Plaque on teeth, why, and prevention?

[panacea]

I went to the dentist today, and she told me that plaque will develop even if I were to eat or drink nothing, assuming I was kept alive by IV water/nutrients, because plaque doesn't come from food but from our saliva. Is this true?

I got to wondering, why would our own body produce something that hurts our teeth?

Surely our ancestors did not have such horrible tooth pain like we would if we were not to take care of our teeth with sharp metal tools for removing tartar and toothpastes and toothbrushes for plaque, so what is the logic I'm missing here?

Is it because they ate fibrous fruits frequently in small meals, each bite cleaning the plaque off, and this is why it was never a threat?

My dentist also told me water/OJ/ and other liquids don't clean off but about one third of the plaque, even if swished.

Also, is there any way to prevent plaque? My dentist told me by going to sleep with a little bit of Listerine mouthwash coating left on my teeth, that plaque wouldn't form as fast.

[RRM]

plaque doesn't come from food but from our saliva. Is this true?

I think so.

why would our own body produce something that hurts our teeth?

I think its actually protection against acids, but nobody likes to wear it on their teeth, naturally.

Is it because they ate fibrous fruits frequently in small meals, each bite cleaning the plaque off, and this is why it was never a threat?

That might be it.

Also, is there any way to prevent plaque?

I think its best not to remove (or prevent) it constantly / vigorously.
Just remove that whats noticeable.

My dentist told me by going to sleep with a little bit of Listerine mouthwash coating left on my teeth, that plaque wouldn't form as fast.

Its not a coating, but a harsh cleansing regiment which impairs your mouth flora.
You may get a lot more saliva because of it.

[Oscar]

Plaque basically consists of food debris, bacteria and saliva. There are many unanswered questions, unfortunately.
The bacteria in the plaque can produce lactic acid, which is believed to cause cavities. When plaque hardens, it can become tartar. Gingivitis and periodontitis can be the result of that.

[coconutty]

Seconding what Oscar said, plaque contains a lot of bacteria.

The plaque gradually hardens after 48 hours, and after 2 weeks have gone by it solidifies to such a state that you cannot remove it by normal brushing. You have to go to a dentist or get them "scaled". The reason that antibacterial mouthwashes are recommended is because they kill the bacteria that cause plaque. However, their efficacy is not entirely that strong, partially because many mouthwashes contain alcohol which change the pH content of the mouth.

It is incorrect to say that plaque is only from saliva and not from food. The bacteria in the mouth feed off of primarily fructose and starches. Saliva, while a component of plaque, also helps the teeth by re-establishing a normal pH level which helps the teeth to remineralize after the bacteria have gotten to them.