Po večeři si moje dcera čistí zuby kartáčkem.

Because the preposition po means after here, and in this meaning it requires the locative case.

• dictionary form: večeře = dinner
• locative singular: večeři

So:

• po večeři = after dinner

This is a very common pattern:

• po škole = after school
• po práci = after work
• po obědě = after lunch

Si is a reflexive pronoun, here in the dative. In sentences about personal care, Czech often uses this structure where English does not.

So čistit si zuby literally looks like:

• to clean oneself teeth

But in natural English it simply means:

• to brush one’s teeth

The si shows that the action is done for/to oneself. It often appears with everyday routines:

• myju si ruce = I wash my hands
• češu si vlasy = I comb my hair
• čistím si zuby = I brush my teeth

Without si, the sentence would sound incomplete or unnatural in this everyday meaning.

Because čistit si zuby is the normal Czech expression for to brush one’s teeth.

Czech often marks body-part actions with a reflexive pronoun:

• myje si vlasy = he washes his hair
• stříhá si nehty = she cuts her nails
• čistí si zuby = she brushes her teeth

If you say čistí zuby without si, it can sound like she is cleaning teeth in a more general sense, not necessarily her own as part of a routine.

Čistí is the 3rd person singular present tense of the verb čistit.

• infinitive: čistit = to clean / to brush
• já čistím = I clean
• ty čistíš = you clean
• on/ona čistí = he/she cleans

Because the subject is moje dcera (my daughter), we use čistí:

• moje dcera čistí = my daughter cleans / brushes

In this sentence, natural English is brushes.

Zuby is the accusative plural of zub (tooth).

• singular: zub = tooth
• plural: zuby = teeth

After the verb čistit, the thing being cleaned goes in the accusative. Since people normally brush more than one tooth, Czech uses the plural:

• čistí si zuby = brushes her teeth

This works similarly to English, where we also normally say teeth, not tooth.

Kartáčkem is the instrumental singular of kartáček (small brush / toothbrush).

The instrumental case is often used to show the tool or means used to do something:

• píšu perem = I write with a pen
• jím vidličkou = I eat with a fork
• čistí si zuby kartáčkem = she brushes her teeth with a toothbrush

So:

• dictionary form: kartáček
• instrumental singular: kartáčkem

Because Czech can express the instrument without a preposition by using the instrumental case alone.

So both the idea and the grammar are:

• kartáčkem = with a toothbrush

You often do not need s when the instrumental simply shows the tool used to perform an action.

Using s kartáčkem here would not be the normal choice for this meaning.

In this sentence, yes, that is the natural meaning from context.

Literally, kartáček means small brush, but when you are talking about cleaning teeth, it is naturally understood as a toothbrush.

If you wanted to be extra explicit, you could say:

• zubním kartáčkem = with a toothbrush

But in everyday speech, kartáčkem is usually enough when the context is clear.

Both are correct.

• moje dcera
• má dcera

Both mean my daughter.

In many situations, moje sounds a bit fuller or more neutral in ordinary speech, while má can sound a little shorter, sometimes slightly more literary or emphatic depending on context. But the difference is not huge, and both are common.

So this sentence could also be:

• Po večeři si má dcera čistí zuby kartáčkem.

Same basic meaning.

Because Czech has no articles.

English says:

• my daughter
• the teeth
• a toothbrush

Czech simply uses the noun without a/an/the:

• dcera
• zuby
• kartáček / kartáčkem

Whether something is definite or indefinite is usually understood from context.

No, Czech word order is relatively flexible.

The sentence:

• Po večeři si moje dcera čistí zuby kartáčkem.

is natural, but other orders are also possible, for example:

• Moje dcera si po večeři čistí zuby kartáčkem.
• Moje dcera si čistí zuby kartáčkem po večeři.

The basic meaning stays the same, but the emphasis can change.

The original version puts Po večeři first, which nicely sets the time frame: After dinner, ...

Yes, if the context already makes it clear whose daughter you mean.

• dcera = daughter
• moje dcera = my daughter

Czech often leaves out information that is already understood from context. So if you have already been talking about your daughter, dcera alone may be enough.

But if you are introducing her or want to be clear, moje dcera is natural.

Not exactly.

• čistit si zuby = brush one’s own teeth
• čistit zuby = clean teeth, more general, possibly someone else’s or teeth in a broader sense

For a normal daily routine, čistit si zuby is the standard expression.

So when talking about what a person does every evening or morning, you usually want si.

Večeři is approximately pronounced VE-che-rzhi, with stress on the first syllable, because Czech almost always stresses the first syllable.

The difficult sound is ř, which is a special Czech sound. English does not really have an exact equivalent. It sounds somewhat like a mix of r and zh.

So:

• ve- as in veh
• -če- like che
• -ři roughly rzhi

You do not need perfect ř immediately; it takes practice even for many learners at higher levels.

Because the Czech present tense is used both for:

• what is happening now, and
• habitual actions

So:

• Po večeři si moje dcera čistí zuby kartáčkem.

can mean something like:

• After dinner, my daughter brushes her teeth with a toothbrush.
• My daughter brushes her teeth after dinner.

If the context is a general routine, Czech simply uses the present tense.