Zub je oštećen.

• zub = tooth
• je = is (3rd person singular present of biti, to be)
• oštećen = damaged

So grammatically, zub is the subject, je is the verb, and oštećen describes the state of the tooth.

Because zub is the subject of the sentence, it appears in the nominative singular.

• zub = nominative singular, tooth
• zuba can be genitive singular or accusative plural in other contexts

In Zub je oštećen, the sentence is simply stating something about the tooth, so nominative is the correct case.

Je is the present-tense form of biti (to be) for he/she/it is.

Serbian often forms sentences like this the same way English does:

• Zub je oštećen = The tooth is damaged

Without je, the sentence would sound incomplete in standard Serbian.

Oštećen is the past passive participle of the verb oštetiti (to damage), but in sentences like this it often functions very much like an adjective.

So it can mean:

• damaged
• has been damaged
• a resulting state: is damaged

In this sentence, it describes the condition of the tooth.

The form oštećen agrees with zub, which is:

• masculine
• singular
• nominative

So the masculine singular form is oštećen.

Compare:

• Zub je oštećen = masculine singular
• Plomba je oštećena = feminine singular
• Tkivo je oštećeno = neuter singular
• Zubi su oštećeni = masculine plural

Agreement is very important in Serbian.

It can be understood as both, depending on how you look at it.

Grammatically, oštećen comes from a verb, so it has a passive origin:

• oštetiti = to damage
• oštećen = damaged

But in everyday usage, Zub je oštećen is often simply understood as describing a state:

• The tooth is damaged

So for a learner, it is useful to think of it as be + damaged, while remembering that the Serbian form comes from a participle.

Yes. Serbian word order is more flexible than English.

You can say:

• Zub je oštećen — neutral
• Oštećen je zub — puts more focus on damaged
• Je li zub oštećen? — in a question

The most neutral basic version is Zub je oštećen.

Serbian has no articles, so there is no direct equivalent of the or a/an.

That means:

• zub can mean a tooth or the tooth

The exact meaning depends on context. In translation, English usually needs an article, but Serbian does not.

A rough pronunciation guide is:

• o as in off (short and clear)
• š like sh in shoe
• t
• e
• ć is a soft sound, somewhat like a very soft ch or ty
• e
• n

Very roughly: osh-TEH-chen, but with a softer ć than English ch.

Also:

• j in je is pronounced like English y
• so je sounds roughly like ye

It comes from oštetiti, which means to damage.

Useful related forms:

• oštetiti = to damage
• oštetio je zub = he damaged the tooth
• zub je oštećen = the tooth is damaged / has been damaged

You may also encounter the imperfective partner oštećivati, meaning to be damaging or to damage repeatedly/over time, but the sentence here uses the result form from oštetiti.

Yes, in many contexts it can.

Zub je oštećen often focuses on the current result:

• The tooth is damaged

But depending on context, English might also translate it as:

• The tooth has been damaged

So the Serbian sentence can express a present state that resulted from damage.

You make it negative by changing je to nije:

• Zub nije oštećen. = The tooth is not damaged.

This is the normal way to negate this kind of sentence.

A few common ways are:

• Da li je zub oštećen? = Is the tooth damaged?
• Je li zub oštećen? = Is the tooth damaged?

Both are common.
Da li je... is very clear and standard for learners.

Usually no, or at least not as the best choice here.

• oštećen = damaged
• pokvaren = broken / spoiled / not working

For a tooth, oštećen is the natural word if you mean physical damage.
For example, a chipped, cracked, or otherwise damaged tooth would be oštećen zub.

A tooth can also be described in other ways depending on the problem, such as:

• pokvaren zub = a decayed/bad tooth
• slomljen zub = a broken tooth

So oštećen is specifically a good general word for damaged.