Question about light curing...

[cdmOMR]

I was wondering about this other day in my O.Chem class but forgot to bring it up until I saw another thread...

We were going over reactions that require light, but can not undergo correctly if heat is also applied. I was curious if the curing lights which generate light but no (or very little) heat were designed for these types of reactions? Or is it more of an issue of not damaging any pulp or periodontal tissue with the heat? Both?

(If anyone is curious I believe the reaction was 2+2 "forbidden" cycloadditions, although im sure there are other reactions like this one that needs light but no heat. )

Any ideas out there?

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[dentalman]

That was so long ago. You should ask your ochem prof.

But, that sounds like a curious reaction that cannot proceed with heat. You see, everything has heat. An ice cube has heat. So does a glacier. It is just the temperature that is different, which is the average kinetic energy of the molecules. So, it is either exothermic, or endothermic. What's your question?

"Forbidden" cyclo additions? Sounds pretty rare to me. I think it is just your regular monomer reactions with resins. The light doesn't have much heat, but there are some higher energy lights that don't cure as long but I hear are a little warmer.

 

[cdmOMR]

That was so long ago. You should ask your ochem prof.

But, that sounds like a curious reaction that cannot proceed with heat. You see, everything has heat. An ice cube has heat. So does a glacier. It is just the temperature that is different, which is the average kinetic energy of the molecules. So, it is either exothermic, or endothermic. What's your question?

"Forbidden" cyclo additions? Sounds pretty rare to me. I think it is just your regular monomer reactions with resins. The light doesn't have much heat, but there are some higher energy lights that don't cure as long but I hear are a little warmer.

Well by heat I mean heat beyond room temp (like heating up a reaction to 50*C or whatever). I dont want to bore anybody with the details of this reaction, but it basically uses UV light instead of heat to make a 4-membered ring from two C=C's...like a diels alder if you remember it. Here is the quote from the book

"The [2+2] cycloaddition is therefore photochemically allowed, but thermally forbidden. In most cases, photochemically allowed reactions are thermally forbidden, and thermally allowed reactions are photochemically forbidden."

I was just curious if the reactions that undergo in cements, and composites and the sort involve these "photochemically allowed, but thermally forbidden" reactions. Or are the lights designed to not put out much heat to protect sensitive tissues.

 

[ItsGavinC]

I was curious if the curing lights which generate light but no (or very little) heat were designed for these types of reactions? Or is it more of an issue of not damaging any pulp or periodontal tissue with the heat? Both?

The primary goal would be to emit the proper wavelength to initiate the reaction. The secondary goal would be to limit heat so as not damage pulp. I don't think it has anything to do with heat inhibiting the reaction.

 

[SquidsLife]

Well by heat I mean heat beyond room temp (like heating up a reaction to 50*C or whatever). I dont want to bore anybody with the details of this reaction, but it basically uses UV light instead of heat to make a 4-membered ring from two C=C's...like a diels alder if you remember it. Here is the quote from the book

"The [2+2] cycloaddition is therefore photochemically allowed, but thermally forbidden. In most cases, photochemically allowed reactions are thermally forbidden, and thermally allowed reactions are photochemically forbidden."

I was just curious if the reactions that undergo in cements, and composites and the sort involve these "photochemically allowed, but thermally forbidden" reactions. Or are the lights designed to not put out much heat to protect sensitive tissues.

The heat emitted from either LED or lack of heat from halogen curing lights really have no bearing on the methacryl reaction. There are bigger concerns with polymeric shrinkage in regards to extreme thermal exposure of composite based restorative material and cements. The heat from the LEDs was only a concern regarding patient safety and comfort.

 

[cdmOMR]

Cool, thanks for the information guys. If anyone has any other imput, feel free to reply.

 

[Jaybe]

Cool, thanks for the information guys. If anyone has any other imput, feel free to reply.

Here's my input:

 

[1992Corolla]

Here's my input:

My dad who is long done with school asked me to ask him an ochem question when i was studying for the dat.

I asked him and he replied:

"I don't care anymore! HAHAHAHA!"

lol