here someone states that fluoride inhibits the enzyme adenosine diphosphatase which delivers phosphate into the saliva to remineralize the enamel.
https://www.quantumbalancing.com/news/saveteeth.htm
That page provides no references to support this statement it makes, so I doubt it is true, unless you can find a reference. Fluoride generally speeds up the incorporation of calcium and phosphate into the tooth surface.
The white mineral substance of your tooth enamel is actually called
apatite. As well as the tooth enamel, your bones are also made of apatite.
The apatite enamel coating of your teeth can be manufactured in three different ways, resulting in three forms of apatite:
hydroxylapatite,
fluorapatite and
chlorapatite.
Your saliva contains calcium, phosphate and hydroxyl ions, and these bond together to form hydroxylapatite (under alkaline conditions).
So in the mouth, normally
hydroxylapatite is manufactured from these minerals in the saliva, and so the apatite in your teeth enamel is mostly of the hydroxylapatite form. But if you increase fluoride levels (many regions of the world have fluoride naturally present in the water), then you start to get some
fluorapatite forming as well (so that your tooth enamel apatite then becomes a mixture of mostly hydroxylapatite, but also some fluorapatite).
Fluorapatite is stronger and more resistant to acid attack, so it strengthens the structure of tooth enamel. However, you don't want too much fluorapatite, because when tooth enamel contains too much fluorapatite, it can become a little brittle. So a little bit of fluoride strengthens the teeth, but too much makes the teeth brittle.
The chemical formula for hydroxylapatite is: Ca₁₀(PO₄)₆(OH)₂
I found the following a good explanation of the tooth remineralization process:
Dental caries is the result of an imbalance between demineralisation and remineralization. In health, loss of mineral is balanced by the reparative mechanisms of saliva.
Remineralization is a natural process in which inorganic minerals in saliva are deposited on carious dental surfaces under appropriate conditions, restoring the mineral content of teeth. The effect of this process varies greatly among individuals depending upon enamel composition, oral health and salivary constituents.
An equilibrium always exists between the solvated and solid mineral as:
Ca₁₀(PO₄)₆(OH)₂ ⟷ 10Ca²⁺ + 6PO₄³⁻ + 2OH¹⁻
The solid crystals of the tooth mineral, called hydroxyapatite, dissolve to release calcium, phosphate and hydroxyl ions only if the latter are below saturation concentrations. If above saturation, the reaction will tend to move to the left, and any damaged crystals will be repaired by the acquisition of ions from solution.
Stimulation of saliva flow results in an increase in the washing out of acids (and sugars), and also an increase in the amount and concentration of bicarbonate buffers and of remineralizing ions. The solubility of hydroxyapatite in water is extremely low. Thus it is not the dissolution of enamel that weakens the teeth surface.
At lower pH, higher amounts of calcium are released from the mineral structure as both hydroxide and phosphate concentrations are low. This explains the higher rates of enamel demineralization at lower pH. Remineralization is essentially a reversal of the conditions that cause demineralization. Minerals from food or saliva get dissolved in carbonic acid formed momentarily from the CO2 in breath and are deposited at the damage site of the enamel structure as the acid dissociates.
However this process is naturally inefficient in recalcifying acid eroded enamel surfaces as they are always covered by a pellicle of salivary and bacterial proteins. Thus remineralization helps only if the enamel layer is intact as in a healthy individual or in the white caries lesions. These lesions are formed due to decalcification of inner tooth material and can be treated by enhancing salivary flow (to increase remineralization) and maintaining good hygiene.
Source:
here
now I finally know why bicarbonate is needed to remineralize with calcium and phosphate - because of the alkalinity.
Yes, teeth are better remineralized under alkaline conditions, and sodium bicarbonate can provide this alkalinity.
There is a concept known as
critical pH, and when pH levels in the mouth become too acid and go below this critical pH, then the tooth enamel starts to
demineralize (ie, dissolve away). But when the pH is above the critical pH (more alkaline), then the then the tooth enamel starts to
remineralize (ie, the enamel surface rebuilds and thickens itself from the minerals found in the saliva).
The interesting thing is that the critical pH of hydroxyapatite is around 5.5, and that of fluorapatite is around 4.5. So fluorapatite can stand higher levels of oral acidity before it starts to demineralize. This explains why fluorapatite is more resistant to acid attack, and explains why fluoride strengthens the tooth enamel.
More info:
Dental Remineralization: Simplified
