is a loan for dental implants deductible

A loan?    Did you put the payment for the dental work on a credit card of some kind?   Provide some details.   

If you put it on a credit card or took out a loan you can deduct the full amount even though you pay it over time. If you are on a payment plan with the hospital or doctor, etc. then it's only the amount you pay. Either way you only can deduct the principal amount, not any interest.

The loan amount for the implants is a valid medical expense for the tax year when the loan was used for the implants.

Any loan payments in future years will not be deductible as a medical expense since the loan was used initially for payment.