Yes to all the dental questions. See IRS Publication 502 - https://www.irs.gov/pub/irs-pdf/p502.pdf
Generally, dental treatments for good health are deductible - this includes the co-payments, the cleaning procedures, and bridges.
Generally, you can deduct health insurance premiums (including dental) that you paid with after-tax dollars.
As for Medicare, please read the following:
"Medicare A
If you are covered under social security (or if you are a government employee who paid Medicare tax), you are enrolled in Medicare A. The payroll tax paid for Medicare A isn't a medical expense. If you aren't covered under social security (or weren't a government employee who paid Medicare tax), you can voluntarily enroll in Medicare A. In this situation you can include the premiums you paid for Medicare A as a medical expense.
Medicare B
Medicare B is a supplemental medical insurance. Premiums you pay for Medicare B are a medical expense. Check the information you received from the Social Security Administration to find out your premium.
Medicare D
Medicare D is a voluntary prescription drug insurance program for persons with Medicare A or B. You can include as a medical expense premiums you pay for Medicare D." (see page 9 in Pub 502, link above).
