Method: X-ray attenuation and elemental spatial variations on 1-2µm sections from alveolar bone were identified using transmission X-ray microscopy (TXM, 5.4 keV) and microprobe X-ray fluorescence imaging (µ XRF, 12 keV). Mechanical resistance of specific sites in BB, lamellae and interlamellar spaces of AB were investigated by displacing load at a rate of 100nm/sec using site-specific indentation technique.
Result: Two distinct types of bones marked by differences in X-ray attenuation, calcium (Ca), phosphorus (P), and zinc (Zn) content were identified in AB. Bone with radial fibers, commonly known as bundle bone (BB) was identified as a higher X-ray attenuating material and X-ray micro-fluorescence measurements yielded higher counts of Ca, P, and Zn. Zn is also known to participate in both function- and disease-induced biomineralization of AB. Higher X-ray attenuating bands were observed in inter-lamellae regions of LB. AFM wet scans illustrated hygroscopic lamellae relative to inter-lamellae regions. Interestingly, radial PDL fibers in BB, changed their orientation into circumferential in LB within a junction of 10-30µm illustrating an elastic discontinuity. Chemical and structural heterogeneities were further complemented by elastic modulus values of 23.9 ± 2.8 GPa for lamellae, 33.2 ± 0.4 GPa for inter-lamellae, with significant elastic modulus differences between lamellae and inter-lamellae confirmed via Student’s t-test (P< 0.05).
Conclusion: Higher packing density due to differential collagen fiber orientation, not necessarily mineral changes, within BB and LB could contribute to a higher attenuation. These heterogeneous regions represented by radial-fiber bone and lamellar-bone could be adaptive features to maintain the “functional quality” of AB in the fibrous joint.
Keywords: Biomechanics, Bone, Interfaces, Structure and Teeth