 Today's video is a continuation of our topical fluorides. So in topical fluoride video, I have been mentioned about the mechanism of action in each category that is the three categories sodium fluoride, stainless fluoride and ABF. So the mechanism of action of each topical fluoride how this fluoride is getting incorporated into this hydroxyapatite crystal the mechanism and the byproducts of the intermediate products which is formed during this chemical reaction is different in each category means each product is getting formed when we apply these products. So in this video, I will be explaining in detail about the various mechanism of action of sodium fluoride, planus fluoride and ABFO. Let's see what is the mechanism of action. So how this topical fluoride of sodium fluoride helping the tooth to bite against dental caries. In systemic fluoride we have seen the fluoride goes into the enamel and it replaces the hydroxy-lion and it creates a fluorohydroxyapatite or fluorohapatite crystals which is very strong than the normal hydroxyapatite. So let's see what is happening in sodium fluoride mechanism or Knudsen's technique. So when we apply sodium fluoride what happens is this sodium fluoride it reacts with hydroxyapatite crystal and to form calcium fluoride. This is a byproduct which forms calcium fluoride. So it starts getting formed. The calcium fluoride is getting formed on the surface and a thick layer is formed at the end of four minutes. So what happens after that? This thick layer calcium fluoride interferes with further diffusional fluoride. So once this thick layer is formed we apply sodium fluoride again and again there is no point because this thick layer interferes with further diffusion. So there is no point applying sodium fluoride after four minutes. So that is why most of the topical fluorides are applying at a period of four minutes. So this particular process is known as chocking of effect. This is very important. It is sodium fluoride once the calcium fluoride is formed after the application for a four minute period it further prevents the diffusion of fluoride. So it blocks further entry of fluoride ions and it is known as chocking of effect. So this sudden stop of entry of fluoride is termed as chocking of. So this calcium fluoride acts as a reservoir. So this calcium fluoride will be there on the surface and it slowly releases the fluoride. Okay so it is not the sodium fluoride it releases the fluoride for the prevention of dental care. It is actually the calcium fluoride releases the fluoride. So we might think that it is sodium fluoride is releasing fluoride but no it is the calcium fluoride. So calcium fluoride reacts with hydroxyapatite then there will be fluoride hydroxyapatite which increases the concentration of fluoride on the surface and prevent caries. So from calcium fluoride the actual fluoride is releasing out okay not from the sodium fluoride. So that is the chemical reaction happening with the first topical fluoride that is nonsense technique. So all these techniques we have covered in detail in that video. So in this video I will be explaining about the chemical reaction happening and especially this phenomenon known as chocking of effect. Chocking of means we are strangling someone and posing or preventing his breath. So that is chocking off so similar way we are strangling the further entry of fluoride because calcium fluoride act as a barrier it interferes with the further diffusion of fluoride okay. So let's see the second product that is Stannous fluoride. So we are playing almost very high ppm that is 20,000 or around 20,000 ppm. So all these we have discussed already so I will be explaining about the mechanism of action. So when Stannous fluoride is applied at a very low concentration what happens is there is tin hydroxyapatite formation okay. So Stannous is nothing but tin it is a chemical name for tin Sn. So tin hydroxyapatite is formed which gets dissolved in oral tissues. And we apply in low concentration. So that is a scenario when we apply in low concentration but when we apply at very high concentration what happens is there is a formation of calcium trifluorostanate. So this Stannous fluoride reacts with the calcium of hydroxyapatite and forms calcium trifluorostanate. At the same time there is another product which is known as tin trifluorophosphate. So these two products will be formed once Stannous fluoride applied at very high concentration okay. Low concentration there is no attraction only tin hydroxyapatite forms. At high concentration these two products are formed calcium trifluorostanate and tin trifluorophosphate. So this tin trifluorophosphate is responsible for making the tooth structure more stable. So this is the product which actually act as a barrier or prevents dental caries because this is a product which helps tooth to become more stronger than the normal hydroxyapatite. And calcium fluoride is the end product. So after this there will be end product that is calcium fluoride in both low and high concentration which reacts with hydroxyapatite and a small fraction of fluorohydroxyapatite also gets formed. So at the same time along with this there is a very small amount of fluorohydroxyapatite because at the end product calcium fluoride is there. So it reacts with hydroxyapatite and fluorohydroxyapatite but very low amount. In sodium fluoride mechanism calcium fluoride is the main product ok but whereas in Muller's technique of stannous fluoride this tin trifluorophosphate is the main product. There is a calcium trifluorostanate but this is the main product which helps the tooth to prevent caries or make it very hot. So that is the second mechanism of stannous fluoride or Muller's solution. So let's see what is acidulated phosphate fluoride or APF mechanism ok. So here what happens is when APF is applied to teeth in the beginning time there is dehydration and shrinkage of hydroxyapatite crystals because we are applying it at very low pH. So it is applied at 1.23 percentage and 3 pH which is very highly acidic. So it creates dehydration and shrinkage in hydroxyapatite crystals and after that an intermediate product known as DCPD is formed that is di calcium phosphate dihydrate is formed. So this forms in APF. So always there is no need of confusion when we apply sodium fluoride calcium fluoride is formed when we apply stannous fluoride calcium trifluorostanate and tin trifluorophosphate is formed we apply APF DCPD is formed. So the DCPD is very highly reactive and starts forming immediately after APF is applied. The fluoride penetrates into the crystals more deeply through the opening. So there was shrinkage and dehydration. So this fluoride can easily penetrate to the deeper parts of enamel and forms fluoropetite. So this DCPD is a crucial product which forms when we apply APF. So this DCPD formed which will be later converted into fluoropetite. So the compounds which are very vital in APF is DCPD, stannous fluoride which is trifluorophosphate and in sodium fluoride technique it was calcium fluoride and choking of effects seen in sodium fluoride. These are the three techniques which we use to apply topical fluorides and the mechanism and its chemical reactions. So that's all about the mechanism of action which is associated with topical fluorides. So after that we have seen all this the comparison which we have discussed already the pH percentage and all other things and fluorides. So I will come up with a new video. So it was just an extension of our topical fluoride video just to give you a brief idea about the chemical reaction which is happening with the topical fluoride application. Thank you.