Tricare Standard (the old CHAMPUS) works just like regular insurance, you get to pick your doctor. If the doctor you choose accepts Tricare, then you will pay him 20%, and he will bill them for the rest. Tricare will pick up 80% of the allowable charges. If he doesn't accept Tricare, you will have to pay him, then file with Tricare. Tricare will then reimburse you for 80% of allowable charges, and you will be responsible for the rest.
So, if the doctor doesn't accept Tricare, and he charges you $100, you will have to pay the $100. If Tricare considers $100 to be the allowable charge for that service, you will be reimbursed $80. However, if Tricare feels that $80 is the allowable charge, then you will only be reimbursed $64 (80% of allowable).
Dental is totally separate from Tricare Standard medical. Tricare Dental must be purchased with a monthly premium.
Hope this helps some!