Je me demande si cette douleur vient vraiment d’une carie ou seulement de ma mâchoire.

Because demander and se demander mean different things.

• demander = to ask someone for something, or to ask a question
  
  • Je demande au dentiste. = I ask the dentist.
• se demander = to wonder / to ask oneself
  
  • Je me demande... = I wonder...

So in this sentence, je me demande is the natural way to say I wonder.

Here, si means whether / if.

After verbs like se demander, French usually uses si to introduce an indirect yes/no question:

• Je me demande si... = I wonder if / whether...

So:

• Je me demande si cette douleur vient...
  = I wonder whether this pain comes...

This is different from some other uses of si, such as:

• si = if
• si = so (in some contexts, like si grand = so big)

Here, venir de means to come from / to be caused by.

So:

• cette douleur vient d’une carie = this pain comes from a cavity / is caused by a cavity

This is a very common way in French to talk about the source or cause of something.

Be careful: venir de can also mean to have just done something, but only when it is followed by an infinitive verb:

• Je viens de manger. = I have just eaten.

That is not what is happening here, because d’une carie is a noun phrase, not an infinitive.

Because in French, de + une contracts to d’une before a vowel sound.

• de + une carie → d’une carie

This kind of contraction is very normal in French:

• de + le → du
• de + les → des
• before a vowel, de often becomes d’

So d’une carie is just the correct contracted form.

Une carie means a cavity or tooth decay.

In everyday dental context:

• avoir une carie = to have a cavity

So in this sentence, the speaker is wondering whether the pain is really coming from a cavity.

Cette douleur means this pain.

Using cette points to a specific pain the speaker is currently feeling or talking about. It is more specific than la douleur, which would simply mean the pain.

So:

• cette douleur = this particular pain
• la douleur = the pain

In many contexts, either could be grammatically possible, but cette douleur sounds very natural when someone is focusing on a pain they are experiencing right now.

French often uses a definite article for body parts, especially with reflexive verbs:

• Je me lave les mains. = I wash my hands.

But in this sentence, de ma mâchoire emphasizes the source as my jaw specifically. It is not part of a reflexive body-part construction like I wash my hands.

So de ma mâchoire is completely natural here and corresponds well to English from my jaw.

The sentence is:

• vient vraiment d’une carie ou seulement de ma mâchoire

The preposition de is connected to vient: the pain comes from something.

French can repeat the preposition before the second item for clarity, and here it does:

• d’une carie
• de ma mâchoire

That makes the two alternatives clear:

• from a cavity
• or only from my jaw

If de were omitted before ma mâchoire, the sentence would sound incomplete or awkward here.

French adverbs like vraiment often come after the conjugated verb.

So:

• vient vraiment = really comes / really is coming from

This is a very normal position in French.

Similarly:

• Il est vraiment fatigué. = He is really tired.
• Je comprends vraiment. = I really understand.

In this sentence, vraiment emphasizes doubt: is the pain really coming from a cavity?

Seulement means only / just.

Here it limits the second possibility:

• ou seulement de ma mâchoire = or only just from my jaw

The idea is:

• maybe it comes from a cavity,
• or maybe it comes only from the jaw and not from a cavity.

Its position is natural because it directly modifies that second option.

Because the subject is cette douleur, which is singular.

• cette douleur vient = this pain comes

If the subject were plural, the verb would change:

• ces douleurs viennent = these pains come

So vient is just the correct il/elle/on form of venir in the present tense.

Yes, you could say:

• ... d’une carie ou bien seulement de ma mâchoire.

That would still be correct. Ou bien can sound a little more explicit or contrastive, but simple ou is perfectly natural and more common in many cases.

So the original sentence sounds completely normal.

Mâchoire is pronounced approximately ma-shwar.

A few pronunciation points in the sentence:

• Je me demande → the e sounds are weak and reduced in normal speech
• si cette douleur → cette is pronounced roughly set
• vient → sounds like vyan
• d’une → roughly dun
• mâchoire → roughly ma-shwar

One important thing: the circumflex in mâchoire does not usually change modern pronunciation very much here; it mainly reflects spelling/history.

It is natural and perfectly normal French.

It sounds like something someone might say when trying to figure out the source of pain, especially in a medical or dental context.

It is not overly formal, but it is a little more complete and careful than very casual spoken French. In very casual speech, someone might shorten or simplify it, but the original sentence is clear, natural, and standard.