Histological Evaluation of Early and Immediately Loaded Implants Retrieved from Human Jaws

The only way to evaluate the short- and long-term response of human bone tissue to the insertion of dental implants and to corroborate the results of in vitro and of animal experimental studies is to study well-integrated human-retrieved dental implants, with surrounding human bone tissue, possibly after different time periods after the insertion in the bone. Several papers report that moderately rough implant surfaces are, probably, the best in terms of mineralized tissues response at the bone-implant interface. Results from our Laboratory, in a span of 30 years, have found that immediate loading did not create adverse effects regarding the formation of mineralized tissues at the interface with dental implants and has, probably, a beneficial effect on the peri-implant bone response, producing changes in the peri-implant bone microstructure. Osseointegration is a very dynamic ongoing process with the peri-implant bone tending to become more organized over the years; these higher degrees of organization are reflected by the large quantity of remodeling areas in the mature, lamellar bone, indication of multiple remodeling cycles over the years of loading. Bone remodeling is a prerequisite for dental implants to support functional loading in the long term, and remodeling, very well-organized, mineralized, lamellar bone is found at the interface of retrieved implants even after three decades of loading. Bone-implant contact (BIC) and bone mechanical properties were found to increase over time, and the bone tissue adapted to loading conditions to increase its biomechanics. In the specimens evaluated in our Laboratory, high percentages of bone-implant contact was found in all well-integrated retrieved implants, with the presence of mineralized, mature, lamellar bone in close contact with the metal surface, around all the implant perimeter, with no epithelium migration downward or presence of fibrous, connective tissue. In the specimens evaluated in our Laboratory over several decades, the bone-implant contact percentage was found to vary from 32 to 37% to more than 90–95%. These results point to the fact that dental implants could function with different percentages of mineralized tissues at the interface, and even implants with a low bone-implant contact percentage were stable, well-integrated, and able to bear loading conditions over the years. Mineralized bone was absent at the base of the threads in unloaded implants, and, at the tip of the threads in loaded implants, osteocytes (the mechanosensors in bone) were always found in the peri-implant bone, with a significantly higher number in loaded implants than in unloaded implants. Loaded implants presented a significantly higher number and thickness of bone trabeculae.