Если десна кровоточит, зубной нитью нужно пользоваться особенно осторожно.

Russian often leaves out possessive words like your, his, or my when the owner is obvious from context, especially with body parts.

So Если десна кровоточит... can naturally mean If your gum is bleeding... even though your is not stated.

If you want to make it explicit, you could say:

• Если у вас кровоточит десна...
• Если ваши дёсны кровоточат...

Both are possible, but the original sentence is perfectly normal without a possessive.

That is a very natural question for an English speaker.

Десна is the singular form, meaning gum. In Russian, the singular can sometimes be used in a general or medical-style way, referring to gum tissue.

However, in everyday speech, many people would also say the plural:

• Если дёсны кровоточат... = If your gums bleed / are bleeding...

So the original sentence is grammatical, but the plural version may feel more natural to an English speaker because English usually says gums.

Also notice the verb changes with the number:

• десна кровоточит = singular
• дёсны кровоточат = plural

Десна is in the nominative singular.

It is the subject of the verb кровоточит:

• десна = the gum
• кровоточит = is bleeding / bleeds

So this part works very simply:

• десна кровоточит = the gum is bleeding

Russian often uses the present tense in general statements and instructions like this.

Here the sentence means something like:

• Whenever the gum is bleeding, dental floss should be used especially carefully.

So кровоточит is not just describing what is happening right now at this second. It can also express a general condition or situation.

This is very similar to English sentences like:

• If it rains, we stay inside.
• If your gums bleed, use floss carefully.

Because Если десна кровоточит is a subordinate clause introduced by если.

Russian normally separates this kind of if-clause from the main clause with a comma:

• Если десна кровоточит, зубной нитью нужно пользоваться особенно осторожно.

This is standard punctuation.

Because the verb пользоваться requires the instrumental case.

The dictionary form is:

• зубная нить = dental floss

But after пользоваться, it changes to instrumental:

• зубной нитью = with dental floss / using dental floss

Form by form:

• зубная → зубной
• нить → нитью

So:

• пользоваться зубной нитью = to use dental floss

Yes, that is the normal pattern.

Пользоваться + instrumental means to use or to make use of something.

Examples:

• пользоваться словарём = to use a dictionary
• пользоваться компьютером = to use a computer
• пользоваться зубной нитью = to use dental floss

This is something you mostly just have to learn as part of the verb.

Нужно + infinitive is a very common Russian way to express general advice, necessity, or recommendation.

So:

• нужно пользоваться = it is necessary to use / one should use

This sounds more like a general instruction or guideline.

If Russian used an imperative, it would sound more direct:

• Пользуйтесь зубной нитью особенно осторожно. = Use dental floss especially carefully.

Both are possible, but the original sentence sounds more neutral and instructional, which fits medical or health advice.

Because the sentence is giving a general recommendation about how to do something, not talking about one single completed action.

Пользоваться is the imperfective verb and is the normal choice for repeated, habitual, or general use:

• нужно пользоваться = one should use

A perfective verb such as воспользоваться would usually suggest a more one-time or specific use, and it is not the most natural choice in this kind of general health instruction.

So the imperfective makes good sense here.

Because осторожно is an adverb, and the sentence needs an adverb here.

It describes how one should use the floss:

• пользоваться осторожно = to use it carefully

An adjective like осторожный would describe a noun, not the action.

Compare:

• осторожный человек = a careful person
• пользоваться осторожно = to use carefully

So осторожно modifies the verb phrase.

Особенно means especially or particularly.

So:

• осторожно = carefully
• особенно осторожно = especially carefully

It adds the idea that extra care is needed in this situation.

Yes. Russian word order is fairly flexible, though some versions sound more natural than others.

For example, you could also say:

• Если десна кровоточит, нужно пользоваться зубной нитью особенно осторожно.
• Зубной нитью нужно пользоваться особенно осторожно, если десна кровоточит.

These all mean roughly the same thing, but the emphasis shifts a little.

The original version puts зубной нитью early, which highlights the instrument being discussed. That works well in an instructional sentence.