Recently, Mike Chan, a thirteen-year-old boy from Shanghai wanted to know if the blue light that dentists use to cure fillings and sealants can hurt your teeth when used for a long period of time.
He told me that when he was at the dentist's office getting sealants placed on his back teeth, they shined a light in his mouth. After the sealants were put on, the dental assistant hardened (cured) the sealants by shining a blue light on them. He noticed that after the blue light had shut off automatically, the dental assistant would press the button to get it to turn on again and continue curing the sealants.
Chan wanted to know if the blue light can burn, irradiate or otherwise hurt someone's teeth when used longer than it should be.
About the LED Blue Dental Curing Light
Before I answer Chan's question, here's a little background information for those who aren't familiar with the blue dental curing light. When a dentist puts a white filling (or a sealant, or a light-cured filling material) in your mouth, it is in a liquid or semi-solid state so that the dentist can put it exactly where it needs to go and shape it correctly. In order for the material to harden so that it can withstand the forces of chewing, it needs to be cured.
Curing the material is accomplished by shining a blue light on it. Not just any blue light will do. It has to be a certain shade of blue.
The blue dental curing light emits light at a wavelength of around 450 to 490 nm, a blue light. The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm.[1] In terms of frequency, this corresponds to a band in the vicinity of 400–790 THz. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can only be made by a mix of multiple wavelengths.
The very first light-activated filling materials used ultraviolet light. Fortunately, today dentists only use materials that are cured by visible light as the use of UV cured materials has pretty much died out due to the dangers posed by ultraviolet light.
Can the Blue Dental Curing Light Hurt Your Teeth?
Fortunately, the blue dental curing light normally won't hurt your teeth. Most of the modern curing lights use a blue LED light for curing. In some of the old models, the tip could get really hot. This heat could cause damage to the dental pulp — the innermost tissue composed of nerves and blood vessels inside of your tooth.
A good test to see if the curing light is too hot is to hold your finger 2-3 mm away from the curing light for 20 seconds. If your finger gets too hot, then the curing light could do damage to the teeth.
The Blue Dental Curing Light Can Hurt Your Eyes!
One of the major dangers of the blue dental curing light is that it can hurt your eyes! When we were learning how to do white fillings, our professors always advised us to never look at the blue light.
Although there is minimal potential for radiation damage to surrounding soft tissue inadvertently exposed to visible light, caution should be used to prevent retinal damage to the eyes. Because of the high intensity of the light, the operator should not look directly at the tip or the reflected light from the teeth.
The orange filter that you can see on the curing light above filters out the visible light, allowing the dentist or assistant to see what they are doing without looking directly at the light.
Conclusion
To answer Chan's question, there could be some harm in holding the light on your teeth for too long if it heated up your teeth. Since you probably weren't numb when the sealants were placed, you would have felt pain if your teeth had gotten too hot. Other than that, as long as they didn't shine the light in your eyes, no damage was done, since they used visible light rather than ultraviolet light.
The dental assistant probably just wanted to make sure that the sealant was hardened all the way, and didn't want to leave any room for doubt.
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