Are you talking about the GEMB CareCredit card?
That is a credit card. It is not an installment loan, because you can go back and reuse the card as you pay it down. An installment loan would not leave credit available as you paid it down. The contract is fairly clear.
What happens is you apply for the credit card, and it arrives with the amount you used for the medical procedure already debited against the card. For example, I needed my wisdom teeth out, which cost $952. CareCredit offered me a $1000 credit line. I took it, and got my wisdom teeth out. A few weeks later, got the actual card in the mail with $48 of credit still available, and pmts of $22/mo. I've paid it down to $300 and now have $700 available for unexpected medical expenses.
It will be in your best interest to pay it down as quickly as possible though. Your score probably dropped because it is likely near the max, since they usually offer you a CL that is just a few dollars more than your procedure cost. Also, if you only pay the min due, you will usually NOT have the card paid off by the end of the introductory period, leaving you with the default rate applied to the ENTIRE past balance. My intro was 0% for 10 months, and only $28/mo min payment. But with a $952 balance, obviously I would have been left with a big boo-boo once the 10 months passed and the rate defaulted to 19-30% APR.
Once you pay it down, you'll likely see your score rise quite quickly.