Når en tand gør ondt, bestiller jeg tid hos tandlægen med det samme.

Når usually means when, and in sentences like this it often has the sense of whenever.

So Når en tand gør ondt means something like When a tooth hurts or Whenever I have a toothache in a tooth.

A learner might wonder whether if would also work. Danish often uses:

• når for something expected, repeated, or seen as a normal situation
• hvis for a more uncertain if

Here, the sentence sounds like a general habit: whenever this happens, I book an appointment.

En tand means a tooth. Danish often uses an indefinite noun for a general situation, where English might also say a tooth or sometimes my tooth, depending on context.

So Når en tand gør ondt is a general statement, not necessarily about one specific tooth. It is like saying:

• When a tooth hurts...
• When I get tooth pain...

If you said min tand, it would sound more specifically like my tooth.

Gør ondt is the standard Danish expression for hurts or is painful.

Literally, it is:

• gør = does / makes
• ondt = painfully / bad

So the phrase is idiomatic. You should learn gøre ondt as a set expression meaning:

• to hurt
• to be painful

Examples:

• Det gør ondt. = It hurts.
• Min arm gør ondt. = My arm hurts.

English uses a single verb, but Danish normally uses this fixed phrase instead.

This is because Danish is a V2 language in main clauses. That means the finite verb usually comes in the second position.

The sentence begins with the subordinate clause:

• Når en tand gør ondt

After that, the main clause comes, and the verb must come before the subject:

• bestiller jeg tid hos tandlægen med det samme

So the order is:

1. subordinate clause
2. finite verb
3. subject

That is why it is bestiller jeg, not jeg bestiller.

Compare:

• Jeg bestiller tid hos tandlægen med det samme.
• Når en tand gør ondt, bestiller jeg tid hos tandlægen med det samme.

Both are correct; the word order changes because of what comes first.

Yes, literally it looks like order time, but idiomatically bestille tid means:

• to make an appointment
• to book an appointment

This is a very common Danish expression.

Examples:

• Jeg skal bestille tid hos lægen. = I need to make an appointment with the doctor.
• Hun bestilte tid til fredag. = She booked an appointment for Friday.

So you should understand bestille tid as a fixed phrase, not word by word.

Hos is often used when talking about being at or going to a professional person, especially for services or treatment.

So:

• hos tandlægen = at the dentist’s / with the dentist

Common examples:

• hos lægen = at the doctor’s
• hos frisøren = at the hairdresser’s
• hos tandlægen = at the dentist’s

For an English speaker, hos is worth learning as a special preposition often used with people in professional roles.

Tandlægen means the dentist. Danish often uses the definite form in expressions like this, especially when referring to the usual type of professional service.

So hos tandlægen means at the dentist’s in a general sense, not necessarily one previously mentioned dentist.

This is very natural in Danish. English does something similar when we say:

• I’m going to the dentist
• She’s at the doctor’s

So even though no specific dentist has been introduced earlier, the definite form is still normal.

Med det samme means:

• immediately
• right away
• at once

It is a common expression and should be learned as a chunk.

In this sentence, it shows that the speaker books the appointment without delay.

Examples:

• Kom med det samme! = Come immediately!
• Jeg gjorde det med det samme. = I did it right away.

It most naturally sounds like a habitual or general statement.

Because of Når, the sentence suggests:

• Whenever a tooth hurts, I book an appointment with the dentist right away.

If you wanted to talk about one specific future event, the context would matter more. But on its own, this sentence sounds like a general rule or personal habit.

Not in the same way.

• En tand gør ondt = A tooth hurts
• Jeg har ondt i en tand = I have pain in a tooth / My tooth hurts

So both are possible ideas in Danish, but the structure changes:

• the tooth can be the thing that hurts: Tanden gør ondt
• the person can be the one experiencing pain: Jeg har ondt i tanden

Your sentence uses the first pattern, where the tooth is the subject.

The comma separates the subordinate clause from the main clause.

• Når en tand gør ondt = subordinate clause
• bestiller jeg tid hos tandlægen med det samme = main clause

In standard Danish writing, this comma is normally used there. It helps show where the introductory clause ends and where the main clause begins.