Dental Curing Lights & Post-Operative Sensitivity

I would like to comment on what I think are a few mis-understandings about dental curing lights. These are the units that cause dental materials, such as composites, sealants, and cements, to set or polymerize in the mouth. These units produce a visible blue light that these materials absorb, causing them to set. The first point is that the unit produces visible light, not ultraviolet light. Every dental curing light today is a visible blue light and does not produce ultraviolet light, which would not generally be safe for you, or the patient. So these lights are not UV lights. The confusion arises from the fact that dental curing lights once were UV lights. The inventor of this system was not familiar with visible light curing chemistry at the time, and therefore selected UV chemistry, which was quickly replaced by blue, visible light curing chemistry.

A second point is that of heat build-up caused by some of our polymerizable materials. Today we have two different kind of curing lights, those that are halogen (bulb) lights and those that are LED (light emitting diode). The LED lights do not themselves produce heat, unlike the older bulb lights that come with cooling fans. This unit unlike an LED can get really, and I mean really hot. Too hot to touch!

This heating effect or non-heating effect of the light unit is however not the most important thermal effect. It is the heat produced by curing of the material, its heat of reaction, that I am focusing on. The light itself however can and does contribute to providing heat to the tooth. A simple test is to put the light tip close your hand and feel how much heat you can detect. Again, the heat build-up by the material overall is the thermal effect that is most important. This brings me to my concern.

Some of the current high powered lights are recommended to cure a material within one second. These lights put out a tremendous power (4000 mW/cm2) compared to typical lights that emit either 600 or 1200 mW/cm2 and are recommended to cure a material within 20 seconds. The big difference between these high powered units and the typical units is that the material is forced to set all at once with no heat dissipation during the curing time. This amount of heat build up is sufficient to cause skin burns and tissue damage.

Several clinicians and researchers speak of how the material reacts to this instant cure, whether the material has internal stresses built-up, or not, and whether a ramping up of curing is preferred to reduce these "internal" stresses. There is some disagreement about this. However, I think this misses the point that it should be the heat build-up in the tooth and surrounding tissue that we should be of most concern.

Remember that when we cure dental materials that the patient is often anesthetized and can not feel this heat. My recommendation is to avoid the ultra high powered lights that promise to cure something in 1 to 3 seconds. Take a little more time, or at least move such a high powered light further back off the tooth and then slowly bring the light closer to your normal curing distance. This will avoid another possible source of post operative sensitivity.

28 comments:

  1. From an engineering point of view the LED unit is comparable, if not preferable, to the traditional curing light for all the points you've mentioned: compact, rapid cure, and most importantly patient safe. Your concern of a "too" rapid cure is surely valid from a material development perspective. However, I'm wondering if you would suggest using LED units over lower powered curing lights all together? What are the disadvantages, if any, in using the LED? Why has there not been a bigger integration of the LED light in the dental office?

    Thanks for the wonderful topics!
    MaterialGirl

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  2. You are correct that LED units have many practice advantages. The portable LED lights are great to use, quiet, small, and very reliable. One aspect of wider use is that many of the older chair units have traditional lights supplied with them. Thank you for your comments.

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  3. Dear Dr. Stannard,

    As you know, sensitivity is a key issue for our clients. Thank you for your insightful discussion explaining the importance of curing time related to polymerization heat build up and possible sensitivity. I now feel better equipped to discuss this with my clients.

    Thanks again!

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  4. Yes, taking a little more time to prevent heat build up, and to also insure a well cured material, is worth it. I know it can get tedious doing this all day long, but when adhesives are not cured "well" unfortunate things can happen.

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  5. you are such a big help to our practice, more power to you jan... mabuhay

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  6. Hi,

    Dental curing light is becoming one of the most used pieces of equipment in your operatory. Thank you...

    Curing Light

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  7. Yes, you make a very good point. Thank you.

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  8. Yesterday I had a tooth repaired with a composite which required a curing blue light. All went well except when the dentist moved the light to the base of the tooth. It felt as if my gum was burning. The burning pain subsided when the light was repositioned elsewhere on the tooth. This was repeated several times. Today, the roof of my mouth where where the light was placed feels like sandpaper and is slightly swollen. After reading your comments, I now am sure I the gum tissue was burned. I know the dentist has to reach every part of the composite to get it hardened, so how can he avoid burning some gum tissue? Also, is there anything I can do to help my gum heal more quickly? Thanks.

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  9. Two days ago my dentist used a white light probe, not hot, for a few seconds. He advised the light photons stimulate the electrons in the cement mix, so a very even and quick set, not using heat. I thought photons would "bounce off" most materials and just pass energy as heat. Can you explain the science please?

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  10. Photons (intense blue light) are absorbed by a yellow compound, camphorquinone. Camphorquinine is decomposed and passes along this energy to an amine, which in turn lowers the activation energy to create a free radical polymerization.

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  11. I had a two fillings by a dentist who was too booked to do the work himself and was getting me in to do a filling that I wanted filled. The hygenist did the numbing shots. The dentist drilled. The hygenist filled the cavities while the front desk clerk held the blue light. She was laying at an angle against my lip (and leaving it until two beeps were heard). I kept reaching up and pulling my lip out of the way. I thought it was being pinched. When I got home I had a big blister and small blister forming on my lip that felt like a burn. The next day I realized I had big blister like white formations in my mouth too. I called them within a hour to leave a message that I was burned. I left a message yesterday that I had blisters (they are closed on Wednesdays) and was seen this morning. My dentist took pictures and said the wand cannot burn even though he said it did look like burns. Unfortunately the burns inside my mouth have healed after 2 days and while visible last night, the skin peeled off this morning right before the dentist visit. Only the lip burn is still visible and raw/goopy. I read the above information but I am still unclear...is he right that some of these blue light wands cannot burn no matter how long or close they are to skin? What question would I ask him to find out about the kind of wand he uses? Also, he said his employees "did nothing wrong"--is there a wrong way to hold/use the wand? Is laying against the lips okay?

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  12. Thank you for your comment. I would ask the dentist, What is the curing light that was used, what is the brand name of this light, and what was the exposure time used? Did you yourself take any pictures? I would be interested to see them. Best of luck.
    Dr. Jan Stannard

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  13. hi Dr. Jan Stannard,thanks for your great article,now i have some question about curing light,We are a Chinese curing light manufacturers,our curing light intensity can be up to 2200-2600mw/cm2,it is 6-8 seconds can cure 3*3 mm resin.Many dentists very like them,but according to your theory , the actual curing time should be base on the material of resin,is it right?Another problem, about the intensity of curing light, now no international standard, each company's light meter have different stardard,are there a correct way to measure the accurately intensity of curing light?what should be measure of curing light criteria?

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  14. There are many established methods to measure light intensity. As you correctly point out, in the dental industry we use mW/cm(2) as the amount of light that a surface is exposed to. This however is not enough information to indicate to a practitioner how long to cure a specific product. The curing time depends upon material composition, such as shade, opacifyers, depth of the material placed, etc. For this reason, the instructions for use are specific for each product. Please see some of my earlier posts on this topic. Thank you for your comments.

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  15. I was watching my son get a cavity filled. I was holding is hands since he is only 4. I watched the entire procedure including looking directly at the blue curing light for about a minute. Could this have hurt my eyes? They didn't warn me or give me safety glasses!

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  16. I am not aware of any long-term damage due to limited viewing of a dental curing light. It is common to experience a temporary, yellow blinding effect due to viewing such a high intensity blue light. This generally lasts only a few seconds.

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  17. I had some composite fillings placed in front teeth. The wand of the curing light was resting against my lip, it felt warm but I didn't think anything of it. A few hours later a nasty burn blister appeared on my lip. I told the dentist, but she was adamant it wasn't possible and said that I must have burned myself afterwards. I know it was from the wand. Does that mean the wand was faulty, or is that possible. Many thanks.

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    1. Depending on the type of dental curing light used, the tip of the light, as well as the energy coming from the light, can generate considerable heat. These types of lights are high output and marketed to cure composites or sealants in 3-5 seconds. When a patient is anesthetized, feeling any pain during application is significantly reduced. The end of the curing light should not contact either the treatment area or any adjacent tissue. This procedure also helps protect the patient from contamination. Thank you for your comments.

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  18. Hi Dr. Jan Stannard ,
    I'm a biomedical student.
    Now I'm working out on dental light curing materials and equipments. so your discussion helped me a lot. Thank you.
    Best wishes

    saeed mp

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  19. You are welcome. Good luck in your studies.

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  20. In regards to the January 5th/2012 comment regarding "blister like burns":
    Curing lights can cause burns, this is absolutely true. Especially when the light is held by an inexperienced user, like the dental receptionist.
    The FDA and Health Canada classify dental curing lights as Class 1 medical devices that do not require individual licenses to be issued for each light by manufacturers. The only requirement is that the device be clearly labelled so that the device can be used safely and effectively. The FDA has stated that upgrading skills for the safe use of dental curing lights is "The responsibility of the Dentist", certainly not the responsibility of the dental receptionist, who had no business operating the light in the first place. Would you want a surgeon handing his scalpel to his receptionist to take out your gall bladder? Probably not, so why should a dentist rely on a receptionist to cure fillings.
    Probably a harsh analogy; nevertheless, a curing light to a dentist is like a scalpel to a surgeon, a medical instrument that can hurt you.
    Remember, do no harm (Hippocratic Oath)
    My recommendation to anyone that has experienced such a burn: report the incident to the FDA or Health Canada. Incidents like this should be reported using the "Mandatory Reporting Guidelines" set up by both governments.
    It troubles me that this type of incident can occur.
    Report these incidents so they don't happen to anyone else.
    Nova Scotia, Canada

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    1. Thank you for your comment. I would agree that proper use of a dental curing light is required. I also agree that follow up to these incidents is important for all involved. Certain curing lights have become known to cause these problems, as well as, approaches to rapidly curing materials can also cause additional problems.

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  21. I have just had blue light to build to gradually build the back of a split tooth. The Blue light was used many times. Today the roof of my mouth is very sore. Does the light burn skin tissue as per sunburn style damage?
    What tests have been done on using intense light curing with reference causing skin cancer? Thanks John W

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