If your implant dentist is following the Malo Protocol then there is over 20-30 years of data on the success or failure rates of All-on-4® implants. The lower jaw has a slightly higher success rate as the bone is generally stronger compared with the upper jaw.
In saying that, the upper jaw still has a 98% success rate.
It is important to remember that if an implant fails in the initial healing period it will be replaced at no cost. This generally does not mean you will lose your initial bridge, but it may just become shorter on one side until the replacement implant takes. This means there may be a delay getting the final bridge and you may have to wear your initial bridge for a bit longer.