Evaluation of Apically Positioned Dental Implants with a Sandblasted with Large Grit and Acid-Etched Surface 1 Day After Initial Placement Using Micro-CT and Nondecalcified Tissue Slide Images in a Rabbit Model

Purpose: Optimal positioning of implant placement is difficult in several conditions. In cases of thin alveolar ridges or irregular alveolar crests, the dental implant thread is not always fully submerged in the alveolar bone. The response of surrounding bone to dental implants placed apically several days after the initial surgery has yet to be fully revealed. This study evaluated apically positioned dental implants with sandblasted with large grit and acid-etched (SA) surfaces 1 day after initial placement with treatment of saline or tetracycline. Materials and Methods: Twelve rabbits were used in this study, and the surgeries were performed on both sides of the mandibular bone. Twenty-four implants were placed and classified into three groups. In the control group, implant placement was performed following recommendations, with the SA surface submerged in the bone. In the saline and tetracycline groups, 1 mm of the SA surface was exposed above the cortical bone. On the following day, the implants were apically positioned after treatment using a cotton pellet soaked with sterile saline (saline group) or tetracycline solution (tetracycline group). The images from the nondecalcified tissue slide were compared with microcomputed tomography (micro- CT) images. The bone-to-implant contact ratio and bone area ratio were measured using micro-CT images 4 weeks after implant placement. Results: The bone-to-implant contact ratio (mean ± standard deviation, %) of the control group was 87.9 ± 13.7, and those of the saline and tetracycline groups were 83.7 ± 15.46 and 86.9 ± 18.5, respectively. No statistically significant differences were noted among the three groups (P > .05). The bone area ratio (mean ± standard deviation, %) was 90.1 ± 12.2, 96.6 ± 4.3, and 88.7 ± 22.3 for the control, saline, and tetracycline groups, respectively (P > .05). The results from the transverse plane showed no significant differences among the three groups. Conclusion: This study evaluated the effects of apically positioned dental implants with SA surfaces 1 day after initial placement, and uneventful healing was observed irrespective of treatment with saline or tetracycline. Apical positioning of the dental implant within a few days of initial placement may be acceptable without compromising osseointegration. However, further studies in large animal models with larger sample sizes may be necessary before clinical application is recommended. Keywords: apical positioning, dental implants, micro-CT, modified placement, osseointegration, replantation