خيط الأسنان قرب فرشاة الأسنان.

A careful pronunciation is:

khayṭu l-asnān qurba furshāti l-asnān

In everyday reading without case endings, you will often hear something closer to:

khayṭ al-asnān qurb furshat al-asnān

A few sound notes:

• خ = a rough kh sound, like in Scottish loch or German Bach
• ط = an emphatic/heavier t
• الأسنان = al-asnān, not as-s..., because أ is not a sun letter

Because Arabic usually omits the verb to be in the present tense.

So:

• خيط الأسنان قرب فرشاة الأسنان = The dental floss is near the toothbrush

There is no separate word for is here. This is completely normal in Arabic.

If you wanted the past tense, then Arabic would use a verb, for example:

• كان خيط الأسنان قرب فرشاة الأسنان = The dental floss was near the toothbrush

It is a nominal sentence.

You can think of it as:

• خيط الأسنان = the topic / subject
• قرب فرشاة الأسنان = the predicate / location

So the structure is basically:

• [noun phrase] + [location phrase]

That gives the meaning The dental floss is near the toothbrush.

Because both are iḍāfa constructions, often called the construct state.

In an iḍāfa:

• the first noun usually does not take الـ
• the second noun can make the whole phrase definite

So:

• خيط الأسنان = literally thread of the teeth, meaning dental floss
• فرشاة الأسنان = literally brush of the teeth, meaning toothbrush

Even though خيط and فرشاة do not have الـ, the whole phrase is definite because الأسنان is definite.

Because Arabic commonly builds these everyday object names with an iḍāfa pattern:

• خيط الأسنان = dental floss
• فرشاة الأسنان = toothbrush

English often uses compact noun compounds like toothbrush. Arabic often expresses the same idea as X of the teeth.

So repeating الأسنان is natural Arabic, not awkward repetition.

That is just a difference between how the two languages form compounds.

English often uses the singular in compounds:

• toothbrush
• toothpaste

Arabic often uses the plural in these kinds of expressions:

• فرشاة الأسنان = toothbrush
• معجون الأسنان = toothpaste
• خيط الأسنان = dental floss

So even though English says tooth-, Arabic naturally says of the teeth.

قرب means near or close to here.

Traditionally, it is often analyzed as a noun/adverb of place used in a preposition-like way. For a learner, the easiest way to understand it is:

• قرب + noun phrase = near + noun phrase

So:

• قرب فرشاة الأسنان = near the toothbrush

The noun after قرب is in the genitive relationship.

A very common alternative is:

• بالقرب من فرشاة الأسنان = near the toothbrush

Both are natural, though قرب is shorter and more direct.

Because فرشاة is the first word in an iḍāfa construction: فرشاة الأسنان.

When a word ending in ة is read in isolation, it often sounds like -a or -ah. But when it is grammatically connected, especially in an iḍāfa, the ة is pronounced as t.

So:

• by itself: فرشاة ≈ furshāh / fursha
• in the sentence: فرشاة الأسنان = furshat al-asnān

This is very common in Arabic.

A fully vowelled version is:

خَيْطُ الأَسْنَانِ قُرْبَ فُرْشَاةِ الأَسْنَانِ

Very roughly:

• خيطُ = nominative, because it is the subject/topic
• الأسنانِ = genitive, because it is the second noun of an iḍāfa
• قربَ = accusative as an adverbial expression of place
• فرشاةِ = genitive after قرب in this construction
• الأسنانِ = genitive again as part of the second iḍāfa

In normal printed Arabic, these short vowels are usually not written.

Yes.

These are both natural:

• خيط الأسنان قرب فرشاة الأسنان
• خيط الأسنان بالقرب من فرشاة الأسنان

The second version is a little more explicit because بالقرب من clearly means close to / near.

So for a learner:

• قرب = shorter, compact
• بالقرب من = very common and often easier to recognize at first

Both are good Arabic.