Medpor or Silicone Jaw Implants?

Surrounding tissue does not grow into/through silicone, therefore it is easier to remove at a future date should the need arise. It can also shift in position at any future date since there is little or no ingrown tissue to keep it in place.
Porex Medpor does develop tissue ingrowth or incorporation. The ingrowth may not be 100% but ingrowth prevents future shifting in position. It also decreases the risk of infection. Ingrowth should be complete within a few weeks, fixing the implant in position.
Because silicone lacks ingrowth, you would need to take antibiotics prior to any dental procedure. That is not the case with incorporated Medpor because the body does not treat incorporated implants as foreign bodies.
The advantages of silicone are ease of removal and ease of placement through asmaller incision. The disadvantages of porex medpor are difficult removal after incorporation. They are as much a foreign body as non-porous silicone until incorporation is completed.
Medpor is much less pliable than silicone so if not temporarily softened just prior to placement to achieve a custom fit, it can rock. This can occur even after incorporation is complete. Medpor implants therefore have a smaller margin for error in terms of an exact fit compared to more pliable silicone implants.
Even though silicone is easier to remove, defects after removal can be as bad or worse than those after medpor removal.

I have used both and have essentially returned to silicone implants for two reasons:
1) the Medpor is desireable because the density and structure is comparable to bone. It promotes tissue ingrowth and it does not tend to erode the underlying bone which the older silicone implants had a tendency to do. The problems I encountered were the larger incisions, difficulties in placement, problems with contouring to the underlying bone, and complicated removal.
2) Silicone implants do not necessarily have a higher rejection rate, to the best of my knowledge, but have eroded the bone in the past. Modifications in the surfaces of current implants should limit this tendency. For this reason, I have returned to the use of silicone implants and have been pleased.

We perform a great number of silicone chin implants and the rejection rate is almost nil.
Reoperations, if they are ever necessary, are very easy with silicone implants. They are a nightmare with Medpor because of the adherence of Medpor to the underlying bone. So if you are not happy with the shape of your chin, hope you had a silicone implant.