A fogszuvasodás komoly.

Because Hungarian often leaves out the verb to be in the present tense when the subject is third person and the predicate is a noun or adjective.

So:

• A fogszuvasodás komoly. = Tooth decay is serious.
• not A fogszuvasodás van komoly.

This is called the zero copula.

You do use van in other situations, for example:

• past tense: A fogszuvasodás komoly volt. = Tooth decay was serious.
• future: A fogszuvasodás komoly lesz. = Tooth decay will be serious.
• location/existence: A fogorvos itt van. = The dentist is here.

Fogszuvasodás means tooth decay or dental caries.

It is a single Hungarian compound word:

• fog = tooth
• szuvas = decayed, cavity-ridden
• -odás / -ás helps form a noun referring to a process or condition

So the whole word refers to the condition/process of teeth becoming decayed.

Hungarian very often packs ideas into one long word like this.

In Hungarian, a general statement about a thing or category often uses the definite article.

So:

• A fogszuvasodás komoly.

can still mean a general idea like Tooth decay is serious.

This is normal Hungarian usage. English often drops the article in general statements, but Hungarian frequently keeps it.

Also, a is the form of the used before a consonant sound. Before a vowel sound, Hungarian uses az.

• a fogszuvasodás
• az alma

Because Hungarian commonly writes compounds as one word.

English often uses separate words:

• tooth decay

Hungarian often combines them:

• fogszuvasodás

This is very typical in Hungarian, especially with established terms and technical vocabulary.

A rough English-friendly pronunciation is:

FOG-soo-vaw-sho-daash

A few useful pronunciation points:

• stress is on the first syllable: FOG
• sz sounds like English s
• plain s sounds like English sh
• á is a long vowel, roughly aa

So the middle and end are important:

• szu = soo
• vaso contains sh because of the Hungarian s
• dás = daash

Komoly means serious.

In this sentence it means that tooth decay is not trivial and should be taken seriously.

Depending on context, komoly can also mean:

• serious
• grave
• important
• not joking

Here the medical sense is clearly serious.

In this sentence, komoly stays in its basic form because the subject is singular: a fogszuvasodás.

Hungarian adjectives do not change for gender, because Hungarian has no grammatical gender.

So there is no masculine/feminine/neuter difference to worry about.

With a plural subject, predicate adjectives often do take a plural ending:

• A problémák komolyak. = The problems are serious.

But in your sentence the subject is singular, so komoly is correct as it is.

Yes. Hungarian word order is flexible, but different orders can change the emphasis.

Neutral statement:

• A fogszuvasodás komoly.

More emphasis on serious:

• Komoly a fogszuvasodás.

Both are possible, but the first one is the most neutral and straightforward for a learner.

Yes, it is natural and correct.

It sounds like a clear, general statement, especially in educational, medical, or warning contexts.

It is a bit broad and formal in tone, similar to saying:

• Tooth decay is serious.

In everyday speech, a Hungarian speaker might also use more specific sentences depending on context, but your sentence is perfectly normal.