Se o dentinho continuar doendo, a médica vai olhar a boca da bebê amanhã.

Because after se meaning if, Portuguese usually uses the future subjunctive when the condition refers to the future.

So:

• Se o dentinho continuar doendo = if the little tooth keeps hurting

For regular -ar verbs, the future subjunctive looks exactly like the infinitive, so continuar here is not just an infinitive by chance; it is the correct tense.

Compare:

• se continuar = if it continues / if it keeps on
• se for = if it goes / if it is
• se tiver = if it has

Using continua here would not sound right in standard Portuguese for this kind of future condition.

In Brazilian Portuguese, continuar + gerund is very common and natural.

So:

• continuar doendo = keep hurting / continue hurting

You may also see:

• continuar a doer

That is also correct, but it sounds less typically Brazilian and can feel more formal or more European Portuguese in style. In everyday Brazilian speech, continuar doendo is the more expected choice.

Doendo is the gerund of doer, which means to hurt or to ache.

So:

• o dentinho está doendo = the little tooth hurts / is aching
• continuar doendo = keep hurting / continue to ache

Portuguese often uses the painful body part as the subject. So the sentence is not saying the tooth is doing something actively; it is just the normal way to express pain.

Dentinho is the diminutive of dente.

• dente = tooth
• dentinho = little tooth

In Brazilian Portuguese, diminutives like -inho / -inha can mean:

• physically small
• affectionate
• cute
• child-related

Here, dentinho sounds very natural because the sentence is about a baby. It suggests a baby tooth or just uses a tender, affectionate tone.

Portuguese uses definite articles much more often than English.

In this sentence, each noun is specific:

• o dentinho = the specific little tooth
• a médica = the doctor already identified in the situation
• a boca = the baby's mouth
• a bebê = the baby girl

English often leaves articles out where Portuguese keeps them. So even if it feels repetitive to an English speaker, this is normal and natural Portuguese.

Because the doctor is female.

Portuguese marks grammatical gender on many nouns and articles:

• o médico = the male doctor
• a médica = the female doctor

So a médica vai olhar... means the female doctor is going to look/check...

Because ir + infinitive is the most common way to talk about the future in spoken Brazilian Portuguese.

So:

• vai olhar = is going to look / will look

The simple future is also correct:

• olhará

But olhará sounds more formal, written, or less conversational. In everyday Brazilian Portuguese, vai olhar is much more natural.

Da is a contraction of de + a.

So:

• da bebê = of the baby girl

That gives:

• a boca da bebê = the baby's mouth

Why da and not do?

• o bebê = the baby boy / the baby in a masculine reference
• a bebê = the baby girl

Here the baby is female, so it becomes da bebê.

Why not sua boca?

Because sua can be ambiguous in Portuguese. It can mean her, his, your, and sometimes even their depending on context. A boca da bebê is clearer.

In this context, it means check or examine the mouth.

Portuguese olhar can sometimes be broader than English look at. In a medical context, vai olhar a boca sounds natural and means the doctor will inspect it.

A more technical verb like examinar is possible, but it sounds more formal:

• A médica vai examinar a boca da bebê

The original sentence sounds more everyday and conversational.

Yes, it could go somewhere else. Portuguese word order is fairly flexible.

These are all possible:

• A médica vai olhar a boca da bebê amanhã.
• Amanhã, a médica vai olhar a boca da bebê.
• A médica amanhã vai olhar a boca da bebê.
  This one is possible, but less neutral.

Putting amanhã at the end is very natural and common. It gives the sentence a smooth, neutral word order.