Collagen fiber orientation in human peri-implant bone around immediately loaded and unloaded titanium dental implants

Background: The main factor in determining the mechanical properties of bone is the collagen configuration. Methods: This study investigated the birefringence in human bone around loaded and unloaded titanium dental implants to evaluate the collagen fiber orientation using circularly polarized light (CPL) and scanning electron microscopy (SEM). A total of 10 titanium dental implants, five immediately loaded and five unloaded, were used. The birefringence measurements were performed on digitized images of both loaded and unloaded implants. All images detected at 50x were measured using a software image analysis. Results: In the bone around loaded implants, the transverse collagen fiber area was 45,481 +/- 3,037 pixel(2) (mean +/- SD), while the area of longitudinal collagen fibers was 13,676 +/- 2,232 pixel(2) (mean +/- SD). In the unloaded implants, the transverse collagen fiber area was 32,174 +/- 2,554 pixel(2) (mean +/- SD), while the area of longitudinal collagen fibers was 89,073 +/- 1,960 pixel(2) (mean +/- SD). The CPL measurements of the birefringence for transverse collagen fibers of loaded versus unloaded implants indicated that the differences were statistically significant (P < 0.05). The results for the longitudinal collagen fibers of loaded versus unloaded implants were also statistically significant (P < 0.05). Conclusions: In the bone around loaded dental implants, transverse collagen fibers were more abundant, while in the unloaded implants, collagen fibers run more longitudinally. The load seemed to determine the collagen fiber orientation.