Trabecular Adaptation to Continuously Loaded Endosseous Implants

Abstract

Several studies have shown endosseous implants placed in areas of thick cortical bone to be an effective means of anchorage in complex orthodontic cases. The purpose of this study was to examine the viability of endosseous implants as orthodontic/orthopedic anchorage when placed in this cancellous bone. Eighteen 6-month-old male rabbits were used and stratified into three groups of six animals. Two implants placed (bilaterally) in the dorsal surface of the nasal bones. After a 12-week healing period, the control group (C) had a passive spring placed between the implants, and the 1 Newton constant group (1 NC) received a spring that delivered a constant compressive load of 1N. A 1N load was applied to the progressive load group (3NP) and sequentially increased to 3N over the course of the study. Bone labels were administered throughout the experiment at designated time intervals to provide quantification of the physiologic activity. Following histologic processing, analyses were conducted on midfrontal sections using microradiography and fluorescent microscopy. The implants were divided into three regions: supraflange, coronal, and apical. Within each region the percent woven and lamellar bone was recorded as well as the percent bone in contact with or near the implant surface. Remodeling activity was observed by using fluorescent bone labels. In the sections analyzed using fluorescent microscopy, the regions were further subdivided into zones. Using the bone label data, bone was categorized as old bone, new woven bone, new lamellar bone and marrow space. Within animal, paired t tests revealed no significant difference between right/left implants. Data was pooled and an ANOVA run to test for difference between groups. Few significant differences were seen. Student Newman-Keuls sequential range tests were used to test between region and zone. The coronal region showed trends of more bone overall in the 1NC and the 3NP load groups p < 0.10. The apical region had less bone overall. The fluorescent data showed few significant differences between groups; however, the coronal region showed trends of more bone overall. A RAP effect was observed in the zonal analysis for new lamellar bone. Sutural remodeling was observed at the cortical plate over the nasal suture. A significant trabecular response was not seen in this study; however, the implants in the experimental groups remained stable throughout the study possibly due to the implant design. It was concluded that implants placed in thin cancellous bones are suitable for use as orthodontic/orthopedic anchorage.