Krunica je na zubu.

Because na here expresses a location, so the noun after it goes into the locative case.

• zub = tooth
• na zubu = on the tooth

A very useful rule is:

• na + accusative = movement onto something
• na + locative = being on something

Compare:

• Stavljam krunicu na zub. = I am putting the crown onto the tooth.
• Krunica je na zubu. = The crown is on the tooth.

So in your sentence, nothing is moving; it is simply located there.

In this sentence, zubu is in the locative singular.

The base form is:

• zub = tooth

With the preposition na meaning on, when it describes location, Serbian uses the locative:

• na zubu = on the tooth

You may also learn that zubu can look the same as the dative singular form. That is normal in Serbian: many nouns have the same form for dative and locative. Here, though, the function is locative, because it follows na in a location meaning.

Serbian does not have articles like English a and the.

So:

• Krunica je na zubu.

can mean something like:

• The crown is on the tooth
• A crown is on the tooth

Which one sounds best depends on context.

Serbian usually shows definiteness through context, word order, or by adding other words if needed. English speakers often look for the, but Serbian simply does not require it.

Je is the 3rd person singular present form of the verb biti = to be.

So:

• krunica = crown
• je = is
• na zubu = on the tooth

Together:

• Krunica je na zubu. = The crown is on the tooth.

This is completely parallel to English is, although Serbian often allows different word orders around it.

Yes. Krunica is a feminine noun, and the ending -a is a strong clue.

Its basic form is nominative singular:

• krunica

Many Serbian feminine nouns end in -a, although not all nouns ending in -a behave identically. In this sentence, krunica is the subject, so it stays in the nominative.

Yes. Krunica is related to kruna (crown) and often has a diminutive feel historically or structurally.

Depending on context, krunica can mean different things, such as:

• a small crown
• a dental crown
• in some contexts, even a rosary

In your sentence, the medical/dental meaning is clearly intended.

This is useful to know because Serbian learners often notice that one word can have several related meanings depending on context.

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

The neutral version is:

• Krunica je na zubu.

But you could also hear:

• Na zubu je krunica.

Both are grammatical. The difference is mainly in focus or emphasis:

• Krunica je na zubu. → focuses more naturally on krunica as the topic
• Na zubu je krunica. → puts more attention on where it is

English is much stricter, but Serbian often moves elements around for emphasis.

Because na often means on, at, or onto, depending on context.

Here it means:

• on the tooth

That fits the idea that the crown is attached to/on the tooth.

For English speakers, choosing between Serbian prepositions can be tricky because they do not always match English one-to-one. In this sentence, na is the normal choice for something positioned on a surface or attached to it.

A simple approximate pronunciation for an English speaker is:

• KROO-nee-tsa yeh na ZOO-boo

A few details:

• kr at the start of krunica is pronounced together, without a vowel in between
• c in Serbian is pronounced like ts
• j is pronounced like English y
• zubu has two clear u vowels, like oo

So:

• Krunica ≈ KROO-nee-tsa
• je ≈ yeh
• na ≈ nah
• zubu ≈ ZOO-boo

Yes, it is natural and correct, especially in a dental or medical context.

It is a short, straightforward descriptive sentence:

• subject: Krunica
• verb: je
• location: na zubu

In real conversation, a speaker might also say longer versions depending on context, for example:

• Krunica je stavljena na zub. = The crown has been placed on the tooth.
• Ima krunicu na zubu. = He/She has a crown on the tooth.

But your original sentence is perfectly natural as a simple statement.

No. Here zubu is clearly singular.

The singular dictionary form is:

• zub = tooth

In this sentence:

• na zubu = on the tooth

If you wanted on the teeth, you would need a plural form, not zubu.

So an English speaker should read this sentence as referring to one tooth, not several.