Q. Bone Loss - criteria for endosteal implants?
Crestal bone loss after intial healing is a primary indicator of the need for initial preventive therapy. Early loss of crestal bone is usually a result of excess stress at the permucosal site. It is suggested that an implant be inserted at or above the bone crest to avoid an increase in the Sulcus Depth subsequent to abutment placement. The initial bone loss after the abutment is connected and during the 1st 2 years of function is usually a result of excessive stress at the crestal implant bone interface. Secondly, bone loss around an implant is usually a compound condition created by bacteria and increased stress (a result of parafunction and / increasing crown height from crestal bone loss and anaerobic bacteria forming once the sulcus is > 4 to 5 mm). Clinical observations obtained by probing or radiographic measurements of 0.1 mm per year for bone loss are operator sensitive and not reliable. Instead the threaded implant pitch (distance between the threads) is usually 0.6 mm and can be used as a radiographic marker. Probing changes of 0.5mm or more are also more realistic to monitor. In general, if more than 1 half of the implant height has lost crestal bony contact, the implant is at significant risk and considered a failure regardless of the intial amount of implant bone contact.