The effectiveness of the stress-breaking system of the superstructure on the hydroxylapatite-coated implants.

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The purpose of this study was to evaluate the effectiveness of the stress-breaking system installed with the superstructure of the hydroxylapatite(HA)-coated dental implant. High resilient polyurethane elastmer(Biotron R) was selected as the material of this stress-breaking system because of these characteristics as the easiness of model shaping and control of elastic constant. In vitro study, little change of elastic constant and volume of the material was seen in Biotron R-M25, whereas some significant changes were seen in Biotron R-M8, M12 and M17. In vivo study, four monkeys were used. Four HA-coated implants were inserted into the edentulous mandible of each animal. Two superstructures with stress-breaking system by Biotron R-M25(stress-breaking group) and two superstructure without stress-breaking system (non-stress-breaking group) were set on the respectively implants. During 12-month follow-up period, all implants were clinically stable. Some swelling was observed around the periimplant gingiva of a few implants, but no other drastic change was seen around the implant. In the histological evaluation, the surrounding bone was apposed directly to the surface of both implants. Histomorphometric ally, implants in stress-breaking group showed higher bone contact ratio and bone volume than implants in non-stress-breaking group.These results show that the implants set on the superstructure with the stress-breaking system can obtain more stable bone anchorage than the implants set on the superstructure without the stress-breaking system.