La dentisto metis kronon sur la muelodonton.

Because -is marks the past tense in Esperanto.

• meti = to put, to place
• metas = puts / is putting
• metis = put / placed

So La dentisto metis... means The dentist put/placed...

The -n shows the direct object: the thing directly affected by the action.

In this sentence, the dentist is putting a crown, so kronon is the object of metis.

Compare:

• La dentisto metis kronon. = The dentist put a crown.
• Krono falis. = A crown fell.
  Here krono is the subject, so there is no -n.

This is a very common question. In Esperanto, a noun after a preposition normally does not take -n, but it can take -n when there is movement toward a place.

So:

• sur la muelodonto = on the molar, located there
• sur la muelodonton = onto the molar, toward that surface

In La dentisto metis kronon sur la muelodonton, the crown is being moved onto the tooth, so -n is used.

A useful contrast:

• La krono estas sur la muelodonto. = The crown is on the molar.
  (location only)
• La dentisto metis la kronon sur la muelodonton. = The dentist put the crown onto the molar.
  (movement toward that place)

La is the definite article, meaning the.

It is used before both nouns because both are definite in the sentence:

• la dentisto = the dentist
• la muelodonto = the molar

Esperanto uses la for all genders and numbers. There is only one definite article.

Dentisto means dentist. It is built from:

• dent- = tooth
• -ist- = a person professionally involved with something
• -o = noun ending

So dentisto literally means something like tooth-professional.

This -ist- ending is very common:

• pianisto = pianist
• artisto = artist
• kuracisto = doctor

It is a compound word.

• muel- = grind
• dento = tooth

So muelodonto is literally a grinding tooth, that is, a molar.

Esperanto often builds vocabulary this way, by combining meaningful parts. That is one reason many learners find it easy to understand new words.

Yes. Krono normally means crown, and context tells you which kind.

In this sentence, because we are talking about a dentist and a tooth, krono clearly means a dental crown.

Esperanto often lets context do this kind of work, just as English does with words like crown.

Yes. Sur means on, upon, or onto, depending on context.

In this sentence, because there is placement onto a surface, sur is very natural:

• sur la muelodonton = onto the molar

If there were no idea of movement, it would simply mean on the molar.

The basic order is subject – verb – object, just like normal English:

• La dentisto = subject
• metis = verb
• kronon = direct object
• sur la muelodonton = prepositional phrase

So the structure is:

The dentist / put / a crown / onto the molar

Esperanto word order is fairly flexible, but this is the most straightforward and neutral version.

Yes, Esperanto allows more flexibility than English because the endings show grammatical roles.

For example, you could say:

• La dentisto metis kronon sur la muelodonton.
• Kronon la dentisto metis sur la muelodonton.

Both are understandable because kronon has -n, so you still know it is the object.

However, the original version is the most neutral and natural for a learner to use.

Esperanto has no indefinite article. So kronon can mean a crown or just crown, depending on context.

That means:

• la krono = the crown
• krono = a crown / crown

In this sentence, English naturally uses a crown, but Esperanto just says kronon.

This sentence shows some of the most important Esperanto endings:

• -o = noun
  
  • dentisto
  • krono
  • muelodonto
• -n = accusative / direction
  
  • kronon
  • muelodonton
• -is = past tense verb
  
  • metis

These endings are a big part of how Esperanto grammar works.

Not always, but it would mean something slightly different.

• sur la muelodonto focuses on location: on the molar
• sur la muelodonton focuses on movement toward that place: onto the molar

With metis (put/placed), many speakers prefer sur la muelodonton because the action places the crown onto the tooth.

So sur la muelodonto is not necessarily impossible, but sur la muelodonton expresses the idea more precisely.