I assume that you mean pre-pay for the expenses in 2017 for a procedure to be performed in 2018.
Yes you can pay for a medical expense in 2017 for a procedure in 2018 and report the amount paid with out of pocket funds as an itemized medical deduction on the 2017 Form 1040 Schedule A. However, only your total medical expenses that are greater than 10% of your Adjusted Gross Income (AGI) can be deducted. Your total itemized deductions reported on Form 1040 Schedule A must be greater than the standard deduction for your filing status to have any tax benefit.
Standard deductions for 2017
- Single - $6,350 add $1,550 if age 65 or older
- Married Filing Separately - $6,350 add $1,250 if age 65 or older
- Married Filing Jointly - $12,700 add $1,250 for each spouse age 65 or older
- Head of Household - $9,350 add $1,550 if age 65 or older
The wording the most recent pub 502 (2019) is different. It states:
"What Expenses Can You Include This Year?
You can include only the medical and dental expenses you paid this year, but generally not payments for medical or dental care you will receive in a future year."
What you can do is pay for the total expected cost of dental expenses like braces or dentures in December even if the work will take more than one tax year. But you cannot prepay for unscheduled estimated costs in the future. The doctor needs to actually accept the full payment ... you cannot just put money "on account" to make a deduction.