Zubař říká, že když mě bude zub bolet i zítra, mám přijít ráno.

Czech often expresses physical sensations differently from English.

With bolet (to hurt / to ache), the person who feels the pain is usually in the accusative:

• Mě bolí zub. = My tooth hurts.
• literally closer to A tooth hurts me.

So in mě bude zub bolet:

• mě = me (the person affected)
• zub = the thing that hurts
• bude bolet = future of hurts / will hurt

English makes my tooth the subject, but Czech often keeps this pattern where the pain affects me.

Putting mě early in the clause is also very natural, because short unstressed pronouns often come near the beginning.

Mě here is accusative.

That is because bolet takes the affected person in the accusative:

• Bolí mě hlava. = My head hurts.
• Bolí ho ruka. = His arm hurts.

Mi is usually dative, and it would not be correct with bolet in this sentence.

So:

• mě = accusative = correct here
• mi = dative = not used with bolet

Yes, bolet is imperfective, and that is exactly why the future is formed with být:

• bude bolet = will hurt

In Czech, imperfective verbs usually make the future with být + infinitive:

• budu dělat = I will do / I will be doing
• bude pršet = it will rain
• bude bolet = it will hurt

There is no separate simple future form for most imperfective verbs.

Because zub is the grammatical subject of bolet.

In the structure:

• mě bude zub bolet

the thing that hurts is zub, so it stays in the nominative.

A useful pattern is:

• Bolí mě zub.
• Bolí mě záda.
• Bolí ho noha.

Even though English says my tooth hurts, Czech does not need a possessive every time. The subject is just tooth, head, leg, etc., while the affected person is shown separately with mě, ho, ji, and so on.

Because it is usually unnecessary.

If you say:

• Bolí mě zub

it is already clear that it is your tooth, because mě tells us who is affected.

Czech often avoids possessives where the meaning is obvious, especially with body parts:

• Bolí mě hlava. = My head hurts.
• Zlomil si ruku. = He broke his arm.

You could say můj zub, but in a normal sentence like this it would sound less natural unless you want special emphasis.

Because they do different jobs.

• že introduces what the dentist says: that
• když introduces the condition/time clause: if / when

So the structure is:

• Zubař říká, že ... = The dentist says that ...
• inside that clause: když mě bude zub bolet i zítra ... = if my tooth still hurts tomorrow ...

So:

• že = starts reported content
• když = starts the subordinate clause inside that content

In English we often also use both:

• The dentist says that if ...

Here it is best understood as if.

Czech když can mean:

• when
• if, especially in everyday speech for real or likely conditions

In this sentence, the meaning is conditional:

• if my tooth still hurts tomorrow

A more explicitly conditional option would be jestli, but když is very common and natural here.

So the idea is not really whenever tomorrow comes, but in the event that it still hurts tomorrow.

Here i is best understood as also / still / even depending on how you translate naturally.

The phrase:

• i zítra

adds the idea that the pain continues into tomorrow too.

So in natural English:

• if my tooth still hurts tomorrow

That is usually the best translation in context, even though Czech literally uses i.

You will see i used in several related ways:

• i dnes = today too / even today
• i já = me too / even I
• i kdyby... = even if...

So here it contributes the sense of continued pain tomorrow as well.

Literally, mám přijít is built from mít + infinitive:

• mám přijít = I am to come / I should come / I’m supposed to come

In this sentence it expresses an instruction or recommendation from the dentist.

It is softer and more matter-of-fact than musím přijít:

• mám přijít = I should come / I’m supposed to come
• musím přijít = I must come

So the dentist is giving directions:

• If it still hurts tomorrow, come in the morning.

Czech often uses mám + infinitive for something one is expected or instructed to do.

Because the sentence refers to a single completed action: coming / arriving once.

• přijít = perfective = to come, to arrive as one completed event
• přicházet = imperfective = repeated or ongoing coming

Here the dentist means one specific visit:

• mám přijít ráno = I should come in the morning

That is why přijít is the natural choice.

Because ráno can function adverbially by itself, meaning in the morning.

So:

• přijít ráno = to come in the morning

This is very common with time expressions in Czech:

• dnes = today
• zítra = tomorrow
• večer = in the evening
• ráno = in the morning

You can also find prepositional phrases in Czech for time, but here the simple adverbial form is the most natural one.

Because Czech word order is flexible, but not random.

The version in your sentence is natural because:

• short pronouns like mě tend to come early
• the clause flows from the affected person to the thing causing pain
• the most neutral, everyday phrasing often puts the clitic pronoun near the start

So:

• když mě bude zub bolet sounds normal and smooth

Other orders may be possible, but they often sound marked, emphatic, or less natural:

• když zub bude bolet mě would strongly emphasize me
• když bude mě bolet zub is possible, but less standard-sounding than the given version

For learners, it is safest to remember the very common pattern:

• mě bolí zub
• mě bude zub bolet

Because říká is present tense: says / is saying.

So the sentence presents the dentist’s statement as current:

• Zubař říká... = The dentist says...

If you used řekl, it would mean:

• The dentist said...

Both are possible in different contexts, but they describe different time frames.

Yes. It behaves a bit differently from verbs that match English directly.

With bolet:

• the thing that hurts is the grammatical subject
• the person feeling pain is in the accusative

Compare:

• Zub bolí. = The tooth hurts.
• Mě bolí zub. = My tooth hurts.
• Bude mě bolet zub. = My tooth will hurt.

This is why the Czech sentence may feel inside-out to an English speaker. But it is a very common and important pattern, especially with body parts and pain.

Yes, jestli is possible:

• Zubař říká, že jestli mě bude zub bolet i zítra, mám přijít ráno.

That would also mean if my tooth still hurts tomorrow.

The difference is mostly one of style and feel:

• jestli is a straightforward if / whether
• když is also very common in spoken Czech for real conditions

In everyday Czech, the original sentence with když sounds natural.