Can I use use my flexible spending account(FSA) to cover the PPE
charge from my dentist?
Yes you can. This is a fee charged by your dentist. This is to pay for the equipment the doctor used. It wasn't a mask that you walked out of the office with.
First I would check with the insurance company about your responsibility for the fee. In many cases an in-network doctor/dentist is limited in what they allowed to charge for. They can't make you pay more than what the insurance company considers your responsibility for the deductible or the co-pay. So your responsibility could be zero even if the insurance company doesn't pay for the item.
During this crisis some insurance companies have protected their customers by not allowing medical offices to charge for the extra expenses this year. Others have not addressed the issue. I have been to doctors and dentists during this crisis and haven't had to pay any extra fees.
If you have to pay this fee, then I would have the funds sent directly from the FSA to the dentist office. This generally doesn't require you to submit an Explanation of Benefit (EOB). It also may be possible to pay with the debit card connected to the FSA.