Histological evaluation of collagen fiber orientation around grafted bone in human

Introduction. The main factor in determining the mechanical properties of bone is the collagen configuration1. Collagen fiber orientation is a regionally dependent phenomenon influenced by loading2: transversally oriented collagen fibers best resist to compression, while longitudinally fibers best resist to tension. Aim of this study is to evaluate the orientation and amount of collagen fibers in unloaded dental implants 6 months after bone regeneration with three different grafted materials in human, to better understand the bone growth and the entity of the load to be applied after implant placement. Materials and Methods. The comparison was made among Bio-Oss®*, a deproteinized bovine bone material, Engipore®**, a porous engineered pure hydroxyapatite, and PepGenP-15***, a combination of natural bovine-derived hydroxyapatite matrix coupled with a synthetic cell-binding peptide. Five patients for each group of biomaterial (5 male and 10 female, mean age of 52,8) and one sample for each patient, retrieved 6 months after sinus lift augmentation, were analyzed. Birefringence was used to evaluate the bone microstructure around the biomaterial using Polarized Light Microscopy. The variation of the amount of transverse and longitudinal collagen fibers orientation inside each group was made using Unpaired t-Test Results. Bio-Oss showed no significant difference for transverse (18.4 ± 2.7%) and longitudinal (16.3 ± 1.8%) bone collagen fibers (P = 0.195). Engipore showed a significant difference between transverse (4 ± 0.7%) and longitudinal (7.6 ± 2.5%) bone collagen fibers (P=0.015). Finally, PepGen P-15 15 showed no significant difference for transverse (3.8 ± 1.6%) and longitudinal (4.9 ± 1.2%) bone collagen fibers (P=0.279). Conclusions. The evaluation of collagen fiber orientation in the new bone showed an absence of a predominantly spatial orientation, with no dominance between transverse and longitudinal fibers, showing a newly formed bone of woven type, not yet ready to support an immediate load. In practice, on implants placed in bone regenerated with biomaterials, the load procedures should be progressively applied and the occlusion entity carefully controlled.