Of Dental Bondage

Last Updated (Tuesday, 15 December 2009 11:32) Written by Raymond Nakamura

A minor dental emergency involving my daughter exposed me to a mysterious blue light. It was used to harden an adhesive and looked like something out of Star Trek or Harry Potter. I guess they've been around for a while, but I saw this as a chance to begin filling in some cavities in my knowledge about this blue light and the wonderful world of photopolymers.

Resin Shine

Materials that harden when exposed to light are being used in all kinds of applications in various fields, from making printing plates to decorative fingernail gels. Most dentists now stick to light cured composite materials to fill their adhesive and filling requirements, instead of using amalgam. 

Composites can be mixed to match the colour of your teeth and doesn't require removing bits of your tooth. They are made of powdered glass for hardness, resins to hold it together, and a photoinitiator that hardens the resin when exposed to a specific wavelength of light (468 nanometers), which out to be blue. When the material absorbs this wavelength, it releases ions that cause the composite material to harden in seconds.

An Inconvenient Tooth

Materials technology continues to evolve. One woman tried to get the government to outlaw amalgam because of the mercury). Mind you, composites contain BPA, the stuff that led to plastic baby bottles being pulled, although in this case, it is supposedly in non-significant amounts. Some scientists are working on yet another alternative made from bile acids.

Sources of Enlightenment

This blue light can be produced in a few different ways. 

Using halogen lights, like the ones in those energy inefficient torchieres you're not supposed to use anymore, generates lots of heat and requires a filter to produce the appropriate wavelength. Another problem is that their output tends to decrease over time, which changes the curing time. 

Lasers could produce a concentrated light of a precise wavelength, but they are extra expensive and not energy efficient in this case. As well, they would require extra careful handling because of the concentration of the beam.

 LEDs, which have already taken over the Christmas light market and our geodesic dome also seem to be useful in this application. Recent improvements in their output have made them well suited to this application. They can produce light in the appropriate wavelength, tend to be more stable in their output over time, are energy efficient, so they can come in a light sabre size range. 

Out of the Blue

On a lighter note, blue light is being investigated as a possible cure for cancer. Curing with light usually means causing the plastic to harden. In this case, it also seems to cause cancer cells to stop growing and die, while leaving regular cells unaffected.

What light changing experiences have you had?