Light-emitting diode light-curing (LED) units are now a mainstay of many general practice offices. These units are an effective choice for replacing alternative light sources such as quartz-tungsten-halogen (QTH) and high-intensity units. LED units are lightweight, typically portable (battery-driven), effective, and in some circumstances able to outperform other light types with respect to unit durability and curing performance.
Advantages
- Battery powered
- Portable — compact, lightweight
- Energy efficient — long battery life
- Durable — diodes last 5,000 hours
Disadvantages
- Narrow spectral range — most units only work with CQ photo-initiator
- Heat generated in chip
- Heat generated at tip
The LED source
LED chips used in dental light-curing units have not been specifically designed for dental use. Rather, the need for light-based communication, concentrated digital data storage, and large-screen video displays fueled the quest for a solid-state source that was “blue.” Shortly after the introduction of these chips for other uses, it was found that the main output wavelengths of the blue LEDs serendipitously fell within a major absorption band of the most common photo-initiator used, camphorquinone (CQ). By activating CQ with power within its most abundant absorption range, the LED light proved to be more effective than a QTH, even though it generated a lower total power output.
Clinical tips
- Minimize heat by having the assistant direct a stream of air or a high-volume vacuum over the tooth crown during light curing. Placing a wet cotton roll directly on the tooth crown opposite the side of exposure will also lessen temperature rise, but not to the same extent as using air.
- Minimize direct exposure to light sources using effective “blue-blocking” eyeglasses or shields for the clinician and patient.
- Determine the loss of beam intensity with distance by holding the light guide at different distances from a dental curing radiometer. Curing potential of a restorative material depends on total energy received. Determine power at tip end, and multiply that by the recommended exposure duration — the product is the light energy intensity delivered. When moving the tip away, measure that power level and divide it into the light energy intensity calculated above. The result will be the exposure duration needed to account for power loss with increasing distance.
- Evaluate a light’s heat dissipation capabilities by applying the longest sequence of typical exposure durations used in practice, and determine if the unit shuts off or if heat greatly decreases during that time.
- Periodically evaluate the output of a light-curing unit with a radiometer to detect changes in intensity.
Questions and answers
Q: What is unique about high-intensity LED units?
A: High-intensity LED units increase driving power to the chip to obtain higher output levels. These units commonly use an internal fan to cool the chip or use metal-coated unit bodies to help dissipate internal heat.
Q: Is it still important to use a radiometer?
A: Periodic evaluation of LED light performance with a radiometer is recommended. Typically, LED chips do not fail instantly, but have reduced output with prolonged use. There is no clinically relevant difference between radiometers for LED and QTH units, and absolute values from radiometers cannot be used to predict the potential for curing. Tip diameter can also greatly affect measurements. Use of these devices should be restricted to evaluating operating performance over time of a specified curing light/light guide combination.
Q: What new features are available in LED units?
A: Some new units generate light at two or more different wavelengths (poly-wave lights) to provide radiant energy to polymerize materials having CQ as well as other photo-initiators, where a higher frequency (around 400 nm) is needed. Also some lights have two or three intensity levels available.
Q: Are the temperatures generated by LED units important?
A: With the advent of high-intensity lights, temperatures from exposure to LED units have become a significant clinical issue. Although LED light-curing units have been advertised as being “cool” and not raising tooth temperature, temperatures are raised (see pages 4 and 5). Heat emitted from LED tips may affect pulpal vitality, patient comfort, and curing of the resin.
To read more, including Clinical Notes and which curing lights TDA recommends, visit www.dentaladvisor.com.
