Yes it is possible to have gum disease more than once. In fact it is common. The treatments you get from your dentist cannot be successful unless you increase your oral hygiene and eliminate factors such as smoking.
No, but it is not clean to wear underwear more than once without washing it.
No, a litre is more than a fifth.
Yes one fifth is more than one tenth.
A little more than 25 ounces in a fifth (25.36 to be more precise).
No. After you get a disease like smallpox, your body is able to develop permanent defenses against it. This makes you "Immune" to the disease. This is the principle on which vaccines work.
no
No.
It can occur more than once.
No if you have one fifth you have more 1 out of 5 or 1 out of 9
You can be be exposed to it more than once
More than 1/5.