convenient charging. Smart Recharge Technology checks the battery conditions and initiates the proper charging mode: “automatic quick charging mode” for 5 minutes of cure time with just a 10-minute charge, “standard charging mode” to achieve a full charge in less than 3 hours, and “standby mode” which prevents overcharging when SmartLite Focus is not is use. The SmartLite Focus Replaceable Battery Pack offers stable energy output even after prolonged storage.
Simple operation. It features a single-button 20-second curing cycle and ergonomic design, and weighs only 90 g.
A 26-year-old woman presented for a composite resin restoration on the disto-occlusal of tooth No. 30 (Figure 2). After local anesthesia with one carpule of 4% Articadent™ (DENTSPLY Pharmaceutical, www.dentsplypharma.com) the preparation was completed with a high-speed handpiece using carbide burs. The preparation was isolated with the Palodent® Plus Sectional Matrix System (DENTSPLY Caulk) and restored using flowable and hybrid composite (Figure 3). To direct the light beam at a 90° angle to the material to be cured, the author preferred to use the SmartLite Focus rather than a light-curing unit with a curved light guide. Figure 4 shows the difference in access achieved using the SmartLite Focus versus another light-curing unit with a curved light guide. Figure 5 shows the composite resin being cured during the restoration of tooth No. 30. The final restoration is shown in Figure 6.
Proper light curing of composites is another vital step in creating consistently excellent restorations. By managing CORE variables of light curing and using a high quality light-curing unit like the SmartLite Focus, clinicians can safeguard against negative outcomes related to insufficiently cured composite resins.
1. El-Mowafy O, El-Badrawy W, Lewis DW, et al. Intensity of quartz-tungsten-halogen light-curing units used in private practice in Toronto. J Am Dent Assoc. 2005;136(6):766-773; quiz 806-807.
2. Price RB, Felix CM, Whalen JM. Factors affecting the energy delivered to simulated class I and class v preparations. J Can Dent Assoc. 2010;76:a94.
3. Price RB. Light energy matters. J Can Dent Assoc. 2010;76:a63.
4. The Four CORE™ Variables. BlueLight Analytics website. www.curingresin.com/scientific-evidence/the-four-core-variables. Accessed April 25, 2014.
5. Rencz A, Hickel R, Ilie N. Curing efficiency of modern LED units. Clin Oral Investig. 2012;16(1):173-179. doi: 10.1007/s00784-010-0498-3.
6. Price RB, Dérand T, Sedarous M, Andreou P, Loney RW. Effect of distance on the power density from two light guides. J Esthet Dent. 2000;12(6):
7. Volchansky A, Cleaton-Jones P. Clinical crown height (length)--a review of published measurements. J Clin Periodontol. 2001;28(12):1085-1090.
ABOUT THE AUTHOR
Jason H. Goodchild, DMD
Clinical Associate Professor
Department of Oral Medicine,
University of Pennsylvania School of Dental Medicine
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