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Do Teeth Whitening Lights Work?

Teeth whitening with a LED light is hotly debated and extremely divisive among the dental community. One side vehemently opposes it saying that it does nothing and it is a gimmick just to sell you additional whitening products. The other side swears by it, alleging that it is a magical blue light that will make the bleaching faster and more effective.


crest whitening strips with LED light
crest whitening strips with LED light

So, who is right and who is wrong?


That is what we're trying to figure out and after extensive research, we've to say that both sides are selling you a half-truth. The teeth whitening light does help activate the hydrogen peroxide within the whitening gel but its effects are vastly overstated.


As evidence to back up our statement, we will go over all available research and what they say. Then we'll validate the alleged claims from both sides with research and common sense.


What scientific research says about the whitening lights

Unfortunately, you will not get a clear cut answer simply by digging through available research on the whitening lights. There are plenty of studies which show that the light does help improve the whiteness of your teeth. Then to make matters worse, there is an equivalent amount of studies that have shown the light did nothing for the brightness of your teeth.


So, which is it? Does it help or does it not help? We still couldn't figure it out just by looking at studies since there is evidence coming from both sides saying that it does and it doesn't help.


Browsing through studies will only make you more confused... Since there were studies which supported both sides, we would actually count that AGAINST the LED light side as being effective. Our reasoning is that if the light is truly effective, there SHOULDN'T be any studies which showed otherwise right?


Studies which support the use of the light

There were a plethora of studies which showed that the LED blue light helped in whitening your teeth. We'll list a few of them here as supporting evidence.

  • Study - Blue light significantly increases bleaching rate and final achievable ΔE.

  • Study - A major tooth color increase was found after the in-office LED/gel treatment stage. However only an insignificant further improvement was noted after the additional 14 day at-home treatment period. Overall the total color increase was low.

  • Study - The light whitened the upper teeth more effectively than lower teeth. Subjects were unable to distinguish a difference.

  • Study - Found that lights were effective but a downside was that it increased the temperature of the tooth a lot. Recommendation was to find a low heat emitting light source.

  • Study - Light assisted hydrogen peroxide was more effective than peroxide alone in whitening teeth.


Studies which shows the light was ineffective

The studies above showed promise for the effectiveness of the light but unfortunately there was an equivalent amount which showed it to be ineffective.

  • Study - The use of light activators did not increase the efficacy nor accelerate the bleaching.

  • Study - The use of light activation did not show any advantages compared to chemical bleaching. The light only increased the temperature of the tooth pulp.

  • Study - Using a split arch technique, half the mouth used a light while the other half did not. There was no color difference at the two week follow up.

  • Study - The use of light activator sources with in-office bleaching treatment of vital teeth did not increase the efficacy of bleaching or accelerate the bleaching.

  • Study - Use of light showed an immediate color change but after 7 days there was a significant color rebound. The light also caused a lot of sensitivity.


There were some studies which showed that the light did whiten the teeth but the color rebounded after about a week or two. This is most likely due to the light dehydrating the teeth and making them look whiter temporarily. Once the teeth were rehydrated, the color rebound effect was noted.


Arguments against the whitening light

Dr Rod Kurthy makes one of the most compelling arguments for why the whitening light does not activate the hydrogen peroxide whitening gel. According to Dr Kurthy, the breakdown of hydrogen peroxide is an exothermic reaction so it does not require the input of energy to initiate the reaction.


kor whitening without led light

Therefore the use of a light activator, which beams photons at the peroxide will do nothing to speed up the reaction. Only endothermic reactions require the input of energy in order for it to be activated.


However for full disclosure, Dr Kurthy is the inventor of KoR Whitening and their treatments do not utilize light activation for any of their products. Nonetheless, we will validate his alleged statement.


Is hydrogen peroxide an exothermic reaction?

Oh, yes it certainly is! In fact, hydrogen peroxide is considered highly exothermic in that it releases a lot of heat once it decomposes.


An easy way to distinguish an exothermic reaction from an endothermic one is if the end product produces heat or not. Perhaps just telling you this is not enough, so here is a science experiment which proves that peroxide does release heat as a byproduct.



In the video you can see where students are hovering their hands over the experiment and it feels hot. It feels hot because heat is being released as the hydrogen peroxide is decomposing and breaking down.


The fact that it is an exothermic reaction has been proven and thus the chemical breakdown formula for it is as such: 2H2O2 → 2H2O + O2 + heat

  • The breakdown of hydrogen peroxide leads to water, oxygen, and heat.


Therefore the breakdown of hydrogen peroxide actually releases energy and it does not require the input of energy in order for it to activate. So, yes Dr Kurthy is correct in saying that it is an exothermic reaction and not an endothermic one.


Le Chatelier's principle

If we actually examine this from Le Chatelier's principle as Dr Kurthy states, adding energy into the system will actually retard the reaction. In other words, it will impede or even slow down the hydrogen peroxide decomposition if you illuminate it with LED lights.


Since most lights generate heat, if you are shooting rays of light at the peroxide, it should cause the reaction to shift towards the reactant side of the equation and not the products.


Arguments for the use of the LED light

If Dr Kurthy is correct in that hydrogen peroxide decomposition is an exothermic reaction then does that mean the alleged claims that LED lights activate it are false? Surprisingly the answer is yes and no.


zoom led whitening light

It is true that the reaction does not require the input of energy for it to proceed. However, the LED light can still help "activate" the reaction but via a different mechanism. The breakdown of peroxide may not need energy but shooting photons at it can destabilize the oxygen-oxygen bond and thus cause it to decompose.


Hydrogen peroxide molecular structure - Neurotiker
Hydrogen peroxide molecular structure - Neurotiker

The peroxide bond which is the oxygen-oxygen bond is incredibly weak and unstable. Subjecting it to light energy will make it decompose and breakdown, thus initiating the reaction.


Evidence of this can be seen in everyday life, based on the fact that hydrogen peroxide is sold in brown bottles. The dark colored bottles are to protect it from light, which makes it decompose faster. In fact, the substance itself naturally decomposes all on its own since it's so unstable to begin with.


hydrogen peroxide in brown bottle

According to the EPA, the half life for hydrogen peroxide was 24 hours in atmospheric pressure. With photolysis (with light) it is about 2.14 days. So yes even when left alone, the substance naturally breaks down. This also means that if you have an old bottle of peroxide lying around, it may not be as effective as when you first bought it.


Evidence that light energy does activate hydrogen peroxide

Teeth whitening studies were not helpful in understanding whether light activated caused any additional benefits. Therefore we've decided to look for studies which did NOT have to do with teeth whitening since those would be less biased.


Hydrogen peroxide works on more than just teeth and we found evidence of UV light activating it in waste water. This study found that UV light caused the peroxide to more readily break down into the hydroxyl free radicals when it was exposed to it. When there was no UV light, it didn't break down as readily


It really doesn't matter if the hydrogen peroxide is in waste water or its in your mouth, if it can activate it, it will cause it to breakdown.


The Verdict - Does the light help whiten your teeth?

Basically, the decomposition of hydrogen peroxide does not require energy since it is exothermic but since it is an unstable substance, light can help "activate" it. The light activation is via destabilizing the peroxide bond and not so much as it is needed for the reaction to occur.


The big question is, why are there so many conflicting studies about its efficacy if it does seem to have an effect?


The conclusion that we came to was that using a chemical catalyst was significantly more effective than using light activation. In other words, adding a chemical catalyst to the hydrogen peroxide will break it down a lot faster than trying to shoot LED lights at it.


In lieu of LED lights, here are some common chemical catalysts for decomposing hydrogen peroxide:

  • Silver catalyst

  • Maganese compounds

  • Potassium dichromate

  • Iron oxide

  • Photocatalytic decomposition on TiO surface


Experiments which show chemical catalysts are extremely effective

As evidence, look no further than popular chemistry lab experiments involving hydrogen peroxide. There are plenty which show the decomposition and exothermic reaction of the substance by mixing in chemical catalysts.



The video above shows six different catalysts that were mixed with the peroxide. As you can see, the reaction proceeded at different rates depending on the catalyst that was used. Simply leaving the substance out in regular daylight did not help speed up the reaction.




Here is another video from Jimmy Kimmel which shows the violent reaction of hydrogen peroxide when mixed with a catalyst. It wasn't until the catalyst was added that the substance started to explode.


We have never seen any science experiments which can cause hydrogen peroxide to do the same thing as these catalysts did with an LED light.


Since there ARE studies which have shown that light can activate it but due to the absence of such experiments, we have concluded that LED lights are a WEAK activator. It is significantly inferior to the use of a chemical activator.


Summary

The conclusion that we came to was that the LED light does potentially help whiten your teeth but the benefits are marginal at best. The potential increase in benefits are such that we don't believe it is important to use the inclusion of a light as your main determining fact for which whitening system to use.


If you want to choose a system with a light then go for it! There is no real harm in doing so. However if you go with a non-lighted whitening system, you'll still have your white teeth. You won't be missing out on all that much.


Most of the reactivity is probably from the chemical catalysts that are in the whitening gel. Evidence of that are all in the science experiments which were conducted. All powerful reactions were induced with chemical catalysts and not with LED lights. The lights may mildly help but we're not sure if you'd even notice a difference.


However what we realized after doing all of this research is that hydrogen peroxide is highly unstable and will naturally decompose on its own. For this reason, it is supposed to be kept out of light and heat to preserve its effectiveness.


This actually adds support to KoR Whitening's principle of keeping all of their whitening gels refrigerated from the date of production to when it reaches your hands. They claim that makes their gels more effective and we do have to agree with that.


However that leaves us with one big question... So why aren't all whitening gels refrigerated? Perhaps that may be the reason why your teeth whitening isn't as effective as it can be...

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About the author: Dr David Chen, DDS

Hello, I'm Dr Chen and I'm an actively practicing dentist in Long Island City, NY. I graduated from Columbia University College of Dental Medicine in 2016 but prior to going to dental school I was already working in the dental field. It's been more than a decade since I first got to know dentistry and let me tell you, time flies by quickly. Since then I've developed a fondness for writing, which is how this all got started!

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Medical Disclaimer:

This blog is purely meant for information purposes and should not be used as medical advice. Each situation in your mouth is unique and complex. It is not possible to give advice nor diagnose any oral conditions based on text nor virtual consultations. The best thing to do is to go in person to see your dentist for an examination and consultation so that you can receive the best care possible.

The purpose of all of this oral health information is to encourage you to see your dentist and to inform you of what you may expect during your visit. Due to the unfortunate nature of dentistry, there isn't really any true home remedies that will get rid of dental problems. Roughly 99.99% of them require in-person intervention by a healthcare professional.

Hint: That is the reason why you can't eliminate seeing dentists in your life!

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