Multiscale Effects of Collagen Damage in Cortical Bone and Dentin

The denaturation of collagen at the molecular level in bone and dentin can impact their structure and properties, leading to increased brittleness in pathological diseases such as osteogenesis imperfecta, dentinogenesis imperfecta, diabetes, and cancer. This study investigates the relationship between collagen denaturation and the macroscale resistance of bone and dentin. Through heat treatment at 160∘C on bovine bone and human dentin, the effects of collagen denaturation on macroscale flexural strength, scanning electron microscopy, and transmission electron microscopy imaging of micro- and nanostructure were studied. The results show that collagen denaturation decreases the resistance of bone and dentin to fracture, even though collagen denaturation did not impact the mineral organization around and inside collagen fibrils. This is attributable to (1) a reduction in bone and dentin ability to deform (e.g., 40–75% decrease in strain to failure) and to resist fracture (e.g., 83–95% decrease in work to fracture) properties and (2) to a smoother crack path with less crack deflection around microstructural features. Reduction in deformation and toughness not only removed plastic deformation but also drastically decreased elastic deformation and elastic work to fracture in all tissues. However, the elastic modulus was only affected in radial-oriented bone samples where collagen fibrils are oriented perpendicularly to crack opening forces. This study highlights the crucial role of collagen molecule integrity and orientation in bone/dentin deformability and resistance.