Yes--orthodontia is a medical expense that can be entered with other medical, dental and vision expenses under medical deductions. But --- only the amount you paid in 2021 can be used---not the full amount if you are on a payment plan with the orthodontist. And you are subject to the very tough threshold to use any medical expenses as a deduction.
The medical expense deduction has to meet a rather large threshold before it can affect your return. The amount of medical (including dental, vision, etc.) expenses that will count toward itemization is the amount that is OVER 7.5% of your adjusted gross income. You should only enter the amount that you paid in 2021—do not include any amounts that were covered by insurance or that are still outstanding. Of course, your medical expenses plus your other itemized deductions still have to exceed your standard deduction before you will see a difference in your tax due or refund.
To enter your medical expenses go to Federal>Deductions and Credits>Medical>Medical Expenses
2021 STANDARD DEDUCTION AMOUNTS
SINGLE $12,550 (65 or older + $1700)
MARRIED FILING SEPARATELY $12,550 (65 or older + $1350)
MARRIED FILING JOINTLY $25,100 (65 or older + $1350 per spouse)
HEAD OF HOUSEHOLD $18,800 (65 or older +$1700)
Legally Blind + $1350