Traditional sense of Dental / Vision care / Hearing Aid are not covered by Medicare. If the care is caused by Medical Reasons, such as you fall down and lost 2 front teeth, need some surgery, or you have cataract need surgery - those are covered.
Some part C has Flexi $ (in limited regions, California does not have it as far as I know).
The Flexi $ is a fixed amount deposited into a Visa card on January 1st each year. (They send you the card in Dec, you need to activate it but only see the $ in it after 12am 01/01). The amount varies by plan. You can use this $ only in Dental/Vision/Hearing expenses, not incl the cosmetic option in Dental.
For Hearing Aids, your best bet is to use Costco's service. Still costs you a couple thousands for a pair but not any near the highly inflated prices by those hearing aids companies.
You can also order the "personal sound amplifiers" online. Amazon has plenty to choose from. Try them out.