Stomatologul tratează caria.

Because -ul is the definite article for many masculine singular nouns in Romanian. Instead of putting a separate word like the before the noun, Romanian usually attaches the article to the end.

• stomatolog = dentist
• stomatologul = the dentist

This is one of the biggest differences from English.

Romanian normally uses an enclitic definite article, which means the article is attached to the noun itself.

So:

• stomatologul = the dentist
• caria = the cavity / the tooth decay

English says the dentist; Romanian says dentist-the, in effect.

Carie is the indefinite form: a cavity or tooth decay in a general sense.

Caria is the definite singular form: the cavity.

So:

• carie = a cavity
• caria = the cavity

This is the feminine singular definite form of the noun.

Tratează is the 3rd person singular present tense of a trata = to treat.

Here it agrees with stomatologul, which is singular:

• eu tratez = I treat
• tu tratezi = you treat
• el/ea tratează = he/she treats

So Stomatologul tratează caria means The dentist treats the cavity.

Because the most neutral Romanian word order here is Subject + Verb + Object, just like in English:

• Stomatologul = subject
• tratează = verb
• caria = direct object

So the structure is very familiar to an English speaker.

Romanian can change word order more easily than English for emphasis, but this version is the standard, neutral one.

Yes, but the emphasis would change.

For example:

• Stomatologul tratează caria. = neutral statement
• Caria o tratează stomatologul. = stronger focus on the cavity or on who treats it

A beginner should usually learn the basic order first: Subject + Verb + Object.

Because pe is often used with specific animate direct objects, especially people.

For example:

• Văd profesorul. = I see the teacher
• Îl văd pe profesor. = I see the teacher

But caria is not a person or animate being, so pe is not used here.

A rough guide:

• stomatologul ≈ sto-ma-to-LO-gul
• tratează ≈ tra-tea-ZĂ
• caria ≈ ca-RI-a

A few useful sound notes:

• ă is a short central vowel, somewhat like the a in about
• z is pronounced like English z
• c before a is a hard k sound, so caria begins with ka-

It refers to dental decay, often translated as the cavity or the tooth decay depending on context.

So Romanian carie/caria does not always refer only to a visible hole in a tooth. It can also refer more generally to dental decay.

Yes. Stomatolog is a standard Romanian word for dentist.

You may also hear dentist, especially in modern or informal usage, but stomatolog is completely normal and very common.

So stomatologul is a perfectly natural way to say the dentist.

You would make both nouns indefinite:

• Un stomatolog tratează o carie.

Compare:

• Stomatologul tratează caria. = The dentist treats the cavity.
• Un stomatolog tratează o carie. = A dentist treats a cavity.

So Romanian marks definiteness very clearly on nouns.