Histologic evaluation of immediate versus delayed placement of implants after tooth extraction

Full osseointegration is necessary to achieve long-term success of dental implants. We aimed to find out the relative merits of immediate and delayed insertion of implants after dental extraction.

We completed a histologic and histomorphometric examination of the tissue adjacent to delayed and immediate implants in 8 beagle dogs. In 4 dogs, implants were inserted immediately after the extraction of second premolars; in the remaining 4, the implants were inserted 6 months after the extraction. Fluorochrome bone markers were injected on 2 occasions before the dogs were killed 8 months after the implants had been inserted. Each implant and its surrounding tissue was examined macroscopically and microscopically. Both histologic dynamic and histologic static histomorphometry were used in this analysis. Statistical significance was tested by using the Student t test for paired and unpaired observations, the Dunnett t test, and Fisher's least significant difference method for multiple comparisons.

The implants placed immediately had 76% of their surface covered with bone, whereas the implants placed after bony healing had 81% of their surface covered with bone. The fibrous tissue at the cervical end of the implant was more dense; the delayed implants also had a greater number of adhesive epithelial elements (hemidesmosomes). Use of dynamic and static histomorphometry revealed no significant differences between the 2 groups.

We found new soft and hard tissue around dental implants 8 months after their insertion in both groups. Pseudoankylotic healing was seen in the osseous part. The lower level of osseointegration in the immediately placed implants was attributable to the early resorption of bone in the crestal part, resulting in a larger part of the implant being surrounded by soft tissue.