Understanding peri-implant endosseous healing.

If dental implantology is an increasingly successful treatment modality, why should we still need to understand the mechanisms of peri-implant bone healing? Are there differences in cortical and trabecular healing? What does "poor quality" bone mean? What stages of healing are most important? How do calcium phosphate-coated implants accelerate healing? What is the mechanism of bone bonding? While there are still many aspects of peri-implant healing that need to be elucidated, it is now possible to deconvolute this biological reaction cascade, both phenomenologically and experimentally, into three distinct phases that mirror the evolution of bone into an exquisite tissue capable of regeneration. The first and most important healing phase, osteoconduction, relies on the recruitment and migration of osteogenic cells to the implant surface, through the residue of the peri-implant blood clot. Among the most important aspects of osteoconduction are the knock-on effects generated at the implant surface, by the initiation of platelet activation, which result in directed osteogenic cell migration. The second healing phase, de novo bone formation, results in a mineralized interfacial matrix equivalent to that seen in the cement line in natural bone tissue. These two healing phases, osteoconduction and de novo bone formation, result in contact osteogenesis and, given an appropriate implant surface, bone bonding. The third healing phase, bone remodeling, relies on slower processes and is not considered here. This discussion paper argues that it is the very success of dental implants that is driving their increased use in ever more challenging clinical situations and that many of the most important steps in the peri-implant healing cascade are profoundly influenced by implant surface microtopography. By understanding what is important in peri-implant bone healing, we are now able to answer all the questions listed above.