Is it true that after two years or so after the gums keep shrinking the all-on-4 procedure separates from the gum line?

We allow 6 months of healing time from the time that your temporary teeth are placed the day of your surgery, to the time of placing the final teeth. This we have found is sufficient time for bone and gum remodeling. The way we prepare/preserve the bone ridge at the time of surgery, may have something to do with us seeing minimal to no space formation underneath the final prosthesis.

This is a possibility as there is little stimulation to the bone underneath.  If the prosthesis is snug, it creates a light surface stimulation that keeps the gums near longer. Same concept applies to dental bridges.If you get the typical all-on-4 bulky plastic teeth over metal, you can always have more pink plastic added beneath.  I find that many of my patients have irritated/inflamed gums with the plastic temporaries, so I rarely do those since I charge the same fee. If you get a porcelain or zirconium bridge, it may happen after many many years, like a natural tooth bridge.  The bridge is cemented so you don't have screw holes or bulky unnecessary material on your palate.You can also snap your teeth in & out, and those can also be refitted with pink plastic.  They are an economical alternative.