S obzirom na otok, stomatolog pregleda desni.

S obzirom na is a fixed expression meaning considering, given, in view of, or with regard to.

In this sentence, S obzirom na otok means something like Considering the swelling or Given the swelling.

It is best learned as a whole chunk, because the meaning is not very natural if you translate each word separately.

Because the standard expression is s obzirom na.

In Serbian, s and sa are variants of the same preposition, and sa is usually used when pronunciation would otherwise be awkward, especially before certain consonant clusters or words beginning with s, š, z, or ž. Here, s obzirom na is the normal fixed form.

So this is something you should memorize as: s obzirom na + accusative

Because s obzirom na takes the accusative case.

The noun otok is masculine singular and inanimate. For masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• otok = nominative
• otok = accusative

That is why the sentence has na otok.

Not really. In this sentence, you should not interpret na literally as on.

Inside the fixed phrase s obzirom na, the whole expression works like a single unit meaning considering or in view of. So even though na often means on, here the phrase as a whole has a different function.

This is very common in Serbian: prepositions inside fixed expressions do not always match English word-for-word.

Pregleda is the 3rd person singular verb form: he/she examines.

Here it agrees with stomatolog, which is singular:

• stomatolog pregleda = the dentist examines

Also, Serbian present tense does not separate examines and is examining as strictly as English does. Depending on context, pregleda can correspond to either one.

Here desni is the noun meaning gums.

A learner may expect a different ending, but desni is commonly used as a plural noun, and in this sentence its form stays desni.

So:

• pregleda desni = examines the gums

Also, do not confuse this with the adjective desni meaning right in some other contexts. Here it is clearly the noun gums.

Because stomatolog is in the nominative case, and it matches the verb as the doer of the action.

So the structure is:

• stomatolog = subject = the dentist
• pregleda = verb = examines
• desni = object = the gums

Serbian often relies on case and verb agreement more than English does, so you do not always need a fixed word order to identify the subject.

Yes, stomatolog means dentist.

But there is a nuance:

• stomatolog = more formal or medical
• zubar = more everyday, conversational

Both are common and understood. In a textbook or medical-style sentence, stomatolog sounds perfectly natural.

Because S obzirom na otok is an introductory phrase that sets the context for the main clause.

The comma helps mark a pause:

• S obzirom na otok, stomatolog pregleda desni.

This is very natural in writing. In some cases Serbian punctuation can be a little flexible with short introductory phrases, but here the comma is helpful and common.

Yes. Serbian word order is more flexible than English word order.

This version:

• S obzirom na otok, stomatolog pregleda desni.

puts the circumstance first, so it sounds like: Given the swelling, the dentist examines the gums.

You could also move things around, but the emphasis would change. The original order is natural because it introduces the reason or relevant condition first.

Yes, but the nuance changes.

• zbog otoka = because of the swelling
• s obzirom na otok = considering / given the swelling

Zbog sounds more directly causal.
S obzirom na sounds a bit more formal and means that the swelling is something being taken into account.

So both can work, but they are not exactly identical.