The main difference between PAP and PAP+ whitening products is that the PAP+ contains an additional ingredient called nano-hydroxyapatite (nHap). Aside from that one distinction, they are virtually identical formulation wise.
However, the inclusion of the hydroxyapatite will bestow an additional benefit, namely an increase in product safety while teeth whitening.
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Both contain PAP
Both PAP and PAP+ teeth whitening products utilize phthalimidoperoxycaproic acid (PAP) as the primary whitening agent. They use this in lieu of hydrogen peroxide to bleach out tooth stains and make your teeth whiter.
How phthalimidoperoxycaproic acid whitens teeth
PAP whitens teeth by oxidizing stains on teeth but it does so without forming free radicals, which is different from peroxide.
Instead of free radicals, PAP oxidizes the conjugated double bonds of stain molecules via epoxidation.
PAP converts the carbon-carbon double bond into an epoxide.
Epoxides look distinctively like a triangle on molecular formulas.
End result is that the double bond has been converted to a single bond.
Ultimately, the loss of the double bond results in a decolorization of the stain.
How hydrogen peroxide whitens teeth
These free radicals convert the double conjugated bonds of stain molecules into single bonds.
As stain molecules lose double bonds, they will absorb less light and reflect more of it. Thus, these dark colored chromogens will become whiter in color.
Only PAP+ contains nano-hydroxyapatite
The big difference between PAP and PAP+ is that the latter has an additional ingredient, nano-hydroxyapatite, while the former does not.
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Hismile whitening toothpaste
The nano-hydroxyapatite is a remineralization agent and is made of the same type of material as your teeth. It's just that it is nano-sized hence the name. In other words, it's purpose is to reverse cavities similar to fluoride.
What the nHap does not do is contribute to the whitening process. It is the PAP that is solely responsible for whitening the teeth.
Difference in enamel safety
A big selling point of PAP+ whitening is its enhanced safety for your enamel. It is often marketed as an alternative to peroxide that is safer for your teeth. A bonus perk is that it can also desensitize your teeth which is helpful since bleaching can cause teeth sensitivity.
How it's safer
The reason PAP+ is less harmful for your teeth is because it contains nano-hydroxyapatite, a tooth remineralization agent. In other words, it can neutralize the demineralization process of the whitening process thus negating any harmful effects.
How the process works:
Teeth whitening will cause enamel demineralization (loss of minerals).
However, the nano-hydroxyapatite will initiate remineralization (regain of minerals).
In summary, the demineralization from PAP whitening gets balanced out or neutralized by remineralization from nHap.
Teeth sensitivity is a well known adverse effect of whitening. Fortunately for you, the ADA states that it usually goes away after about 4 days once you cease using the product. What makes PAP+ unique is that the nano-hydroxyapatite has a desensitizing effect which is why all toothpastes with it can be used for sensitive teeth.
How it works:
Exposed open dentinal tubules can cause teeth sensitivity.
nHap will occlude the open tubules thus blocking nerve stimulation.
It works in a very similar way in how stannous fluoride blocks sensitivity. They both occlude patent dentinal tubules thus preventing stimuli from interacting with the tooth nerve.
Is it a fair comparison?
Unfortunately, the alleged claim that PAP+ is safer than hydrogen peroxide (HP) in whitening teeth is an unfair comparison. It is comparing a whitening+remineralization product (PAP+) vs a whitening only product (HP).
Yes, studies have shown that when hydroxyapatite is added to PAP, there is no resultant decrease in enamel microhardness after whitening.
Regardless, that is an unfair comparison because for a study to be equivalent, it should be PAP+ vs hydrogen peroxide plus nano-hydroxyapatite. That way, both bleaching agents have a remineralization agent in it.
With that being said, there are plenty of peroxide based whitening products which have fluoride in it, a different remineralization agent. Colgate makes all of their optic white toothpastes with that very formulation, hydrogen peroxide + fluoride.
There are also professional whitening products which already include fluoride in it.
In case you were wondering, fluoride in whitening gel does not impede nor affect its efficacy in bleaching your teeth.
PAP+ whitening products are identical to PAP products except it contains an additional ingredient, nano-hydroxyapatite. What this extra ingredient does is make the whitening process safer and less sensitive since it is a tooth remineralization agent as well as a desensitizer.
For the record, I love the fact that Hismile is adding nano-hydroxyapatite to all of their whitening products. It does make it safer and frankly I don't understand why more manufacturers don't do it... If you want to check out a PAP+ product, Hismile has a whitening toothpaste which does it.