Which porcelain repair kits are best for repairing a porcelain-fused-to-metal bridge that keeps fracturing in one area?

There are not many kits specifically packaged for porcelain repair. However, several companies sell all of the materials needed for porcelain repair. Two excellent products I am aware of are manufactured by Kuraray America and Ivoclar Vivadent. Both sell a ceramic primer and a metal primer. Ivoclar Vivadent’s product is just one bottle for both substrates. The best technique for repairing fractured porcelain is first to micro-etch or roughen the surface to be repaired with a diamond bur, and then add a metal or a ceramic primer (silane) depending on which type of surface is exposed. Next, place an unfilled resin bonding agent, cure, then a flowable composite to enhance the wetting area of the composite to the substrate, and finally, restorative composite, if the section is very large. There are opaque flowable composites that can more fully hide the color of the metal, if necessary. In general, porcelain repairs give variable results. Much of the success depends on the design of the metal substructure, and the thickness of unsupported porcelain. Make sure that your lab never lets unsupported porcelain thickness be greater than 2mm.