Det gør ondt at tygge.

Here det is a dummy subject, like English it in It hurts to chew.

It does not point to a specific thing. Danish often needs a subject in this kind of sentence, so det is used even when there is no concrete noun.

So:

• Det gør ondt = It hurts
• Det gør ondt at tygge = It hurts to chew

Gøre ondt is the normal Danish expression for to hurt.

So Danish says:

• Det gør ondt = It hurts

and not normally det er ondt.

Think of gøre ondt as a fixed expression you should learn as a whole.

More examples:

• Min tand gør ondt. = My tooth hurts.
• Det gør ondt i halsen. = My throat hurts / It hurts in the throat.

Ondt is the form used in the expression gøre ondt.

It is related to the adjective ond, but in this sentence you should mainly understand gør ondt as a set phrase meaning hurts.

So instead of translating word by word, it is better to learn:

• gøre ondt = to hurt

At tygge is the infinitive, meaning to chew.

After expressions like Det gør ondt ..., Danish often uses an infinitive phrase with at:

• Det er svært at forstå. = It is difficult to understand.
• Det er rart at sove. = It is nice to sleep.
• Det gør ondt at tygge. = It hurts to chew.

So at tygge tells you what action causes the pain.

Yes. That is also a very natural sentence.

The difference is:

• Det gør ondt at tygge. = It hurts to chew
  
  • more general
• Det gør ondt, når jeg tygger. = It hurts when I chew
  
  • focuses more on the pain happening at the time you chew

Both are common and correct.

Not completely. Danish pronunciation can be tricky.

A rough guide:

• Det ≈ deh or very reduced d sound in fast speech
• gør has a vowel sound that English does not really have
• ondt often has a soft, compressed sound
• tygge begins with ty-, which also has a vowel not found in normal English

The safest advice is to listen to native audio and repeat the whole sentence as a chunk:

• Det gør ondt at tygge.

Trying to master it word by word from spelling alone is hard in Danish.

The basic structure is:

• Det = subject
• gør = verb
• ondt = part of the expression gør ondt
• at tygge = infinitive phrase

So:

• Det gør ondt at tygge.

Danish main clauses usually put the finite verb in second position, and that is exactly what happens here: gør is the finite verb and comes right after det.

No, not in a normal full sentence.

Danish usually needs the subject, so you say:

• Det gør ondt at tygge.

Leaving out det would sound incomplete.

You would usually mention the body part directly. For example:

• Min tand gør ondt, når jeg tygger. = My tooth hurts when I chew.
• Det gør ondt i tanden at tygge. = It hurts in the tooth to chew.

Both are possible, but the first one is often simpler for learners.

Yes. Tygge means to chew, and it can be used with or without an object.

Examples:

• Jeg tygger. = I am chewing.
• Jeg tygger maden. = I chew the food.

So you could say:

• Det gør ondt at tygge mad. = It hurts to chew food.

It is neutral everyday Danish.

It sounds completely natural in normal conversation, for example at the dentist or doctor:

• Det gør ondt at tygge.
• Det gør ondt, når jeg spiser.

So this is a very useful real-life sentence.