Photo initiated resins have been around since the late 1970's but have recently become inexpensive enough for general use. In dentistry the first ones were indeed UV light initiated, but the wavelength was soon changed due to a concern about carcinogenicity, even though the exposure time was very short. Manufacturers moved to the blue part of the spectrum- around 480 nm. This worked very well until the introduction of LED lights, when some materials would not cure with lights from other manufacturers due to the vary narrow spectral range of the LEDs. This was soon dealt with by using a group of LEDs with slightly different wavelengths in the lights. Cures and color stability became more reliable. I am fairly sure that none of the resins currently on the market are UV initiated. They would have to be checked with a photometer to be sure. They probably all come out of the same barrel from a chemical company in Germany. Small companies could not do the chemical production required..
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