When should I use a metal primer?

Metal primers [Alloy Primer (Kuraray America); Metaltite (Tokuyama Dental Corp./Tokuyama America Inc.] are effective for repairing ceramic-metal restorations for removable partial dentures with composite or acrylic. A recommended technique is:

• Clean the metal and roughen the surface with a diamond bur.
• Apply the metal primer to the clean surface, dry, and then apply unfilled resin and cure.
• Apply the composite