يحشو طبيب الأسنان السن.

Because verb–subject–object order is very common in Modern Standard Arabic.

So:

• يحشو = fills / is filling
• طبيب الأسنان = the dentist
• السن = the tooth

Literally, the structure is:

• fills
  • the dentist
    • the tooth

Arabic can also use subject–verb–object order, but starting with the verb is very normal and often feels more neutral in narration.

There are two main clues:

1. Word order
   In a verbal sentence like this, the noun right after the verb is often the subject, and the following noun is often the object.

2. Case endings in full vocalization
   If fully vowelled, the sentence is:

   يَحْشُو طَبِيبُ الأَسْنَانِ السِّنَّ

   Here:

   • طبيبُ ends with -u → nominative → subject
   • السِّنَّ ends with -a → accusative → direct object

So the dentist is doing the action, and the tooth is receiving it.

Because the subject is still just one person: the dentist.

طبيب الأسنان is a noun phrase meaning the dentist, not multiple people. The second word الأسنان is part of the expression and does not make the subject plural.

So the verb stays singular masculine:

• يحشو = he fills / is filling

If the subject were plural, the verb form would change.

It is an iḍāfa construction, often called a genitive/possessive construction.

Literally, it is:

• طبيب = doctor
• الأسنان = the teeth

So word-for-word it is something like doctor of the teeth, which is how Arabic says dentist.

Important points about iḍāfa here:

• the first noun (طبيب) does not take الـ
• the second noun (الأسنان) is in the genitive
• the whole phrase can still be definite

So طبيب الأسنان means the dentist, not just a dentist, in this sentence.

Because in an iḍāfa construction, the first noun normally does not take الـ.

Definiteness comes from the second noun:

• طبيب أسنان = a dentist / tooth doctor
• طبيب الأسنان = the dentist / the doctor of the teeth

So even without الـ on طبيب, the whole phrase can still be definite because الأسنان is definite.

This is a very common feature of Arabic grammar.

That is simply the natural Arabic way to express this profession.

English often uses noun compounds like:

• tooth doctor
• school bus
• coffee cup

Arabic usually prefers an iḍāfa structure instead:

• doctor of the teeth
• bus of the school
• cup of coffee

So طبيب الأسنان is the normal idiomatic way to say dentist.

Because the profession is named in relation to teeth in general.

• سنّ = tooth
• أسنان = teeth

So طبيب الأسنان literally means doctor of the teeth, which is the standard Arabic way to say dentist.

Arabic often uses a plural body-part noun in job titles or set expressions where English may use a singular word.

It is in the imperfect verb form, which often covers:

• present: the dentist fills the tooth
• ongoing present: the dentist is filling the tooth
• habitual: the dentist fills teeth

In Arabic, the exact English tense often depends on context. By itself, يحشو most naturally means something like fills or is filling.

The dictionary form is حشا.

This verb means things like:

• to stuff
• to fill
• in dental context, to fill a tooth

So:

• حشا = he filled
• يحشو = he fills / is filling

Because this verb ends in a weak letter in its root, its forms may look a little unusual at first, but you can simply learn يحشو as the standard imperfect form.

A fully vocalized version is:

يَحْشُو طَبِيبُ الأَسْنَانِ السِّنَّ

A helpful pronunciation guide:

• يَحْشُو = yaḥshū
• طَبِيبُ = ṭabību
• الأَسْنَانِ = al-asnāni
• السِّنَّ = as-sinna

So the whole sentence is approximately:

yaḥshū ṭabību l-asnāni s-sinna

In normal connected pronunciation, the sounds flow together smoothly.

Because of sun letters and moon letters.

In السن

The word begins with س (s), and س is a sun letter.
So the ل of الـ is not pronounced; it assimilates into the س.

So السن is pronounced:

• as-sinn(a), not al-sinn

In الأسنان

The word begins with أ (a hamza sound), not with س.
So there is no assimilation of the ل.

It is pronounced:

• al-asnān

So even though both words are related to teeth, the article behaves differently because the next sound is different.

If we write the full endings, we get:

يَحْشُو طَبِيبُ الأَسْنَانِ السِّنَّ

Here is the breakdown:

• طبيبُ → nominative (-u) because it is the subject
• الأسنانِ → genitive (-i) because it is the second term of an iḍāfa
• السِّنَّ → accusative (-a) because it is the direct object

These endings are very useful for understanding grammar, even though in normal unvowelled writing they are usually not shown.

Yes. That would also be correct.

Compare:

• يحشو طبيب الأسنان السن → The dentist fills/is filling the tooth
  This is a normal verbal sentence with a neutral, action-first feel.

• طبيب الأسنان يحشو السن → The dentist fills/is filling the tooth
  This is more subject-first, and it can sound slightly more emphatic about the dentist.

Both are grammatical. Arabic often allows both patterns, with small differences in focus or style.

No. سنّ can also mean age in other contexts.

For example, in a different sentence:

• كم سنك؟ = How old are you? (literally, What is your age?)

But in this sentence, because we have a dentist and the verb يحشو in a dental context, السن clearly means the tooth.

Context usually removes any ambiguity.