List and describe the functions of the first layer of porcelain in:

List and describe the functions of the first layer of porcelain in:

1. a. alloy-bonded

   • • In metal-bonding porcelains, Opaque powder is used to:
     • - Enhance the bond of the porcelain to the metal substructure.
     • - Mask out the dark colour of the metal substructure.
     • - Initiate the shade of the restoration.
   • • Shoulder/Margin porcelain is used to create perfect aesthetics in the cervical area of metal ceramic restorations.
   • • They have a higher opacity than the dentine/body powders to fulfil their main function: masking out the underlying core.
   • • They prevent the crown from suffering from dark margins due to the shadow caused by the metal.

2. b. zirconia-bonded crowns.

   • • Zirconia Frame Modifier helps to provide the bond and background colour.
     • Should have a slight sheen
       • This sheen helps to bounce light back, delfecting from the darker interior coping
     • Frame modifier leaves an uneven surface
       • This scatters the reflected light through the crown
   • • After this the first layer of porcelain is applied: Dentine porcelain.
   • • Dentine porcelains function is to govern the shape and shade of the restoration.
   • • The dentine powders are somewhat translucent, to mimic the natural reflective and refractive properties of dentine.
   • • The dentine layer of a restoration will contain the largest bulk of porcelain. It may be supplied in more than 1 powder to aid the technician in matching the patient’s dentition.