Time Course of Osseous Healing at Endosseous Implant Interfaces

Abstract

The purpose of this study was to examine the time course of endosseous implant healing in trabecular bone. Thirty-six, six month old rabbits were used and stratified into three groups of twelve animals (six control, six experimental). Each experimental animal had two implants placed, bilaterally, in the dorsal surface of the nasal bones. Control animals had soft tissue reflection on the left side nasal dorsum and soft tissue reflection with periosteal removal on the right side nasal dorsum. Prior to surgical procedures and implant placement, a series of intravital bone labels were initiated for all animals. The three groups were allowed to heal four, eight, and 12 weeks, respectively. Immediately after euthanizing the animals, torque test procedures were performed on all left side implants. Following histologic processing, analyses were conducted on midfrontal sections of control sites and implants using microradiography, polarized-light microscopy and epifluorescent microscopy. The implants were divided into three regions: supraflange, coronal, and apical. Control sites were separated into cortical and trabecular regions.

Within each implant region, the percent woven and lamellar bone was recorded as well as the percent of bone in contact with or near the implant. Osseous remodeling was detected by fluorescent bone labels. Using these markers, data were categorized as old bone, new bone (woven or lamellar), and unmineralized tissue.

In control animals, periosteal removal from the rabbits' nasal dorsum had a limited effect on producing noticeable differences in physiologic response compared to the soft tissue reflection-only control sites. The primary responses found in experimental animals were in the coronal implant region. Significantly more new and old bone was present within this region than in the supraflange and apical regions for all healing times. The only significant time factor found was the increased amount of new woven bone in the four week healing group of the coronal and apical regions.

Implant geometry, length and the presence of a flange, appears to have been a more significant influence on osseous response than healing time. Little periosteal woven callus and essentially no trabecular response were observed in experimental animals at the time studied. Because of the shortness of the implant (4.0 mm), the most apical portion had limited extension into trabecular anatomy. Limited proximity to osseous tissue in the apical region may explain the lack of trabecular response. The majority of bone and its physiologic adaptation response occurred in the coronal region since this area is more cortical in nature.