All you need is the letter of entitlement (comes in a see through wallet with your national insurance on if I remember correct.
They will ask you to sign 2 sides of an a5 form called the fp17, on the back you tick the jsa box and enter your national insurance no. This only entitles you to NHS dentistry.
Ofcourse if you prefer private treatment you will have to pay for that. Certain elements can be mixed eg. Have your examination on nhs and treatment private. Your dentist should offer all treatment clinically necessary to secure the health of your mouth on the nhs.