Why keep brushing?!
Question: The reason to brush your teeth is to replace the hydroxide in your enamel (hydroxyapetate) with flourine in order to make your teeth less reactive to acids.
But after you have brushed your teeth for your lifetime, why do you need to keep brushing them?
Wouldn't you have already replaced all the hydroxyapetite with flouroapetite at a certain point?
Answers: The reason to brush your teeth is to replace the hydroxide in your enamel (hydroxyapetate) with flourine in order to make your teeth less reactive to acids.
But after you have brushed your teeth for your lifetime, why do you need to keep brushing them?
Wouldn't you have already replaced all the hydroxyapetite with flouroapetite at a certain point?
To answer this question, you need to understand the mechanism of decay, in order for a cavity to start, it needs three things:
1) Bacteria (mostly S.Mutans)
2) Carbohydrates (food for the bacteria)
3) Host (your teeth)
You can reduce or eliminate the decay you have, by altering these elements.
1) Bacteria can be controlled by removing the plaque accumulation, and using mouthwash, even though fluoride is considered anti-bacterial, most bacterial reduction happens with physical removal of plaque accumulation on your teeth by brushing, followed by antibacterial activity of a mouthwash.
2) Carbohydrates are the great food for bacteria, cut off the carbs supply and bacteria will die, give more carbs and bacteria will be happy metabolizing this food producing acid that will decay your teeth, again the fluoride in the tooth paste will have no effect on your carbs intake; it's really what you eat, and when you eat it.
3) Host. Which is your teeth, and here is where the fluoride shines, and now your statement start making sense "replace the hydroxide in enamel (hydroxyapetate) with fluoride in order to make teeth less reactive to acids" so fluoride in a toothpaste, or any supplement fluoride like fluoridated water, or supplement flouride tablets will make your teeth enamel more resistant to bacterial acid.
So the fluoride in the toothpaste will help reduce decay, but will not eliminate it. All three factors should be properly controlled for decay to stop.
When fluoride was introduced into dentistry, some studies showed that it dropped decay rate by more than 60% in population, however it didn't eliminate it.
About brushing, it's said that it helps fighting periodontal disease rather than cavities. So if you don't brush, regardless of your fluoride intake, the plaque accumulation will lead to gingivitis followed by a more advanced stage called periodontitis, which involves the teeth supporting bone, since your question didn't involve periodontal disease, I will not go into details here, but I hope what I wrote explained the advantage of fluoride.
so there is no plaque and your breath is good thats like asking why do we take a shower everyday
Brushing would still remove plaque and tartar. Also, it would remove stains, and food particles that could rot in between and on your teeth. Brushing also helps keep your breath fresh.
you also brush to remove plaque buildup dude.
So your teeth don't rot.
so your breath smells minty, and you wont get cavities, and prevent getting plaque
The reason you brush your teeth (you do, right...?) is to remove deposits of plaque from the teeth. Plaque is a sticky film of bacteria that adheres to teeth and this plaque does two things. First the bacteria in plaque stimulate your body to present an immune response leading to inflammation, bleeding etc (gingivitis/periodontitis). Leaving plaque on your teeth i.e not brushing properly would eventually lead to the teeth being loose and falling out of your head.
Secondly with regards to fluoroapatite, the bacteria in plaque love to feast on sugars from the diet. They release acids as waste products and this acids attack the enamel structure and demineralize it (i.e cavities, caries , tooth decay) Addition of fluoride to enamel makes it more resistant to this acid attack, it doesn't make it acid proof. In addition, the fluoride rich layer is very thin and is easily abraded so you need to keep replenishing it by brushing.
Lastly, if you don't brush, your breath will not be too pleasant ;-)