Die vulsel en tandkroon is oud.

In Afrikaans, one die can introduce two nouns joined by en when both are definite and are being treated as one combined phrase.

So:

• Die vulsel en tandkroon = the filling and crown

You could also say:

• Die vulsel en die tandkroon

That is also grammatical, but repeating die is often unnecessary unless you want extra clarity or emphasis.

Because Afrikaans verbs do not change form the way English verbs do.

In English, you say:

• the filling is old
• the filling and crown are old

But in Afrikaans, is stays is:

• Die vulsel is oud
• Die vulsel en tandkroon is oud

So is works for both singular and plural subjects in this kind of sentence.

Vulsel means filling, especially in a dental context here.

It can also mean a filling or stuffing in other contexts, but in this sentence, because of tandkroon, the meaning is clearly dental.

Tandkroon means dental crown or tooth crown.

It is a compound noun:

• tand = tooth
• kroon = crown

Afrikaans, like Dutch and German, often writes compound nouns as one word. So tandkroon is normal and correct.

This is the normal word order for a simple statement in Afrikaans:

• Subject + verb + adjective/complement

So:

• Die vulsel en tandkroon = subject
• is = verb
• oud = complement

That is why oud comes last here.

Because oud is being used after the verb is. In that position, Afrikaans adjectives usually stay in their basic form.

So:

• Die tandkroon is oud. = The crown is old.

When an adjective comes before a noun, the form may change:

• 'n ou tandkroon = an old crown

So this sentence uses oud because it is a predicate adjective, not an adjective directly before a noun.

Yes, absolutely.

Both are possible:

• Die vulsel en tandkroon is oud
• Die vulsel en die tandkroon is oud

The version with one die sounds a bit more compact. The version with two die can sound a little more explicit, as if you are clearly identifying both items separately.

It normally means one filling and one crown.

Both nouns are singular:

• vulsel = filling
• tandkroon = crown

Together they form a coordinated subject, but each item is singular on its own.

If you wanted plurals, the sentence would need different noun forms.

Yes, very much so.

En simply means and and joins words or phrases together:

• vulsel en tandkroon = filling and crown

It works very similarly to English and.

Yes. It is a natural, straightforward Afrikaans sentence.

It is a simple descriptive statement:

• Die vulsel en tandkroon is oud.

A speaker would understand that both the filling and the crown are old.

Oud is pronounced roughly like the ow sound in now, but with a final t/d-type ending that is softer than in English.

A rough English-friendly guide is:

• oud ≈ owt/owd

The exact sound depends on accent, but the main thing is that ou in Afrikaans is usually a diphthong similar to the vowel in now.

Not if you mean The filling and crown are old.

• Die vulsel en tandkroon is oud means they are old.
• Die ou vulsel en tandkroon would mean something more like the old filling and crown, where old is directly describing the noun phrase.

So the original sentence is making a statement about them. Your alternative would just be a noun phrase, not a complete sentence.