Temu janji pergigian ialah hari ini.

A natural breakdown is:

• temu janji = appointment
• pergigian = dental / related to dentistry
• ialah = is
• hari ini = today

So the structure is basically:

• Temu janji pergigian = dental appointment
• ialah hari ini = is today

Because it is a fixed Malay expression made up of two separate words:

• temu = meeting / meet
• janji = promise / arrangement

Together, temu janji means appointment.

English speakers often want to treat it as one single chunk, but in standard writing it is normally written as two words in this kind of use.

Pergigian is the more formal word for dental or related to teeth/dentistry.

• gigi = tooth / teeth
• pergigian = dental / dentistry-related

So:

• temu janji pergigian = dental appointment

If you use gigi by itself, it usually just means tooth/teeth, not the broader idea of dental.

In everyday conversation, many speakers might say something more direct, such as:

• temu janji doktor gigi = dentist appointment
• temu janji dengan doktor gigi = appointment with the dentist

Because in Malay, words like this and that usually come after the noun, not before it.

For example:

• buku ini = this book
• rumah itu = that house
• hari ini = this day = today

So hari ini follows normal Malay word order.

Ialah is a linking word, similar to is in English.

In this sentence, it connects:

• Temu janji pergigian
  and
• hari ini

So it works like a copula: The dental appointment is today.

A useful learner rule is:

• ialah is often used before a noun phrase

Here, hari ini behaves like a noun phrase, so ialah fits.

You can often leave it out, especially in everyday Malay.

So these are both possible:

• Temu janji pergigian ialah hari ini.
• Temu janji pergigian hari ini.

The version with ialah sounds more formal or more written.
The version without it sounds more natural in casual speech.

Malay does not use articles like the or a/an the way English does.

So temu janji pergigian can mean:

• a dental appointment
• the dental appointment

The exact meaning depends on context.

If you want to make it more clearly definite, Malay can use words such as itu:

• Temu janji pergigian itu hari ini. = That / the dental appointment is today.

Because Malay usually puts the main noun first and the modifier after it.

So:

• temu janji pergigian = appointment dental
• natural English order = dental appointment

This is very common in Malay. Compare:

• doktor gigi = tooth doctor = dentist
• klinik pergigian = dental clinic
• rawatan pergigian = dental treatment

It is understandable and correct, but it sounds somewhat formal because of ialah and pergigian.

In everyday conversation, a speaker might say something like:

• Saya ada temu janji dengan doktor gigi hari ini. = I have a dentist appointment today.
• Temu janji doktor gigi saya hari ini. = My dentist appointment is today.
• Temu janji pergigian saya hari ini. = My dental appointment is today.

So the original sentence is fine, but not the most casual way to say it.

Not always exactly, but in many situations it means the same thing in practice.

• temu janji pergigian = dental appointment
• temu janji dengan doktor gigi = appointment with the dentist

The first is a little broader and more formal.
The second is more conversational and specifically mentions the dentist.

So if you are speaking casually, dengan doktor gigi is often the easier and more natural choice.