Dentystka powiedziała, że ta plomba jest już stara i trzeba ją wymienić.

Dentystka is the feminine form of dentysta (dentist).

Because the sentence is about a female dentist, Polish uses the feminine noun:

• dentysta = male dentist / sometimes a general dictionary form
• dentystka = female dentist

This also affects the past tense verb later in the sentence: powiedziała is feminine, matching dentystka.

Powiedziała is the past tense, feminine singular form of powiedzieć (to say / to tell).

It agrees with dentystka, which is feminine singular.

Compare:

• dentystka powiedziała = the female dentist said
• dentysta powiedział = the male dentist said

Also, powiedzieć is a perfective verb, so powiedziała means she said it as a complete act.

Że means that and introduces a subordinate clause.

So:

• Dentystka powiedziała = The dentist said
• że ta plomba jest już stara... = that this filling is already old...

In Polish, że is extremely common after verbs of saying, thinking, knowing, noticing, etc.

Examples:

• Wiem, że... = I know that...
• Myślę, że... = I think that...
• Powiedział, że... = He said that...

Because plomba is a feminine noun, the demonstrative must also be feminine.

Polish this changes by gender:

• ten for masculine
• ta for feminine
• to for neuter

So:

• ten ząb = this tooth
• ta plomba = this filling
• to okno = this window

Since plomba ends in -a, it is feminine, so ta is the correct form.

This is a very common point for English speakers.

In English, after said, we often shift the tense back:

• The dentist said that the filling was old

In Polish, you usually do not have to do that kind of tense backshifting. If the filling is still old at the time being discussed, Polish naturally says:

• powiedziała, że ta plomba jest już stara

Literally: she said that this filling is already old

So jest is completely normal here.

If you used była, it would suggest more strongly that it was old at that time, without necessarily focusing on its current state.

Już usually means already, but in many contexts it can sound more natural in English as now, by now, or just as emphasis.

So:

• jest już stara = is already old / is old by now

Here już suggests that the filling has been in place long enough that it should no longer be kept.

It adds the idea of at this point or by now.

Stary/stara/stare can describe both people and things.

For objects, it simply means old, aged, not new anymore.

So:

• stary samochód = an old car
• stara plomba = an old filling

In this sentence, stara implies the filling is no longer in good condition because of age.

Trzeba is an impersonal word meaning:

• it is necessary
• one has to
• it needs to be done

Polish often uses impersonal constructions where English might use we, you, or the passive.

So:

• trzeba ją wymienić = it’s necessary to replace it / it needs to be replaced

There is no personal subject because trzeba does not refer to a specific person. It just expresses necessity in a general way.

Compare:

• Musimy ją wymienić = We have to replace it
• Trzeba ją wymienić = It has to be replaced / One has to replace it

Ją is the accusative form of ona (she/it), and here it means it, referring to plomba.

Because plomba is feminine, the pronoun must also be feminine.

So:

• plomba = filling
• ją = it (feminine object)

Why accusative? Because wymienić takes a direct object:

• wymienić plombę = to replace a filling

Instead of repeating plombę, Polish uses the pronoun:

• trzeba ją wymienić = it needs to be replaced

This is about aspect.

• wymienić = perfective = to replace something completely, as a finished action
• wymieniać = imperfective = to be replacing / to replace in a repeated or ongoing sense

Here the dentist means one complete action: the filling should be taken out and replaced. So the perfective infinitive wymienić is the natural choice.

Compare:

• Trzeba ją wymienić. = It needs to be replaced.
• Trzeba ją wymieniać co kilka lat. = It needs to be replaced every few years.

Polish object pronouns like go, ją, je, mi, ci often come before the infinitive or other verb element in neutral word order.

So:

• trzeba ją wymienić is the most natural order

You may sometimes hear different word orders for emphasis, but ją before wymienić is the standard, unmarked pattern here.

Plomba is in the nominative case because it is the subject of jest.

In the clause:

• ta plomba jest już stara

the filling is the thing being described, so nominative is used:

• ta plomba = this filling

Later, when it becomes the object of wymienić, it would be accusative:

• wymienić plombę = to replace the filling

That is why the noun would change if you said it directly instead of using ją.

Yes. That is a very literal breakdown of the Polish structure:

• Dentystka = the female dentist
• powiedziała = said
• że = that
• ta plomba = this filling
• jest już stara = is already old
• i trzeba ją wymienić = and it is necessary to replace it

But in natural English, you would usually say something smoother, such as:

• The dentist said that this filling is old and needs to be replaced.
• The dentist said that this filling is already old and should be replaced.

So the Polish structure is a little more explicit than the most natural English version.