Learn Farsi: دندان‌هایم سفید است.

First, make the noun plural: dandān (tooth) + -hā (plural). Then, add the possessive ending for 'my'. Because -hā ends in a vowel, we insert a 'y' sound to bridge the gap, using -yam instead of just -am. This gives us dandān-hā-yam (my teeth).

Why does the sentence use the singular verb ast (is) for plural teeth?

In Farsi, when the plural subject is an inanimate object (a non-living thing like teeth, chairs, or books), the verb is almost always in the singular form. So literally, the sentence is saying 'My teeth is white.'

Does the adjective sefid (white) need a plural marker to match the teeth?

No, Farsi adjectives never change to match the number of the noun they describe. Whether you have one white tooth or many white teeth, the adjective stays exactly the same: sefid.

Could I say this using the independent word for 'my' instead of the attached ending?

Yes! You could use the Ezafe connector and say dandān-hā-ye man. Both ways are perfectly correct, but using attached endings like dandān-hā-yam is very common and natural in everyday Farsi.