Potassium nitrate is a depolarizing agent which numbs the nerve of sensitive teeth thus desensitizing them when it is used twice per day. This desensitizing agent is commonly found in sensitive toothpastes and the prime example would be the Sensodyne pronamel.
We will explain the desensitization mechanism, factors that affect its efficacy, side effects, and alternative desensitizers. Of course, we'll provide evidence for all of our statements with research studies.
Table of contents:
Overview
Potassium nitrate (KNO3) is a common desensitizing toothpaste ingredient that is found in sensitive toothpastes. However, unbeknownst to most, another name for potassium nitrate is saltpeter, which is a major constituent in gunpowder, fireworks, and rocket propellants.
Yes, KNO3 is still a safe and effective sensitivity agent despite it's alternative uses.
According to PubChem, it is approved under Title 21, Code of Federal Regulations (21 CFR), Part 355. An addendum states that such products may contain up to 5% potassium nitrate as a tooth desensitizing ingredient.
Background
Prior to the approval, the first toothpaste with potassium nitrate was first released by Sensodyne and it was combined with fluoride. It was touted as the first dentifrice to fight cavities and decrease teeth sensitivity.
However shortly after being released to the market, the US government brought a lawsuit against the toothpaste maker saying it was not approved for use! It's absolutely fascinating but you don't have to read the decision if you don't want to. Nonetheless, fortunately for you after much deliberation, this desensitizing agent ultimately got approval for use in toothpastes.
How it works
Potassium nitrate reduces teeth sensitivity by depolarizing the tooth nerve thus effectively numbing it. Essentially, the tooth is still feeling the external stimuli but it is simply not bothered by it. It is analogous to your dentist using local anesthetics on your tooth and proceeds to drill on it but you feel no pain.
KNO3 desensitization mechanism:
It is applied topically onto the tooth surface via toothpaste.
The potassium ions (K+) travel through the dentinal tubules to reach the nerve.
An overabundance of K+ reverses the natural concentration gradient which effectively prevents propagation of action potentials.
In other words, no pain signals can be fired.
For the sake of simplicity, you can just think of this desensitizing ingredient as a tooth nerve numbing agent.
Why excess potassium prevents action potentials
In order to understand why applying potassium prevents pain signal generation we need to review how action potentials are generated. The cardinal rule is that for diffusion, molecules move from an area of high concentration to an area of low concentration.
The initial state:
There is a low concentration of potassium outside of the cell.
Therefore, potassium readily diffuses from intracellular to extracellular.
Tooth brushed with potassium nitrate:
There is now a high concentration of potassium outside of the cell.
Since the concentration gradient is now reversed, potassium will not diffuse from intracellular to extracellular.
This effectively blocks the generation of an action potential.
Of course, the first step of action potential generation is sodium going from extracellular to intracellular but this step is unaffected by KNO3. It is the second and next step which is affected, when its the potassium's turn to diffuse.
Does it work?
Potassium nitrate based toothpastes are effective in decreasing and sometimes completely eliminating teeth sensitivity. We will review two studies which tested its efficacy.
The first studies compared KNO3 to a control group.
Subjects were instructed to brush their teeth twice a day with 5% KNO3 toothpaste.
Significant decrease in hypersensitivity were reported at weeks 4, 8, and 12.
Symptoms improved over subsequent weeks leading up to the 12th week.
67% of test subjects had complete resolution of subjective symptoms.
The second study tested the efficacy of KNO3 when used with teeth bleaching.
Whitening was done with 9.5% hydrogen peroxide.
During first week of whitening, significant number of those who used potassium nitrate were sensitivity free.
After the 14 day treatment period, there were much more sensitivity free days for the group who used KNO3.
That's right, patients whitened their teeth in conjunction with desensitizing them. As we all know, bleaching exacerbates and induces sensitivity. Therefore, if this ingredient is potent enough to desensitize bleached teeth, it will work for your cold water sensitive dentition.
Factors affecting efficacy
While potassium nitrate is a proven desensitizer, there are other factors which can affect its efficacy during daily use. Lifestyle habits and improper use of this dentifrice has consequences.
Factors increasing efficacy:
Brushing for at least 2 minutes.
Applying toothpaste towards gum line.
Reducing acidic foods.
Brushing after every meal.
Not rinsing after brushing.
Factors decreasing efficacy:
Brushing for less than 2 minutes.
Not applying toothpaste at gum line.
Diet high in acidic foods.
Inconsistent use of toothpaste, brushing less than twice a day.
There are three points we wish to expand upon due to them being overlooked.
Applying toothpaste towards gum line
Typically the most sensitive part of the teeth is near the gingival margin (gum line). That where gum recession tends to occur which results in exposed root surfaces that are sensitivity prone.
If you're not brushing the toothpaste with the desensitizer into the sensitive spot, you're using this product incorrectly. You're essentially desensitizing the surfaces that don't need it while missing the areas that do need it. So, be sure to brush the toothpaste INTO the gum line area.
Minimizing acidic foods
Foods that generally trigger sensitivity are generally acidic or low in pH. When you consume a lot of it, you're basically throwing oil into the fire and inducing pain signals. You need to stop doing that and minimize the amount of acidic foods whenever possible.
Acidic foods:
Fruits and juices
Sodas & sport drinks
Wine
Sugary beverages and foods
Sour & spicy foods
If this is your situation, it may not be the toothpaste's fault but rather your lifestyle habits that are sabotaging your own efforts.
Don't rinse after brushing
We do endorse rinsing after brushing your teeth because you're not supposed to swallow toothpaste with fluoride in it. However, the NHS does recommend not rinsing afterwards in order to reap the full effect of fluoride.
We find NHS's recommendation to be impractical on a daily basis because you have to continually spit out toothpaste if you don't rinse. However, if you needed an extra boost in desensitization from potassium nitrate you should consider not rinsing afterwards.
Doing so will allow the toothpaste to desensitize your teeth for a longer period of time. Don't forget that this ingredient works topically which means the longer it stays on your teeth the longer it gets work.
Side effects
We are not aware of any specific adverse effects from potassium nitrate in toothpastes. Most of the warning labels, precautions, and overdose are in regards to the fluoride in the toothpaste.
Below you can find the FDA label for a 1.1% sodium fluoride with 5% potassium nitrate toothpaste. It is prescription strength but if you read all of the warnings, they're all about ingestion of the fluoride but not the KNO3.
With that being said, we did find a hazardous substance sheet by the NJ dept of health for potassium nitrate but it isn't toothpaste specific.
Hazard summary:
Breathing it in can irritate the nose, throat, and induce sneezing and coughing.
Contact can cause eye and skin irritation
High concentrations can interfere with oxygen in the blood thus causing; headache, fatigue, dizziness, and blue color to skin/lip (methemoglobinemia).
Higher levels can result in trouble breathing, collapse and death.
It can affect the kidneys causing anemia.
Alternative desensitizers
Potassium nitrate is the only nerve depolarizing desensitizing ingredient in toothpaste. However, there are plenty of other desensitizers that work via occluding exposed dentinal tubules.
Alternative desensitizing agents in toothpaste:
Stannous fluoride. The primary ingredient in Sensodyne rapid relief.
Hydroxyapatite. Toothpaste made of tooth mineral, it works by blocking exposed dentinal tubules by inserting itself directly into it.
Strontium chloride. Tubular occlusion agent which used to be in Sensodyne toothpastes but has been replaced by KNO3.
Arginine. Another tubular occlusion agent which Colgate used to make but is no longer available in the US. You can still find this toothpaste in their overseas markets.
The effects can be individualistic so if sensitive toothpaste isn't working for you, perhaps you should try a different one to see if it helps more.
Takeaway
Sensitive toothpastes with potassium nitrate reduces teeth sensitivity by depolarizing the nerve. It effectively numbs the tooth thus rendering it unexcitable, meaning it can no longer fire pain signals. That's everything that our dentists in Long Island City have to say about this.
