Do I need proof for my dental bill? I pay with card and cash. But lost the proof that I pay with cash. Would it affect me for applying it to Standard deduction?

Q.  Do I need proof for my dental bill? 

A. No. At least not to claim it on your tax return.  If audited, you might need proof. But, that should be available form your dentist or dental insurance. 

Q. Would it affect me for applying it to Standard deduction?

A. No. Medical expenses (including dental) are itemized deductions.  If you don't have enough deductions to itemize, you get the standard deduction.  Everybody gets the standard deduction. No documentation is required an no expenses are applied to it.  You just get it. 

Also be aware, even when you do itemize,  only the amount of your total medical expenses exceeding 7.5% of your income (AGI) are deductible.