Good question! First of all, you are correct in thinking that monolithic zirconia, such as BruxZir® Solid Zirconia (Glidewell Laboratories; Newport Beach, Calif.), is the strongest all-ceramic bridge material that we have. This time last year, I would have hesitated to recommend that a dentist prescribe BruxZir Solid Zirconia for an anterior bridge. The esthetic nature of BruxZir restorations has really improved over the last year, although it hasn’t quite caught up with its monolithic brethren, such as IPS e.max. An anterior PFM bridge is probably the strongest solution, although the ceramic material can certainly chip off the metal understructure, and the esthetics can be compromised by the lack of translucency and possibly exposed metal margins.
I am not sure I would want to go with the zirconia-layered-with-ceramic option you mention, as we have noticed more chipping with that combination of materials than we have with porcelain fused to metal. In fact, porcelain fused to zirconia would probably be my last choice after BruxZir Solid Zirconia, IPS e.max and PFM.
You also asked about making the lingual of the bridge in solid zirconia, similar to a metal lingual on a PFM restoration. While we do fabricate bridges like that on request from dentists, we don’t get many requests for it. Perhaps the reason is that the strength of BruxZir Solid Zirconia comes from its monolithic nature — the fact that it doesn’t have any ceramic material fused to it. As a result, it fractures and/or chips less than any other restoration in the lab (except cast gold, of course). When we do make a BruxZir restoration like that, we typically place the ceramic material on the facial and carry it from the gingival down to the incisal edge, without wrapping the incisal edge. We want to allow the patient to function in protrusion on the zirconia, rather than the porcelain. But doing this takes it from being a monolithic BruxZir restoration to a bilayered restoration, which is more prone to chipping.
While there are no absolutes, my first choice today is IPS e.max for a 3-unit bridge in the anterior on a patient who does not show a lot of wear. For that same bridge in a patient who does show signs of wear, my choice is BruxZir Solid Zirconia, especially if the patient has previously chipped a PFM restoration. As the size of the bridge increases beyond 3 units, I begin to consider PFM as my choice because of the superior strength of the metal connectors when compared to any all-ceramic system, especially when there is a lack of room for the connectors. As always, your mileage may vary.
Hope that helps!