March 1, 2005
by Scott Dudley
Rapid advancements in technology today often make it difficult to establish reliable product evaluation criteria to assist with purchasing decisions. The most notable is the recent growth in Light Emitting Diode or LED curing light technology. This article is intended to provide a working definition of LED technology with its benefits; while outlining a number of product features for consideration prior to the purchase of an LED curing light.
A Light Emitting Diode is a semi-conductor optical device. This device requires a lower level of electricity to produce light energy. One of the more common applications of LED technology today is energy efficient lighting. However, blue light emitting diodes coupled with a light engine can produce sufficient energy to cure dental materials.
LED curing lights comprised of blue light emitting diodes offer a number of potential advantages to today’s dental practice. These units emit blue visible light in a narrow bandwidth that corresponds closely with the absorption peak of Camphoroquinone (CPQ), the most commonly used photoinitiator in light activated materials. LEDs with an emission spectrum that closely matches CPQ’s peak (480nm) offer the best polymerization results with products containing this photoinitiator.
The primary goal of curing light manufacturers in development of light technology has been increased efficiency. This development has been characterized by several key features such as higher output, increased speed, durability, ergonomics and economy. While various light sources have provided one or more benefits; few have scored well in all categories deemed important by clinicians. Historically, the conventional halogen has been among the most preferred light sources available to clinicians1 (Table 1).
LED technology offers a number of potential advantages over halogen such as efficiency, lower heat, portability, durability and improved ergonomics.2 These features continue to entice prospective buyers as a growing number of doctors are convinced as to the safety and effectiveness of LED technology.3 In fact, according to a recent issue of CRA, “LED curing technology has made significant inroads into clinical dentistry in just four years.”4
Manufacturers have responded to this increased demand, thus the number of LED curing lights has grown exponentially. While the benefits of LEDs are numerous and compelling, practitioners believe completeness of cure, reliability, cures all materials, track record, and service and support from supplier to be the most important considerations.5
However, this increasing competition has lead to a confusing landscape, as manufacturers market curing lights promoting one or two features against a backdrop of sex appeal or low cost. In fact, it might surprise readers to learn a recent evaluation of LED curing lights by CRA noted that 38 percent of the units were actually corded. Yet CRA’s own 2004 curing light survey identified cordless as one of ten important features to clinicians!6 This point only serves to underscore the importance of thoroughly evaluating prospective lights to ensure best value for dollar spent.
Perhaps today’s LED selection criteria should include among others, light intensity, battery type, heat management system, radiometer, accessory choice, manufacturer reputation, and warranty.
As stated, LEDs are a combination of two different semiconductors which, when voltage is applied, electrons connect to produce a specific wavelength of light closely matched to the CPQ photoinitiator. Quality and quantity of LED light output depends both on the number of light emitting diodes; as well as the wavelength of each diode employed. While much has been said about LED curing lights’ inability to cure all materials; the key point to remember is that the LED output is matched to Camphoroquinone. As most products today employ CPQ as the initiator, prospective purchasers can simply confirm the type of photoinitiator used when questions arise. As LEDs increase in popularity many products that do not contain CPQ are being reengineered. For example, Touch and Bond (Parkell), now Bush and Bond has be reformulated as well as Panavia F (Kuraray), now Panavia F 2.0.
Placing diodes closely matched to CQP’s peak (480nm) in high numbers (four to five diodes) can provide both high quality and high intensity light. While it is unlikely clinicians will be able to ascertain the number and wavelength range of the diodes employed in curing lights, certain evaluation methods still exist. Measuring the light output with a radiometer is very important. High intensity light consistently improves the hardness of resin based materials.7 Additionally, clinicians consult other sources to learn about curing lights including dental products evaluating organizations, dental publications, and colleagues to name a few.8 Third party evaluations by CRA, Reality, Dental Advisor, and Dental Products provide detailed LED evaluations.
Nickel metal hydride and lithium ion are two battery types (Table 2).
Nickel Metal Hydride batteries with over-charge and over-discharge protection have a number of benefits over Lithium ion, such as less heat build up and longer life cycles. Prospective purchasers would be wise to consider LED units that incorporate a low power warning, and provide two batteries for uninterrupted use. In all cases it is important for users to consult manufacturers’ instructions regarding battery charging and storage. One note of caution, the output of some LED units drops significantly when battery levels are low; a radiometer is an important tool to avoid the problems associated with low battery power levels.
While it is true LEDs produce lower levels of heat than halogen; internal heat management is still important. As electricity is converted to light energy heat is produced as a by-product. This internal heat can cause the light emitting diodes to weaken over time, resulting in lower output. Reality evaluators noted increased temperatures in the handpieces and some tips of LED units which did not employ a fan.9 A number of manufacturers have employed either a fan or thermostat to mitigate the undesirable characteristics of internal heat build-up.
Alice Volpe, senior product manager for Demetron Research Corporation describes it this way: “During our initial research light emitting diodes were exposed to prolonged and repeated use to measure performance and life expectancy. During the tests you could actually watch the diodes turn yellow and exhibit reduced output because of over heating. It was clear a cooling mechanism of some sort was required to ensure the highest integrity and maximum diode life. We decided on installing a fan, rather than the less expensive thermostat which would only shut the unit down inconveniencing the doctor.” The choice appears to have been the right one because the LEDemetron 1 not only received top honors from Reality and Dental Advisor, it was the overwhelming LED choice of respondents in CRA’s January 2004 readers’ survey.10
Some manufacturers embed diodes in the tips of curing units presenting other shortcomings such as; no choice of light guides, expensive asepsis barrier protection and costly replacement or repair if the diodes are damaged. Additionally, these units will quickly reach temperatures in excess of 50 degrees Celsius or 125 Fahrenheit at the tip which could not only damage tissue, but the integrity of the diodes. Temperature can be easily measured with a heat meter or by placing your finger on the tip while running the unit. Diode placement is not only important for proper heat management; it can also impact service and maintenance. Certain companies place the LEDs in a package that can be replaced as the technology advances. This means the diode technology is replaced rather than the entire light unit; which can be costly; particularly as this technology is advancing rapidly.
Reality’s 2004 review of LED curing lights noted that the power output was variable in LED units; indicating weekly testing is important.11 Type and quality of radiometer influence the degree of confidence doctors can place in output measurements. Radiometers incorporating color coded lights such as red, green or yellow; illustrate output, rather than quantify it. Analog or digital radiometers offer specific numeric readings of higher quality. The type of radiometer is equally important, as LED curing lights require an LED radiometer, not a halogen meter because the two light sources are different.
Owen Gill, electrical design engineer at Demetron research explains, “The LED Radiometer is calibrated with an LED light source which does not have the wide light spectrum containing IR and UV wavelengths found in Halogen units. Therefore measuring LED output with a radiometer calibrated with an LED light source will yield a more accurate reading than a radiometer calibrated with a halogen source”. With certain LED units light intensity can be a function of battery life; so again measuring output periodically with a radiometer is vital.
As benefits like portability and improved ergonomics entice new LED users, certain features of halogen curing lights are lost. One shortcoming with many LED units is the limited number of accessories available, such as light guides or mounts for handpieces. Light guides that increase output, focusing light with pinpoint accuracy have become commonplace today. So the fact that Reality noted the poor selection of light guides with many LED units in their 2004 review of LED curing lights illustrates this accessory’s importance to clinicians.12
Light guides enhance patient comfort, improve ergonomics, and increase polymerization results where access is less favorable. Consider the value of a 4mm tip in the case of pediatric dentistry, or a 2mm tip for spot tacking during veneer placement, or even the slender design of an 8mm turbo light+ guide for orthodontics. Light guides have become an important part of the practitioner’s armamentarium today, so consideration should be given to those products that offer the best selection. LED units that incorporate diodes in the tips of curing units eliminate any choice for the doctor. Additionally, some units now offer holders that allow the handpiece to be mounted in convenient locations such as the dental unit. It is worth enquiring about the number and type of light guides included with units, as well as a handpiece holder for the dental unit.
Manufacturer Reputation & Warranty
Most readers might be surprised to learn that few LED curing lights are actually manufactured by the companies which market them. In fact, most lights are assembled for a number of value-added resellers. OEMs or original equipment manufacturers are scarce in the dental curing light market today. Two companies that produce lights today are Ivoclar, which assembles units at its operation in Lichtenstein, and Demetron Research Corporation, which manufacturers curing lights at a facility in Danbury. CT.
Questions about a manufacturer’s history, experience, and track record in curing light production are as important as the questions about the light itself. Does the seller actually manufacturer the unit and where? How long has the company been in business? What is its track record? Does the company manufacturer or assemble? Is a demo unit available? Are there local field personnel to support sales and service?
Warranty and after sale service are excellent measuring sticks of a company’s confidence in its light, separating the strong performers from the pedestrian. A two-year warranty is the standard, but a close examination of the terms is critical. Is the warranty replacement or repair? Does is cover parts or labor only, or is it complete? Must the unit be shipped at the owner’s expense? Is there a loaner available? What is the turnaround time?
Reality’s 2004 review of LED curing lights provides good information about warranties, repairs and loaner programs for various LED units.13 A number of third party evaluations are available from other reputable groups such as CRA, Dental Advisor, and Dental Town to inform clinicians about LED choices. In short, knowledge is power. So ask as many pointed questions about the light as possible before purchasing.
Next to handpieces, curing lights may be the most frequently used equipment in the dental office today, so purchase decisions should be informed ones. An informed purchase is the most satisfying. In a world where you get what you pay for… the only sure way to get what you want… is to ask… and ask… and ask again. OH
Scott Dudley is senior district manager, Kerr Corporation.
Oral Health welcomes this original article
1.Dental Products Report. Survey report: Curing lights. May 2002. Page 20.
2.Contemporary Esthetics and Restorative Practice. December 2001. Page 68.
3.Dental Products Report. Survey report: Curing lights. May 2002. Page 19.
4.CRA News Letter April 2004 Vol. 28, Issue 4.
5.Dental Products Report. Survey report: Curing lights. May 2002. Page 22.
6.CRA Newsletter LED Resin Curing Lights. April 2004 Vol. 28, Issue 4.
7.Hardening of Dual-cure Resin Cements and a Resin Composite Restorative cured with QTH and LED Curing Units. JCDA May 2004, Vol.70, No. 5.
8.Dental Products Report. Survey report: Curing lights May 2002. Page 26.
9.Reality: Dental Curing Lights Vol. 18 2004.
10.CRA Newsletter Resin Curing Lights. April 2004 Vol. 28 Issue 4.
11.Reality: Dental Curing lights. Vol. 18 2004 Page 210.
12.Reality: Dental Curing lights. Vol. 18 2004 Page 210.
13.Reality: Dental Curing lights. Vol.18 2004.