Åh, tandbylden bliver større.

Åh is an interjection, like English Oh.

In this sentence, it adds an emotional reaction, probably worry, pain, or frustration. It is not part of the main grammar of the clause; it just sets the tone.

The comma after Åh is normal, because the interjection is separated from the rest of the sentence.

Because Danish very often forms compound nouns as a single word.

Here you have:

• tand = tooth
• byld = abscess, boil

So tandbyld means tooth abscess or dental abscess as one compound noun.

Then the definite ending is added to the whole compound:

• en tandbyld = a tooth abscess
• tandbylden = the tooth abscess

-en is the usual definite ending for a common-gender noun in Danish. It corresponds to English the.

So:

• en tandbyld = a tooth abscess
• tandbylden = the tooth abscess

This shows that tandbyld is a common-gender noun, not a neuter noun.

In Danish, the definite article is usually attached to the end of the noun instead of appearing as a separate word.

So English:

• the abscess

becomes Danish:

• bylden

and not normally den byld.

A separate definite word such as den is mainly used when there is an adjective or some other modifier before the noun:

• den store tandbyld = the big tooth abscess

But in your sentence, there is no adjective directly before the noun, so the attached ending is the normal choice:

• tandbylden

Here bliver means is becoming or is getting.

It is the present tense of blive, which often means to become.

So:

• tandbylden bliver større = the abscess is getting bigger

This is different from er, which would simply mean is.

Also, blive can have other uses in Danish, such as in passive constructions, but in this sentence it clearly means become/get.

Because bliver større emphasizes change over time.

• bliver større = is getting bigger, is becoming bigger
• er større = is bigger

So bliver større suggests that the size is increasing.

If you said tandbylden er større, that would usually sound more like a comparison or a description of its current state, not necessarily a change happening now.

Because Danish normally uses a comparative form of the adjective, just as English uses bigger rather than more big.

The adjective stor has the comparative:

• stor = big
• større = bigger
• størst = biggest

This is an irregular pattern, so you simply have to learn it.

So:

• bliver større = gets bigger

not bliver mere stor.

Ignoring the interjection Åh, the clause is:

• tandbylden = subject
• bliver = verb
• større = predicative adjective

So the basic structure is:

subject + verb + complement

That is very natural Danish word order for a main clause.

The Åh at the beginning does not change the clause structure; it sits outside it as an emotional comment.

A rough guide:

• Åh has a vowel somewhat like aw in saw for many English speakers.
• The y in byld does not sound like English y. It is closer to French u or German ü.

So the tricky part for English speakers is usually y, because English does not really have that exact vowel.

Also, the ending -en is usually unstressed.

As always with Danish pronunciation, it is best to listen to native audio, because spelling often does not tell the whole story.