6 Implants in Maxilla and 6 in Mandible: Restore this?

Cross arch one bridge screw retained on the upper , 3 separate bridges on the lower ........ dependant on patient bite maybe porcelain upper and Gradia lower .... Peter

Yes that is may standard protocol .......here agree the placement on the lowers creates an issue so yes possibly cantilever the canines

I would never do a full arch cemented implant prosthesis.You will have a nightmare for checkups ot incase there is any ceramic chipping.Again a full arch single piece is the best option .You can a screw-retained even in the upper jaw and a cemented crown on the lateral.

This looks like it will have a very nice final result...the implants seem to be well placed. I would go along with a one piece upper prosthesis....... gives more support in the weaker bone.......... but if you have read Carl Misch's book, he makes a strong point in saying that there is the possibility of flexure in the mandible.... ... so it would be OK if you were to splint the anterior with one posterior section, and keep the other posterior section separate.

My recommendations would be for the upper, do an IRM cemented one piece upper, so that you can easily remove the prosthesis should any implant or its supporting bone get into any problems in future years. I would normally say screw retained, but you seem to imply difficulty because of the labial inclination of the lateral implants. If you can do a screw-retained one piece, that is preferable, but the intermediate cement (IRM) works very well also. Obviously you must be careful to remove all cement. For the lower, Misch and other researches showed that the flexure of the mandible is in the midline. Therefore, I see no benefit in dividing this case into 3 sections, but rather would propose 2 sections, I would put a semi precision interlock in the middle of the bridge between 24-25, which, from the x-rays, show a wide space for the central incisor pontics. Interlock would go there assuming adequate room. The patient would then have a right side bridge and a left side bridge, each of which engaged 3 implants. This would be very strong and would also permit the development of a cuspid protected occlusion with good support from the 3 implalns.

You should restore the upper with a single piece cross arch screw retained bridge on multi-unit type abutments. The lower should be two independant quadrant screw retained bridges - do not join across the midline. Mandible flexex and narrows distally plus rotates to the lingual slightly when the jaw opens and you have implants in the 1st molar site. If you had implants interforaminally the another single piece cross arch bridge with cantilver molars would be an option. The 1st molar implants means if you do a 1-piece bridge then screw loosening / fractures will occur.

Retrievability!!!! Maxilla.... Even if the implants in the lateral regions are in bucco-version, a one piece prosthesis can be made retrievable. Custom abutments for the lateral implants. Screw retained for the other four. Tempbond/vaseline mix as cement for the lateral abutments. When, not if, the porcelain fractures, the bridge can be easily repaired. Mandible.... Two screw retained prostheses.....retrievable. With no proprioception, the porcelain in gonna "CLANK" and need repaired.