In 4 unit porcelain bridge ( 2 teeth & 2 false teeth), does each of the two tooth is still protected by the underlying metal or all is porcelain.

It could be either: Both types are used, although it is probably more likely for you to have a metal substructure under the porcelain. Therefore, there is no way for us to know with any certainty what you have in your particular situation. Your own dentist can answer that question for you.

Ask the dentist: The porcelain bridge can either be "all porcelain" where the entire bridge is made of porcelain or it can be a "porcelain fused to metal" bridge where the understructure is metal. You would have to ask the dentist which type of bridge is being fabricated.

Porcelain/metal: Some bridges are made of all porcelain, and some have an understructure of metal. You should ask your dentist which kind is in your mouth. Only he/she would know.

Hard to answer: As a rule, the amount of precious metal under a porcelain bridge is kept to a minimum, the supporting teeth have less precious metal than the replacement teeth. I would estimate the amount to be between 1-2 oz of precious metal.

Depends: You can have all ceramic or ceramic bonded to metal. Ask your dentist.

Usually they are: Normally four unit bridges require the strength of the underlying metal on the two abutments and across the bridge space. This metal support is then stacked with esthetic porcelain to complete the four unit restoration.

Metal or porcelain: The fixed bridge can be a porcelain fused to metal in which case the supporting teeth are covered by underlying metal, or can be complete porcelain coverage which the supporting teeth are covered by porcelain, usually zirconium base to add strength.

Sealer: Please know that a thin layer of sealer (cement) is flowed into the microscopic space between the crowns and the teeth. As long as the sealer remains intact it prevents bacteria from entering the space between the crown and the tooth and causing decay. Take care of your bridge and have your dentist check it regularly.