Experimental study of natural root form implants

Objective: Recently, immediate implantation of dental implants after tooth extraction has been performed to shorten the treatment period. However, it is considered that implantation of a ready-made implant will encounter problems related to the shape of the extraction socket in the maxillary incisor region. We speculated that such implantation complications could be reduced if an implant formed in the shape of the extraction socket was used. In this study, we investigated changes in the bone and microvasculature surrounding natural root form (NRF) implants in extraction sockets. Methods: Crab-eating monkeys were used. The mucosal flap in the maxillary incisor region was raised and the incisors extracted under general anesthesia. Immediately thereafter, the extracted teeth were cut into 2 parts and an impression was made of the root of the tooth, after which the root portions of the teeth were replanted into the socket and the mucosal flap was sutured. NRF implants were made with a titanium cast from the impressions and 1 week after the initial extraction, the replanted roots were removed and the NRF implants were implanted into the tooth extraction sockets, after which the mucosal flap was carefully sutured under general anesthesia. The animals were euthanatized at 2, 4, and 8 weeks after implantation of the implant. Bone and microvascular corrosion casts around the implant were prepared using a plastic injection method and examined by scanning electron microscopy. Results: The NFR were maintained after implantation into the extracted socket for 1 week. Two weeks after implantation, a newly-formed vascular network was observed between the implant and socket wall. Newly-formed bone contacting the implant surface was observed at 4 to 8 weeks after implantation. Conclusions: Our results showed that an NRF implant in an extraction socket can be expected to undergo osseointegration.