La dentiste regarde ma gencive et dit que ma mâchoire est un peu tendue.

Dentiste can refer to a male or female dentist. Here, la shows that the dentist is female.

In French, many job titles can change gender through the article, even if the noun itself stays the same:

• le dentiste = the male dentist
• la dentiste = the female dentist

Some speakers may also use other forms depending on region or style, but la dentiste is completely normal.

Because the subject is la dentiste, which is she / the dentist, so the verb must be in the third-person singular form.

The verb is regarder = to look at.

Present tense:

• je regarde
• tu regardes
• il / elle regarde

So:

• La dentiste regarde... = The dentist looks at...

French verbs change form depending on the subject, just like I look, you look, she looks in English.

Gencive means gum (the tissue around the teeth).

So:

• ma gencive = my gum

It is a feminine noun, which is why it uses ma:

• la gencive
• ma gencive

Even though English often says my gums, French can use the singular if it is talking about one specific gum area.

French often uses the definite article with body parts, but especially in structures with a reflexive verb, such as:

• Je me lave les mains. = I wash my hands.

In your sentence, there is no reflexive structure. The dentist is talking about your gum and your jaw, so using the possessive ma is very natural:

• ma gencive
• ma mâchoire

So this is not a special body-part construction like je me brosse les dents. It is just ordinary possession.

Here, que means that.

• dit que... = says that...

So:

• La dentiste ... dit que ma mâchoire est un peu tendue.
• The dentist ... says that my jaw is a little tense.

In English, that is often optional:

• She says that my jaw is tense.
• She says my jaw is tense.

In French, que is normally required here.

Because mâchoire is a feminine singular noun, and the adjective must agree with it.

• mâchoire = feminine singular
• tendu = masculine singular form
• tendue = feminine singular form

So:

• un muscle tendu = a tense muscle
• une mâchoire tendue = a tense jaw

This is standard French adjective agreement.

Because mâchoire is feminine.

French possessive adjectives agree with the noun possessed, not with the owner:

• mon = my + masculine singular noun
• ma = my + feminine singular noun
• mes = my + plural noun

So:

• mon bras = my arm
• ma mâchoire = my jaw
• mes dents = my teeth

One small note: before a feminine noun beginning with a vowel sound, French often uses mon for pronunciation reasons, as in mon amie. But mâchoire begins with a consonant sound, so it stays ma mâchoire.

Un peu means a little or somewhat.

So:

• un peu tendue = a little tense

It softens the statement. It sounds less strong than just saying:

• ma mâchoire est tendue = my jaw is tense

This is very common in French when someone wants to sound less blunt or more measured.

Here it means physically tense or tight.

When talking about a jaw, muscles, shoulders, or similar body parts, tendu / tendue usually means there is physical tension.

So in this sentence:

• ma mâchoire est un peu tendue = my jaw is a little tight / tense

It does not mean the jaw is emotionally stressed; it describes muscular tension.

French often uses the present tense to describe what is happening in the moment:

• regarde = looks at / is looking at
• dit = says / is saying
• est = is

English may choose either a simple present or a progressive form depending on context:

• The dentist looks at my gum and says...
• The dentist is looking at my gum and saying...

French usually just uses the present tense here, and the context tells you it is happening now.

Et dit is completely normal.

Once the subject la dentiste has already been stated, French does not need to repeat elle unless there is a special reason to emphasize it or avoid confusion.

So:

• La dentiste regarde ma gencive et dit que... is natural and smooth.

You could say:

• La dentiste regarde ma gencive et elle dit que... but that usually sounds more emphatic or less elegant unless you really want to stress she.

Mâchoire is pronounced roughly like ma-shwar.

A more careful approximation:

• mâ sounds like mah
• choire sounds somewhat like shwar

The â shows a circumflex accent. In modern French, it usually does not drastically change pronunciation for learners, but it is part of the spelling. Often it reflects historical spelling.

So the important thing for a learner is:

• recognize mâchoire as jaw
• remember it is feminine
• pronounce it approximately mah-shwar