Bone layers

The jawbone is composed of a hard outer layer (the cortex) and a spongy inner mass (cancellous bone) that will yield even to slight finger pressure.
It is therefore obvious that this spongy substance is unable to resist strong forces such as occurring during mastication. The typical act of intraoral food reduction as practised in our culture produces masticatory loads of 5 to 25 N. Peak forces acting on vertically loaded teeth may reach 50 N.
The hard component of the jawbone (which comes in two different incarnations, the relatively thick mandibular or lower or the extremely delicate maxillary or upper cortex) will tolerate up to 560 N of compressive or tensile forces. Although such loads will compress the cortex, they are not strong enough to prevent its full recovery.
After a phase of relief, allowing the bone to expand to the point of complete recovery, it will be as load-tolerant and flexible as before.

 
The black curved lines are created by the LASER light used to demonstrate and mesure shifts in bony structures resulting from load transmission to the bone via the implant.   Same area after a recovery phase


The load capacity of spongy bone is only about one-tenth that of cortical bone. The maximum impact of load transmission must therefore be attained in the cortical bone. The human maxilla or upper jaw rarely contains a firm cortical layer along whose contours the cylindrical crestal implants can find firm support.