يخدر طبيب الأسنان السن بالمخدر الموضعي.

Because Arabic very often uses verb-first word order, especially in straightforward statements.

So:

• يخدر = He numbs / numbs
• طبيب الأسنان = the dentist
• السن = the tooth
• بالمخدر الموضعي = with the local anesthetic

This is a normal VSO pattern: Verb – Subject – Object.

You could also say:

• طبيب الأسنان يخدر السن بالمخدر الموضعي

That is also correct, but it shifts the structure to Subject – Verb – Object, which can sound a bit more like you are emphasizing the dentist.

يخدر means he numbs or he anesthetizes.

It comes from the root خ د ر. This root is related to numbing, anesthesia, or loss of sensation.

In this sentence, يخدر is a present-tense verb in the 3rd person masculine singular, so literally it is:

• he numbs

Since the subject is طبيب الأسنان (the dentist), the verb matches it.

If fully vowelled, it is usually written:

• يُخَدِّرُ

That doubled middle consonant shows this is a Form II verb, which often has a causative or intensive sense. So the idea is roughly to cause to become numb.

Because طبيب الأسنان is the normal Arabic expression for dentist.

Literally, it is:

• طبيب = doctor
• الأسنان = the teeth

So the phrase means something like doctor of the teeth, but in natural English we simply say dentist.

This is a very common type of Arabic expression: a noun followed by another noun in a possessive/genitive relationship.

Here:

• طبيبُ الأسنانِ

means:

• doctor of the teeth
• naturally: the dentist

That is just how Arabic expresses this profession. Arabic commonly uses طبيب الأسنان with teeth in the plural.

So even though English uses the single word dentist, Arabic uses a noun phrase meaning:

• doctor of the teeth

This does not mean the sentence is talking about multiple teeth in this specific action. The actual tooth being numbed is shown separately by:

• السن = the tooth

So the sentence contains both:

• طبيب الأسنان = the dentist
• السن = the tooth

In Arabic, nouns are often definite when the context makes them specific or known.

Here, السن means the tooth, which sounds natural because in a dental situation the tooth being treated is usually a specific tooth.

Arabic uses the definite article الـ much like English uses the.

So:

• سن = a tooth / tooth
• السن = the tooth

In real usage, Arabic often prefers the definite form in medical or situational contexts where the object is understood to be specific.

The preposition بـ usually means with, by, or using depending on context.

Here it means:

• with / using

So:

• بالمخدر الموضعي = with the local anesthetic

This phrase tells you the instrument or means by which the numbing is done.

Breakdown:

• بـ = with / by means of
• المخدر = the anesthetic
• الموضعي = local

So the whole phrase means:

• with the local anesthetic
• or more naturally, using a local anesthetic

In Arabic, adjectives normally come after the noun they describe.

So:

• المخدر = the anesthetic
• الموضعي = local

Together:

• المخدر الموضعي = the local anesthetic

This is the standard noun + adjective order in Arabic.

Also, the adjective must match the noun in:

• definiteness
• gender
• number
• case

Since المخدر is definite, the adjective is also definite:

• المخدر الموضعي
• not المخدر موضعي

The basic structure tells you that:

• يخدر = the action: numbs
• طبيب الأسنان = the subject: the dentist
• السن = the direct object: the tooth
• بالمخدر الموضعي = a prepositional phrase: with the local anesthetic

So the dentist is the one doing the numbing, and the tooth is what gets numbed.

If the sentence is fully vowelled, this becomes even clearer:

• يُخَدِّرُ طبيبُ الأسنانِ السِّنَّ بالمُخَدِّرِ الموضعيِّ

The endings show:

• طبيبُ = subject
• السِّنَّ = direct object
• بالمُخَدِّرِ = after a preposition, so genitive

In normal unvowelled writing, readers understand this from word order and context.

A fully vocalized version is:

• يُخَدِّرُ طبيبُ الأسنانِ السِّنَّ بالمُخَدِّرِ الموضعيِّ

Here is the grammar:

• يُخَدِّرُ
  present tense verb, ending in ـُ

• طبيبُ
  subject of the verb, so it is in the nominative

• الأسنانِ
  second term of the iḍāfa (طبيب الأسنان), so it is in the genitive

• السِّنَّ
  direct object, so it is in the accusative

• بالمُخَدِّرِ
  after the preposition بـ, so it is in the genitive

• الموضعيِّ
  adjective describing المخدر, so it matches it in the genitive

These endings are often omitted in normal writing, but they are important for understanding formal grammar.

Arabic usually does not use a separate word meaning of in this kind of structure. Instead, it uses the iḍāfa construction.

So:

• طبيب الأسنان

literally means:

• doctor the-teeth

But grammatically it means:

• doctor of the teeth

This is one of the most important patterns in Arabic.

A few examples:

• باب البيت = the door of the house
• كتاب الطالب = the student’s book / the book of the student
• طبيب الأسنان = the dentist

So the meaning of of is built into the noun combination itself.

This is a very common point of confusion.

In an iḍāfa construction, the first noun usually does not take الـ. The definiteness of the whole phrase is determined by the second noun.

So:

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

Even though طبيب itself does not have الـ, the entire phrase is definite because الأسنان is definite.

This is one of the special rules of iḍāfa phrases.

It is pronounced as-sinn.

That is because س is a sun letter. When الـ comes before a sun letter, the ل sound is not pronounced, and the following consonant is doubled.

So:

• written: السن
• pronounced: as-sinn

Similarly:

• الأسنان is pronounced al-asnān, because it begins with hamza, not a sun letter after الـ
• المخدر is pronounced al-mukhaddir
• الموضعي is pronounced al-mawḍiʿī

So only السن shows that sun-letter assimilation here.

They are singular and plural forms of the same noun.

• سن = tooth
• أسنان = teeth

In the sentence:

• طبيب الأسنان uses the plural teeth as part of the profession name
• السن refers to one specific tooth being numbed

So both appear naturally in the same sentence, but they are doing different jobs.

Yes, depending on context, that can be a natural English translation.

Literally, it means:

• with the local anesthetic
• using the local anesthetic

But in smoother English, you might say:

• The dentist numbs the tooth with a local anesthetic.
• The dentist numbs the tooth under local anesthesia.

The exact English wording depends on whether you want to stay close to the Arabic structure or sound more natural in English.

Because the true subject is طبيب (doctor), not الأسنان (the teeth).

The phrase طبيب الأسنان is one unit meaning the dentist. The head noun is طبيب, which is singular masculine, so the verb is also singular masculine:

• يخدر = he numbs

The word الأسنان is only part of the iḍāfa phrase and does not control the verb agreement here.

A careful fully vowelled version is:

• يُخَدِّرُ طَبيبُ الأَسنانِ السِّنَّ بِالمُخَدِّرِ المَوْضِعِيِّ

A rough pronunciation guide:

• yu-khad-dir-u
• ṭa-bī-bu l-as-nā-ni
• as-sin-na
• bil-mu-khad-di-ri
• al-maw-ḍi-ʿiy-yi

In connected reading, some vowels may sound lighter, but this version shows the formal grammar clearly.