The effects of a stress-absorbing system involved in the superstructure supported by hydroxyapatite-coated implants in monkeys.

To evaluate the effects of a stress-absorbing superstructure on the interface of an integrated implant, the bone/hydroxyapatite-coated (HA-coated) implant interface was histologically and histomorphometrically analyzed using monkeys. A total of 12 HA-coated implants were placed in the edentulous mandible of three monkeys. Polyurethane elastomer was selected as the stress-absorbing material. A superstructure incorporating a stress-absorbing system was placed on six implants (stress-absorbed group) and a superstructure without such a system was set on the other six implants (non-stress-absorbed group). After 12 months, undecalcified ground sections were prepared and the bone/implant interface was analyzed. Clinically, all implants in both groups were immobile and mild inflammation around the peri-implant gingiva was seen. Histologically, direct bone contact was observed around all of the implants in both groups. However, histomorphometrically, the amount of bone around implants was greater in the stress-absorbed group. Bone was more highly apposed to the implant at the apical portion than at the axial portion. These different findings could be the result of stress-breaking against functional loading to the bony interface of these HA-coated implants.