“The message here is don’t take your curing light for granted; test it periodically for light output, and if it is being held together with duct tape, as one of your basic tools, do the right thing—spring for a new one.”
|The frequencies of the 4 LEDs in Ultradent’s VALO.|
|The Bluephase 20i Curing Light and Bluephase Meter II.|
Every dentist owns one or more curing lights. We have new ones and old ones that we hate to throw out in case we need them for use or for parts. The reasons we get new ones are that the latest models are smaller, maybe cordless, and use LEDs, either directly in a wand shape or through some type of fiber-optic pipe. Also, these LEDs are lighter in weight, have a full spectrum for curing, and “last forever.”
Some of this, of course, is a stretch and can lead us into a false sense of security. When a composite fails, most of us assume there was an issue with the material or technique. But what if for some reason the material was not cured completely? We assume that you just fire the light for 20 seconds or so, and it is all set. There are also many studies on depth of cure as well as on the pluses and minuses of bulk fill. And incidentally, a few new composites are appearing that are self- and/or dual-cure, so the light may not be necessary at all! And just to confuse things further, if you have a dual-cure, and you light it too soon, you could end up with problems. Let’s examine a few basic facts about composites and curing.
Composites have photo-sensitive catalysts (initiators) that make this all happen. Gary DeWood, DDS, wrote a summary of them in the Spear Institute Journal, stating, “The 3 light-sensitive initiators—camphorquinone (CQ), phenyl-propanedione (PPD), and trimethylbenzoyl-diphenyl-phosphine oxide (TPO)—acted as the triggers that set off polymerization in all of the available products when light was applied. CQ was the most commonly used initiator in all applications. The color of the initiators is quite different—CQ being quite yellow before it’s cured—and it represented a problem with color-matching composites to teeth prior to the cure.”
TPO is the least “colored” of the initiators and made possible clear flowable resins that could be used to seal things. Clear sealants use TPO as an initiator. Dr. DeWood explains: “The spectrum of absorption by these initiators was not a problem when quartz-halogen was the only available source. However, with the introduction of the LED light, the initiator became a factor in the cure as single-wave LED lights, most of which emitted in the 430 to 500 nm range, did not interact well with TPO, which absorbs in the 350 to 430 nm range.”
What this translates to is that you have to know a bit about the frequency range of the light you are using as well as the composition of your composite. Some of the single-wave LEDs have a range of 430 or 450 nm to 480 nm. This cuts off the ability to cure TPO. Other companies use a couple of LEDs with different frequencies, using names like polywave (Ivoclar Vivadent [ivoclarvivadent.com]) or multiwave (Ultradent [ultradent.com]) that extend the range to as wide as 380 to 515 nm. It may seem like we are splitting hairs, but the chemicals are quite specific in their sensitivity.
Light intensity is also critical, and here is where things can really go wrong. The standard output seems to be 1,000 mw/cm2 for “normal” composite restorations. Keep in mind that there are many factors that determine the amount of light and the time of cure. Darker colors, for example, may require longer cure times. DentLight’s new Fusion 5 (dentlight.com) claims to be 2,700 mWcm2 or more, which should cure anything in its path. The distance of the light tip to the surface of the composite is certainly a factor, and it is recommended that you not only cure from the occlusal but also the buccal and lingual. I have seen some interesting techniques—for example, if you are using a sectional band, you can get the light down to the gingival once you remove the ring and before you actually remove the band. This will ensure you’ve gotten to the bottom of the box. With a full-metal band, the light tip can be slipped between the band and the tooth as it is peeled back both buccally and lingually. Even the reflection off of the band will ensure that gingival cure. It takes more time (but less than needed to replace a failed composite).
Despite the longevity of the LEDs themselves, light output can degrade with time. Some causes are physical—material buildup on the light’s tip, scratches on the lens, etc. Also, despite the assumption that LEDs emit no heat, there may be enough at the component level to disrupt the actual LED and cause it to receive less electrical current, thus reducing the output.
There are many ways to measure the light output. Some lights come with a built-in radiometer, and since it is usually calibrated to that specific light in terms of the diameter of the spot and frequency of the unit, it is best used with that device only. There is a service (Blue Light Analytics [curingresin.com]) that your local supplier can contact that can dispatch a representative to your practice with a more robust radiometer and examine all your lights. There are also radiometers that you can purchase that offer various price points and features. Kerr has the compact Demetron LED Radiometer, and SDI has a nice in-office unit. The newest one is the Ivoclar Bluephase Meter II, which can accommodate any size light tip, is full spectrum, and has a digital display. Note that some of the light manufacturers claim the accuracy of these in-office devices is not as accurate as larger, more expensive units used by testing labs. While true, with an in-office meter, you can test your lights when they first arrive (or at a start date) and monitor them from that point on to see the relative degradation and realize when the light has to be repaired or replaced. To further clarify the use of radiometers, Ultradent Products recently posted a PDF online entitled “An Explanation of Dental Radiometers.”
The message here is don’t take your curing light for granted; test it periodically for light output, and if it is being held together with duct tape, as one of your basic tools, do the right thing—spring for a new one.