Retention of crestal bone subsequent to implant placement was never a major concern. For years, loss to the first thread on the fixture was accepted as the norm. Insane yes, but accepted nonetheless. AstraTech, Straumann, Nobel and now Zimmer have restructured their product line to include bone level fixtures and collar and platform design that will ensure crestal bone loss is either negligible or non-existent.
From Dr. Bicuspid